Steel Metal

Aluminum and its alloys can be joined by more methods than any other metal, but aluminum has several chemical and physical properties that need to be understood when using the various joining processes. The specific properties that affect welding are its oxide characteristics, its thermal, electrical, and nonmagnetic characteristics, lack of color change when heated, and wide range of mechanical properties and melting temperatures that result from alloying with other metals. Oxide. Aluminum oxide melts at about 2050 oC which is much higher than the melting point of the base alloy. If the oxide is not removed or displaced, the result is incomplete fusion. In some joining processes, chlorides and fluorides are used in order to remove the oxide contain. Chlorides and fluorides must be removed after the joining operation to avoid a possible corrosion problem in service. Hydrogen Solubility. Hydrogen dissolves very rapidly in molten aluminum. However, hydrogen has almost no solubility in solid aluminum and it has been determined to be the primary cause of porosity in aluminum welds. High temperatures of the weld pool allow a large amount of hydrogen to be absorbed, and as the pool solidifies, the solubility of hydrogen is greatly reduced. Hydrogen that exceeds the effective solubility limit forms gas porosity, if it does not escape from the solidifying weld. Electrical Conductivity. For arc welding, it is important that aluminum alloys possess high electrical conductivity — pure aluminum has 62% that of pure copper. High electrical conductivity permits the use of long contact tubes guns, because resistance heating of the electrode does not occur, as is experienced with ferrous electrodes. Thermal Characteristics. The thermal conductivity of aluminum is about 6 times that of steel. Although the melting temperature of aluminum alloys is substantially bellow that of ferrous alloys, higher heat inputs are required to weld aluminum because of its high specific heat. High thermal conductivity makes aluminum very sensitive to fluctuations in heat input by the welding process. Forms of Aluminum. Most forms of aluminum can be welded. All the wrought forms (sheet, plate, extrusions, forgings, rod, bar and impact extrusions), as well as sand and permanent mold castings, can be welded. Welding on conventional die-castings produces excessive porosity in both the weld and the base metal adjacent to the weld because of internal gas. Vacuum die-castings, however, have been welded with excellent results. Powder metallurgy (P/M) parts also may suffer from porosity during welding because of internal gas. The alloy composition is a much more significant factor than the form in determining the weldability of an aluminum alloy. Filler Alloy Selection Criteria When choosing the optimum filler alloy, the application (end use) of the welded part and its desired performance must be prime considerations. Many alloys and alloy combinations can be joined using any one of several filler alloys, but only one filler may be optimal for a specific application. The primary factors commonly considered when selecting a welding filler alloy are: * Ease of welding * Tensile or shear strength of the weld * Weld ductility * Service temperature * Corrosion resistance * Color match between the weld and the base alloy after anodizing * Sensitivity to Weld Cracking. Ease of welding is the first consideration for most welding applications. In general, the non-heat-treatable aluminum alloys can be welded with a filler alloy of the same basic composition as the base alloy. The heat-treatable aluminum alloys are somewhat more metallurgically complex and more sensitive to "hot short" cracking, which results from heat - affected zone (HAZ) liquidation during the welding operation. Generally, a dissimilar alloy filler having higher levels of solute (for example, copper or silicon) is used in this case. * The high-purity 1xxx series alloys and 3003 are easy to weld with a base alloy filler, 1100 alloy, or an aluminum - silicon alloy filler, such as 4043. * Alloy 2219 exhibits the best weldability of the 2xxx series base alloys and is easily welded with 2319, 4043 and 4145 fillers. * Aluminum-silicon-copper filler alloy 4145 provides the least susceptibility to weld cracking with 2xxx series wrought copper bearing alloys, as well as aluminum-copper and aluminum-silicon-copper aluminum alloy castings * The cracking of aluminum-magnesium alloy welds decreases as the magnesium content of the weld increases above 2%. * The 6xxx series base alloys are most easily welded with the aluminum-silicon type filler alloys, such as 4043 and 4047. However, the aluminum-magnesium type filler alloys can also be employed satisfactorily with the low-copper bearing 6xxx alloys when higher shear strength and weld metal ductility are required. * The 7xxx series (aluminum-zinc-magnesium) alloys exhibit a wide range of crack sensitivity during the welding. Alloys 7005 and 7039, with a low copper content (<0.1%), have a narrow melting range and can be readily joined with the high magnesium filler alloys 5356, 5183 and 5556. The 7xxx series alloys that possess a substantial amount of copper, such as 7975 and 7178, have a very wide melting range with a low solidus temperature and are extremely sensitive to weld cracking when are welded. Welding Processes The GTAW (gas-metal arc welding) process has been used to weld thicknesses from 0,25 to 150 mm and can be used in all welding positions. Because it is relatively slow, it is highly maneuverable for welding tubing, piping and variable shapes. It permits excellent penetration control and can produce welds of excellent soundness. Weld termination craters can be filled easily as the current is tapered down by a foot pedal or electronic control. The ac - GTAW process provides an arc cleaning action to remove the surface oxide during the positive electrode half of the cycle and a penetrating arc when the electrode is operated at negative polarity. The dc - GTAW Process. Negative electrode polarity direct current can be used to weld aluminum by manual and mechanized means. Other arc welding processes include shielded metal arc welding (SMAW), as well as electroslag and electrogas welding (ESW, EGW). SMAW with flux-coated rods has been replaced to a very substantial degree by the GMAW process. The oxyfuel gas welding (OFW) process uses a flux and either an oxyacetylene or oxyhydrogen gas flame. When the oxyacetylene flame is used, a slightly reduced flame is required, which causes a carbonaceous deposit that obscures the weld and slows the travel speed. Electron - beam welding (EBW) in a vacuum chamber produces a very deep, narrow penetration at high welding speeds. The low overall heat input produces the highest as-welded strengths in the heat treatable alloys. The high thermal gradient from the weld into the base metal creates very limited metallurgical modifications and is least likely to cause intergranular cracking in butt joints when no filler is added. Laser-beam welding (LBW) is now considered to be a viable fusion joining process for aluminum with the advent of commercially available, stable, high-power laser systems. Because of aluminum`s high reflectivity, effective coupling of the laser beam and aluminum requires a relatively high power density.

Phosphor bronzes are alloys consisting of tin, phosphorus and copper as main constituents, sometimes with additions of zinc and lead. The structure is made up of three phases:

    * A matrix of copper with tin in solid solution, known as the alpha phase, which is comparatively soft
    * A tin rich delta phase which is hard and interspersed throughout the matrix
    * A hard constituent of copper phosphide associated with the delta constituent, which is also hard but brittle.

The duplex structure of the alloy is ideal for bearing purposes. The toughness and hardness of the alloy can be varied with the tin and phosphorus content. In general, increases of tin give added toughness as well as hardness; increases in phosphorus give added hardness, but a tendency to brittleness. To avoid this brittleness care must be taken to limit the amount of phosphorus in the alloy to a maximum of 1-5%.

The phosphor bronzes can be sand cast, chill cast, continuously cast and centrifugally cast; they are largely used in the chill cast form, in which, owing to the quick cooling, the amounts of the hard constituents are increased and much more finely dispersed throughout the matrix than in the sand cast state giving an extremely tough and hard wearing alloy.

The grain structure of the chill cast and continuously cast alloy is not only finer than the sand cast alloy, but usually freer from porosity. The centrifugally cast alloy is usually sounder even than the chill cast alloy, equal in strength to it and higher in ductility.

The phosphor bronzes can be recommended for all services where toughness, wear resistance and hardness are required; they have good corrosion resistance to tap waters, mine waters, mild alkalis and petroleum derivatives. As their thermal and electrical conductivities are only a little inferior to the gunmetals, they are often useful when such properties are required because of their high mechanical strength.

The above properties make the phosphor bronzes very suitable for the following uses:

    * Bearings and bushes subject to varying loads and duties, gear and worm wheels
    * Parts for air compressors, aero engines, diesel engines
    * Marine parts, generator and mining machinery, hoist fittings, piston rings, chemical pressure vessels, zinc free pump bodies, casings and impellers, acid resisting castings.

PB1C (B.S.1059, STA7-CP5): Sn min. 10.0%; P min. 0.50%
This is a very high grade phosphor bronze, free from zinc, with low lead (0.25% max.) which was originally introduced for use in the mines and was later developed for the aircraft industry as B8 and subsequently 2B8.

It is used for gears, bearings and bushes for heavy loads and high duty with adequate lubrication, and for duty with hard steel shafts. Typical are bearings for aero engines, diesel engines, electrical generators and rolling mills. The alloy is also greatly used for gear and worm wheels, for pump parts particularly in mine waters and for marine work. The alloy can be chill cast, continuously cast, centrifugally cast and sand cast. For bearings and bushes a large amount is produced in the form of chill cast stick and continuously cast tubes and rods. For gears the alloy is mostly centrifugally, continuously or chill cast.

PB4C (SAE 65): Sn min. 9.5%; Pb max. 0.75%; Zn max. 0.5%; P min. 0.5%
For parts required for Air Ministry and Admiralty work of the highest quality, the alloy PB1 is necessary but where conditions are less onerous there is a place for an alloy of a similar type, but with a wider tolerance of impurities such as zinc, lead and nickel. To meet this need, the alloy PB4 has been introduced. The tin content is 0.5% lower than PB1 and lead is permitted up to 0.75% compared with 0.25% in PB1; zinc, which is absent from PB1, is permitted up to 0.5%.

PB2C (B.S.421, STA7-CP6, SAE 65): Sn=11.0-13.0%; Pb max. 0.50%; P min 0.15%
This alloy has a higher tin content than PB1 and lower phosphorus. It is tougher and therefore eminently suitable for gear and worm wheels which is its main use. It is resistant to shock and will stand heavy loading when used for bearing purposes. The alloy can be sand cast, chill cast, continuously cast and centrifugally cast.

PB3 (SAE65): Sn=8.0-11.0%; Pb max. 0.25%; P=0.10-0.40%
This alloy, which has a lower phosphorus content than PB1, is primarily intended for use as a zinc free copper-tin alloy for corrosion resistant and pressure tight castings. It has a very low impurity limit (0.30% excluding lead) and is used chiefly for chemical plant such as pressure vessels, pump bodies, casings and impellers.

LPB1C (B.S. 1061, STA7-CP3): Sn=6.5-8.5%; Pb=2.0-5.0%; P=min. 0.30%; Zn max. 2.0%; Ni max. 1.0%
This alloy has a lower tin and phosphorus content than PB1 and also contains up to 5% lead and may contain up to 2% of zinc and 1% of nickel. The lead is dispersed throughout the structure in fine globules. It is suitable for bearings and bushes for lighter duties, and due to the lead content, for use with limited lubrication. It is very easily machined.

The alloy can be sand cast, chill cast and centrifugally cast; large quantities are used in chill cast stick form for various types of bearings and bushes; it is also used for plant not required to stand the rigorous duties.

The term gunmetal applied today originates from the mid-19th century, when zinc was first added to binary bronze ordnance parts to improve their casting characteristics. British Admiralty gunmetal, with its nominal composition 88% copper, 10% tin, and, 2% zinc, was thus developed. Similar specifications also became standard, the French ordnance alloy being Cu-90%, Sn-6% Zn-4%, and the U.S. Ordnance alloy Cu-88%, Sn-8% Zn-4%, this latter specification being now covered by G2-C.

Although these alloys are now no longer used for ordnance parts the term "gunmetal" has remained; they are extensively used today in many different engineering fields. Gunmetal has good casting characteristics, particularly as a sand casting, and so is often employed in the production of pump casings and for similar components where comparatively high strength, coupled with pressure tightness and corrosion resistance are important requirements.

G1-C is often specified for various types of valve guides, bearings and bushes, particularly in the gas and oil engine field and where bearing/shaft alignments can be ensured and lubrication is good. Gunmetal has a low coefficient of friction. Very good corrosion resisting properties makes its use commonplace in marine engine ring.

With nickel content at 1%, gunmetals are often employed for valves and gears or for those applications where hardness and toughness are important attributes. Overall, the wear resistance of gunmetal is not as good as phosphor bronze.

G3 alloy, particularly in the sand-cast condition "as cast", shows improved tensile strength, elongation, compressive strength, hardness and impact resistance compared with Admiralty Gunmetal G1. However, its production is slightly more difficult and calls for special care of techniques of manufacture. These mechanical properties can be improved still further by heat treatment but at the expense of some impact resistance and ductility.

The G3 alloy finds particular use in atmospheric corrosive conditions, especially where the concentration of sulfur dioxide reaches a high level. Wear resistance properties are better in the "as cast" condition than the heat treated condition and for slow moving bearings, it is quite satisfactory for many applications. In the heat treated condition, it is used for bearing cages, pump and valve parts, impellers, liners, electrical switch gear components, trolley hangers, etc. This alloy is, however, not satisfactory for use at elevated temperatures because it is age hardenable, and becomes embrittled.

Leaded Gunmetals
The alloys in this group (LGI-C, LG2-C, LG3-C and LG4-C) have lower tin contents than the gunmetals and contain lead.

LG1-C     Sn=2.0-4.0%;     Pb=3.0-6.0%;     Zn=7.0-10.0%;     Ni=1.0%;     Cu=Rem.
LG2-C     Sn=4.0-6.0%;     Pb=4.0-6.0%;     Zn=4.0-6.0%;     Ni=2.0%;     Cu=Rem.
LG3-C     Sn=6.0-8.0%;     Pb=1.0-3.0%;     Zn=3.0-5.0%;     Ni=2.0%;     Cu=Rem.
LG4-C     Sn=6.5-7.5%;     Pb=2.5-3.0%;     Zn=1.5-3.0%;     Ni=2.0%;     Cu=Rem.

Their most common application is for all types of general and constructional castings, particularly in the form of pump casings, valve bodies, miscellaneous housing and water pump fitments where strength is not an important factor. They possess excellent pressure tightness qualities, which, many authorities claim, improve with increase of zinc content. The corrosion resistance properties of leaded gunmetals are generally good.

Chill cast leaded gunmetals are widely used for miscellaneous small bushes of low stressing but they are, of course, considerably less wear resistant than gunmetal and phosphor bronzes.

Of the group, probably leaded gunmetal LG2-C is most commonly employed where pressure tightness is essential. Similarly, leaded gunmetal of the LG4 type is extensively used for low stressed bushes.

Principal Uses
Gl-C (DIN1705-Rg.10; ASTM.B.143-52.1A, etc). This is the most commonly used lead free gunmetal and is considered a high grade alloy used extensively for corrosion resistance in marine conditions and for pressure tightness.

The alloy has many uses such as for bearings and bushes, pumps and pump fittings, valves, valve bodies and valve guides. It is also used to some extent for gears, particularly when the nickel content, which gives the toughness and hardness required, is near the top limit of 1%. It must, however, be remembered that its overall wear resistance properties are inferior to the phosphor bronzes.

G2-C. Because of its slightly lower tin content this alloy is sometimes favored on economic grounds. Whilst its applications are similar to those of G1-C, it is not nearly so commonly used.

G3-C. This alloy is used for corrosive conditions and is finding increasing use in the electrification of the railways for insulator hanger supports. It is also used for cast components, such as actuating nuts, valve and pump and similar components at normal temperatures. It responds to heat treatment on the improved permanent set stress and ultimate strength with some loss of elongation.

LG1-C. This alloy is by far the least used of the leaded gunmetals, although its uses must be considered as similar in some respects to LG2-C.

LG2-C. The principal uses of this alloy are for valve bodies, pump bodies, elbows, pipes, taps and cocks and other hydraulic fittings where pressure tight properties are important. Its corrosion resistance properties rate fairly high and it also finds application in low-stressed bearings and moving parts.

LG3-C. A general purpose alloy for pressure components used for pump and valve parts, elbows, pipes, etc.

LG4-C. A very old established alloy extensively used on the railways and elsewhere for bearing and engine components, tractor parts, etc., and also for pressure components, pumps, valve parts, elbows, pipes, etc.

Leaded Bronzes
Leaded bronzes are alloys containing tin, lead and copper as the main constituents, sometimes with the addition of zinc and nickel. The structure consists of a matrix of copper with tin in solid solution, known as the alpha phase, which is comparatively soft, with a hard tin rich delta phase interspersed throughout the matrix.

Lead is insoluble in the copper base alloys and is distributed in fine globules throughout the alloy. Lead additions make the alloys more plastic and in bearing practice this is useful with softer shafts; if any slight misalignment has to be accommodated where variable or alternating loading is involved or where only limited lubrication is possible.

The general strength, toughness and resistance to shock of the bronzes is considerably lowered by the addition of lead; nevertheless the alloys find considerable use in certain limited fields. Because of the high working temperature possible with high-leaded bronze LB5, compared with white metals, it is used a great deal for steel backed bearings in the motor and aircraft industries.

All the leaded bronzes can be sand cast, chill cast or continuously cast and LB1, LB2, LB3 and LB4 can also be centrifugally cast.

These alloys are used for bearings and bushes for mining machinery, to resist corrosive waters and for poor lubrication conditions. As unlined bearings for certain rolling mills, and for liners in the paper making industry where resistance to corrosion is necessary, railway bearings, and steam packing metals, pump parts for mildly corrosive conditions, bearings for use in the oil industry and the high leaded bronze as steel backed bearing for the high working temperature which it supports.

LB1-C:
Sn=8.0-10.0%;     Pb=13.0-17.0%;     Zn=max.1.0%;     Ni= max.2.0%;     Cu=Rem.
LB2-C:
Sn=9.0-11.0%;     Pb=8.5-11.0%;     Zn= max.0.75%;     Ni=max.2.0%;     Cu=Rem.
LB3-C:
Sn=9.0-11.0%;     Pb=4.0-6.0%;     Zn=max.1.0%;     Ni=max.2.0%;     Cu=Rem.
LB4-C:
Sn=4.0-6.0%;     Pb=8.0-11.0%;     Zn=max.2.0%;     Ni=max.2.0%;     Cu=Rem.
LB5-C:
Sn=4.0-6.0%;     Pb=18.0-23.00%;     Zn=max.1.0%;     Ni=max.2.0%;     Cu=Rem.

LB1. It is sometimes used for bearings in mining machinery in corrosive water conditions and for unlined bearings under poor lubrication conditions. The alloy is soft enough to allow for some misalignment of the bearings.

LB2. The alloy is used for lower loads and medium speeds than straight tin bronzes and has good resistance to wear and to corrosive mine waters. Very extensively used in chill cast, centrifugally cast and continuously cast form for bushes for general purposes. It is also used for mill bearings, railway bearings and in the oil industry.

LB3. A general purpose alloy of reasonable mechanical properties; has good resistance to wear and to corrosive mine waters; for any applications of lower loads and medium speeds. It is principally used in the chill cast, centrifugally cast and continuously cast form for bushes.

LB4. A general purpose bearing bronze, which is reasonably tolerant of faulty lubrication and minor misalignment conditions. It has similar applications to LB2 but has a lower tin content and wider composition tolerances.

LB5. This alloy is of high lead content and is used for steel backed motor and aero engine bearings for use at higher temperatures than the traditional white metal linings. It is also used for its self-lubricating properties under conditions where lubrication is difficult.

Aluminum Bronzes
The cast aluminum bronzes are basically copper-aluminum alloys, but they fall into two distinct groups:

AB1 (B.S. 1400)           Al=8.5-10.5%, Fe=1.5-3.5%, Mn=max.1.0%, Ni=max1.0%, and
AB2 (B.S. 1400)           Al=8.5-10.5%, Fe=3.5-4.5%, Mn=max.1.5%, Ni=4.5-6.5%

Structurally, alloys such as AB1 consist of two principal phases, alpha and beta, the iron addition appearing as a separate minor phase, while those alloys such as AB2, containing nickel and iron, have more complex structures.

Aluminum bronzes AB1 are alloys of medium strength, with good ductility and resistance to shock; they also retain a useful proportion of their strength at elevated temperatures. Corrosion resistance is reasonable, but dependent on casting section and rate of cooling as well as environment.

The complex alloys are alloys of much higher strength, with superior corrosion resistance and good resistance to erosion, fatigue and corrosion fatigue. These alloys also retain well their properties at elevated temperatures with a good resistance to creep at temperatures up to 400°C, and have useful strength at considerably higher temperatures when creep resistance is not of over-riding importance. The complex alloys have properties which make it frequently possible to use them instead of stainless steel, with the added advantage that they are more suitable for the production of castings.

Both types of alloys are suitable for both die-casting and sand casting. The alloy AB1 is more suitable for the economic production of die-castings and is, therefore, more normally used if its properties are adequate for the service requirements.

These alloys can be welded and are, therefore, suitable for castings which have to be included in fabrications.

Because of their inherent resistance to corrosion these alloys find wide application in marine engineering and in the petroleum, oil and chemical industries. They are used in engineering generally for their high strength, resistance to fatigue and wear resistance.

In the sand casting field, particular reference might be made to pressure-tight castings, such as for pump work, particularly where resistance to erosion is required, for water turbine impellers and casings, marine castings generally and gearwheels, when loads are heavy and speeds slow, or where high resistance to shock is required.

Die-castings are widely used in the automobile industry, for cars, commercial vehicles, tractors, heavy military vehicles and motorcycles. Typical applications include gearbox parts, clutch shoes, rocker brackets, impellers, tractor glands, locking bars, housings for gear levers, bearing cages and hot spot tongues. Other items are cylinders for heavy duty hydraulic brakes and mounting brackets. In marine engineering the main applications are buckets, pistons for feed water pumps, clutch plates, glands, nuts, seats, and sleeves for valves, and various components for sanitary fittings. In the aircraft industry components are supplied for radar equipment, stowage buckles, and high pressure oil feed buckets, but the use of the alloy is limited because of its high specific gravity.

Aluminum bronze die-castings are also finding application in atomic engineering for heavy components for high duty valve gears; they are widely used in electrical engineering for brush boxes, switchgear components and coal mine switch and control gear. In general engineering the applications are too numerous for a representative list to be given, but they include examples such as components for bottle-washing machinery, papermaking machinery, printing presses, sight feed lubricators, flue gas recorders, metal window furniture and bevel gears.

Manganese Bronzes (High Tensile Brasses)
High tensile brasses or manganese bronzes are alloys of copper and zinc in which the strength normally associated with straight copper-zinc-alloys is very considerably increased by the addition of elements such as aluminum, manganese, tin, iron and nickel.

HTB1           Cu=min.55.0%, Fe=0.5-2.0%, Mn=max3.0%, Al=max.2.5%, Ni=max.1.0%, Pb=max.0.5%, Sn=max.1.5%, Zn= Rem.
HTB2           Cu=min.55.0%, Fe=0.5-2.5%, Mn=max3.0%, Al=max.5.0%, Ni=max.2.0%, Pb=max.0.5%, Sn=max.0.5%, Zn= Rem.
HTB3           Cu=min.55.0%, Fe=1.5-2.5%, Mn=max 4.0%, Al=3.0-6.0%, Ni=max.1.0%, Pb=max.0.2%, Sn=max.0.2%, Zn= Rem.

The structure of the brasses (copper-zinc-alloys) containing up to about 36.5% zinc, consists of a single phase, alpha. With more than 36.5% zinc a second phase, beta, is formed which increases in proportion as the zinc increases, until at about 46.5% zinc the alloy consists of the beta phase only.

Some of the added elements (e.g. aluminum and tin) have a considerable influence on the structure in that they act in equivalence to zinc and alter the proportion of the alpha and beta phases; others, particularly manganese and iron, can, if present in sufficient quantities, lead to the formation of separate phases. Normally, the amount of manganese added is not sufficient to form a separate phase, but it is important that sufficient iron is present to produce the iron-rich phase which is essential to proper grain refinement.

The high tensile brasses which are in general use, i.e. HTB1 and HTB2, have alpha-beta structures, throughout which is distributed the complex iron-rich phase.

There is a third higher strength alloy, HTB3, which is of all-beta structure (also with the grain refining phase) which is susceptible to stress corrosion cracking, as are all the all-beta alloys.

It will probably be observed that the specified composition limits for these alloys are widely set; they have been developed during the last 70 years, often for specific applications and it is important that a particular alloy should have a suitable proportion of copper and zinc, together with a combination of added elements designed to give the tensile strength and other characteristics which might be required, such as resistance to sea water corrosion. To obtain the varied properties which may be required wide ranges of composition are permitted by the specification and it is strongly recommended that castings in these alloys should be obtained only from those foundries which have the necessary experience in their manufacture.

Whilst these alloys have excellent strength characteristics, which can be superior to those of the aluminum bronzes (particularly with regard to proof stress), the fatigue and corrosion fatigue values cover a considerable range from not quite as good as aluminum bronze to very much inferior. These alloys are characterized by a rapid falling in properties with increase in temperature and should, therefore, not be used for applications involving temperatures in excess of 150°C.

These alloys can be tinned although some compositions are more suitable than others. They are all slightly ferro-magnetic to varying degrees. HTB1 is suitable for sand and die-casting; HTB2 and HTB3 can be sand cast only.

Typical applications for which high tensile brasses HTB1 and HTB2 are employed are components highly stressed at normal temperatures, marine propellers and cones, rudders and rudder posts, gun mountings, hydraulic equipment, water turbine equipment, locomotive axle boxes, pump casings and marine castings and fittings.

The high strength all-beta alloy, HTB3, is used for heavy rolling mill housing nuts, rolling-mill slipper castings, and spur and gear wheels which are heavily loaded and slow moving. The warning is repeated that HTB3 is susceptible to stress-corrosion cracking, that is, if it is subjected simultaneously to the influence of stress and corrosion (including certain atmospheres) it is liable to crack and for this reason great caution must be exercised in its use.

Castings required for high strength and resistance to fatigue
For those applications in which high strength or resistance to fatigue are important the alloys normally used are the high tensile brasses, aluminum bronzes or copper-manganese-aluminum alloys.

It is very important that the designer should be aware of the precise factors, which are significant in any particular case. For example, tensile strength is rarely significant in that the designer is not interested in the stress under which a component will break but rather in the stress under which it will start to deform; therefore, under conditions of static stress, proof stress is the more useful indication of the suitability of the material.

While proof stress in itself indicates deformation under load, the property most readily determined as a means of testing material is the permanent set stress, the values for which, in the case of the high tensile brasses and aluminum bronzes, can be taken as being approximately 14MPa (1 ton per square inch) higher than the corresponding proof stress values. Under conditions of cyclic loading or vibration, the significant factor is fatigue, or, if corrosion is also involved, corrosion fatigue.

It is important that full consideration should be given to other properties which are required in any particular application, such as general corrosion resistance or wear resistance. It can be generally accepted that the aluminum bronzes and copper-manganese-aluminum alloys (CMA) alloys are superior to high tensile brasses in both these respects. Under marine conditions the high tensile brasses are suitable, provided a suitable composition is used. Generally, the high tensile brasses should not be used in applications involving rubbing. More details are given concerning corrosion and wear resistance in the appropriate sections.

High tensile brasses, aluminum bronzes and the CMA alloys can be supplied in the form of sand or die-castings. Sand castings can be undertaken of the order of 60 tons or more in cast weight.

Castings required for pressure tightness
Hydraulic or gas pressure is a particularly searching test of the quality of a casting, revealing defects which might have quite insignificant effects on the strength of the casting. Any discontinuities through the metal forming the wall of the casting, however small, are potential sources of leakage.

Given a reasonable design, it is possible to make pressure tight castings from any of the copper base alloys. The aluminium bronzes, high tensile brasses and CMA alloys require careful foundry techniques, but it is possible to make excellent pressure tight castings from these alloys. Because of the greatly increased mechanical properties it is possible to make weight reductions in the castings which should more than compensate for the extra costs involved in producing them.

The best alloys of all for the production of pressure tight castings are those containing substantial amounts of lead and the majority of pressure tight castings are made either from leaded gunmetals or plumbers’ brass. These leaded alloys are also very much more easily machined than other copper base alloys; an important consideration with such castings as valves and pump bodies.

In designing castings for these applications sudden changes in thickness in adjacent sections should be avoided as far as possible. Where this cannot be done the angles should be rounded or filleted. The greatest number of failures in pressure tightness occurs round areas where there are sudden changes of wall thickness. Machining allowances should be kept to a minimum to avoid taking away too much of the close-grain metal near the skin.

A test of pressure tightness frequently applied to small valve bodies and similar castings is that in which air is applied to the casting submerged in water. Air at 100 lb. per sq. in. (0,07 bar) is generally used. This test is applied to castings such as valve bodies with weights between 4oz (0,1 kg) and 24lb (10 kg) approximately. For larger castings it is more usual to test under hydraulic pressure.

Castings required for resistance to corrosion
Copper and copper base alloys are noteworthy for their resistance to corrosion and this is often the main reason for their use. For certain applications, some of the alloys have better corrosion resistance than others and these notes are intended to give general guidance on the selection of an alloy.

It must be emphasized most strongly that it is impossible to do more than give general guidance as local conditions can materially alter the behavior of an alloy so that full details of the service conditions must always be taken into account. The user is strongly recommended to consult his supplier unless he has previous experience of the behavior of copper alloys in the particular circumstances concerned.

Atmospheric Corrosion. All cast copper alloys have good resistance to atmospheric corrosion, although most undergo superficial tarnishing generally resulting in the development of the well-known greenish patina. Corrosion rates of copper base alloys are higher in sulphur bearing atmospheres, and are not, therefore, so suitable where the concentration of sulphur dioxide in the atmosphere reaches a high level as in chimneys and railway tunnels, with the exception of alloy G3 which has now been included in the standard because of its suitability for this application.

Natural Waters. Corrosion rates in natural waters are generally negligible and the cast brasses are traditionally used for plumbing and similar fittings. Some mine waters may be appreciably acid in character and these are more aggressive, especially where they contain iron salts, particularly ferric chloride. The phosphor bronzes, aluminum bronze alloys are the most suitable alloys for such applications.

Seawater. The phosphor bronzes and gunmetals have notably good resistance to corrosion by seawater and are used for such purposes as pipe fittings, cocks and pump bodies. The high zinc brasses tend to undergo slow de-zincification, but this is very much reduced by the addition of tin and for most applications where temperatures are normal they are satisfactory. High tensile brasses of suitable composition are widely used for marine propellers. (De-zincification is selective attack on the zinc-rich constituents in a brass and can be deeply penetrative. It is confined mainly to high zinc brasses and to a large extent is inhibited by the inclusion of tin in an alloy of suitable composition.) Aluminium bronze suffers de-aluminification under some circumstances in sea-water selective form of attack similar to de-zincification.

Waters. Phosphor bronzes and gunmetals are used for handling boiler feed waters. Aluminium bronze AB2 and the CMA alloys are also satisfactory for this purpose. The brasses tend to undergo de-zincification and are not so suitable; de-aluminification of aluminum bronze AB1 may sometimes occur.

Acids. Copper alloys are not completely resistant to attack by acids, but rates of attack in dilute acids where conditions are non-oxidizing are very low, ranging from about 0.002-0.08 inch per year according to the concentration and degree of aeration. The best resistance to attack is afforded by aluminum bronze AB2. The phosphor bronzes are also very suitable for handling dilute acids. Leaded bronzes are sometimes recommended for dilute sulphuric acid. Brasses are not generally so satisfactory. Corrosion rates are higher with hydrochloric acid than with sulphuric acid, but phosphor bronze, aluminium bronze and the CMA alloys are frequently used. Strong aeration of the solution or the presence of oxidizing salts can considerably increase the rate of attack. Oxidizing acids such as nitric acid or strong sulphuric acid cannot be handled with copper alloys.

Alkalis. The resistance of the copper alloys to alkaline solutions is not so high as to acid solutions and, although they can be used for handling dilute caustic alkalis, ferrous materials are generally more satisfactory. All the alloys with the exception of the CMA alloys suffer considerable attack in solutions of ammonia or ammonium salts and they are unsatisfactory for these applications.

Food Products. Copper alloys are widely used for handling food products, though in many cases they are given a heavy coating of tin. This is not so much to protect the alloys against attack, but rather to avoid risk of traces of copper affecting the food. Very small amounts of copper can cause discoloration or an alteration in the flavor of certain foods.

Stress Corrosion. There is a danger of stress corrosion with highly stressed components cast in beta brass HTB3. Failure takes the form of cracks spreading rapidly with little or no general corrosion. Two conditions are necessary: first, the presence of high stresses and, secondly, the presence of a corrosive medium such as seawater or an industrial or marine environment.

Castings required for service at elevated temperatures
When considering service at elevated temperatures, important factors are load carrying capacity, structural stability and resistance to oxidation.

Resistance to Oxidation. Some of the copper base alloys contain additions of aluminum and these have exceptional resistance to oxidation. The aluminum bronzes and certain of the high tensile brasses remain practically unaffected by oxidation almost up to the melting point. This property is used in certain applications such as moulds for glassware, which are frequently made from aluminum bronze, an application involving very high operating temperatures but where the stresses are quite low. The casting alloys containing no aluminum are less resistant to oxidation but suffer no more than superficial tarnishing at temperatures up to 320°C.

Load Carrying Capacity. Despite the relatively good room temperature mechanical properties of some of the alloys, none of the cast copper base alloys is suitable for sustaining high loads at high temperatures. Their high temperature applications are mainly in cases where resistance to corrosion and oxidation are important and steel is unsuitable.

In connection with load carrying capacity at elevated temperatures, it must be emphasized that the mechanical properties of an alloy at room temperature are not a reliable guide to its performance at elevated temperatures nor is it safe to base design stresses on the results of short time tensile tests carried out at the operating temperature.

Safe working stresses can only be determined from the results of creep tests of several thousand hours duration in which the deformation of the specimen under load is recorded as time proceeds. Under sustained stress at high temperatures metals undergo slow permanent deformation (plastic strain) and the most useful information to the designer is the load which will cause not more than a certain amount of plastic strain in a given time.

Although they have good room temperature properties, all the brasses begin to fall in strength at temperatures above 150°C and they are not suitable for load carrying applications at higher temperatures, but there are many applications where the loads involved are very low and the resistance of the brasses to oxidation and corrosion makes them a good choice.

Superheated Steam. Many years of service experience have proved the suitability of gunmetal components for handling superheated steam at temperatures up to 290°C (550°F). Aluminum bronzes have also been used for similar applications, but under service conditions where the steam contains chemically active impurities selective attack on these alloys has been experienced. The aluminum bronzes are not recommended for handling steam at high temperatures if the steam is contaminated with small amounts of sulphur dioxide or chlorides.

After iron and aluminum, copper is the third most-prominent commercial metal because of its availability and attractive properties: excellent malleability (or formability), good strength, excellent electrical and thermal conductivity, and superior corrosion resistance. Copper offers the designer moderate levels of density (8.94 g/cm3, or 0.323 lb/in.3), elastic modulus (115 GPa, or 17x106 psi), and melting temperature (1083°C, or 1981°F). It forms many useful alloys to provide a wide variety of engineering property combinations and is not unduly sensitive to most impurity elements. The electrical conductivity of commercially available pure copper, about 101% IACS (International Annealed Copper Standard), is second only to that of commercially pure silver (about 103% IACS). Standard commercial copper is available with higher purity and, therefore, higher conductivity than what was available when its electrical resistivity value at 20°C (70°F) was picked to define the 100% level on the IACS scale in 1913. The thermal conductivity for copper is also high, 391 W/mK (226 Btu/ft.h.°F). Copper and the majority of its alloys are highly workable hot or cold, making them readily commercially available in various wrought forms: forgings, bar, wire, tube, sheet, and foil. In 1995, copper used in wire and cable represented about 50% of U.S. production and in flat products of various thickness another 15%, rod and bar about 14%, tube about 14.5%, with foundries using about 5% for cast products, and metal powder manufacturers about 0.6%. Besides the more familiar copper wire, copper and its alloys are used in electrical and electronic connectors and components, heat-exchanger tubing, plumbing fixtures, hardware, bearings, and coinage. As with other metal systems, copper is intentionally alloyed to improve its strength without unduly degrading ductility or workability. However, it should be recognized that additions of alloying elements also degrade electrical and thermal conductivity by various amounts de- pending on the alloying element, its concentration and location in the microstructure (solid solution or dispersoid). The choice of alloy and condition is most often based on the trade-off between strength and conductivity. Copper and its alloys are readily cast into cake, billet, rod, or plate-suitable for subsequent hot or cold processing into plate, sheet, rod, wire, or tube-via all the standard rolling, drawing, extrusion, forging, machining, and joining methods. Copper is hot worked over the temperature 750 to 875°C (1400 to 1600°F), annealed between cold working steps over the temperature range 375 to 650°C and is thermally stress relieved usually between 200 and 350°C. Many of the applications of copper and its alloys take advantage of the work-hardening capability of the material, with the cold processing deformation of the final forming steps providing the required strength/ductility for direct use or for subsequent forming of stamped components. Copper is easily deformed to more than 95% reduction in area. The amount of cold deformation between softening anneals is usually restricted to 90% avoid excessive crystallographic texturing, especially in rolling of sheet and strip. Wrought Copper Alloys The purpose of adding alloying elements to copper is to optimize the strength, ductility (formability), and thermal stability, without inducing unacceptable loss in fabricability, electrical/thermal conductivity, or corrosion resistance. A list of selected wrought copper alloy compositions and their properties is given in Table 1. In this table, the alloys are arranged in their common alloy group: the coppers (99.3% min Cu), the high-coppers (94% min Cu), brasses (copper-zinc), bronzes (copper-tin, or copper-aluminum, or copper-silicon), copper-nickels, and the nickel silvers (Cu-Ni-Zn). Composition and property data are given by the Copper Development Association (CDA) and are incorporated in the ASTM numbering system, wherein alloys numbered by the designations (now UNS) C10100 to C79900 cover wrought alloys and C80100 to C99900 apply to cast alloys. Copper alloys show excellent hot and cold ductility, although usually not to the same degree as the unalloyed parent metal. Even alloys with large amounts of solution-hardening elements — zinc, aluminum, tin, silicon — that show rapid work hardening are readily commercially processed beyond 50% cold work before a softening anneal is required to permit additional processing. The amount of cold working and the annealing parameters must be balanced to control grain size and crystallographic texturing. These two parameters are controlled to provide annealed strip products at finish gage that have the formability needed in the severe forming and deep drawing commonly done in commercial production of copper, brass, and other copper alloy hardware and cylindrical tubular products. The pure copper alloys, also called the coppers (C10100 to C15900), are melted and cast in inert atmosphere from the highest-purity copper in order to maintain high electrical conductivity (oxygen-free, or OF, copper, C10200). Copper is more commonly cast with a controlled oxygen content (0.04% O as in electrolytic tough pitch, or ETP, copper, C11000) to refine out impurity elements from solution by oxidation. Included in this group are the alloys that are deoxidized with small addition of various elements such as phosphorus (C12200, Cu-0.03P) and the alloys that use minor amounts of alloy additions to greatly improve softening resistance, such as the silver- bearing copper alloys (C10500, Cu-0.034 min Ag) and the zirconium-bearing alloys (C 15000 and C15100, Cu-0.lZr). High-copper alloys (C16000 to C19900) are designed to maintain high conductivity while using dispersions and precipitates to increase strength and softening resistance: iron dispersions in Cu-(1.0-2.5)Fe alloys (C19200, C19400), chromium precipitates in Cu-1Cr (C18200), and the coherent precipitates in the Cu-(0.3-2.0)Be-Co-Ni age-hardening alloys (C17200, C17410, and C17500). Brass alloys are a rather large family of copper-zinc alloys. A significant number of these are binary copper-zinc alloys (C20500 to C28000), utilizing the extensive region of solid solution up to 35% Zn, and offering excellent formability with good work-hardening strength at reasonable cost. The alloys below 15% Zn have good corrosion and stress-corrosion resistance. Alloys above 15% Zn need a stress-relieving heat treatment to avoid stress corrosion and, under certain conditions, can be susceptible to dezincification. Alloys at the higher zinc levels of 35 to 40% Zn contain the bcc beta phase, especially at elevated temperatures, making them hot extrude able and forgeable (alloy C28000 with Cu-40Zn, for example). The beta alloys are also capable of being hot worked while containing additions of 1 to 4% Pb, or more recently bismuth, elements added to provide the dispersion of coarse particles that promote excellent machinability characteristics available with various commercial Cu-Zn-Pb alloys (C31200 to C38500). The tin-brasses (C40400 to C49000) contain various tin additions from 0.3 to 3.0% to enhance corrosion resistance and strength in brass alloys. Besides improving corrosion-resistance properties in copper-zinc tube alloys, such as C44300 (Cu- 30Zn-1Sn), the tin addition also provides for good combinations of strength, formability, and electrical conductivity required by various electrical connectors, such as C42500 (Cu-10Zn- 2Sn). A set of miscellaneous copper-zinc alloys (C66400 to C69900) provide improved strength and corrosion resistance through solution hardening with aluminum, silicon, and manganese, as well as dispersion hardening with iron additions. Bronze alloys consist of several families named for the principal solid-solution alloying element. The familiar tin-bronzes (C50100 to C54400) comprise a set of good work-hardening, solid-solution alloys containing from nominally 0.8% Sn (C50100) to 10% Sn (C52400), usually with a small addition of phosphorus for deoxidation. These alloys provide an excellent combination of strength, formability, softening resistance, electrical conductivity, and corrosion resistance. The aluminum-bronze alloys contain 2 to 15% Al (C60800 to C64200), an element adding good solid-solution strengthening and work hardening, as well as corrosion resistance. The aluminum- bronzes usually contain 1 to 5% Fe, providing elemental dispersions to promote dispersion strengthening and grain size control. The silicon-bronze alloys (C64700 to C66100) generally offer good strength through solution- and work- hardening characteristics, enhanced in some cases with a tin addition, as well as excellent resistance to stress corrosion and general corrosion. Cupronickels are copper-nickel alloys (C70100 to C72900) that utilize the complete solid solubility that copper has for nickel to provide a range of single-phase alloys (C70600 with Cu-10Ni-1.5Fe, and C71500 with Cu-30Ni- 0.8Fe, for example) that offer excellent corrosion resistance and strength. The family of copper-nickel alloys also includes various dispersion- and precipitation-hardening alloys due to the formation of hardening phases with third elements, such as Ni2Si in C70250 (Cu-3Ni-0.7Si-0.15Mg) and the spinodal hardening obtainable in the Cu- Ni-Sn alloys (C72700 with Cu-10Ni-8Sn, for example). Copper-nickel-zinc alloys, also called nickel-silvers, are a family of solid-solution-strengthening and work-hardening alloys with various nickel-zinc levels in the Cu-(4-26)Ni-(3-30)Zn ternary alloy system valued for their strength, formability, and corrosion and tarnish resistance, and, for some applications, metallic white color. Strengthening Mechanisms for Wrought Copper Alloys Copper can be hardened by the various common methods without unduly impairing ductility or electrical conductivity. The metallurgy of copper alloys is suited for using, singly or in combination, the various common strengthening mechanisms: solid solution and work hardening, as well as dispersed particle and precipitation hardening. The commonly used solid-solution hardening elements are zinc, nickel, manganese, aluminum, tin, and silicon, listed in approximate order of increasing effectiveness. Commercial alloys represent the entire range of available solid-solution compositions of each element: up to 35% Zn, and up to (and even beyond) 50% Ni, 50% Mn, 9% Al, 11% Sn, and 4% Si. Work hardening is the principal hardening mechanism applied to most copper alloys, the degree of which depends on the type and amount of alloying element and whether the alloying element remains in solid solution or forms a dispersoid or precipitate phase. Even those alloys that are commercially age hardenable are often provided in the mill hardened tempers; that is, they have been processed with cold work preceding and/or following an age-hardening heat treatment. Table 1. Compositions and properties of selected wrought copper alloys Alloy UNS No. Nominal composition Treatment Tensile strength (MPa) Yield strength (MPa) Elongation (%) Rockwell hardness Pure copper OFHC C10200 99.95 Cu … 221-455 69-365 55-4 … High-copper alloys Beryllium-copper C17200 97.9Cu-1.9Be-0.2Ni or Co Annealed 490 … 35 60 HRB Beryllium-copper C17200 97.9Cu-1.9Be-0.2Ni or Co Hardened 1400 1050 2 42 HRC Brass Gilding, 95% C21000 95Cu-5Zn Annealed 245 77 45 52 HRF Gilding, 95% C21000 95Cu-5Zn Hard 392 350 5 64 HRB Red brass, 85% C23000 85Cu-15Zn Annealed 280 91 47 64 HRF Red brass, 85% C23000 85Cu-15Zn Hard 434 406 5 73 HRB Cartrige brass, 70% C26000 70Cu-30Zn Annealed 357 133 55 72 HRF Cartrige brass, 70% C26000 70Cu-30Zn Hard 532 441 8 82 HRB Muntz metal C28000 60Cu-40Zn Annealed 378 119 45 80 HRF Muntz metal C28000 60Cu-40Zn Half-hard 490 350 15 75 HRB High lead brass C35300 62-Cu-36Zn-2Pb Annealed 350 119 52 68 HRF High lead brass C35300 62-Cu-36Zn-2Pb Hard 420 318 7 80 HRB Bronze Phosphor bronze, 5% C51000 95Cu-5Sn Annealed 350 175 55 40 HRB Phosphor bronze, 5% C51000 95Cu-5Sn Hard 588 581 9 90 HRB Phosphor bronze, 10% C52400 90Cu-10Sn Annealed 483 250 63 62 HRB Phosphor bronze, 10% C52400 90Cu-10Sn Hard 707 658 16 96 HRB Aluminium bronze C60800 95Cu-5Al Annealed 420 175 66 46 HRB Aluminum bronze C60800 95Cu-5Al Cold rolled 700 441 8 94 HRB Aluminum bronze C63000 81.5Cu-9.5Al-5Ni-2.5Fe-1Mn Extruded 690 414 15 96 HRB Aluminum bronze C63000 81.5Cu-9.5Al-5Ni-2.5Fe-1Mn Half hard 814 517 15 98 HRB High-silicon bronze C65500 96Cu-3Si-1Mn Annealed 441 210 55 66 HRB High-silicon bronze C65500 96Cu-3Si-1Mn Hard 658 406 8 95 HRB Copper nickel Cupronickel, 30% C71500 70Cu-30Ni Annealed 385 126 36 40 HRB Cupronickel, 30% C71500 70Cu-30Ni Cold rolled 588 553 3 86 HRB Nickel silver Nickel silver C75700 65Cu-23Zn-12Ni Annealed 427 196 35 55 HRB Nickel silver C75700 65Cu-23Zn-12Ni Hard 595 525 4 89 HRB

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In determining the uses of copper and copper alloys, the properties of major significance are electrical conductivity, thermal conductivity, corrosion resistance, machinability, fatigue characteristics, malleability, formability and strength. In addition, copper has a pleasing color, is nonmagnetic, and is easily finished by plating or lacquering. Copper can also be welded, brazed and soldered satisfactorily.

When it is desirable to improve certain of these basic properties, especially strength, and when such an improvement can be effected with the sacrifice of no other properties except those of limited significance in the intended application, alloying often solves the problem, and such widely used commercial materials as the brasses, leaded brasses, bronzes, copper-nickel alloys, nickel slivers, and special bronzes have been developed in consequence. Nominal compositions of the principal alloys are listed in Table 1.

The greatest single field of use for copper results from the high electrical conductivity of the metal. The reasons for the use of copper for electrical conductors and in the manufacture of all types of electrical equipment are so commonly understood that a detailed discussion is unnecessary. However, even in the electrical industry, high conductivity alone does not give copper great economic value; it is rather the combination of this property with high resistance to corrosion and ease of formability. Even with very high electrical conductivity, a material that is unable to be drawn or fabricated with ease or is subject to rapid corrosion when exposed to normal atmospheric conditions would be impractical in the electrical industry.

Electrolytic tough pitch copper is the preferred material for current-carrying members. Conductivity is 101 % IACS (Table 2) in the soft temper with 220 MPa tensile strength, and 97% in spring rolled temper at 345 to 380 MPa tensile strength.

Temperatures above 200°C will soften tough pitch copper to a tensile strength of 300 to 240 MPa. The three silver-bearing coppers resist softening up to about 340°C, and are less susceptible to creep rupture in highly stressed parts such as turbo generator windings and high-speed commutators. Softening characteristics are important for applications such as commutators that are baked or "seasoned" at elevated temperature to set mica between the copper bars. Copper must not be softened by this treatment.

If electrolytic tough pitch copper is exposed to temperatures above 370°C and reducing gases, especially illuminating gas and hydrogen, embrittlement will almost certainly take place. Oxygen-free copper or phosphor-deoxidized copper is then specified, at higher cost.

The tensile properties of all the coppers are similar at room temperature, although slight differences may influence selection of a specific conductor. Deoxidized copper with no residual deoxidant (oxygen-free copper) has excellent ductility and is used for most severe deep drawing and cold working.

A combination of 480 MPa tensile strength with conductivity of 80% and higher, suited to spot welding tips and seam welding wheels, can be obtained with heat treated chromium copper. Where tensile strength up to about 1350 MPa and fatigue strength of 240 MPa are required and where the penalty of 17% conductivity and high cost are tolerable, heat treated beryllium copper can be used, if the combined effect of ambient temperature and electrical resistance of the part holds temperatures below 370°C.

Conducting springs, contacts and similar highly stressed members that also may have to be formed may use either chromium copper or beryllium copper. Parts are shaped soft and then strengthened by heat treatment. Parts that must be highly machined and highly conductive are made from the free-machining coppers. Widely used is tellurium copper, which has 90% minimum conductivity and a machinability rating of 80 to 90 (free-cutting brass = 100). Leaded copper (1% Pb) or sulfurized copper is also used because of the 80% machinability rating, with most other properties similar to copper. If tensile strengths of 440 to 525 MPa are required at 80% machinability, heat-treated and hard drawn forms of tellurium-nickel copper may be chosen, provided electrical conductivity of 50% is permissible.

Telecommunication parts that carry low currents but require good fatigue properties because of the hundreds of thousands of contacts that are made and broken, may be fabricated from cartridge brass to give a suitable compromise between strength and e lectrical conductivity. If corrosion or severe fatigue are factors to be considered, the more expensive but stronger nickel silvers, phosphor bronzes or beryllium coppers will serve.

Table 1. Nominal composition of Wrought Copper Materials

Alloy	Composition
Coppers
Electrolytic tough pitch (ETP)	99.90 Cu - 0.04 O
Phosphorized. high residual phosphorus (DHP)	99.90 Cu - 0.02 P
Phosphorized, low residual phosphorus (DLP)	99.90 Cu - 0.005 P
Lake	Cu - 8 oz/t Ag
Silver-bearing (10-15)	Cu - 10 to 15 oz/t Ag
Sliver-bearing (25-30)	Cu - 25 to 30 oz/t Ag
Oxygen-free (OF) (no residual deoxidants)	99.92 Cu (min)
Free-cutting	99Cu - 1 Pb
Free-cutting	99.5 Cu - 0.5 Te
Free-cutting	99.4 Cu - 0.6 Se
Chromium copper (heat treatable)	Cu+Cr and Ag or Zn
Cadmium copper	99 Cu - 1 Cd
Tellurium-nickel copper (heat treatable)	98.4 Cu - 1.1 Ni - 0.5 Te
Beryllium copper (heat treatable)	Cu - 2 Be - 0.25 Co or 0.35 Ni
Plain Brasses
Gliding %	95 Cu - 5 Zn
Commercial bronze 90%	90 Cu - 10 Zn
Red brass 85%	85 Cu - 15 Zn
Low brass 80%	80 Cu - 20 Zn
Cartridge brass 70%	70 Cu - 30 Zn
Yellow brass 65%	65 Cu - 35 Zn
Muntz metal	60 Cu - 40 Zn
Free-Cutting Brasses
Leaded commercial bronze (rod)	89 Cu - 9.25 Zn - 1.75 Pb
Leaded brass strip (B121-3)	65 Cu - 34 Zn - 1 Pb
Leaded brass strip (B121-5)	65 Cu - 33 Zn - 2 Pb
Leaded brass tube (B135-3)	66 Cu - 33.5 Zn - 0.5 Pb
Leaded brass tube (B135-4)	66 Cu - 32.4 Zn - 1.6 Pb
Medium-leaded brass rod	64.5 Cu - 34.5 Zn - 1 Pb
High-leaded brass rod	62.5 Cu - 35.75 Zn - 1.75 Pb
Free-cutting brass rod (B16)	61.5 Cu - 35.5 Zn - 3 Pb
Forging brass	60 Cu - 38 Zn - 2 Pb
Architectural bronze	57 Cu - 40 Zn - 3 Pb
Miscellaneous Brasses
Admiralty (inhibited)	71 Cu - 28 Zn -1 Sn
Naval brass	60 Cu - 39.25 Zn - 0.75 Sn
Leaded naval brass	60 Cu - 37.5 Zn - 1.75 Pb - 0.75 Sn
Aluminum brass (inhibited)	76 Cu - 22 Zn - 2 Al
Manganese brass	70 Cu - 28.7 Zn - 1.3 Mn
Manganese bronze rod A (B138)	58.5 Cu - 39 Zn - 1.4 Fe - 1 Sn - 0.1 Mn
Manganese bronze rod B (B138)	65.5 Cu - 23.3 Zn - 4.5 Al - 3.7 Mn - 3 Fe
Phosphor Bronzes
Grade A	95 Cu - 5 Sn
Grade B (rod, B139, alloy B1)	94 Cu - 5 Sn - 1 Pb
Grade C	92 Cu - 8 Sn
Grade D	90 Cu - 10 Sn
Grade E	98.75 Cu - 1.25 Sn
444 bronze rod (B139, alloy B2)	88 Cu - 4 Zn - 4 Sn - 4 Pb
Miscellaneous Bronzes
Silicon bronze A	Cu - 3 Si - 1 Mn
Silicon bronze B	Cu - 1.75 Si - 0.3 Mn
Aluminum bronze, 5%	95Cu - 5 Al
Aluminum bronze, 7%	91 Cu - 7 Al - 2 Fe
Aluminum bronze, 10%	Cu - 9.5 Al
Aluminum-silicon bronze	91 Cu - 7 Al - 2 Si
Nickel-Containing Alloys
Cupro-nickel, 10%	88.5 Cu - 10 Ni - 1.5 Fe
Cupro-nickel, 30%	69.5 Cu - 30 Ni - 0.5 Fe
Nickel silver A	65 Cu - 17 Zn - 18 Ni
Nickel silver B	55 Cu - 27 Zn - 18 Ni
Leaded nickel silver rod (B151)	62 Cu - 19 Zn - 18 N - 1 Pb

Table 2. Comparative Electrical Conductivity of Wrought Copper Materials

Alloy	% IACS
Coppers
Electrolytic (ETP)	101
Silver-bearing, 8 oz/t	101
Silver-bearing, 10 to 15 oz/t	101
Silver-bearing, 25 to 30 oz/t	101
Oxygen-free (OF)	101
Phosphorized (DLP)	97 to 100
Free-cutting (S, Te or Pb)	90 to 98
Chromium coppers	80 to 90
Phosphorized (DHP)	80 to 90
Cadmium copper (1%)	80 to 90
Tellurium-nickel copper	50
Copper Alloys
Brasses	25 to 50
Phosphor bronze E	25 to 50
Naval brass	25 to 50
Admiralty	25 to 50
Phosphor bronze A, C, D	10 to 20
Aluminum bronze, 5%	10 to 20
Silicon bronze B	10 to 20
Beryllium copper	10 to 20
Cupro-nickel, 30%	5 to 15
Nickel silver	5 to 15
Aluminum bronze (over 5% Al)	5 to 15
Silicon bronze A	5 to 15

All values are for the annealed condition. Cold worked alloys may be as much as 5 points lower. Compositions are given in the Table 1.

The important alloys of copper and tin from an industrial point of view are the bronzes comprised within certain limits of tin content. As in the case of the brasses, the addition of tin to copper results in the formation of a series of solid solutions. The constitutional diagram of copper-tin alloys is very complex, but that part of it which deals with alloys of industrial importance is reproduced in Fig. 1.

Figure 1. Constitutional Diagram of the Copper-Tin Alloys

The addition of tin to copper results in the formation of a series of solid solutions which, in accordance with usual practice, are referred to in order of diminishing copper content as the á, â, a, etc., constituents. The diagram may be summarized as follows:

Percentage composition		Constituent just below the freezing point	Constituent after slow cooling to 400°C
Copper	Tin
100 to 87	0 to 13	á	á
87 to 86	13 to 14	á + â	á
86 to 78	14 to 22	á + â	á + ä
78 to 74	22 to 26	â–>(á + â)	á + ä

Further changes on cooling from 400°C to room temperature are so sluggish that they only occur in conditions very far removed from actual practice.

The á solution is the softest of the constituents; it may be rolled or stamped cold, but it hardens under this treatment much more rapidly decreases than á-brass.

The â and a constituents do not exist in the alloy slowly cooled to room temperature: this is due to successive changes occurring at 586°C and 520°C whereby â is resolved into á +a and a into á + ä.

The ä constituent has the crystal structure of a-brass. It has a narrow range of composition corresponding approximately to the formula Cu_3lSn₈ and, like all intermetallic compounds, is extremely hard and brittle. The ä -> (á + l) change at 350°C does not occur in commercial practice, though alloys richer in tin may contain the a constituent, which corresponds to Cu₃Sn, and the ç solid solution, which approximates to the composition CuSn.

95:5 Copper-Tin Alloy

On cooling from the liquid condition, the solid solution which first forms contains only about 2 percent of tin. Thus the cast metal has a cored structure and the coring is very marked because of the long range between liquidus and solidus; but it may be eliminated by diffusion on cooling more slowly or by annealing.

Any absorption of oxygen occurring during manufacture results in the presence of SnO₂ in the alloy, tending to make it brittle. A deoxidizer such as zinc is therefore frequently added. The addition of zinc, as in coinage bronze, causes no change in the microscopical appearance of the homogeneous á constituent. The zinc, however, exerts its deoxidizing effect in the liquid, and slight hardening effect on the solid solution. The structure of a bronze coin shows marked deformation of the crystals. On annealing, recrystallization takes place with subsequent crystal growth. Twinning is a characteristic feature of the cold-worked and annealed alloy.

90:10 Copper-Tin Alloy

This is typical gun-metal, most varieties of which, however, contain a deoxidizer, frequently zinc (e.g. Admiralty gun-metal, copper 88%, tin 10%, zinc 2%). The structure of the cast material depends on the rate of cooling, both through the range of solidification and below.

On account of the wide solidification range of the alloy and the slow rate of tin diffusion, the apparent solubility limit of the á solution is well below that shown in the diagram. The cast structure is always definitely dendritic and if coring is pronounced, some â solution may be formed at 798°C This interdendritic â, on cooling, gives rise to the hard ä constituent. On the other hand, after slow cooling or prolonged annealing, the homogeneous á constituent may be produced. A chill-cast gun-metal will therefore be very different in structure and properties from one which has been annealed.

85:15 Copper-Tin Alloy

This chemical composition is typical for a number of bronzes used as bearing metals, most of which, however, contain a little zinc as a deoxidizer. It is also the approximate composition of bell metal.

Immediately after solidification the alloy consists of the á and â constituents. If rapidly cooled, these are preserved. If slowly cooled, the â (or a) is completely broken down below 520°C into a complex á + ä. The á + â structure is being replaced by á + (á + ä) complex in the slowly cooled alloy. This accounts for the fact that sand castings of this alloy are much harder than chill castings. It also provides the basis of heat treatment method, applied in the one case to bells and in the other to bearing metals.

The copper alloys may be endowed with a wide range of properties by varying their composition and the mechanical and heat treatment to which they are subjected. For this reason they probably rank next to steel in importance to the engineer.

The important alloys of copper and zinc from an industrial point of view are the brasses comprised within certain limits of zinc content. That portion of the constitutional diagram which refers to these alloys is given in the Figure 1.

Figure 1. Constitutional Diagram of the Copper-Zinc Alloys

The addition of zinc to copper results in the formation of a series of solid solutions which, in accordance with usual practice, are referred to in order of diminishing copper content as the a, b, g, etc., constituents. The diagram may be summarized as follows:

Percentage composition		Constituent just below the freezing point	Constituent after slow cooling to 400°C
Copper	Zinc
100 to 67.5	0 to 32.5	a	a
67.5 to 63	32.5 to 37	a + b	a
63 to 61	37 to 39	b	a
61 to 55.5	39 to 45.5	b	a + b`
55.5 to 50	45.5 to 50	b	b`
50 to 43.5	50 to 56.5	b	b` + g
43.5 to 41	56.5 to 59	b + g	b` + g

Further changes in composition of the a and b` phases below 400°C are only observed after prolonged annealing.

There is a certain connection between the properties and the microstructure which may be expressed in general terms.

The tensile strength increases with increase in zinc content, rises somewhat abruptly with the appearance of b, and reaches a maximum at a composition corresponding roughly to equal parts of a and b. It falls off rapidly at the appearance of the g constituent.

Elongation rises to a maximum and begins to fall again before the composition reaches the limit of the a solution. It falls considerably as the amount of b increases, and is very small in the presence of g.

The a constituent shows the greatest resistance to shock. This is diminished by the presence of b, and the alloy becomes extremely brittle when g is present.

Hardness is greatly increased by the presence of b and still further when g appears.

Alloys containing a phase only are specially suitable for cold working, and may be hot- or cold rolled. Those containing a and b will suffer very little deformation without rupture in the cold rolling and may only be hot rolled. The b constituent may also be forged, rolled or hot extruded, but alloys containing g should invariably be avoided for any mechanical treatment.

Designation system of brasses

The brasses of industrial importance are often designated by their copper and zinc content.

C 23000 - Red Brass (85 Cu, 15 Zn)

This alloy is used for ornaments and for cheap jewellery which is to be gilded: it withstands cold-work, cupping, etc. On account of the range of solidification, the cast material has a dendritic structure.

If cooled very slowly or annealed, diffusion takes place, yielding polyhedral grains of uniform composition. The process of diffusion is assisted by mechanical deformation of the grains by hot- or cold work followed by annealing. The changes which occur in rolling and annealing are similar to those described for 70:30 brass.

C 26000 - Cartridge Brass (70 Cu: 30 Zn)

This alloy, which is used widely for tubes, sheets and wires, also shows a dendritic structure of the a solid solution when chill fast. The b constituent does not begin to appear in the cast structure until the zinc exceeds 32% except in the presence of an additional element like aluminum or tin.

After annealing, the alloy consists of homogeneous solid solution, and it is specially suitable for cold-working. To withstand this treatment, especially drawing, it is necessary that the brass should be perfectly sound and free from impurities.

Since high grade 70:30 brass is usually made from the purest copper and zinc available without admixture of any but the cleanest scrap, these impurities are chiefly inclusions of dross (oxides or silicates) or charcoal. Such inclusions, if present, frequently lead to failure of the material during manufacture or in use. They become entrapped in the solidifying metal, either by splashing or by rapid solidification in moulds of small cross section.

It is a frequent procedure in casting brass to draw it into rod to employ very long moulds of very small cross section, in order to minimize subsequent mechanical treatment. Ingots made in such moulds are most liable to contain inclusions and to show piping to a great depth, resulting in central unsoundness over a considerable length of the ingot. To ensure soundness it is necessary to cast in a mould such that the cross section is large enough to give relatively slow cooling. The mould and stream of molten metal should be so arranged as to avoid splashing; the dimensions of the mould and speed of pouring should be such as to result in the ingot solidifying from bottom upwards.

The effect of cold-work on the microstructure is to break down the crystal grains by plastic deformation, and so crush them into confused debris. Annealing after cold-work results in recrystalization and subsequent crystal growth.

C 28000 - Muntz Metal (60 Cu: 40 Zn)

The molten metal begins to freeze at about 905°C, and dendrites of the b solution are formed. With sufficiently slow cooling through the range of solidification the alloy consists of homogeneous b constituent when just solid, but, on cooling, this solution retains less copper and at 770°C the a constituent separates from the homogeneous b and increases in amount as the temperature falls. The structure on reaching atmospheric temperature is therefore a mixture of a and b, the relative proportions of which may be controlled to some extent by the rate of cooling.

For example, a thin section of 60:40 brass quenched from 800°C consists of homogeneous b. With a larger section it is impossible to suppress completely the separation of a, but a specimen rapidly cooled from this temperature always contains more b than a specimen more slowly cooled. These microstructural characteristics are accompanied by changes in mechanical properties which can be deduced from the known hardness and brittleness of the b constituent and the softness and ductility of the a constituent.

Hot-rolled 60:40 brass, the rolling of which has been stopped above 700°C, shows a uniform structure in longitudinal and transverse directions. After the separation, the a and b constituents are each elongated in the direction of rolling, giving the normal structure of rolled 60:40 brass. The lower temperature of finishing, the smaller will be the grain size. If, however, rolling is continued much below 600°C, recrystalization does not keep pace with the deformation and the metal is cold-worked.

Brazing solder (50 Cu: 50 Zn)

This alloy, if cooled sufficiently slowly through the range of solidification, consists of homogeneous b solution, which, however, may decompose on cooling if the copper content is less than 50%. At atmospheric temperature the b solution will retain a maximum of just 50% of zinc if no impurities are present, but any content of zinc over 50% causes the separation of the g constituent, which increases in amount as the temperature falls. Its presence renders the alloy extremely hard and brittle.

Pure copper is extremely difficult to cast as well as being prone to surface cracking, porosity problems, and to the formation of internal cavities. The casting characteristics of copper can be improved by the addition of small amounts of elements including beryllium, silicon, nickel, tin, zinc, chromium and silver.

Copper alloys in cast form (designated in UNS numbering system as C80000 to C99999) are specified when factors such as tensile and compressive strength, wear qualities when subjected to metal-to-metal contact, machinability, thermal and electrical conductivity, appearance, and corrosion resistance are considerations for maximizing product performance. Cast copper alloys are used for applications such as bearings, bushings, gears, fittings, valve bodies, and miscellaneous components for the chemical processing industry. These alloys are poured into many types of castings such as sand, shell, investment, permanent mold, chemical sand, centrifugal, and die casting.

The copper-base casting alloy family can be subdivided into three groups according to solidification (freezing range). Unlike pure metals, alloys solidify over a range of temperatures. Solidification begins when the temperature drops below the liquidus; it is completed when the temperature reaches the solidus. The liquidus is the temperature at which the metal begins to freeze, and the solidus is the temperature at which the metal is completely frozen.

Group I alloys
Group I alloys are alloys that have a narrow freezing range (about 50oC), that is, a range of 50oC between the liquidus and solidus temperature. Group I alloys includes: copper (UNS No. C81100), chromium copper (C81500), yellow brass (C85200, C85400, C85700, C85800, C87900), manganese bronze (C86200, C86300, C86400, C86500, C86700, C86800), aluminum bronze (C95200, C95300, C95400, C95410, C95500, C95600, C95700, C95800) nickel bronze (C97300, C97600, C97800), white brass (C99700, C99750).

Pure Copper and Chromium Copper. Commercially pure copper and high copper alloys are very difficult to melt and are very susceptible to gassing. In the case of chromium copper, oxidation loss of chromium during melting is a problem. Copper and chromium copper should be melted under a floating flux cover to prevent both oxidation and the pickup of hydrogen from moisture in the atmosphere. In the case of copper, crushed graphite should cover the melt. With chromium copper, the cover should be a proprietary flux made for this alloy. When the molten metal reaches 1260oC, either calcium boride or lithium should be plunged into the molten bath to deoxidize the melt. The metal should then be poured without removing the floating cover.

Yellow Brasses. These alloys flare, or lose zinc, due to vaporization at temperatures relatively close to the melting point. For this reason, aluminum is added to increase fluidity and keep zinc vaporization to a minimum. The proper amount of aluminum to be retained in the brass is 0.15 to 0.35%. Above this amount, shrinkage takes place during freezing, and the use of risers becomes necessary. After the addition of aluminum, the melting of yellow brass is very simple, and no fluxing is necessary. Zinc should be added before pouring to compensate the zinc lost in melting.

Manganese Bronzes. These alloys are carefully compounded yellow brasses with measured quantities of iron, manganese, and aluminum. The metal should be melted and heated to the flare temperature or to the point at which zinc oxide vapor can be detected. At this point, the metal should be removed from the furnace and poured. No fluxing is required with these alloys. The only addition required with these alloys is zinc. The amount required is that which is eeded to bring the zinc content back to the original analysis. This varies from very little, if any, when an all-ingot heat is being poured, to several percent if the heat contains a high percentage of remelt.

Aluminum Bronzes. These alloys must be melted carefully under an oxidizing atmosphere and heated to the proper furnace temperature. If needed, degasifiers can be stirred into the melt as the furnace is being tapped. By pouring a blind sprue before tapping and examining the metal after freezing, it is possible to tell whether it shrank or exuded gas. If the sample purged or overflowed the blind sprue during solidification, degassing is necessary. Degasifiers remove hydrogen and oxygen. Also available are fluxes that convert the molten bath. These are in powder form and are usually fluorides. They aid in the elimination of oxides, which normally form on top of the melt during melting and superheating.

Nickel Bronzes. These alloys, also known as nickel silver, are difficult to melt. They gas readily if not melted properly because the presence of nickel increases the hydrogen solubility. Then, too, the higher pouring temperatures aggravate hydrogen pickup. These alloys must be melted under an oxidizing atmosphere and quickly superheated to the proper furnace temperature to allow for temperature losses during fluxing and handling. Proprietary fluxes are available and should be stirred into the melt after tapping the furnace. These fluxes contain manganese, calcium, silicon, magnesium, and phosphorus and do an excellent job in removing hydrogen and oxygen.

White Manganese Bronze. There are two alloys in this family; both of them are copper-zinc alloys containing a large amount of manganese and, in one case, nickel. They are manganese bronze type alloys; they are simple to melt, and can be poured at low temperatures because they are very fluid. They should not be overheated, as this serves no purpose. If the alloys are unduly superheated, zinc is vaporized and the chemistry of the alloy is changed. Normally, no fluxes are used with these alloys.

Group II alloys
Group II alloys are those that have an intermediate freezing range, that is, a freezing range of 50 to 110oC between the liquidus and the solidus. Group II alloys are: beryllium copper (C81400, C82000, C82200, C82400, C82500, C82600, C82800), silicon brass (C87500), silicon bronze (C87300, C87600, C87610, C87800), copper-nickel (C96200, C96400).

Beryllium Coppers. These alloys are very toxic and dangerous if beryllium fumes are not captured and exhausted by proper ventilating equipment. They should be melted quickly under a slightly oxidizing atmosphere to minimize beryllium losses. They can be melted and poured successfully at relatively low temperatures. They are very fluid and pour well.

Silicon Bronzes and Brasses. The alloys known as silicon bronzes, UNS alloys C87300, C87600, and 87610, are relatively easy to melt and should be poured at the proper pouring temperatures. If overheated, they can pick up hydrogen. While degassing is seldom required, if necessary, one of the proprietary degasifiers used with aluminum bronze can be successfully used. Normally no cover fluxes are used here. The silicon brasses (UNS alloys C87500 and C87800) have excellent fluidity and can be poured slightly above their freezing range. Nothing is gained by excessive heating, and in some cases, heats can be gassed if this occurs. Here again, no cover fluxes are required.

Copper-Nickel Alloys. These alloys (90Cu-10Ni, UNS C96200 and 70Cu-30Ni, UNS C96400) must be melted carefully because the presence of nickel in high percentages raises not only the melting point but also the susceptibility to hydrogen pickup. In virtually all foundries, these alloys are melted in coreless electric induction furnaces, because the melting rate is much faster than it is with a fuel-fired furnace. When ingot is melted in this manner, the metal should be quickly heated to a temperature slightly above the pouring temperature and deoxidized either by the use of one of the proprietary degasifiers used with nickel bronzes or, better yet, by plunging 0.1% Mg stick to the bottom of the ladle. The purpose of this is to remove all the oxygen to prevent any possibility of steam-reaction porosity from occurring. Normally there is little need to use cover fluxes if the gates and risers are cleaned by shot blasting prior to melting.

Group III alloys
Group III alloys have a wide freezing range. These alloys have a freezing range of well over 110oC, even up to 170oC. Group III alloys are: leaded red brass (C83450, C83600, C83800), leaded semi-red brasses (C8400, C84800), tin bronze (C90300, C90500, C90700, C91100, C91300), leaded tin bronze (C92200, C92300, C92600, C92700), high-leaded tin bronze (C92900, C93200, C93400, C93500, C93700, C93800, C94300).

These alloys, namely leaded red and semi-red brasses, tin and leaded tin bronzes, and high-leaded tin bronzes, are treated the same in regard to melting and fluxing and thus can be discussed together. Because of the long freezing ranges involved, it has been found that chilling, or the creation of a steep thermal gradient, is far better than using only feeders or risers. Chills and risers should be used in conjunction with each other for these alloys. For this reason, the best pouring temperature is the lowest one that will pour the molds without having misruns or cold shuts. In a well-operated foundry, each pattern should have a pouring temperature, which is maintained by use of an immersion pyrometer.

Fluxing. In regard to fluxing, these alloys should be melted from charges comprised of ingot and clean, sand free gates and risers. The melting should be done quickly in a slightly oxidizing atmosphere. When handled at the proper furnace temperature and cooled to the proper pouring temperature, the crucible is removed or the metal is tapped into a ladle. At this point, a deoxidizer (15% phosphor copper) is added. The phosphorus is a reducing agent (deoxidizer). This product must be carefully measured so that enough oxygen is removed, yet a small amount remains to improve fluidity. This residual level of phosphorus must be closely controlled by chemical analysis to a range between 0.010 and 0.020% P. If more is present, internal porosity may occur and cause leakage if castings are machined and pressure tested.

In addition to phosphor copper, pure zinc should be added at the point at which skimming and temperature testing take place prior to pouring. This replaces the zinc lost by vaporization during melting and superheating. With these alloys, cover fluxes are seldom used. In some foundries in which combustion cannot be properly controlled, oxidizing fluxes are added during melting, followed by final deoxidation by phosphor copper.