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Copper: These castings are ordinarily of high copper content because other elements adversely affect the conductivity of copper. Fittings, cable connections, cable dead ends, spacers, inductor heads, switch parts, etc., require differing degrees of conductivity of copper. Although the best conductivity is obtained with pure copper, the metal is soft, low in strength, difficult to machine, and has less desirable casting properties than many of its alloys. The thermal conductivity property behaves in a manner analogous to electrical conductivity. Castings for water-cooled blast-furnace tuyeres, cooling glands, heat-exchanger parts, and similar applications may be made of conductivity coppe

Copper-Zinc: The solubility of zinc in copper exceeds 30% with higher contents having a stable hard, but brittle, phase. The practical maximum zinc content is 36% because of the loss of ductility. The color of copper-zinc alloys is greatly influenced by zinc content as follows:

Sometimes color is an important reason for using yellow brasses for castings. A particular casting may be required to blend in color with wrought brass parts, for example. Yellow brasses are primarily used for small castings because the mechanical properties are not especially good and casting difficulties due to shrinkage are aggravated in larger castings

The density of copper-zinc alloys decreases with increasing zinc content and decreasing copper content but does depend on the presence of other elements such as lead and tin.

Actual casting brasses are not simple Cu-Zn alloys nor do they have simple microstructures. The compositions may be complicated by the presence of tin, lead, antimony, iron, sulfur, nickel, silicon, aluminum, manganese, phosphorus, and other elements. The leaded red brasses are very commonly used for valves, valve seats, handles, plumbing fixtures, nuts hardware, lock parts, etc. In this group 85% Cu, 5% Sn, 5% Pb, 5% Zn alloy is the most commonly used copper base casting alloy and accounts for the bulk of copper base castings. Leaded yellow brasses have less desirable casting properties but are used because of better corrosion resistance when in contact with fuel oil, or other petroleum products.

High strength yellow brasses, leaded or not, are employed where high mechanical properties are desired in the as-cast condition. Ship propellers illustrate an application requiring high strength as well as resistance to the corrosive effects of salt water. The presence of aluminum in these alloys improves strength since 1% of Al is equivalent to about 6% Zn. Iron in these alloys assists in obtaining a finer grain size as it may in any of the copper casting alloys. Tin may be present to enhance corrosion resistance.

Copper-Tin: The alloying behavior of tin in copper is similar to that of zinc but with lower solubility. Tin is more effective percentage wise in strengthening copper than zinc but also must be balanced because of the loss of ductility at increasing amounts. Alloys having from 5 to 15% tin have an unusually long freezing temperature range, over 400F. The long solidification range makes castings of these alloys very hard to riser adequately and also promotes severe coring.

The tin bronzes based on the Cu-Sn system have strength, hardness, and bearing qualities which make them suitable for gears, worms, bearing plates, turntables sleeves, and liners. Because of corrosion resistance, these applications find frequent use in marine construction, naval vessels, bridges, dams, hydroelectric plants, chemical-processing industries and the like. The alloy 88% Cu, 10% Sn, 2% Zn is known as G-bronze or gun metal. The alloys are possessed of better all around resistance to sea water than the brasses so that they are used extensively in that field. Bell bronzes contain 20 to 23% tin, are relatively hard and brittle, and have the ability to produce musical tones when struck, which makes for their use in bell castings. Lead is added to tin bronzes for machinability or to obtain antifrictional properties. High-leaded tin bronzes are useful for sleeves, bushings, and bearings for railroad, rolling mill, and papermaking applications where good bearing qualities against steel or iron surfaces are needed.

Copper-Lead: The solubility of lead in copper is very low resulting in copper alloys having most of their lead present as islands of the element distributed throughout the microstructure. Since the lead is precipitated late during freezing of the metal, it segregates in areas which freeze last. At the end of freezing it may fill in areas which might otherwise become shrinkage porosity. Lead in copper thus often makes it easier to produce leakproof castings for valves and fittings. Another beneficial effect of lead is its use for improving machinability of copper alloys. The weak lead islands make machining soft, tough copper alloys to a fine finish easier by causing machining chips to form, break, and flow more easily from cutting tools.

In castings, the distribution of the lead islands is greatly determined by the lead content, rate of solidification of the casting, and the presence of other elements. The strength of brasses and bronzes is lowered below maximum by the presence of excess lead, and it therefore may be considered as an impurity in some of the high strength alloys, even though it is beneficial in other alloys.

Copper-Aluminum: Aluminum is soluble in copper to approximately 7% aluminum. At higher percentages, about 12% aluminum, a eutectoid forms allowing the castings to be heat treated in a manner similar to steel. Quenching after holding at 1450F to 1600F and then reheating to 650F to 1250F gives optimum combinations of strength, hardness and ductility. The highest strength and hardness among copper base alloys are found in heat treated aluminum bronzes and also in heat treated Cu-Be bronzes.

The narrow freezing temperature range of copper aluminum alloys, 20 to 50F, results in a large apparent solidification shrinkage and requires heavy risering to produce sound castings. However, the narrow freezing range makes it possible to produce castings of maximum soundness with less tendency for micro-shrinkage than in long freezing range alloys. Melting of the alloy is complicated because of its ability to reduce water vapor and as such is prone to hydrogen pick-up. An oxidizing atmosphere around the liquid metal can cause a low surface tension dross which can be mechanically agitated into the metal during melting or pouring.

Aluminum bronzes are of both a low and high aluminum types. The lower aluminum types are softer and have better ductilty and are not heat treated. The higher aluminum types take advantage of the heat treating capabilities to achieve the higher hardness and strength. Both classes of alloys contain appreciable percentages of iron. This element is necessary to achieve grain size control of the cast alloy. In the absence of iron, these alloys would have a very coarse grain size with poor mechanical properties. More than .75% iron is needed for grain refinement but excessive amounts can cause iron segregation and hard spots in the casting.

Aluminum bronzes also sometimes contain manganese and cickel as alloying elements. The alloys are used for applications requiring a combination of high strength, hardness and corrosion resistance. Examples are worm gears, sliding plates, bearing sleeves, pickling baskets, bearings and sleeves for paper mills, castings for marine use, and the like. Non-sparking tools and non-magnetic instruments are further uses of these casting alloys.

Copper-Beryllium: Beryllium is soluble in copper to approximately 2.0% Be. Typical Be contents are about 1.0% with alloys containing additions of cobalt and nickel. The alloys can be solution heat-treated and precipitation hardened to high hardness and strength. Their combination of low alloy content and high strength obtainable by heat treatment qualifies them as high-strength high conductivity copper casting alloys. More extensive use of this alloy group is precluded by the high toxicity of beryllium from both a casting and machining perspective.

Nickel Brasses and Bronzes: Nickel brasses and bronzes are nickel bearing alloys which have a silver or white color rather that the copper, brass, or bronze colors of other copper base alloys. Because of their appearance they may be called "nickel silver" or german silver". The white or silver color presents a pleasing appearance, especially with monel, stainless steels, aluminum, or other metals with a silvery luster. Nickel brasses have only enough of their zinc content substituted by nickel to give a white color. Nickel bronzes contain more nickel than zinc, over 10% nickel, and some tin. The leaded alloys contain 1.0 to 11.0% lead to improve casting, machining, and pressure tightness. The uses of these alloys include hardware and ornamental fittings, valves, dairy and food handling equipment castings, trim for ships and other marine use, soda fountains, and such. Generally an application where a white color and moderate corrosion resistance is desired.

Another group of white-colored copper base alloys are the cupronickels. Their uses are similar to the nickel brasses and bronze but they have somewhat better corrosion resistance.

Summary of Copper Base Alloys: Another approach to understanding copper base alloys is to think of them as falling in one of three general categories, General Purpose Alloys, Engineering Alloys and Art Alloys. The leaded alloys are using considered to be the general purpose alloys because of their traditional use over many years employing the basic advantages of copper. The engineering alloys are in contrast and exhibit a designing of an alloy to assure the reaching of a minimum physical property for a specific application such as minimum strength, minimum electrical conductivity, etc. The third art grouping use the very good casting characteristics of some alloys to produce a casting which has good durability and appearance in everyday encounters with people. As an example, Silicon Bronze is very widely used for this type of application.

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