Copper Alloys C
ast copper alloys are known for their versatility. T ey are used in plumbing fi xtures, ship propellers, power plant water impellers and bushing
and bearing sleeves because they are easily cast, have a long history of suc- cessful use, are readily available from a multitude of sources, can achieve a range of physical and mechanical properties and are easily machined, brazed, soldered, polished or plated.
Properties Following is a list of physical and
mechanical properties common to cast copper alloys. Although not every property is applicable to every alloy, the range isn’t found in any other alloy group: • good corrosion resistance, which contributes to durability and long-term cost-eff ectiveness;
• mechanical properties ranging from pure copper, which is soft and ductile, to manganese-bronze, which ap- proaches the mechanical properties of quenched and tempered steel. Almost all copper alloys retain their me- chanical properties, including impact toughness, at low temperatures;
• thermal and electrical conductivity greater than any metal except silver. T e conductivity of copper drops when alloyed, but it still conducts heat and electricity better than other corrosion-resistant materials;
• bio-fouling resistance, as copper inhibits marine organism growth. Although this property (unique to copper) decreases upon alloying, it is retained at a useful level in many alloys, such as copper-nickel;
• low friction and wear rates, such as with the high-leaded tin-bronzes, which are cast into sleeve bearings and exhibit lower wear rates than steel;
• good castability. All copper alloys can be sand cast, and many can be centrifugal, continuous, permanent mold and die cast;
• good machinability. Leaded copper alloys are free-cutting at high ma- chining speeds, and many unleaded alloys, such as nickel-aluminum bronze, are readily machinable at recommended feeds and speeds with proper tooling;
2013 CASTING SOURCE DIRECTORY
• ease of post-casting processing, as good surface finish and high tolerance control can be achieved. Many cast copper alloys are pol- ished to a high luster, and plating, soldering, brazing and welding also are routinely performed;
• wide alloy choice, since several al- loys may be suitable candidates for any given application depending on design loads and environment corrosivity;
• comparable costs to other metals due to high yield, low machining costs and little requirement for surface coatings, such as paint.
Types Coppers (C80100 to 81200)—
T ese alloys are pure copper (99.7% minimum) with traces of silver (for annealing resistance) or phosphorus (a de-oxidizer for welding). T ese alloys are used in high thermal and electri- cal conductivity applications, such as electrical connectors. High Coppers (C81400 to C82800)—High copper alloys (more than 95.1% copper) are unique in that they combine high strength with high
thermal and electrical conductivity. Chromium-Copper (C81400 to
81540)—Containing up to 1.5% chromium, the strength of these alloys is twice that of pure copper, but its electrical conductivity is 80% of pure copper. Applications include welding clamps and high-strength electrical connectors. Copper-Beryllium (C82000 to C82800)—T ese alloys contain 0.35- 2.85% beryllium as the major alloying element and are age- or precipitation- hardened. T ey achieve high strength due to the precipitation of a fi ne second phase during heat treatment. Copper beryllium alloys either achieve high conductivity at moderate strength or moderate conductivity at high strength. Brasses (C83300 to C85800 and
C89320 to C89940)—T e brasses are the most common casting alloys and are made of copper and zinc. Red Brass (C83300 to 83810)—T e red
brasses include zinc (1-12%) and tin (0.2- 6.5%) and may contain lead (0.5-7%). In red brass, lead is present to promote pres- sure tightness in service and to facilitate free machining during manufacturing. T e red color is due to low zinc content. T e
The bronze alloy used for this dental suction pump was selected for its high strength, mechanical properties and wear resistance.
METAL CASTING DESIGN & PURCHASING 33
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