Copper-Base Alloys Harold T. Michels Copper Development Assn., Inc., New York C


ast copper alloys are known for their versatility. They are used in plumbing fix- tures, ship propel- lers, power plant


water impellers and bush- ing and bearing sleeves because they are easily cast, have a long histo- ry of successful use, are readily available from a multitude of sources, can achieve a range of physical and mechanical properties and are easily machined, brazed, sol- dered, polished or plated. Following is a list of


physical and mechani- cal 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 con- tributes to durability and long-term cost-effectiveness;


• mechanical properties ranging from pure copper, which is soft and ductile, to manganese-bronze, which approaches the mechanical properties of quenched and tempered steel. Almost all copper alloys retain their mechanical proper- ties, including impact toughness, at low temperatures;


• thermal and electrical conductivity greater than any metal except silver. The conductivity of copper drops when alloyed, but it still conducts heat and electricity better than other corrosion- resistant materials;


• bio-fouling resistance, as copper inhib- its 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


2010 Casting sourCe DireCtory


The bronze alloy used for this dental suction pump was selected for its high strength, mechanical properties and wear resistance.


addition, this phase impairs room temperature ductility but increases elevated temperature ductility.


bronze, are readily machinable at recommended feeds and speeds with proper tooling;


• ease of post-casting processing, as good surface fi nish and high tolerance con- trol can be achieved. Many cast copper alloys are polished to a high luster, and plating, soldering, brazing and welding also are routinely performed;


• wide alloy choice, since several alloys 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.


Using Copper Alloys Cast copper alloys are identifi ed by the


Unifi ed Numbering System (UNS) in which each alloy is assigned a number ranging from C80000 to C99999 (Table 1). From a metallurgical viewpoint, many cast copper alloys are single-phase solid solutions in which the alloying elements such as zinc, tin and nickel are substituted for copper in the copper matrix. Examples of cast single-phase solution alloys are red brass, which contains up to 6% zinc and 2% tin, copper-nickel, which contains up to 10% nickel, and tin-bronze, which contains up to 8% tin and 4% zinc. As the alloy content increases, a second


phase may form. In the case of brass, when the zinc content is increased, a hard second phase (called beta) forms with the copper- rich matrix. This phase is found in yellow brass, which contains up to 41% zinc. In


Role of Lead Lead is commonly added to many cast


copper alloys. Because of the low solubility of lead in copper, true alloying does not occur to any measurable degree. During the solidi- fi cation of castings, some constituents in a given alloy form crystals at higher tempera- tures relative to others, resulting in tree-like structures called dendrites. The small spaces between the dendrites can interconnect to form micropores. This micro porosity is a consequence of the solidifi cation process. The role of lead is to seal these intraden- dritic pores. This results in a pressure-tight casting, which is important for fl uid han- dling applications. Lead also allows the machining of


castings to be performed at higher speeds without the aid of coolants because it acts as a lubricant for cutting tool edges and promotes the formation of small, discon- tinuous chips that can be cleared easily. This results in improved machined surface fi nishes. Lead also plays a role in providing lubricity during service, as in cast copper bearings and bushings. Lead does not have an adverse effect on strength unless present in high concentrations, but it does reduce ductility. Although lead-containing copper alloys can be soldered and brazed, they cannot be welded. Following is a list of the various cast copper alloy families.


Coppers Coppers (C80100 to 81200)—These


alloys are pure copper (99.7% minimum) with traces of silver (for annealing resis- tance) or phosphorus (a de-oxidizer for


Metal Casting Design & PurChasing 33


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