The family of copper-based alloys offers a wide range of engineering properties and fabrication characteristics in extruded parts. Among the desirable characteristics of the various alloys are: Excellent electrical and thermal conductivity, high corrosion and wear resistance, good ductility, high yield strength and excellent machinability. Perhaps even more important, most of these alloys can be extruded into highly intricate shapes.

This article discusses material selection. Recommendations for designing extruded parts of copper-based alloys and tolerances are discussed in Technical Tip #2.The commonly extruded copper-based alloys are divided here into three categories:

Group A:
Architectural bronze, brasses and manganese bronze. The greatest volume of extruded shapes produced in these materials is made from Group A alloys. Group A alloys resist scuffing and atmospheric corrosion. Shapes are furnished in the As-Extruded condition.

Group B:
Nickel silvers and aluminum-silicon bronze. Composition and properties of the prominent alloys in this group are available from the Copper Development Association. Group B alloys, supplied in the As-Extruded condition, offer high strength, high wear resistance and excellent corrosion resistance properties.

Intricacy:
An intricacy index has been assigned to each our production alloys (See Table 1) to serve as a guide to the selection of the most suitable alloys for extruded parts. These factors apply only to our production capability. The Index is based on a rating of 'A' for architectural bronze, the most extrudable alloy. A Rating of 'A' indicates that intricate shapes are feasible. A rating of 'B' indicates that shapes can be moderately intricate. Alloys with intricacy ratings of 'C' are not recommended for shapes with fine detail.

Table 1

Intricate parts with nonuniform sections are common production items in the brasses. Some copper alloys, such as manganese bronze and nickel silver, are more difficult to extrude than the brasses, bronzes and coppers. With these materials, extrusions are limited to relatively simple shapes of nearly uniform thickness. At present most intricate copper-based extrusions are extruded as semi-hollows or solids. Many hollow parts can be made up of one or more pieces held together by some type of mating joint. Parts with sliding fits are alos possible.Slices may be cut from extruded shapes to make forging preforms, thus minimizing the number of forging steps required.

Finish and Assembly:
Copper alloys can be polished, plated and chemically etched or colored (such as the statuary bronzes or patinas). They can be joined by brazing, soldering or fusion welding. In addition, the leaded alloys can be easily drilled and tapped.