Copper-gold alloys electrical resistivity

The effect of long-range order on the electrical resistivity of copper-gold alloys is shown in Figure 8.6. The increased periodicity produced by ordering during annealing at 200 °C decreases the resistivity. 

Ordering lowers the electrical resistivity of copper-gold alloys. Adapted from C. S. Barrett, Structure of Metals and Alloys (New York McGraw-Hill, 1943), p. 244, figure 14. 

Joe. 24.—Effect of Composition on Electrical Resistance and Hardness of Copper-Gold Alloys (a) Quenched. 1 )isordoied-Solid Solution, (b) Slowly Cooled. Ordered-Solid Solution. 

Metallic coatings such zinc and its alloys are commonly used to protect steel against atmospheric corrosion. Copper and brass are often coated with metals for decorative purposes as well as for improved corrosion resistance. Examples include chromium coated water faucets or gold coated electric contacts in printed circuit boards. Metallic coatings also serve for wear protection in tribological applications. 

Aluminum is indeed used for interconnects in some integrated circuits even though its electrical conductivity is shghtly lower than the values for silver, copper, and gold, its extremely low diffusion coefficient makes it the material of choice for this application. An alumi-num-copper-silicon alloy (94.5 wt% Al wt% Cu-1.5 wt% Si) is sometimes also used for interconnects it not only bonds easily to the surface of the chip, but is also more corrosion resistant than pure aluminum. 

Metallic Pigments. These pigments are metal flakes of various sizes made up of aluminum, copper, zinc, and/or their alloys. The aluminum flakes develop the silver metallic colors, whereas the copper, zinc, and aluminum alloys produce the gold, copper, brass, and bronze colors. The metal effect is modified, not only by shape and size, but also by perticle size distribution within a given product. Since aluminum, in particular, as a fine dry powder, can form explosive mixtures with air, most of these materials are commercially available in paste or liquid concentrates. In addition, surface treatments of these materials enhance their appearance and performance. Flakes of other metals, such as stainless steel, are used for surface protection purposes such as corrosion resistance and electrical conductivity. 

Metals and alloys are malleable and ductile, and they conduct electricity. When a metal can be poimded or rolled into thin sheets, it is called malleable. Gold is an example of a malleable metal, as shown in Figure 9.11. A chimk of gold can be flattened and shaped by hammering imtil it is a thin sheet. Ductile metals can be drawn into wires. For example, copper can be pulled into thin strands of wire and used in electric circuits, as illustrated in Figure 9.11. Electrical conductivity is a measure of how easily electrons can flow through a material to produce an electric current. Metals such as silver are excellent conductors because there is low resistance to the movement of electrons in the metal. These properties— malleability, ductility, and electrical conductivity—are the result of the way that metal atoms bond with each other. 

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