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Annealed Tempers

ball grid array packages Photo Courtesy of IBM
The annealed tempers of single phase coppers are determined by the grain size. Grain size can be accurately measured in these materials and because properties such as tensile strength, yield strength and ductility vary in a consistent manner with grain size, it is used as the basis for determining temper. Generally, hardness and strength decrease and ductility (elongation) increases with increasing grain size. An exception to this would exist where the material is very thin and the grain size is very large resulting in very few grains through the thickness. In this case both strength and ductility decrease with increasing grain size.

Generally, copper and copper alloys have a specific and predictable recrystallization grain growth response to annealing. After cold-working to a specified reduction in thickness, the copper or copper alloy can be annealed to any of several grain size ranges.

The most commonly specified nominal grain sizes in annealed tempers are: 0.015 mm, 0.025 mm, 0.035 mm, 0.050 mm, 0.070 mm, and 0.100 mm.

Some alloys, such as C26000, cartridge brass can be annealed to a number of grain size ranges, including very small sizes. Because such grain sizes are difficult to measure, tensile strength is the preferred measurement for these tempers. The tensile strength ranges produced by annealing to these very small grain sizes are similar to the tensile strengths resulting from cold rolling reduction in thickness. As a result, these temper are referred to as "annealed-to-temper" and can be expressed as "annealed-to-temper ¼ hard" or "annealed-to-temper ½ hard." This process is used because the fine grain size produced gives a smooth surface after forming, while the lower yield strengths and higher elongations provide excellent formability.