Microstructure Engineering to Optimize Hardness and Conductivity in Electrolytic Tough Pitch Copper

Extensive investigations were carried out on the mechanical strength, electrical conductivity, and microstructure of commercially pure copper, which was rolled at room temperature to deformations less than 23 pct and subsequently heat treated at a range of temperatures less than 0.5T_m. For various reductions in samples thickness, we have identified the optimum heat treatment temperature that yields higher mechanical strength and electrical conductivity than the as-received sample. Specifically, with increasing deformation, the optimum heat treatment temperature decreases. We are able to correlate the properties with the microstructure which is composed of deformed grains that enhance strength and the relatively deformation-free grains that enhance electrical conductivity. More importantly, the optimum properties are achieved when the volume fraction of the relatively deformation-free grains are in the range 65 to 70 pct. We also show that the grain orientation spread obtained using electron back-scattered diffraction is ideal, in these studies, to distinguish between deformed and relatively deformation-free grains.