Effects of Annealing Temperature on Tensile Property of Recrystallized Commercial Pure Coppers

Recent trends toward smaller diameter in fine copper wire and smaller thickness in rolled copper foil require improvement in workability of materials. Generally, workability can be estimated by the strain hardening exponent obtained from the true stress-true strain curve in the tensile test. In this work, work hardening behavior of three kinds of recrystallized commercial pure coppers was investigated. The effect of the increase in the annealing temperature is summarized as follows. (1) In oxygen free copper, the flow stress increases due to the locking hardening by sulfur, but the strain hardening exponent does not change. (2) In phosphorus deoxidized copper, the flow stress decreases and the strain hardening exponent increases due to phosphorus in the solid solution. (3) In electrolytic tough pitch copper, the flow stress decreases due to the coarsening of Cu2O particles and the strain hardening exponent increases due to oxygen in solid solution. The difference in work hardening behavior between three kinds of commercially pure coppers seems to be brought about by the difference in the interaction between dislocations or stacking faults and atoms of the above trace elements.