Effect of Thermo-Mechanical Treatment on Ductility of Cu–0.29 mass%Zr Alloy Wires

Abstract

In our previous study, a thin wire of a Cu–0.29 mass%Zr alloy was produced by annealing after rolling and two subsequent intermediate annealing steps during wire drawing (IA wire). The produced IA wire had an ultimate tensile strength, σ_u, of 610 MPa and a small total elongation, ε_t, of 1.2% despite a small grain size, D, of 240 nm. In this study, a thin wire of the same alloy was produced by annealing after rolling and subsequent wire drawing (S wire). Even though the S wire had almost the same values of σ_u = 620 MPa and D = 230 nm as the IA wire, the S wire exhibited a larger ε_t = 2.9%. This study investigated the cause of this smaller value of ε_t for the IA wire. In both the IA and S wires, voids were formed by decohesion of the interface between the Cu matrix and particles consisting of a eutectic (Cu + Cu₅Zr) during wire drawing; however, the fraction of eutectic particles with voids was larger in the IA wire than the S wire. The IA wire exhibited lower ductility as a result of easier coalescence of the voids during tensile testing. In addition, the larger fraction of eutectic particles with voids in the IA wire is attributed to the larger size of recrystallized grains generated by the intermediate annealing during wire drawing than that of the grains before intermediate annealing. As a result, dislocations accumulated significantly around the eutectic particles during the subsequent wire drawing, resulting in a high stress concentration.

 

This Paper was Originally Published in Japanese in J. Japan Inst. Copper 59 (2020) 76–79. The captions of all figures and table have been modified slightly.

Fig. 5 Fraction of eutectic particles with voids (f_e) as a function of the inverse of the diameter (d⁻¹) for the IA, S, and ECAP wires.