Effects of annealing process on interface and mechanical properties of silver clad aluminum wires

Abstract

The billet was prepared by putting the aluminum bar into the silver tube, and the silver clad aluminum wire was fabricated through cold hydrostatic extrusion and subsequent drawing. The effects of annealing parameters on the interface and properties of the wires were investigated. The results showed that when the annealing temperature was below 150°C and annealing time was less than 30min, no new phase was observed obviously, while new phase could be observed when the temperature reached above 200°C. The results of energy spectrum analysis showed that new phase were mainly Ag3Al electronic compound (μ phase) which was hard brittle phase with the β-Mn structure. The effects of annealing temperature and time on the interface were different: for any annealing time in this study, the width of the interface rose markedly with the increase of annealing temperature, while annealing time had no significant effect on the width of interface when the temperature was low. Only when the temperature was comparatively high, the increment rate of width of the interface gradually increased with the rise of annealing time. The width of interfaces was 5∼7μm, 7∼9μm and 10∼12μm after annealing treatment under the temperature of 150°C, 200°C and 300°C respectively for 30minutes. If the annealing temperature was lower than 200°C, the main way was that silver diffused towards aluminum, but when the annealing temperature was up to 300°C, the reverse diffusion occurred. When annealing temperature was 150°C or 200°C, the tensile strength of composite wire decreased after increased with the increment of annealing time, while when it was 300°C, the tensile strength always increased. The elongation percentage of composite wire had an adverse change compared to that of tensile strength. The reason for the change of mechanical properties of composite wire is mainly that mechanical properties was synthetically influenced by three mechanisms called annealing softening, diffusion phase transformation of interface and alloying of sheath and core because of their interdiffusion. Annealing softening produced dominant effect in lower annealing temperature and shorter annealing time condition, while the other two mechanisms had main effect in higher annealing temperature and longer annealing time condition.