Semisolid processing of short and long freezing range Cu alloys by electric current

Abstract

The present study reports the effect of ac (50 Hz) electric current treatment (ECT) on short freezing range (Cu–Ni) and long freezing range (Cu–Sn) alloys. This treatment was conducted during the semisolid state of the alloys, i.e. during casting in sand moulds. In isomorphous Cu–Ni alloy, with gradual increase in the electric current, first, the dendrites are refined; then, the refined dendrites are fragmented; and finally, the fragmented dendrites are refined. The ECT also reduces homogenisation treatment time. It is observed that a small amount of electric energy spent during sand casting saves considerable amount of energy for homogenisation treatment. The sand castings of Cu–Sn (peritectic) alloys are very much prone to interdendritic shrinkage. Thus, the density of castings is reduced. However, the ECT during casting increases the density of castings by reducing interdendritic shrinkage, modifies phase diagram of Cu–Sn alloy, increases volume fraction of the primary α phase (Cu) and reduces volume fraction of the peritectic phase. The ECT also refines the peritectic phase that transforms to δ phase on cooling to room temperature.