The effect of trace elements on the sintering of Al-Cu alloys

Trace additions of Sn, In, Bi, Sb and Pb have been used to activate the liq uid phase sintering of an Al-4Cu-0.15Mg alloy. Additions of as little as 0. 05 wt% (similar to 0.01 at.%) increases the sintered density from 88 to 92% of the theoretical density. The elements which aid sintering have both hig h vacancy binding energies and high diffusivities in Al. It is suggested th at the trace element diffuses into the Al, and forms trace element-vacancy clusters. This reduces the diffusivity of the Cu in the Al matrix, delaying Cu dissolution therefore causing the liquid to persist for longer times. T his enhances sintering and therefore densification. (C) 1999 Acta Metallurg ica Inc. Published by Elsevier Science Ltd. All rights reserved.