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 liquid phase sintering of an Al–4Cu–0.15Mg alloy. Additions of as little as 0.05 wt% (∼0.01 at.%) increases the sintered density from 88 to 92% of the theoretical density. The elements which aid sintering have both high vacancy binding energies and high diffusivities in Al. It is suggested that 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. This enhances sintering and therefore densification.