Influence of Silicon Addition on Precipitation Behavior in an Al-Cu-Mg Alloy

Abstract

Influence of silicon (Si) addition on aging precipitation behavior of an Al-4Cu-1.3Mg alloy was investigated by hardness measurements and TEM analysis. The results indicated that each of the Si-containing alloys exhibits an enhanced age-hardening response, a cubic phase, previously designated sigma phase, was obtained. The sigma phase was showed to be a (semi-)coherent and coplanar phase with the Al matrix, i.e.,{100}(sigma)//{100}(Al) and <100>(sigma)//<100>(Al). In addition, S' phase was observed. Si addition played an important role on the formation of sigma phase. sigma phases were observed in the Si containing alloy for all the aging conditions studied but was absent in Si-free alloy. The content of Si significantly influenced the volume fraction of sigma in the alloy. Prolongation of aging time will be conducive to precipitation of a greater number of sigma phases.