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

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 σ phase, was obtained. The σ phase was showed to be a (semi-)coherent and coplanar phase with the Al matrix, i.e.,{100}_σ//{100}_Al and <100>_σ//<100>_Al. In addition, S’ phase was observed. Si addition played an important role on the formation of σ phase. σ 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 σ phase in the alloy. Prolongation of aging time will be conducive to precipitation of a greater number of σ phases.