Control of mechanical and wear properties of a commercial Al-Si eutectic alloy

Abstract

The properties examined as a function of microstructural modification were ultimate tensile strength, fracture elongation, Vickers hardness and wear resistance. The microstructural modification was achieved by rapid cooling and additions of small amounts of strontium and lithium master alloys into the eutectic melt. In all experiments the commercial ETIAL 140 alloy was cast instead of a high-purity aluminium-silicon eutectic. This allowed determination of the effect of modification treatment, both on silicon and intermetallic phases. It was found that the slowly cooled and unalloyed castings which contained coarse silicon flakes showed highest wear resistance and lowest ultimate tensile strength, fracture elongation and Vickers hardness values. Rapid cooling and also additions of strontium and lithium master alloys reduced the eutectic interphase spacing and refined the silicon phase. This usually corresponded to a significant increase in all properties except the wear resistance. It was noted, however, that the size of the intermetallic phase particles increased abruptly above 0.04% Sr content which resulted in a sharp reduction in all mechanical properties. Unlike the strontium effect, the lithium addition did not influence the intermetallic size significantly and, therefore, the mechanical properties were not impaired. In addition, the wear resistance also remained relatively unaffected because lithium solid solution hardened the primary aluminium dendrites appeared in the modified alloys.