Influence of trace Zr on the microstructure and elevated temperature properties of an Al-Si-Cu-Ni-Mg piston alloy

The effect of trace Zr on the microstructure, precipitates and mechanical properties on an Al-12.6 wt% Si-4 wt% Cu-1.5 wt% Ni-1.5 wt% Mg piston alloy was studied in this paper. The alpha-Al dendrites are refined, resulting in a more compact distribution of primary intermetallics. The main precipitates are S (Al2CuMg) after T6 heat treatment. It was found that the S precipitates are denser and finer in the Zr- contained alloy whereas L1(2)-ZrAl3 particles also precipitate. The hardness and elevated temperature tensile strength of the piston alloy were both improved, indicating the positive effect of trace Zr.