2023 年 64 巻 2 号 p. 406-413
Precipitation-hardened Al–Si 356 cast alloys are widely used in fabricating the automotive engine parts due to their excellent castability and strength/weight ratio. However, with the increasing demand of the engine service temperature at 250–350°C, the mechanical properties of Al–Si 356 alloys greatly deteriorate owing to the rapid coarsening of precipitates at elevated temperatures. In this study, individual and combined transition elements (V, Zr and Mo) were introduced into Al–Si 356 type cast alloys to form thermally stable dispersoids, and their influences on the strength and creep resistance at 300°C was investigated. During thermal exposure (300°C/100 h) after T7 treatment, the nano-scale β′ and Q′ precipitated during aging were transformed to the equilibrium coarse β and Q phases, loosing their contribution to mechanical strength. However, different types of dispersoids formed during the solution treatment were stable during the thermal exposure, resulting in the different but promising contribution to the elevated-temperature properties. The combined additions of V, Zr and Mo showed the highest mechanical and second highest creep properties at 300°C, which possess 22% and 100% improvement on the strength and creep resistance compared to the base alloy.
