Microstructure and Tensile Properties of a Cast Eutectic Al–Si–Cu Alloy Modified by Zr and V

Minor Zr and V were added individually and jointly to Al–12.5Si–1Cu alloy to develop heat-resistant aluminum alloys. The as-cast microstructure, room temperature, and high temperature (350 °C) tensile properties and the strengthening mechanism of the modified alloys were investigated. The results show that the rod-like (Al, Si)3Zr and hexagonal (Si, Al)2V precipitates are respectively found in the alloys with individually added Zr or V. At the same time, they were transformed into (Al, Si)3(Zr, V) and (Si, Al)2(V, Zr) when Zr and V were added together. Individually added Zr or V could change the eutectic silicon aspect ratio, but the largest effect was recorded for the combined addition 0.3 wt% Zr + 0.4 wt% V. The addition of Zr and V had no significant impact on the room temperature tensile strength of the alloys but improved the yield strength. Individual additions of Zr and V caused negligible improvements in high-temperature tensile strength of alloys tested. In contrast, the combined Zr + V additions resulted in the substantial improvement with tensile strength at 350 °C reaching 79.4 MPa, i.e. 89% higher than the base alloy. The analysis shows that the increase of eutectic silicon aspect ratio and the solution strengthening of trace V in eutectic silicon is the leading cause of improving high-temperature tensile strength. The brittle, blocky primary silicon, coarse rod-like (Al, Si)3(Zr, V), and hexagonal (Si, Al)2(V, Zr) precipitates are detrimental to high-temperature properties.