Enhancing mechanical performances by unconventional Si precipitates obtained in pressure-induced Al-Si-Cu-(Mg) solid solutions

Abstract

The influence of 6 GPa-level high pressure on the microstructures and mechanical properties of Al-7Si-3Cu and Al-7Si-3Cu-0.4 Mg alloys is investigated. It is found that both alloys break the solubility limit of Si and become near-complete solid solutions of Al under 6 GPa. Upon direct aging treatment, the precipitates of Al-7Si-3Cu alloy consist of θ′ phases, coarse irregular Si particles, and Al2Cu particles, while unconventional fine rod-like Si particles lying along the <100>Al directions precipitate in Al-7Si-3Cu-0.4 Mg alloy, which leads to the superior mechanical properties with a compressive stress of 1161.9 MPa and a microhardness of 259.6 HV. The APT analysis further shows that these unconventional Si phases are enriched with Mg and segregated by Cu. The mechanism behind the precipitation and the corresponding mechanical performance are further explored.