Optimizing the tensile properties of Al–Si–Cu–Mg 319-type alloys: Role of solution heat treatment

• Effect of Cu addition on the occurrence of incipient melting.
• Role of solution heat treatment in controlling the tensile properties of Al–Si–Cu cast alloys.
• Phase identification using WDS analysis.
• Effect of Mg addition on the alloy performance.

The work presented in this study was carried out on Al–Si–Cu–Mg 319-type alloys to investigate the role of solution heat treatment on the dissolution of copper-containing phases (CuAl2 and Al5Mg8Cu2Si6) in 319-type alloys containing different Mg levels, to determine the optimum solution heat treatment with respect to the occurrence of incipient melting, in relation to the alloy properties. Two series of alloys were investigated: a series of experimental Al–7 wt% Si–3.5 wt% Cu alloys containing 0, 0.3, and 0.6 wt% Mg levels. The second series was based on industrial B319 alloy. The present results show that optimum combination of Mg and Sr in this study is 0.3 wt% Mg with 150 ppm Sr, viz. for the Y4S alloy. The corresponding tensile properties in the as-cast condition are 260 MPa (YS), 326 MPa (UTS), and 1.50% (%El), compared to 145 MPa (YS), 232 MPa (UTS), and 2.4% (%El) for the base alloy with no Mg. At 520 °C solution temperature, incipient melting of Al5Mg8Cu2Si6 phase and undissolved block-like Al2Cu takes place. At the same time, the Si particles become rounder. Therefore, the tensile properties of Mg-containing alloys are controlled by the combined effects of dissolution of Al2Cu, incipient melting of Al5Mg8Cu2Si6 phase and Al2Cu phase, as well as the Si particle characteristics.