Influence of Mg and solution heat treatment on the occurrence of incipient melting in Al–Si–Cu–Mg cast alloys

This article was undertaken to investigate the effects of single-step and two-step solution treatment on the occurrence of incipient melting in experimental and industrial 319 alloys using tensile testing, microstructural analysis, and porosity measurements. Castings were prepared from alloy melts containing Mg levels of 0–0.6 wt%. The alloys were solution heat treated in the range of 490–540 °C for the single-step solution treatment, and at 505 °C followed by 520 °C or 530 °C for the two-stage solution treatment. The results showed that both Mg concentration and solution temperature play an important role in the occurrence of incipient melting. With respect to the two-stage solution treatment, the second stage solution temperature should not exceed 520 °C even if a higher temperature homogenizes the alloy. Compared to the experimental 319 alloys, the industrial alloy shows greater resistance to incipient melting, which may be accounted for in terms of the reaction between Cu and trace elements such as Fe and Ni present in the alloy.