Enhanced mechanical properties and homogeneous T5 age-hardening behavior of Al-Si-Cu-Mg casting alloys

In this study, the effects of melt-holding temperatures on the mechanical properties and T5 age-hardening behavior of Al-Si-Cu-Mg alloys were investigated. An enhanced yield strength, tensile strength, and elongation were observed simultaneously as the melt-holding temperature was increased from 720 °C to 820 °C. The enhanced mechanical property of the T5-treated Al-Si-Cu-Mg alloy with high melt-holding temperature was attributed to several microstructural changes, including a refinement of the microstructure and an acceleration of the precipitation kinetics caused by enhanced second-phase dissolution. The high melt-holding temperature was particularly effective in changing the precipitation kinetics. This was demonstrated by the formation of a single peak upon homogenization of the solute distribution, replacing the double hardness peaks found in the Al-Si-Cu-Mg alloy with a low melt-holding temperature. The homogeneous solute distribution not only increased the number of Si- and β-type precipitates in the alloy with a high melt-holding temperature but also refined their size. In addition, the high melt-holding temperature accelerated the segregation behavior of Cu on the Si precipitates, which is critical for the refinement of precipitates. •Solute distribution of as-cast Al-Si-Cu-Mg alloy was changed by melt-holding treatment at high temperature.•High melt holding temperature significantly changed T5 age-hardening response and precipitation kinetics.•Strength and elongation can be simultaneously enhanced when the melt-holding temperature was increased.•The number density of precipitates increased, whereas their size decreased when the melt-holding temperature was high.