Effect of a short solution treatment time on microstructure and mechanical properties of modified Al–7wt.%Si–0.3wt.%Mg alloy

Abstract

Microstructural change caused by a short solution treatment and the corresponding change in tensile properties and impact energy of a strontium modified Al–7wt.%Si–0.3%Mg cast alloy were studied. It was found that a solution treatment of 10 min at 540 or 550 °C is sufficient for the α-aluminium phase to homogenise and achieve the maximum level of magnesium and silicon as predicted by the solubility and alloy composition limits. A solution treatment of 30 min causes spheroidisation, coarsening and an increase in inter-particle spacing of the eutectic silicon particles leading to a significant improvement in ductility and impact resistance. Compared with a standard 6 h solution treatment, solution treatment of 30 min at 540 or 550 °C is sufficient to achieve more than 90% of the maximum yield strength and more than 95% of the maximum UTS and the maximum average elongation to fracture. However, only 80% of the maximum impact energy can be attained by the short solution treatment. The values of the ductility and impact energy pass through a minimum between 1.5 and 10 min of solution treatment time indicating that solution treatments of less than 10 min should be avoided.