Investigation of solution treatment and natural aging on the microstructural modification of the A356.2 aluminum alloy: effect on the alloy’s strength and conductivity

The transportation sector continues to make strides toward the lightweighting of vehicles; however, many potential alloys considered for novel applications lack adequate thermal and electrical conductivity properties. In this study, as-cast aluminum alloy A356.2 was solution-treated and naturally aged to examine the effect of thermal processing on the microstructure evolution and subsequent mechanical and conductive properties of the alloy. The morphological transformation of key constitutive phases was tracked during the solution treatment. The microhardness and electrical conductivity were incrementally characterized from as-cast to the naturally aged conditions. Subsequently, samples with optimal properties were evaluated for tensile strength and high-temperature electrical and thermal conductivities. The effect of aging, whether natural or artificial, is generally considered a process that purifies the matrix, resulting in an overall increase in electrical conductivity. However, this study’s results show that the effect of phase evolution during natural aging, commonly accepted to be limited to the precipitation of GP-I zone clusters, causes a decrease in thermal and electrical conductivity. Initially, the electrical conductivity of the 12-hour T4 sample increased by 13.1% after solutionizing; however, natural aging decreased this by 3.7% compared to the as-cast alloy. In contrast, the clusters and silicon refinement contributed to increases of 21.7% in microhardness, 24.1% in yield strength, 24.4% in ultimate tensile strength, and a 101% increase in elongation. The room temperature thermal conductivity of the naturally aged sample increased by 5.9%. • Observing specific A356 phase particle modification from solution treatment. • Thermo-Calc Si and Mg diffusion simulations corelated with observed behaviour. • Optimal solution treatment of 12 hours at 510 °C identified. • Longest treatment resulted in smallest aspect ratio and highest conductivity.