Effects of T6-Treatment on the Defect Susceptibility of Tensile Strength to Microporosity Variation in Low Pressure Die-Cast A356 Alloy

This study aims to investigate the contribution of microstructural changes to the variability in the tensile strength during T6 heat treatment and to suggest a set of conditions for optimal heat treatment in terms of the defect susceptibility of tensile strength to microporosity variation and the maximum tensile strength achievable in a defect-free condition. The test specimens were taken from the section of an automotive wheel with 5 spokes, which was fabricated through the low pressure die-cast process, and the porosity measurement was performed by SEM fractography analysis on all test specimens. The decrease in the defect susceptibility was fundamentally due to microstructural changes such as the shape and spacing between Si particles, secondary dendrite arm spacing and the total fraction of Si particles on solutionising treatment, with hardening effect on artificial aging. A solution treatment at 540 degrees C for 6 h and aging at 160 degrees C for 48 h are suggested as the optimum heat treatment conditions for enhancing yield strength and ultimate tensile strength, as well as for minimising the defect susceptibility of tensile strength to microporosity variation.