Effect of Artificial Ageing on the Defect Susceptibility of Tensile Properties to Porosity Variation in A356 Aluminium Alloys

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The present study aims to estimate the dependence of the tensile properties on microporosity variation in low-pressure die-cast A356 aluminium alloys with respect to various T6 treatment conditions and to investigate the relative contribution of the strain-hardening exponent and damage evolution of eutectic Si particles in terms of the defect susceptibility of the tensile properties to effective void area fraction. The solution treatment was performed for 3, 6 and 12 h at 540 °C, and the artificial ageing was conducted for 4, 16 and 48 h at 140–180 °C. The defect susceptibility of the tensile properties to microporosity variation depends practically upon the ageing time, whereas the solutionising time has a minor effect on the variability in the defect susceptibility. Additionally, the maximum value of the ultimate tensile strength (UTS) achievable in a defect-free condition remarkably increases with the ageing treatment, and it also slightly increases with the solutionising time. The maximum value of the tensile elongation for a defect-free condition depends practically upon the solutionising time, even though it generally decreases with ageing treatment. The main reason that the UTS and elongation exhibit different responses with regard to the solutionising and ageing treatments is the variation in the strain-hardening exponents associated with the T6 treatment. The frequency of the damage evolution of eutectic Si particles by the cracking mode is considerably decreased with the ageing treatment, and this transition under ageing treatment has additional contributions to the variation in the defect susceptibility of tensile properties to effective void area fraction.