On mechanical properties of SLM Al-Si alloy: Role of heat treatment-induced evolution of silicon morphology

This study investigates the effect of different heat treatment procedures on tensile, hardness, and fatigue properties of additively manufactured AlSi10Mg. Tensile properties were evaluated for different material conditions, i.e., as-built (AB), direct aging (DA), solution treatment (ST), and T6 heat treatment. It was observed that the as-built samples had the highest yield and tensile strength with limited ductility while increasing the peak heat treatment temperature improves the ductility but at the cost of strength. The microhardness also followed a declining trend with an increase in peak heat treatment temperature. An empirical correlation, validated by experimental data, was established to predict the properties based on peak heat treatment temperatures. Based on the observed test results, four material conditions were selected for evaluating the high cycle fatigue (HCF) properties, i.e., AB, SR, DA, and T6. The as-built samples displayed superior fatigue resistance while that of T6 heat treated samples were most deteriorated. The heat treatment -induced microstructural transformation influences the tensile, hardness, and fatigue properties of the SLM AlSi10Mg, mainly due to the disintegration of continuous Al-Si cellular network and the subsequent formation of discrete Si-particles at high temperatures. The interaction between microstructurally-controlled mechanical properties, associated heat treatment process and the intrinsic damage mechanisms was investigated in detail and discussed later in this study.