Effect of a Stress Relief Heat Treatment of AlSi7Mg and AlSi10Mg Alloys on Mechanical and Electrical Properties According to Silicon Precipitation

Selective laser melting (SLM) as an additive manufacturing (AM) technique shows great potential to produce complex and high-density three-dimensional structures at high speeds. Currently, alloy materials based on aluminum–silicon (AlSi), including AlSi7Mg and AlSi10Mg, are widely used in AM technology. However, the residual stress caused by rapid cooling was one of the critical issues affecting the tensile and yield strength, dimensional accuracy, and reliability of fabricated parts. In this study, we systematically investigated changes in the microstructure, residual stress, and mechanical properties of AlSi7Mg and AlSi10Mg materials after a heat treatment. The changes in electrical properties were also investigated. The heat treatment process reduced the residual stress of the materials. After the heat treatment, the silicon (Si) network structure and Si dissolved in the Al matrix were completely precipitated and existed as an independent fine spherical precipitate. The AlSi7Mg material has a weaker solid-solution hardening effect due to lower volume fraction of Si, resulting in lower tensile strength, lower hardness, and higher elongation than the AlSi10Mg material. After the heat treatment, the tensile and yield strength of both materials decreased, and the elongation increased. On the other hand, the electrical conductivity of the materials was improved after the heat treatment due to the Si which precipitated in the Al matrix, acting as an impurity. The electrical conductivity and mechanical properties of the AlSi alloy depend on the Si content of the materials. Therefore, the electrical and mechanical properties can be enhanced by optimizing the appropriate Si content in the material.