Effect of heat treatment on microstructure, mechanical and thermal properties of selective laser melted AlSi7Mg alloy

AlSi7Mg alloy manufactured by selective laser melting (SLM) was subjected to different heat treatments to satisfy the need for excellent mechanical and thermal properties. Effect of direct aging (DA), annealing (AN) and solution + aging (SA) treatment on microstructure, mechanical and thermal properties of SLMed AlSi7Mg alloy was investigated. The results showed that the molten pool boundaries which can be clearly observed in the as-built sample fade away with the increasing heat treatment temperature. The heat treatments have slight effects on the morphology and size of α-Al grains. However, significant differences can be observed in the characteristics of substructure. For the DA treatment, the Al-Si network becomes discontinuous and simultaneously promotes the precipitation of nano-sized Si particles from the supersaturated Al matrix. The original Al-Si network becomes discontinuous and coarsening in the AN sample. For the SA sample, the original cellular structure and eutectic Al-Si network completely disappeared. Coarsened and irregularly shaped Si particles, fine equiaxed Si particles as well as the needle shaped Fe-rich precipitations were observed. The room temperature tensile test showed that the strength of DA sample is the highest, followed by as-built, AN, and SA samples in a descending order. The thermal diffusivity of SA sample is the highest, followed by AN, DA and as-built sample in a descending order.