Influences of platform heating and post-processing stress relief treatment on the mechanical properties and microstructure of selective-laser-melted AlSi10Mg alloys

This study focused on two essential issues in the fabrication strategy utilized in selective laser melting (SLM) technology: 1) the influence of the hot-build platform and 2) the effects of a post-processing stress relief (SR) treatment on the mechanical properties and microstructure of an AlSi10Mg alloy manufactured by SLM. To examine the mechanical properties, surface hardness measurements and split Hopkinson pressure bar (SHPB) experiments were conducted on samples in the as-fabricated condition and following SR treatment. The samples were extracted from the original SLM product at constant distances from the build platform. Considerable variations in the mechanical properties and damage accumulation resulting from the fabrication process and subsequent post-processing SR treatment were successfully correlated to fundamental characteristics in terms of relative porosity, “on-surface” residual stress, microstructure and texture, solubility, and phase composition. It was found that with increasing distance from the heated build platform, there was a graded increase in the surface hardness and dynamic performance, which are attributed to several competing strengthening mechanisms that were activated owing to the fast cooling rates. Conversely, the reduced thermal gradient and lower solidification rate close to the base led to a higher relative density, as indicated by the smaller size of the keyhole pores. The SR treatment resulted in microstructural changes with uniform and low residual stresses, which led to a significant softening in the mechanical properties, regardless of the building height.