Effect of the Distance from Build Platform and Post-Heat Treatment of AlSi10Mg Alloy Manufactured by Single- and Multi-Laser Selective Laser Melting

In the present study, AlSi10Mg samples produced by selective laser melting (SLM) were studied. Samples were machined from two types of bars obtained through different methods: either single laser (SL) or multiple laser (ML) machine setup. The bars were built perpendicular to the platform, which was pre-heated at 150 °C (working temperature), up to a height of 300 mm. The effect of the distance from the platform on the mechanical properties was investigated through tensile samples in as-built condition and after unconventional heat treatments (U-HT). Tensile strength changed by 80 MPa along the Z-axis (build direction) for SL case and by 100 MPa for ML case in the as-built samples. Vickers microhardness revealed an analogous gradient. This was correlated to a gradient in intra-granular precipitates' distribution along the Z-axis, as revealed by scanning electron microscopy (SEM). An unconventional heat treatment at 175 °C for 6h slightly improves the mechanical strength; higher temperature treatments at 200 and 225 °C for the same duration cause a progressive decrease in strength with an increase in elongation. The amount and size of the precipitates and the thickness of eutectic Si change with the heat treatment temperature, justifying the mechanical behavior.