Microstructural Analysis of Selective Laser Melted AlSi10Mg

Abstract

Selective laser melting (SLM) is a manufacturing method where computer models are built layer by layer using a laser as heat source to melt powder in selected areas. The method allows for creating parts that would be impossible using traditional methods, enabling for weight reduction of parts without compromising structural integrity through topology optimisation. Due to high thermal gradients and the inherent SLM process, a unique macro and microstructure are produced. SLMed AlSi10Mg was examined by microscopy, and mechanical properties were investigated. Two identical sets of parts were built using RF-PS processed powder with process parameters which gave a high value for the energy input per unit length. One of the sets were given a stress-relief heat treatment (300°C for 2h) to reduce residual stress.

The stress relief greatly affected mechanical properties and residual stresses in the specimens. This is attributed to the change in the microstructure as the heat treatment dissolves the fibrous Si network. The hardness was found to be a function of building height for the as-printed vertically printed specimen. Despite the high laser power used during production, no signs of evaporation were found. The results from this study showed that the process parameters used are deemed sufficient as there were low porosity sufficient overlap between melt pools, acceptable residual stresses and satisfactory results from mechanical testing. The recommended value range for energy input per unit length reported in the literature can hence be questioned.