Effect of heat treatment on microstructure and mechanical properties of AlSi10Mg fabricated using laser powder bed fusion

Thermal heat treatment is an important step in many metal additive manufacturing processes, particularly laser powder bed fusion (PBF-LB), as it can homogenize the microstructure and enhance the properties of the resulting parts. The effects of post-processing via direct ageing (DA), stress-relieving (SR), and DA or SA followed by annealing or hot isostatic pressing (HIP), on the microstructure, porosity, and resultant mechanical properties of AlSi10Mg samples manufactured using PBF-LB were investigated in this study. Samples were fabricated over a range of processing conditions to probe different starting microstructures and pore features. Porosity and sub-grain solidification cells were characterized because these features are known to influence strength, ductility, and microhardness. DA increased strength at the expense of ductility due to the precipitation of Si-rich particles while SR improved ductility at the expense of strength due to the broken Al/Si eutectic microstructure. Subsequent annealing of DA samples resulted in further breakdown of the Al/Si eutectic microstructure as well as coarsening of Si-rich precipitates, resulting in lower strength and higher ductility than DA alone. HIP resulted in near fully dense and homogenized samples with coarse Si particles, significantly increasing elongation over all other heat treatments. This study shows that processing parameters and heat treatments can be used to tailor porosity, cell size, and resultant mechanical properties of PBF-LB AlSi10Mg.