Selective laser melting of Er modified AlSi7Mg alloy: Effect of processing parameters on forming quality, microstructure and mechanical properties

Selective Laser Melting (SLM) was used to fabricate Erbium-modified AlSi7Mg alloy. The work aims to investigate the effects of laser volumetric energy density and focus shift on surface quality, internal defects and microstructure during the SLM process. Based on the optimized process parameters, the effect of rare earth element Er to AlSi7Mg alloy on its microstructure and mechanical properties were studied. With a raise of volumetric energy density, the size of aluminum sub-cells increases, and the high energy density promotes the in-situ precipitation of supersaturated silicon elements in the form of dispersed silicon particles. It was thought that the laser focus shift could change the energy density and the molten pool size, which affected the internal defects and the size of sub-cells plus eutectic silicon particles. The alloy (A357 + 0.2Er wt.%) fabricated by SLM was operating with the optimized processing parameters, then a small amount of equiaxed grains were formed at the boundary of the molten pool, which would promote the refinement of columnar grains and improve the mechanical properties. Meanwhile, the yield strength was 297 MPa, the tensile strength was 441 MPa and the elongation was 8%.