Influence of laser polishing on the material properties of aluminium L-PBF components

In this study, the influence of laser polishing on the microstructural and mechanical properties of additively manufactured aluminium AlSi10Mg Laser Powder Bed Fusion (L-PBF) parts is analysed. The investigation is carried out on a 5-axis laser cell equipped with 1D Scanner optics driven by a solid-state disc laser at a wavelength of 1030 nm. Laser polishing is performed with pulsed or continuous laser radiation on samples in the initial L-PBF state or after stress relief treatment in a furnace. The metallurgical investigation of the remelting zone with a depth of 101–237 µm revealed an unchanged and homogeneous chemical composition, with a coarsened α-phase and a changed grain structure. The hardness within the remelting zone is reduced to 102–104 HV 0.1 compared to 146 HV 0.1 at the L-PBF initial state. Below the remelting zone, within the heat affected zone, a reduced microhardness, which can reach a thickness up to 1.5 mm, occurs. Laser polishing results in a reduction in residual stresses and resulting distortions compared to the L-PBF initial state. Nevertheless, the re-solidification shrinkage of the polished surface layer introduces additional tensions, resulting in sample distortions well above ones remaining after a stress relieve heat treatment of the initial state. The mechanical properties, analysed on laser polished flat tensile specimens, revealed an increase in the ultimate elongation from 4.5% to 5.4–10.7% and a reduction in the tensile strength from 346 N/mm² to 247–271 N/mm² through laser polishing. Hence, the strength resulting from this is comparable to the initial L-PBF specimens after stress relieve heat treatment.