Effect of focal spot size on AlSi10Mg alloy parts fabricated by laser powder bed fusion: Process window, mechanical properties, and microstructure

This study investigated the effect of the laser focal spot size on the process window, part properties, and microstructure of an AlSi10Mg alloy fabricated via the laser powder bed fusion (LPBF) process. In LPBF, process windows of different spot sizes (60 µm and 120 µm) were established to fabricate dense AlSi10Mg parts with an excellent density of 99.96% using optimal process parameters. The tensile results indicated that parts made using a large spot size had greater ductility because their coarse grain structure with an average grain size of 41 µm, as measured by the electron backscattered diffraction (EBSD) technique, reduced the resistance of dislocation movement, thus enhancing their elongation. In contrast, parts made using a small spot size had stronger yield strength because their finer grains with an average grain size of 14.6 µm enhanced their strength. The differences in their grain structures were attributed to their different cooling rates. In addition, X-ray diffraction (XRD) analysis showed a slight shift towards a lower diffraction angle at the Al-(200) peak of the parts fabricated using a smaller spot size owing to its finer grains. Moreover, the LPBF-fabricated parts using a large spot size of 120 µm exhibited a smoother surface roughness with a S_a value of 1.69 µm compared to those parts with a S_a value of 4.36 µm using a small spot size.