Fatigue life of laser powder bed fusion (L-PBF) AlSi10Mg alloy: effects of surface roughness and porosity

Abstract The fatigue life of components manufactured by the laser powder bed fusion (L-PBF) process is dominated by the presence of defects, such as surface roughness and internal porosity. The present study focuses on the relative effect of surface roughness and porosity in determining the fatigue properties of AlSi10Mg alloy produced by L-PBF process built in the Z-direction for the as-built (AB), machined (M) and machined & polished (M&P) conditions. As-built L-PBF samples possess higher average surface roughness, Ra (1.5–2 µm) compared to that of the machined (0.8–1.0 µm) or polished ones (0.3–0.75 µm). For similar loading conditions, the machined or machined & polished samples have a longer fatigue life than those of the as-built samples. For the as-built samples, surface roughness was found to be the dominant factor affecting fatigue life. However, for a small variation of roughness, particularly for machined or machined & polished samples, the subsurface porosity becomes the dominant factor affecting fatigue failure. Besides, the pore size and location effects are analysed using linear elastic fracture mechanics, and these are found to have a higher effect on fatigue failure than overall porosity. Based on the results of X-ray computer tomography (XCT) and fracture surface characterisation, the critical stress intensity factors (K IC ) for L-PBF AlSi10Mg alloy samples are estimated. In addition to this, the calculated critical stress intensity factors are used to predict the fatigue life by developing an empirical formula. The result from this empirical relationship is found to match closely with the experimentally determined fatigue life. This suggests that fatigue life can be predicted based on XCT images of machined samples. The findings can help minimize detrimental effects of defects by optimising mechanical or structural designs in attaining the desired structural integrity and durability.