Roughness vs. Sub-Surface Porosities: Key Factors in Fatigue Behavior of AlSi10Mg LPBF Alloy

The presence of porosities and poor surface quality in samples produced by L-PBF significantly impacts mechanical performance, particularly under cyclic loading. To ensure reliable performance in engineering applications without resorting to time-intensive post-processing, efforts have focused on optimizing the L-PBF process to reduce both porosity and surface roughness 1, 2. This study investigates the interplay between surface roughness and sub-surface porosities in determining the fatigue behavior of AlSi10Mg LPBF samples. Previous work has demonstrated that minimizing the surface roughness of AlSi10Mg often comes at the cost of introducing sub-surface porosities 2. Specifically, employing the keyholing mode for contouring can reduce roughness to below 5 microns but simultaneously creates keyhole-induced porosities in the contours. To evaluate the trade-off between reducing surface roughness and introducing sub-surface porosities, fatigue tests were conducted on three types of as-build samples: (1) high roughness (2) medium roughness (3) low roughness with sub-surface porosities. The roughness was controlled by using different contouring strategies. To highlight the impact of sub-surface porosities and thus dissociate it from the influence of roughness, the three sets of samples were also tested in their mirror-polished state. The three types of as-built samples and polished samples were then compared to sandblasted samples, which represent the standard surface treatment for improving fatigue performance. While the low-roughness samples showed better fatigue properties, the results indicate that the fatigue resistance of all three sample types remains poor, making post-treatment necessary. It also shows that, while sandblasting slightly increases the roughness of the low-roughness sample, it significantly improves the fatigue resistance of the samples.