Fatigue-defect criticality in laser powder bed fused aluminum alloys

This study investigated the influence of volumetric defects on the fatigue behavior of laser powder bed fused AlSi10Mg and Scalmalloy, two aluminum alloys with distinct microstructures and potentially different defect sensitivity. Specimens were fabricated in three orientations with different energy inputs, to intentionally induce volumetric defects of varying geometries at reasonable populations. The stress-life fatigue data for both alloys exhibited significant scatter, owing to the differences in the defect characteristics of specimens. Fatigue notch factor-based life estimations, relying on the fatigue limit as a function of the critical defect size, were found to be effective in predicting the stress-life behavior for AlSi10Mg. For Scalmalloy, the location of the defects relative to the bimodal grain structure, as well as some fine-grained regions often serving as crack initiation sites, introduced significant uncertainty in the fatigue limit predictions. As a result, crack growth-based models —instead of notch factor-based ones— were able to sufficiently describe the fatigue behavior of both alloys, with predictions either within a scatter band of 3 or on the conservative side of experimental fatigue lives.