Influence of Heat Treatment and Thermal Aging on the Fatigue Performance of LPBF Fabricated AlSi10Mg Alloy

This investigation explores fatigue performance of laser powder bed fusion (LPBF)-fabricated AlSi10Mg alloy subjected to various post-processing treatments: stress relief (SR), Hot Isostatic Pressing (HIP), and HIP + T6, all followed by prolonged thermal aging at 177 °C for up to 1000 h. Microstructural evolution, hardness, density, and uniaxial fatigue performance, including SEM fractography, were examined to recommend practical service life thresholds. Microstructural analysis confirmed that HIP and HIP + T6 treatments effectively eliminated process induced lack of fusion porosity, which was identified as the direct cause of premature elastic regime failure in SR-treated samples. While HIP + T6 achieved the highest initial hardness, both HIP-treated groups showed susceptibility to thermal degradation. The HIP-only samples, in particular, suffered a fatigue life reduction of up to 38% after just 10 h of aging. Fracture analysis showed that unaged SR samples failed in a comparatively more brittle manner, characterized by tear ridges, whereas HIP and HIP + T6 samples displayed an initially ductile fracture with prominent dimple features. Prolonged aging caused the HIP + T6 samples to replace ductile dimple features with a mix of dimple features along with uneven patterns, which may correlate with their decreased fatigue performance. The results of this paper conclusively demonstrate that while HIP post- processing provides robust initial fatigue strength, its benefits are severely compromised by thermal exposure. And for applications limited to the elastic regime, SR post-processing may be suitable, as long as printing parameters are optimized to prevent lack of fusion defects.