Surface integrity, heat treatment and in-situ ageing effects on the fatigue behaviour of PBF-LB AlSi10Mg

The fatigue performance of additively manufactured AlSi10Mg is strongly affected by surface integrity, defect population, thermal history, and the microstructural state induced during laser powder bed fusion (PBF-LB). This study investigates the route-dependent influence of powder condition, platform temperature, heat treatment, and surface state on the high-cycle fatigue (HCF) behaviour of PBF-LB AlSi10Mg. Specimens were produced using two commercial PBF-LB systems with different process strategies, shielding atmospheres, platform temperatures, and powders, including virgin and once-sieved feedstocks. Surface states included as-built, machined, and machined-plus-polished conditions, while post-processing included direct ageing, stress-relief, and higher-temperature treatments. Fatigue behaviour was characterized by uniaxial S–N testing, supported by tensile testing, hardness measurements, porosity analysis, and fractography. Surface condition was found to be a dominant factor controlling HCF life when large lack-of-fusion defects did not govern crack initiation. Within the Aconity TWO route, reducing the roughness from Ra = 24.46 µm in the as-built condition to Ra = 0.12 µm after machining and polishing increased the fatigue strength at 10⁷ cycles from 43 MPa to 66 MPa. Within the CLM2 routes manufactured without elevated platform preheating, heat treatment improved HCF performance, especially at higher treatment temperatures, but reduced static strength and impaired fatigue resistance at higher stress amplitudes. In contrast, the Aconity TWO route manufactured at a platform temperature of approximately 220°C showed only limited additional benefit from subsequent heat treatment, consistent with substantial in situ thermal exposure during fabrication. The once-sieved powder provided fatigue performance comparable to the virgin powder under the investigated CLM2 conditions. The results support a route-specific process-selection hierarchy in which critical defects and harmful surface features should first be controlled, after which heat treatment should be selected according to the process-induced thermal state and remaining microstructural response.