The competing role of defects and surface roughness on the fatigue behavior of additively manufactured AlSi10Mg alloy

• Assessment of the fatigue behavior of AlSi10Mg alloy fabricated using LPBF in as-built and surface treated conditions. • Application of a novel chemo-mechanical surface treatment to achieve extremely low surface roughness and enhanced fatigue limit. • Evaluation of the competing roles of surface roughness and internal defects in controlling fatigue properties. • Assessment of fracture toughness of the material based on comprehensive fractography analysis. • Application of a simplified defects-based modelling approach to obtain first-order approximations of fatigue life . The fatigue behavior of AlSi10Mg alloy processed by laser-based powder bed fusion of metals (PBF-LB/M) in as-built (AB) and surface treated conditions, is assessed. A new chemo-mechanical polishing (CMP) surface treatment is applied to AB specimens to achieve an average surface roughness of S a ≈ 0.3 μm which is more than two orders of magnitude lower than that of AB specimens ( S a ≈ 48.6 μm). The CMP surface treatment led to a significant improvement in fatigue strength of the alloy as compared to the AB material. The fatigue life of AB + CMP specimens is discovered to be governed by surface or near surface defects, whereas the deepest surface roughness valleys play a dominant role in controlling the fatigue behavior of the AB material. A simplified fracture mechanics-based fatigue life modeling approach was developed by combining real-time defects distribution data from 3D computed tomography (CT) and surface profilometry measurements. The model provided a quick and effective medium for obtaining reasonable first-order fatigue life approximations for AlSi10Mg alloy fabricated using PBF-LB/M.