The effect of process-induced defects on fatigue life in high-strength Al2139 alloy produced by laser powder bed fusion

The present study investigates the role of process-induced defects on the fatigue performance of high-strength Al2139 alloy fabricated by laser-based powder bed fusion of metals (PBF-LB/M). Specimens of two surface conditions: as-built and machined, underwent high-cycle uniaxial fatigue testing to evaluate the combined influence of surface state and defect characteristics. Fractographic examination using scanning electron microscopy identified gas pores and lack-of-fusion (LoF) defects as the dominant crack initiation sites. The LoF defects were further classified into regular LoF defects with relatively compact morphology and shallow, irregularly shaped LoF defects exhibiting larger projected areas. Despite the removal of surface roughness effects, machined specimens exhibited greater scatter in the S–N response and, in several cases, shorter fatigue lives than as-built counterparts tested at identical stress levels. Premature failures in the machined group were consistently associated with shallow, irregular LoF defects with a larger effective size that were exposed at the surface by the machining operation. This concludes that defect morphology and projected area govern fatigue performance more critically than nominal surface finish. Defect severity was quantified using Murakami’s √area parameter. An equivalent defect radius was calculated by idealising defects as semicircular surface cracks on a cylindrical specimen to determine the corresponding stress intensity factor (SIF). A clear correlation between SIF and fatigue life was established, enabling a defect-based life prediction method. The proposed framework provides a quantitative basis for defining allowable defect sizes at given stress levels and contributes to defect-tolerant design strategies for PBF-LB/M Al2139 components.