Defect-correlated fatigue resistance of additively manufactured Al-Mg4.5Mn alloy with in situ micro-rolling

Hybrid in situ rolled wire + arc additive manufacturing (HRAM) is a potential 3D printing method that combines traditional wire and arc additive manufacturing (WAAM) with in situ micro-rolling. Here, the manufacturing defects and mechanical and fatigue strength were explored for an HRAM- and WAAM-processed Al-Mg4.5 Mn alloy. The results show that advanced HRAM can result in significant grain refinement and enhance the material failure resistance compared with standard WAAM. High-resolution X-ray tomography was adopted to identify the defect density, morphology, distribution, and size, which showed that the defect population and size produced by HRAM were considerably lower than those produced by WAAM. Based on high-cycle fatigue tests, fatigue failure was observed entirely from metallurgical defects. Finite element simulations of the defect images based on computed tomography scans showed that lack-of-fusion defects are more dangerous than gas porosity in terms of increasing the local stress. Finally, the defect-controlled fatigue lifetime was predicted by combining the peaks-over-threshold method with a modified NASGRO model.