Study on microstructure-defects-properties and failure mechanisms of WAAM Al-Zn-Mg-Cu alloys

This study systematically investigates the relationship between microstructural defects and mechanical properties in wire arc additive manufacturing (WAAM). The roles of pores and grains in governing failure mechanisms were elucidated using quasi-in-situ EBSD experiments. The tensile strengths of the top, middle, and bottom regions were measured as 467 MPa, 437 MPa, and 489 MPa, respectively. A strong negative correlation was observed between strength and defect roundness, with a correlation coefficient of −0.99. Moreover, the orientation of defects was found to significantly influence elongation. To improve predictive accuracy, a modified empirical model incorporating pore orientation was established. Quasi-in-situ EBSD analysis revealed that crack initiation and propagation were strongly dictated by pore morphology, grain boundaries, and crystallographic orientation. Stress concentration was more pronounced at small pores than at large ones, whereas in spherical pores it was transferred to adjacent grain boundaries, promoting crack nucleation. The incompatibility of deformation among neighboring grains, combined with high Schmid factors, further facilitated crack growth. Lack-of-fusion defects tended to concentrate stress at the early deformation stage, with nucleation determined by local curvature and Schmid factor. Defects aligned parallel to the columnar grain length promoted cracking along {100} planes, while cracks propagating across the grain width exhibited a “dual-path” behavior: the inner crack experienced more severe deformation, leading to cleavage fracture along {110} planes inside the columnar grain. These findings provide mechanistic insights into defect-property interactions in WAAM aluminum alloys and offer guidance for tailoring process parameters to mitigate defect formation and improve service performance.