Periodic microstructure of Al–Mg alloy fabricated by inter-layer hammering hybrid wire arc additive manufacturing: Formation mechanism, microstructural and mechanical characterization

Inter-layer plastic deformation is an effective method to improve the mechanical properties of wire arc additive manufacturing (WAAM) components. In this study, the inter-layer hammering hybrid WAAM process was applied, and a periodic microstructure composed of alternate coarse and fine grain regions was obtained. These regions were defined as the work hardening region (W region) and recrystallization region (R region) according to the respective formation mechanism. The grain size, texture intensity, grain boundary misorientation angle, phase structure, and dislocation density in these two regions were systematically investigated, and their contributions to the mechanical properties were analyzed. The results show that hammering, especially with increase of hammering times, maintains the depth of recrystallization of each layer at 1.0 mm and increases the ratio of the R region. The grain size in the R region was significantly refined, and the dislocation density in the R region was lower than that in the W region due to the dislocation release by recrystallization caused by subsequent deposition heat, and sub-grains were formed in the W region. The best tensile properties were achieved in the horizontal direction when the inter-layer region was hammered 3 times. The ultimate tensile stress (UTS) exceeded 400 MPa and the elongation exceeded 13%. However, the change in pore morphology caused anisotropy in hammered samples.