Evaluating the welding quality of longitudinal welds in a hollow profile manufactured by porthole die extrusion: Experiments and simulation

Aluminum alloy hollow profiles have wide applications in many fields, owing to their light weight and recyclability. Longitudinal welds are inevitable in hollow profiles manufactured by porthole die extrusion, and thereby their welding quality plays a critical role in the performance of profiles. In the present study, the microstructure and mechanical properties of longitudinal welds in an aluminum alloy non-fully symmetrical hollow profile was studied using chemical erosion, optical microscopy, electron backscatter diffraction, tensile tests and fracture analysis, and the welding quality of longitudinal welds was predicted by determining physical variables, flow paths, welding paths, and the geometry and location of longitudinal welds, calculating welding quality indexes, and comparing welding criteria. It was found that, the welds with micro-voids and clearly visible bonding interfaces after being chemically etched have poor welding quality and mechanical properties, and the fractures present groove structures and small dimple structures. On the contrary, the welds without any micro void and bonding interface after being chemically etched have good welding quality and mechanical properties, and the fractures present large dimple structures. The effective strain at welds and at the inner and outer surfaces is larger than that at other locations of the profile. The distribution of the effective strain can reflect the geometry of welds, and the distribution law of the effective strain at welds is almost consistent with that of the welding quality. According to the method proposed in this study and the welding criterion considering the stress triaxiality and the effective strain, the welding quality of longitudinal welds in the aluminum alloy non-fully symmetrical hollow profile was predicted successfully, and the optimization of the extrusion die was carried out to improve the welding quality.