Experimental-numerical insights into heat-affected zone failure of welded aluminum alloys

Abstract

This research elucidates the failure mechanisms of the heat-affected zone in welded aluminum alloys. Heat-affected zone softening, which leads to localized loss of strength and hardness, is a significant issue in welded aluminum components. This issue prevents the welded components from achieving their full load capacity, leading to premature failure in their heat-affected zone, despite acceptable weld quality. Accordingly, this study investigates the failure mechanisms of the heat-affected zone in non-heat-treatable 5754-H22 and heat-treatable 6082-T6 aluminum alloys. Samples are welded with different welding processes and heat inputs to clarify the influence of the welding procedure on the failure mechanism. Microstructural analyses, simulated thermal gradients using finite element, CALPHAD, and strength analytical approaches were employed to investigate the softening phenomenon. According to the results, the softening in the non-heat-treatable base metal was mainly due to dislocation recovery, while precipitation coarsening caused softening in the heat-treatable base metal. Tensile tests conducted in conjunction with digital image correlation revealed that the mechanical behavior of the welded joints followed that of their softened heat-affected zone. Furthermore, hardness-strength and stress-plastic strain empirical models were capable of predicting the deformation behavior of softened heat-affected zones, and thus, welded aluminum structures. However, the model parameters need to be adjusted for each specific base metal. Finally, autogenous laser welding showed reduced softening. However, it led to undercut defects and premature failure due to the absence of filler material, suggesting that using filler material in laser welding could be a viable solution to reduce softening in aluminum alloys.