Structural characteristics and mechanical properties of 2219 aluminum alloy DC A-TIG welding joints

Abstract

Based on the direct-current active TIG welding（DC A-TIG welding）process of 2219 aluminum alloy, combined with engineering practice, three main parameters of welding current, welding speed, and rotation speed were selected for process testing. The significant changes in microstructure of various micro regions of the DC A-TIG welded joint of 2219 aluminum alloy specimens were studied. The results showed that by optimizing the process parameters for welding the test plates, the internal quality and external morphology of the welded joints were good, meeting the forming requirements. The 2219 aluminum alloy DC A- TIG welding joint included the weld zone, fusion zone, heat affected zone, and base metal. Among them, the hardness of the fusion zone was the lowest, and the fusion zone was the weak position of the welding joint. There was a narrow non dendritic equiaxed zone (EQZ) at the melting boundary near the heat affected zone, The joint hardness in this area had reached a high value. As it moved away from the fusion zone, the trend of microhardness gradually incresed to the hardness of the base material. The fracture mode of welded joints was a combination of intergranular and transgranular fractures. The weld zone presented uniform and coarse equiaxed dendrites, the number of precipitate phases θ was very small and insufficient to produce a significant precipitation strengthening effect. The distribution of microstructure in the fusion zone was uneven, and the area near the weld zone was a columnar crystal zone. A large amount of coarse eutectic structure would precipitate between the grain boundaries and dendrites in the fusion zone and weld zone. The equilibrium phase θ of the heat affected zone was severely coarsening, and severe overaging occurred. The grain boundarieof welded joints were prone to dissolution, resulting in precipitation free zones. In addition, a large number of tangled dislocations were prone to occur at the welded joint, which helped to improve the strength of the joint.