A quasi-in-situ EBSD study on the effect of abnormal grain growth on mechanical properties of the friction-stir welds of 2219 aluminum alloy

Abnormal grain growth appears in the friction stir welds of 2219 aluminum alloy during solution treatment. In this study, the effect of abnormal grain growth on the mechanical properties of the friction-stir welds of 2219 aluminum alloy was investigated, combined with the quasi-in-situ EBSD experiment. The results show that the solution-treated welds with coarse grains have lower tensile strength and elongation than the base metal, but the fracture mode remains the same. According to the bulging testing results, the limiting dome height and ultimate bulging rate of the solution-treated tailor-welded blanks are 85 % and 77 % of the base metal, respectively. After T6 treatment, the mechanical properties of the weld with coarse grains, especially the elongation after fracture, further decrease compared to the base metal. The stress concentration caused by abnormal grains is the main reason for the decreased mechanical properties of the solution-treated weld. There are copper-poor zones along the grain boundaries because of the rapid precipitation at grain boundaries during T6 treatment. Therefore, abnormal grain growth makes intergranular cracks easier to initiate and propagate, which results in the decrease of elongation of the T6-treated weld.