Microstructural evolution and corrosion property of Al-Mg alloy friction stir welding joint

Based on electron backscatter diffraction (EBSD) and potentiodynamic polarization, the paper explores the microstructure, corrosion property and mechanical property of Al-Mg alloy AA5083-H112 friction stir welding (FSW) joint, reveals the evolution mechanism of the microstructure of Al-Mg alloy FSW joint, and clarifies the influence of microstructure on its corrosion property and mechanical property. The results show that the microstructure evolution of 5083-H112 aluminum alloy FSW joint from base metal zone (BMZ) to nugget zone (NZ) conforms to the mechanism of continuous dynamic recrystallization. The average grain size of the joint from the BMZ to the NZ at 800 r/min increases and then decreases, and the fraction of high angle grain boundaries (HAGBs) decreases and then increases. With the increasing of rotating rate, the average grain size in the NZ increases gradually, and the fraction of HAGBs decreases at first and then increases due to the influence of welding heat input and post-welding cooling time. The corrosion tendency in different zones of the joint at the same rotating rate and in the NZ of the joints with different rotating rates show a positive correlation with the fraction of HAGBs, and the corrosion site is mainly in the grain boundaries, and the corrosion morphology is characterized by intergranular corrosion and exfoliation corrosion. The hardness of each zone of the joint is consistent with the microstructure, but is insensitive to changes in rotating rate. The tensile strength of the joints reached more than 97% of the base metal in the range of 600 r/min and 1000 r/min, while the elongation is close to that of the base metal.