| Summary: | Microstructural changes and texture evolution during underwater friction stir welding of dissimilar 7003/6060 aluminum alloys were investigated via electron backscatter diffraction technique. In the stir zone, equiaxed fine grains were formed through continuous dynamic recrystallization. Due to the enhanced cooling rate, the average grain size of the stir zone was much finer than that of normal friction stir welds. In the heat affected zone, static recovery was the main mechanism for microstructure evolution, resulting in similar grain structure as compared with base materials, while the fraction of low angle grain boundary increased. In the thermo-mechanical affected zone, dynamic recovery and partial crystallization took place on the advancing side of 7003, and a mixed grain structure was formed; dynamic recovery was the dominant evolution mechanism on the retreating side of 6060, and the fraction of low angle grain boundary was increased. The texture in the heat affected zone was almost the same as the base material, and simple shear texture B/ B- {112}<110> was formed in the stir zone. With the distance to the weld center decreasing, the texture density of relevant zone decreased.
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