Reason for the occurrence of bright circle at the edge of 6082 aluminum alloy extrusion rod

A bright circle appeared on the edge of a 6082 aluminum alloy extrusion rod. The reason for the formation of bright circles at the edge of the extrusion rod was analyzed using methods such as chemical composition analysis, low magnification inspection and metallographic examination. The results show that after the low magnification corrosion test, the deformation of the extrusion rod core metal was smaller than that of the edge metal, the dislocation density was low, the driving force for recrystallization was insufficient, the microstructure was rose-shaped grains, and the longitudinal section retained fibrous grain morphology. The edge metal distortion energy was high, the dislocation density was high, the driving force for recrystallization was large, the proportion of recrystallization was high, and there were more fine grains in the cross-section, and there were fine recrystallized grains in the longitudinal cross-section. The deformation of the edge metal and the core metal was inconsistent, resulted in unstable recrystallized structures at the edge of extrusion rod. Differences in grain size led to different diffuse reflections of light, resulting in color differences in brightness and darkness of the extrusion rod, leading to bright circle at the edge of the extrusion rod.