Abstract: The 5083H321 aluminum alloy plate was jointed by friction stir welding. The comparative studies of the organization of weld and base metal were conducted with optical microscopy, scanning electron microscopy, electron back scattered diffraction and orientation imaging microscopy. The results show that there are no macroscopic defects in the weld. The organizational characteristics are obviously different between the welding seam and the base metal. Friction stir welding makes a large number of lowangle grain boundaries transform into highangle grain boundaries in the nugget zone. The grain size distribution of the base metal and the nugget zone is 6~55 μm and 15~30 μm respectively while the shape aspect ratio is 2~8 and 15~3 respectively. The grains of the nugget zone show homogeneous and equiaxed morphology characteristics of dynamic recrystallization.

Key words: 5083 aluminum alloy; friction stir welding; microstructures; evolution; weld