High resolution EBSD analysis of the grain structure in an AA2024 friction stir weld

The grain structures formed during friction stir welding of a typical aluminium aerospace alloy have been studied by high resolution EBSD analysis. The grain structures reflect the local deformation conditions, and due to the high temperatures and strains, show characteristics typical of different stages of dynamic recrystallisation. The large strains and high density of second phase particles in the nugget zone result in a very fine 2-3 mu m equiaxed grain size. There is an abrupt transition in grain structure between the nugget and the TMAZ at the side of the weld. A very fine grain structure was also observed near to the top surface of the weld that was in contact with the tool shoulder. The nugget zone, "onion ring" structure was attributed to bands of different densities of second phase particles, rather than any significant difference in the local grain structure or texture.