Heterogeneity of the Nugget Microstructure in a Thick 2050 Al Friction-Stirred Weld

The current article deals with 19-mm-thick welds of AA 2050. These joints obtained by friction stir butt welding on half penetration were subsequently strained and artificially aged. The nugget's hardness weakens along the plate thickness from the top surface. This evolution is explained by the modification of the precipitation state, which overcomes the effects of the changes of size and preferred orientation of grains along the nugget's depth. This modification of microstructure arises from the various strains, strain rates, and temperatures encountered in the different areas in the nugget. The postwelding treatment did not manage to suppress either the undermatching of the original nugget compared to the base material or the differences of thermal stabilities at the different depths in the nugget.