The microstructures responsible for property variations across the heat affected zone (HAZ) and thermo-mechanically affected zone (TMAZ) of friction stir welds (FSWs) in Al 2519 were analyzed by electron microscopy and related to the results of microhardness tests, thermal simulations, and modeling. Mapping the microhardness across a transverse cross section of the FSW reveals a soft band at the HAZ/TMAZ boundary. Transmission electron microscopy was used to characterize the microstructural variations across this soft band. The thermal fields responsible for these microstructural changes were modeled with an inverse-problem approach that was scaled according to the results of experimental thermal simulations. These studies reveal the precipitate coarsening, dissolution, and reprecipitation that produce this soft band in friction stir welding of this alloy.
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