A study of residual stresses and microstructure in 2024-T3 aluminum friction stir butt welds

Three-dimensional residual stress mapping of an aluminum 2024-T3 arcan specimen, butt-welded by the friction stir technique, was performed by neutron diffraction. Results indicate that the residual stress distribution profiles across the weld region are asymmetric with respect to the weld centerline, with the largest gradients in the measured residual stress components occurring on the advancing side of the weld, with the longitudinal Stress, sigma(L), oriented along the weld line, as the largest stress. Within the region inside the shoulder diameter, the through-thickness stress, sigma(Z), is entirely compressive, with large gradients occurring along the transverse direction just beyond the shoulder region. In addition, results indicate a significant reduction in the observed residual stresses for a transverse section that was somewhat closer to the free edge of an Arcan specimen. Microstructural studies indicate that the grain size in the weld nugget, is approximately 6.4 microns, with the maximum extent of the recrystallized zone extending to 6 mm on each side of the weld centerline. Outside of this region, the plate material has tin unrecrystallized grain structure that consists of pancake shaped grains ranging up to several mm in size in two dimensions and 10 microns in through-thickness dimension.