Weld line

Abstract: Although friction stir welding (FSW) has been successfully used to join materials that are difficult-to-weld or unweldeable by fusion welding methods, it is still in its early development stage and, therefore, a scientific knowledge based predictive model is of significant help for thorough understanding of FSW process. In this paper, a continuum based FEM model for friction stir welding process is proposed, that is 3D Lagrangian implicit, coupled, rigid-viscoplastic. This model is calibrated by comparing with experimental results of force and temperature distribution, then is used to investigate the distribution of temperature and strain in heat affect zone and the weld nugget. The model correctly predicts the non-symmetric nature of FSW process, and the relationships between the tool forces and the variation in the process parameters. It is found that the effective strain distribution is non-symmetric about the weld line while the temperature profile is almost symmetric in the weld zone.

Abstract: The effect of tool traverse and rotation speeds on the residual stresses are quantified for welds between non-age-hardening AA5083 and age-hardening AA6082 and compared to single alloy joints made from each of the two constituents. The residual stresses have been characterised non-destructively by neutron diffraction and synchrotron X-ray diffraction. The region around the weld line was characterised by significant tensile residual stress fields which are balanced by compressive stresses in the parent material. The rotation speed of the tool has been found to have a substantially greater influence than the transverse speed on the properties and residual stresses in the welds, particularly on the AA5083 side where the location of the peak stress moves from the stir zone to beyond the edge of the tool shoulder. The changes in residual stress are related to microstructural and hardness changes as determined in a previous study [1,2]. In particular the larger stresses under the weld tool on the AA5083 side compared to the AA6082 side are related to a transient reduction in yield stress due to dissolution of the hardening precipitates during welding prior to natural aging after welding.

Abstract: 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, σ L , oriented along the weld line, as the largest stress Within the region inside the shoulder diameter, the through-thickness stress, σ 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 64 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 an 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