A Study of Residual Stresses and Microstructure in 2024-T3 Aluminum Friction Stir Butt Welds

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, σL, oriented along the weld line, as the largest stress. Within the region inside the shoulder diameter, the through-thickness stress, σZ, 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 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.

Residual Stress in Friction Stir Welding and Laser-Assisted Friction Stir Welding by Numerical Simulation and Experiments

“…The transverse residual stress values are roughly constant in the plate with a value of 60 MPa and, in agreement with Sutton et al [16], are about 70% of the longitudinal one. The residual stress results show a good agreement between experimental and numerical data, although some little discrepancies exist.…”

“…The stress in the transverse direction is roughly constant with values between 50 and 60 MPa along all the transverse directions of the plate. Moreover, according to the observations reported by Sutton et al [16], the transverse stress has lower values than longitudinal stress and it is about 70% of the this one.…”

“…Furthermore, they have proven that the longitudinal stresses increase with increasing the traverse speed. Sutton et al [16] and also Donne et al have proven that the longitudinal is the most important component in the residual stresses analysis in FSW process and that the transverse is about 70% of the longitudinal component.…”

The simulation of residual stresses in friction stir welds

“…Webster et al [2001] reported the measurement of residual stress in FSW by the X-ray technique and found that the longitudinal residual stress varies in the range from 60 to 140 MPa. Sutton et al [2002] investigated the residual stress in 2024-T3 aluminum friction stir butt welds using the neutron diffraction technique. The results show that the highest stress occurs near the crown side of the weld over the entire FSW region.…”

Desarrollo de métodos para la acotación de la incertidumbre en medidas de tensiones residuales en materiales metálicos tratados por LSP

“…En la figura 6.10(a), 6.10(b) y 6.10(c) se muestran respectivamente las tensiones residuales , y . es la tensión según la dirección longitudinal de la probeta, es la tensión según la dirección perpendicular a , y es la tensión tangencial 1-3.En general, el valor de las tensiones calculadas es muy bajo, compatible con las placas laminadas de Al2024 T351 utilizadas [Sutton02]. Además, se observan ciertas tensiones residuales de compresión en los primeros puntos en profundidad de y , es decir, las probetas se reciben con ciertas tensiones de compresión cerca de la superficie y estas tensiones están afectando a los resultados obtenidos en las secciones 6.2.2.1 y 6.2.2.2.…”