Residual stresses for friction stir welded Al sheets

The residual stresses for friction stir welded 3 mmthick 2024-T4 aluminum alloy sheets had been investigated by using Mathar method.To reduce the influence of drilling process induced strains on the experimental results, stress-free 2024 aluminum alloy sheets were drilled and the relieved strains were measured.The results showed that the longitudinal residual stresses are much greater than the transverse residual stresses in the friction stir welded joint; the longitudinal tensile residual stresses are concentrated near the tool shoulder direct affected zone and asymmetrically distributed at the different sides of the weld center and it is high at the advancing side and relatively low at the retreating side;the longitudinal residual stresses at outside the tool shoulder direct affected zone are decreasing remarkably and become compressive residual stresses away from the weld center;the peak value of the longitudinal residual stresses is 164.5 MPa.The mechanism of the residual stresses distribution of the welded joint was discussed preliminarily.