Study on residual stress distribution of 2024-T3 and 7075-T6 aluminum dissimilar friction stir welded joints

Abstract

Friction stir welding (FSW) can weld 2024-T3 and 7075-T6 aluminum parts into one integral aircraft assembly. In order to perform the integrity assessment of the dissimilar welded structure, the first thing is to identify its residual stress distribution. In this paper, 2024 and 7075 dissimilar aluminum plates were welded by FSW, and the residual stress profiles of the dissimilar welded specimen were measured by the neutron diffraction method. A three-dimensional finite element model was used to calculate and compare the residual stress distributions of different welding parameters. Microstructure characteristics in different FSWed zones were studied by the electron backscattered diffraction (EBSD) method. It is shown that the longitudinal residual stress of 7075 side is higher than that of 2024 side, and the maximum residual stress decreases from the top scan line to the bottom scan line. The transverse and the normal residual stresses are tensile in 7075 side, while that of 2024 side is compressive. The numerical simulation results agree with the neutron diffraction measurements. The KAM map of the thermo-mechanical affected zone shows larger local plastic deformation than that of the stirred zone, which leads the longitudinal residual stress has the “double peak” shape.