Residual Stress Analysis of Laser Welded Aluminium T-Joints using Neutron Diffraction

Abstract

In this study the distribution and magnitude of residual stresses in a T-joint of aerospace grade aluminium alloy weldment was determined using neutron diffraction. A 2 mm thick AA 6013 sheet (as clip) was laser beam welded to a 6 mm thick AA 6056 base plate (as skin) to resemble the “short distance” welded clip-skin joints of an airframe. The total length of the weld was 120 mm and it was welded using 3.3 kW Nd:YAG laser source and 12 % Si containing wire from one side only. No post weld heat treatment was applied after the welding. Start (run-in) and end (run-out) locations of the T-joints are generally considered as high risk areas with respect to solidification cracking and crack initiations under external loadings. It is of interest to investigate the weld residual stress fields at these locations to develop optimum joint design. Therefore, strain measurements have been performed not only in the middle of the weld seam, but also at the run-in and run-out locations of these short distance welds. Higher longitudinal tensile residual stresses are detected at the run-out locations than at the run-in locations. The measurements in the clip showed that the clip has a longitudinal tensile stress peak away (about 8 mm) from the weld seam.