Improvement of Temperature and Residual Stress Distribution in Friction Stir Welding of Aluminum 7075-T6

Friction stir welding (FSW) is a relatively new welding process that gradually increases its application in joining aluminum components and other difficult-to-weld metals. It is well understood that consistent axial force is desirable to produce good weld quality. With constant welding parameters, however, the axial force can vary significantly due to the changes in workpiece temperature and other process variables. It is therefore necessary to examine the temperature evolution and the resultant residual stresses during FSW. In this work, power control is implemented to maintain constant power to investigate the effect of temperature history on resultant residual stresses in the friction welding of aluminum alloy 7075-T6.  The temperature history of the workpiece and the residual stress of the welded plate are measured by an IR camera and an X-ray diffraction (XRD) system.  To remove the detrimental tensile residual stresses of the welded plate, laser shock peening (LSP) is applied on the workpiece. A comparison of residual stresses before and after LSP is presented and a considerable decrease of residual stress in the laser treated workpiece is observed.