Residual stress evolution analysis in AZ31 friction stir welds using X-Ray and neutron diffraction

Abstract

The challenges of weight reduction in aerospace industry have drawn considerable interest in magnesium alloys technologies. Assessing the efficiency of new joining techniques, as Friction Stir Welding (FSW) is then required. During FSW, the welding tool motion induces frictional heating and severe plastic deformation. Then, in addition to the microstructure and texture evolutions generally observed, significant residual stresses can result from this process. The Friction Stir Welds have been processed using 2 mm thick hot rolled plates of AZ31 Magnesium alloy. Residual stress analysis was carried out on a Friction Stir Weld processed using optimum welding parameters. Laboratory X-ray diffraction and Neutron diffraction were performed. Indeed, the use of Neutron diffraction was especially interesting because it avoids matter removal required with X-ray technique. Moreover, with FSW, the complex thermo-mechanical input induces complex stress gradients. Then, the high penetration capability of the Neutron diffraction technique was thus essential to allow the determination of stress gradients in a nondestructive way. Hahn Meitner Institute (Germany) E3 instrument and Institute Laue Langevin (France) SALSA instrument were used. Sin2ψ method was used to determine residual stresses obtained with X-ray diffraction and HMI Neutron diffraction, whereas the triaxial method was used to determine residual stresses obtained with ILL Neutron diffraction. The aim of this study is to investigate the residual stress distribution in Magnesium Friction Stir Welds and to compare the results obtained using several techniques.