Mechanical Behaviour of Joints in FSW: Residual Stress, Inherent Strain and Heat Input Generated by Friction Stir Welding

Abstract

For ordinary arc welding processes such as MIG, welding deformation, residual stress and inherent strain are important factors to control the reliability of weldments. Friction stir welding (FSW) is a new welding method, especially for light metals. The distortion of FSW is reportedly small but reasons can not be determined in detail. This paper deals with thermal cycles and inherent strains which create both residual stresses and welding deformations, in order to make clear effective factors that lower apparent strains on FSW than on MIG. Inherent strains were measured by using the layer removal technique. Thermal cycles and maximum temperature rise were measured by type K thermocouples. It is concluded from experimental data that the main cause lowering apparent strain in FSW is the compressive load that makes tensile plastic strain in weldments. The second cause is that the heat input is smaller than in ordinary arc welding processes.