Microstructural Changes and the Localised Mechanical and Crack Growth Properties in High and Low Speed FSW of 5182-H111 Alloy

Abstract

Abstract Achieving high speed friction stir welding has proven to be challenging for 5xxx-series alloys, as they experience strain hardening during plastic deformation, which is inherent in the FSW process. An earlier publication has discussed the conditions under which welding speeds of up to 1.5 m/min can be achieved in 5182-H111 alloy [1]. The mechanical performance of high speed friction stir welds in 5182-H111 alloy is both surprisingly good and relatively unexplored. Using plates of this alloy welded at a low linear speed of 0.2 m/min as well as at a high speed of 1.5 m/min, the present work evaluated local mechanical properties (microhardness, yield and tensile strength, and fatigue crack growth), in terms of the variation in local microstructure and residual stress. Microstructural variation was investigated via electron back-scatter diffraction (EBSD) and residual stresses were obtained using synchrotron X-ray diffraction strain scanning. The results obtained explain the increased, but different, yield strengths observed in the stir zone and TMAZ regions of the high speed weld and the crack growth rate thresholds.