Optimising FSW process parameters to minimise defects and maximise fatigue life in 5083-H321 aluminium alloy

This paper presents a systematic approach to optimising FSW process parameters (tool rotational speed and feed rate) through consideration of frictional power input. Frictional power governs the tensile strength and the fatigue life in this 5083-H321 alloy through its effect on plastic flow processes in the thermo-mechanically affected zone (TMAZ) of the weld. Although, a close relationship therefore exists between tensile strength and fatigue performance, this arises from their joint dependence on the occurrence of certain defect types that are apparently specific to certain strain hardened aluminium alloys that are FS welded. These defects are related to plastic flow processes and have a strong influence on crack paths in FS welded 5083-H321 alloy. Weld residual stresses have been extensively measured using synchrotron X-ray diffraction strain scanning and are governed by heat input into the weld. There is no clear relationship between peak values of residual stresses and fatigue performance. The work indicates that rotational speed is the key parameter governing tool torque, temperature, frictional power and hence tensile strength and fatigue performance.