Parametric analysis of FSW dissimilar 2017A-7075 aluminium alloy joints
By Damjan Klobcar (University of Ljubljana), Boris Bell (ESAB AB), Zoran Bergant (University of Ljubljana), Roman Sturm (University of Ljubljana), Uros Trdan (University of Ljubljana)

In this study we conducted a parametric analysis of FSW dissimilar 2017A-T451 and 7075-T651 aluminium alloy joints. During the FSW process welding speed, tool rotation speed, direction of welding and tool offsets were changed and the output variables evaluated. In the first portion, to obtain an insight of the different parameters on residual stress (RS) generation during FSW process and additional cooling measurements across the weld face and toe in the longitudinal and transversal direction were performed using an X-Ray Diffraction method. Afterwards, a set of samples for tensile tests and macrosections were prepared and measured properties analysed. Microhardness was analysed in a predefined horizontal and vertical/cross-sectional direction to thoroughly investigate specific weld regions. Results have confirmed that with a proper FSW parameters a sound, fault-free dissimilar 2017A/7075 welds can be obtained. It was established that the welds with highest transversal compressive RS also exhibited the highest tensile strength. The longitudinal RS in the weldments showed tensile behaviour with slightly lower values in the nugget/stirring zone, compared to the HAZ region, due to the dynamic recrystallization (DRX) effect. Highest RS, obtained in the HAZ region achieved values around 100 MPa, which changed to compressive state outside the weld. Results confirmed almost symmetrical shape of longitudinal RS profile across the weld face and toe indicating homogeneous heat distribution during the FSW process.