Influence of the tool shape and weld configuration on microstructure and mechanical properties of the Al 6082 alloy FSW joints

The paper deals with an investigation of the influence of tool shape and weld configuration on the microstructure and mechanical properties of Al 6082 alloy FSW joints. Three types of tool with different probe shapes and shoulder surfaces and two weld configurations (one-sided and two-sided) were used in experiments. It was shown that all tool types produce high quality butt joints free from defects or imperfections. The best tensile performance was obtained for FSW joints produced by a conventional and Triflute tool. The results obtained for joints produced by a simple unthreaded probe without grooves and with a flat shoulder are significantly lower. The joint configuration influenced mechanical properties – the two-sided welds exhibited lower mechanical properties due to greater heat transference into the material during the second pass. The changes in mechanical properties reflected changes in weld microstructure, in particular, the softening of the weld nugget was associated with intense dynamic recovery producing grains that were nearly free of dislocations. A hypothesis explaining the well-known differences in microstructure between the advancing and retreating sides is also advanced. The differences were predicted based on a recently elaborated coupled thermal/flow model developed for FSW joints.