Influence of friction stir processing tool design on microstructure and superplastic behavior of Al-Mg alloys

Friction stir processing is one of the most efficient techniques for microstructure refinement and has a potential for enhancing the deformation behavior of metallic materials at elevated temperature. The design of the tool has been shown to play a decisive role in microstructure modification. In this work, the effect of tool design on superplastic behavior of friction stir processed Al-Mg alloys has been investigated. The alloy was friction stir processed at 400 rpm and 0.42 m/s. Four different tools were used and compared. The pin was right-handed screw type in all cases. Very fine microstructures with grain sizes less than 3 µm were obtained with all the tools. Abnormal grain growth was observed after high temperature exposure using some of the tools. Maximum tensile elongations in the range of 575-810% were achieved with three of the tools. The tool with a larger shoulder area allowed more plastic deformation on the microstructure generating a more suitable microstructure for high temperature deformation.