Superplastic Forming of Friction Stir Welded AA6061-T6 Alloy Sheet with Various Tool Rotation Speed

This study attempts to investigate the superplastic forming (SPF) of friction stir welded (FSW) AA6061-T6 alloy sheet at various tool rotation speeds in the range of 500 to 2000 rpm. The effect of FSW on SPF free blow forming of AA6061-T6, pole height, pole thickness, equivalent strain rate, and equivalent flow stress were investigated at constant pressure and constant temperature. Using the Cheng model the pole thickness, the equivalent strain rate, and equivalent flow stress were determined from superplastic free blow forming experiment. The finite element modeling and simulation is performed over the SPF of FSW specimens using selective superplasticity method. Experimental results indicate that tool rotation speed is the critical parameter during friction stir welding that has a greater influence on SPF. The theoretical modeling results exhibit that the SPF of friction stir welding can be practically applied to determine pole thickness, strain rate, flow stress, and strain rate sensitivity index. The finite element modeling results were found to be fairly agreeing with the experimental results. Hence, superplasticity can be significantly enhanced by friction stir welding by varying the FSW tool rotation speed.