Effect of Processing Route During Double-Pass FSP Along with Low Heat Input in the Second Pass on the Superplastic Behavior of AZ31B Alloy

Effect of processing route during double-pass Friction Stir Processing (FSP) with low heat input during the second pass on the superplastic behavior of the AZ31B alloy was experimentally examined at 450 °C and 1.3 × 10–3 S−1 strain rate. Double-pass friction stir processing is found to be the advanced processing technique that results in grain refinement. Mainly, two processing parameters, i.e., tool rotational speed and tool traverse speed, play a significant role during the FSP, as these parameters cause dynamic recrystallization. Initially, the grain size of the base metal AZ31B alloy was 15.42 microns. After the experimental analysis, the processed sample, with a change in route in the second pass and low heat input, achieved grain refinement up to 6.81 microns. The result concludes that grain refinement occurs in the double-pass FSP along with low heat input during the second pass. Grain refinement has an impact on achieving superplastic deformation. Optical microscopy (OM) was conducted to capture the microstructural images of processed samples and further analyze the grain refinement. In order to determine the superplastic quality of the processed samples, hot tensile testing (HTT) was also carried out.