Microstructural Refinement And Control In Friction Stir Processed Aluminum Alloys For Superplasticity

Friction Stir Processing (FSP) is being developed as a potential grain refinement technique in aluminum alloys. It leads to microstructures consisting of very fine grains and high grain boundary misorientations, microstructural features that are considered necessary for enhanced superplasticity. In this paper, we review the recent observations of superplasticity in several friction stir processed commercial aluminum alloys. High strain rate superplasticity has been observed in a number of FSP aluminum alloys. A critical issue is the observation of abnormal grain growth at high temperatures. In some cases, the abnormal grain growth can limit the superplastic temperature range. New approaches are presented to minimize or eliminate this problem and realize the full potential of FSP for high strain rate superplasticity.