High strain rate superplasticity in friction stir processed Al–Mg–Zr alloy

Al–4Mg–1Zr extruded bar was subjected to friction stir processing (FSP), resulting in generation of a fine microstructure of 1.5 μm grain size. Superplastic deformation behavior of FSP Al–4Mg–1Zr alloy was investigated in strain rate range of 1×10−3 to 1 s−1 and temperature range of 350–550 °C and compared with that of as-rolled one. It is indicated that the FSP alloy exhibited significantly enhanced superplasticity at a high strain rate of 1×10−1 s−1, and a maximum elongation of 1280% was obtained at 525 °C and 1×10−1 s−1. Further, the FSP Al–4Mg–1Zr alloy exhibited excellent thermal stability at high temperature, and a large elongation of 1210% was observed at 550 °C and 1×10−1 s−1. Moreover, FSP resulted in a significant decrease in the flow stress in Al–4Mg–1Zr alloy. At a strain rate of 1×10−2 s−1, the flow stress (∼7 MPa) of FSP Al–4Mg–1Zr at 450 °C was comparable to that of as-rolled alloy at 550 °C.