Achieving high superplasticity of a new Al-Mg-Sc-Zr alloy sheet prepared by a simple thermal-mechanical process

A new fine-grained Al-Mg-Sc-Zr alloy sheet with the grain size of 2.5 μm was prepared by simple rolling and thermal treatment process. Superplastic investigations in the temperature range of 450-550 °C and initial strain rate range of 1×10−3 s−1-1×10−1 s−1 show that a maximum elongation of 3250% is achieved at 525 °C and 5×10−3 s−1. The alloy also exhibits excellent superplastic ductility (>2390%) in the temperature interval 475-500 °C at 5×10−2 s−1. Analyses on the superplastic data reveal that the average values of the strain rate sensitivity and activation energy of the Al-Mg-Sc-Zr alloy are about 0.45 and 83 KJ/mol, respectively. The microstructure results show that the studied alloy is characterized by a high fraction of low angle grain boundaries and strong Copper, Brass and Cube texture. During superplastic deformation, low angle grain boundaries gradually transfer into high angle grain boundaries and the grains gradually orientate randomly. The fine coherent Al3(Sc, Zr) particles play an important role in obtaining excellent superplasticity. Grain boundary sliding is the predominant deformation mechanism.