Achieving exceptional superplasticity in a fine-grained Mg-Gd-Y-Zn-Zr alloy fabricated by friction stir processing
摘要
In this work, a fine-grained Mg-Gd-Y-Zn-Zr alloy was prepared by friction stir processing (FSP), which exhibited uniform and fine equiaxed grains with an average grain size of 3.1 μm. The proportion of high-angle grain boundaries reached 91.7%, and the grain orientation was random. The dispersed block-shaped 18R long-period stacking ordered (LPSO) structural phase was mainly distributed at the grain boundaries of the Mg matrix, while the needle-like 14H LPSO phase was distributed within the grains of the Mg matrix. The superplastic tensile tests were then conducted at the temperatures of 340 ℃, 370 ℃, 400 ℃ and 430 ℃ and strain rates of 1 × 10−3 s−1, 5 × 10−3 s−1 and 1 × 10−2 s−1. The results showed that the superplastic elongations of the fine-grained Mg-Gd-Y-Zn-Zr alloy exceeded 400% under all deformation conditions in this work. Excellent superplasticity with an elongation of 1341% was obtained at 400 ℃ and 5 × 10−3 s−1. Under this condition, the strain rate sensitivity index of the present alloy was 0.48, and the average deformation activation energy was 177.7 kJ/mol, which indicated that grain boundary sliding was the main superplastic deformation mechanism.
Graphical abstract