Abstract
Mg-7Zn-5Gd-0.6Zr (wt%) alloy strengthened with quasicrystal phase (I-Mg3Zn6Gd phase) is prepared through hot extrusion and subsequent heat treatments. The low temperature (range from 25 °C to 250 °C) superplastic deformation behavior of the as-extruded, aging treated (T5) and solution and aging treated (T6) alloys are investigated. The results reveal that a superior superplastic elongation of 863% is obtained at 250 °C and strain rate of 1.67 × 10−3 s−1 and the elongation of this alloy increases with the increasing tensile temperature. Detailed microstructural analyses show that I-Mg3Zn6Gd phase and W-Mg3Gd2Zn3 phase are crushed into small particles during extrusion. A high density of nanoscale I-phase precipitates after T5 treatment. Dynamic recrystallization occurs in as-extruded Mg-7Zn-5Gd-0.6Zr alloy. The T5-treated Mg-7Zn-5Gd-0.6Zr alloy shows a relatively weak basal texture intensity, a large number fraction of high angle boundaries and a very finer grain structure (3.01 μm). During superplastic deformation, the nanoscale I-phase is slightly elongated and the microstructure is still equiaxed grains. The superplastic mechanism of the alloy is grain boundary sliding (GBS) accommodated by dislocation movement and static recrystallization. The cavity nucleation at the nanoscale I-phase/α-Mg matrix boundaries or grain boundaries and the cavity stringer formation leads to final fracture.
Highlights
Magnesium alloys are the lightest structural materials in the earth which have received considerable attention for applications leading to fuel efficiency and green environment[1,2,3]
The optimal elongation of 863% is achieved from the specimen tested at 250 °C and 1.67 × 10−3 s−1, in which the diffusional necking appears within the uniform gauge length
The lower-temperature superplastic behavior of E, E + T5 and E + T6 GZ57K alloy with I-phase is studied by tensile tests with the strain rate of 1.67 × 10−3 s−1 and temperatures range from 25 °C to 250 °C
Summary
Magnesium alloys are the lightest structural materials in the earth which have received considerable attention for applications leading to fuel efficiency and green environment[1,2,3]. The Mg-5Gd-7Zn-0.6Zr (wt%) alloy containing I-Mg3Zn6Gd phase is manufactured by traditional casting and indirect extrusion to investigate the superplastic behavior at temperatures less than 250 °C through the microstructural characterization, cracking behavior and texture evolution. This is important for processing technology and alloy component design, so as to fabricate lower cost magnesium alloys
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