Achieving excellent superplasticity of Mg-7Zn-5Gd-0.6Zr alloy at low temperature regime

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.

Grain Rotation Accommodated GBS Mechanism for the Ti-6Al-4V Alloy during Superplastic Deformation

“…Great ductility can also be obtained in some ceramics and geological materials [7]. Although some attempts have been tried to optimize the SPF process windows by changing the metallography structures of materials [8][9][10][11], the current mainstream view still holds that the superplasticity of metals needs two compulsory requirements: a high temperatures and certain strain rate regions [5]. For the Ti-6Al-4V alloy, the elevated temperatures are at about 900 • C and the controlled strain rates need to be within the range of 10 −4 to 10 −2 /s.…”

Improving the corrosion resistance of MgZn1.2Gd Zr0.18 (x = 0, 0.8, 1.4, 2.0) alloys via Gd additions

“…[20]. Our previous research also obtained a superior plasticity of 863% at 250 °C and excellent room-temperature strength in Mg-7Zn-5Gd-0.6Zr (wt.%) alloy with quasicrystal Iphase [21]. The ultimate tensile strength, tensile yield strength and elongation of extruded ZK30 (MgZn1.2Zr0.18 (at.%)) alloy were about 300 MPa, 215 MPa and 9%, respectively [22].…”

Research on AZ80 + 0.4%Ce (wt %) Ultra-Thin-Walled Tubes of Magnesium Alloys: The Forming Process, Microstructure Evolution and Mechanical Properties

“…Meanwhile, it can be noticed that a certain number of twins appear during the backward extension and first extension (shown in Figure 6a,b), which are important in the deformation of magnesium alloys. As for the Mg alloys with the structure of HCP, they are difficult to deform because of the short slip system at a low temperature like 240 • C. The twinning does not act on the plastic deformation directly, but adjusts the orientation of the crystal and release stress concentration, which further stimulates the slipping system and make the slipping and twinning act on the deformation together [26]. With the accumulation of strain, the orientation of the grains turns in the direction that is most favorable to the slip and the twins disappear (shown in Figure 6c,d).…”