Effect of Isothermal Repetitive Upsetting Extrusion on the Microstructure of Mg-12.0Gd-4.5Y-2.0Zn-0.4Zr Alloy
Abstract
:1. Introduction
2. Materials and Methods
3. Results and Discussion
3.1. The Microstructures of the As-Cast and As-Homogenized Alloys
3.2. Load-Displacement Curves
3.3. Microstructure Evolution
4. Conclusions
- The microstructure of an as-cast alloy consists of α-Mg grains, grayish Mg5(Gd,Y,Zn) phases, block-shaped LPSO phases, a cubic-shaped RE-rich compound, and fine-lamellar LPSO phases. After homogenization treatment at 793 K for 16 h, almost all Mg5(Gd,Y,Zn) phases and fine-lamellar LPSO phases dissolved into the matrix. Only some block-shaped LPSO phases remained along the grain boundaries, primarily at triple junctions.
- At the beginning stage of the upsetting process, the load rapidly increased and gradually reached a steady state. When the RUE passes increased to three passes, the steady state load reached a minimum of 2 kN. At the beginning stage of the extrusion process, the load curve first shows a steady increase, reaching a maximum, but then dropping with increasing ram displacement. The maximum load of extrusion fell to a minimum of 11 kN after three RUE passes.
- After one RUE pass, a few DRXed grains appeared in the interior of the deformed grains and along grain boundaries. From one to three RUE passes, average volume fractions of DRXed grains increased from 43.9% to 65.8%, and that of fine-lamellar and block-shaped LPSO phases gradually decreased.
- All the samples exhibited a typical bimodal microstructure consisting of some initial grains containing fine-lamellar LPSO phases, but consisting mostly of fine-DRXed grains with a mean grain size of 6 μm. Because of an increase in the accumulated strains, the coarse grains were substituted with fine-DRXed grains, the grains were gradually refined, and the microstructure distribution became more homogeneous.
Author Contributions
Funding
Conflicts of Interest
References
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Zhang, G.; Zhang, Z.; Du, Y.; Yan, Z.; Che, X. Effect of Isothermal Repetitive Upsetting Extrusion on the Microstructure of Mg-12.0Gd-4.5Y-2.0Zn-0.4Zr Alloy. Materials 2018, 11, 2092. https://doi.org/10.3390/ma11112092
Zhang G, Zhang Z, Du Y, Yan Z, Che X. Effect of Isothermal Repetitive Upsetting Extrusion on the Microstructure of Mg-12.0Gd-4.5Y-2.0Zn-0.4Zr Alloy. Materials. 2018; 11(11):2092. https://doi.org/10.3390/ma11112092
Chicago/Turabian StyleZhang, Guanshi, Zhimin Zhang, Yue Du, Zhaoming Yan, and Xin Che. 2018. "Effect of Isothermal Repetitive Upsetting Extrusion on the Microstructure of Mg-12.0Gd-4.5Y-2.0Zn-0.4Zr Alloy" Materials 11, no. 11: 2092. https://doi.org/10.3390/ma11112092