Construction of Hot Processing Map of Solutionized Mg-10Gd-6Y-1.5Zn-0.5Zr Alloy and Microstructure Evolution
BAO Chengli1, LI Hao1, HU Li1(), ZHOU Tao1, TANG Ming2, HE Qubo3, LIU Xiangguo4
1 College of Materials Science and Engineering, Chongqing University of Technology, Chongqing 400054, China 2 College of Mechanical and Electrical Engineering, Harbin Engineering University, Harbin 150001, China 3 Chongqing Material Research Institute Co. Ltd., Chongqing 400707, China 4 Chongqing Zhonglei Tech. Co. Ltd., Chongqing 400800, China
Cite this article:
BAO Chengli, LI Hao, HU Li, ZHOU Tao, TANG Ming, HE Qubo, LIU Xiangguo. Construction of Hot Processing Map of Solutionized Mg-10Gd-6Y-1.5Zn-0.5Zr Alloy and Microstructure Evolution. Acta Metall Sin, 2025, 61(4): 632-642.
Mg-rare earth (RE)-Zn alloys with long period stacking ordered (LPSO) phases have received extensive attention in the past few years because of their excellent mechanical properties compared with conventional wrought Mg alloys. However, the corresponding hot deformation behaviors and microstructure characteristics of Mg-RE-Zn alloys are rather complex. An in-depth investigation into this would broaden their engineering applications. In this work, hot compression experiments of solutionized Mg-10Gd-6Y-1.5Zn-0.5Zr alloys at 350-500 oC and a strain rate of 0.001-1 s-1 have been conducted to investigate the hot deformation behavior, construct the hot processing map, and determine the hot working window. Afterward, the interaction between dynamic recrystallization (DRX) and kink deformation of LPSO phase during hot deformation has been studied through microstructure characterization. Results show that the flow stress decreases with the increase of temperature and the decrease of strain rate. When deformed at a relatively high strain rate, the sensitivity of flow stress to temperature is evident. When deformed at a relatively low temperature, the sensitivity of flow stress to strain rate is prominent. The corresponding hot processing map was constructed based on Murty criterion. Under a strain of 0.7, two optimal processing areas are found at 400-450 oC (0.001-0.027 s-1) and 450-487 oC (0.12-1 s-1). The accuracy of the constructed hot processing map has been verified by using microstructure characterization (via volume fraction analysis of recrystallized grains) of deformed samples, which correspond to different regions in the constructed hot processing map. By analyzing the softening stress of the flow curve at different temperatures (peak stress minus state stress), DRX volume fraction and kinking angle of the lamellar LPSO phase, the degree of kink deformation of the lamellar LPSO phase decreases with the increase of deformation temperature. In addition, the DRX volume fraction increases with the increase of deformation temperature. Moreover, the kink deformation of the lamellar LPSO phase has an inhibitory effect on DRX and the softening stress of the flow curve could be jointly affected by DRX and the kink deformation of the lamellar LPSO phase.
Fund: Fellowship of China Postdoctoral Science Foundation(2021M703592);Special Funded Project of Chongqing Postdoctoral Research Program(2021XM1022);Qingnian Project of Science and Technology Research Program of Chongqing Education Commission of China(KJQN202101141);Postgraduate Innovation Project of Chongqing(CYS22640);Graduate Science Research Project of Chongqing University of Technology(KLA21024)
Corresponding Authors:
HU Li, associate professor, Tel: 17358428920, E-mail: huli@cqut.edu.cn
Fig.1 Schematic of isothermal hot compression process (T—temperature, —strain rate)
Fig.2 FESEM image and EDS element distribution maps of Mg-10Gd-6Y-1.5Zn-0.5Zr alloy after solution treatment
Point
Atomic fraction / %
Morphology
Phase
Mg
Gd
Y
Zn
Zr
I
96.25
2.10
1.23
0.36
0.06
Matrix
Mg
II
87.02
3.86
2.86
6.26
-
Blocky
LPSO phase
III
75.74
8.39
15.47
0.40
-
Cuboid
RE-rich phase
Table 1 EDS results of Mg-10Gd-6Y-1.5Zn-0.5Zr alloy after solution treatment in Fig.2a
Fig.3 OM images of surfaces perpendicular (a) and parallel (b) to ED in Mg-10Gd-6Y-1.5Zn-0.5Zr alloy after solution treatment and distributions of grain sizes (c) (ED—extrusion direction)
Fig.4 True stress-true strain curves of solid-solution Mg-10Gd-6Y-1.5Zn-0.5Zr alloys at different deformation temperatures (Insets in Fig.4a show the macroscopic morphologies of fractured samples at 350 oC, 0.1 s-1 and 350 oC, 1 s-1) (a) 350 oC (b) 400 oC (c) 450 oC (d) 500 oC
Fig.5 Sensitivity analyses of the peak stress for solid-solution Mg-10Gd-6Y-1.5Zn-0.5Zr alloys (a) under different strain rates (b) under different deformation temperatures
Fig.6 3D power dissipation coefficient (η) maps of solid-solution Mg-10Gd-6Y-1.5Zn-0.5Zr alloys under 0.1 (a), 0.3 (b), 0.5 (c), and 0.7 (d) strains
Fig.7 Hot processing maps of solid-solution Mg-10Gd-6Y-1.5Zn-0.5Zr alloys under 0.1 (a), 0.3 (b), 0.5 (c), and 0.7 (d) strains
Fig.8 EBSD images (a-e) and the corresponding dynamic recrystallization (DRX) fractions (f) of Mg-10Gd-6Y-1.5Zn-0.5Zr alloy deformed samples under deformation conditions of 400 oC and 1 s-1 (point A in Fig.7d) (a), 400 oC and 0.1 s-1 (point B in Fig.7d) (b), 400 oC and 0.01 s-1 (point C in Fig.7d) (c), 450 oC and 0.01 s-1 (point D in Fig.7d) (d), and 500 oC and 1 s-1 (point E in Fig.7d) (e) (CD—compression direction, TD—transverse direction, ND—normal direction. Inset in Fig.8f shows the macroscopic morphology of fractured sample at 500 oC and 1 s-1)
Fig.9 OM images of Mg-10Gd-6Y-1.5Zn-0.5Zr alloy deformed samples under constant strain rate 0.01 s-1 and temperatures of 350 oC (a), 400 oC (b), 450 oC (c), and 500 oC (d) (The angles in Figs.9a-c are the kink band angles)
Fig.10 Statistical analysis of kink angles (180°-θ) of lamellar LPSO phases and DRX grain fractions of deformed samples in Fig.9 (θ—kink band angle)
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