Microstructure, Texture, and Mechanical Properties of Mg-8Gd-1Er-0.5Zr Alloy by Multi-Directional Forging at High Strain Rate
DING Ning1, WANG Yunfeng2, LIU Ke1, ZHU Xunming2, LI Shubo1, DU Wenbo1()
1.Faculty of Materials and Manufacturing, Beijing University of Technology, Beijing 100124, China 2.Weihai Wanfeng Magnesium S&T Development Co. , Ltd. , Weihai 264209, China
Cite this article:
DING Ning, WANG Yunfeng, LIU Ke, ZHU Xunming, LI Shubo, DU Wenbo. Microstructure, Texture, and Mechanical Properties of Mg-8Gd-1Er-0.5Zr Alloy by Multi-Directional Forging at High Strain Rate. Acta Metall Sin, 2021, 57(8): 1000-1008.
Magnesium alloys have attracted significant attention due to their excellent characteristics, such as low density, high specific strength, high thermal conductivity, and superior damping ability. The prominent advantages of using magnesium-alloy parts are environmental protection, energy conservation, and emission reduction, especially forged magnesium-alloy parts, which are used to reduce the weight of equipment in transportation and aerospace fields. Presently, there are relatively few investigations on the forged Mg-RE alloys. Based on Mg-Gd binary alloy, a series of Mg-Gd-Er-Zr alloys were developed, exhibiting excellent room-temperature mechanical properties and high-temperature creep resistance. In this study, the Mg-8Gd-1Er-0.5Zr (mass fraction, %) alloy was conducted using a multi-directional forging (MDF) at a high strain rate. The microstructure and texture evolution in various accumulated strains (ΣΔε) were examined, and their effects on the mechanical properties of the alloy were discussed. The results showed that the {} extension twinning was activated within most grains in the early stage of forging. With an increase in ΣΔε, the area fraction of twin decreases, while the area fraction of recrystallization increases. Continuous dynamic recrystallization (CDRX) was the dominant mechanism, supplemented by discontinuous dynamic recrystallization (DDRX) and twin-induced recrystallization (T-DRX). The grain refinement was attributed to the twin-breaking, and the grain size decreased from 33.0 μm to 13.1 μm when ΣΔε was less than 1.32. However, it was attributed to the dynamic recrystallization, and the grain size was further refined to 4.2 μm when ΣΔε was greater than 1.32. As ΣΔε increases, the texture of the alloy changed from basal to double-peak texture, and its intensity increased. When ΣΔε = 0.66, the tensile strength, yield strength, and elongation at room-temperature of the MDFed-alloy reached 295 MPa, 252 MPa, and 13.8%, respectively, which were 80%, 157%, and 13.1% higher than those of the as-solution state.
Fig.1 Schematic of the forging process flow (FD—forging direction; A, B, and C represent different forging surfaces)
Fig.2 OM image (a) and XRD spectrum (b) of as-solution Mg-8Gd-1Er-0.5Zr (GE81K) alloy
Fig.3 Inverse pole figures (a, b) and twin distribution maps (c, d) of as-solution GE81K alloy at accumulated strain ΣΔε = 0.66 (a, c) and ΣΔε = 1.32 (b, d); low angle grain boundary (LAGB) in the deformed grains (e) and LAGB in twins or around twin boundaries (f) at ΣΔε = 0.66 (TD—transverse direction; LFD—last forging direction)
Fig.4 Inverse pole figures (a, b) and twin distribution maps (c, d) of as-solution GE81K alloy at ΣΔε = 1.98 (a, c) and ΣΔε = 2.64 (b, d) (DRX—dynamic recrystallization)
Fig.5 EBSD analyses of as-solution GE81K alloy
Fig.6 {0001} plane pole figures of as-solution GE81K alloy at ΣΔε = 0.66 (a), ΣΔε = 1.32 (b), ΣΔε = 1.98 (c), and ΣΔε = 2.64 (d)
Fig.7 Distributions of angle between normal direction (ND) of the basal planes and FD of as-solution GE81K alloy at ΣΔε = 0.66 (a), ΣΔε = 1.32 (b), ΣΔε = 1.98 (c), and ΣΔε = 2.64 (d)
Fig.8 Area fraction of twin and average grain size of as-solution GE81K alloy as a function of the accumulated strain
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