Deformation Behavior of Ultra-Strong and Ductile Mg-Gd-Y-Zn-Zr Alloy with Bimodal Microstructure
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THE rising demands for improving fuel efficiency and reducing exhaust emissions have encouraged the development of high-strength Mg alloys due to their large potential for weight reduction in transportation vehicles.[1–6] Microstructure design via precipitation hardening is an effective way to enhance the strength of the alloys. The Mg-Gd-Y alloys exhibit high strength, due
C. XU is with the School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, P.R. China and also with the Research Center for Advanced Magnesium Technology, Nagaoka University of Technology, Nagaoka 940-2188, Japan. G.H. FAN, Y.Q. CHI, X.G. QIAO, G.J. CAO, T.T. ZHANG, M. HUANG, K.S. MIAO, and M.Y. ZHENG are with the School of Materials Science and Engineering, Harbin Institute of Technology. Contact emails: [email protected], [email protected] T. NAKATA and S. KAMADO are with the Research Center for Advanced Magnesium Technology, Nagaoka University of Technology. X. LIANG is with the Institute of Materials, Shanghai University, Shanghai 200072, P.R. China. H.L. XIE is with the Shanghai Synchrotron Radiation Facility, Shanghai 201204, P.R. China. Manuscript submitted August 8, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
to the remarkable age-hardening response generated by the precipitation of the metastable b¢ phases on the prismatic plane of the a-Mg matrix,[3–9] which have become popular. In addition to the increment of the number density and aspect ratio of the prismatic b¢ precipitates, the strength could be further increased if the closed volumes surrounded by precipitates along basal and prismatic planes are formed to block dislocation movements within them.[10] Previous studies have shown that the addition of Zn to Mg-HRE alloys induced the formation of long-period stacking ordered (LPSO) phases and/or c¢ precipitates on the basal planes,[4,11–20] i.e., Mg-Gd-Y-Zn alloys may achieve an ideal microstructure that obtain both basal LPSO phases/c¢ precipitates and prismatic b¢ precipitates, giving them the potential to be an ultra-high-strength Mg alloy. Thermo-mechanical processing leads to grain refinement by dynamic recrystallization (DRX), strong texture, and dynamic precipitation. Wrought Mg products demonstrate higher strength and ductility than cast products.[21–30] The microstructure of the extruded Mg-Gd/Y-Zn alloys is generally characterized by the bimodal microstructure, comprising hot-worked coarse
grains with strong fiber texture and fine dynamically recrystallized (DRXed) grains with random orientations.[3,4,23–28] The hot-worked Mg grains and the block-shaped LPSO phases conspire to the strength, while the DRXed grains improve ductility of the alloy.[23] This method should be effective in obtaining the desired mechanical properties by microstructure design. The control of the DRXed ratio, grain size, texture, and dynamic precipitation of the alloys via hot extrusion, as well as the control of the morphology and the number density of the precipitates could be obtained with the aging tr
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