Evolution of LPSO Phases and Their Effect on Dynamic Recrystallization in a Mg-Gd-Y-Zn-Zr Alloy
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TRODUCTION
THE compelling need for lightweight, energy-efficient, and environmentally benign engineering systems motivates a wider spread application of magnesium (Mg) alloys since Mg exhibits the lowest density among all common metallic materials.[1] Particularly, Mg-TM (transition metal)-RE (rare earth) alloys that contain LPSO phases are considered as promising materials because of their excellent mechanical[2–10] and physical[11,12] properties. LPSO phases exhibit higher thermal stability,[13,14] elastic modulus,[15,16] and microhardness[17,18] compared with the Mg matrix. Besides, they can increase the critical resolved shear stress (CRSS) of the basal slip[19] and activate the non-basal slip in the Mg matrix,[19,20] which may simultaneously improve the strength and ductility of the alloys.[19,21] In addition, it was indicated that the morphology of LPSO phases varied depending on the initial alloy state[22] and heat treatment schedule.[23] Dynamic recrystallization (DRX) of the Mg matrix can also be influenced by LPSO phases during thermo-mechanical processes.[7,23–27] This aroused an interest in enhancing the mechanical properties of Mg alloys by utilizing XIAO-JIE ZHOU, YONG-HAO GAO and ZHI-YONG CHEN are with the School of Materials Science and Engineering, Central South University, Changsha, 410083, China. CHU-MING LIU is with the School of Materials Science and Engineering, Central South University and also with the School of Materials Science and Engineering, Hunan University of Science and Technology, Xiangtan, 411201, China. Contact e-mail: [email protected] SHU-NONG JIANG is with the School of Civil Engineering, Central South University, Changsha, 410083, China. XIU-ZHU HAN is with the Beijing Institute of Spacecraft System Engineering, Beijing, 100094, China. Manuscript submitted December 29, 2016. Article published online March 22, 2017 3060—VOLUME 48A, JUNE 2017
LPSO phases. On one hand, the block-like LPSO phases at the a-Mg grain boundaries (designated as interdendritic LPSO hereafter) have been manipulated to regulate the mechanical properties.[7,25] Michiaki et al.[7] prepared a series of Mg-Zn-Y alloys containing LPSO phases that had a different secondary dendrite arm spacing (SDAS). The SDAS modified the DRX ratio, texture, and eventually mechanical properties. O~ norbe et al.[25] investigated the effect of the LPSO volume fraction on the microstructure and mechanical properties. They suggested that the size of DRX-ed grains decreased as the volume fraction of LPSO phases increased, since LPSO phases enhanced the nucleation of DRX-ed grains via the particle-stimulated nucleation (PSN) mechanism. On the other hand, LPSO phases in the grain interior (designated as intragranular LPSO hereafter) were also investigated to clarify their effect on DRX.[23,27] Jona et al.[23] suggested that both fineshaped LPSO phases and solute-segregated stacking faults (SFs) in the a-Mg matrix may restrain the DRX of a-Mg grains, while coarse block-shaped LPSO phases could promote DRX via the PSN mechanism. However, more
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