An Investigation on Hot Tearing of Mg-4.5Zn-(0.5Zr) Alloys with Y Additions
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IT has been widely recognized that hot tearing, also known as hot cracking, hot shortness, or hot brittleness, is a major defect formed during solidification. It is defined as a failure occurring in the mushy zone of a freezing alloy.[1] Previous studies have revealed that hot tearing occurs at last stage of solidification when some liquid is still present due to an obstructed contraction of the solidifying alloy, often at hot spots where the casting solidifies last or at areas with sudden changes of cross section. A comprehensive review on hot tearing of aluminum alloys has been provided by Eskin et al.,[2] but less works have been reported on hot tearing of magnesium alloys. For the hot tearing of Mg alloys, most of previous studies were carried out only on Mg-Al and Mg-Zn series.[3–7] Cao et al.[3] studied the hot tearing susceptibility (HTS) of magnesium alloys which contained 0.25 to 8 wt pct Al using constrained rod casting (CRC) in a steel mold. The curve of the crack susceptibility vs the Al content showed a peak near 1 wt pct Al. They also investigated the effects of alloying elements such as Ca ZHI WANG, Doctor, formerly with MagIC-Magnesium Innovation Centre, Helmholtz-Zentrum Geesthacht, Max-Planck-Str. 1, 21502 Geesthacht, Germany, is now with the School of Materials Science and Engineering, Shenyang University of Technology, Shenyang 110870, People’s Republic of China. Contact e-mail: [email protected] JIANGFENG SONG, Ph.D. Student, YUANDING HUANG, Doctor, KARL ULRICH KAINER, Professor, and NORBERT HORT, Doctor, are with MagIC-Magnesium Innovation Centre, Helmholtz-Zentrum Geesthacht. AMIRTHALINGAM SRINIVASAN, Doctor, is with MagIC-Magnesium Innovation Centre, HelmholtzZentrum Geesthacht, and also with CSIR-National Institute for Interdisciplinary Science and Technology (NIIST), Trivandrum 695019, India. ZHENG LIU, Professor, is with the School of Materials Science and Engineering, Shenyang University of Technology. Manuscript submitted May 22, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS A
and Sr on the HTS of Mg-Al alloys.[4,5] Their results indicated that the additions of these two elements decreased the HTS of Mg-Al alloys. Zhen et al.[8] investigated the effect of different mold temperatures on HTS of Mg-1 wt pct Al, and found that increasing the mold temperature improved the hot tearing resistance. Recently, Zhou et al.[6,7] used thermodynamic calculations and quantitative methods to evaluate the hot tearing of Mg-Zn-(Al) alloys, and found that the hot tearing of these alloy was largely influenced by the content of Zn and initial mold temperature. Considering the fact that rare earth (RE) elements play a significant role in modifying the properties of magnesium alloys,[9–11] the investigations on their effects on HTS of magnesium alloys should be very interesting. Recently, Mg-Zn-Y wrought magnesium alloy has attracted significant interests. It was reported that the Mg-Zn-Y alloys containing icosahedral phase (I-phase) as a secondary phase exhibit good mechanical properties at room temperatur
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