Transactions of Nonferrous Metals Society of China The Chinese Journal of Nonferrous Metals

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Transactions of Nonferrous Metals Society of China

Vol. 22    No. 11    November 2012

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Effects of on-line solution and off-line heat treatment on microstructure and hardness of die-cast AZ91D alloy
XU Yu-lei1, 2 , ZHANG Kui1, LI Xing-gang1, LEI Jian3, YUAN Hai-bo3, LIU Zheng4

1. State Key Laboratory for Fabrication and Processing of Nonferrous Metals,
General Research Institute for Nonferrous Metals, Beijing 100088, China;
2. School of Materials and Metallurgy, Inner Mongolia University of Science and Technology,
Baotou 014010, China;
3. Material Technology Institute of Commercial Vehicle Technical Center,
Dongfeng Motor Co., Ltd., Shiyan 442001, China;
4. School of Materials Science and Engineering, Shenyang University of Technology,
Shenyang 110870, China

Abstract:The effects of on-line solution, off-line solution and aging heat treatment on the microstructure and hardness of the die-cast AZ91D alloys were investigated. Brinell hardness of die-cast AZ91D alloy increases through on-line solution and off-line aging treatment but decreases after off-line solution treatment. By X-ray diffractometry, optical microscopy, differential thermal analysis, scanning electron microscopy and X-ray energy dispersive spectroscopy, it is found that the microstructures of the die-cast AZ91D magnesium alloy before and after on-line solution and off-line aging are similar, consisting of α-Mg and β-Al12Mg17. The precipitation of Al element is prevented by on-line solution so that the effect of solid solution strengthening is enhanced. The β-Al12Mg17 phases precipitate from supersaturated Mg solid solution after off-line aging treatment, and lead to microstructure refinement of AZ91D alloy, so the effect of precipitation hardening is enhanced. The β-Al12Mg17 phases dissolve in the substructure after off-line solution treatment, which leads to that the grain boundary strengthening phase is reduced significantly and the hardness of die cast AZ91D is reduced.


Key words: die-cast magnesium alloy; AZ91D alloy; on-line solution; off-line solution treatment; aging treatment; β-Al12Mg17 phases; microstructure refinement; precipitation hardening

ISSN 1004-0609
CN 43-1238/TG

ISSN 1003-6326
CN 43-1239/TG

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