Effects of on-line solution and off-line heat treatment on microstructure and hardness of die-cast AZ91D alloy  

在线固溶及离线热处理对压铸AZ91D镁合金组织及硬度的影响(英文)

作　　者：徐玉磊[1,2] 张奎[1] 李兴刚[1] 雷健[3] 袁海波[3] 刘正[4] 

机构地区：[1]北京有色金属研究总院有色金属制备加工国家重点实验室,北京100088 [2]内蒙古科技大学材料与冶金学院,包头014010 [3]东风汽车有限公司商用车技术中心工艺研究所,十堰442001 [4]沈阳工业大学材料科学与工程学院,沈阳110870

出　　处：《Transactions of Nonferrous Metals Society of China》2012年第11期2652-2658,共7页中国有色金属学报（英文版）

基　　金：Projects (2011BAE22B01, 2011BAE22B06) supported by the National Key Technologies R&D Program During the 12th Five-Year Plan Period of China;Project (2010NC018) supported by the Innovation Fund of Inner Mongolia University of Science and Technology, China

摘　　要：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.研究在线固溶处理、离线固溶处理和时效处理对压铸AZ91D镁合金组织及硬度的影响。结果表明:在线淬火和离线时效处理可提高压铸AZ91D合金的布氏硬度,但是离线固溶处理使合金的硬度下降。通过X射线物相分析、光学显微组织分析、差热分析、扫描电镜及能谱分析,发现在线固溶和时效处理后合金的组织与压铸AZ91D的基本相同,仍由α-Mg及β-Al12Mg17组成。在压铸镁合金冷却过程中,在线固溶处理使温度急剧降低从而阻止了β-Al12Mg17相的继续析出,增强了Al元素固溶强化的效果。时效处理后,Al12Mg17从Mg的过饱和固溶体中析出并细化组织,改善了细晶强化的效果。离线的固溶处理使Al12Mg17分解,导致其固溶强化效果得到增强但是晶界强化相大幅度减少,从而使合金的硬度降低。

关 键 词：die-cast magnesium alloy AZ91D alloy on-line solution off-line solution treatment aging treatment β-Al12Mg17 phases microstructure refinement precipitation hardening 

分 类 号：TG166.4[金属学及工艺—热处理]