压铸AZ91D镁合金母材气孔在重熔过程的遗传性研究
收稿日期: 2012-04-28
修回日期: 2012-08-16
网络出版日期: 2012-12-11
基金资助
国家自然科学基金青年基金项目51105393, 中央高校基本科研业务基金项目CDJXS11132226, 以及重庆大学大型仪器设备开放基金项目2011121508资助
STUDY ON HEREDITARY OF PORES IN LASER REMELTING OF DIE CASTING AZ91D MAGNESIUM ALLOY
Received date: 2012-04-28
Revised date: 2012-08-16
Online published: 2012-12-11
Supported by
Supported by National Natural Science Foundation of China (No.51105393), Fundamental Research Funds for the Central Universities (No.CDJXS11132226) and Chongqing University Open Fund of Large Equipment (No.2011121508)
对压铸AZ91D镁合金进行CO2激光局部重熔, 采用OM和SEM观察了母材预存气孔和重熔区气孔特征, 利用粒径分析软件Nano measure 1.2测量了气孔尺寸, 着重研究了重熔区气孔同母材气孔的关联性.结果表明: 压铸镁合金母材预存气孔在重熔过程表现出明显的遗传性; 重熔区出现的微观气孔具有近圆形截面, 内壁光滑, 是氢致气孔; 重熔区出现的宏观气孔呈蠕虫状, 内壁存在气体通道, 并具有明显的金属冲刷痕迹. 分析认为, 氢致气孔主要遗传于母材固溶的原子氢和存于压铸缺陷的分子氢, 宏观气孔主要遗传于母材压铸过程卷入的气体. 分析了两类气孔的形成机制, 建立了母材预存气孔同重熔区宏观气孔内在关联的数学模型.
王向杰 游国强 张均成 龙思远 . 压铸AZ91D镁合金母材气孔在重熔过程的遗传性研究[J]. 金属学报, 2012 , 48(12) : 1437 -1445 . DOI: 10.3724/SP.J.1037.2012.00239
Porosity has been a main problem for die casting magnesium alloy welding and casting defect repair. In order to study the formation mechanism of pores in fusion welding of die casting magnesium alloy, in this research, experiment of die casting AZ91D magnesium alloy CO2 laser re–melting was carried out. OM and SEM were employed to observe the characteristics of pores existing at both the base metal and re–melted zone, and a software for particle size analysis called nano measure 1.2 was adopted to measure the pores’ size. During analysis, the work mainly focused on the relationship of pores in re–melted zone associated with that preexisting in the base metal. The results showed that: porosity in die cast magnesium alloy base metal showed apparently hereditary characteristic in the process of re–melting. Porosity preexisting in the die casting AZ91D magnesium alloy was mainly produced at the junction region of multi–grains, with high pressure of inner gas, small size and irregularity in shape. However, pores in the re–melting zone showed diversity. Specifically, the micro–pore was small in size, nearly round in cross section and smooth in the inner wall, which was induced by hydrogen stored in the base metal. The macro–pores were vermiculate, with gas channel and metal erosion traces at the inner wall. It’s considered that the micro–pore was mainly inherited from the atomic hydrogen solution in the base metal and molecular hydrogen stored in the die casting defects. In the re–melting process, gas bubble of hydrogen was formed through nucleation and development two steps, and there was no sufficient time to grow up. As a result, the hydrogen induced pore was great in number and small in size. While the macro–pores were inherited from porosity preexisting in the base metal, the corresponded gas bubble did not require nucleation, was directly formed from the involved gas in preexisting porosity during die–casting process. Development of gas bubble for macro–pore mainly was coalescence of small gas bubbles, which made the macro–pore show channel and crude in the inner wall. Furthermore, formation mechanism of the two types of pores were analyzed, and mathematical model on relationship of macro–pore in re–melted zone associated with that in the base metal was established.
Key words： die casting magnesium alloy; laser re–melting; pore; inheritance mechanism
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