Structure and formation mechanism of phosphate conversion coating on die-cast AZ91D magnesium alloy

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	Structure and formation mechanism of phosphate conversion coating on die-cast AZ91D magnesium alloy
	W. Q. Zhou; D. Y. Shan; E. H. Han; W. Ke
	2008
发表期刊	Corrosion Science
ISSN	0010-938X
卷号	50 期号:2 页码:329-337
摘要	Phosphate conversion coating, which is considered as all alternative to chromium conversion coating for improving the corrosion resistance of die-cast AZ91D magnesium alloy is studied. The structure and formation mechanism of the coating was investigated in details using ESEM/EDX, XRD, EPMA, ICP and electrochemical method. It was found that the conversion coating was composed of complex phosphate containing magnesium and aluminum and showed amorphous structure. The thickness of the coating was about 10 mu m. A possible formation mechanism for phosphate conversion coating was proposed. Local pH rise due to the evolution of hydrogen in the vicinity of micro-cathode attributed to the movement of hydrolysis reaction balance for manganese dihydro phosphate in treating solution and resulted in the phosphate coating precipitated oil metal surface. Initial depositing position was related to the microstructure of substrate. Galvanic effect between alpha phase and beta phase caused the flower-like phosphate nuclei preferential depositing oil beta phase. Ball-like phosphate nuclei deposited mainly in alpha phase interior due to the micro-galvanic effect within alpha phase. The primary alpha phase was removed from the metal matrix due to the corrosion dissolution, which suggested the anodic dissolution mechanism during phosphate conversion coating growth. The inner stress in dried film resulted in random distribution of the network micro-cracks oil film surface, the crack site did not correspond to beta phase. (C) 2007 Elsevier Ltd. All rights reserved.
部门归属	[zhou, wanqiu; shan, dayong; han, en-hou; ke, wei] chinese acad sci, inst met res, shenyang 110016, peoples r china. [zhou, wanqiu] beijing inst chem technol, beijing 100029, peoples r china.;zhou, wq (reprint author), chinese acad sci, inst met res, shenyang 110016, peoples r china;wqzhou@imr.ac.cn
关键词	Magnesium Sem Epma Passive Films Corrosion Protection
URL	查看原文
WOS记录号	WOS:000254076500005
引用统计	被引频次：235[WOS] [WOS记录] [WOS相关记录]
文献类型	期刊论文
条目标识符	http://ir.imr.ac.cn/handle/321006/33395
专题	中国科学院金属研究所
推荐引用方式 GB/T 7714	W. Q. Zhou,D. Y. Shan,E. H. Han,et al. Structure and formation mechanism of phosphate conversion coating on die-cast AZ91D magnesium alloy[J]. Corrosion Science,2008,50(2):329-337.
APA	W. Q. Zhou,D. Y. Shan,E. H. Han,&W. Ke.(2008).Structure and formation mechanism of phosphate conversion coating on die-cast AZ91D magnesium alloy.Corrosion Science,50(2),329-337.
MLA	W. Q. Zhou,et al."Structure and formation mechanism of phosphate conversion coating on die-cast AZ91D magnesium alloy".Corrosion Science 50.2(2008):329-337.