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
刊名	Corrosion Science
	2008
卷号	50 期号:2 页码:329-337
关键词	magnesium SEM EPMA passive films corrosion protection
ISSN号	0010-938X
中文摘要	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.
原文出处	://WOS:000254076500005
公开日期	2012-04-13
内容类型	期刊论文
源URL	[http://210.72.142.130/handle/321006/33395]
专题	金属研究所_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.