Plasma electrolytic oxidation coating on AZ91 magnesium alloy modified by neodymium and its corrosion resistance

✍ Scribed by Y.L. Song; Y.H. Liu; S.R. Yu; X.Y. Zhu; Q. Wang

• Publisher: Elsevier Science
• Year: 2008
• Tongue: English
• Weight: 905 KB
• Volume: 254
• Category: Article
• ISSN: 0169-4332
• DOI: 10.1016/j.apsusc.2007.10.043

✦ Synopsis

Ceramic coatings on the surfaces of Mg-9Al-1Zn (AZ91) magnesium alloy and Mg-9Al-1Zn-1Nd magnesium alloy (AZ91 magnesium alloy modified by neodymium, named as AZ91Nd in this paper) are synthesized in aluminate electrolyte by plasma electrolytic oxidation (PEO) process, respectively. X-ray diffraction and X-ray photoelectron spectroscopy analyses show the PEO coating on the Mg-9Al-1Zn-1Nd alloy comprises not only MgO and Al 2 O 3 , which are found in the coating on the AZ91 alloy, but also a trace amount of Nd 2 O 3 . Microstructure observations indicate the addition of Nd can decrease the sizes of b phases and form Al 2 Nd intermetallics in the AZ91 alloy. The fine b phases can effectively restrain the formation of unclosed-holes and greatly decrease the sizes of pores in the coating during the PEO process. In addition, the Al 2 Nd intermetallics can be completely covered due to the lateral growth of the PEO coatings formed on the a and b phases. As a result, the coating on the AZ91Nd alloy possesses a dense microstructure compared with that on the AZ91 alloy. The following corrosion tests indicate the corrosion resistance of the PEO coating on the AZ91Nd alloy is evidently higher than that of the PEO coating on the AZ91 alloy.