Improved corrosion resistance of Mg alloy by a green phosphating: insights into pre-activation, temperature, and growth
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Improved corrosion resistance of Mg alloy by a green phosphating: insights into pre-activation, temperature, and growth mechanism Tao Li1,2,*, Shifang Wang1,3, Hongtao Liu1, Jianhua Wu1, Shouqiu Tang1, Yuansheng Yang1,2, Xitao Wang1, and Jixue Zhou1,3,* 1
Shandong Provincial Key Laboratory of High Strength Lightweight Metallic Materials, Advanced Materials Institute, Qilu University of Technology (Shandong Academy of Sciences), Jinan 250014, China 2 Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China 3 Shandong Engineering Research Centre of Lightweight Automobiles Magnesium Alloys, Advanced Materials Institute, Qilu University of Technology (Shandong Academy of Sciences), Jinan 250014, China
Received: 8 May 2020
ABSTRACT
Accepted: 1 September 2020
Poor corrosion resistance of magnesium alloys remains a major obstacle to their extensive application. Phosphate conversion coating (PCC) is one of the most direct and effective strategies to enhance the corrosion resistance of magnesium alloys. To overcome the environmental damage of traditional phosphating technology, a PCC free of fluorine, chromium and nitrite was prepared in the present work. The effects of surface pre-activation process and preparation temperature on the surface morphology and corrosion resistance of PCC on ZK60 magnesium alloy were investigated. Surface pre-activation could significantly reduce the ultimate grain size of phosphate. At 90 °C, the prepared PCC showed perfect morphology and corrosion resistance. To better understand the phosphating nucleation and growth process, the surface and cross-sectional morphologies of PCC prepared for different times were observed. The phase composition of the prepared PCC was detected to be Hureaulite (Mn5(PO4)2(PO3OH)24H2O) and the coating growth mechanism was suggested in the end.
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Springer Science+Business
Media, LLC, part of Springer Nature 2020
Introduction Magnesium alloys are recognized as one of the most potential lightweight structural materials. However, the poor corrosion resistance of magnesium alloys
remains a major obstacle to their extensive application [1, 2]. To enhance the corrosion resistance of magnesium alloys, a variety of protection methods have been developed, such as alloying, heat treatment, plastic deformation, surface modification and
Handling Editor: David Balloy.
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https://doi.org/10.1007/s10853-020-05288-w
J Mater Sci
coating [3–11]. In which, surface coating is one of the most direct and effective strategies. In order to coat the surface of magnesium alloys, various treatment methods have been adopted, including physical methods, chemical methods, electrochemical methods, and combinations thereof [12–17]. In engineering application area, phosphating technology is mostly adopted to optimize the corrosion behavior of magnesium alloys, for its low-cost superiority and operation convenience [18–23]. In the recent years, phosphating is also widely adopted for improving bio
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