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The Preparation, Characterization and Formation Mechanism of a Calcium Phosphate Conversion Coating on Magnesium Alloy AZ91D

by Dong Liu 1,2,3, Yanyan Li 1, Yong Zhou 2 and Yigang Ding 2,*
1
School of Chemistry and Environmental Engineering, Wuhan Institute of Technology, Wuhan 430205, China
2
Key Lab for Green Chemical Process of Ministry of Education, Wuhan Institute of Technology, Wuhan 430205, China
3
State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu 610500, China
*
Author to whom correspondence should be addressed.
Materials 2018, 11(6), 908; https://doi.org/10.3390/ma11060908
Received: 21 April 2018 / Revised: 18 May 2018 / Accepted: 22 May 2018 / Published: 28 May 2018
The poor corrosion resistance of magnesium alloys is one of the main obstacles preventing their widespread usage. Due to the advantages of lower cost and simplicity in operation, chemical conversion coating has drawn considerable attention for its improvement of the corrosion resistance of magnesium alloys. In this study, a calcium phosphate coating was prepared on magnesium alloy AZ91D by chemical conversion. For the calcium phosphate coating, the effect of processing parameters on the microstructure and corrosion resistance was studied by scanning electron microscope (SEM) and electrochemical methods, and the coating composition was characterized by X-ray diffraction (XRD). The calcium phosphate coating was mainly composed of CaHPO4·2H2O (DCPD), with fewer cracks and pores. The coating with the leaf-like microstructure provided great corrosion resistance to the AZ91D substrate, and was obtained under the following conditions: 20 min, ambient temperature, and no stirring. At the same time, the role of NH4H2PO4 as the coating-forming agent and the acidifying agent in the conversion process was realized, and the formation mechanism of DCPD was discussed in detail in this work. View Full-Text
Keywords: magnesium alloy; calcium phosphate coating; corrosion resistance; SEM; formation mechanism magnesium alloy; calcium phosphate coating; corrosion resistance; SEM; formation mechanism
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Liu, D.; Li, Y.; Zhou, Y.; Ding, Y. The Preparation, Characterization and Formation Mechanism of a Calcium Phosphate Conversion Coating on Magnesium Alloy AZ91D. Materials 2018, 11, 908.

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