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Open AccessArticle

Investigation of Protective Performance of a Mg-Rich Primer Containing Aluminum Tri-Polyphosphate on AZ91D Magnesium Alloy in Simulated Acid Rain

by Xiangyu Lu 1,2,3, Sichen Sun 1,2, Qiqi Fan 1,2, Xiangjun Pei 3,*, Yuchao Dun 4, Xingguo Feng 1,2, Chen Zou 1,2 and Wang Lu 1,2
1
Jiangsu Key Laboratory of Coast Ocean Resources Development and Environment Security, Hohai University, Nanjing 210098, China
2
College of Harbour, Coastal and Offshore Engineering, Hohai University, Nanjing 210098, China
3
State Key Laboratory of Geohazard Prevention and Geoenvironment Protection, Chengdu University of Technology, Chengdu 610059, China
4
AVIC Manufacturing Technology Institute, Beijing 100024, China
*
Author to whom correspondence should be addressed.
Coatings 2019, 9(10), 649; https://doi.org/10.3390/coatings9100649
Received: 11 September 2019 / Revised: 1 October 2019 / Accepted: 6 October 2019 / Published: 9 October 2019
(This article belongs to the Section Corrosion, Wear and Erosion)
Mg-rich primer (MRP) containing aluminum tri-polyphosphate functions via a galvanic mechanism to protect AZ91D alloy from corrosion in the 3 wt % NaCl solution. However, its protective performance can be strongly affected by the testing environment. Therefore, it is important to investigate the performance of the primer on magnesium alloys in an acid rain environment. In the present study, the protective performance of MRP with or without aluminum tri-polyphosphate was investigated via open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), scanning electronic microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) in the simulated acid rain. Compared to the primer without aluminum tri-polyphosphate, the MRP containing aluminum tri-polyphosphate pigments exhibited better protective performance in the simulated acid rain condition. In the initial stage, the acidic condition prompted the aluminum tri-polyphosphate pigments to release phosphates and H+ to form magnesium phosphates on Mg particles, retarding their consumption rate. The Mg-rich primer with aluminum tri-polyphosphate can provide cathodic protection to AZ91D alloy for about 49 days in the simulated acid rain solution. Simultaneously, the corrosion products of Mg particles, magnesium oxides and phosphates, precipitated on the Mg particles and improved the stability of the primer. In addition, a protective film, consisting of magnesium oxides and phosphates, formed on the AZ91D substrate. Consequently, all these factors contributed to the long cathodic protection and improved corrosion resistance of MRP containing aluminum tri-polyphosphate in the simulated acid rain. View Full-Text
Keywords: magnesium alloy; acid rain; corrosion; Mg-rich primer; EIS; XPS magnesium alloy; acid rain; corrosion; Mg-rich primer; EIS; XPS
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Lu, X.; Sun, S.; Fan, Q.; Pei, X.; Dun, Y.; Feng, X.; Zou, C.; Lu, W. Investigation of Protective Performance of a Mg-Rich Primer Containing Aluminum Tri-Polyphosphate on AZ91D Magnesium Alloy in Simulated Acid Rain. Coatings 2019, 9, 649.

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