The Formation Mechanism and Corrosion Resistance of a Composite Phosphate Conversion Film on AM60 Alloy.

Jun Chen,Qinyong Zhang,Xiangna Lan,Chao Wang

doi:10.3390/ma11030402

Jun Chen, Qinyong Zhang + Show 2 more

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https://doi.org/10.3390/ma11030402

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Abstract

Magnesium alloy AM60 has high duc and toughness, which is expected to increase in demand for automotive applications. However, it is too active, and coatings have been extensively studied to prevent corrosion. In this work, a Ba-containing composite phosphate film has been prepared on the surface of AM60. The composition and formation mechanism of the film have been investigated using a scanning electronic microscope equipped with energy dispersive X-ray spectroscopy, Fourier transform infrared, X-ray photoelectron spectroscopy, and X-ray diffractometry tests. The corrosion resistance of the film has been measured by electrochemical and immersion tests. The results show that the deposition film has fully covered the substrate but there are some micro-cracks. The structure of the film is complex, and consists of MgHPO4·3H2O, MnHPO4·2.25H2O, BaHPO4·3H2O, BaMg2(PO4)2, Mg3(PO4)2·22H2O, Ca3(PO4)2·xH2O, and some amorphous phases. The composite phosphate film has better anticorrosion performance than the AM60 and can protect the bare alloy from corrosion for more than 12 h in 0.6 M NaCl.

Highlights

With excellent properties, such as low density, mechanical stability, and high damping capacity, magnesium (Mg) alloys are attracting much recent attention
Mg alloys have not been widely used yet due to the poor corrosion resistance, which is the main undesirable property [1]
Phosphate conversion coatings (PCCs) are promising coatings because most metal phosphates are insoluble in water and have high chemical stability [3]

Summary

Introduction

With excellent properties, such as low density, mechanical stability, and high damping capacity, magnesium (Mg) alloys are attracting much recent attention. Mg alloys have not been widely used yet due to the poor corrosion resistance, which is the main undesirable property [1]. Surface treatment is a general way to control corrosion by forming a barrier layer to isolate the bare alloys from the environment [2]. Phosphate conversion coatings (PCCs) are promising coatings because most metal phosphates are insoluble in water and have high chemical stability [3]. PCCs on Mg alloys have been investigated widely [7,8,9,10,11,12,13,14,15,16,17,18,19].

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