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

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.

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

“…Due to their low density, high strength/weight ratio, good machinability, and excellent recyclability, magnesium (Mg) and its alloys are becoming increasingly popular for use in various industries, including transportation, communication, and personal electronics [ 1 , 2 , 3 , 4 ]. Unfortunately, the poor corrosion and high chemical reactivity of Mg and its alloys, especially in chloride-containing environments, restrict their widespread usage [ 5 , 6 , 7 , 8 ].…”

Microstructure and Corrosion Behavior of Composite Coating on Pure Mg Acquired by Sliding Friction Treatment and Micro-Arc Oxidation

“…The small peaks in curves for the CG and SFT sample indicate the transition between activation and passivation [ 40 , 42 ]. The corrosion tendency of materials can be predicted by corrosion potential (E corr ), and the higher E corr value represents lower corrosion susceptibility [ 1 , 30 ]. The E corr (−1.255 ± 0.002 V) of FG-MAO coating is the highest in the midst of all samples, indicating FG-MAO coating is much more stable and has considerably less corrosion susceptibility.…”

“…Commercial pure Mg and its alloys show enormous application potential in automotive, aviation and electric component fields, because of such factors as low density and excellent machinability [ 1 , 2 , 3 ]. They are also current prospective implant materials in orthopedics because of favorable biocompatibility, and a similar elastic modulus to that of human bone tissue [ 4 , 5 , 6 ].…”

De-alloying Behavior of Mg–Al alloy in Sulphuric Acid and Acetic Acid Aqueous Solutions

“…Magnesium and its alloys have attracted huge interest as engineering materials for industry and electronics applications because of their low density and good mechanical properties [1,2,3]. The poor corrosion resistance has limited the wide use of magnesium alloys [4,5,6].…”