Online from: 1954
Subject Area: Mechanical & Materials Engineering
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|Title:||Formation process and properties of phytic acid conversion coatings on magnesium|
|Author(s):||Jian-Rui Liu, (State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi'an, China), Yi-Na Guo, (State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi'an, China), Wei-Dong Huang, (State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi'an, China)|
|Citation:||Jian-Rui Liu, Yi-Na Guo, Wei-Dong Huang, (2012) "Formation process and properties of phytic acid conversion coatings on magnesium", Anti-Corrosion Methods and Materials, Vol. 59 Iss: 5, pp.225 - 230|
|Keywords:||Acids, Alloys, Chemical conversion coatings, Coatings, Corrosion resistance, Formation mechanism, Magnesium, Phytic acid|
|Article type:||Research paper|
|DOI:||10.1108/00035591211265488 (Permanent URL)|
|Publisher:||Emerald Group Publishing Limited|
|Acknowledgements:||This work was supported by the Research Fund of the State Key Laboratory of Solidification Processing (NWPU) (Grant Nos. 29-T-2009).|
Purpose – The purpose of this paper is to investigate a chromium-free conversion coating treatment for magnesium with phytic acid solution.
Design/methodology/approach – Pure magnesium was selected for the tests. Phytic acid solution was used as the conversion solution of surface treatment. The samples of magnesium were immersed in the solution under certain conditions to form a conversion coating on the surface of magnesium. The formation process of phytic acid conversion coating was studied by detecting the open circuit potential (OCP) and weight change of the pure magnesium for different conversion treatment times. Scanning electron microscopy (SEM) and electron energy spectrum (EDS) were used to examine the morphologies and compositions of the coatings, respectively.
Findings – The experimental results showed that the conversion coating had a multideck structure with netlike morphology, which is similar in nature to chromate conversion coatings, and was composed mainly of Mg, P, O and C. The contents of C and P and the size of the cracks in different conversion layers decreased from the external layer to the inner layer. The thickness of the conversion coating varied from 1.0µm to 15µm according to the processing parameters. The hydroxyl groups and phosphate carboxyl groups in the coating, which have similar properties to an organic paint coat, are beneficial to the combination of substrate and organic paint coating. The formation mechanism and thickness variation of the conversion coatings also are discussed.
Originality/value – The paper shows that phytic acid conversion coating could improve the electrochemical properties of magnesium and provide effective protection, which can improve the corrosion resistance of magnesium.
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