The Role of Electrolyte Additives on the Corrosion Behavior of Ceramic Coatings Formed on ZM21 Magnesium Alloy by Plasma Electrolytic Oxidation

Abstract:

The present study emphasizes the effect of addition of sodium citrate (C₆H₅Na₃O₇.2H₂O) and sodium tungstate (Na₂WO₄.2H₂O) to a silicate based electrolyte system on the corrosion behavior of PEO treated ZM21 magnesium alloy. The phase composition of the as-developed coating was evaluated by X-ray diffraction (XRD) analysis, while its surface morphology, thickness and elemental distribution were observed using scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). Potentiodynamic polarization tests were done in 3.5 wt% NaCl solution to analyze the corrosion behavior of the ceramic coatings in simulated marine environment. The results of XRD showed that the phase composition of all coatings comprised of Mg₂SiO₄ and MgO irrespective of the additive used. In addition to Mg, Si and O, the presence of W, C in EDS spectrum indicated that these elements were incorporated into the coating from the electrolyte system containing tungstate and citrate. The corrosion test results revealed that the PEO coatings obtained in tungstate containing electrolyte solution showed higher corrosion resistance than those formed in citrate containing electrolyte solution.

• Periodical: Materials Science Forum (Volume 710)
• Pages: 683-688
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.710.683
• Online since: January 2012
• Authors: D. Sreekanth, Rameshbabu Nagumothu, K. Ramaswamy Choudary, K. Prasad Rao
• Keywords: Corrosion, Magnesium Alloy, Plasma Electrolytic Oxidation (PEO), Sodium Citrate, Sodium Tungstate

References

[1] J.E. Gray, B. Luan, Protective coatings on magnesium and its alloys - a critical review, J. Alloys Compd. 336 (2002) 88-113.

DOI: 10.1016/s0925-8388(01)01899-0

[2] J. Yang, F. Cui, I.S. Lee, Surface modifications of magnesium alloys for biomedical applications, Ann. Biomed. Eng. 39 (2011) 1857-1871.

DOI: 10.1007/s10439-011-0300-y

[3] L. Rama Krishna, K.R.C. Somaraju, G. Sundararajan, The tribological performance of ultra-hard ceramic composite coatings obtained through microarc oxidation, Surf. Coat. Technol. 163-164 (2003) 484-490.

DOI: 10.1016/s0257-8972(02)00646-1

[4] L. Rama Krishna, G. Poshal, G. Sundararajan, Influence of electrolyte chemistry on morphology and corrosion resistance of micro arc oxidation coatings deposited on magnesium, Metall. Mater. Trans. A 41 (2010) 3499-3508.

DOI: 10.1007/s11661-010-0412-2

[5] J. Ding, J. Liang, L. Hu, J. Hao, Q. Xue, Effects of sodium tungstate on characteristics of microarc oxidation coatings formed on magnesium alloy in silicate-KOH electrolyte, Trans. Nonferrous Met. Soc. China 17 (2007) 244-249.

DOI: 10.1016/s1003-6326(07)60079-x

[6] H.P. Duan, K.Q. Du, C.W. Yan, F.H. Wang, Electrochemical corrosion behavior of composite coatings of sealed MAO film on magnesium alloy AZ91D, Electrochim. Acta. 51 (2006) 2898-2908.

DOI: 10.1016/j.electacta.2005.08.026

[7] F. Zhao, A. Liao, R. Zhang, S. Zhang, H. Wang, X. Shi, M. Li, X. He, Effects of sodium tungstate on properties of micro-arc coatings on magnesium alloys, Trans. Nonferrous Met. Soc. China 20 (2010) s683-s687.

DOI: 10.1016/s1003-6326(10)60562-6