Characterization of Microstructure and Composition of Plasma Electrolytic Oxide Film Formed on AZ31 Mg Alloy

Abstract:

Magnesium alloy has been widely investigated as a biodegradable implant material owing to its unique properties to degrade spontaneously in human body fluid without causing toxicity. However, the degradation rate needs to be controlled. An effective way to lower down the degradation rate of Mg alloy is by coating with plasma electrolytic oxidation (PEO) technique. In this research, the microstructure and mechanical hardness of the PEO film formed on AZ31 were investigated. The film was prepared under a constant current of 400 A/m² in the Na₃PO₄ solution at 30°C. The voltage-time curve showed an immediate increase of current during the first 25 s before reaching a steady-state voltage of 150 V. The spark discharge revealed as white micro discharges. The film formed for 3 min exhibited a high surface roughness with a large variety of thickness in the range of 1-20 µm. The film contained pores and cracks. The big pores with diameter size 10-20 µm were formed as a result of gas entrapment, while the small pores with a radius of 1-3 µm were associated with the discharge tunnel during the PEO process. The X-ray diffraction pattern indicated that the film composed of crystalline Mg₃(PO₄)₂.

• Periodical: Key Engineering Materials (Volume 860)
• Pages: 213-217
• DOI: https://doi.org/10.4028/www.scientific.net/KEM.860.213
• Online since: August 2020
• Authors: Efrina Hidayati, Anawati Anawati*
• Keywords: Hardness, Magnesium, Microstructure, PEO

References

[1] M. Pekguleryuz, K. Kainer, A. Kaya, Fundamentals of Magnesium Alloy, Woodhead Publishing Ltd., Cambridge, UK, (2013).

[2] G. Song, Control of biodegradation of biocompatable magnesium alloys, Corros. Sci. 49 (2007) 1696–1701.

DOI: 10.1016/j.corsci.2007.01.001

[3] M. Echeverry-Rendon, V. Duque, D. Quintero, S.M. Robledo, M.C. Harmsen, F. Echeverria, Improved corrosion resistance of commercially pure magnesium after its modification by plasma electrolytic oxidation with organic additives, J. Biomater. Appl. 33 (2018) 725–740.

DOI: 10.1177/0885328218809911

[4] J.L. Patel, N. Saka, Microplasmic ceramic coating, InterCeram Int. Ceram. Rev. 50 (2001) 398–401.

[5] L. White, Y. Koo, S. Neralla, J. Sankar, Y. Yun, Enhanced mechanical properties and increased corrosion resistance of a biodegradable magnesium alloy by plasma electrolytic oxidation (PEO), Mater. Sci. Eng. B Solid-State Mater. Adv. Technol. 208 (2016) 39–46.

DOI: 10.1016/j.mseb.2016.02.005

[6] R.O. Hussein, D.O. Northwood, X. Nie, The effect of processing parameters and substrate composition on the corrosion resistance of plasma electrolytic oxidation (PEO) coated magnesium alloys, Surf. Coatings Technol. 237 (2013) 357–368.

DOI: 10.1016/j.surfcoat.2013.09.021

[7] C. Blawert, W. Dietzel, E. Ghali, G. Song, Anodizing treatments for magnesium alloys and their effect on corrosion resistance in various environments, Adv. Eng. Mater. 8 (2006) 511–533.

DOI: 10.1002/adem.200500257

[8] H. Asoh, S. Matsuoka, H. Sayama, S. Ono, Anodizing under sparking of AZ31B magnesium alloy in Na3PO4 solution, J. Japan Inst. Light Met. 60 (2010) 608–614.

DOI: 10.2464/jilm.60.608

[9] L. Li, J. Gao, Y. Wang, P. Bala Srinivasan, J. Liang, C. Blawert, M. Störmer, W. Dietzel, Anawati, H. Asoh, S. Ono, Effect of current density on the microstructure and corrosion behaviour of plasma electrolytic oxidation treated AM50 magnesium alloy, Surf. Coatings Technol. 272 (2015) 182–189.

DOI: 10.1016/j.apsusc.2008.11.008

[10] A. Anawati, H. Asoh, S. Ono, Effects of alloying element ca on the corrosion behavior and bioactivity of anodic films formed on AM60 mg alloys, Materials 10 (2017) 11.

DOI: 10.3390/ma10010011

[11] A. Anawati, H. Asoh, S. Ono, Enhanced uniformity of apatite coating on a PEO film formed on AZ31 Mg alloy by an alkali pretreatment, Surf. Coatings Technol. 272 (2015) 182–189.

DOI: 10.1016/j.surfcoat.2015.04.007

[12] J. Martin, A. Nominé, F. Brochard, J.L. Briançon, C. Noël, T. Belmonte, T. Czerwiec, G. Henrion, Delay in micro-discharges appearance during PEO of Al: Evidence of a mechanism of charge accumulation at the electrolyte/oxide interface, Appl. Surf. Sci. 410 (2017) 29–41.

DOI: 10.1016/j.apsusc.2017.03.088

[13] S.A. Adeleke, S. Ramesh, A.R. Bushroa, Y.C. Ching, I. Sopyan, M.A. Maleque, S. Krishnasamy, H. Chandran, H. Misran, U. Sutharsini, The properties of hydroxyapatite ceramic coatings produced by plasma electrolytic oxidation, Ceram. Int. 44 (2018) 1802–1811.

DOI: 10.1016/j.ceramint.2017.10.114

[14] T.W. Clyne, S.C. Troughton, A review of recent work on discharge characteristics during plasma electrolytic oxidation of various metals, Int. Mater. Rev. 64 (2019) 127–162.

DOI: 10.1080/09506608.2018.1466492