MSA  Vol.5 No.3 , March 2014
Processing-Microstructure Relationships in the Plasma Electrolytic Oxidation (PEO) Coating of a Magnesium Alloy
ABSTRACT

In the plasma electrolytic oxidation (PEO) coating of light metal alloys, changing the electrical parameters and electrolytic composition can change the discharge behaviour and, ultimately, the thickness, surface morphology and porosity of the coating. In the present study a combination of cathodic and anodic current pulses with suitable Ton and Toff periods were used to control the porosity and other structural defects of PEO coatings of an AM60B magnesium alloy. In order to investigate the effect of a current mode on the plasma discharge behaviour and coating microstructure during the PEO treatment of magnesium alloy, the emission intensities of six different spectral lines from the plasma species were recorded simultaneously as a function of both time and current mode using optical emission spectroscopy (OES) system. The fluctuations in signal intensities and temperature during the coating process reflect differences in location of both the discharge initiation, and discharge type. The coating surface morphology and microstructure that are obtained can be linked to the plasma discharge behavior. These results are discussed in relation to the discharge behaviour, and how such changes in discharge behaviour relate to the coating mechanisms.


Cite this paper
Hussein, R. , Northwood, D. and Nie, X. (2014) Processing-Microstructure Relationships in the Plasma Electrolytic Oxidation (PEO) Coating of a Magnesium Alloy. Materials Sciences and Applications, 5, 124-139. doi: 10.4236/msa.2014.53017.
References
[1]   Hakamad, M., Furut, T., Chino, Y., Chen, Y.Q., Kusud, H. and Mabuchi, M. (2007) Life Cycle Inventory Study on Magnesium Alloy Substitution in Vehicles. Energy, 32, 1352-1360. http://dx.doi.org/10.1016/j.energy.2006.10.020

[2]   Shrestha, S. (2010) Magnesium and Surface Engineering. Surface Engineering, 26, 313-316.
http://dx.doi.org/10.1179/026708410X12736782825894

[3]   Ghasemi, A., Raja, V.S., Blawert, C., Dietzel, W. and Kainer, K.U. (2008) Study of the Structure and Corrosion Behavior of PEO Coatings on AM50 Magnesium Alloy by Electrochemical Impedance Spectroscopy. Surface and Coatings Technology, 202, 3513-3518. http://dx.doi.org/10.1016/j.surfcoat.2007.12.033

[4]   Yerokhin, A.L., Nie, X., Leyland, A., Matthews, A. and Dowey, J. (1999) Plasma Electrolysis for Surface Engineering. Surface and Coatings Technology, 122, 73-93. http://dx.doi.org/10.1016/S0257-8972(99)00441-7

[5]   Walsh, F.C., Low, C.T.J., Wood, R.J.K., Stevens, K.T., Archer, J., Poeton, A.R. and Ryder, A. (2009) Review. Plasma Electrolytic Oxidation (PEO) for Production of Anodised Coatings on Lightweight Metal (Al, Mg, Ti) Alloys. Transactions of the Institute of Metal Finishing, 87, 122-135. http://dx.doi.org/10.1179/174591908X372482

[6]   Curran, J. (2011) Plasma Electrolytic Oxidation for Surface Protection of Aluminium, Magnesium and Titanium Alloys. Transactions of the Institute of Metal Finishing, 89, 295-297.
http://dx.doi.org/10.1179/174591911X13188464808830

[7]   Hussein, R.O., Nie, X. and Northwood, D.O. (2013) The Application of Plasma Electrolytic Oxidation (PEO) to the Production of Corrosion Resistant Coatings on Magnesium Alloys: A Review. Corrosion and Materials, 38, 55-65.

[8]   Liang, J., Srinivasan, P.B., Blawert, C., Stormer, M. and Dietzel, W. (2009) Electrochemical Corrosion Behaviour of Plasma Electrolytic Oxidation Coatings on AM50 Magnesium Alloy Formed in Silicate and Phosphate Based Electrolytes. Electrochimica Acta, 54, 3842-3850. http://dx.doi.org/10.1016/j.electacta.2009.02.004

[9]   Cakmat, E., Tekin, K.C., Malsyooglu, U. and Shrestha, S. (2010) The Effect of Substrate Composition on the Electrochemical and Mechanical Properties of PEO Coatings on Mg alloys. Surface and Coatings Technology, 204, 1305.
http://dx.doi.org/10.1016/j.surfcoat.2009.10.012

[10]   Wei, C.B., Tian, X.B., Yang, S.Q., Wang, X.B., Fu, R.K.Y. and Chu, P.K. (2007) Anode Current Effects in Plasma Electrolytic Oxidation. Surface and Coatings Technology, 201, 5021-5024.
http://dx.doi.org/10.1016/j.surfcoat.2006.07.103

[11]   Curran, J.A. and Clyne, W.T. (2005) Thermo-Physical Properties of Plasma Electrolytic Oxide Coatings on Aluminum. Surface and Coatings Technology, 199, 168-176. http://dx.doi.org/10.1016/j.surfcoat.2004.09.037

[12]   Arabal, R., Matykina, E., Hashimoto, T., Skeldon, P. and Thompson, G.E. (2009) Characterization of AC Coatings in Magnesium Alloys. Surface and Coatings Technology, 203, 2207-2220.
http://dx.doi.org/10.1016/j.surfcoat.2009.02.011

[13]   Hussein, R.O., Nie, X. and Northwood, D.O. (2013) The influence of Pulse Timing and Current Mode on the Microstructure and Corrosion Behaviour of a Plasma Electrolytic Oxidation (PEO) Coated AM60B Magnesium Alloy. Electrochimica Acta, 112, 111-119. http://dx.doi.org/10.1016/j.electacta.2013.08.137

[14]   Gnedenkov, S.V., Khrisanfova, O.A., Zavidnaya, A.G., Sinebryukhov, S.L., Egorkin, V.S., Nistratova, M.V., Yerokhin, A. and Matthews, A. (2010) PEO Coatings Obtained on an Mg-Mn Type Alloy under Unipolar and Bipolar Modes in Silicate-Containing Electrolytes. Surface and Coatings Technology, 204, 2316-2322.
http://dx.doi.org/10.1016/j.surfcoat.2009.12.024

[15]   Hussein, R.O., Northwood, D.O., Su, J.F. and Nie, X. (2013) A Study of the Interactive Effects of Hybrid Current Modes on the Tribological Properties of a PEO (Plasma Electrolytic Oxidation) Coated AM60B Mg-Alloy. Surface and Coatings Technology, 215, 421-430. http://dx.doi.org/10.1016/j.surfcoat.2012.08.082

[16]   Hussein, R.O., Northwood, D.O. and Nie, X. (2012) The Influence of Pulse Timing and Current Mode on the Microstructure and Corrosion Behaviour of a Plasma Electrolytic Oxidation (PEO) Coated AM60B Magnesium Alloy. Journal of Alloys and Compounds, 541, 41-48. http://dx.doi.org/10.1016/j.jallcom.2012.07.003

[17]   Dunleavy, C.S., Curran, J.A. and Clyne, T.W. (2011) Self-Similar Scaling of Discharge Events through PEO Coatings on Aluminium. Surface and Coatings Technology, 206, 1051-1061. http://dx.doi.org/10.1016/j.jallcom.2012.07.003

[18]   Hussein, R.O., Nie, X., Northwood, D.O., Yerokhin, A.L. and Matthews, A. (2010) Spectroscopic Study of Electrolytic Plasma and Discharging Behaviour during the Plasma Electrolytic Oxidation (PEO) Process. Journal of Physics D: Applied Physics, 43, Article ID: 105203. http://dx.doi.org/10.1088/0022-3727/43/10/105203

[19]   Klapkiv, M.D., Nykyforchyn, H.M. and Posuvailo, V.M. (1994) Spectral Analysis of an Electrolytic Plasma in the Process of Synthesis of Aluminium Oxide. Materials Science, 30, 333-343. http://dx.doi.org/10.1007/BF00569685

[20]   Hussein, R.O., Zhang, P., Northwood, D.O. and Nie, X. (2011) Improving the Corrosion Resistance of Magnesium Alloy AJ62 by a Plasma Electrolytic Oxidation (PEO) Coating Process. Corrosion and Materials, 36, 38-49.

[21]   Dunleavy, C.S., Golosnoy, I.O., Curran, J.A. and Clyne, T.W. (2009) Characterization of Discharge Events during Plasma Electrolytic Oxidation. Surface and Coatings Technology, 203, 3410-3419.
http://dx.doi.org/10.1007/BF00569685

[22]   Hussein, R.O., Nie, X. and Northwood, D.O. (2012) A Spectroscopic and Microstructural Study of Oxide Coatings Produced on a Ti-6Al-4V Alloy by Plasma Electrolytic Oxidation. Materials Chemistry and Physics, 134, 484-492.
http://dx.doi.org/10.1016/j.matchemphys.2012.03.020

[23]   Griem, H.R. (1997) Principles of Plasma Spectroscopy. Cambridge University Press, Cambridge.
http://dx.doi.org/10.1017/CBO9780511524578

[24]   Dunleavy, C.S., Curran, J.A. and Clyne, T.W. (2013) Time Dependent Statistics of Plasma Discharge Parameters during Bulk AC Plasma Electrolytic Oxidation of Alu. Applied Surface Science, 268, 397-409.
http://dx.doi.org/10.1016/j.apsusc.2012.12.109

[25]   Sansonettiand, J.E. and Martin, W.C. (2005) Handbook of Basic Atomic Spectroscopic Data. Journal of Physical and Chemical Reference Data, 34, 1559-2259. http://dx.doi.org/10.1016/j.apsusc.2012.12.109

[26]   Lianga, J., Guoa, B., Tiana, J., Liua, H., Zhoua, J., Liua, W. and Xu, T. (2005) Effects of NaAlO2 on Structure and Corrosion Resistance of Microarc Oxidation Coatings Formed on AM60B Magnesium Alloy in Phosphate-KOH Electrolyte. Surface and Coatings Technology, 199, 121-126. http://dx.doi.org/10.1016/j.surfcoat.2005.03.020

[27]   Griem, H.R. (1964) Plasma Spectroscopy. Cambridge, McGraw-Hill.

[28]   Sullivan, S.A. (1963) Experimental Study of the Absorption in Distilled Water, Artificial Sea Water, and Heavy Water in the Visible Region of the Spectrum. Optics InfoBase: Journal of the Optical Society of America, 53, 962-967.
http://dx.doi.org/10.1364/JOSA.53.000962

[29]   Cheng, Y., Wu, F., Dong, J., Wu, X., Xue, Z., Matykin, E., Skeldon, P. and Thompson, G.E. (2012) The Influences of Microdischarge Types and Silicate on the Morphologies and Phase Compositions of Plasma Electrolytic Oxidation Coatings on Zircaloy-2. Corrosion Science, 59, 307-315. http://dx.doi.org/10.1016/j.corsci.2012.03.017

[30]   Cheng, Y., Xue, Z., Wang, Q., Wu, X., Matykin, E., Skeldon, P. and Thompson, G.E. (2013) New Findings On Properties of Plasma Electrolytic Oxidation Coatings from Study of an Al-Cu-Li Alloy. Electrochimica Acta, 107, 358-378. http://dx.doi.org/10.1016/j.electacta.2013.06.022

[31]   Curran, J.A. and Clyne, T.W. (2006) Porosity in Plasma Electrolytic Oxide Coatings. Acta Materialia, 54, 1985-1993.
http://dx.doi.org/10.1016/j.actamat.2005.12.029

[32]   Zhang, P., Nie, X. and Northwood, D.O. (2009) Influence of Coating Thickness on the Galvanic Corrosion Properties of Mg Oxide in an Engine Coolant. Surface and Coatings Technology, 203, 3271-3277.
http://dx.doi.org/10.1016/j.surfcoat.2009.04.012

[33]   MacKenzie, J.K. (1950) The Elastic Constants of a Solids Containing Spherical Holes. Proceedings of the Physical Society, B63, 2-11. http://dx.doi.org/10.1088/0370-1301/63/1/302

[34]   McColm, I.J. (1990) Ceramic Hardness. Plenum Press, New York. http://dx.doi.org/10.1007/978-1-4757-4732-4

 
 
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