Effect of bath pH on microstructure and corrosion behavior of manganese phosphate coating on SCM420H steel

Document Type : Research Paper


1 Department of Materials Engineering, Faculty of Sciences and Modern Technologies, Graduate University of Advanced Technology, Kerman, Iran

2 Department of mechanical engineering, Higher Education Complex of Bam, P. O. Box: 76615-314, Bam, Kerman, Iran.


In order to improve the surface quality and prevention of corrosion and reduction of wear in the components like gears and bearings, they can be covered with phosphate coatings. SCM420H alloy steel was coated with manganese phosphate deposition. The microstructure and corrosion resistance of the coating was studied by change of bath pH. In order to investigate the phase analysis and coating microstructure, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used, respectively. XRD analysis from the coated surface revealed the phases of MnFe2(PO4)2(OH)2H2O, Mn(PO)3، Fe(PO)3 and (Mn,Fe)5H2(PO4)4·4H2O. Results showed the obtained coating at pH=2.1 was uniform and continuous and no crack or porosity was observed. The phosphate surface at pH=1.9 and pH=2.4 was non-uniform and included cracks. In order to investigate the corrosion resistance, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests were applied on coated and uncoated specimens in 3.5% NaCl solution. The results of potentiodynamic polarization and electrochemical impedance spectroscopy tests were in agreement with microscopic images. The results of electrochemical impedance spectroscopy demonstrated that the formed manganese phosphate deposition in the bath with pH=2.1 had the highest polarization resistance (28020 Ω) compared to the formed coating in the bath at pH=1.9 (1480 Ω) and the formed coating in a bath with pH=2.4 (3155 Ω).


Main Subjects

[1] C. Fang, J. Shi, L. Zhu, Research and Development of High Grade Gear Steel SCM420H for Automobile. Adv. Mater. Research. Vol. 859, 2014, pp. 11-14.                          
[2] M. T. Devlin, T. L. Turner, K. Thompson, K. Kolakowski, K. Garelick, J. M. Guevremont, T. Jao, Effect of Phosphate Coatings on Fatigue and Wear, Presented at the NLGI 74th Annual Meeting, Scottsdale, Arizona, (2007).
[3] J.R. Davis, Surface Engineering for Corrosion and Wear Resistance, ASM International, USA. 2001, pp. 95-124.
[4] M.A. Kuehner, Phosphate Conversion Coating.Metal Finishing. Vol. 83, 1985, pp. 8-15.             
[5] Ch-M. Wang, H-Ch. Liau, W-Ta. Tsai, Effects of temperature and applied potential on the microstructure and electrochemical behavior of manganese phosphate coating. Surf. Coat. Technol., Vol. 201, 2006, pp. 2994-3001.
[6] B-l. Lin, J-t. Lu, G. Kong, Synergistic corrosion protection for galvanized steel by phosphating and sodium silicate post-sealing. Surf. Coat. Technol., Vol. 202, 2008, pp. 1831-1838.
[7] J.F.Andrew, S.G. Clarke, E.E. Longhurst, The Protective Properties of Various Phosphate Coatings on Steel. J. Chem. Technol. Biot.Vol. 4, 1954, pp.581-595.
[8] D.Weng, P.Jokiel, A. Uebleis, H. Boehni, Corrosion and protection characteristics of zinc and manganese phosphate coatings. Surf. Coat. Technol., Vol. 88, 1997, pp.147-156.
[9]  F.Pastorek, K.Borko, S.Fintová, D. Kajánek, B.Hadzima, Effect of Surface Pretreatment on Quality and Electrochemical Corrosion Properties of Manganese Phosphate on S355J2 HSLA Steel.Coatings. Vol. 6, 2016, pp. 46-54. 
[10] E. Klusmann, J.W. Schultze, pH-Microscopy: technical application in phosphating solutions. Electrochim. Acta.,Vol. 48, 2003, pp. 3325-3332.                                           
[11] X.Zhang, G-y. Xiao, C-c.Jiang, Bing.Liu, N-b.Li, R-f. Zhu, Y-p.Lu, Influence of process parameters on microstructure and corrosion properties of hopeite coating on stainless steel. Corros. Sci.,Vol. 94, 2015, pp. 428-437.
[12] F. Li, G.Wang,A Black Phosphate Conversion Coating on Steel Surface Using Antimony(III)-Tartrate as an Additive. J. Mater. Eng. Perform. Vol. 25, 2016, pp.1864-1869.
[13] X. Ding, L. Xue, X-Ch. Wang, K-H. Ding, S-L. Cui, Y-C. Sun, M-S. Li,Influence of bath PH value on microstructure and corrosion resistance of phosphate chemical conversion coating on sintered Nd–Fe–B permanent magnets. J. Magnet. Magnetic. Mater.Vol. 416, 2016, pp.247-255.
[14] K. Abdalla, A. Rahmat, A. Azizan, The Effect of pH on Zinc Phosphate Coating Morphology and its Corrosion Resistance on Mild Steel. Adv. Mater. Research. Vol. 626, 2013, pp. 569-574.
[15] L.J.Boucher,L.Gmelin, K. Koeber, D. Tille, Gmelin handbook of inorganic chemistry, in: Mn-Manganese, D4toD8:Coordination Compounds, 8th ed", Springer,  Heidelberg, Germany. 1988.
[16] F. Mangolini, L. Magagnin, P. L. Cavalloti, Pulse plating of Mn–Cu alloys on steel. J. Electrochem. Soc.,Vol. 153, 2006, pp.623-628.
[17] S. R. Taylor, Encyclopedia of Materials: Science and Technology, Coatings for Corrosion Protection: Inorganic,Elsevier,  Virginia, Usa. 2001, 1263-1269.
[18]T.S. N. Sankara Narayanan, Surface pretreatment by phosphate conversion coatings. Rev. Adv. Mater. Sci., Vol. 9, 2005, pp. 130–177.
[19] L. Fang, L.Xie,Study  on  the  growth  and  corrosion  resistance  of  manganese  phosphate  coatings  on  30CrMnMoTi  alloy  steel. Physics Procedia. Vol. 18, 2011, pp. 227–233.
[20] F. Fang, J. Jiang, Characteristics  of  a  fast  low-temperature  zinc  phosphating  coating  accelerated  by  an  ECO-friendly  hydroxylamine  sulfate. Surf. Coat. Technol., Vol. 204, 2010, pp.2381–2385.
[21] Y.Su,Y.Guo,Z.Huang,Z.Zhang,G. Li, J. Lian, L.Ren,Preparation and corrosion behaviors of calcium phosphate conversion coating on magnesium alloy. Surf. Coat. Technol., Vol. 307, 2016, pp. 99-108.
[22] H.Y. Su, C-S. Lin, Effect of additives on the properties of phosphate conversion coating on electrogalvanized steel sheet, Corros. Sci.,Vol. 83, 2014, pp. 137-146.
[23] B-L. Lin, J-T. Lu, G. Kong, Effect of molybdate post-sealing on the corrosion resistance of zinc phosphate coatings on hot-dip galvanized steel. Corros. Sci.,Vol. 50, 2008, pp. 962-967.
[24] L. A. Oliveira, O. V. Correa,A. A. Z. Páez, M. C. L. Oliveira, R. A. Antunes, Effect of silicate-based films on the corrosion behavior of the API 5L X80 pipeline steel. Corros. Sci.,Vol. 139, 2018, pp. 21-34.
[25] D. Huang, J. Hu, G-L. Song, X. Guo, Inhibition effect of inorganic and organic inhibitors on the corrosion of Mg–10Gd–3Y–0.5Zr alloy in an ethylene glycol solution at ambient and elevated temperatures. Electrochim. Acta.,Vol. 56, 2011, pp. 10166‐10178. 
[26] I.D.Raistrick, D.R. Franceschetti, J.R.Macdonald, Impedance Spectroscopy Theory, Experiment, and Application. John Wiley & Sons, New Jersey. 2005.
[27] M.A. Amin, K.F.Khaled, Q. Mohsen, H.A. Arida, A study of the inhibition of iron corrosion in HCl solutions by some amino acids. Corros. Sci.,Vol. 52, 2010, pp. 1684–1695.
[28] J. Bajat, V. B. MiškovicStankovic, N. Bibic, D. M. Drazic, The influence of zinc surface pretreatment on the adhesion of epoxy coating electrodeposited on hot-dip galvanized steel. Prog. Org. Coat.,Vol. 58, 2007, pp. 323-330.
[29] J. Bajat, V. B. MiškovicStankovic, J. P. Popic, D. Drazic, Adhesion characteristics and corrosion stability of epoxy coatings electrodeposited on phosphated hot-dip galvanized steel. Prog. Org. Coat.,Vol. 63, 2008, 201-208.