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44 NOVEMBER 2017 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 56, NO. 11 COATINGS & LININGS th e samples decreased from 0.0097 to 0.0002 g and the corrosion rate was reduced from 0.568 to 0.016 g/m 2 ·h. This result indi- cates the corrosion resistance of MAO coating improved with an increase of the cathode voltage. 14 Figure 3 illustrates the surface mor- phologies of the samples after salt spray treatment for 96 h. Figure 3(a) shows the surfaces prepared with a cathode voltage of 4 V. A great amount of peeling on the surface of the ceramic coating, which leads to serious corrosion, can be seen. Serious corrosion pits are not observed in the mor- phology of the MAO coating applied with a cathode voltage of 24 V (Figure 3[b]). This indicat e s that c orro sion re si st anc e of t h e M A O c o a t i n g d e p o s i t e d s i g n i f i - cantly improved with increased cathode voltage. 15 Conclusions MAO coatings were applied on the sur- face of aluminum alloy drill pipe for off- shore platforms at different cathode volt- ages. Test results showed that increasing the cathode voltage inf luences the MAO coating performance. When the cathode voltage was increased from 4 to 24 V, the surface of the coating became more com- pact and smooth, and the corrosion rate decreased from 0.568 to 0.016 g/m 2 ·h. Addi- tionally, the corrosion resistance of the MAO coatings formed with increased cath- ode voltage was remarkably improved after salt spray treatment for 96 h. Acknowledgments The authors would like to express their sincere gratitude for the financial support extended by the National Natural General F o u n d a t i o n o f J i a n g s u P r o v i n c e ( N o . 1 6 K J B 5 8 0 0 1 3 ) , J i a n g s u O v e r s e a s Research & Training Program for Univer- sity P romin ent Youn g & Mi d d l e- A ged Teachers and Presidents, Qing Lan Project of Jiangsu Province, and the Youth National Natural Science Foundation of China (No. 51301086). Th e authors w oul d li ke to extend their thanks to several colleagues, without whose help this paper would not have been published. References 1 Y.G. Liu, et al., "A Study on Axial Cracking Failure of Drill Pipe Body," Eng. Fail. Anal. 59 (2016): p. 434. 2 S. Moradi, K. Ranjbar, "Experimental and Computational Failure Analysis of Drill- strings," Eng. Fail. Anal. 16, 3 (2009): p. 923. 3 W.S. Miller, et al., "Recent Development in Aluminium Alloys for the Automotive Indus- tr y," Mat. Sci . Eng. A-Struct. 280, 1 (2000): p. 37. 4 S.M. Z amani , S.A. Hassanzadeh-Tabri zi , H. Sharifi, "Failure Analysis of Drill Pipe: A Review," Eng. Fail. Anal. 59 (2016): p. 605. 5 W. Ping, et al., "Effect of NaAlO 2 Concentra- tions on the Properties of Micro-Arc Oxida- tion Coatings on Pure Titanium," Mater. Lett. 170 (2016): p. 171. 6 X.Y. Lu, et al., "Evaluation of the Micro-Arc Oxidation Treatment Effect on the Protec- tive Performance of a Mg-Rich Epoxy Coat- ing on AZ91D Magnesium Alloy," Surf. Coat. Tech. 270 (2015): p. 227. 7 Y.K. Lee, "Effects of Electrical Parameters on Titania Film Grown by Micro Arc Oxidation," Mod. Phys. Lett. B. 23, 16 (2009): p. 2,035. 8 W.M. Xiong, et al., "Effect of Positive Voltage on Phase Structure of Micro-arc Oxidation Films of Magnesium Alloy," Rare. Metal. Mat. Eng. 40, 12 (2011): p. 2,236. 9 C.Y. Han, et al., "Effect of Cathode Voltage in Micro-Arc Oxidation on Ceramic Coating Film of ZAlSi12Cu2Mg1 Alloy," Rare. Metal. Mat. Eng. 36 (2007): p. 117. 10 X.H. Yao, et al., "Microstructure and Antibac- terial Properties of Cu-Doped TiO 2 Coating on Titanium by Micro-Arc Oxidation," Appl. Surf. Sci. 292 (2014): p. 944. 11 Y.P. Pan, Y. Shen, P.K. Sahoo, "Effect of Nano- MoS 2 Particles on Properties of Micro-Arc Oxidation Coating Prepared on the Surface of Aluminum Alloy Drill Pipe for Offshore Platform," 35th International Conference on Ocean, Of fshore and Arctic Engineering, paper no. OMAE2016-54685 (New York, NY: ASME, 2016), p. 5. 12 C.C. Tseng, et al., "The Influence of Sodium Tungstate Concentration and Anodizing Conditions on Microarc Oxidation (MAO) Coatings for Aluminum Alloy," Surf. Coat. Tech. 206, 16 (2012): p. 3,437. 13 F. Guo, R.M. Liu, P.F. Li, "Influence of Voltage Parameters on Formation Process of MAO Ceramic Coating on Aluminum Alloy," Adv. Mat. Res. 189-193 (2011): p. 931. 14 M.H. Zhu, et, al., "Fretting Wear Behaviour of Ceramic Coating Prepared by Micro-Arc Oxi- dation on AlSi Alloy," Wear 263 (2007): p. 472. 15 R.O. Hussein, X. Nie, D.O. Northwood, "Influ- ence of Process Parameters on Electrolytic Plasma Discharging Behaviour and Alumi- num Oxide Coating Microstructure," Surf. Coat. Tech. 205, 6 (2010): p. 1,659. YAN SHEN is a lecturer at the School of Naval Architecture and Ocean Engineer- ing, Jiangsu Maritime Institute, Nanjing, China, email: shenyan926@hotmail.com. Shen is a visiting scholar at the Florida Institute of Technology (2016 to 2017), has been a lecturer at Jiangsu Maritime Insti- tute from 2007 to the present, and pub- lished the paper, "A Study of Nanocom- posite Coatings on the Surface of Ship Exhaust Pipe," in the July 2017 issue of Surface Review and Letters. PRASANTA K. SAHOO is a researcher at the Department of Ocean Engineering and Science at the Florida Institute of Technol- ogy, Melbourne, Florida, USA. YIPENG PAN is a researcher at the Depart- ment of Ocean Engineering and Science at the Florida Institute of Technology. FIGURE 3 Surface morphologies of MAO coatings after salt spray treatment with various cathode voltages: (a) 4 V and (b) 24 V.