Self-Lubricating PEO Coating on an Al Alloy Produced by Vacuum Impregnation Post-treatment

• Published in: Acta metallurgica sinica : English letters 2015-08, Vol.28 (8), p.965-974
• Main Authors: Hong, Ling, Wang, Dong, Bian, Guang-Dong, Wang, Lin-Lin, Hu, Shu-Gen
• Format: Article
• Language: English
• Subjects: 6061铝合金; Alloys; Aluminum alloys; Aluminum base alloys; Characterization and Evaluation of Materials; Chemistry and Materials Science; Coating; Coefficient of friction; Corrosion; Corrosion and Coatings; Direct current; Electrolytes; Friction; Frictional wear; Graphite; Impregnation; Lubricants; Lubricants & lubrication; Lubricating oils; Materials Science; Mechanical properties; Metallic Materials; Morphology; Nanotechnology; Organometallic Chemistry; Oxidation; Powder metallurgy; Pressure; Protective coatings; Pulsed current; Self lubricating materials; Self lubrication; Si3N4陶瓷; Sliding friction; Spectroscopy/Spectrometry; Tribology; Ultrasonic vibration; Wear resistance; Wear tests; 摩擦磨损性能; 浸渍处理; 真空; 自润滑涂层; 陶瓷膜; 高耐磨性
• ISSN: 1006-7191; 2194-1289
• DOI: 10.1007/s40195-015-0280-2

The objective of this research was to develop a novel self-lubricating coating on an AA6061 aluminum alloy.Three coatings were prepared by the plasma electrolytic oxidation（PEO） process using 50-, 500-, and 1000-Hz pulsed direct current, respectively. The as-deposited coatings were then post-treated using two different methods, viz., ultrasonic vibration-aided vacuum oil impregnation（UVOI） and oil impregnation under ambient pressure（OIAP）. After posttreatment, an oil-containing, self-lubricating top layer was formed on the coatings. The effects of the coatings＇ surface morphologies and structures on their oil-holding capabilities were discussed. The results revealed that coatings prepared with higher frequency had a greater oil-holding capacity using OIAP post-treatment, while those prepared with lower frequency had a greater oil-containing capability using UVOI post-treatment. These phenomena are related to the morphologies of the coatings produced with various current modes. The tribological properties of the coatings before and after post-treatments were investigated by pin-on-disc sliding wear tests. Due to the formation of a lubricant-containing top layer, the post-treatment coatings had a lower friction coefficient and improved wear resistance compared with the asdeposited coatings. In addition, the coatings after UVOI treatment had better wear performance than those post-treated using the OIAP process. Among all coatings, the coating produced with a 50-Hz pulsed current followed by UVOI posttreatment achieved the lowest friction coefficient（0.03） and best wear resistance when sliding against a Si3N4 ceramic counterface. This study indicates that a novel self-lubricating coating can be prepared by a PEO process combined with vacuum oil impregnation post-treatment.