Study of Scanning Micro-arc Oxidation and Coating Development

• Published in: Journal of materials engineering and performance Vol. 26; no. 11; pp. 5323 - 5332
• Main Authors: Xia, Lingqin, Han, Jianmin, Domblesky, Joseph P., Yang, Zhiyong, Li, Weijing
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.11.2017
• Subjects: Characterization and Evaluation of Materials; Chemistry and Materials Science; Corrosion and Coatings; Engineering Design; Materials Science; Quality Control; Reliability; Safety and Risk; Tribology; spraying micro-arc oxidation; surface deposition; inter-electrode spacing; liquid impingement; scanning cathode
• ISSN: 1059-9495; 1544-1024
• DOI: 10.1007/s11665-017-2861-x

Micro-arc oxidation (MAO) continues to be the focus of numerous investigations, whereas relatively few studies have considered scanning micro-arc oxidation (SMAO). In the present work, an experimental study was performed using stationary and moving electrodes to investigate coating development in SMAO and discern the effect of key process parameters. Examination of oxide deposits made on A356 aluminum show that coating thickness and growth rate are inversely related to inter-electrode spacing and travel speed. An evaluation of SMAO deposits made by stationary and moving nozzles revealed that coating thickness profiles follow a Gaussian distribution due to the electrolyte flow field in the impingement zone. Hardness surveys and scanning electron microscope analysis of SMAO coatings revealed that micro-hardness distributions and cross-sectional morphology are similar to MAO for a stationary nozzle but that a denser outer layer develops when a moving nozzle is used. This is attributed to a high density of discharge occurring in micropores of the oxide film and remelting which results from the moving electrolyte column. Analysis of voltage–current characteristic curves shows that the resistance of the electrolyte column is essentially linear over the range considered and results indicate that it can be modeled as a variable length resistor. While further testing is needed, results confirm that SMAO is suitable for coating large, planar parts and for repairing worn surfaces.