Investigation of the Scanning Microarc Oxidation Process

Abstract

Scanning microarc oxidation (SMAO) is a coating process which is based on conventional microarc oxidation (MAO). The key difference is that deposition in SMAO is achieved by using a stainless steel nozzle to spray an electrolyte stream on the substrate surface as opposed to immersing the workpiece in an electrolyzer. In the present study, SMAO discharge characteristics, coating morphology, and properties are analyzed and compared to results obtained from MAO under similar conditions. Results show that MAO and SMAO have comparable spark and microarc lifetimes and sizes, though significant differences in incubation time and discharge distribution were evident. Results also showed that the voltage and current density for MAO and SMAO demonstrate similar behavior but have markedly different transient and steady-state values. Results obtained from coating A356 aluminum sheet show that oxide thickness and growth rate in SMAO are strongly dependent on interelectrode spacing and travel speed. Analysis of the SMAO coating morphology and structure showed that a denser and slightly harder layer was deposited in comparison to MAO and is attributed to reduced porosity and increased formation of -Al 2 O 3 . Preliminary results indicate that SMAO represents a viable process for coating of aluminum surfaces.

Review of the Soft Sparking Issues in Plasma Electrolytic Oxidation

“…If this is true, the porous top layer is not redundant; it assists with preserving the heat, which is constantly dissipating in a water-cooled electrolytic cell. Viewing the heat preservation issue from another angle, raising the α-Al 2 O 3 content is expected to be more difficult if researchers attempt work on scanning PEO [76,77]. Under the operation conditions of scanning PEO, the heat is easily dissipated since the heat source (plasma) is moving and restricted in its coverage area.…”

The role of cathodic current in plasma electrolytic oxidation of aluminium: current density ‘scanning waves’ on complex-shape substrates

“…The importance of the interelectrode distance in PEO under galvanostatic conditions was also reported in [8,9]. The extension of this technique is the so-called 'scanning micro arc oxidation', wherein a small-area counter electrode is moved through the surface of a larger substrate, allowing uniform coatings to be produced on the large and complex substrates [10,11]. Numerical calculation of the primary electric field distribution through the surface of complex shape substrates with deep internal dead holes under PEO conditions has been performed in [12].…”