• Proceedings of the Materials Research Society of Korea Conference
• /
• 2007.11a
• /
• pp.152.1-152.1
• /
• 2007

• Journal of the Korean Vacuum Society
• /
• v.12 no.S1
• /
• pp.21-27
• /
• 2003

Micro-arc discharge oxidation (MDO) is a cost-effective plasma electrolytic process which can be used to improve the wear and corrosion resistance of Al-alloy parts by forming a alumina coating on the component surface. However, the MDO coated Al-alloy components often exhibit relatively high friction coefficients and low wear resistance fitted with many counterface materials, additionally, the pitting corrosion for the MDO coated AI-alloy components, especially for a thinner alumina coating, often occurs in atmosphere circumstance due to the porous alumina coats. Therefore, a duplex treatment, combining a MDO coated ahumina thin layer with a TiN coating, prepared by magnetron sputtering (MS), has been investigated. The Vicker's microhardness, pin-on-disc, electrochemical measurement, salt spray, XRD and SEM tests were used to characterize and analyze the treated samples. The work demonstrates that the MDO/MS coated samples have a combination of a very low friction coefficient and good wear resistance as well as corrosion since the micro-holes on alumina coating are partly or fully covered by TiN material.

• Corrosion Science and Technology
• /
• v.5 no.4
• /
• pp.149-152
• /
• 2006

$BaTiO_3$ coatings were prepared by micro arc oxidation (MAO) method. Only $Ba(OH)_2$ was dissolved in the electrolyte and process time was less than 30 min. Commercial purity $Ba(OH)_2$ (97%) containing $BaCO_3$ as impurity was used in preparing the electrolyte. XRD showed that the coating was composed of largely $BaTiO_3$, and in some process conditions, small quantity of impurity, $BaCO_3$, was characterized in the coating layer. The quantity of $BaCO_3$ could be controlled to negligible quantity by regulating the applied voltage and duration time of the MAO process.

• Journal of Powder Materials
• /
• v.18 no.6
• /
• pp.575-582
• /
• 2011

MAO(Micro-Arc Oxidation) method was used to make $Al_2O_3$ surface on 6063 Al specimen. This study was focused on an influence of voltage, density of electrolyte and a period of treatment on the change of surface microstructure by using SEM(Scanning Electron Microscope), EDS(Energy Dispersive X-ray Spectroscopy). The microstructure shows higher roughness and thicker oxidized layer with increase of voltage and maintaining period of treatment. The density of electrolyte affected a formation of more dense surface and increase of a oxidized layer.

• Corrosion Science and Technology
• /
• v.9 no.4
• /
• pp.171-174
• /
• 2010

MAO (micro-arc oxidation) is an eco-friendly convenient and effective technology to deposit high-quality oxide coatings on the surfaces of Ti, Al, Mg and their alloys. The roles of the electrolyte concentration and relative cathode electrode area sizes in the grown oxide film during titanium MAO were investigated. The higher the concentration of the electrolyte, the lower the $R_{total}A$ value. The oxide film produced by the lower concentration of the electrolyte is thinner and less uniform than the film by the higher concentration, which is thick and porous. The cathode area size must be bigger than the anode area size in order to minimize the voltage drop across the cathode. The ratio of the cathode area size to the anode area size must be bigger than 8. Otherwise, the cathode will be another source for voltage drop, which is detrimental to and slows down the oxide growth.

• Journal of the Korean institute of surface engineering
• /
• v.50 no.5
• /
• pp.421-426
• /
• 2017

Herein, we investigated surface morphological characteristics of anodic films on Al6061 alloy prepared by unipolar pulsed Micro-arc oxidation (MAO) in a mixed solution of $Na_2SiO_3$ + KOH. The number and size of pores as well as craters on anodic alumina surface were studied as a function of different voltages, duty cycles and applied anodic current densities. The morphological characteristics of all samples were investigated by scanning electron microscopy, conforming that the most uniform surface morphology of MAO films on Al1050 alloy was obtained at high applied current density with low duty cycle.

• Journal of Powder Materials
• /
• v.19 no.3
• /
• pp.196-203
• /
• 2012

$TiO_2$ was successfully formed on a Ti specimen by MAO (Micro-Arc-Oxidation) method treated in $Na_3PO_4$ electrolyte. This study deals with the influence of voltage and working time on the change of surface microstructure and phase composition. Voltage affected the forming rate of the oxidized layer and surface microstructure where, a low voltage led to a high surface roughness, more holes and a thin oxidized layer. On the other hand, a high voltage led to more dense surface structure, wider surface holes, a thick layer and fewer holes. Higher voltage increases photocatalytic activity because of better crystallization of the oxidized layer and good phase composition with anatase and rutile $TiO_2$, which is able to effectively separate excited electrons and holes at the surface.

• Proceedings of the Korean Institute of Surface Engineering Conference
• /
• 2009.05a
• /
• pp.221-222
• /
• 2009

AZ31 마그네슘 합금에 AC 전류를 인가하여 MAO(micro-arc oxidation) process로 양극산화 할 때 알카리 전해액에 첨가되는 sodium silicate(Na2SiO3)의 농도에 따라 형성되는 양극 피막의 구조와 부식특성을 평가하였다. 전해질의 조성은 10g/1 KOH와 4g/1 KF 혼합 전해액에 sodium silicate를 (5, 10, 20, 40, 80)g/1로 달리하여 첨가한 후 $40mA/cm^2$의 전류밀도로 20분간 MAO 처리한 후 양극피막의 조직을 SEM, XRD, EPMA를 이용하여 분석하였고 동전위 분극시험으로 부식 거동을 평가하였으며 micro-vickers 경도계를 이용하여 단면의 경도를 측정하였다.

• Journal of the Korean institute of surface engineering
• /
• v.55 no.5
• /
• pp.292-298
• /
• 2022

In this study, PEO (plasma electrolytic oxidation) film formation behavior of AZ31 Mg alloy under application of 300 Hz pulse current was studied by the analyses of V-t curve, arc generation behavior, PEO film thickness and morphology of PEO films with treatment time in 0.05 M NaOH + 0.05 M Na₂SiO₃ + 0.1 M NaF solution. PEO films was observed to grow after 10 s of application of pulse current together with generation of micro-arcs. PEO film grew linearly with treatment time at a growth rate of about 5.58 ㎛/min at 200 mA/cm² of pulse current but increasing rate of film formation voltage became lowered largely with increasing treatment time after passing about 250 V, suggesting that resistivity of PEO films during micro-arc generation decreases with increasing film formation voltage at more than 250 V.

• Journal of Welding and Joining
• /
• v.32 no.3
• /
• pp.27-33
• /
• 2014

This paper presents a brief summary on a relatively new plasma aided electrolytic surface treatment process for light metals. A brief discussion regarding the advantages, principle, process parameters and applications of this process is discussed. The process owes its origin to Sluginov who discovered an arc discharge phenomenon in electrolysis in 1880. A similar process was studied and developed by Markov and coworkers in 1970s who successfully deposited an oxide film on aluminium. Several investigation thereafter lead to the establishment of suitable process parameters for deposition of a crystalline oxide film of more than $100{\mu}m$ thickness on the surface of light metals such as aluminium, titanium and magnesium. This process nowadays goes by several names such as plasma electrolytic oxidation (PEO), micro-arc oxidation (MOA), anodic spark deposition (ASD) etc. Several startups and surface treatment companies have taken up the process and deployed it successfully in a range of products, from military grade rifles to common off road sprockets. However, there are certain limitations to this technology such as the formation of an outer porous oxide layer, especially in case of magnesium which displays a Piling Bedworth ratio of less than one and thus an inherent non protective oxide. This can be treated further but adds to the cost of the process. Overall, it can be said the PEO process offers a better solution than the conventional coating processes. It offers advantages considering the fact that he electrolyte used in PEO process is environmental friendly and the temperature control is not as strict as in case of other surface treatment processes.