Research on Properties and Formation Mechanism of Ceramic Coatings Prepared by Micro-Arc Oxidation on 2024 Aluminum Alloy Surface

Abstract

In this paper, ceramic coatings prepared on 2024 Al alloy surface in electrolyte by micro-arc oxidation are studied. The parameter of discharge and rate of ceramic coating formation are investigated. We analyzed microstructure and phase composition of the coatings by scanning electronic microscopy (SEM) and X-ray diffraction (XRD), and studied the tribological performance of the coatings. The reactions on the electrode surface are deduced and the mechanism of coating formation has been analyzed. The results show that the relation between the thickness and reaction time is not linear. The ceramic coatings contain phase γ-Al2O3 andα-Al2O3; there is a big difference in contents of phase composition between inner coating and outer coating due to the different cooling rates of them. In MAO process, the coating undergoes a course of melting, solidifying and cooling. The coating can be divided into three layers, namely, transition layer, compact layer, and loose layer. The coating and substrate adheres firmly by a metallurgical process. Not only the elements of electrolyte (K, Si) and substrate (Cu) are found in the coatings but also the element of cathode (Fe). The Si-Al-O complex compound is formed in the discharge channels under high energy density condition.

Effect of Treatment with Microarc Oxidation Technology on Tribological Properties of Nonvalve Metal Low-Carbon Steel

“…9 MAO is a technology that utilizes high voltage to create a wear-resistant and corrosion-resistant coating on valve metal. 10,11 This technology offers environmental benefits, and the coatings produced have high resistance to abrasion and corrosion. MAO is the process of modifying the surface of valve metals, such as aluminum (Al), 12 magnesium (Mg), 13 titanium (Ti), 14 and zirconium (Zr).…”

“…Surface treatment processes, such as physical vapor deposition, , chemical vapor deposition, , thermal spraying, and microarc oxidation (MAO), are commonly used to create wear-resistant coatings on metal surfaces . MAO is a technology that utilizes high voltage to create a wear-resistant and corrosion-resistant coating on valve metal. , This technology offers environmental benefits, and the coatings produced have high resistance to abrasion and corrosion. MAO is the process of modifying the surface of valve metals, such as aluminum (Al), magnesium (Mg), titanium (Ti), and zirconium (Zr) .…”

Microstructure and Reciprocating Sliding Tribological Performance of Micro-Arc Oxidation Coating Prepared on Al-Si Alloy

“…The MAO technique is an electrochemical formation of anodic films on non-ferrous metals by spark/arc micro-discharges, which are initiated at potentials above the breakdown voltage of the growing oxide film and move rapidly across the anode surface [11,12]. Although the MAO technique has become research hotspot for several years, there were some problem(such as the preparation cost was higher, the chemical state and change of the elements in alloys during micro-arc oxidation process was unclear, and few research really revealed the oxidation mechanism), which has seriously affected the process optimization and industrial application [13][14][15].…”