Micro-Arcs Oxidation Layer Formation on Aluminium and Coatings Tribological Properties—A Review

Abstract

This review proposes to carry out a state-of-the-art associated with micro-arc oxidation. Firstly, the different aspects of the growth mechanisms of the oxides are detailed. Then, the formation of micro-arcs and the case of soft-spark treatment are discussed. Then, the electrolytic reactions involved in the layer construction are outlined. We focused on the influence of aluminium alloys on the appearance of the coating and its characteristics before considering the electrolyte formulation. We have concentrated some of our efforts on silicate-based electrolytes, mainly used in research and industry. The importance of electrical parameters in layer formation is detailed later. The main factors studied in the literature are the current source, current density, treatment frequency and duration, and duty cycle. We have also noted the different phase compositions identified in the literature. Finally, since the process is particularly advantageous for protecting the surfaces of aluminium parts against wear, we conclude this review by presenting work on the tribological properties of this coating. In this final section, we highlight the work on the wear-reducing properties and tribological mechanisms identified in the literature. Particular attention is paid to the relationship between the nature of the substrates used, the role of the electrolyte and the counterpart choice on the friction and wear results.

The Tribological Properties of Plasma Electrolytic Oxidation Layers Synthesized on Arc Spray Coatings on Aluminum Alloys in Contact with Various Friction Materials

“…The expansion of the functionality of thermally sprayed aluminum coatings after their modification using PEO processing has already been demonstrated previously [42][43][44][45][46][47][48]. For the same purpose, plasma or cold spray deposition of aluminum coatings is also used [49,50], and aluminum, steel and titanium are used as the substrates [51][52][53][54][55][56][57][58].…”

“…Its hardness was 55% higher than an aluminum oxide coating formed using plasma spraying in the atmosphere (940 HV 0.1 ). X-ray diffraction analysis showed that, as a rule, the lower hardness of the PEO layer on an aluminum alloy deposited using cold spraying is due to its lower content of α-Al 2 O 3 [42]. A technological layer forms on the outer surface of the PEO layer, which has fairly high mechanical properties under wear conditions and provides good protection against corrosion.…”

Effect of HfO2 Particles on Ceramic Coating Fabricated on Ti6Al4V Alloy via Plasma Electrolytic Oxidation

“…Figure 7 shows the polarization curve of the substrate and the two coated samples. The corrosion current density (I corr ) and rate (V corr ) were obtained via Tafel fitting according to the Stern-Geary equation (Equation (7), where β a is the anodic Tafel slope and β c is the cathodic slope), and Faraday's Law (Equation (8), where N is the equivalent weight and ρ is the density), respectively [7,27]. The results of the Tafel-fitted polarization curves are listed in Table 2.…”

“…Plasma electrolytic oxidation (PEO), also called microarc oxidation (MAO), has been one of the commonly used surface treatment technologies for valve metals (aluminum, magnesium, titanium, and zirconium as well as their alloys) in recent years [7][8][9]. The ceramic coatings, which have the advantages of wear and corrosion resistance, low thermal conductivity, and a high bonding strength with the substrate, can be fabricated via PEO [10][11][12].…”

Plasma Electrolytic Oxidation of Al-Zn-Mg-Ni-Fe “Nikalin” Alloys

“…Functional protective coatings formed on aluminum alloy products through plasma electrolytic oxidation (PEO) widely broaden their applications and substantially increase the hardness and wear and corrosion resistance of alloy products [8][9][10]. Moreover, the significant advantages of this process are high productivity (the synthesis of coatings is carried out in the range of 30-40 min) and environmental friendliness, provided by the use of alkaline water-based electrolytes [11][12][13]. This process is widely applied in various industries, including the production of PEOcoated aluminum details for the oil and gas sector [14], moving mechanisms for marine applications [15], aircraft engineering [16], and the automotive industry [17], demonstrating its versatility and effectiveness across multiple fields.…”