Plasma electrolytic oxidation (PEO) for production of anodised coatings on lightweight metal (Al, Mg, Ti) alloys

Abstract

The introduction of plasma electrolytic oxidation (PEO) as a surface finishing technique has enabled a range of hard, dense oxide coatings to be produced on aluminium, magnesium, titanium and other lightweight alloy substrates. As with all surface coating technologies, successful development of PEO coatings requires adequate attention to substrate pretreatment together with careful control of electrolyte conditions and process variables. The principles and applications of the PEO coating process are considered, including the fundamentals of oxide deposition, the technology involved and the typical characteristics of the coatings. Industrial applications are considered together with their coating requirements. Plasma electrolytic oxidation coating is a specialised but well developed process. Suitable control of electrolyte and process conditions can realise a novel range of coatings having technologically attractive physical and chemical properties. The development of PEO technology over the last decade has provided coatings having controlled appearance, hardness, corrosion resistance and other tribological properties across an extending range of industrial sectors. Continuing developments are concisely reviewed and the PEO process is illustrated by the characterisation of anodised coatings on an AZ91 magnesium alloy surface.

Plasma Electrolytic Oxidation Coatings on Lightweight Metals

“…The applied voltage is increased from tens of volts to hundreds of volts, which is the breakthrough of traditional anodizing. The voltage forms developed from DC to continuous pulse, and then to AC, resulting in corona, glow, spark discharge and even micro-arc discharge phenomenon in the surface of the samples [12]. The general comparison between conventional DC anodizing and PEO technique was shown in Table 1 …”

“…The tank is insulated from ground and mounted in the safety interlocked enclosure (1), the latter being equipped with fume extraction facilities (5) and a window (6) to allow the PEO process to be viewed. The electrolyte is typically mixed (7) and recycled via a flow circuit containing a heat exchanger/chiller and a 50 to 100 mm filter (8) [12].…”

Characterization of Coatings Created on Selected Titanium Alloys by Plasma Electrolytic Oxidation

“…Nowadays the electrochemical treatments, such as electropolishing (EP) [1][2][3][4][5], magnetoelectropolishing (MEP) [6][7][8][9][10][11][12][13], high-current density electropolishing (HDEP) [14][15] as well as Plasma Electrolytic Oxidation (PEO) known also as Micro Arc Oxidation (MAO) [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] of biomaterial surfaces are very often used due to the biocompatibility effect. Most important is to fabricate the porous surface enriched in antibacterial elements such as silver and/or copper [30][31][32][33][34][35] with the least amount of toxic elements to the human body, such as vanadium, aluminum, and nickel [30,[36][37][38][39][40][41][42][43].…”

“…According to these requirements the best metallic biomaterials are metals such as titanium, niobium, zirconium, tantalum and their alloys [16][17][18][19][20][21][22]. However, till now the biomaterials such as titanium alloys, NiTi and Ti6Al4V, containing harmful elements [24][25][26][27][28][29][30] are very popular and still used. Therefore, a new approach with novel technologies to eliminate the harmful elements are proposed and developed.…”

Formation and properties of composite nanostructured PEO-coatings on metals and alloys

“…or alloys [1,2]. The oxide coatings have controllable morphology and composition, excellent adhesion to substrate, good electrical and thermal properties, high microhardness, wearproof and corrosion resistance.…”