Fabrication and Characterization of Ceramic Coating on Al7075 Alloy by Plasma Electrolytic Oxidation in Molten Salt

Abstract

The fabrication of a ceramic coating on the metallic substrate is usually applied to achieve the improved performance of the material. Plasma electrolytic oxidation (PEO) is one of the most promising methods to reach this performance, mostly wear and corrosion resistance. Traditional PEO is carried out in an aqueous electrolyte. However, the current work showed the fabrication and characterization of a ceramic coating using PEO in molten salt which was used to avoid disadvantages in system heating-up and the formation of undesired elements in the coating. Aluminum 7075 alloy was subjected to the surface treatment using PEO in molten nitrate salt. Various current frequencies were applied in the process. Coating investigations revealed its surface porous structure and the presence of two oxide layers, α-Al2O3 and γ-Al2O3. Microhardness measurements and chemical and phase examinations confirmed these results. Potentiodynamic polarization tests and electrochemical impedance spectroscopy revealed the greater corrosion resistance for the coated alloy. Moreover, the corrosion resistance was increased with the current frequency of the PEO process.

Influence of Applied Frequency on Thermal Physical Properties of Coatings Prepared on Al and AlSi Alloys by Plasma Electrolytic Oxidation

“…A-type discharges occur on the surface of PEO coatings. Type B refers to strong discharges between PEO coatings and the substrate surface, and during this process, a number of molten oxides eject instantaneously from the discharge channels, which forms a relatively large-size "pancake" structure on the surface of the coatings [23][24][25]. C-type discharges occur under PEO coatings.…”

Characterization of MAO + Cu Composite Coatings on Aluminum Alloy

“…It was found that the addition of graphite reduced the surface porosity of oxide film, improved the mechanical and tribological properties of oxide film, and extended the service life of the composite oxide film [1]. Sobolev uses Plasma electrolytic oxidation to perform surface treatment on 7075 aluminum alloy and found that the addition of oxide coating has significantly improved the corrosion resistance [6]. The surface modification treatment technology used in the above industrial production does not affect the aluminum alloy matrix and also gives the aluminum alloy surface better performance and improves its range of applications.…”

Special Issue: Plasma Electrolytic Oxidation (PEO) Coatings

“…In the case of PEO coated Al alloys 4 works are dedicated to cover different features [8][9][10][11]. The research published by del Olmo et al [8] investigates environmentally friendly alternatives to toxic Cr (VI)-based surface treatments for corrosion protection of Al alloys focused on multifunctional PEO-layered double hydroxides (LDH) coatings.…”

“…Moving to other properties, the production of phosphorescent coatings is reported by Auzins [10] using Sr0.95Eu0.02Dy0.03Al2O4-δ powder and Plasma Electrolytic Oxidation. In addition, Sobolev et al [11] investigates the use of molten salt during the development of PEO coatings on AA7075 from the point of view of fabrication and characterization.…”