Plasma Electrolytic Oxidation Coating on 6061 Al Alloy Using an Electrolyte Without Alkali Ions

Abstract

Plasma electrolytic oxidation (PEO) technique is well known to use for modifying the surface of valve metal such as Al, Mg and Ti, which improves mechanical and corrosion resistance properties. PEO is an electrochemical process of oxidation by creating microdischarges on the surface of metal immersed in an electrolyte under applying a high voltage. Electrolyte used in PEO process is almost based on alkali ions such as Na ion. The report on PEO process using free-alkali ion is very rare. In this study, the oxide layer on 6061 Al alloy was produced in a free-alkali ion electrolyte containing calcium phosphate and ammonia water by PEO method. Microstructure, micro-hardness and corrosion resistance of PEO coated were investigated and discussed. Surface morphology analysis indicated the coating characterized by micro-pores, pan-cakes like, and micro-crakes with pore size and percentage of pores on coating surface are smaller than 1 μm and 2.5 %, respectively. Micro-hardness and corrosion resistance of PEO coated are greatly improved compared to the bare Al alloy. Free-alkali-ions in oxide layer coated on Al alloy is important for many applications today.

Surface Modification of 6xxx Series Aluminum Alloys

“…They also correlated the process parameters, thickness, and corrosion resistance of the PEO coating. Tran [57] explored the possibility of an electrolyte that is alkali-free. They explored an electrolyte containing calcium phosphate and ammonia water for PEO of 6061 Al alloy.…”

Plasma Electrolytic Oxidation Coatings on Aluminum Alloys: Microstructures, Properties, and Applications

“…Although in PEO process the impact of electrolyte temperature on coating properties is less compared to the convectional anodization process, it is still very necessary that temperature of the electrolyte is controlled, in most recent studies temperatures are controlled in the range of 20-40 °C [29,55,71].…”

“…and potentiodynamic polarization (PDP) are most widely used [16,71,81,84], and an aqueous 3.5wt% NaCl solution (similar to that of natural seawater) is used as the electrolyte. For PEO coatings intended for biocompatibility applications the corrosion performance is normally performed in Hanks solution.…”

“…This is one of the reasons why PEO coatings prepared on different aluminum alloys exhibit significant differences in hardness. In previous studies the hardness of PEO coatings are mostly determined using Vickers hardness tester, eddy current gage, and light microscopy[60,71,84]. Interestingly, previous studies have also shown that abrasive wear rate of PEO coated 6061…”

Effect of Hydrogen on the Wear Resistance of Steels upon Contact with Plasma Electrolytic Oxidation Layers Synthesized on Aluminum Alloys

“…The synthesis of oxide layers on aluminum alloys by the method of plasma electrolytic oxidation (PEO) in weakly alkaline electrolytes can be an alternative to galvanic chrome plating. Oxide layers synthesized on aluminum alloys have a high hardness (1200 HV 0.2-2000 HV 0.2) and wear and corrosion resistance [7][8][9][10][11][12][13][14][15][16]. In addition, PEO layers synthesized on lightweight alloys have significant advantages over other coatings used in Metals 2019, 9, 280 2 of 14 friction units.…”