Abstract
Phosphate and aluminate electrolytes were used to prepare plasma electrolytic oxidation (PEO) coatings on 6061 aluminum alloy. The surface and cross-section microstructure, element distribution, and phase composition of the PEO coatings were characterized by SEM, EDS, XPS, and XRD. The friction and wear properties were evaluated by pin-on-disk sliding tests under dry conditions. The corrosion resistance of PEO coatings was investigated by electrochemical corrosion and salt spray tests in acidic environments. It was found that the PEO coatings prepared from both phosphate and aluminate electrolytes were mainly composed of α-Al2O3 and γ-Al2O3. The results demonstrate that a bi-layer coating is formed in the phosphate electrolyte, and a single-layered dense alumina coating with a hardness of 1300 HV is realizable in the aluminate electrolyte. The aluminate PEO coating had a lower wear rate than the phosphate PEO coating. However, the phosphate PEO coating showed a better corrosion resistance in acidic environment, which is mainly attributed to the presence of an amorphous P element at the substrate/coating interface.
Highlights
The awareness of sustainable development and environmental stability has been deeply rooted in various fields in recent decades
The results indicate that the phosphate plasma electrolytic oxidation (PEO) coating shows much better corrosion protection performance in an acidic corrosion environment than the aluminate coatings after thethe anti-corrosion property teststests in acid
PEO coatings were fabricated on 6061 aluminum alloy in phosphate and aluminate electrolytes, respectively, and the wear and acid corrosion resistance were compared
Summary
The awareness of sustainable development and environmental stability has been deeply rooted in various fields in recent decades. In terms of the properties, Al alloys are characterized by high specific strength and low specific weight compared with conventional ferrous material, wide adaptability of heat treatment, and superior processability for casting, forging, welding, and machining [1,2,3]. Up to now, they have been widely employed as structural components in the fields of spacecraft, aircraft, automotive, and 3C products [4,5,6]. The PEO coatings have superior mechanical properties and chemical stability that can protect the Al alloy substrate from corrosion and wear failures [13,14].
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