Alloys Comparative Study on Microstructure and Corrosion Resistance of Alumina Coats on Al2024 and Al6061alloys Coated by Plasma Electrolytic Oxidation Technique

In this study, alumina was coated on Al2024 and Al6061 using plasma electrolytic oxidation method and the effects of Al substrate and applied voltage on the properties of coated samples were investigated. Scanning electron microscopy and X-ray diffraction were used to study the microstructure of coated samples and microhardness and corrosion tests were employed to evaluate the final properties of the coats. The results showed that with increase of applied voltage, α-alumina increased in the coats of both alloys however it enhanced more moderately for Al2024. Generally, the amount of α-alumina in Al2024 specimens was less than that of Al6061. The presence of more alloying elements in Al2024 led to the more metallic ions in its coat preventing the gammato- alpha alumina transition. Moreover, the highest corrosion resistance belongs to the Al2024 coated by 400 V and the Al6061 coated by 425 V and the corrosion potential values for them were measured -0.571 V and -0.549 V, respectively. The corrosion test also indicated that 67-68% α-alumina in the coatings can lead to the highest corrosion resistance. The microhardness test indicated that the maximum hardness value belongs to the samples coated by 450 V so that the values for the Al2024 and Al6061 coats were 1360 and 1475 Vickers, respectively.