Direct current micro-arc oxidation coatings on Al-Zn-Mg-Mn-Zr extruded alloy with tunable structures and properties templated by discharge stages. (April 2018)

• Record Type: Journal Article
• Authors: Zhao, Zequan; Pan, Qinglin; Yan, Jikang; Ye, Ji; Liu, Yaru
• Is Part Of: Vacuum. Volume 150(2018)
• Page Start: 155
• Page End: 165
• Publication Date: 2018-04
• Subjects: Extruded alloy -- Direct current (DC) -- Micro-arc oxidation (MAO) -- Current density -- Micro-arc stage -- Mullite; Vacuum -- Periodicals; 621.55
• DOI: 10.1016/j.vacuum.2018.01.040
• Languages: English
• ISSNs: 0042-207X

Abstract

Abstract: In order to improve the surface performance of Al-Zn-Mg-Mn-Zr extruded alloy, alumina coatings were directly prepared on the alloy in silicate electrolytes by direct current micro-arc oxidation technique. The relationship between discharge stages and technology parameters was studied, and then the growth behaviors, structure, composition and properties of coatings were further analyzed. Our work suggests that appropriately prolonging of the oxidation time at a low current density of 2 A/dm 2 can help to extend the action time of the micro-arc stage (Stage III) and to form a thicker layer with fewer inner defects. The compact inner structure promotes the hardness, elastic modulus as well as the corrosion resistance of the coatings. In contrast, the higher the current density, the earlier the discharge enters into the big arc stage (Stage IV), which has an adverse impact on the structure and properties of the coatings. In the Stage IV, the porosity of the coatings increases with the generation of mullite within the coatings comprise of γ-Al2 O3 and α-Al2 O3 . The growing direction of coatings changes from outward mainly to inward in the late stage of the micro-arc oxidation (MAO) process. Highlights: Technology parameters greatly influence the spark discharge stages. Higher current density promotes the transformation of discharge to the later stage. The Stage Ⅲ has positive effects to the improvement of coating properties. The Stage Ⅳ is more of a destructive action during the formation of coatings. The compactness of coatings has significant impacts on coating properties.