Preparation of Black Coating on AM50 Alloys by Microarc Oxidation (MAO)

Abstract

The black microarc oxidation (MAO) coating containing Cu²⁺ was prepared on AM50 magnesium alloys. When the additives (CuSO₄ and C₄H₄KNaO₆ · 4H₂O) were added into the NaAlO₂ solution, the color of the prepared coatings appearance changed from white to black. The effects of CuSO₄ concentration and treatment time on the color of the coatings were investigated. The optimum formula of black coatings prepared by MAO has been acquired by a single-factor experiment and orthogonal experiment of L₉(3⁴) with four factors and three levels. The estimated optimum values of the process parameters are corresponding to NaAlO₂ 10 g/L, C₄H₄KNaO₆ · 4H₂O 1 g/L, CuSO₄ 1 g/L, and pH 11. The surface morphologies, structure, composition, and corrosion resistance of the MAO coatings were analyzed by scanning electron microscopy, X-ray diffraction (XRD), and electrochemical tests. The results of the above series of tests have shown that the properties and characteristics of the black coatings are improved. The black coating is irregular porous structure, which aperture size is about 0.1 ∼ 0.2 µm. The black coating mainly consists of MgO, MgAl₂O₄, and Cu₃MgO_4.

Keywords:

• Alloys
• Black
• Coatings
• Corrosion
• Magnesium
• Mao

Notes

^a the amount of corrosion rate at A _i /3.

^b .