Preparation of Dark-Red Membrane by Micro-Arc Oxidation on AM50 Alloys

The dark-red membrane was prepared on AM50 magnesium alloys by using chemical conversion and micro-arc oxidation (MAO). The effects of MAO electrolyte and chemical conversion solution were researched through L₉(3⁴) orthogonal test to obtain formulation for the aforementioned process. Surface morphology, composition, and corrosion resistance were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical test. A dark-red membrane can be obtained by the following steps: first, a chemical conversion was carried out on AM50 alloys by placing them in a solution of 50 g/L KMnO₄ and 100 g/L NH₄H₂PO₄ at 50°C for 11 min; second, the prepared alloys were placed into MAO electrolytes containing 10 g/L Na₂SiO₃ and 5 g/L NaOH in order to obtain the dark-red-colored MAO ceramic membranes. The membranes that are mainly composed of SiO₂, MnO, MnP, MgSiO₃, and Mg₂SiO₄ have porous structures. MnO and MnP were identified to be responsible for giving color to the membrane.