Effect of Surface Properties on Corrosion Resistance of ZK60 Mg Alloy Microarc Oxidation Coating

Abstract

Microarc oxidation (MAO) is performed on ZK60 magnesium alloy at 250–400 V. For this paper, a direct current (dc), unipolar (UP), and bipolar (BP) power modes are used to produce a dense and uniform oxide coating that increases the corrosion resistance of ZK60 alloy. The compositions and microstructures of the oxide coatings that are formed using different working parameters are determined by X-ray diffraction and scanning electron microscopy. The corrosion resistance of the coatings is evaluated in a 3.5 wt% NaCl solution using potentiodynamic polarization tests. The average roughness is then measured. The results show that the mode of the applied power (dc, UP, and BP modes) has a significant effect on the coating’s morphology and corrosion resistance. For the same pulsed-power supply, the number of pores in the coating decreases as the applied voltage is increased and the average pore size increases so cracks gradually appear. The ZK60 magnesium alloy that is prepared at 400 V using BP power has the least porosity and the best corrosion resistance.