Effect of Constant Pressure Time on Microstructure and Properties of Constant Current and Constant Pressure MAO Coatings on ADC12 Alloy

The work aims to explore the influence of the combination of the constant current first and then plus constant voltage on the microstructure and properties of ADC12 high Si-Al alloy micro-arc oxide coating and select the optimal oxidation time combination. The MAO coatings were prepared under constant current of 11 A/dm2 for 35 min first and then plus constant voltage of 550 V for different oxidation time (5 min, 15 min, 25 min, 35 min) by bipolar pulse power, and they were studied by scanning electron microscope (SEM), X-ray diffraction (XRD), HT-600 friction and wear testing machine and electrochemical work station. The results showed the thickness of the coating first increased and then decreased as the oxidation time increases under the method of first constant current and then constant voltage, and When the oxidation time was the constant current for 35 min first and then plus constant voltage for 25 min, the thickness of the coating was 25 μm. α-Al2O3, γ-Al2O3 and Al2SiO5 phases existed in the MAO coating; with the increase of oxidation time, the wear rate of coating increases first and then decreases. And when the oxidation time was the constant current for 35 min first and then plus constant voltage for 5 min, the friction coefficient of the coating was the smallest, only 0.78; Different oxidation time had a significant effect on the corrosion resistance of ADC12 aluminum alloy MAO coating. The corrosion potential increases first and then decreases with the increase of oxidation time. Meanwhile, the change trend of corrosion current is the same as that of corrosion potential. Hence, when the oxidation time was the constant current of 11 A/dm2 for 35 min first and then plus constant voltage of 550 V for 25 min, the coating is of thicker coating, better density and better corrosion resistance. © 2021, Chongqing Wujiu Periodicals Press. All rights reserved.