Influence of duty cycle on the growth behavior and wear resistance of micro-arc oxidation coatings on hot dip aluminized cast iron

The effect of the duty cycle of AC pulsed power on the growth behavior and wear resistance of micro-arc oxidation (MAO) coatings deposited on hot-dipped aluminized high‑phosphorus cast iron was investigated. The ceramic coatings were prepared using a constant voltage and various duty cycles between 20% and 45%. The thickness of the coatings was measured using a coating thickness meter and metallographic microscope. With increasing duty cycle, the thickness of the coatings increased and the growth mode changed from inward to outward growth. When the duty cycle was 45%, the coating thickness reached about 65 μm, where the ratio of outward to inward growth was about 74.67%. XRD results showed that the ceramic coatings mainly consisted of α-Al2O3 and γ-Al2O3; with increasing duty cycle, the unstable γ-Al2O3 gradually transformed into stable α-Al2O3. When the duty cycle was < 40%, the roughness of the coating increased slowly with increasing duty cycle; the roughness increased significantly when the duty cycle reached 45% and was about 1.6 times that of the coating produced at a duty cycle of 40%. The hardness of the coatings was the maximum (about 950 HV) at a duty cycle of 40%. The friction coefficient of the oxidation layer increased with increasing duty cycle and the wear rate of the cast iron after MAO treatment reduced significantly. The wear rate reached the minimum value of 1.399 × 10− 4 mm3/(Nm), which was 40% of that of the cast iron substrate, when the duty cycle was 40%.