Optimization of Duty Cycle and Frequency Parameters of ZK60 Magnesium Alloy under Two-Step Voltage-Increasing Mode

Micro-arc oxidation (MAO) process was conducted on ZK60 Mg alloy under an optimized two-step voltage-increasing mode to investigate the effects of duty cycle and frequency on the evolution and characteristics of the coatings. Scanning electron microscopy, electrochemical impedance spectroscopy, and other methods are used to characterize the microstructure and corrosion behavior of the coating. Voltage-time curves under different duty cycles and frequencies show that duty cycle and frequency have a great influence on the microstructure and performances of the coatings under two-step voltage-increasing mode. A higher current peak combined with a wider basic peak width can provide enough driving force and longer duration, which contributes to producing a thick and compact coating with good corrosion resistance. When the duty cycle was 30%, it is favorable for developing a compact and smooth MAO coating which exhibits good corrosion resistance. Too high duty cycle would make the coating poor in corrosion resistance due to the loose coating resulting from the excessive energy. When the frequency is 600 Hz, the coating growth is greater in both stages, which leads to a dense and uniform coating and results in a high thickness of 22.4 mu m. The MAO coating with the best corrosion resistance can be conducted when the duty cycle is 30% and the frequency is 600 Hz.

Automated summary

The effects of duty cycle and frequency on the evolution and characteristics of coatings were investigated during the micro-arc oxidation process on ZK60 Mg alloy. The results showed that a higher current peak combined with a wider basic peak width contributed to the formation of a thick and compact coating with good corrosion resistance. When the duty cycle was 30%, a compact and smooth MAO coating with good corrosion resistance was developed. When the frequency was 600 Hz, a dense and uniform coating with a high thickness was obtained.