Enhancement of the corrosion resistance of the Mg alloy ZW61 by dual-frequency ultrasonic vibration

Ultrasonic vibration was introduced into the casting of quasicrystal-reinforced magnesium alloy ZW61. The microstructure, mechanical properties, and corrosion resistance were studied. The dual-frequency ultrasonic field (DUF) treatment reduced the α-Mg grain size from 502 µm to 69 µm, and the aggregated lamellar I-phase was refined into tiny dot-like shapes with a smaller area fraction. Static corrosion and electrochemical tests indicated that DUF decreased the corrosion rate from 10 mm·y⁻¹ to 3 mm·y⁻¹ with a denser protective oxide film. DUF not only significantly enlarged the effective cavitation area but also reduced the dependence of transient cavitation on the initial bubble radius. The ratio R_max³/t_c was used to qualitatively characterize the cavitation strength, and cavitation dynamics calculations indicated that DUF had higher cavitation strength compared to single-frequency ultrasonic field (SUF). An equation for corrosion rate versus microstructural parameters (grain size, second phase fraction, potential difference) was developed, which could well predict the corrosion rate of magnesium alloy ZW61 without and with different ultrasonic vibrations.