Corrosion behavior and mechanism of Mg-Y-Zn-Zr alloys with various Y/Zn mole ratios

- A mechanism of eutectic W-phase to accelerate transgranular corrosion is proposed.
- The corrosion barrier effect of X-phase relies on its distribution pattern.
- A collapse mechanism of corrosion product layer is summarized.
- The corrosion product layer provides hardly any protection to the substrate.

The effect of Y/Zn mole ratio on microstructure, corrosion behavior, corrosion product and electrochemical behavior of MgY1.72Zn2.81Zr0.17, MgY3.83Zn3.03Zr0.17 and MgY2.58Zn1.27Zr0.15 alloys (at.%) are investigated. The weight loss and electrochemical tests all reveal that MgY2.58Zn1.27Zr0.15 alloy (at.%) has the best corrosion resistance among the three investigated alloys. The second phases in the three alloys transform from eutectic W-phase to continuous wide plate-like X-phase and further to compact plate-like X-phase with the increase of Y/Zn mole ratio. The type and distribution pattern of second phase play the key roles in determining the corrosion mechanism and rate. Eutectic W-phase leads to serious transgranular corrosion by forming many micro-pores. Compact plate-like X-phase acts as corrosion barrier and effectively protects the substrate from further corrosion. The porous, petal-like Mg(OH)2 corrosion product layer is hardly able to provide any protection to the substrate. Additionally, this hydroxide layer is unstable and easily to detach from the substrate due to the mechanical stress and hydrogen evolution. The open-circuit potential curves and the polarization curves are acquired through electrochemical test and the results have been discussed.

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