Influence of specific second phases on corrosion behaviors of Mg-Zn-Gd-Zr alloys

The corrosion behavior and mechanism of as-cast and as-extruded Mg-Zn-Gd-Zr alloys with specific ternary phases are investigated using scanning electron microscope (SEM), scanning Kelvin probe force microscope (SKPFM), immersion and electrochemical tests. Lamellar X-Mg12GdZn, net-like W-Mg3Gd2Zn3 and strip-like I-Mg3Zn6Gd phases form successively. The eutectic W-phase owns the highest potential difference of 120 mV with Mg matrix, accelerating micro-galvanic corrosion. Continuously distributed and undersized I-phase leads to uniform corrosion. The as-extruded Mg-3Zn-11Gd-0.6 Zr alloy exhibits superior corrosion resistance, due to the relatively low potential difference between X-phase and matrix, the corrosion barrier effect and typical {0002} < 10 - 10 > texture components.