Microstructure and corrosion behavior of rapidly solidified Mg-Zn-Y alloys

The effect of a minor change in alloy composition on the microstructure and corrosion properties of melt spun Mg_98.3-xZn_xY _1.7 ribbons with x=9-12 is studied by X-ray diffractometry, differential scanning calorimetry, transmission electron microscopy and a dynamic polarization test. The ribbon specimens with x=9-10 revealed an in-situ composite microstructure consisting of icosahedral quasicrystalline phase (I-phase) particles distributed in an α-Mg matrix. The ribbon specimens with x=11 and 12 contained a minor MgZn₂ phase together with an α-Mg phase and I-phase. With increasing Zn content, the corrosion potential increased because of a mixed potential effect, but the formation of a MgZn₂ phase deteriorated the corrosion property through preferential attack, causing an irregular boundary between the corrosion product and the substrate. These results indicate that it is important to control alloy chemistry not to form the MgZn₂ phase in developing an I-phase strengthened Mg-Zn-Y alloy for structural applications.