Corrosion behavior of as-cast Mg_(68)Zn_(28)Y_4 alloy with I-phase

Mg68Zn28Y4 alloys with stable icosahedral quasicrystals(Zn60Mg30Y10)were prepared by cast method.By simulating the environment of ocean,the alloy was eroded in 3.5%(mass fraction)NaCl for 2,4 and 30 h.The microstructures of the samples and eroded alloys were analyzed by OM and SEM.The compositions and the quasiperiodic structures were identified respectively by EDS and TEM.And the corrosion potential and corrosion current density before and after immersion were measured by potentiodynamic polarization measurements in 3.5%NaCl.The results show that I-phases grow in the mode of conglomeration, piling and transfixion.The Mg7Zn3 matrix andα(Mg)solid solution are eroded badly,while W-phase is eroded partially.At the same time,the I-phases exhibit excellent corrosion resistance property.The resistance to corrosion of Mg68Zn28Y4 alloy is improved by increasing exposed I-phases.With adding element Y to Mg68Zn32 alloy,the corrosion current is decreased by one order of magnitude. And after the immersion of as-cast Mg68Zn28Y4 alloy for 30 h,the corrosion current density is reduced by two orders of magnitude compared with that of uneroded Mg68Zn32 alloy.

Mg68Zn28Y4 alloys with stable icosahedral quasicrystals （Zn60Mg30Yto） were prepared by cast method. By simulating the environment of ocean, the alloy was eroded in 3.5% （mass fraction） NaCl for 2, 4 and 30 h. The microstructures of the samples and eroded alloys were analyzed by OM and SEM. The compositions and the quasiperiodic structures were identified respectively by EDS and TEM. And the corrosion potential and corrosion current density before and after immersion were measured by potentiodynamic polarization measurements in 3.5% NaCl. The results show that/-phases grow in the mode of conglomeration, piling and transfixion. The Mg7Zn3 matrix and a（Mg） solid solution are eroded badly, while W-phase is eroded partially. At the same time, the/-phases exhibit excellent corrosion resistance property. The resistance to corrosion of Mg68Zn28Y4 alloy is improved by increasing exposed/-phases. With adding element Y to Mg68Zn32 alloy, the corrosion current is decreased by one order of magnitude. And after the immersion of as-cast Mg68Zn28Y4 alloy for 30 h, the corrosion current density is reduced by two orders of magnitude compared with that of uneroded Mg68Zn32 alloy.