Study on corrosion behavior of Mg-based bulk metallic glasses in NaCl solution

In this work, bulk metallic glasses Mg60Cu30Y10, Mg65Cu20Y10Zn5 and Mg65Cu20Y10Ni5 (BMGs) in the form of plates with thickness of 1 mm were successfully synthesized by the high-pressure casting. The microstructure of bulk glassy alloys was examined by high-energy synchrotron X-ray diffraction, scanning and high-resolution electron microscopy. The immersion and electrochemical polarization measurements in 5% NaCl solution revealed that the Mg-based metallic glasses manifested higher polarisation resistance than conventional crystalline Mg sample. The electrochemical results show that the single phase structure of metallic glasses has an important role for the corrosion behavior. Moreover, the addition of alloying elements (e.g. Cu, Ni) can change a corrosion potential into an anode direction. In order to further understand the corrosion behavior of the studied alloys, the XPS measurements were used to determine the elemental composition of corrosion products after polarization. The corrosion surface films were identified to be Mg(OH)2 and MgO. The corrosion mechanism was also considered and described by observing a morphology of the corroded samples versus immersion time. The EDS, XPS and XRD results suggest that magnesium hydroxides/oxides and other oxides were mainly formed as corrosion products on the surface of studied alloy.