Surface microstructure and corrosion resistance characterization of Mg-based amorphous alloys

Mg-based amorphous alloys have broad applications due to disordered atomic structure, thermal stability, crystallinity, low elastic modulus and high strength. In the present study, Mg–Ni–Gd–Yb–Ag alloys were prepared by vacuum arc melting combined with copper roll melt spinning. The addition of trace amounts of ytterbium (Yb) improved the corrosion resistance of Mg_73-XNi₁₅Gd₁₀Yb_XAg₂ (x = 2,4,6,8 at.%). Electrochemical experiments, immersion tests and analysis of corrosion products by XPS and EDS showed that Mg₆₇Ni₁₅Gd₁₀Yb₆Ag₂ exhibited the best corrosion resistance with an Ecorr of − 968 mV and an Icorr of 5.93 µA/cm². The superior corrosion performance was attributed to the presence of corrosion passivation films comprising MgO, Mg(OH)₂, Ni(OH)₂, Ag₂O, AgCl, Ca₅(PO₄)₃(OH), as well as rare-earth oxides Gd₂O₃ and Yb₂O₃. These compounds efficiently shield the matrix, and the microstructure corrosion mechanism of Mg–Ni–Gd–Yb–Ag involves a cyclic process that includes surface film layer dissolution, matrix corrosion and film layer regeneration, leading to oxide attachment. The addition of the appropriate amount of rare-earth element Yb to Mg-based amorphous alloys can improve the corrosion resistance, thereby increasing the application prospects of alloys.