Effect of Sn Element on Corrosion Resistance of Homogeneous Mg-6Zn-0.25Ca Magnesium Alloy

Abstract:

The effect of adding 1wt% Sn on the corrosion resistance of homogeneous Mg-6Zn-0.25Ca alloy was studied. The corrosion resistance of Mg-6Zn-Sn-0.25Ca and Mg-6Zn-0.25Ca alloys was analyzed by OM, XRD, SEM, hydrogen evolution, mass loss and polarization curve experiments. The results show that the main secondary phase in Mg-6Zn-0.25Ca alloy is Mg₂Ca phase, and after Sn addition, the main existence form of the secondary phase in Mg-6Zn-Sn-0.25Ca alloy is Mg₂Sn phase, Mg₂Ca phase and a small amount of CaMgSn phase. After adding Sn, the secondary phase of the alloy is more evenly distributed and the average grain size of the alloy decreases from 145.6 μm to 114.2 μm, because the Mg₂Sn phase with high melting point can act as a heterogeneous nucleation core for non-spontaneous crystallization of the α-Mg matrix, thereby refining the grain size. Under their combined effect, the oxide film produced during alloy corrosion becomes denser, thereby preventing the hydrogen evolution reaction. In addition, the polarization curves show that the self-corrosion potential and self-corrosion current density of Mg-6Zn-0.25Ca alloy are –1.729 V and 2.106×10^-5 A/cm², respectively. After adding 1wt% Sn, the self-corrosion potential increases to –1.525 V, while the self-corrosion current density decreases to 8.561×10^-6 A/cm², which enhances the corrosion resistance of Mg-6Zn-Sn-0.25Ca alloy.