First-principles study of the corrosion of Mg alloys and Mg-based composites in Cl-containing electrolyte

Abstract

The effect of different elements and their concentrations on the work function of low index crystal planes of pure Mg was studied. The corrosion mechanisms of pure Mg and Mg-based composites in electrolytes with different NaCl concentrations were investigated. The results showed that the work function difference of the Mg-Zn-Ca alloy surfaces decreased with addition of the O atoms. The (0001) surface exhibited the highest work function for the pure Mg and Mg1Zn1Ca2O composites, with values of 3.762 eV and 3.789 eV, respectively. Compared to Cl atoms, O atoms and O₂ molecules were more likely to adsorb on the Mg(0001) and Mg1Zn1Ca2O(0001) surfaces. Cl atoms weakened the Mg-O bonding energy, leading to the destruction of the passivation film and subsequent oxidation and corrosion of the inner layers Mg atoms. The binding energy between the corroded and uncorroded atomic layers decreased with increasing Cl concentration, indicating increased destruction of the Mg atomic layers. After the passivation film was broken, the repassivation process was hindered by Cl. Experimental results showed that the corrosion rates of extruded pure Mg and Mg-1Zn-0.5CaO composites increased with increasing NaCl concentration. The Mg-1Zn-0.5CaO composite exhibited higher corrosion resistance due to the dense and stable corrosion product layer.