Theoretical Investivation On The Corrosion Resistance Of Mg-Ge Alloy

The corrosion mechanism of Mg alloys and improvement of their corrosion resistance have always been the research hotspots.In the present study,the galvanic corrosion behavior of the Mg-Ge alloys was investigated systematically with first principles calculations,which was reported to have good corrosion resistance by experiments.Models built in this work based on thermodynamics and kinetics are potential in guiding the design of corrosion resistance Mg alloys.The Mg-Ge alloys are composed of Mg matrix and Mg2Ge second phase.According to the dissolution potential proposed in this work and calculations of the interface and work function,it is proved theoretically that Mg will serve as dissolving anode and Mg2Ge as cathode where hydrogen evolution takes place during the galvanic corrosion.The possible solute Ge atoms in the matrix have little impact on the work function and local potential of Mg matrix surface,so that their influence on the anodic dissolution behavior of Mg matrix is negligible.The most stable surface of Mg2Ge is(111)plane,upon which the hydrogen evolution reaction in near neutral and base solutions was analyzed.Relavant thermodynamic and kinetic parameters are calculated,including water dissociation barrier,hydrogen/hydroxyl adsorption energy,hydrogen diffusion and recombination.Theorectical insight is provided into how Mg2Ge poisoning the cathodic reaction:the transition states in the reaction,namely,hydrogen adsorption and diffusion barrier on the surface are much higher than Cu or Ni electrode;hydroxyl adsorption is more energetic favored,which may poisoning the hydrogen evolution as a competitive reaction.Models proposed in this work also provide guidance in depressing the galvanic corrosion of Mg alloys and laid the theoretical foundation in corrosion resistant Mg design with high-throughput calculations:the dissolution potential can predict the corrosion potential of the second phase in Mg alloys and help evaluate the galvanic corrosion tendency between Mg matrix;work function and local potential shift can be used in screening the solute atoms depressing the anodic dissolution of Mg matrix;parameters like hydrogen/hydroxyl adsorption energy can be used to screening for second phases poisoning the hydrogen evolution like Mg2Ge.