Corrosion Behavior Of Rolled Mg-8Li Magnesium Alloys

Mg-Li alloy is the lightest metal material with high specific strength and specific stiffness and good cold and hot deformation performance.It has obvious competitive advantages and application prospects in the fields of automobile,aerospace,electronics industry and military industry.However,due to the active chemical properties of the dual-phase Mg-Li alloy,the Mg-Li alloy is prone to corrode in the service environment,which seriously affects its engineering application.The influence of pre-soaking time,solution concentration and?-Mg phase distribution on the corrosion resistance of rolled Mg-8Li alloy was analyzed by electrochemical impedance spectroscopy test,polarization curve test,hydrogen evolution test,surface morphology observation and sectional morphology observation.When the solution concentration is the same,the longer the pre-soaking time,the worse the corrosion resistance of the Mg-Li alloy,and the more serious the alloy corrosion;in the process of corrosion,pitting corrosion first occurs at the phase interface,and then extends to?-Mg phase in the form of filamentous corrosion.With the extension of corrosion time,the corrosion gradually extends to the?-Li phase.When the pre-soaking time is the same,the higher the concentration of Na Cl solution,the more serious the corrosion and the worse the corrosion resistance of Mg-Li alloy.Mg-8Li alloys with different?-Mg phase distributions have different corrosion resistance.TD-oriented Mg-Li alloy is easier to corrode than RD-oriented Mg-Li alloy,namely,RD-oriented Mg-Li alloy has a better corrosion resistance.The phytic acid conversion coating was prepared on the rolled Mg-8Li alloy.Through the observation of surface morphology and cross section morphology,it is known that the phytate conversion film is"dry mud"and there are cracks on the surface,which may be caused by drying and dehydration after transformation.EDS spectra showed that the phytic acid conversion coating was mainly a metal chelate formed by Mg²⁺and phytic acid.Through electrochemical impedance spectroscopy test,polarization curve test,and hydrogen evolution test,it is known that the phytic acid conversion coating can significantly improve the corrosion resistance of the alloy.However,there is little difference in corrosion resistance between the two orientations after phytic acid conversion.According to the comparison of impedance fitting data,polarization curve and data,the corrosion resistance value of TD-oriented Mg-Li alloy changes more,indicating that the phytic acid conversion coating has a better protection effect on TD-oriented Mg-Li alloy.