Study Of The Corrosion Behavior Of Pure Magnesium And Magnesium Alloys Under Thin Electrolyte Layers

The corrosion behavior of pure magnesium,Mg-10Gd-2Y-0.5Zr alloy(GW102K) and AZ91D under various thin layer thicknesses,the role of oxygen on the corrosion of pure magnesium under thin electrolyte layers,and the effect of T4 trealment on the corrosion of AZ91D under thin electrolyte layers were investigated by means of cathodic polarization curve,electrochemical impedance spectroscopy(EIS),electrochemical noise(EN) and SEM.Based on shot noise theory and stochastic theory,the EN results of the whole corrosion process of pure magnesium and GW102K alloy under thin electrolyte layers were quantitatively analyzed by using the Weibull and Gumbel distribution function, respectively,and the corrosion mechanism of pure magnesium and GW102K alloy under thin electrolyte layers were discussed.The experimental results revealed that both the cathodic and the anodic process of the corrosion of pure magnesium and it's alloys under thin layer were inhibited,and the corrosion type under thin layer was more localized than that in bulk solution.The cathodic process of the corrosion of pure magnesium and it's alloys was dominated by hydrogen reduction not only under thin layer but also in bulk solution. With the decreasing of thin layer thickness,the cathodic process was retarded.Cathodic process was retarded slightly while the anodic process was inhibited significantly,which indicated that both the cathodic and anodic process were inhibited in the present of oxygen.Thin layer had two opposite effects on anodic process of pure magnesium corrosion.On one hand,the pit initiation rate was retarded.The frequency of corrosion events under thin layer was greatly lowered compared to that in bulk solution.On the other hand,the pit growth probability was increased.The metastable pit on pure magnesium had a higher probability to become larger pit cavity than that in bulk solution.Pit initiation rate had greater influence on the anodic process than pit growth probability,which led to the inhibition of the anodic process of pure magnesium with the decreasing of thin layer thickness.There exist two kinds of effects for thin electrolyte layer on the corrosion behavior of GW102K alloy:(1) the rate of pit initiation was evidently retarded compared to that in bulk solution;(2) the probability of pit growth decreased,which should be the real reason why the corrosion rate of GW102K alloy decreased with the decreasing of layer thickness.The corrosion mechanism of AZ91D did not change after T4 treatment.