The effect of Ag micro-alloying on the microstructure and corrosion behavior of the as-casted Mg-2Zn-0.2Ca(ZX20)alloy were investigated by means of OM,SEM,electrochemical tests,and hydrogen evolution mass loss method.The results reveal that the addition of 0.5％(mass fraction)Ag af-fects adversely the corrosion resistance of ZX20 alloy.The corrosion rate increases from 1.63±0.17 mm/a for the ZX20 alloy to 4.06±0.68 mm/a for the Ag-containing alloy(ZXQ200),primarily due to the potential difference between the second phase and the matrix.The dendrite arm spacing of the ZX20 alloy(69.8±24.9 μm)is smaller than that of the ZXQ200 alloy(85.9±23.9 μm),potentially contributing to the greater local corrosion depth observed in the ZXQ200 alloy.The two alloys all consist of α-Mg and Ca2Mg6Zn3 phases with a similar volume fraction of the second phase,and no Ag-rich compounds have been detect-ed for the Ag-alloyed ones.However,the Ag segregation in the second phase results in a heightened po-tential difference between the second phase and the substrate,elevating it from approximately 60 mV(ZX20)to about 200 mV(ZXQ200).This segregation enhances the micro-galvanic corrosion driving force in the ZXQ200 alloy,resulting in a shorter pitting gestation period and an increase in local corrosion sites.
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