Electrochemical Corrosion Behavior of Backward Extruded Mg-Zn-Ca Alloys in Different Media

摘要

Mg-1.0Zn-xCa (x=0.2, 0.5, 0.8, 1.0; wt. %) alloys were prepared by zone purifying solidificationfollowed by backward extrusion technology. The microstructures, electrochemical corrosion behaviorsand the mechanisms in 0.9 wt. %, 3.5 wt. % NaCl solutions and simulated body fluid (SBF) wereevaluated at ambient temperature. The corrosion properties of the specimens were remarkablyinfluenced by the compositions of the media. According to electrochemical impedance spectroscopy(EIS), it revealed that the samples (lower 1.0 wt. % Ca) in the 0.9 wt. % and 3.5 wt. % NaCl solutionsshowed a single conductive loop. Conversely, Mg-1.0Zn-1.0Ca alloy was combined of a conductiveloop and an inductive loop. In the case of SBF, EIS of all the samples turned to two conductive loopsand an inductive loop. The BE-Mg-1.0Zn-0.5Ca alloy exhibited the most anti-corrosion properties inboth 0.9 wt. % NaCl solution and SBF, while it changed to BE-Mg-1.0Zn-0.8Ca alloy in 3.5NaClsolution. The corrosion mechanism confirmed that the micro-alloying Ca element can purify the meltsto improve the corrosion resistance. On the contrary, much Ca element contributed to form thesecondary phase, accelerating the pitting corrosion.