Equal Channel Angular Pressing And Aging Treatment On Electrochemical Corrosion Behavior Of ZK60 Mg Alloy

Equal-channel angular pressing(ECAP) is an effective method to improve mechanical properties of bulk metallic materials by grain refinement. However, little research has been done on corrosion behaviors, due to the fast development of ultrafine-grained (UFG) or nanocrystalline (NC) materials, the corrosion behavior research of UFG/NC materials can provide strong support for its further application.ZK60 alloy is a commercial Mg alloy. Herein, UFG ZK60 alloy was obtained by multi-pass ECAP and the second phases in a-Mg matrix was redistributed by post-aging. Corrosion behaviors of the solution-treated Mg alloy after ECAP plus aging were studied by electrochemical tests integrated microstructure and corrosion morphology observation, with aim to revealing the effect of microstructure feature and the protective ability of corrosion product on the corrosion resistance of ZK60 Mg alloy.Constant immersion tests show that the mass loss rate of ZK60 Mg alloy in 3.5% NaCl increases with ECAP passes and decreased with immersion time. After post-aging, the mass loss rate of ECAP samples decreased. The UFG alloy with more ECAP passes has a higher corrosion current density (Icorr) and a smaller charge transfer resistance (Rt). Corrosion resistance of the UFG ZK60 Mg alloy was slightly improved by post-ECAP aging due to the relief of internal stress and better protective ability of corrosion product by the redistribution of second phase. LEIS results showed that the impedance first increased and then decreased with the immersion time. It could be ascribed to the formation of corrosion product, which first stack on the surface, then dissolve and fall off with immersion time.The corrosion resistance of ECAP ZK60 Mg alloy was obviously improved in 0.01M NaOH solution, which has the lower Icorr and the larger Pt value. It was verified to be n-type semiconductor by Mott-Schottky tests. The values of Ufb becomes lower with immersion time showed that thicker passive film was formed on the surface, thus provide better corrosion protection.Scanning-kelvin-probe tests under normal circumstance showed that anodic and cathode sites were homogeneously distributed on the surface of the UFG Mg alloy, and the volta potential linearly decreased with the increasing ECAP pass. It also showed that the ZK60 alloy with more ECAP passes had the higher electrochemical activity and thus the lower corrosion resistance in corrosive solution.