Electrochemical Behavior Of Mg-Al-Pb-Zn-Mn And Mg-Li-Al-Pb-Zn-Mn Alloys In Seawater

Metal semi-fuel cells using seawater as electrolyte in general, have the advantages of high energy density, stable discharge voltage, reliability, low cost and environmentally friendly. They are attractive undersea power sources.But. the Mg alloys acted as negative pole of the battery request overcome some questions, such as the low current efficiency due to its severe parasitic corrosion reaction resulting in the evolution of hydrogen and the "negative difference effect", potential lagging, declining of the electrochemical activity and so on. Doping magnesium with other alloy elements is effective ways for the improvement of magnesium anode performance. Therefore, it is useful to investigate new Mg alloys.In the article, the discharge performance and current efficiency of Mg-Al-Pb-Zn-Mn alloys and Mg-Li-Al-Pb-Zn-Mn alloys formed by adding Li to Mg-Al-Pb-Zn-Mn alloy are investigated by means of potentiodynamic polarization, galvanostatic oxidation and electrochemical impedance technique. The surface morphology after discharge was examined using scanning electron microscopy. The effect of thermal treatment and rolling process on Mg-Al-Pb-Zn-Mn alloy discharge performance was studied. According to test results of metallographic microscope and XRD, the changes in microstructure of the reasons for discharge performance of alloy is discussed. Results indicate that, in sea water solutions Mg-Li-Al-Pb-Zn-Mn alloy exhibits more negative open circuit potential, higher discharge activity, but lower current efficiency than Mg-Al-Pb-Zn-Mn alloy. The voltage of Mg-Li-Al-Pb-Zn-Mn alloy electrode discharged at 10mA cm-2 reached -1.45 V. Both alloys show the "negative difference effect", and the discharge efficiency under high-current is less than the efficiency of the small current. Mg-Li-Al-Pb-Zn-Mn alloy surface is more uniform corrosion, and the discharge product loosely packed on the electrode surface.But, Mg-Al-Pb-Zn-Mn alloy have quickly response to load changes than Mg-Li-Al-Pb-Zn-Mn alloy. Heat treatment process plays an important role in the influence on the microstructure. composition distribution, electrode potential and current efficiency of the magnesium alloy. Comparing to other annealing temperature sample, the annealing Mg-Al-Pb-Zn-Mn alloy at 400℃has smaller recrystallization size, homogeneous composition, and reticular tissue in grain boundary that consisted of Mg2Pb. It leads to more negative and stable electrode potential, easier to peel off of corrosion output. Discharged at 10mAcm-2, electrode potential of the annealing at 400℃reached -1.51 V. negatively more than the as-cast alloy electrode 0.21 V. electrode potential of hot-rolled alloy electrode reached -1.59 V. negatively more than the as-cast alloy electrode 0.29 V.