Microstructure,electrochemical Properties And Corrosion Resistance Of Mg-6Al-3Pb-xLa(x=0,0.5,1,2) Alloys

Magnesium alloy anode due to its more negative electrode potential,stable discharge,short activation time,high energy density,rich reserves and many other advantages received lots of researchers concern.The Mg-6Al-5Pb anode alloy has been widely studied due to its relatively negative stable potential and hight Coulomb efficiency when discharged at high current density.However,Pb is harmful to the environment.The purpose of this paper is to study the discharge performance of Mg alloys with the negative standard La potential added on the basis of reducing the content of Pb in Mg-6Al-5Pb alloy.This article mainly uses the microstructure characterization,electrochemical testing and immersion experiments to study the discharge performance and corrosion resistance in chlorination sodium solution of the the La element on low Pb content of Mg-6Al-3Pb alloy anode,which deal with three methods such as alloying,heat treatment and extrusion deformation respectively.The specific content and related research results are as follows:The microstructures,discharge performance and corrosion resistance of as-casted Mg-6Al-3Pb-xLa(x=0.5,1,2)alloy anodes was studied in 3.5 wt.%NaCl solution.The experimental results showed that the addition of La increases the volume fraction of the second phase of the alloys.The volume fraction of the second phase increases with the increase of La content,and the grain size of the alloys were refined.In addition,the AP63-1La alloy show the most negative discharge potential and its average discharge potential is-1.71V(vs.SCE)while discharged at the current density of 10mA/cm~2.The corrosion resistance of AP63-xLa alloys increases first and then decreases with the increase of La content,and the AP63-2La alloy inhibit the corrosion due to the higher proportion of acicular second phase.The microstructure,discharge performance and corrosion resistance of Mg-6Al-3Pb-xLa(x=0,0.5,1,2)alloys after 400°C for 24 h followed by water quenching were investigated.The results showed that,heat treatment increases the volume fraction of the second phase and enhances the discharge activity of the alloys.The discharge performance of AP63-1La alloy still shows the most negative discharge potential.Although the average discharge potential of heat-treated AP63-1La alloy is the same as the as-cast one,the activation time was shorter and the most negative potential was more negative.Secondly,the corrosion rate of the alloys decreased due to the increase of the volume fraction of the needle-like second phases of the alloys after heat treatment,this needle-like second phases could inhibit the extend of corrosion to improve the corrosion resistance of the alloys.Therefore,the heat-treated AP63-1La alloy is more suitable for magnesium alloy battery anode than the as-cast alloy.Furthermore,the microstructures,discharge properties and corrosion properties of extruded AP63-0.5La and AP63-1La alloys were also studied.After extrusion,the size of the second phase in the alloys were finer,and the fine second phases are uniformly distributed in the vertical extrusion direction(RD)and zonal distribution along the extrusion direction(ED).The grain orientation in the RD and ED directions of the alloys is also different.The discharge performance of the as-extruded AP63-1La(RD)alloy is the best among those extruded alloys,and the average discharge potential was-1.707V(vs.SCE),it is slightly lower than the heat-treated AP63-1La alloy.Although the as-extruded AP63-1La(RD)alloy have a shorter activation time and could activate the more negative potential then other two state alloys,its corrosion rate is much higher than the other two state alloys.Combined with the cost of processing considerations,the heat-treated AP63-1La alloy is best suited for magnesium alloy anode electrode in this paper.