Effects of intermetallic phases on electrochemical properties of powder metallurgy Mg-6%Al-5%Pb anode alloy used for seawater activated battery

The changes in intermetallic phases of Mg-6%Al-5%Pb (Mg-Al-Pb) alloy prepared by powder metallurgy and their effects on electrochemical properties were studied. Experimental results showed that coarse Mg _17 Al _12 phases (with size ranges from 20 μ m to 70 μ m) and fine Mg _2 Pb phases (with the size of 100 nm scale) formed in the mixed Al, Pb and Mg powder during the hot press sintering procedure. Fine Mg _2 Pb phases exhibit strong diffusional ability to diffuse into Mg _17 Al _12 phases. Extruding further promotes the diffusion of Mg _2 Pb phases into Mg _17 Al _12 phases. Solution treatment produced a mixed microstructure which is Mg _17 Al _12 phase containing Mg _2 Pb phases inside and made other Mg _2 Pb phases homogeneously distributed in Mg matrix. Mg _17 Al _12 phases and the gathered Mg _2 Pb phases will accumulate the Mg(OH) _2 corrosion products, which impedes the subsequent discharge behavior. Homogeneously distributed Mg _2 Pb phases will fall off during discharge, which makes the discharge curve more stable. The mixed microstructure has positive effect on corrosion resistance and discharge potential. Therefore, solution-treated alloy shows the highest negative potential and the smoothest curve during the galvanostatic discharge test. Compared with the commercial AZ61 sheet, solution-treated alloy exhibit much higher anode properties in Mg/PbCl _2 battery test. Thus, the solution-treated alloy could serve as an excellent anode in seawater-activated batteries.