| Mg-air batteries is a special fuel cell with Mg metal as fuel.which has many advantages such as high theoretical energy density,environmental protection,safety,low cost,abundant reserves and so on.It has a good application prospect in marine communication,military equipment and emergency reserve power supply.However,the Mg anode is faced with the problems of peeling off the corrosion products and low anode utilization efficiency,which limits the wide application of Mg-air batteries.On the basis of composition optimization,the discharge performance of Mg-air batteries largely depends on the microstructure of the Mg anode material,such as grain size,size and morphology of the second phase,etc.In addition,the dense hexagonal structure of Mg leads to poor plasticity at room temperature.The conventional plastic deformation such as rolling,extrusion and forging needs to be carried out in the heating state,and it has to be heated repeatedly,which results in high energy consumption and the grains are difficult to be significantly refined.And it is easy to cause high dislocation density and stronger crystal preferred orientation,which affecting the discharge performance of Mg anode.Therefore,it is very important to find a method to prepare Mg alloy anode with excellent properties at room temperature.In this thesis,ultrafine grain Mg-Al based alloy anode materials(AS61 and AZ31)were prepared by copper-mold rapid solidification(RS),high-energy ball milling+spark plasma sintering(SPS)and friction stir processing(FSP),and based on the microstructure characterization and electrochemical reaction to analyze corrosion electrochemical behavior.The main results are as follows:1)The as-cast AS61 alloy anode material was obtained by rapid solidification method(RS)with a thick-walled copper mold.The experimental results show that the AS61alloy prepared by rapid cooling can obtain fine and dispersed second phase?-Mg17Al12and rare-earth?-Al2(Ce,Y)phase microstructure.The structure of AS61 alloy anode material leads to better dicharged activity.And the anode utilization efficiency of assembled Mg-air batteries at 10 mA cm-2and 20 mA cm-2current densities can reach 78.4±1.7%and 79.5±1.6%respectively.It is much higher than pure Mg and traditional cast AS61 alloys.2)Ultra-fine AZ31 alloy anode materials were prepared by high-energy ball milling and spark plasma sintering(SPS).The experimental results show that high-energy ball milling can significantly refine the grain size of AZ31 magnesium alloy to 28.8±0.09 nm,at room temperature And the bulk AZ31 alloy anode was prepared by powder consolidation has fine grain size(?665±74 nm),low dislocation density and weak preferred orientation.This structure makes AZ31 alloy anode material assembled into Mg-air batteries with higher discharge platform,higher anode utilization efficiency and higher discharge capacity.The discharge voltages at 10 mA cm-2and 20 mA cm-2current densities are 1.211±0.004 V and1.026±0.007 V,the anode utilization efficiency was 69.1±0.9%and 70.2±1.0%,the capacity is 1530±20 mAh g-1and 1555±22 mAh g-1,respectively.And the discharge corrosion products are porous,exhibit excellent electrochemical performance.3)The fine grain AS61 alloy anode material was obtained by friction stir processing(FSP)through severe plastic deformation at room temperature.The experimental results show that FSP processing changes the microstructure of AS61 magnesium alloy anode,and promotes grain refinement and uniform distribution of?-Al2(Ce,Y)particles in?-Mg matrix.The structure resulted in the dissolution of the surface film of the anode material of AS61 alloy,which made the anode surface of Mg alloy exposed to active corrosion in the electrolytes.The corrosion morphology tends to be relatively uniform rather than serious localized corrosion,which has beneficial to improving the anode utilization efficiency and discharge platform,and comprehensively improving the electrochemical performance of the Mg alloy anode. |
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