Influence Of Mn, Zn Alloying On Microstructure And Electrochemical Performance Of Al-Ga-Mg-Sn Anode Alloys

As an ideal battery system, aluminum-air battery has a broad application prospects and advantages such as large energy density, a rich material source, environment friendly, etc. Pure aluminum has a large corrosion rate and poor discharge performance at high current density in blank alkaline solution, it is unsuited to be used as aluminum-air battery cathode material directly. Multicomponent aluminum alloys have been developed by using microalloying, which can significantly improve the electrochemical properties and corrosion properties of the aluminum anodes.In this paper, by adding the two alloy elements Mn and Zn into Al-Ga-Mg-Sn quaternary alloy respectively, the Al-Ga-Mg-Sn-xMn and Al-Ga-Mg-Sn-xZn quinary alloys were prepared. In order to investigate the effects of Mn or Zn content on the microstructure, electrochemical performance and corrosion properties of Al-Ga-Mg-Sn anode alloy, experimental techniques such as SEM, EDX, metallographic microscope and electrochemical measurements were used, the effects of electrolyte additive and heat treatment on the electrochemical performance of Al alloy anodes were also researched.Experimental results indicate that after adding0.05%~0.2%(wt.%) Mn into Al-0.1Ga-1Mg-0.1Sn alloy, the number of the precipitates in the alloys increased, which refined the crystal grains and further activated the alloy, along with open circuit potential and galvanostatic discharge potential negatively shifted, but at the same time the hydrogen evolution rate of the alloy increased. Al-0.1Ga-1Mg-0.1Sn-0.1Mn alloy has good comprehensive performance, having the open circuit potential of1.716V (vs Hg/HgO), hydrogen evolution rate of0.322ml·cm-2·min-1, discharge potential of1.403V (vs Hg/HgO) at the current density of100mA·cm-2, output voltage of1.53V in a monomer cell at the output current of20mA, and homogeneous corrosion morphology. The EIS spectra of Al-0.1Ga-1Mg-0.1Sn-xMn alloys have smaller high frequency capacitive-reactance arcs than the base alloy, which shows the activation of alloys has been enhanced, but the low frequency capacitive-reactance arcs of Al-Ga-Mg-Sn-xMn alloys are more noticeable, this suggests that the dissolution or desorption rate of the corrosion product film on the surface of the alloy declines.Most of the precipitates in Al-0.1Ga-1Mg-0.1Sn-xZn alloys are mainly rich in tin, element Zn mainly dissolves into Al matrix. After0.5%or1%(wt.%) of Zn was added into the base alloy, the corrosion resistance of the alloy improved, negative shifts of the open circuit potential and galvanostatic discharge potential were also observed. The Al-0.1Ga-1Mg-0.1Sn-1Zn alloy has good corrosion resistance, electrochemical properties and presenting uniform corrosion, with OCP of-1.721V(vs Hg/HgO), hydrogen evolution rate of0.202ml·cm-2·min-1, discharge potential of-1.416V(vs Hg/HgO) at the current density of100mA·cm-2, and the output voltage of1.55V in a monomer cell at the output current of20mA. Compared to the base alloy, the high frequency capacitive reactance radius increases slightly when the volumes of Zn addition are0.5%and1%, and the low frequency capacitive-reactance arc shrinks, this implies that the corrosion products on the sufaces of Al-Ga-Mg-Sn-0.5/1Zn alloys are easy to break off. When the Zn content are1.5%and2%, the high-frequency capacitive reactance of the alloy decreases significantly and the low-frequency capacitive reactance is obvious, the corrosion products are not easy to fall off.After sodium thiosulfate has been added into4M NaOH solution, the self-corrosion rate of the Al-0.1Ga-1Mg-0.1Sn-0.1Mn alloy increases, the open circuit potential, corrosion potential and discharge potential shift negatively, these results demonstrate that thiosulfate ion further activate the alloy. Thiosulfate ion can cause pitting corrosion on the alloy which is similar to the effect of chloride ion. In4M NaOH+0.1M Na2S2O3solution, the alloy has the discharge voltage of-1.442V which is about40mV more negative than that in4M NaOH solution.Solid solution and annealing treatment have small effects on the microstructure, corrosion properties and electrochemical performance of the Al anode alloys, this is related to the microstructure of micro-alloying alloy itself.