Study On Depositional Mechanism Of La,Pr And Sm In Molten Salts On Mg And Al Cathodes

Mg based and Al based alloys were widely applied in various fields such as aerospace,automotive and electronic industries.However,A1 based and Mg based alloys had the weaknesses of low strength and low Young's modulus,which limit their wide-ranging application in aerospace industry.The addition of rare earth elements could be effective improve the properties of alloy.The typical method of preparing Mg based and A1 based alloys was directly mixing and fusing the metallic element.Herein,the Mg based and Al based alloys were prepared by molten salt electrolysis.Originally,the depositional mechanism of La,Pr,Sm on Mg,Al electrodes was investigated by different electrochemical methods.Afterwards,the Mg based and Al based alloys with AlxRE(A1l4La,Al2Pr,Al4Sm)intermetallic compound whiskers were manufactured by the methods of co-deposition,cathodic alloying and liquid cathode.Finally,the Mg-Li-La alloy was prepared by the method of co-deposition.The phase composition and the grain size of Mg-Li-La alloy could be controlled by adjusting the concentration of MgCl2.The main contributions were as following:The depositional mechanism of Sm on A1 electrode was investigated by different electrochemical methods in LiCl-KCl melts.On the solid A1 electrode,three kinds of Al-Sm intermetallic compounds(Al2Sm,Al3Sm and Al4Sm)could be formed.The Al-Sm alloys with different phase compositions were prepared by the method of cathodic alloying.On the liquid Al electrode,only one kind of Al-Sm intermetallic compound(Al4Sm)was formed.The Al-Li-Sm alloys were manufactured by the method of liquid cathode.The Al-Li-Sm alloys with Al4Sm intermetallic compound whiskers were prepared by adjusting the cooling rate.The micro hardness,Young's modulus and corrosion potential were measured.The results revealed that,with the assistance of Al4Sm intermetallic compound whiskers,the micro hardness and corrosion potential of Al-Sm alloys improved 15%and 2.3%,respectively.The micro hardness and Young's modulus of Al-Li-Sm alloys improved 17.1%and 4%,respectively.The depositional mechanism of La on Al electrode was investigated by different electrochemical methods in LiCl-KCl melts.In LiCl-KCl-LaCl3-SmCl3 melts,the Al-La alloys with different phase compositions were prepared by the method of cathodic alloying.XRD patterns illustrated that the Al-La alloys mainly contain Al11La3 and Al2.12La0.88 phases.On the liquid Al electrode,the Al-Li-La alloys with Al4La intermetallic compound whiskers were prepared by galvanostatic electrolysis.The properties of micro-hardness and Young's modulus of Al-Li-La alloys were measured.The results exhibited that micro hardness and Young's modulus of Al-Li-La alloys improve 14.13%and 4.37%,respectively.On inert electrode,the depositional mechanism of La(?),Li(I),Mg(?)were investigated by cyclic voltammetry,square wave voltammetry,open circuit chronopotentiometry and chronopotentiometry.Chronopotentiometry exhibited that the co-deposition of Mg(?),Li(?),La(?)ions will be realized when the current intensity was more than-250mA.The Mg-Li-La alloys with different phase compositions were successfully prepared on the W electrode.XRD patterns exhibited that the prepared Mg-Li-La alloys mainly contain Mg17La2,Mg3La and MgLa phases.The phase of Mg-Li-La could be controlled by adjusting the concentrations of MgC12.SEM images illustrated that the phase size can also be controlled by adjusting the concentrations of MgCl2.On solid Mg electrode,the electrochemical behavior of L(?)was studied by cyclic voltammetry,open circuit chronopotentiometry and cathodic polarization test.The Mg-La alloys were prepared by the method of cathodic alloying.The results from XRD and SEM illustrated that the phase composition and thickness of alloy film can be controlled by adjusting the electrolytic potential.In LiCl-KCl-MgCl2-AlCl3-LaCl3 melts,the co-deposition mechanism of Mg(?),Li(?),Al(?),La(?)ions was investigated by cyclic voltammetry,square wave voltammetry,open circuit chronopotentiometry and chronopotentiometry on W electrode at 1023 K.Chronopotentiometry shown that the co-deposition of Mg(?),Li(?),Al(?),La(?)ions will be realized when the current intensity was more than-190 mA.The Mg-Li-Al-La alloy containing A12La and Al11La3 phases was prepared by galvanostatic electrolysis on W electrode.Subsequently,the Mg-Li-Al-La alloy containing Al4La intermetallic compound whiskers was manufactured by galvanostatic electrolysis on liquid Mg electrode.The micro-hardness of Mg-Li-Al-La alloy was measured by the micro-hardness test.The results illustrated that micro hardness of Mg-Li-Al-La alloy containing Al4La intermetallic compound whiskers improves 11.68%.At 973 K,the co-deposition mechanism of Mg(?),Li(?),Al(?),Pr(?)ions was investigated by different electrochemical measurements in LiCl-KCl-MgCl2—AlCl3-PrCl3 melts on W electrode.Chronopotentiometry exhibited that the co-deposition of Mg(II),Li(I),Al(?),Pr(?)ions will be realized when the current intensity was more than-200mA.On the W electrode,the Mg-Li-Al-Pr alloy with Al2Pr,Al3Pr and Mg12Pr phases was prepared by galvanostatic electrolysis.Subsequently,the Mg-Li-Al-Pr alloy containing Al2Pr intermetallic compound whiskers was prepared by galvanostatic electrolysis on liquid Mg electrode.The micro-hardness of Mg-Li-Al-Pr alloy was also measured by the micro-hardness test.The results exhibited that,the micro hardness of Mg-Li-Al-Pr alloy containing Al2Pr intermetallic compound whiskers improves 18.6%.