Study On The Preparation And Mechanism Of Mg-Li-Mn,Al-Li-Mn And Mg-Li-Al-Mn Alloys In Molten Salt

Mg–Li alloys with low density,high specific stiffness,outstanding damping and excellent electromagnetic shielding properties have been widely used in fields of automotive,computer,electronics,chemical and aerospace,etc.However,the strength and corrosion resistance of Mg–Li and Al–Li based alloys are low and poor.Adding alloying elements in Mg–Li alloys is an effective way to improve their properties.In this paper,Mg–Li–Mn,Al–Li–Mn and Mg–Li–Al–Mn alloys were prepared by molten salt electrolysis.X–ray Diffraction?XRD?and scanning electron microscope?SEM?with energy dispersive spectrometry?EDS?were employed to characterize and analyzed the alloys.Moreover,MnO₂was firstly used as raw material and the chlorization effect of MgCl₂ and AlCl₃ on MnO₂ was investigated.The electrochemical behavior of Mg?II?was studied by square wave vo1tammtery,open circuit chronopotentiometry and cyclic voltammtery on Mo electrodes.The results showed that the reduction of Mg?II?to Mg?0?was consisted of one step with two electrons exchanges,and the reduction reaction was reversible.The diffusion coefficient of Mg?II?ions in the melts was 3.41×10^–5 cm²·s^–1.The electrochemical behavior of Mn?II?was studied by square wave vo1tammtery and cyclic voltammtery in LiCl–KCl–MgCl₂–MnO₂ melts.The results showed that the reduction of Mn?II?to Mn?0?was consisted of one step with two electrons exchanges,and the reduction reaction was irreversible.The diffusion coefficient of Mn?II?ions in the melts was 2.32×10^–5 cm²·s^–1.The codeposition process of Mg?II?,Li?I?and Mn?II?ions was explored by chronopotentiometry and open circuit chronopotentiometry.Mg–Li–Mn alloys were prepared by potentiostatic electrolysis at-2.1 V for 3 h.XRD,SEM and EDS were employed to characterize and analyze the alloys.The electrochemical behavior of Al?III?was studied by square wave vo1tammtery,open circuit chronopotentiometry and cyclic voltammtery on Mo electrodes.The reduction of Al?III?to Al?0?was consisted of one step,and the reduction reaction was incomplete reversible.The diffusion coefficient of Al?III?ions in the melts was 3.41×10^–5 cm²·s^–1.Al–Li–Mn alloys were prepared by galvanostatic electrolysis at–1.0 A for 3 h,Al₆Mn phase was identified by XRD in the alloy.SEM and EDS were used to analysis the microstructural of the alloy.The chlorization effects of MgCl₂ and AlCl₃ on MnO₂ were investigated in LiCl–KCl molten salts on Mo electrode.The optimal proportion of MgCl₂,AlCl_3,MnO₂ was found to be1:3:1.Mg–Li–Al–Mn alloys were prepared by potentiostatic electrolysis at–2.0 V for 3 h.XRD,SEM and EDS were employed to characterize and analyze the alloys.In this thesis,Mg–Li–Mn,Al–Li–Mn and Mg–Li–Al–Mn alloys were formed by electro-codeposition in molten salt.MnO₂ was firstly used as raw material,which provides a new method for preparation of alloys.