Electrodeposition Of Rare Earth Magnesium Alloys In Choline Chloride Urea Ionic Liquid And Its Mechanism Study

Because of its unique properties,rare earth magnesium alloys are widely used in aerospace and other fields.At present,the main preparation methods are mechanized alloy method,melting method,electrodeposition and so on.Compared with other methods,electrodeposition has the advantages of simple equipment,low cost,and controllable deposition conditions.In order to obtain the homogeneous and corrosion-resistant rare earth magnesium alloys,firstly,the ChC l-Urea ionic liquid was prepared.The structure of the choline chloride urea ionic liquid was preliminarily analyzed by infrared technology and differential thermal analysis technology.The viscosity of the ChCl-Urea ionic liquid was studied by the control variable method.The law of the influence of electrical conductivity.At the same time,the optimal combination of choline chloride dehydration to MgCl₂·6H₂O was studied by the combination of response surface method and orthogonal analysis,which provided conditions for the electrodeposition experiment.In the three electrode system,the reduction process and mechanism of metal cations such as Co???,Ni???,Mg???,La?III?,Pr?III?and Gd?III?were studied by cyclic voltammetry in the three electrode system.In oil bath,the Pr-Mg-Co and La-Mg-Co,Gd-Mg-Co,Pr-Mg-Ni,La-Mg-Ni alloy films were prepared by constant potential technology under the condition of 353 K.The condition of alloy films respectly were optimized by the response surface method.The optimum deposition conditions of the alloy films and the maximum content of the rare earth elements in the alloy films were obtained.The nucleation mechanism of each alloy membrane was studied by single potential step timing method.Finally,the morphology and composition of the alloy films were analyzed by SEM,EDX,XRD and Mapping scanning,and the corrosion resistance of the alloy films under the alkaline and medium conditions was studied by the Tafel curve method.The results of the study show as following.1.The mixture of choline chloride and urea is liquid at room temperature,only the two phases of choline chloride and urea,its viscosity decreases with the increase of temperature,the conductivity increases with the increase of temperature,and the viscosity and electrical conductivity meet the Walden rule.2.Because of its water absorption,the six water magnesium chloride can be removed from 5 crystalline water molecules under the vacuum heating condition,and the six water magnesium chloride after dehydration can be directly used in the electrodeposition experiment.3.Cyclic voltammetry test results show that Co???and Ni???can be reduced to single substance in the choline chloride urea ionic liquid,and the reduction process is an irreversible reaction of diffusion control.Mg???,La?III?,Pr?III?and Gd?III?can not be reduced separately in this system,but can be induced by iron ions such as Co???and Ni???.The mechanism of the induced codeposition reaction is consistent with the three-dimensional instantaneous nucleation mechanism.4.The optimum deposition conditions are different of 5 three element alloy films,such as Pr-Mg-Co,La-Mg-Co,Gd-Mg-Co,Pr-Mg-Ni and La-Mg-Ni,but the common characteristics are that the deposition potential is around-1.00 V,and the concentration of the iron ions in the deposition is not the greater the better,and the Mapping scanning results show that the elements in the alloy film are evenly distributed.When the deposition time is 20 min,the surface of each deposition film is most uniform and compact,and the corrosion resistance of the film is better when the rare earth content is the largest.All alloy films are amorphous.Except for the Pr-Mg-Ni alloy film,the other alloy films are crystallized from amorphous to crystalline,and the alloy films have XRD after crystallization at 800?.The small angle diffraction peak indicates that there is a microporous structure inside the alloy membrane.