【作者】 陈增；

【导师】 张密林；

【作者基本信息】 哈尔滨工程大学 ， 材料学， 2008， 博士

【摘要】 镁合金作为绿色工程材料,近年来备受关注。镁锂和镁锆合金在航空和宇航等工业领域具有广泛的应用。本论文在LiCl-KCl熔盐体系中采用熔盐电解法制备了镁锂和镁锆合金,对金属锂和锆的电沉积过程以及制备镁锂和镁锆合金的电解工艺进行了探索。采用循环伏安法、计时电位法、计时电流法和恒电位电解等方法在低共晶组成的LiCl-KCl熔盐体系中研究了Li⁺分别在钼电极和镁电极上的电化学还原过程。研究结果表明,在熔盐体系的温度为450℃时,Li⁺在钼电极上的还原是通过一步电子转移反应完成的,并且反应不可逆,Li⁺的扩散系数为6.68（±0.07）×10^-6cm²/s,锂在钼电极上的电沉积过程存在成核极化现象,且成核过程为瞬时成核过程;金属锂在镁电极上析出时存在去极化作用,并通过控制沉积电位制备了不同相组成的镁锂合金。在低温熔融LiCl-KCl电解质体系中制备镁锂合金,优化了电流密度、电解温度和电解时间等电解工艺参数,研究低温条件下制备镁锂合金的最佳工艺条件,并考察了电解装置在进行连续电解实验时的稳定性,试验结果表明采用此工艺实现镁锂合金电解的方案可行。由于金属Zr在镁合金中具有强烈的晶粒细化作用,本文试用熔盐电解法制备Mg-Zr合金。文中采用循环伏安法、计时电位法、计时电流法和恒电位电解等方法在K₂ZrF₆-LiCl-KCl熔盐体系中研究了Zr（Ⅳ）在钼电极、钨电极和液态镁电极上的电化学还原过程。实验结果表明Zr(（Ⅳ）的还原是通过两步电子转移反应完成的,其中间产物是Zr（Ⅱ）,锆在钼电极上的沉积过程也存在成核极化现象;Mg-Zr合金存在两种形成机制:（ⅰ）锆在液态镁电极上电沉积形成Mg-Zr合金;（ⅱ）会属Mg还原Zr（Ⅳ）和Zr（Ⅱ）形成Mg-Zr合金。利用熔盐电解法制备镁锆合金,通过研究电流密度、电解温度、电解时间及电解质浓度对Mg-Zr合金中Zr含量的影响,制备Mg-Zr合金并确定了工艺参数,即电解温度为725℃、电流密度为5.66mA/cm²、K₂ZrF₆的浓度为5 wt.%以及电解时间为1h时,可以使制备的Mg-Zr合金中Zr的含量达到1.55%左右。更多还原

【Abstract】 As a kind of green engineering material,Mg alloy have recently attracted great attention in academic research and industry application.Mg-Li and Mg-Zr alloys were extensively applied in the aviation and aerospace field.In this thesis,the Mg-Li and Mg-Zr alloys were prepared through electrolysis method in the molten LiCI-KCl eutectic.The electrodepositi.on mechanism of Li and Zr as well as the electrolysis process parameters of Mg-Li and Mg-Zr alloys were studied.The electrochemical behaviour of Li⁺ was studied at the molybdenum and magnesium electrodes in the molten LiCl-KCl eutectic.Transient electrochemical techniques,such as cyclic voltammetry,chronoamperometry and chronopotentiometry were used in order to explore the deposition mechanism of Li.The results showed that the electroreduction of Li⁺ proceeds via a single step at 450℃and the reaction is irreversible.The diffusion coefficient of Li⁺ was determined to be 1.86×10^-6cm²/s.Nucleation polarization was observed during the electrodeposition of Li.This nucleation is an instantaneous process.At Mg electrode,the electroreduction of Li⁺ took place at a less cathodic potential values than that at Mo electrode for the depolarization of the formation of Mg-Li alloy. Two kinds of Mg-Li alloy with different phase were prepared through the controlling of electrolysis potential.Mg-Li alloy was prepared in the molten LiCl-KCl electrolyte at low temperature.The electrolysis process parameters such as current density, temperature and electrolysis time were optimized.The stability of the electrolysis equipment were also investigated.The results showed that the optimized electrolysis process was a practicable manufacturing scheme.The addition of zirconium element can significantly refine the microstructure of magnesium alloy.Molten salt electrolysis method was used to produce Mg-Zr alloy.The electroreduction process of Zr（Ⅳ） was studied in LiCl-KCl-K₂ZrF₆ melt at molybdenum,tungsten and liquid magnesium electrodes.Transient eletrochemical techniques,such as cyclic volmmetry,chronoamperometry and chronopotentiometry were used.The results showed that Zr（Ⅳ） was reduced to Zr metal by a two-step mechanism corresponding to the Zr（Ⅳ）/Zr（Ⅱ） and Zr（Ⅱ）/Zr transitions.The intermediate product was identified as Zr（Ⅱ） by X-ray diffraction. Nucleation polarization was also observed during the electroreduction process of Zr at molybdenum electrode.Two formation mechanism of Mg-Zr alloy were promoted:（ⅰ） Zirconium is electrodeposited on the magnesium electrode,and （ⅱ） Zr（Ⅳ） and Zr（Ⅱ） ions are reduced by Mg metal.The factors which might affect the Zr content were investigated,such as current density,temperature,electrolysis time and the K2ZrF6 concentration.The optimized electrolysis process was determined as follows:electrolyte composition: 53%KCl-42%LiCl-5%K₂ZrF₆（mass%）,electrolysis temperature:998 K, electrolytic time:1 h,cathode current density:5.66 mA cm^-2.The Zr content of Mg-Zr alloy could be as high as 1.55 wt%.更多还原