【作者】 颜永得；

【导师】 张密林；

【作者基本信息】 哈尔滨工程大学 ， 材料学， 2009， 博士

【摘要】 镁锂合金堪称超轻合金,在轻量化要求的工业领域有着诱人的前景。镁锂合金的制备都是采用对掺法,本论文用熔盐电解的方法制备镁锂基合金,并对其电化学过程和机理、合金相结构等进行了深入的研究。在金属的沉积过程、合金化过程、合金的相控制、合金成分的控制等方面取得了重要成果。本论文第一部分工作是在LiCl-KCl熔盐体系中,用阴极合金化法在固态镁电极上制备了镁锂合金,在480℃下,通过选择电解参数可以控制生成合金的相组成。在-2.26、-2.30和-2.39V(vs.Ag／AgCl)电位下恒电位电解30分钟分别得到厚度为182、365和2140μm的α、α+β和β相Mg-Li合金。本文第二部分工作是在惰性电极上,670℃时通过共电沉积方法直接从KCl-LiCl-MgCl2熔盐体系中电解得到镁锂合金。采用循环伏安法、计时电位法、计时电流法测定了Mg(II)离子在熔盐中的扩散系数,并研究了镁和锂共电沉积的条件。通过恒电流电解制备了三种不同相的镁锂合金,并考察了电解参数及MgCl2浓度对镁锂合金中锂含量的影响。在含有5wt.%MgCl2的熔盐中,MgCl2的极限电流密度为0.35 A·cm-2,超过此值时,Mg和Li就能产生共电沉积；在电流密度为6.21 A·cm-2电解2h条件下,只有当MgCl2浓度小于10wt.%时,才能得到Mg-Li合金。共电沉积法具有工序简单和能耗较低的优点。本文第三部分工作是在670℃时,在钼电极上,从LiCl-KCl-MgCl2-XCln(X=A1、Zn和Y,n=2或3)熔盐中直接共电沉积制备镁锂铝、镁锂锌和镁锂钇合金。采用不同的电化学技术研究了Mg(II)、Li(Ⅰ)和第三种合金化元素x(X=A1、Zn和Y)的电还原过程和共沉积条件。首次运用计时电流和计时电位等方法判断各种金属的沉积顺序及合金形成过程。从而实现一种从源头开始,集合金组分共电沉积-合金化-均匀化于一体的熔盐电解制备Mg-Li及Mg-Li基合金的新方法。研究中发现在LiCl-KCl-MgCl2-XCln熔盐体系中,在钼电极上首先形成的是Mg-X合金(X=A1、Zn和Y),之后锂在预先沉积的Mg-X上的欠电位沉积会形成Mg-Li-X合金。三种镁锂基合金共电沉积条件分别为：在含有1 Wt.%AICl3的LiCl-KCl-MgCl2 (5 wt.%)熔盐中,当电流密度低于-0.47A·cm-2或电极电位负于-2.100V时会发生镁、锂和铝的共电沉积；在含1 wt.%ZnCl2的LiCl-KCl-MgCl2 (8 wt.%)熔盐中,当电流密度低于-0.78 A·cm-2或电极电位负于-2.000V时会发生镁、锂和锌的共沉积；镁、锂和铝共电沉积的开始电位是-2.100V,当时会发生发镁、锂和铝的共电沉积；在含5 wt.%YCl3的LiCl-KCl-MgCl2 (5 wt.%)喀盐中,当电流密度低于-0.47 A·cm-2时会发生镁、锂和钇的共沉积。通过恒电位和恒电流电解,制取了不同Li和X(X=A1、Zn和Y)含量的镁锂基合金,并对合金产品进行了XRD、金相显微镜、扫描电子显微镜、能谱和ICP等分析。改变MgCl2和XCln浓度和电解参数,可以控制镁锂基合金中锂和X的含量。本论文首次研究了多元Mg-Li-X (X=Al、Zn和Y)合金共电沉积机理。其低温电解、液态阴极去极化作用和合金化作用使得电解条件温和,易于实现工业化,为新合金的研究提供了一条可靠的工艺路线。更多还原

【Abstract】 Mg-Li alloys, is called superlight alloys. These alloys have great potential in the fields of industry for light materials. In general, Mg-Li alloys are conventionally prepared by directly mixing and fusing the metallic elements. In this thesis, Mg-Li based alloys are prepared by electrolysis in molten salts. Moreover, the electrochemical process, the electrochemical mechanism, phase structures of Mg-Li based alloys and so on were deeply investigated. In the aspects of the process of metallic deposition, the alloying procee, phase control of alloys and composition control of alloys, we obtained important achievements.In the first section of this thesis, Mg-Li alloys were prepared by cathodic alloying method on solid magnesium electrode in a molten LiCl-KCl (50:50 wt.%) system at 480℃. The phase structures of Mg-Li alloys could be controlled by parameters of electrolysis in molten salt system at low temperature, a, a+P andβphases Mg-Li alloys with the thickness of 182,365 and 2140μm were obtained by potentiostatic electrolysis at-2.26,-2.30 and-2.39 V (vs. Ag/AgCl) for 30 min, respectively.In the secnod section of this thesis, Mg-Li alloys were directly prepared by co-electrodeposition method on an inert electrode in a molten LiCl-KCl (50:50 wt.%) system at 670℃. The diffusion coefficient of magnesium ions in the melts was determined by cyclic voltammtery, chronopotentiometry and chronoampertry. The condition of co-electrodeposition of Mg and Li was investigated. Three kinds of phases Mg-Li alloys were prepared via galvanostatic electrolysis. The codepositon of Mg and Li happens when the current indensity exceed about 0.35 A-cm-2 (value of limited current density of MgCl2) in KCl-LiCl melts containing 5 wt.% MgCl2. Under the electrolytic condition of 6.21 A·cm-2 for 2 h, only MgCl2 concentration is lower than 10 wt.%, Mg-Li alloys can be obtained. The method of co-electrodeposition have some advantages, whish are short process time and low energy consumption.In the third section of this thesis, this work presents an electrochemical study on the codeposition of Mg, Li and X (X=Al, Zn and Y) on a molybdenum electrode in LiCl-KCl-MgCl2-XCln (X=Al, Zn and Y, n=2 or 3) melts at 670℃to form Mg-Li-X alloys. The electrochemical reduction process and co-electrodeposition conditions of Mg(Ⅱ), Li (Ⅰ) and the third alloying elements were investigated by different electrochemical techniques. The chronopotentiometry and chronoampertry were first applied to investigate deposition order of different metals and alloy formation process. Consequently, Mg-Li and Mg-Li based alloys were prepared by a new method of electrolysis in molten salts. This method can start from origin and incorporate co-electrodeposition, alloying and uniformity into an entire. In LiCl-KCl-MgCl2-XCln system, the first formed alloy is Mg-X alloy. The succeeding underpotential deposition of lithium on pre-deposited Mg-X leads to the formation of a Mg-Li-X alloy. The codeposition conditions of three kinds of Mg-Li based alloys is:The codepositon of Mg, Li and Al occurs at current densities lower than-0.47 A-cm-2 or electrode potentials more negative than-2.100 V in LiCl-KCl-MgCl2 (5 wt.%) melts containing 1 wt.% AlC13. The codepositon of Mg, Li, and Zn occurs at current densities lower than-0.78 A cm-2 or electrode potentials more negative than-2.000 V in LiCl-KCl-MgCl2 (8 wt.%) melts containing 1 wt.% ZnCl2. The codepositon of Mg, Li, and Y occurs at current densities lower than-0.47 A-cm-2 in LiCl-KCl-MgCl2 (5 wt.%) melts containing 5 wt.% YCl3.Mg-Li based alloys with different lithium and X (X=Al, Zn and Y) contents were obtained via potentiostatic and galvanostatic electrolysis. The obtained alloys were characterized by XRD, optical microscope, scanning electron microscopy, energy dispersive spectrometry and inductively coupled plasma (ICP). And the lithium and X contents of Mg-Li-X alloys can be controlled by MgCl2 and XCln concentrations and the electrolytic parameters.In this thesis, co-electodeposition mechanism of ternary Mg-Li-X (X=Al, Zn and Y) alloys was first investigated. The advantages low temperature electrolysis, the depolarization effect of liquid cathode and the effect of alloying make electrolysis condition moderate and is easy to bring about industrialization. All of this supply a reliable technical routine for new alloy materials.更多还原