Preparation And Basic Study Of Mg-Sr And Mg-Li-Sr Alloy By Molten Salt Electrochemical Reduction

Mg-Sr alloys areone of the heat-resistant magnesium alloys,the research reportsabout which are mainly Mg-Al-Sr and Mg-Li-Sr,but there are still few reportsconcerning Mg-Zn-Sr alloys.Mg-Li alloys,known as “Urltralight magnesium alloys” allalong,have a series of advantages:low density, high intensity and stiffness, good thandamping performance and plastic deformation ability. So the preparation and research ofMg-Li alloys is very significant.The preparation of Mg-Zn-Sr by electrochemical reduction （or electrolysis） werestudied in this thesis,on this base,the preparation of Mg-Li-Zn-Sr alloy byelectrochemical codeposition of Li and Sr were also researched.The divece adapted tothe electrochemical reduction of Li and Sr was designed and prepared;The density ofmolten salt system with different composition were investigated by comparativemethod,and the electrolyte systems used as raw materials were determined;Thedehydration and volatile of electrolyte were tested by TG/DSC method,and the solubilityand actual decomposition voltage of electrolyte systems were measured,too;theinfluence of different reaction conditions on the electrochemical reduction currentefficiency of Sr were discussed;the main components of the products alloy wereanalylized by XRF and AAS,and the microstructure and phase of the products werecharacterized with OM,SEM and XRD;the design of no-separator magnesiumelectrolysis cell was preliminarilyexplored,too. The results show that:①For KCl-SrCl₂molten salt system,when the mole ratio of SrCl₂increased from30%to50%,the density of the system enlarged from1.436g/cm³to2.074g/cm³,forLiCl-SrCl₂system,as the mole ratio of SrCl₂increased from25%to45%,the density varedfrom1.336g/cm³to1.915g/cm³,so the ideal electrolyte was certainly KCl-30%SrCl₂andLiCl-25%SrCl₂;②Thevolatility and corrosivity of LiCl were stronger than that of SrCl₂, butdehydrated more easily. Only small portion of liguid Sr was dissolved in the KCl-SrCl₂molten salt,there were still partly blended into the cathode alloys, although most liquidLi rised in the LiCl-SrCl₂molten system.③In KCl-SrCl₂system,the cell voltage of Sr reductionwas more or less4.5V,which was lower than5V of Li、Sr through codeposition in the LiCl-SrCl₂moltensalts; ④From the I-t curve of electrochemical reduction process,wheather Sr depositionsinglely or Li、Sr codeposition,the current were both more and more lower,and becamestable at last,current has a minor fluctuations in the reduction process;⑤The current efficiency of Sr electrochemical reduction process was mainlyfluenced by the factors of reductiontemperature、time、curent density and electrodedistance,and it would lead to low current efficiency if the value was too small or toolarge,the high current efficiency could be obtained none but under the appropriateparameters;⑥The microstructure of Mg-Zn alloy before reduction was compounded of α-Mgmatrix and alarge mount of “snowflake” second phase, but it was obviously fined afterredution,and the second phase became discontinuous network distribution,and new “fineneedle” compound phase of Mg₁₇Sr₂and other Sr、Zn phase.