Scandium Fluoride Molten Salt - Aluminum-magnesium Thermal Reduction Mechanism And The Middle Of The Aluminum Magnesium Scandium Alloys New Preparation

Based on thermodynamics calculation and analysis about the reduction reaction of ScF3, 80203 metallic thermoreduction, the paper put forward to a new preparation method of Al-Mg-Sc master alloys by means of ScF3-Mx-Mg (Al) metallic thermoreduction; It studied the mechanism of ScF3-MF-Mg thermoreduction reaction using DTA and phase diagram analysis and computed reaction progression and reaction activation energy using the Freeman-Carrol method and the Kissinger method, and then on the basis of these results chose the most suitable molten salt system of the thermoreduction reaction. It also optimized the experimental conditions of the new technics preparing Al-Mg-Sc master alloys in which the recovery of Sc is 80% and got the Al-Mg-Sc master alloys with 2% Sc content; And then a sheet of Al-Mg alloys with and without Sc was manufactured by using these Al-Mg-Sc master alloys, whose microstructure and properties were studied contrastively and whose application was valued.The results of thermodynamics calculation indicated that ScF3 can be reduced to scandium by magnesium, but Sc2O3 can not be reduced to scandium by magnesium and aluminum .If reduction reaction are proceeded in aluminum bath, the entropy of system will be increased because of the formation of the stable intermetallic compound Al3Sc whose standard Gibbs formation free energy is estimated to be about -138KJ/mol. Owing to the sequent formation of Al3Sc, thermodynamics tendency of reduction will be greatly enhanced and equilibrium constants and conversion ration of reduction will be greatly enlarged. Therefore Al-Mg-Sc master alloy can be gained well by reducing ScF3 using magnesium in aluminum bath. At 1100K ,the empirical equilibrium constants of ScF3-MX-Mg(Al) reduction system is 6.6 109 .Principles of scandium oxide solid fluorinating and ScF3-Mg thermoreduction reaction were researched by thermal analysis (DTA). The results indicated that scandium oxide was fluorinated by the reaction with hydrogen fluoride gas coming from NH4HF2 decomposing and ScF3-Mg system starts ScF3(s)-Mg(s) solid-solid phase reduction at 590 C, ScF3(s)-Mg(l) solid-liquid phase reduction at 740 C, ScF3-LiF-Mg system starts ScLiF4(s)-Mg(s) solid-solid phase reduction at 496 C ,(ScF3-LiF)(l)-Mg(l) liquid-liquid phase reduction at 650 C .The kinetics parameters of ScF3-Mg reaction were calculated. The activation energy E=48.62KJ/mol, reaction progression n=1.03.The optimum reduction temperature of ScF3-MX-Mg(Al) to manufacture Al-Mg-Sc master alloy is 1100 C,time is 40 min, the concentration of scandium inSc-bearing master is more than 1.99%. All recovery can be up to 91.9% afterfluoridating and reduction secondly.Most part of minor scandium in pure Al and Al-Mg alloys exists in form of primary of secondly A13Sc,only a few of then stayed in a (Al) based solid solution .The primary AlsSc particles precipitating from melt of alloy during cooling act as inhomogeneous nuclei and fining grain size effectively. Most part of scandium stayed in magnesium based solid solution in our composition because magnesium and scandium don't act each other to form intermetallic compound when scandium concentration is low.Al-5Mg-Sc ingots were manufactured by mixing Al-Mg-Sc master alloy with metals needed. When scandium concentration is about 0.2%, the effect of grain fining of master alloy prepared was not remarkably. When scandium concentration is about 0.4%, the effect of grain fining of master alloy prepared was remarkably. The effect of grain fining of master alloy prepared was most remarkably, when scandium concentration is about 1.45%.