Study On Calculation Of The Thermodynamic Properties Of Magnesium Alloys

Mg alloy has many good characters, such as low density, high specific strength and rigidity, good cast performance, high size stability and good mechanical processing, etc. It had been used extensively in auto industry, aircraft industry and telecommunications and had a good performance. But the theoretical research of this alloy is still very weak, some important thermodynamics data about them also are still very scarce. So it is very necessary to carry on research to the thermodynamics nature of the Mg alloy. In this field, getting excess fuctions, activity and its interaction parameter of components is an important aspect of researching the thermodynamics characters of alloy. Because of the complex and equipment of experiment being very difficult to guarantee good accuracy under high-temperature, high-temperature experiment is still very difficult at present. So, it is very significant to obtain the thermodynamics data through thermodynamics calculating.Under each model of predicting the thermodynamics characters of alloy, Miedema model and embedded atom method have been developing as comparatively a good and accurate model in recent years. Through calculating, Miedema model has been choosen, which is the higher accuracy. So in this work, the formation enthalpy of the Mg alloys have been calculated by Miedema mode, which include the most of the alloys formed Mg and the metal elements inⅡB～ⅤA subgroup in periodic system of element, according to the Miedema model . Further, the formula of calculating activity had been deduced, and the activity of the solute components in these alloys also had been calculated. Combining the Kohler model, Toop model and Chou model on the base of Miedema model, the activity parameters in very weak solution and interaction parameters of the solute components in Mg-Al-Zn, Mg-Zn-Zr, Mg-Mn-Sc had been calculated. Based on the free volume theory calculating the excess entropy, the formula of calculating activity had been improved. The solute components activity curve had been calculated used this improved formula. Finally, the solute and the liquid phase equilibrium lines of Mg-Al phase diagram including 0~5wt%Al had been measured. The information which get from the phase diagram had used to estimate the activity of Mg and former calculating value had been verified.The research results indicate that the Miedema model is applicable to the alloys based on Mg. In the aspect of predicting alloy formation enthalpy, the formatting enthalpy...