Thermodynamic Calculation Methods Of Multicomponent Alloy And Their Application In Researches Of Mg-Zn-Gd-Y And Mg-Zn-Zr-Y Alloys

The thermodynamic properties of materials are very important on predicting and understanding the stability and precipitation properties of phase.At present,the application of magnesium alloy lags far behind that of aluminum alloy and steel.The most important reason of the great gap between its development potential and actual application status is that the theoretical thermodynamic study of magnesium alloy is not detailed enough and the thermodynamic data lacks precision.Generally speaking,the thermodynamic data can be measured experimentally.However,the amount of data to be measured is very large and the experiment is time consuming and laborious.Therefore,the thermodynamic prediction model is an effective approach to obtain thermodynamic properties of the magnesium alloy.Based on the Miedema model,this paper modifies the thermodynamic model of the multicomponent alloy.The modified thermodynamic models are written into a software by Matlab and this paper studies the thermodynamic properties and influencing factors of the multicomponent magnesium alloy with this software.Miedema model is the most mature semi-empirical thermodynamic model and can predict formation enthalpies of many binary alloys.The thermodynamic data of multi-magnesium alloys can be extrapolated by extended models from Miedema model,such as Chou model.However,the prediction error of Miedema model effects its computing accuracy.Besides,the error accumulation of extended Miedema model can also effect the computing accuracy of calculated results of multi-magnesium alloys.This paper revises the electronegativity parameters and introduces the size factor to modify the Miedema model.The results show that the calculated values of the modified Miedema model are more consistent with experimental results than that of the original Miedema model.Extended form the modified Miedema model,the ternary Chou model to predict the thermodynamic properties such as enthalpies,excess entropies,excess free energies and activities of ternary magnesium alloys.A new deviation function is introduced to extend the ternary Chou model to obtain a new quaternary geometric model.In this paper,the modified thermodynamic models are written into a software by Matlab.The software can be used to calculate the thermodynamic properties of various binary,ternary and quaternary alloys in different states.In addition,the software can output the diagram of the relationship between the thermodynamic property and composition.Firstly,this paper explores the effect of Zr addition on the precipitation behavior of Mg-6Zn-xZr(x=0?0.6 wt%)ternary alloys with the help of the thermodynamic software.The calculation results show that the addition of Zr can thermodynamically hinder the nucleation of Mg₇Zn₃,MgZn₂ and MgZn strengthened phases,and can also kinetically hinder the growth of these strengthened phases.After thermodynamic calculation,the precipitation temperature of MgZn phase is predicted to be 308?.The calculation result is consistent with the experimental result in the literature.Secondly,the thermodynamic properties of the Mg-Zn-Gd-Y and Mg-Zn-Zr-Y quaternary alloys are calculated in this paper.The thermodynamic properties of the Mg-Zn-Gd-Y quaternary alloys are calculated by the thermodynamic software and verified by literature reports.The consistency between the literature reports and the prediction results verified the applicability of the modified model in the multiple magnesium alloys and the accuracy of the software calculations.The influence of the change in Y/Zn content ratio on the thermal stability and precipitation behavior of Mg-Zn-Zr-Y quaternary alloys and its thermodynamic mechanism are explored.The results obtained in this paper can provide reference guidance for the design of multiple magnesium alloys in the future.