Study On Interaction Function And Thermodynamics Of Phase Transformation In Al-Mg-Mn-Zr-Er Alloy

Because of special physical and chemical properties, minor elements Er, Zr added into Al-Mg alloys that have a great interaction with other main alloying elements have improved the structure and mechanical properties of Al-Mg alloys. Thermodynamic properties and valence electron structure of Al-Mg alloys were calculated based on revised Miedema model and empirical electron theory (EET) in solid, and analyse and explore mutual interaction energy bewteen elements, and the effect of Er on the phase transformation thermodynamica of Al-Mg-Mn-Zr-Er alloy system, focus on thermodynamic property and forming mechanism of binary and ternary intermetallic compound.Electronegative parameter and size difference factor of rare-earth elements were modified based on fully considering sepcial properties, and mixing enthalpy of Al-rare earth alloys system and formation enthalpy of partly binary intermetallic compounds were calculated. Compared the results calculated by classical Miedema model and modified Miedema model, the calculating error can be reduced from 36% to 3.5%. According to the relationship between bond property and formation enthalpy, bond conbination in most of binary intermetallic compounds of Al-Re with formation enthalpy from -40KJ/mol to 60KJ/mol are co-valence bond. Those high reliable datas could be added into MTDATA database to supply necessary thermodynamic data for alloy design.Interaction energy equation between alloy elements in solution model was modified in view of physical property of actual solution model, and was used to calculaiton interaction energy between two and three elements in Al-Mg-Mn-Zr-Er alloys system the results show that interaction energy of Al-Er is the most negative that indicate a strong interaction and a great tendency to segregate between Al and Er. Ternary interaction energy of Al-Mg-Mn, Al-Mg-Er, Al-Mg-Zr and Al-Zr-Er are also calculated, and the value for Al-Zr-Er is the most negative. And formation enthalpy of ternary intermetallic compounds based on extended Miedema model was calculated,Al₃(Zr1-xErx) with the most negative formation enthalpy has the greatest tendency to form, which was in accord with experimental result. DSC experimental results show that Er element improve the high temperature stability due to thermodynamic property of Al₃Er phase is stable. The Al₃Er phase start to melt when the temperature is up to 810℃, and dissolution activation energy is near 90-123KJ/mol, Al₃Er has a higher stability compared to Al₃Sc calculated by MTDADA software.According to empirical electron theory (EET) in solid , valence electron structure of prue Al and Er, Al₃Er, Al-Er solid solution, together with Al-Mg-Zr-Er alloy were calculated, the result shows that hybital level of pure crystal cell for Al and Er are on the fourth, and the valence electron number of most strongest bond Al-Er is 3.5798 in Al₃Er cell. Also Al₃Er,Al₃Zr,Al₃(Zr_xEr_1-x) were calculated , mainly focus on the effect of Er on valence electron structure of Al-Mg-Zr alloy system and Al₃(Zr_xEr_1-x). The results show that as the content of Zr is on the rise, the value of nA for Al₃(Zr_xEr_1-x) decrease step by step, whereas the value ofρincrease firstly and decrease later, which indicate that adding of Zr does good to improve comprehensive mechanical property, and strength and plastic match well when the content of Zr in Al₃(Zr_xEr_1-x) is 8.0at.%. Phase structure forming factor S is on the decrease, which show that Al₃Er has priority to precipitate during solidification and Al₃(Zr_xEr_1-x)and Al₃Zr precipitate in the process of heattreatment, which play an important role on improving alloy comprehensive mechanical property.