Phase Diagram Determination And Thermodynamic Description Of Al-Si-Zr-Cu Partial System For Cast Al-Si Alloy

In recent years,regulations on exhaust gas emission have become increasingly stringent,leading to continuous improvement of the engine efficiency of automobiles,the high-temperature strength and heat-resistant fatigue properties of traditional cast Al-Si alloys are approached their limits currently,which can't meet the developed requirements of new high-power engines.Alloying is the significant approach to solve the insufficient high temperature performance of cast Al-Si alloys.Through the ways of solution strengthening,dispersion strengthening,eliminating high temperature metastable phase and improving microstructure,the property requirements for cast Al-Si alloys can be satisfied.However,excessive content of the alloying elements would form brittle phases and deteriorate the properties of the alloy.Therefore,the high temperature properties of the alloy can be improved homogeneously by adding an appropriate amount of alloying elements.The properties of the alloy have a close relationship with the phase diagram.The phase diagram shows the relations between the alloy composition and structure,intuitively,providing a theoretical basis for the quantitative research of materials design.At present,the CALculation of PHAse Diagram(CALPHAD)technique has been greatly developed based on experimental data.The CALPHAD technique can be used to calculate the phase composition and fraction of the multi-component material systems,simulate the structure evolution and phase transformation process,provide accurate and effective information for the research and development of Al-Si based alloys.In this paper,the balance alloy method is used to experimentally determine the partial regions of the Al-Si-Zr and Cu-Si-Zr ternary systems.The Al-Si-Zr and Cu-Si-Zr ternary systems are optimized by means of CALPHAD technique combined with the measured and reported literature information.Then,the thermodynamic database of Al-Si-Zr-Cu quaternary system is established,the thermodynamic properties of some alloys is calculated.The main research contents are as follows:(1)X-ray diffraction(XRD),scanning electron microscopy(SEM)and energy dispersive spectrometer(EDS)were used to determine the phase equilibria relations of the Zr-rich region of Al-Si-Zr ternary system at 973 and 1173 K in the present work.In the973K isothermal section,the AlZr₃+(Zr)+Si Zr₃ and AlZr₂+Al₂Zr₃ phase regions were measured;in the 1173 K isothermal section,the AlZr₃+(Zr)+Si Zr₃ and(Zr)+Si Zr₃ phase regions were determined.Combined with the measured and reported experimental data,a reliable thermodynamic assessment of the Al-Si-Zr ternary system was achieved and a set of self-consistent thermodynamic parameters was obtained as well.The calculated isothermal section at 773 K was experimentally determined and the three three-phase regions Al₂Zr+Al₃Zr+?Si Zr,Si Zr₃+(Zr)+Si Zr₃ and AlZr₂+Al₂Zr₃ are consistent with the optimization results.(2)The phase equilibria relations of Cu-Si-Zr ternary system(Si at.%<40%)at 1023and 1173 K were measured experimentally through XRD,SEM and EDS methods in the present work.In the 1023 K isothermal section,six three-phase regions Cu₁₀Zr₇+Cu₈Zr₃+Si Zr₂,(Cu)+?₅+?₆,?Cu₃₃Si₇+hcp+?₄,Cu₅Zr₇+CuZr₂+Si Zr₃,Cu₁₀Zr₇+Si Zr₂+Si Zr₃ and Cu₅₁Zr₁₄+Si₂Zr₃+?₆were measured;in the 1023 K isothermal section,four three-phase regions(Cu)+?₅+?₆,liquid+(Si)+?₁,Cu₅Zr₇+CuZr₂+Si Zr₃ and Cu₅₁Zr₁₄+Si₂Zr₃+?₆ were determined.Combined with the present and reported experimental information,the Cu-Si-Zr ternary system was assessed,the calculated results turned out to be in good agreement with the available experimental data.(3)According to the thermodynamic parameters of the Al-Cu-Si and Al-Cu-Zr ternary systems newly reported in the literature,combined with the thermodynamic parameters of the Al-Si-Zr and Cu-Si-Zr ternary systems calculated by this work.The thermodynamic database of Al-Si-Zr-Cu quaternary system was investigated,and the isothermal sections at973 and 1173 K composed of 4 ternary systems were reproduced.Total solid phase fraction in Scheil solidification simulation of Al-7Si-0.2Zr-2Cu and Al-7Si-4Zr-5Cu alloys,vertical sections of Al-7Si-5Zr-(0.6-3.5)Cu and Al-7Si-(5-10)Zr-11Cu alloys were calculated.In addition,the Eu-Ga binary system was thermodynamically optimized using CALPHAD technique through the experimental data reported in the relevant literature.In the Eu-Ga system,the substitutional solution and associate models were used for the liquid phase,the stoichiometric model were used for the compounds Eu Ga₂,Eu Ga₄,Eu Ga,Eu₂Ga₃,Eu₂Ga₅ and Eu₅Ga₃.The optimization results indicate that the associate model was more suitable for the Eu-Ga binary system than the substitutional solution model.