Phase Diagram Of The Al-Mg-Si-M(M=Er/Zr/Y) Ternary System And Its Thermodynamic Description

With the improvement of science and technology,research related to new high performance aluminium alloys has ushered in a new era.New high-performance aluminium alloys are widely used for their excellent performance,especially in high-end fields such as aerospace,effectively promoting the development of social and economic development.Of course,the requirements for high-strength aluminium alloys in the high-tech sector are getting higher and higher,so there is still a need for continuous development and research into new high-performance aluminium alloys.It is a very important structural material in modern society.After a lot of research by the majority of material scientists,it has been shown that micro-alloying to improve the strength of aluminium alloys is a very effective method,especially when the added alloying elements form a thermodynamically stable L1₂-Al₃M ordered phase structure with Al,the strengthening effect is better.Therefore,a basic study of high performance aluminium alloys based on the L1₂-Al₃（Er Zr）strengthened phase was done to complete the collection of thermodynamic data on the ternary systems Al-Mg-Er,Al-Zr-Er and Al-Si-Y to obtain the phase diagram of the ternary system Al-Mg-Si-M（M=Er/Zr/Y）.Further exploratory work was then carried out by combining phase diagram calculations with experiments.In this paper,the isothermal phase diagrams and vertical cross-section phase diagrams of the ternary systems Al-Mg-Er,Al-Zr-Er and Al-Si-Y are investigated in depth,and finally the design of high-performance Al-Mg-Er-Zr series alloys is based on the establishment of the Al-Mg-Er-Zr thermodynamic database,and the research can be divided into the following three parts:（1）Based on literature research,the thermodynamic parameters of the Al-Mg-Er and Al-Zr-Er ternary systems were collected and a thermodynamic database was established to obtain the relevant binary phase diagrams of the Al-Mg-Er and Al-Zr-Er systems,as well as the phase diagrams of the isothermal and vertical cross-sections of the Al-Mg-Er ternary system.The alloys were prepared by melting and annealing,and their phases were analysed according to XRD,SEM/EDS and EPMA characterisation results,and the phase equilibria and solid solution zones of the Al-Zr-Er system at 500°C were constructed.The annealed alloy in the vertical cross-section of the Al-Zr-Er ternary system was studied by using differential thermal analysis technique,and the analysis was carried out by DSC to complete the verification of the phase diagram of the vertical cross-section of the Al-Zr-Er alloy system,and then a complete thermodynamic database of the Al-Mg-Er-Zr alloy system was obtained.（2）The Al-Si-Y ternary alloy was prepared by the phase equilibrium alloy method,and the phase equilibrium of the Al-Si-Y system at 500°C was constructed by combining XRD,SEM and EPMA characterisation techniques to analyse the individual phases.Alloy samples in the Al-rich end phase region at x（Al）=0.9,0.8,0.7 and 0.6 vertical cross-sections were studied and the phase transition temperatures of representative alloys were obtained by DSC testing.The solidification organisation of the ternary alloys in the Al-Si-Y system in the Al-rich zone was analysed using backscatter diagrams（BSE）,EPMA-WDS and thermal analysis curves of the key alloy samples.Finally,it was found that the experimental point of phase transition temperature in the vertical cross-section was in general agreement with the results of the phase diagram data obtained from the calculation of the vertical cross-section,thus further verifying the accuracy of the thermodynamic database of the Al-rich end of the Al-Si-Y alloy system.（3）In this study,the Al-Mg-Er series alloys were designed on the basis of the establishment of the Al-Mg-Er thermodynamic database,and the alloy compositions with the best mechanical properties were obtained and verified by microstructural observations and mechanical property tests.The tensile strengths of both the cast and annealed alloy samples were the best when w（Er）=6%,with tensile strengths of 258.06MPa and 262.89 MPa respectively,and their alloy samples had the most uniform microscopic particle distribution,the finest eutectic organisation and the finest grain size,i.e.the best mechanical properties of the Al-5Mg-6Er alloy.Therefore,the Al-Mg-Er-Zr series alloys were designed based on the best mechanical properties obtained for the Al-Mg-Er series alloys.The tensile strength and elongation at break of the annealed alloy samples were the best when w（Zr）=5%,with an elongation at break of 22.57%and a tensile strength of 280.10 MPa,compared to the Al-5Mg-6Er alloy.The tensile strength was 6.55%higher than that of the Al-5Mg-6Er alloy.The microscopic particle distribution of the alloy samples was more uniform,with finer eutectic structure and finer grain size,i.e.the best mechanical properties of the Al-5Mg-1Er-5Zr alloy.The microscopic morphology and structure of the best alloy Al-5Mg-1Er-5Zr were further analysed.