Double-layer oxide film defect evolution rule research method under thermal-dynamic constraint condition in aluminum alloy casting process

Abstract

The invention relates to the field of aluminum alloy casting, in particular to a double-layer oxidation film defect evolution rule research method under the thermal-dynamic constraint condition in the aluminum alloy casting process, which comprises the following steps: step 1, obtaining a multi-scale double-layer oxidation film defect organization structure and a distribution rule thereof; 2, the movement behavior of the double-layer oxide film defects in the liquid / semi-solid melt is determined; 3, a defect evolution mechanism of the double-layer oxidation film in the solidification process. The method has the following beneficial effects that the coupling relation between the defect feature morphology of the double-layer oxidation film and the thermodynamic forming condition of the double-layer oxidation film is analyzed, and the relevance between the defects of the multi-scale double-layer oxidation film and a casting partition structure is clarified; the cooperative relationship between the deformation rule and the motion trail of the double-layer oxide film defect in the liquid / semi-solid melt is disclosed, and the motion behavior of the defect in the flow field is clarified; the relevance between the double-layer oxide film defect and the air hole and the shrinkage cavity is clarified, and the dynamic evolution mechanism of the double-layer oxide film defect in the solidification process is clarified.

Description

Technical Field

[0001] The invention relates to a method for studying the evolution law of double-layer oxide film defects under thermal-dynamic constraints in an aluminum alloy casting process, and belongs to the field of aluminum alloy casting. Background Art

[0002] The rapid development of the aerospace field has put forward increasingly stringent requirements on the metallurgical quality and service performance of complex aluminum / magnesium alloy components. Therefore, defect control in the casting process has become the primary research target of researchers. Although the formation and control of traditional casting defects such as cracks, segregation, pores, stress concentration and deformation, inclusions, shrinkage cavities, etc. have been quite mature and recognized by the industry so far. However, there is still a large gap between the performance of castings and the theoretical performance limit of alloys. In recent years, with the advancement of detection technology, a form of non-wetting and non-metallurgical oxide film overlap structural defects (professor John Campbell of the University of Birmingham in the UK calls it a double-layer oxide film) is gradually coming into people's sight. This defect is formed in the casting filling stage and seriously damages the comprehensive mechanical properties of the casting, especially in the important load-bearing parts of aluminum and magnesium alloy thin-walled complex castings such as aircraft engine housings and space satellite hydrazine bottle brackets. The double-layer oxide film defect has become one of the potential sources of sudden failure during the service of castings.

[0003] It has become a consensus among researchers that the direct cause of the double-layer oxide film defect is the detachment of the molten oxide film from the initial surface position due to surface turbulence and droplet splashing during the filling process. In fact, the entrained oxide film, as the precursor of the double-layer oxide film defect, folds and deforms and overlaps each other under the coupling of subsequent flow and solidification, and its final shape determines the degree of influence of this type of defect on the mechanical properties of the casting. However, current research focuses on the instantaneous moment of the entrainment process, and rarely involves the subsequent dynamic transformation behavior of the double-layer oxide film defect during the filling and solidification process. There is still a lack of systematic understanding of how the complete process of the double-layer oxide film defect from detaching from the melt surface to becoming a metallurgical defect of the casting, the coupled thermal-dynamic organizational structure and characteristic morphology of the double-layer oxide film defect, and the displacement deformation of the double-layer oxide film defect under the synergy of flow field and temperature field affect the formation process of the double-layer oxide film defect. Summary of the invention

[0004] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a method for studying the evolution law of double-layer oxide film defects under thermal-dynamic constraints during aluminum alloy casting, so as to solve the problems raised in the above background technology.

[0005] In order to achieve the above object, the present invention is implemented by the following technical scheme: a method for studying the evolution law of double-layer oxide film defects under thermal-dynamic constraints during aluminum alloy casting, comprising the following steps:

[0006] Step 1: Multi-scale double-layer oxide film defect structure and its distribution law;

[0007] Based on thermodynamic calculations and high-precision analysis of defect microstructures, the influence of alloying elements on the defect composition and phase structure of double-layer oxide films is studied, the thermodynamic conditions for their formation are revealed, and the relationship between the film composition and the defect morphology of double-layer oxide films is clarified;

[0008] Combining casting zoning anatomy and defect multi-dimensional characterization, the spatial relationship between different types of double-layer oxide film defects and casting structure is revealed by analyzing the correlation between multi-scale double-layer oxide film characteristics and defect interval distribution laws. The final state of double-layer oxide film defects and the coupling relationship between their existence positions are studied to lay the foundation for the analysis of subsequent motion evolution processes.

[0009] Step 2: Movement behavior of double-layer oxide film defects in liquid / semi-solid melts;

[0010] Through free liquid surface calculation simulation, the agglomeration characteristics of double-layer oxide film defects during the liquid melt filling flow process are studied, and their deformation and fragmentation are analyzed to reveal the deformation law of double-layer oxide film defects in liquid melt;

[0011] Carry out numerical simulation of rigid particle tracer particles, and study the motion trajectory of double-layer oxide film defects based on fluid-solid coupling by adjusting the size and shape of double-layer oxide film defects, and analyze the influence of defect structure on motion behavior under the same flow field conditions;

[0012] Combined with the viscosity of the melt solidification process and the change of the solid / liquid phase ratio in the mushy zone, the hindering effect of the semi-solid melt on the movement of the pre-set double-layer oxide film defects is studied, and the coupling relationship between the deformation law and the movement trajectory of the double-layer oxide film defects is clarified;

[0013] Step 3: Evolution mechanism of double oxide film defects during solidification;

[0014] Based on the detection of the mechanical properties of the surface oxide film at different temperatures of the melt, the corresponding relationship between it and the structure and thickness of the oxide film is established, and the evolution law of the mechanical properties of the surface oxide film during the cooling process of the melt from liquid to semi-solid is explained, providing data support for the subsequent study of the evolution of double-layer oxide film defects;

[0015] The deformation behavior of double-layer oxide film defects with different properties under different solidification tensile forces was studied, and the influence of dendrite arm spacing on the deformation process of double-layer oxide film defects was analyzed by adding grain refiners, and the relationship between double-layer oxide film defects and shrinkage cavities was clarified.

[0016] By adjusting the melt purification measures, the effect of gas precipitation during solidification on the expansion volume of the air gap in the double-layer oxide film defect is studied, the connection between the defect and the pores is clarified, and finally a double-layer oxide film defect evolution model under the coupling of solidification shrinkage and gas precipitation is established.

[0017] Specifically, in step 1, the composition of double-layer oxide film defects in different aluminum / magnesium alloys is analyzed by theoretical calculation or Thermo-Calc thermodynamic calculation software; while SEM and TEM analysis and verification are performed, the relationship between the composition / phase structure of the double-layer oxide film and the characteristic morphology of multi-scale defects is revealed, and the formation process of such defects and their influencing factors are analyzed from the perspective of alloy composition;

[0018] Defective samples of aluminum / magnesium alloys with different alloy compositions were cast, and a comprehensive anatomical analysis was performed on the scrapped castings provided by relevant cooperative units to obtain the distribution of double-layer oxide film defects in different parts of the castings. At the same time, SEM and 3D-CT analysis and testing methods were used to analyze the characteristics of double-layer oxide film defects at different scales, and the correspondence between the structure, size, morphology and distribution law of double-layer oxide film defects in actual castings was obtained, which provided modeling data support and a basis for in-depth optimization of the model for subsequent research on the dynamic formation process of double-layer oxide film defects.

[0019] Specifically, in the step 2, the VOF model and melt free surface tracking model of ANSYS Fluent or Flow-3D software are used to analyze the defect movement of the double-layer oxide film defect in the liquid melt filling flow field under different cross-sectional structures (sudden change / gradual change, shunt / merge), different liquid surface merging conditions (simultaneous / differential), different filling speeds (laminar / turbulent) and other parameters, clarify the agglomeration, fragmentation, and deformation process, and explain the movement and deformation law of the double-layer oxide film defect;

[0020] Double-layer oxide film defects of different sizes and shapes were designed, and the motion trajectory of the defect in the flow field was simulated using ANSYS fluid-solid coupling. At the same time, the motion of the tracer particles of rigid particles was simulated to compare the influence of the characteristic structure of the double-layer oxide film defect on the motion trajectory.

[0021] According to the changes in melt viscosity of different alloys and at different temperatures, the influence of solidification temperature gradient on the movement trajectory of double-layer oxide film defects is studied. At the same time, a mushy zone model with different solid / liquid phase ratios is built to simulate the movement of double-layer oxide film defects through semi-solid melts under different conditions. Finally, the correlation between the movement behavior of double-layer oxide film defects and the final staying position is obtained. The correctness of the simulation results is judged by comparing with the double-layer oxide film defects in actual castings.

[0022] Specifically, in step 3, the linear tensile method or the disk torsion method is used to detect the tensile and shear mechanical properties of the oxide film on the surface of the melt with different compositions and different temperatures. The two methods are used together to analyze the comprehensive mechanical properties of the oxide layer under different states, and the corresponding relationship of "structure / thickness-mechanical properties" of the double-layer oxide film defect is established, providing data support for the evolution behavior of the double-layer oxide film defect during the solidification process;

[0023] Based on the LAMMPS implementation of molecular dynamics simulation, a deformation model of double-layer oxide film defects under different solidification tensile forces was established to obtain the interface bonding strength between the defect and the substrate. Combined with the measured mechanical properties of the double-layer oxide film defects, the cohesive force model of COMSOL software was used to analyze its fracture under solidification tensile force. Finally, with the use of grain refiners, the relationship between the dendrite arm spacing and the micro-scale displacement / deformation of the double-layer oxide film defects was revealed. SEM / EDS and TEM were used to verify the above simulation results and the correlation between the double-layer oxide film defects and shrinkage cavities.

[0024] A gas absorption expansion model of double-layer oxide film defects is established, and the melt gas content is adjusted by changing the type and content of refining agents to clarify the relationship between double-layer oxide film defects and pores. Finally, the synergistic effects of solidification shrinkage tension and melt gas precipitation on double-layer oxide film defects are analyzed to clarify the evolution mechanism of double-layer oxide film defects during the solidification process.

[0025] Beneficial effects of the present invention:

[0026] The dynamic formation mechanism of double-layer oxide film defects is taken as the research object to clarify the causes of sudden failure of key load-bearing parts of complex aluminum / magnesium alloy components during service.

[0027] Clarify the coupling relationship between multi-scale double-layer oxide film defects and partitioned casting structure, analyze the influence of filling flow field and solidification temperature field on the movement and evolution of double-layer oxide film defects, reveal the displacement and deformation behavior of double-layer oxide film defects in liquid / semi-solid melt, and construct a correlation model between double-layer oxide film defects and shrinkage holes and pores.

[0028] The coupling relationship between the characteristic morphology of double-layer oxide film defects and their thermodynamic formation conditions is analyzed, and the correlation between multi-scale double-layer oxide film defects and the partition structure of castings is clarified.

[0029] Reveal the synergistic relationship between the deformation law and motion trajectory of double-layer oxide film defects in liquid / semi-solid melts, and clarify the movement behavior of defects in the flow field.

[0030] Clarify the correlation between double-layer oxide film defects and pores and shrinkage holes, and explain the dynamic evolution mechanism of double-layer oxide film defects during solidification.

[0031] The research results can provide theoretical guidance and experimental support for the near-zero defect and performance limit optimization of castings. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0033] Figure 1 It is a technical roadmap of the method for studying the evolution law of double-layer oxide film defects under the thermal-dynamic constraint conditions in the aluminum alloy casting process of the present invention;

[0034] Figure 2 Schematic diagram of 3D-CT analysis of the sample;

[0035] Figure 3 Schematic diagram of molecular dynamics simulation; DETAILED DESCRIPTION

[0036] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the present invention is further explained below in conjunction with specific implementation methods.

[0037] See also Figure 1-Figure 3 The present invention provides a technical solution: a method for studying the evolution law of double-layer oxide film defects under thermal-dynamic constraints during aluminum alloy casting, comprising the following steps:

[0038] Step 1: Multi-scale double-layer oxide film defect structure and its distribution law;

[0039] Based on thermodynamic calculations and high-precision analysis of defect microstructures, the influence of alloying elements on the defect composition and phase structure of double-layer oxide films is studied, the thermodynamic conditions for their formation are revealed, and the relationship between the film composition and the defect morphology of double-layer oxide films is clarified;

[0040] Combining casting zoning anatomy and defect multi-dimensional characterization, the spatial relationship between different types of double-layer oxide film defects and casting structure is revealed by analyzing the correlation between multi-scale double-layer oxide film characteristics and defect interval distribution laws. The final state of double-layer oxide film defects and the coupling relationship between their existence positions are studied to lay the foundation for the analysis of subsequent motion evolution processes.

[0041] Step 2: Movement behavior of double-layer oxide film defects in liquid / semi-solid melts;

[0042] Through free liquid surface calculation simulation, the agglomeration characteristics of double-layer oxide film defects during the liquid melt filling flow process are studied, and their deformation and fragmentation are analyzed to reveal the deformation law of double-layer oxide film defects in liquid melt;

[0043] Carry out numerical simulation of rigid particle tracer particles, and study the motion trajectory of double-layer oxide film defects based on fluid-solid coupling by adjusting the size and shape of double-layer oxide film defects, and analyze the influence of defect structure on motion behavior under the same flow field conditions;

[0044] Combined with the viscosity of the melt solidification process and the change of the solid / liquid phase ratio in the mushy zone, the hindering effect of the semi-solid melt on the movement of the pre-set double-layer oxide film defects is studied, and the coupling relationship between the deformation law and the movement trajectory of the double-layer oxide film defects is clarified;

[0045] Step 3: Evolution mechanism of double oxide film defects during solidification;

[0046] Based on the detection of the mechanical properties of the surface oxide film at different temperatures of the melt, the corresponding relationship between it and the structure and thickness of the oxide film is established, and the evolution law of the mechanical properties of the surface oxide film during the cooling process of the melt from liquid to semi-solid is explained, providing data support for the subsequent study of the evolution of double-layer oxide film defects;

[0047] The deformation behavior of double-layer oxide film defects with different properties under different solidification tensile forces was studied, and the influence of dendrite arm spacing on the deformation process of double-layer oxide film defects was analyzed by adding grain refiners, and the relationship between double-layer oxide film defects and shrinkage cavities was clarified.

[0048] By adjusting the melt purification measures, the effect of gas precipitation during solidification on the expansion volume of the air gap in the double-layer oxide film defect is studied, the connection between the defect and the pores is clarified, and finally a double-layer oxide film defect evolution model under the coupling of solidification shrinkage and gas precipitation is established.

[0049] In step 1, the composition of double-layer oxide film defects in different aluminum / magnesium alloys is analyzed by theoretical calculation or Thermo-Calc thermodynamic calculation software; while SEM and TEM analysis and verification are performed, the relationship between the composition / phase structure of the double-layer oxide film and the characteristic morphology of multi-scale defects is revealed, and the formation process of such defects and their influencing factors are analyzed from the perspective of alloy composition;

[0050] Defective samples of aluminum / magnesium alloys with different alloy compositions were cast, and a comprehensive anatomical analysis was performed on the scrapped castings provided by relevant cooperative units to obtain the distribution of double-layer oxide film defects in different parts of the castings. At the same time, SEM and 3D-CT analysis and testing methods were used to analyze the characteristics of double-layer oxide film defects at different scales, and the correspondence between the structure, size, morphology and distribution law of double-layer oxide film defects in actual castings was obtained, which provided modeling data support and a basis for in-depth optimization of the model for subsequent research on the dynamic formation process of double-layer oxide film defects.

[0051] In step 2, the VOF model and melt free surface tracking model of ANSYS Fluent or Flow-3D software are used to analyze the defect movement of the double-layer oxide film defect in the liquid melt filling flow field under different cross-sectional structures (sudden change / gradual change, flow separation / confluence), different liquid surface confluence conditions (simultaneous / differential), different filling speeds (laminar / turbulent) and other parameters, clarify its agglomeration, fragmentation, and deformation process, and explain the movement and deformation law of the double-layer oxide film defect;

[0052] Double-layer oxide film defects of different sizes and shapes were designed, and the motion trajectory of the defect in the flow field was simulated using ANSYS fluid-solid coupling. At the same time, the motion of the tracer particles of rigid particles was simulated to compare the influence of the characteristic structure of the double-layer oxide film defect on the motion trajectory.

[0053] According to the changes in melt viscosity of different alloys and at different temperatures, the influence of solidification temperature gradient on the movement trajectory of double-layer oxide film defects is studied. At the same time, a mushy zone model with different solid / liquid phase ratios is built to simulate the movement of double-layer oxide film defects through semi-solid melts under different conditions. Finally, the correlation between the movement behavior of double-layer oxide film defects and the final staying position is obtained. The correctness of the simulation results is judged by comparing with the double-layer oxide film defects in actual castings.

[0054] In step 3, the linear tensile method or the disk torsion method is used to detect the tensile and shear mechanical properties of the oxide film on the surface of the melt with different compositions and temperatures. The two methods are used together to analyze the comprehensive mechanical properties of the oxide layer under different conditions, and the corresponding relationship of "structure / thickness-mechanical properties" of the double-layer oxide film defect is established, providing data support for the evolution behavior of the double-layer oxide film defect during the solidification process;

[0055] Based on the LAMMPS implementation of molecular dynamics simulation, a deformation model of double-layer oxide film defects under different solidification tensile forces was established to obtain the interface bonding strength between the defect and the substrate. Combined with the measured mechanical properties of the double-layer oxide film defects, the cohesive force model of COMSOL software was used to analyze its fracture under solidification tensile force. Finally, with the use of grain refiners, the relationship between the dendrite arm spacing and the micro-scale displacement / deformation of the double-layer oxide film defects was revealed. SEM / EDS and TEM were used to verify the above simulation results and the correlation between the double-layer oxide film defects and shrinkage cavities.

[0056] A gas absorption expansion model of double-layer oxide film defects is established, and the melt gas content is adjusted by changing the type and content of refining agents to clarify the relationship between double-layer oxide film defects and pores. Finally, the synergistic effects of solidification shrinkage tension and melt gas precipitation on double-layer oxide film defects are analyzed to clarify the evolution mechanism of double-layer oxide film defects during the solidification process.

[0057] Taking the dynamic formation mechanism of double-layer oxide film defects as the research object, the causes of sudden failure in the service process of key load-bearing parts of complex aluminum / magnesium alloy components are elucidated; the coupling relationship between multi-scale double-layer oxide film defects and partitioned casting structure is clarified, the influence of filling flow field and solidification temperature field on the movement and evolution of double-layer oxide film defects is analyzed, the displacement and deformation behavior of double-layer oxide film defects in liquid / semi-solid melt is revealed, and a correlation model between double-layer oxide film defects and shrinkage cavities and pores is constructed; the coupling relationship between the characteristic morphology of double-layer oxide film defects and their thermodynamic formation conditions is analyzed, and the correlation between multi-scale double-layer oxide film defects and the partitioned structure of castings is clarified; the synergistic relationship between the deformation law and motion trajectory of double-layer oxide film defects in liquid / semi-solid melt is revealed, and the motion behavior of defects in the flow field is clarified; the correlation between double-layer oxide film defects and pores and shrinkage cavities is clarified, and the dynamic evolution mechanism of double-layer oxide film defects in the solidification process is explained. The research results can provide theoretical guidance and experimental support for near-zero defects and performance limit optimization of castings.

[0058] Although this specification is described according to implementation modes, not every implementation mode includes only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A method for studying the evolution of double-layer oxide film defects under thermal-dynamic constraints during aluminum alloy casting, characterized by The following steps are involved: Step 1: Multi-scale double-layer oxide film defect structure and its distribution law; Based on thermodynamic calculations and high-precision analysis of defect microstructures, the influence of alloying elements on the defect composition and phase structure of double-layer oxide films is studied, the thermodynamic conditions for their formation are revealed, and the relationship between the film composition and the defect morphology of double-layer oxide films is clarified; Combining casting zoning anatomy and defect multi-dimensional characterization, the spatial relationship between different types of double-layer oxide film defects and casting structure is revealed by analyzing the correlation between multi-scale double-layer oxide film characteristics and defect interval distribution laws. The final state of double-layer oxide film defects and the coupling relationship between their existence positions are studied to lay the foundation for the analysis of subsequent motion evolution processes. Step 2: Movement behavior of double-layer oxide film defects in liquid / semi-solid melts; Through free liquid surface calculation simulation, the agglomeration characteristics of double-layer oxide film defects during the liquid melt filling flow process are studied, and their deformation and fragmentation are analyzed to reveal the deformation law of double-layer oxide film defects in liquid melt; Carry out numerical simulation of rigid particle tracer particles, and study the motion trajectory of double-layer oxide film defects based on fluid-solid coupling by adjusting the size and shape of double-layer oxide film defects, and analyze the influence of defect structure on motion behavior under the same flow field conditions; Combined with the viscosity of the melt solidification process and the change of the solid / liquid phase ratio in the mushy zone, the hindering effect of the semi-solid melt on the movement of the pre-set double-layer oxide film defects is studied, and the coupling relationship between the deformation law and the movement trajectory of the double-layer oxide film defects is clarified; Step 3: Evolution mechanism of double oxide film defects during solidification; Based on the detection of the mechanical properties of the surface oxide film at different temperatures of the melt, the corresponding relationship between it and the structure and thickness of the oxide film is established, and the evolution law of the mechanical properties of the surface oxide film during the cooling process of the melt from liquid to semi-solid is explained, providing data support for the subsequent study of the evolution of double-layer oxide film defects; The deformation behavior of double-layer oxide film defects with different properties under different solidification tensile forces was studied, and the influence of dendrite arm spacing on the deformation process of double-layer oxide film defects was analyzed by adding grain refiners, and the relationship between double-layer oxide film defects and shrinkage cavities was clarified. By adjusting the melt purification measures, the effect of gas precipitation during solidification on the expansion volume of the air gap in the double-layer oxide film defect is studied, the connection between the defect and the pores is clarified, and finally a double-layer oxide film defect evolution model under the coupling of solidification shrinkage and gas precipitation is established.

2. The method for studying the evolution law of double-layer oxide film defects under thermal-dynamic constraints in aluminum alloy casting according to claim 1, characterized in that: In step 1, the composition of double-layer oxide film defects in different aluminum / magnesium alloys is analyzed by theoretical calculation or Thermo-Calc thermodynamic calculation software; while SEM and TEM analysis and verification are performed, the relationship between the composition / phase structure of the double-layer oxide film and the characteristic morphology of multi-scale defects is revealed, and the formation process of such defects and their influencing factors are analyzed from the perspective of alloy composition; Defective samples of aluminum / magnesium alloys with different alloy compositions were cast, and a comprehensive anatomical analysis was performed on the scrapped castings provided by relevant cooperative units to obtain the distribution of double-layer oxide film defects in different parts of the castings. At the same time, SEM and 3D-CT analysis and testing methods were used to analyze the characteristics of double-layer oxide film defects at different scales, and the correspondence between the structure, size, morphology and distribution law of double-layer oxide film defects in actual castings was obtained, which provided modeling data support and a basis for in-depth optimization of the model for subsequent research on the dynamic formation process of double-layer oxide film defects.

3. The method for studying the evolution law of double-layer oxide film defects under thermal-dynamic constraints in the aluminum alloy casting process according to claim 1, characterized in that: In the step 2, the VOF model and melt free surface tracking model of ANSYS Fluent or Flow-3D software are used to analyze the defect movement of the double-layer oxide film defect in the liquid melt filling flow field under different cross-sectional structures (sudden change / gradual change, shunt / merge), different liquid surface merging conditions (simultaneous / differential), different filling speeds (laminar / turbulent) and other parameters, clarify the agglomeration, fragmentation, and deformation process, and explain the movement and deformation law of the double-layer oxide film defect; Double-layer oxide film defects of different sizes and shapes were designed, and the motion trajectory of the defect in the flow field was simulated using ANSYS fluid-solid coupling. At the same time, the motion of the tracer particles of rigid particles was simulated to compare the influence of the characteristic structure of the double-layer oxide film defect on the motion trajectory. According to the changes in melt viscosity of different alloys and at different temperatures, the influence of solidification temperature gradient on the movement trajectory of double-layer oxide film defects is studied. At the same time, a mushy zone model with different solid / liquid phase ratios is built to simulate the movement of double-layer oxide film defects through semi-solid melts under different conditions. Finally, the correlation between the movement behavior of double-layer oxide film defects and the final staying position is obtained. The correctness of the simulation results is judged by comparing with the double-layer oxide film defects in actual castings.

4. The method for studying the evolution law of double-layer oxide film defects under thermal-dynamic constraints in aluminum alloy casting process according to claim 1, characterized in that: In step 3, the tensile and shear mechanical properties of the oxide film on the surface of the melt with different compositions and different temperatures are detected by a linear tensile method or a disk torsion method. The two methods are used together to analyze the comprehensive mechanical properties of the oxide layer under different conditions, and establish a corresponding relationship between the "structure / thickness-mechanical properties" of the double-layer oxide film defect, so as to provide data support for the evolution behavior of the double-layer oxide film defect during the solidification process; Based on the LAMMPS implementation of molecular dynamics simulation, a deformation model of double-layer oxide film defects under different solidification tensile forces was established to obtain the interface bonding strength between the defect and the substrate. Combined with the measured mechanical properties of the double-layer oxide film defects, the cohesive force model of COMSOL software was used to analyze its fracture under solidification tensile force. Finally, with the use of grain refiners, the relationship between the dendrite arm spacing and the micro-scale displacement / deformation of the double-layer oxide film defects was revealed. SEM / EDS and TEM were used to verify the above simulation results and the correlation between the double-layer oxide film defects and shrinkage cavities. A gas absorption expansion model of double-layer oxide film defects is established, and the melt gas content is adjusted by changing the type and content of refining agents to clarify the relationship between double-layer oxide film defects and pores. Finally, the synergistic effects of solidification shrinkage tension and melt gas precipitation on double-layer oxide film defects are analyzed to clarify the evolution mechanism of double-layer oxide film defects during the solidification process.

Images