Research method of defect evolution law of double-layer oxide film under thermal-dynamic constraint condition in aluminum alloy casting process

Abstract

The present application relates to the field of aluminum alloy casting, and particularly relates to a method for studying evolution law of double-layer oxide film defects under thermal-dynamic constraint conditions in the process of aluminum alloy casting, which comprises the following steps: step 1: multi-scale double-layer oxide film defect organization structure and distribution law; step 2: movement behavior of double-layer oxide film defects in liquid / semi-solid melt; and step 3: evolution mechanism of double-layer oxide film defects in the process of solidification. The present application has the following beneficial effects: the coupling relationship between double-layer oxide film defect characteristic morphology and thermodynamic formation condition is analyzed, the relevance between multi-scale double-layer oxide film defects and casting partition structure is clarified; the synergistic relationship between deformation law and movement trajectory of double-layer oxide film defects in liquid / semi-solid melt is revealed, and the movement behavior of defects in flow field is clarified; the relevance between double-layer oxide film defects and pores and shrinkage holes is clarified, and the dynamic evolution mechanism of double-layer oxide film defects in the process of solidification is clarified.

Description

TECHNICAL FIELD

[0001] The application is a method for researching the evolution law of double-layer oxide film defects under the constraints of thermal dynamics in the aluminum alloy casting process, belonging to the field of aluminum alloy casting. BACKGROUND

[0002] The rapid development of the aerospace field puts increasingly stringent requirements on the metallurgical quality and service performance of aluminum / magnesium alloy complex components, and defect control in the casting process has therefore become the primary research object of researchers. Although so far, the formation and control of traditional casting defects such as cracks, segregation, pores, stress concentration and deformation, inclusions, shrinkage holes, etc. have been quite mature and recognized by the industry. However, there is still a big gap between the performance of the casting and the theoretical performance limit of the alloy. In recent years, with the progress of detection technology, a form of mutually non-wetting, non-metallurgical bonding oxide film lap joint defect (Professor John Campbell of the University of Birmingham in the United Kingdom calls it double-layer oxide film) is gradually coming into people's sight. This defect is formed during 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 satellite hydrazine bottle supports. Double-layer oxide film defects have become one of the potential sources of sudden failure during the service of the casting.

[0003] The direct cause of the double-layer oxide film defect is the separation of the melt oxide film from the initial surface position due to surface turbulence and droplet splashing during the filling process, which has become the consensus of researchers. In fact, the involved oxide film as the precursor of the double-layer oxide film defect folds and deforms under the subsequent coupling of flow and solidification, and its final morphology determines the influence of this type of defect on the mechanical properties of the casting. However, current researches are mostly focused on the instant occurrence of the rolling-in process, and there is little involvement in the subsequent dynamic transformation behavior of the double-layer oxide film defect during the filling and solidification process. The complete process from the separation of the double-layer oxide film defect from the melt surface to the formation of the metallurgical defect, the coupled thermal-dynamic structure and characteristic morphology of the double-layer oxide film defect, and how the displacement deformation of the double-layer oxide film defect under the coordination of the flow field and the temperature field affects the formation process of the double-layer oxide film defect, still lack systematic understanding. SUMMARY

[0004] In view of the deficiencies in the prior art, the purpose of the present application is to provide a method for researching the evolution law of double-layer oxide film defects under the constraints of thermal dynamics in the aluminum alloy casting process, in order to solve the problems raised in the background art.

[0005] In order to achieve the above-mentioned purpose, the present application is realized by the following technical scheme: a method for researching the evolution law of double-layer oxide film defects under the constraints of thermal dynamics in the aluminum alloy casting process, comprising the following steps:

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

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

[0008] Combined with the partition dissection of castings and multi-dimensional characterization of defects, the correlation between multi-scale double-layer oxide film characteristics and defect interval distribution is analyzed, and the spatial relationship between different types of double-layer oxide film defects and the structure of the casting is revealed. Through the study of the coupling relationship between the final state and the location of double-layer oxide film defects, a foundation is laid for the analysis of the subsequent motion evolution process;

[0009] Step 2: Motion behavior of double-layer oxide film defects in liquid / semi-solid melt

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

[0011] Rigid particle tracer numerical simulation is carried out, and by adjusting the size and shape of double-layer oxide film defects, the motion trajectory of double-layer oxide film defects based on fluid-structure interaction is studied, and the influence of defect structure on motion behavior under the same flow field conditions is analyzed;

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

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

[0014] Based on the mechanical property detection of surface oxide film at different temperatures of the melt, the corresponding relationship between its mechanical properties and oxide film structure and thickness is established, and the evolution law of the mechanical properties of surface oxide film during the cooling process from liquid to semi-solid is clarified, 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 pulling forces is studied, and the influence of grain arm spacing on the deformation process of double-layer oxide film defects is analyzed by adding grain refiner, and the relationship between double-layer oxide film defects and shrinkage holes is clarified;

[0016] By adjusting the melt purification measures, the influence of the gas precipitation amount on the gas gap expansion volume of the double-layer oxide film defect in the solidification process was studied, the relationship between the defect and the gas hole was clarified, and finally the evolution model of the double-layer oxide film defect under the coupling action of solidification shrinkage and gas precipitation was established.

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

[0018] Defect samples of aluminum / magnesium alloys with different alloy compositions were cast, and related scrap castings provided by cooperative units were analyzed comprehensively to obtain the distribution of double-layer oxide film defects in different parts of the castings. Meanwhile, SEM and 3D-CT analysis methods were used to analyze the characteristics of double-layer oxide film defects of different scales, and the corresponding relationship between the structure, size, morphology and distribution of double-layer oxide film defects in actual castings was obtained, which provided modeling data support and model optimization basis for the subsequent research on the dynamic formation process of double-layer oxide film defects.

[0019] Specifically, in the step 2, ANSYS Fluent or Flow-3D software VOF model and melt free surface tracking model were used to analyze the movement of double-layer oxide film defects in liquid melt filling flow field under different cross-section structures (sudden change / gradual change, split / join), different liquid surface joining conditions (simultaneous / different times), and different filling velocities (laminar flow / turbulent flow), to clarify the aggregation, fragmentation and deformation process of the defects, and to clarify the movement and deformation rules of the double-layer oxide film defects;

[0020] Different sizes and shapes of double-layer oxide film defects were designed, and ANSYS fluid-structure interaction was used to simulate the movement trajectory of the defects in the flow field. At the same time, the tracer particle motion of rigid particles was simulated, and the influence of the characteristic structure of the double-layer oxide film defect on the movement trajectory was obtained by comparison;

[0021] According to the change of the melt viscosity of different alloys and different temperatures, the influence of the solidification temperature gradient on the movement trajectory of the double-layer oxide film defect was studied, and a paste zone model with different solid / liquid phase ratios was built to simulate the movement of the double-layer oxide film defect through different semi-solid melts. Finally, the correlation between the movement behavior of the double-layer oxide film defect and the final resting position was obtained, and the correctness of the simulation results was judged by comparing with the double-layer oxide film defect in actual castings.

[0022] Specifically, in the step 3, the tensile and shear mechanical properties of the surface oxide film of the melt with different components and at different temperatures are detected by using a linear stretching method or a disc torsion method, the comprehensive mechanical properties of the oxide layer in different states are analyzed by the two methods, the corresponding relationship between the double-layer oxide film defect and the mechanical properties of the structure / thickness is established, and data support is provided for the evolution behavior of the double-layer oxide film defect in the solidification process.

[0023] Based on the LAMMPS implementation of molecular dynamics simulation, a deformation model of the double-layer oxide film defect under different solidification tension is established, the interface bonding strength of the defect and the matrix is obtained, the fracture of the double-layer oxide film defect under the solidification tension is analyzed by using the COMSOL software cohesive force model, finally, the relationship between the grain arm spacing and the micro-displacement / deformation of the double-layer oxide film defect is revealed by using the grain refiner, and the simulation results and the correlation between the double-layer oxide film defect and the shrinkage hole are verified by using SEM / EDS and TEM.

[0024] An adsorption expansion model of the double-layer oxide film defect is established, the gas content of the melt is adjusted by changing the type and content of the refining agent, the relationship between the double-layer oxide film defect and the gas hole is clarified, and finally, the synergistic effect of the solidification shrinkage tension and the melt gas precipitation on the double-layer oxide film defect is analyzed, and the evolution mechanism of the double-layer oxide film defect in the solidification process is clarified.

[0025] The beneficial effects of the present application are as follows:

[0026] The dynamic formation mechanism of the double-layer oxide film defect is taken as the research object, and the sudden failure reason of the key load-bearing part of the complex aluminum / magnesium alloy component during the service process is clarified.

[0027] The coupling relationship between the multi-scale double-layer oxide film defect and the partitioned casting structure is clarified, the influence law of the filling flow field and the solidification temperature field on the movement and evolution of the double-layer oxide film defect is analyzed, the displacement and deformation behavior of the double-layer oxide film defect in the liquid / semi-solid melt is revealed, and the correlation model of the double-layer oxide film defect and the shrinkage hole and the gas hole is constructed.

[0028] The coupling relationship between the characteristic morphology of the double-layer oxide film defect and the thermodynamic formation condition is analyzed, and the correlation between the multi-scale double-layer oxide film defect and the partitioned structure of the casting is clarified.

[0029] The synergistic relationship between the deformation law and the movement trajectory of the double-layer oxide film defect in the liquid / semi-solid melt is revealed, and the movement behavior of the defect in the flow field is clarified.

[0030] The correlation between the double-layer oxide film defect and the gas hole and the shrinkage hole is clarified, and the dynamic evolution mechanism of the double-layer oxide film defect in the solidification process is clarified.

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

[0032] Other features, objects, and advantages of the application will become more apparent from the following detailed description of non-limiting embodiments, when read in conjunction with the accompanying drawings:

[0033] Fig. 1 A technical roadmap for the method for researching the evolution law of the double-layer oxide film defect under the thermal-dynamic constraint condition in the aluminum alloy casting process of the application;

[0034] Fig. 2 A schematic diagram for 3D-CT analysis of a sample;

[0035] Fig. 3 A schematic diagram for molecular dynamics simulation; DETAILED DESCRIPTION

[0036] In order to make the technical means, creative features, purposes and effects achieved by the application easy to understand, the application is further described below in conjunction with specific embodiments.

[0037] Please refer to Figs. 1-3 The application provides a technical solution: a method for researching the evolution law of the double-layer oxide film defect under the thermal-dynamic constraint condition in the aluminum alloy casting process, comprising the following steps:

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

[0039] Based on thermodynamic calculation and high-precision analysis of the defect microstructure, the influence law of alloy composition elements on the composition and phase structure of the double-layer oxide film defect is researched, the thermodynamic condition of the formation is revealed, and the relationship between the film composition and the double-layer oxide film defect morphology is clarified;

[0040] Combined with casting partition dissection and defect multi-dimensional characterization, the correlation between the multi-scale double-layer oxide film characteristics and the defect interval distribution law is analyzed, the spatial relationship between different types of double-layer oxide film defects and the casting structure is revealed. And through the research on the coupling relationship between the final state and the existing position of the double-layer oxide film defect, a foundation is laid for the analysis of the subsequent motion evolution process;

[0041] Step 2: motion behavior of the double-layer oxide film defect in liquid / semi-solid melt;

[0042] Through free surface calculation simulation, the agglomeration characteristics of the double-layer oxide film defect in the liquid melt filling flow process are researched, and the deformation and crushing of the double-layer oxide film defect are analyzed, and the deformation law of the double-layer oxide film defect in the liquid melt is revealed;

[0043] The numerical simulation of rigid particle tracking is carried out, and the motion trajectory of the double-layer oxide film defect based on fluid-structure coupling is studied by adjusting the size and shape of the double-layer oxide film defect. The influence of defect structure on the motion behavior under the same flow field conditions is analyzed.

[0044] Based on the viscosity of the melt solidification process and the solid / liquid phase ratio change of the paste zone, the hindering effect of semi-solid melt on the motion of pre-set double-layer oxide film defect is studied, and the coupling relationship between the deformation rule of double-layer oxide film defect and the motion trajectory is clarified.

[0045] Step 3: Evolution mechanism of double-layer oxide film defect during solidification process

[0046] Based on the mechanical property detection of the surface oxide film of the melt at different temperatures, the corresponding relationship between its and the oxide film structure and thickness is established, and the evolution rule of the mechanical property of the surface oxide film during the cooling process of the melt from liquid to semi-solid is clarified, which provides data support for the subsequent research on the evolution of double-layer oxide film defect.

[0047] The deformation behavior of double-layer oxide film defect with different performance under different solidification tension is studied, and the influence of grain arm spacing on the deformation process of double-layer oxide film defect is analyzed by adding grain refiner, and the relationship between double-layer oxide film defect and shrinkage hole is clarified.

[0048] By adjusting the melt purification measures, the influence of gas precipitation amount on the gas gap expansion volume of double-layer oxide film defect during solidification process is studied, and the relationship between the defect and gas hole is clarified, and finally the evolution model of double-layer oxide film defect under the coupling action of solidification shrinkage and gas precipitation is established.

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

[0050] Defect samples of aluminum / magnesium alloy with different alloy compositions are poured, and related cooperative units provide scrap castings for comprehensive anatomical analysis, and the distribution of double-layer oxide film defect in different parts of the casting is obtained. At the same time, SEM and 3D-CT analysis means are used to analyze the characteristics of double-layer oxide film defect of different scales, and the corresponding relationship between the structure, size, morphology and distribution rule of double-layer oxide film defect in actual casting is obtained, which provides modeling data support and model depth optimization basis for the subsequent research on the dynamic formation process of double-layer oxide film defect.

[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 movement of double-layer oxide film defects in the liquid melt filling flow field under different cross-section structures (abrupt / gradual, split / join), different liquid surface joining conditions (simultaneous / different), different filling velocities (laminar / turbulent), etc. The agglomeration, fragmentation, and deformation process of the double-layer oxide film defects are clarified, and the movement and deformation law of the double-layer oxide film defects are elucidated.

[0052] Different sizes and shapes of double-layer oxide film defects are designed, and the ANSYS fluid-structure coupling is used to simulate the movement trajectory of the defects in the flow field. At the same time, the tracer particle motion of rigid particles is simulated, and the influence law of the characteristic structure of the double-layer oxide film defects on the movement trajectory is obtained by comparison.

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

[0054] In step 3, the tensile and shear mechanical properties of the melt surface oxide film under different compositions and temperatures are detected by the straight tensile method or the disc torsion method. The two methods are used together to analyze the comprehensive mechanical properties of the oxide layer under different conditions, and the corresponding relationship between the structure / thickness of the double-layer oxide film defects and the mechanical properties is established to provide data support for the evolution behavior of the double-layer oxide film defects in the solidification process.

[0055] Based on the LAMMPS implementation of molecular dynamics simulation, a deformation model of the double-layer oxide film defects under different solidification tensions is established, and the interface bonding strength between the defects and the matrix is obtained. Combined with the measured mechanical properties of the double-layer oxide film defects, the fracture of the double-layer oxide film defects under the solidification tension is analyzed using the COMSOL software cohesive model. Finally, the relationship between the interdendritic arm spacing and the micro-displacement / deformation of the double-layer oxide film defects is revealed by using the grain refiner, and the simulation results and the correlation between the double-layer oxide film defects and the shrinkage hole are verified by SEM / EDS and TEM.

[0056] An adsorption expansion model of the double-layer oxide film defects is established, and the gas content of the melt is adjusted by changing the type and content of the refining agent to clarify the relationship between the double-layer oxide film defects and the gas pores. Finally, the synergistic effect of the solidification shrinkage tension and the melt gas precipitation on the double-layer oxide film defects is analyzed to clarify the evolution mechanism of the double-layer oxide film defects in the solidification process.

[0057] Taking the dynamic formation mechanism of double-layer oxide film defects as the research object, the sudden failure reason of key bearing parts of complex aluminum / magnesium alloy components during service process is clarified. The coupling relationship between multi-scale double-layer oxide film defects and partitioned casting structure is clarified. The influence law 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. The correlation model of double-layer oxide film defects and shrinkage cavity, gas hole is constructed. The coupling relationship between double-layer oxide film defect characteristic morphology and thermodynamic formation condition is analyzed. The relevance of multi-scale double-layer oxide film defects and casting partition structure is clarified. The cooperative relationship between deformation law and movement trajectory of double-layer oxide film defects in liquid / semi-solid melt is revealed. The movement behavior of defects in flow field is clarified. The relevance between double-layer oxide film defects and gas hole, shrinkage cavity is clarified. The dynamic evolution mechanism of double-layer oxide film defects in solidification process is clarified. The research results can provide theoretical guidance and experimental support for near-zero defect and performance limit optimization of castings.

[0058] Although the present specification is described in terms of embodiments, not every embodiment contains only one independent technical solution. The description of the specification is only for the sake of clarity, and those skilled in the art should consider the specification as a whole. The technical solutions in each embodiment can be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for studying the evolution law of double oxide film defects under thermo-kinetic constraints during aluminum alloy casting, characterized in that... Includes the following steps: Step 1: Defect microstructure and distribution patterns of multi-scale bilayer oxide films; Based on thermodynamic calculations and high-precision analysis of defect microstructure, this study investigates the influence of alloy composition elements on the defect composition and phase structure of double oxide films, reveals the thermodynamic conditions for their formation, and clarifies the relationship between film composition and defect morphology of double oxide films. By combining the sectional anatomy of castings and the multi-dimensional characterization of defects, and by analyzing the correlation between the characteristics of multi-scale double oxide films and the distribution patterns of defect intervals, the spatial relationship between different types of double oxide film defects and casting structures is revealed. Furthermore, by studying the coupling relationship between the final state of double oxide film defects and their location, a foundation is laid for the subsequent analysis of the motion evolution process. Step 2: Motion behavior of defects in double oxide films in liquid / semi-solid melts; Through free surface computational simulation, the aggregation characteristics of double oxide film defects during the filling flow of liquid melt were studied, and their deformation and breakage were analyzed to reveal the deformation law of double oxide film defects in liquid melt. We conducted numerical simulations of rigid particle tracer particles, and studied the motion trajectory of double oxide film defects based on fluid-structure interaction by adjusting the size and shape of double oxide film defects. We also analyzed the influence of defect structure on motion behavior under the same flow field conditions. By combining the viscosity of the melt during solidification and the change in the solid / liquid ratio in the paste region, the hindering effect of the semi-solid melt on the movement of defects in the pre-placed double oxide film is studied, and the coupling relationship between the deformation law and the movement trajectory of the double oxide film defects is clarified. Step 3: Defect evolution mechanism of double oxide film during solidification; Based on the mechanical properties of the surface oxide film at different temperatures of the melt, the correspondence between the mechanical properties 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 from liquid to semi-solid is clarified, providing data support for subsequent research on the evolution of defects in double oxide films. This study investigates the deformation behavior of defects in double oxide films with different properties under different solidification tensile forces. By adding a grain refiner, the influence of dendrite arm spacing on the deformation process of double oxide film defects is analyzed, clarifying the relationship between double oxide film defects and shrinkage cavities. By adjusting melt purification measures, the influence of gas evolution during solidification on the expansion volume of the defect gap in the double oxide film was studied, the connection between the defect and the pores was clarified, and finally, a defect evolution model of the double oxide film under the coupling effect of solidification shrinkage and gas evolution was established.

2. The method for studying the evolution law of double oxide film defects under thermo-dynamic constraints during aluminum alloy casting according to claim 1, characterized in that: In step 1, the composition of double oxide film defects in different aluminum / magnesium alloys is analyzed using theoretical calculations or Thermo-Calc thermodynamic calculation software. While verifying the results through SEM and TEM analysis, the relationship between the composition / phase structure of the double oxide film and the multi-scale defect morphology is revealed. The formation process and influencing factors of this type of defect are analyzed from the perspective of alloy composition. Defective aluminum / magnesium alloy samples with different alloy compositions were cast, and a comprehensive dissection analysis was conducted in conjunction with scrapped castings provided by relevant collaborating units to obtain the distribution of double 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 oxide film defects at different scales, and the correspondence between the structure, size, morphology and distribution law of double oxide film defects in actual castings was obtained. This provides modeling data support and model depth optimization basis for subsequent research on the dynamic formation process of double oxide film defects.

3. The method for studying the evolution law of double oxide film defects under thermo-dynamic constraints during aluminum alloy casting according to claim 1, characterized in that: In step 2, using ANSYS Fluent or Flow-3D software VOF model and melt free surface tracking model, the defect movement of double oxide film defects in the liquid melt filling flow field is analyzed under different cross-sectional structures, different liquid surface confluence conditions, and different filling speed parameters. The aggregation, breakup, and deformation processes are clarified, and the motion and deformation law of double oxide film defects is explained. The cross-sectional structure includes abrupt / gradual changes and splitting / convergence; the liquid surface confluence includes simultaneous / differential times; and the filling speed includes laminar / turbulent flow. Double-layer oxide film defects of different sizes and shapes were designed, and the motion trajectory of the defects in the flow field was simulated using ANSYS fluid-structure interaction. At the same time, the motion of tracer particles of rigid particles was simulated, and the influence of the characteristic structure of the double-layer oxide film defect on the motion trajectory was obtained by comparison. Based on the viscosity variations of melts of different alloys and at different temperatures, the influence of solidification temperature gradient on the trajectory of double oxide film defects was studied. Simultaneously, models of pasty regions with different solid / liquid phase ratios were constructed to simulate the movement of double oxide film defects through semi-solid melts under different conditions. Finally, the correlation between the movement behavior and final residence position of double oxide film defects was obtained, and the accuracy of the simulation results was judged by comparing them with double oxide film defects in actual castings.

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

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