Ultrasonic-assisted method for reducing residual stress of 3D printing aluminum-based composite material

Abstract

The invention provides a method for reducing residual stress of a 3D printing aluminum-based composite material through ultrasonic assistance, and belongs to the technical field of 3D printing. The method comprises the steps that the 3D printing aluminum-based composite material is prepared, a composite material model is constructed, an ultrasonic-free 3D printing process is simulated, an ultrasonic-assisted 3D printing process is implemented, a microstructure and stress are analyzed, and optimal ultrasonic parameters are determined. Converting the simulation parameters into actual process parameters; the atomic-scale interaction mechanism of an ultrasonic field and a material is accurately analyzed by means of molecular dynamics simulation, ultrasonic vibration is introduced in the key cooling stage, molten pool fluid dynamics is changed through the acoustic streaming effect, the columnar crystal growth inhibition rate is increased, isometric crystal formation is promoted, dendritic crystals are broken through microjet generated by the cavitation effect, the grain boundary area is increased, and stress concentration is dispersed; through quantitative analysis of a dislocation movement track, it is found that the dislocation migration rate is increased and the entanglement density is reduced through ultrasound, the average residual stress of the model is reduced, the peak stress is reduced, and the efficiency is greatly improved.

Description

Technical Field

[0001] The present invention belongs to the field of 3D printing technology, and in particular relates to a method for ultrasonically assisting in reducing residual stress in 3D printed aluminum-based composite materials. Background Art

[0002] With economic development and people's increasing needs, the demand and utilization of 3D printing have been rising. Additive manufacturing is a 3D printing process that builds objects layer by layer by depositing materials based on provided digital data. Compared with traditional manufacturing methods, it reduces cost, time and carbon footprint. Compared with subtractive manufacturing processes, it minimizes the waste of raw materials and produces higher quality parts for prototypes. Complex geometries can be manufactured and customized without the use of tools or molds. Using optimal parameters, the finished product can have better mechanical properties from less porosity. Therefore, additive manufacturing is widely used in aerospace, automotive, medical and construction industries and is of great significance. Although the rapid solidification process of additive manufacturing helps prevent alloying element segregation, this manufacturing process is typically non-equilibrium solidification and still faces many problems. Due to the non-equilibrium solidification during the rapid solidification process, uneven temperature gradients form within the material, resulting in incomplete release of thermal stress. Residual stresses form at grain boundaries and interfaces, causing residual stress accumulation. In addition, the microstructure is uneven. Rapid cooling of the molten pool easily forms coarse columnar crystals, which reduces the mechanical properties and fatigue life of the material. Finally, defects such as pores and lack of fusion further aggravate stress concentration and affect the reliability of the component. Residual stress can cause 3D printed components to deform and crack, and even cause premature failure during use. Currently, the commonly used methods for stress reduction are generally heat treatment: annealing to release stress, but it may cause grain coarsening or performance degradation; mechanical treatment: it can only improve surface stress and has limited effect on internal stress; process parameter optimization: adjusting laser power and scanning strategy, but the effect is limited by the material system and still has the disadvantages of low efficiency, high cost, or a narrow scope of application, making it difficult to meet the needs of high-precision, high-performance components. Summary of the Invention

[0003] In response to the above-mentioned deficiencies in the prior art, the present invention provides an ultrasonically assisted method for reducing residual stress in 3D-printed aluminum-based composite materials, which solves the problems of existing residual stress reduction treatments, such as limited impact on internal stress, material system limitations, low efficiency, high cost, narrow scope of application, and difficulty in meeting the requirements of high-precision and high-performance components.

[0004] In order to achieve the above objectives, the technical solution adopted by the present invention is: an ultrasonic-assisted method for reducing residual stress in 3D printed aluminum-based composite materials, comprising the following steps: S1. Prepare 3D printed aluminum-based composite materials based on aluminum particles and graphene, and build composite material models; S2. Based on the composite material model, simulate non-ultrasonic printing to obtain a first residual stress distribution and a first microstructure under non-ultrasonic conditions, and simulate ultrasonic-assisted printing by introducing ultrasonic vibration during the cooling stage to obtain a second residual stress distribution and a second microstructure under ultrasonic-assisted conditions; S3. Analyze the residual stress distribution and microstructure under non-ultrasound conditions and ultrasound-assisted conditions, and compare the structural evolution and stress changes before and after ultrasound assistance to obtain the reduction effect, determine the optimal ultrasound parameters, and verify the simulated residual stress and mechanical property effects; S4. Combining the reduction effect and the influence of mechanical properties, the optimal ultrasonic parameters are converted into actual process parameters, and the actual internal residual stress of 3D printing is measured. The simulated residual stress and the actual residual stress are compared, and the residual stress reduction is completed in response to the residual stress reduction.

[0005] The beneficial effects of the present invention are as follows: the present invention constructs a composite material model, simulates the 3D printing process, uses molecular dynamics simulation to accurately analyze the atomic-level interaction mechanism between the ultrasonic field and the material, introduces ultrasonic vibration in the critical cooling stage, and uses the acoustic streaming effect to change the fluid dynamics of the molten pool, thereby improving the columnar crystal growth inhibition rate and promoting the formation of equiaxed crystals; and uses the micro-jets generated by the cavitation effect to break up the dendrites, increase the grain boundary area to disperse stress concentration, and through quantitative analysis of the dislocation motion trajectory, improve the dislocation migration rate, reduce the entanglement density, and achieve the reduction of the average residual stress and peak stress of the 3D printed aluminum-based composite material model and greatly improve the efficiency.

[0006] Furthermore, the S1 includes the following steps: S101, using a body-centered cubic structure to construct an iron substrate, and setting a boundary layer at the bottom two atomic layers of the iron substrate, setting a constant temperature layer at the middle three atomic layers of the iron substrate, and setting a Newtonian layer at the top one atomic layer of the iron substrate; S102, using aluminum atoms with a face-centered cubic structure to represent aluminum particles of a preset diameter, the aluminum particles are evenly arranged on the iron substrate at a preset spacing to form an aluminum particle layer, and using carbon atoms to form a single layer of graphene with a hexagonal structure, the single layer of graphene is arranged in the center of the aluminum particle layer; S103, in the XY plane, based on a square network with a preset side length, arranging aluminum particles according to a preset center spacing, aligning the center of the single-layer graphene with the center of the composite material based on a preset initial temperature maintained by the constant temperature layer of the iron substrate, maintaining a planar state by the rigid constraint of the iron substrate boundary layer according to a preset spacing between the graphene and the iron substrate and a preset spacing between the graphene and the aluminum particles, thereby obtaining a 3D-printed aluminum-based composite material; S104. Based on 3D printing of aluminum-based composite materials, set XY-axis periodic boundary conditions to simulate an infinite system in response to atoms moving out of one boundary and entering from equivalent positions on the opposite boundary. Set a Z-axis boundary condition to simulate the free surface during the printing process without constraints on the surface of the top aluminum particles. Use a microcanonical ensemble for initial relaxation to eliminate initial stress and obtain an initial model. S105. Based on the initial model, pre-relaxation is performed and the model energy is minimized. The model energy is iteratively calculated using the conjugate gradient method. The molecular dynamics calculation is performed based on the Newtonian layer of the iron substrate. In response to the interatomic force being less than the preset force threshold, the initial configuration with the lowest energy is obtained. Based on the preset running time and preset time step of the microcanonical ensemble, a composite material model is constructed according to the initial configuration with the lowest energy.

[0007] The beneficial effects of the above further scheme are as follows: the present invention determines the structure and distribution of aluminum nanoparticles, graphene and iron substrate, sets the diameter, spacing and interlayer position of aluminum nanoparticles and graphene, simulates the distribution state of the reinforcing phase and the matrix in the actual composite material, and designs the iron substrate in layers to truly reflect the support and heat conduction effect of the substrate on the material during the printing process; and uses boundary conditions to effectively eliminate the simulated boundary effect, so that the composite material model is approximately an infinite system, and the real physical and chemical environment of 3D printed aluminum-based composite materials is highly restored, thereby improving the reliability and effectiveness of the simulation of ultrasonic-free and ultrasonic-assisted 3D printing processes and stress analysis.

[0008] Furthermore, the S2 includes the following steps: S201. Based on the composite material model, simulate non-ultrasonic 3D printing to obtain the residual stress distribution and microstructure under non-ultrasonic conditions; S202. Perform ultrasonic-assisted 3D printing based on the composite material model, and introduce ultrasonic vibration during the cooling stage to regulate the solidification process and obtain the residual stress distribution and microstructure under ultrasonic-assisted conditions.

[0009] Furthermore, the S201 includes the following steps: S2011. Simulating laser melting based on the composite material model, heating a preset area, and scanning along the Y-axis at a preset speed. In response to complete melting of the aluminum particles, stopping melting, and naturally cooling the composite material model under a microcanonical ensemble to obtain a composite material model containing residual stress. S2012. Analyze the composite material model containing residual stress using the crystal local order parameter to identify a first microstructure; S2013. Calculating a composite material model containing residual stress using a Virial stress formula to obtain a first residual stress distribution; S2014. According to the first microstructure and the first residual stress distribution, dislocation lines are tracked using dislocation diffusion analysis to obtain dislocation lines dominated by Shockley incomplete dislocations, and based on the dislocation lines, the residual stress distribution and microstructure under non-ultrasonic conditions are obtained.

[0010] The beneficial effect of the above further solution is that the present invention provides a clear reference for the ultrasonic assistance effect by quantifying the structure, stress and defect correlation of the traditional printing process.

[0011] Furthermore, the S202 includes the following steps: S2021. Based on the composite material model, simulate laser melting, introduce ultrasonic vibration, set and load ultrasonic vibration parameters, and apply sinusoidal vibration along the Z axis to simulate the vertical excitation of the ultrasonic transducer in the actual process. In response to the laser being turned off, start the ultrasonic vibration and synchronize the ultrasonic vibration with the cooling process. Use a canonical ensemble to maintain the preset printing system temperature, and use the Anderson thermal bath method to eliminate the interference of vibration heat generation, thereby obtaining a composite material model with eliminated vibration interference; S2022. Based on a composite material model that eliminates vibration interference, the ultrasonic field is coupled with the solidification process. Ultrasonic vibration is used to induce stable fluid motion and disturb the direction of heat flow, thereby suppressing the directional growth of columnar crystals along the laser scanning direction to form equiaxed crystal nuclei. S2023. Based on fluid flushing, nucleation is promoted in the edge region to obtain a refined grain size. Based on periodic pressure fluctuations, microbubbles are collapsed to generate microjets, which crush and impact the dendrite arms to update the nucleation sites. Ultrasonic energy is used to stimulate dislocation slip and climb, multiply Shockley partial dislocations and diffuse them into the grain interior, reduce the density of complete dislocations, and transform dislocations from being concentrated at the grain boundaries to being uniformly distributed across the entire region. Based on equiaxed crystal nuclei, a second microstructure is obtained. S2024. Based on the single variable principle, the cooling rate without ultrasonic conditions is used to control the cooling process. The atomic coordinates and velocities are recorded according to the preset recording time to obtain the grain growth path, the atomic diffusion behavior at the interface, and the dynamic response of the aluminum atoms near the graphene, and the ultrasonic influence including the interdiffusion of the interface atoms is obtained; S2025. Based on the ultrasonic influence, the total energy of the printing system is monitored in real time. In response to the printing system not being overheated, a virial stress formula is used to calculate the composite material model with vibration interference eliminated to obtain a second residual stress distribution. S2026. Based on the second microstructure and the second residual stress distribution, by observing the stress evolution trend during the cooling process, the residual stress distribution and microstructure under ultrasonic-assisted conditions are obtained.

[0012] Furthermore, the expression of the composite material model for eliminating vibration interference is as follows: ; ; ; in, Indicates the i Atomic mass, Indicates the i The position vector of each atom, Indicates time, represents the gradient of the interatomic potential energy V, represents the amplitude, represents the angular frequency of ultrasonic vibration, represents the unit vector in the Z-axis direction, represents the Boltzmann constant, Indicates the current temperature, which is the temperature that changes over time. represents Gaussian white noise, represents the cooling time constant, Indicates the total cooldown time.

[0013] The beneficial effects of the above further solution are as follows: the present invention reduces the temperature gradient and slows down the growth rate of columnar crystals by introducing ultrasonic vibration in the critical cooling stage and starting it synchronously with the cooling, and provides a composite material model that eliminates vibration interference, making the simulation more accurate and effective; Through the synergistic effect of the ultrasonic field and the solidification process, triple optimization of grain refinement, interface strengthening and dislocation homogenization is achieved, providing an atomic-level solution for residual stress reduction.

[0014] Furthermore, the S3 includes the following steps: S301, analyzing the residual stress distribution and microstructure under non-ultrasonic conditions and ultrasonic-assisted conditions, and comparing the structural evolution and stress changes before and after ultrasonic assistance to obtain the reduction effect; S302. According to the reduction effect, the optimal ultrasonic parameters are determined by using orthogonal experiments, and the influence of mechanical properties is obtained through verification.

[0015] Furthermore, the S301 includes the following steps: S3011. Perform atomic simulation visualization based on the microstructures under non-ultrasound conditions and ultrasound-assisted conditions to obtain the grain size and atomic type ratio near the graphene interface under non-ultrasound conditions and ultrasound-assisted conditions, and obtain the ultrasound-assisted structural evolution; S3012. Based on the residual stress distribution under non-ultrasound conditions and ultrasound-assisted conditions, stress calculation is performed based on molecular dynamics to obtain the von Mises stress of each atom in the composite material model. Gaussian filtering is used to eliminate noise. The maximum stress and stress gradient in the main body of the aluminum layer are obtained for the non-ultrasound group and the ultrasound group, and the stress value and stress concentration factor at the graphene interface are obtained for the non-ultrasound group and the ultrasound group, respectively. By comparing the data of the non-ultrasound group and the ultrasound group, the stress change after ultrasound-assisted treatment is obtained. S3013. Using a dislocation analysis algorithm, identify dislocation lines, and statistically obtain the total length and type of dislocations in the non-ultrasound group and the ultrasound group. By analyzing the atomic trajectory of dislocation motion, obtain the ultrasound-assisted dislocation effect. S3014. Cutting the middle portion of the composite material model of the non-ultrasound group and the ultrasound group, respectively, balancing the cut portion under an isothermal and isobaric ensemble, and applying a strain rate along the X-axis. In response to the strain reaching a preset percentage, the tensile strength, fracture strain, and fracture mode of the non-ultrasound group and the ultrasound group are obtained, and the ultrasound-assisted mechanical properties are obtained through failure mechanism analysis; S3015. Based on the ultrasonic-assisted structural evolution, stress changes, dislocation effects, and mechanical properties, the stress reduction attribution and the reduction effect are obtained.

[0016] The beneficial effects of the above further scheme are: the present invention obtains ultrasonic-assisted structural evolution through atomic simulation visualization, obtains ultrasonic-assisted stress changes through stress calculation through molecular dynamics, obtains ultrasonic-assisted dislocation influence through dislocation analysis algorithm and analysis, and obtains ultrasonic-assisted mechanical properties through cutting balance, realizing multi-dimensional analysis and verification of ultrasonic-assisted effects, and improving the feasibility and effectiveness of ultrasonic assistance.

[0017] Furthermore, the S302 includes the following steps: S3021. Optimize the ultrasonic parameters using the single factor variable method based on the reduction effect, component thickness, and performance requirements to obtain the optimal parameter range; S3022. Based on the optimal parameter range, determine the initial ultrasonic parameter combination according to the residual stress index formula and the strength index formula; S3023. Based on the initial ultrasonic parameter combination, the composite material model is simulated using an orthogonal test to obtain an initial ultrasonic parameter model. The cutting conditions are set and the standard tensile specimens are cut to obtain the mixed characteristics of the specimen fracture surface. The smooth cleavage surface of the non-ultrasonic group is compared to obtain the interface bonding strength and plastic deformation capacity of the initial ultrasonic parameters. S3024. Based on the interface bonding strength and plastic deformation capacity of the initial ultrasonic parameters, and in combination with the use of low amplitude in ultrasonic assistance to refine grains through cavitation effect, and the use of high amplitude to fuse grains and migrate dislocations over long distances through enhanced acoustic streaming effect, the initial ultrasonic parameter combination is optimized based on the suitable structures of low amplitude and high amplitude to obtain the optimal ultrasonic parameters; S3025. Based on the optimal ultrasonic parameters, the simulated residual stress and mechanical property effects are verified through tensile tests.

[0018] The beneficial effect of the above further solution is that the present invention determines the optimal ultrasonic parameters and verifies their positive impact on mechanical properties through a scientific and systematic research process, thereby improving the feasibility and effectiveness of ultrasonic assistance in actual production.

[0019] Furthermore, the S4 includes the following steps: S401. Combine the reduction effect and the influence of mechanical properties, and map the optimal ultrasonic parameters to actual production according to the scale conversion formula to obtain the actual process parameters; S402. Based on actual production, an ultrasonic vibration module is installed in the laser powder bed fusion equipment. The vibration direction is perpendicular to the printed layer, and the piezoelectric ceramic transducer is used for vibration loading. In response to the completion of laser scanning, ultrasonic vibration is started and continued until interlayer cooling is completed, completing the actual ultrasonic parameter setting. S403, based on the actual ultrasonic parameter settings, setting a non-ultrasound group and an ultrasonic group, printing a standard part of an aluminum-based composite material reinforced with graphene, and measuring the actual 3D printed internal residual stress using X-ray diffraction to obtain the actual residual stress; S404. Based on the simulated residual stress and the actual residual stress, determine whether the deviation between the simulated residual stress and the actual residual stress is greater than a preset threshold. If so, establish a calibration iterative closed loop of simulation prediction, experimental verification, and parameter correction, adjust the actual ultrasonic parameters, and return to step S403. Otherwise, save the actual ultrasonic parameters to the ultrasonic-assisted process database to complete the ultrasonic-assisted reduction of residual stress in 3D-printed aluminum-based composite materials.

[0020] The beneficial effects of the above further solution are as follows: the present invention converts simulated ultrasonic parameters into actual process parameters, specifically sets an actual printing scheme, integrates it into the printing device, and forms an ultrasound-assisted process database through multi-dimensional verification and parameter calibration; Through cross-scale conversion and experimental verification, the atomic-level simulation results are transformed into an operational industrial process, ensuring that ultrasonic-assisted technology can effectively reduce residual stress and improve material properties in actual production, thus achieving ultrasonic-assisted effective reduction of residual stress in 3D-printed aluminum-based composite materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1Flow chart of the method of the present invention. DETAILED DESCRIPTION

[0022] The specific embodiments of the present invention are described below to facilitate understanding of the present invention by those skilled in the art. However, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the appended claims, these changes are obvious, and all inventions and creations utilizing the concepts of the present invention are protected.

[0023] Before describing this embodiment, the following terms are explained: Shockley partial dislocation: Shockley partial dislocation; Perfect full dislocation: complete full dislocation; HCP: hexagonal close-packed lattice; NVE ensemble: microcanonical ensemble; NVT ensemble: canonical ensemble; NPT ensemble; isothermal and isobaric ensemble; Andersen hot bath method: Anderson hot bath method; OVITO: Open Visualization Tool; FCC: face-centered cubic lattice; LAMMPS: Large-Scale Atomic or Molecular Massively Parallel Simulator; DXA algorithm: dislocation analysis algorithm.

[0024] Example like Figure 1 As shown, the present invention provides an ultrasonic-assisted method for reducing residual stress in 3D printed aluminum-based composite materials, and the implementation method is as follows: S1. Prepare 3D printed aluminum-based composite materials based on aluminum particles and graphene, and build a composite material model. The specific steps are as follows: S101, using a body-centered cubic structure to construct an iron substrate, and setting a boundary layer at the bottom two atomic layers of the iron substrate, setting a constant temperature layer at the middle three atomic layers of the iron substrate, and setting a Newtonian layer at the top one atomic layer of the iron substrate; S102, using aluminum atoms with a face-centered cubic structure to represent aluminum particles of a preset diameter, the aluminum particles are evenly arranged on the iron substrate at a preset spacing to form an aluminum particle layer, and using carbon atoms to form a single layer of graphene with a hexagonal structure, the single layer of graphene is arranged in the center of the aluminum particle layer; S103, in the XY plane, based on a square network with a preset side length, arranging aluminum particles according to a preset center spacing, aligning the center of the single-layer graphene with the center of the composite material based on a preset initial temperature maintained by the constant temperature layer of the iron substrate, maintaining a planar state by the rigid constraint of the iron substrate boundary layer according to a preset spacing between the graphene and the iron substrate and a preset spacing between the graphene and the aluminum particles, thereby obtaining a 3D-printed aluminum-based composite material; S104. Based on 3D printing of aluminum-based composite materials, set XY-axis periodic boundary conditions to simulate an infinite system in response to atoms moving out of one boundary and entering from equivalent positions on the opposite boundary. Set a Z-axis boundary condition to simulate the free surface during the printing process without constraints on the surface of the top aluminum particles. Use a microcanonical ensemble for initial relaxation to eliminate initial stress and obtain an initial model. S105. Based on the initial model, pre-relaxation is performed and the model energy is minimized. The model energy is iteratively calculated using the conjugate gradient method. The molecular dynamics calculation is performed based on the Newtonian layer of the iron substrate. In response to the interatomic force being less than the preset force threshold, the initial configuration with the lowest energy is obtained. Based on the preset running time and preset time step of the microcanonical ensemble, a composite material model is constructed according to the initial configuration with the lowest energy.

[0025] In this embodiment, a 3D printed aluminum-based composite material was prepared and a composite material model was constructed. In constructing the composite material model, the model composition and structural parameters were determined. The iron substrate adopted a body-centered cubic structure to simulate the support structure in actual printing. The structure was divided into a boundary layer, a constant temperature layer, and a Newtonian layer. The specific division steps are as follows: The boundary layer is set on the bottom two layers of atoms of the iron substrate to fix the atomic coordinates and simulate the rigid support of the substrate. The isothermal layer is set on the middle three layers of atoms of the iron substrate to maintain a constant temperature of 300K through the velocity recalibration method to simulate the heat conduction from the substrate to the outside world. The Newtonian layer is set on the top one layer of atoms of the iron substrate to participate in molecular dynamics calculations and to exchange heat and interact mechanically with the aluminum particles. Aluminum atoms with a face-centered cubic structure are used to represent aluminum nanoparticles in the simulation. The diameter of the aluminum nanoparticles is 3nm and they are evenly distributed on the iron substrate with a particle spacing of 1nm. Carbon atoms are used to form a single layer of graphene with a hexagonal lattice structure, which is located in the middle of the aluminum particle layer to simulate interlayer reinforcement.

[0026] In this embodiment, the aluminum particles and graphene are initially arranged. In the XY plane, the aluminum particles are arranged in a square grid with a preset side length of 4nm, and the center spacing of the aluminum particles is 4nm. Each aluminum particle is composed of approximately 4000 aluminum atoms. The preset initial temperature of 300K is maintained based on the constant temperature layer of the iron substrate, and the center of the graphene sheet is aligned with the center of the model. The preset spacing between the graphene and the iron substrate is set to 2.4nm, and the initial spacing with the aluminum particles is set to 1nm. The planar morphology is maintained by the rigid constraint of the iron substrate boundary layer to obtain a 3D printed aluminum-based composite material.

[0027] In this embodiment, based on 3D printing of aluminum-based composite materials, boundary conditions and ensembles are set, and XY axis periodic boundary conditions are set. Specifically, when atoms move out of one boundary, atoms are moved in from the equivalent position of the opposite boundary to simulate an infinite system and eliminate edge effects. Set the Z-axis free boundary condition, specifically: set the top aluminum particle surface to be unconstrained to simulate the free surface during printing; The NVE ensemble is used for initial relaxation to maintain the conservation of the number of particles N, volume V, and energy E, eliminating the initial stress in the process of building the composite material model and obtaining the initial model; According to the initial model, pre-relax and minimize the energy of the initial model, use the conjugate gradient method to iteratively calculate, and participate in molecular dynamics calculation based on the iron substrate Newton layer until the interatomic force is less than , obtain the lowest energy initial configuration, and run the preset run time under the NVE ensemble and preset time step , so that the aluminum particles and the iron substrate reach thermal equilibrium through heat conduction, monitor the total energy fluctuations of the system to ensure energy conservation, verify the stability of the model, and construct a composite material model.

[0028] In this embodiment, the structure and distribution of aluminum nanoparticles, graphene, and iron substrate are determined, wherein the diameter, spacing, and interlayer position of the aluminum nanoparticles and the graphene are set to highly simulate the distribution state of the reinforcement phase and the matrix in the actual composite material. The layered design of the iron substrate can truly reflect the support and heat conduction effect of the substrate on the material during the printing process. At the same time, the XY axis periodic boundary conditions effectively eliminate the simulated boundary effect, making the model approximately an infinite system. The Z axis free boundary fits the printing free surface scene. The NVE ensemble is used for initial relaxation to ensure that there is no additional stress interference during model construction, ensuring that subsequent simulation results are based on the material's own characteristics. The conjugate gradient method is used to minimize the interatomic force and obtain the lowest energy configuration. The thermal equilibrium between the aluminum particles and the iron substrate is achieved through the operation of the NVE system, and the energy fluctuation is monitored to ensure the stability of the model, avoiding the influence of the initial state instability on the accuracy of the subsequent 3D printing process simulation. The above steps work together to enable the constructed composite material model to highly restore the actual physical and chemical environment of 3D-printed aluminum-based composite materials, thereby ensuring the reliability and effectiveness of subsequent research results such as ultrasound-free and ultrasound-assisted 3D printing process simulation and stress analysis.

[0029] S2. Based on the composite material model, simulate non-ultrasonic printing to obtain the first residual stress distribution and first microstructure under non-ultrasonic conditions, and simulate ultrasonic-assisted printing, introduce ultrasonic vibration during the cooling stage, and obtain the second residual stress distribution and second microstructure under ultrasonic-assisted conditions. The specific steps are as follows: S201. Based on the composite material model, simulate non-ultrasonic 3D printing to obtain the residual stress distribution and microstructure under non-ultrasonic conditions. The specific steps are as follows: S2011. Simulating laser melting based on the composite material model, heating a preset area, and scanning along the Y-axis at a preset speed. In response to complete melting of the aluminum particles, stopping melting, and naturally cooling the composite material model under a microcanonical ensemble to obtain a composite material model containing residual stress. S2012. Analyze the composite material model containing residual stress using the local order parameter of the crystal and identify the first microstructure.

[0030] In this embodiment, based on the composite material model, the non-ultrasonic 3D printing process is simulated to obtain the residual stress distribution and microstructure under non-ultrasonic conditions, specifically: Simulate laser melting, heat the preset area, which is a circular area with a diameter of 8nm, and heat it along the Y axis at a preset speed Scan, input power , duration When the aluminum particles are completely melted, the melting is stopped, the laser is turned off, and the composite material model is cooled naturally under the microcanonical ensemble. , cooling the temperature to 300K, and obtaining the composite material model of residual stress; Using the local order parameters of the crystal, the structural characteristics of each atom were analyzed and identified. The green FCC aluminum was dominant, with a small amount of red HCP stacking faults and gray amorphous structures. The grains were mainly columnar crystals, the grain boundaries were concentrated at the graphene interface, and the grains in the edge area were coarse, obtaining the first microstructure.

[0031] S2013. Calculating a composite material model containing residual stress using a Virial stress formula to obtain a first residual stress distribution; S2014. According to the first microstructure and the first residual stress distribution, dislocation lines are tracked using dislocation diffusion analysis to obtain dislocation lines dominated by Shockley incomplete dislocations, and based on the dislocation lines, the residual stress distribution and microstructure under non-ultrasonic conditions are obtained.

[0032] In this embodiment, the composite material model containing residual stress is calculated using the Virial stress formula to obtain the first residual stress distribution. The expression of the Virial stress formula is as follows: ; in, represents stress, represents the horizontal component of the stress tensor, Indicates speed, Represents any particle in the composite material model, i.e., an atom , Represents atoms quality, Represents atoms The component of velocity on the horizontal axis, Represents atoms The component of velocity on the vertical axis, i The horizontal axis vector representing the Cartesian coordinate direction, j The vertical axis vector represents the Cartesian coordinate direction, Represents atoms and atoms The horizontal axis component of the relative position vector between Represents atoms Atom The component of the force vector on the vertical axis; The atomic-level stress distribution was calculated using the Virial stress formula, and the maximum residual stress in the aluminum layer was 29.66 GPa, concentrated at the grain boundaries. The stress at the graphene interface reached 92.05 GPa, which was caused by the thermal mismatch between aluminum and graphene. According to the first microstructure and the first residual stress distribution, the dislocation diffusion analysis was used to track the dislocation line. The total dislocation length was 72.83 nm, which was mainly distributed in the grain boundary area in the middle of the model. Shockley incomplete dislocations were dominant. The residual stress distribution and microstructure under non-ultrasonic conditions were obtained.

[0033] In this embodiment, the energy input parameter is a laser heating area with a diameter of 8nm, Scan speed and The power setting is equivalent to the energy density of Typical working conditions ensure that the melting depth is proportional to the actual molten pool size. The natural cooling rate under the NVE ensemble is about , simulating the rapid solidification characteristics in additive manufacturing, which is consistent with the experimentally measured cooling rate of aluminum-based composites, can induce typical non-equilibrium solidification defects. The microstructure is analyzed, and the grain morphology reflects the epitaxial growth characteristics caused by the temperature gradient in traditional printing. The crystal defects indicate that the rapid cooling causes some aluminum atoms to fail to fully relax to the FCC lattice, which is consistent with the diffraction peak broadening phenomenon measured by X-ray diffraction. The residual stress is tested, which confirms that the interface stress is the main stress source of aluminum-based composites. At the same time, the dislocation density and distribution are concentrated in the grain boundary triangle area, reflecting the dislocation multiplication mechanism caused by lattice distortion at the grain boundary. The stagnation of dislocation movement indicates that under the condition of no ultrasound, dislocations are easily pinned by solute atoms to form dislocation entanglements, resulting in the ineffective release of stress, thereby obtaining the residual stress distribution. This embodiment provides a clear reference for the ultrasonic-assisted effect by quantifying the structure-stress-defect relationship of the traditional printing process.

[0034] S202. Perform ultrasonic-assisted 3D printing based on the composite material model, introduce ultrasonic vibration during the cooling stage to regulate the solidification process, and obtain the residual stress distribution and microstructure under ultrasonic-assisted conditions. The specific steps are as follows: S2021. Based on the composite material model, simulate laser melting, introduce ultrasonic vibration, set and load ultrasonic vibration parameters, and apply sinusoidal vibration along the Z axis to simulate the vertical excitation of the ultrasonic transducer in the actual process. In response to the laser being turned off, start the ultrasonic vibration and synchronize the ultrasonic vibration with the cooling process. Use a canonical ensemble to maintain the preset printing system temperature, and use the Anderson thermal bath method to eliminate the interference of vibration heat generation, thereby obtaining a composite material model with eliminated vibration interference; S2022. Based on a composite material model that eliminates vibration interference, the ultrasonic field is coupled with the solidification process. Ultrasonic vibration is used to induce stable fluid motion and disturb the direction of heat flow, thereby suppressing the directional growth of columnar crystals along the laser scanning direction to form equiaxed crystal nuclei. S2023. Based on fluid flushing, nucleation is promoted in the edge area to obtain a refined grain size. Based on periodic pressure fluctuations, microbubbles are collapsed to generate microjets, and dendrite arms are crushed and impacted to update the nucleation sites. Ultrasonic energy is used to stimulate dislocation slip and climb, and Shockley partial dislocations are multiplied and diffused into the interior of the grains, reducing the density of complete dislocations. Dislocations are converted from concentrated at the grain boundaries to uniformly distributed across the entire region, and a second microstructure is obtained based on equiaxed crystal nuclei.

[0035] In this embodiment, an ultrasound-assisted 3D printing process is implemented. Ultrasonic vibration is introduced during the cooling stage to regulate the solidification process to reduce residual stress. The residual stress distribution and microstructure under ultrasound-assisted conditions are obtained, specifically: According to the composite material model, laser melting is simulated, ultrasonic vibration is introduced, ultrasonic vibration parameters are set and loaded, and sinusoidal vibration is applied along the Z axis to simulate the vertical excitation of the ultrasonic transducer in the actual process. According to the vibration equation: ,in, Indicates the amplitude, the default value is 0.2nm, Indicates frequency, preset to , ultrasonic vibration is started immediately after the laser is turned off, and continues synchronously with the cooling process. The NVT ensemble is used to maintain the preset printing system temperature of 300K, and the Andersen hot bath method is used to eliminate the vibration heat interference, and a composite material model with vibration interference eliminated is obtained; The expression of the composite material model for eliminating vibration interference is as follows: ; ; ; in, Indicates the i Atomic mass, Indicates the i The position vector of each atom, Indicates time, represents the gradient of the interatomic potential energy V, represents the amplitude, represents the angular frequency of ultrasonic vibration, represents the unit vector in the Z-axis direction, represents the damping coefficient value, represents the Boltzmann constant, Indicates the current temperature, which is the temperature that changes over time. represents Gaussian white noise, represents the cooling time constant, Indicates the total cooling time; The ultrasonic field is coupled with the solidification process. The ultrasonic vibration induces stable fluid motion in the molten pool, disturbing the direction of heat flow and inhibiting the directional growth of columnar crystals along the laser scanning direction. Equiaxed crystal nuclei form in the center of the molten pool. Fluid scouring promotes nucleation in the edge region, and the grain size is refined to 5nm-10nm. At this time, periodic pressure fluctuations trigger the collapse of microbubbles, generating microjets that impact the dendrite arms, causing the dendrites to break up and form new nucleation sites. Cavitation near the graphene interface is enhanced, weakening the thermal mismatch stress between aluminum and graphene. The dendrite growth direction at the interface tends to be randomized. Ultrasonic energy stimulates dislocation slip and climb, and Shockley partial dislocations proliferate and diffuse into the grain interior. The perfect total dislocation density is reduced, and dislocations are shifted from being concentrated at the grain boundaries to being uniformly distributed across the entire region. The dislocation entanglement density decreases by 50%, significantly reducing the lattice distortion stress, and a second microstructure based on the equiaxed crystal nuclei is obtained.

[0036] In this embodiment, the objective equation of the composite material model for eliminating vibration interference is: ,in, Represents the total energy of the printing system, which is the sum of kinetic energy, potential energy and off-field energy; Total energy of printing system , including kinetic energy K and potential energy V, the expression is as follows: ; in, represents the potential energy of the printing system; Print the total energy expression of the system and take the derivative with respect to time to get the expression as follows: ; Substituting the derived expression into the composite material model for eliminating vibration interference, the expression obtained is as follows: ; in, represents the random force of the heat bath, represents the damping coefficient, with a specific value of 0.1; the potential energy gradient terms cancel each other out, and the expression is as follows: ; And simplify it to get the following expression: ; The above ultrasonic external force term is zero on average over time, that is, ; The above random force terms are expressed as follows: ; Therefore, the expression for the time average of the total energy change rate is as follows: ; Therefore, the objective equation of the composite material model to eliminate vibration interference is .

[0037] S2024. Based on the single variable principle, the cooling rate without ultrasonic conditions is used to control the cooling process. The atomic coordinates and velocities are recorded according to the preset recording time to obtain the grain growth path, the atomic diffusion behavior at the interface, and the dynamic response of the aluminum atoms near the graphene, and the ultrasonic influence including the interdiffusion of the interface atoms is obtained; S2025. Based on the ultrasonic influence, the total energy of the printing system is monitored in real time. In response to the printing system not being overheated, a virial stress formula is used to calculate the composite material model with vibration interference eliminated to obtain a second residual stress distribution. S2026. Based on the second microstructure and the second residual stress distribution, by observing the stress evolution trend during the cooling process, the residual stress distribution and microstructure under ultrasonic-assisted conditions are obtained.

[0038] In this embodiment, the cooling process is controlled to maintain the same cooling rate as that in the absence of ultrasound, ensuring the single variable principle of the comparative experiment, and the preset recording time is followed. , record atomic coordinates and velocities, track grain growth paths and atomic diffusion behaviors at interfaces, focus on observing the dynamic response of aluminum atoms near graphene, verify whether ultrasound promotes interdiffusion of interface atoms, and obtain the ultrasonic effect including interdiffusion of interface atoms; Based on the ultrasonic influence, the energy and stress states are monitored, and the total energy of the system is monitored in real time to ensure that the ultrasonic vibration input energy does not cause the system to overheat. The Virial stress formula is used to calculate the composite material model that eliminates vibration interference, and the atomic-level stress tensor is used to obtain the second residual stress distribution; According to the second microstructure and the second residual stress distribution, the residual stress distribution and microstructure under ultrasonic-assisted conditions were obtained by observing the stress evolution trend during the cooling process.

[0039] In this embodiment, the vibration parameter is designed to be applied along the Z axis. High-frequency and 0.2nm amplitude sinusoidal vibrations are started synchronously with cooling. Thermal interference is eliminated through NVT ensemble temperature control. The acoustic streaming effect in the multi-field coupling effect induces vortices in the molten pool, disrupting the direction of heat flow, reducing the temperature gradient by 35%, slowing the growth rate of columnar crystals by 60%, and increasing the density of equiaxed crystal nuclei by 5 times. The cavitation effect microjet impacts the graphene interface, promoting atomic interdiffusion and reducing the interface stress by 30%. Dislocation regulation increases the proportion of Shockley dislocations to 75%, expands the migration distance by 5 times, reduces the dislocation density by 50%, and increases the stress release efficiency by 4 times. Experimental control maintains the cooling rate ,Every Recording atomic trajectories, interface stress The internal pressure drops by 12 GPa. This embodiment achieves triple optimization of grain refinement, interface strengthening, and dislocation homogenization through the synergistic effect of the ultrasonic field and the solidification process, providing an atomic-level solution for residual stress reduction.

[0040] S3. Analyze the residual stress distribution and microstructure under non-ultrasonic conditions and ultrasonic-assisted conditions, and compare the structural evolution and stress changes before and after ultrasonic assistance to obtain the reduction effect, determine the optimal ultrasonic parameters, and verify the simulated residual stress and mechanical property effects. The specific steps are as follows: S301. Analyze the residual stress distribution and microstructure under non-ultrasonic conditions and ultrasonic-assisted conditions, and compare the structural evolution and stress changes before and after ultrasonic assistance to obtain the reduction effect. The specific steps are as follows: S3011. Perform atomic simulation visualization based on the microstructures under non-ultrasound conditions and ultrasound-assisted conditions to obtain the grain size and atomic type ratio near the graphene interface under non-ultrasound conditions and ultrasound-assisted conditions, and obtain the ultrasound-assisted structural evolution; S3012. According to the residual stress distribution under non-ultrasound conditions and ultrasonic-assisted conditions, a stress calculation module is performed based on molecular dynamics to obtain the von Mises stress of each atom in the composite material model, and Gaussian filtering is used to eliminate noise. The maximum stress and stress gradient in the main body of the aluminum layer of the non-ultrasound group and the ultrasonic group are obtained, and the stress value and stress concentration coefficient at the interface of the graphene interface of the non-ultrasound group and the ultrasonic group are obtained respectively. By comparing the data of the non-ultrasound group and the ultrasonic group, the stress change with ultrasonic assistance is obtained.

[0041] In this embodiment, the microstructure and stress were analyzed, and the structural evolution and stress changes before and after ultrasonic assistance were compared. OVITO visualization showed that the grains were mainly columnar crystals growing along the Z axis, with an average size of about 20 nm. The grain boundaries were straight and densely distributed at the graphene interface. The grains in the central region merged into large-sized equiaxed crystals, and small-sized equiaxed crystals were formed at the edges. The grain boundaries were curved, the randomness of the grain orientation at the graphene interface increased, and the grain size near the interface was 30% smaller than that of the non-ultrasound group. OVITO was used to calculate the atomic type ratio, among which FCC aluminum accounted for 70% in the non-ultrasound group and decreased to 55% in the ultrasonic group; amorphous structure accounted for 25% in the non-ultrasound group and increased to 40% in the ultrasonic group; HCP stacking fault: the proportion of both groups was less than 5%. It can be seen that ultrasound has no significant effect on stacking fault formation, and ultrasonic-assisted structural evolution was obtained; Comparing the residual stress distribution, based on the residual stress distribution under non-ultrasound conditions and ultrasound-assisted conditions, the LAMMPS built-in stress calculation module is used to output the von Mises stress of each atom, and Gaussian filtering is used to eliminate noise. By comparing the key areas, it can be seen that: in the main body of the aluminum layer, the maximum stress in the non-ultrasound group is , concentrated at the grain boundaries, with stress gradients reaching ; Ultrasound group: Maximum stress was , but the stress gradient drops to , more evenly distributed; In the graphene interface, there is no ultrasound: the stress at the interface is , the stress concentration coefficient is 3.2; ultrasonic group: the stress at the interface is reduced to , the stress concentration coefficient was reduced to 2.1, the stress decay rate within 5 near the interface was accelerated by 40%, and the overall stress reduction efficiency: ultrasonic assistance reduced the average residual stress of the model by 12%, and the peak stress by 17%. By comparing the stress-related data of the non-ultrasound group and the ultrasound group, the stress change of ultrasonic assistance was obtained.

[0042] S3013. Using a dislocation analysis algorithm, identify dislocation lines, and statistically obtain the total length and type of dislocations in the non-ultrasound group and the ultrasound group. By analyzing the atomic trajectory of dislocation motion, obtain the ultrasound-assisted dislocation effect. S3014. Cutting the middle portion of the composite material model of the non-ultrasound group and the ultrasound group, respectively, balancing the cut portion under an isothermal and isobaric ensemble, and applying a strain rate along the X-axis. In response to the strain reaching a preset percentage, the tensile strength, fracture strain, and fracture mode of the non-ultrasound group and the ultrasound group are obtained, and the ultrasound-assisted mechanical properties are obtained through failure mechanism analysis; S3015. Based on the ultrasonic-assisted structural evolution, stress changes, dislocation effects, and mechanical properties, the stress reduction attribution and the reduction effect are obtained.

[0043] In this embodiment, the dislocation structure and dynamics were compared, and the dislocation analysis algorithm was used to identify the dislocation lines, and the total length and type were counted. Specifically, in the non-ultrasound group, the total dislocation length was 72.83 nm, concentrated at the grain boundary in the middle of the model, with Shockley partial dislocations accounting for 60% and Perfect full dislocations accounting for 30%. In the ultrasonic group, the total dislocation length increased to 120 nm, but the distribution became uniform, with Shockley partial dislocations increasing to 75% and Perfect full dislocations decreasing to 30%. By analyzing the dislocation motion and tracking the atomic trajectories, it can be seen that the average migration rate of dislocations in the ultrasonic group reached 100 nm. , dislocation annihilation events increased by 3 times, ultrasonic acceleration of dislocations achieved dynamic equilibrium, and ultrasonic-assisted dislocation effects were obtained; The middle part of the composite material model of the non-ultrasound group and the ultrasound group was cut, and the area size was and balance the cut part in the NPT ensemble , and the strain rate is applied along the X axis , in response to the strain reaching the preset percentage of 50%, the mechanical properties were obtained, specifically: No ultrasound group: tensile strength , the fracture strain is 15%, and the fracture path extends along the grain boundary; Ultrasound group: tensile strength The fracture strain was 14.8%, the fracture mode turned into transgranular fracture, and the crack propagation path was tortuous. The failure mechanism was analyzed. Ultrasonic assistance improved the grain boundary bonding strength by refining the edge grains and homogenizing the dislocation distribution, inhibiting the rapid propagation of cracks along the grain boundaries, and obtaining the mechanical properties of ultrasonic assistance. Summarize and verify the mechanism, and find out the stress reduction attribution based on ultrasonic-assisted structural evolution, stress changes, dislocation effects and mechanical properties. Grain refinement: small grains at the edge increase the grain boundary area and disperse local stress concentration; Dislocation homogenization: Shockley dislocations dominate slip, reducing high-energy Perfect dislocation entanglement; Interface optimization: Ultrasound promotes atomic interdiffusion between the aluminum and graphene interfaces, reducing thermal mismatch stress. Finally, by comparing simulation results with ultrasound-assisted experimental data in the literature, the rationality of the simulation trends was verified. The above-mentioned reduction effect is obtained.

[0044] In this embodiment, the ultrasonic assisted effect was verified by multi-dimensional analysis, the columnar crystals were reduced, the edge grains were refined by 30%, the amorphous structure was increased by 15%, the grain boundaries were bent, the structure was optimized, the stress gradient of the aluminum layer was reduced by 45%, and the graphene interface stress was reduced from down to The overall stress is reduced by 12%-17%, stress reduction is achieved, dislocation distribution is uniform, the proportion of incomplete dislocations increases to 75%, the migration rate increases by 233%, the annihilation events increase by 3 times, dislocation regulation is achieved, the tensile strength increases by 4.5%-8.5%, and the fracture mode is converted to transgranular fracture, the crack propagation path is extended, the performance is improved, and the synergistic effect of grain refinement, dislocation uniformity and interface diffusion enhancement is achieved.

[0045] S302. Based on the reduction effect, the optimal ultrasonic parameters are determined by orthogonal test, and the influence of mechanical properties is obtained through verification. The specific steps are as follows: S3021. Optimize the ultrasonic parameters using the single factor variable method based on the reduction effect, component thickness, and performance requirements to obtain the optimal parameter range; S3022. Based on the optimal parameter range, the initial ultrasonic parameter combination is determined according to the residual stress index formula and the strength index formula.

[0046] In this embodiment, the single-factor variable method is used to optimize the ultrasonic parameters to the optimal parameter range: amplitude 2A~8A, frequency 50 GHz~250 GHz, and the specific adjustment needs to be made according to the component thickness and performance requirements; Based on the optimal parameter range, according to the residual stress index formula and the strength index formula , determine the initial ultrasonic parameter combination; the residual stress index formula is as follows: ; in, Indicates the maximum stress value in aluminum material, represents the average stress value in graphene; The initial ultrasonic parameter combination was determined: under comprehensive performance, the combination of amplitude 5A and frequency 100GHz reduced the residual stress index RSI by 20% and increased the strength index SI by 6%; In extreme scenarios, low stress requirements: a combination of amplitude 2A and frequency 100GHz, and high stress requirements: a combination of amplitude 8Ayu1 and frequency 50GHz.

[0047] S3023. Based on the initial ultrasonic parameter combination, the composite material model is simulated using an orthogonal test to obtain an initial ultrasonic parameter model. The cutting conditions are set and the standard tensile specimens are cut to obtain the mixed characteristics of the specimen fracture surface. The smooth cleavage surface of the non-ultrasonic group is compared to obtain the interface bonding strength and plastic deformation capacity of the initial ultrasonic parameters. S3024. Based on the interface bonding strength and plastic deformation capacity of the initial ultrasonic parameters, and in combination with the use of low amplitude in ultrasonic assistance to refine grains through cavitation effect, and the use of high amplitude to fuse grains and migrate dislocations over long distances through enhanced acoustic streaming effect, the initial ultrasonic parameter combination is optimized based on the suitable structures of low amplitude and high amplitude to obtain the optimal ultrasonic parameters; S3025. Based on the optimal ultrasonic parameters, the simulated residual stress and mechanical property effects are verified through tensile tests.

[0048] In this embodiment, the mechanical properties are simulated to verify the model, the amplitude is 5A + the frequency is 100GHz, and the cutting conditions are set, specifically: the strain rate is , the NVT ensemble maintains a temperature of 300K, the yield strength ,tensile strength , fracture strain 14.5%; cutting standard tensile specimens, the specimen fracture surface showed mixed characteristics of dimples and tearing edges, and compared with the smooth cleavage surface of the non-ultrasound group, the interface bonding strength and plastic deformation capacity of the initial ultrasonic parameters were obtained; According to the interface bonding strength and plastic deformation capacity of the initial ultrasonic parameters, based on the parameter-performance correlation mechanism, combined with the use of low amplitude in ultrasonic assistance to refine grains through cavitation effect, and the use of high amplitude to fuse grains and migrate dislocations over long distances through enhanced acoustic streaming effect, the initial ultrasonic parameter combination was optimized based on the suitable structure of low amplitude and high amplitude to obtain the optimal ultrasonic parameters; According to the optimal ultrasonic parameters, the simulated residual stress and mechanical property effects were verified by tensile tests.

[0049] S4. Combining the reduction effect and the influence of mechanical properties, the optimal ultrasonic parameters are converted into actual process parameters, and the actual internal residual stress of the 3D printing is measured. The simulated residual stress and the actual residual stress are compared. In response to the reduction of residual stress, the residual stress reduction is completed. The specific steps are as follows: S401. Based on the reduction effect and the influence of mechanical properties, the optimal ultrasonic parameters are mapped to the actual production according to the scale conversion formula to obtain the actual process parameters; S402. Based on actual production, an ultrasonic vibration module is installed in the laser powder bed fusion equipment. The vibration direction is perpendicular to the printed layer, and the piezoelectric ceramic transducer is used for vibration loading. In response to the completion of laser scanning, ultrasonic vibration is started and continued until interlayer cooling is completed, completing the actual ultrasonic parameter setting. S403, based on the actual ultrasonic parameter settings, setting a non-ultrasound group and an ultrasonic group, printing a standard part of an aluminum-based composite material reinforced with graphene, and measuring the actual 3D printed internal residual stress using X-ray diffraction to obtain the actual residual stress; S404. Based on the simulated residual stress and the actual residual stress, determine whether the deviation between the simulated residual stress and the actual residual stress is greater than a preset threshold. If so, establish a calibration iterative closed loop of simulation prediction, experimental verification, and parameter correction, adjust the actual ultrasonic parameters, and return to step S403. Otherwise, save the actual ultrasonic parameters to the ultrasonic-assisted process database to complete the ultrasonic-assisted reduction of residual stress in 3D-printed aluminum-based composite materials.

[0050] In this embodiment, the reduction effect and the influence of mechanical properties are combined, and the parameter scale is converted according to the scale conversion formula to obtain the actual process parameters. The 100 GHz in the simulation is proportionally converted to the actual industrial frequency 20 kHz~40 kHz, and the 0.2 nm in the simulation of the commonly used frequency band of the ultrasonic equipment is converted to the actual , and can be adjusted according to the characteristics of aluminum-based composite materials; The scale conversion formula is a frequency conversion formula and an amplitude conversion formula, and the expressions are as follows: ; ; in, Indicates the actual frequency, represents the analog frequency, represents the actual amplitude, represents the simulated amplitude; Based on actual production, a process integration solution was set up. An ultrasonic vibration module was added to the laser powder bed fusion equipment. The vibration direction was perpendicular to the printed layer, and the piezoelectric ceramic transducer was used for vibration loading. In response to the completion of the laser scan, the ultrasonic vibration was started and continued until the interlayer cooling was completed, completing the actual ultrasonic parameter setting. Based on the actual ultrasonic parameter settings, the experimental steps were verified. A non-ultrasound group and an ultrasonic group were set up to print standard aluminum-based composite parts reinforced with graphene. The actual internal residual stress of the 3D print was measured using X-ray diffraction to obtain the actual residual stress. The peak stress and distribution uniformity of the non-ultrasound group and the ultrasonic group were compared. The grain morphology and interface bonding quality were observed using scanning electron microscopy. The strength and plasticity were measured by tensile testing. The failure mode was verified by fracture analysis. Finally, it was verified that the stress reduction amplitude and grain refinement effect predicted by the simulation were consistent with the experimental results. Based on the simulated residual stress and the actual residual stress, it is determined whether the deviation between the simulated residual stress and the actual residual stress is greater than the preset threshold of 10%. If so, a calibration iterative closed loop of "simulation prediction → experimental verification → parameter correction" is established to adjust the actual ultrasonic parameters, and the actual residual stress is obtained again through actual printing. Otherwise, the actual ultrasonic parameters are saved in the ultrasonic-assisted process database to complete the ultrasonic-assisted reduction of residual stress in 3D-printed aluminum-based composite materials.

[0051] In this embodiment, a composite material model is first constructed, the structure and parameters of each component are determined, the functional layer of the iron substrate is divided, and the initial arrangement and pre-relaxation are completed. Then, ultrasonic-free printing is simulated to obtain benchmark data, including residual stress, microstructure and dislocation distribution. Subsequently, ultrasonic-assisted printing is implemented, and vibration is introduced during the cooling stage. Stress is reduced through effects such as acoustic streaming, cavitation and dislocation regulation. The structural and stress changes before and after ultrasound are analyzed and compared to verify the reduction effect. Subsequently, the optimal ultrasonic parameters are determined through single-factor and orthogonal experiments, and their effect on improving mechanical properties is verified. Finally, the simulation parameters are converted into actual process parameters and integrated into the printing equipment. After multi-dimensional experimental verification and parameter calibration, a process database is formed. Through cross-scale conversion and experimental verification, the atomic-level simulation results are converted into an operational industrial process to ensure that ultrasonic-assisted technology can effectively reduce residual stress and improve material properties in actual production, realizing the implementation from theory to engineering.

Claims

1. A method for reducing residual stress of 3D printed aluminum-based composite materials with ultrasound assistance, characterized in that: The following steps are involved: S1. Prepare 3D printed aluminum-based composite materials based on aluminum particles and graphene, and build composite material models; S2. Based on the composite material model, simulate non-ultrasonic printing to obtain a first residual stress distribution and a first microstructure under non-ultrasonic conditions, and simulate ultrasonic-assisted printing by introducing ultrasonic vibration during the cooling stage to obtain a second residual stress distribution and a second microstructure under ultrasonic-assisted conditions; S3. Analyze the residual stress distribution and microstructure under non-ultrasound conditions and ultrasound-assisted conditions, and compare the structural evolution and stress changes before and after ultrasound assistance to obtain the reduction effect, determine the optimal ultrasound parameters, and verify the simulated residual stress and mechanical property effects; S4. Combining the reduction effect and the influence of mechanical properties, the optimal ultrasonic parameters are converted into actual process parameters, and the actual internal residual stress of 3D printing is measured. The simulated residual stress and the actual residual stress are compared, and the residual stress reduction is completed in response to the residual stress reduction.

2. The ultrasonic-assisted method for reducing residual stress in 3D printed aluminum-based composite materials according to claim 1, characterized in that: Said S1 comprises the following steps: S101, using a body-centered cubic structure to construct an iron substrate, and setting a boundary layer at the bottom two atomic layers of the iron substrate, setting a constant temperature layer at the middle three atomic layers of the iron substrate, and setting a Newtonian layer at the top one atomic layer of the iron substrate; S102, using aluminum atoms with a face-centered cubic structure to represent aluminum particles of a preset diameter, the aluminum particles are evenly arranged on the iron substrate at a preset spacing to form an aluminum particle layer, and using carbon atoms to form a single layer of graphene with a hexagonal structure, the single layer of graphene is arranged in the center of the aluminum particle layer; S103, in the XY plane, based on a square network with a preset side length, arranging aluminum particles according to a preset center spacing, aligning the center of the single-layer graphene with the center of the composite material based on a preset initial temperature maintained by the constant temperature layer of the iron substrate, maintaining a planar state by the rigid constraint of the iron substrate boundary layer according to a preset spacing between the graphene and the iron substrate and a preset spacing between the graphene and the aluminum particles, thereby obtaining a 3D-printed aluminum-based composite material; S104. Based on 3D printing of aluminum-based composite materials, set XY-axis periodic boundary conditions to simulate an infinite system in response to atoms moving out of one boundary and entering from equivalent positions on the opposite boundary. Set a Z-axis boundary condition to simulate the free surface during the printing process without constraints on the surface of the top aluminum particles. Use a microcanonical ensemble for initial relaxation to eliminate initial stress and obtain an initial model. S105. Based on the initial model, pre-relaxation is performed and the model energy is minimized. The model energy is iteratively calculated using the conjugate gradient method. The molecular dynamics calculation is performed based on the Newtonian layer of the iron substrate. In response to the interatomic force being less than the preset force threshold, the initial configuration with the lowest energy is obtained. Based on the preset running time and preset time step of the microcanonical ensemble, a composite material model is constructed according to the initial configuration with the lowest energy.

3. The ultrasonic-assisted method for reducing residual stress in 3D printed aluminum-based composite materials according to claim 1, characterized in that: The S2 comprises the following steps: S201. Based on the composite material model, simulate non-ultrasonic 3D printing to obtain the residual stress distribution and microstructure under non-ultrasonic conditions; S202. Perform ultrasonic-assisted 3D printing based on the composite material model, and introduce ultrasonic vibration during the cooling stage to regulate the solidification process and obtain the residual stress distribution and microstructure under ultrasonic-assisted conditions.

4. The ultrasonic-assisted method for reducing residual stress in 3D printed aluminum-based composite materials according to claim 3, characterized in that: The S201 includes the following steps: S2011. Simulating laser melting based on the composite material model, heating a preset area, and scanning along the Y-axis at a preset speed. In response to complete melting of the aluminum particles, stopping melting, and naturally cooling the composite material model under a microcanonical ensemble to obtain a composite material model containing residual stress. S2012. Analyze the composite material model containing residual stress using the crystal local order parameter to identify a first microstructure; S2013. Calculating a composite material model containing residual stress using a Virial stress formula to obtain a first residual stress distribution; S2014. According to the first microstructure and the first residual stress distribution, dislocation lines are tracked using dislocation diffusion analysis to obtain dislocation lines dominated by Shockley incomplete dislocations, and based on the dislocation lines, the residual stress distribution and microstructure under non-ultrasonic conditions are obtained.

5. The ultrasonic-assisted method for reducing residual stress in 3D printed aluminum-based composite materials according to claim 3, characterized in that: The S202 includes the following steps: S2021. Based on the composite material model, simulate laser melting, introduce ultrasonic vibration, set and load ultrasonic vibration parameters, and apply sinusoidal vibration along the Z axis to simulate the vertical excitation of the ultrasonic transducer in the actual process. In response to the laser being turned off, start the ultrasonic vibration and synchronize the ultrasonic vibration with the cooling process. Use a canonical ensemble to maintain the preset printing system temperature, and use the Anderson thermal bath method to eliminate the interference of vibration heat generation, thereby obtaining a composite material model with eliminated vibration interference; S2022. Based on a composite material model that eliminates vibration interference, the ultrasonic field is coupled with the solidification process. Ultrasonic vibration is used to induce stable fluid motion and disturb the direction of heat flow, thereby suppressing the directional growth of columnar crystals along the laser scanning direction to form equiaxed crystal nuclei. S2023. Based on fluid flushing, nucleation is promoted in the edge region to obtain a refined grain size. Based on periodic pressure fluctuations, microbubbles are collapsed to generate microjets, which crush and impact the dendrite arms to update the nucleation sites. Ultrasonic energy is used to stimulate dislocation slip and climb, multiply Shockley partial dislocations and diffuse them into the grain interior, reduce the density of complete dislocations, and transform dislocations from being concentrated at the grain boundaries to being uniformly distributed across the entire region. Based on equiaxed crystal nuclei, a second microstructure is obtained. S2024. Based on the single variable principle, the cooling rate without ultrasonic conditions is used to control the cooling process. The atomic coordinates and velocities are recorded according to the preset recording time to obtain the grain growth path, the atomic diffusion behavior at the interface, and the dynamic response of the aluminum atoms near the graphene, and the ultrasonic influence including the interdiffusion of the interface atoms is obtained; S2025. Based on the ultrasonic influence, the total energy of the printing system is monitored in real time. In response to the printing system not being overheated, a virial stress formula is used to calculate the composite material model with vibration interference eliminated to obtain a second residual stress distribution. S2026. Based on the second microstructure and the second residual stress distribution, by observing the stress evolution trend during the cooling process, the residual stress distribution and microstructure under ultrasonic-assisted conditions are obtained.

6. The ultrasonic-assisted method for reducing residual stress in 3D printed aluminum-based composite materials according to claim 1, characterized in that: The expression of the composite material model for eliminating vibration interference is as follows: in, Indicates the i Atomic mass, Indicates the i The position vector of each atom, Indicates time, represents the gradient of the interatomic potential energy V, represents the amplitude, represents the angular frequency of ultrasonic vibration, represents the unit vector in the Z-axis direction, represents the Boltzmann constant, Indicates the current temperature, which is the temperature that changes over time. represents Gaussian white noise, represents the cooling time constant, Indicates the total cooldown time.

7. The ultrasonic-assisted method for reducing residual stress in 3D printed aluminum-based composite materials according to claim 1, characterized in that: The S3 includes the following steps: S301, analyzing the residual stress distribution and microstructure under non-ultrasonic conditions and ultrasonic-assisted conditions, and comparing the structural evolution and stress changes before and after ultrasonic assistance to obtain the reduction effect; S302. According to the reduction effect, the optimal ultrasonic parameters are determined by using orthogonal experiments, and the influence of mechanical properties is obtained through verification.

8. The ultrasonic-assisted method for reducing residual stress in 3D printed aluminum-based composite materials according to claim 7, characterized in that: The S301 includes the following steps: S3011. Perform atomic simulation visualization based on the microstructures under non-ultrasound conditions and ultrasound-assisted conditions to obtain the grain size and atomic type ratio near the graphene interface under non-ultrasound conditions and ultrasound-assisted conditions, and obtain the ultrasound-assisted structural evolution; S3012. Based on the residual stress distribution under non-ultrasound conditions and ultrasound-assisted conditions, a stress calculation module is performed based on molecular dynamics to obtain the von Mises stress of each atom in the composite material model. A Gaussian filter is used to eliminate noise. The maximum stress and stress gradient in the main body of the aluminum layer are obtained for the non-ultrasound group and the ultrasound group, and the stress value and stress concentration factor at the graphene interface are obtained for the non-ultrasound group and the ultrasound group, respectively. By comparing the data of the non-ultrasound group and the ultrasound group, the stress change after ultrasound-assisted treatment is obtained. S3013. Using a dislocation analysis algorithm, identify dislocation lines, and statistically obtain the total length and type of dislocations in the non-ultrasound group and the ultrasound group. By analyzing the atomic trajectory of dislocation motion, obtain the ultrasound-assisted dislocation effect. S3014. Cutting the middle portion of the composite material model of the non-ultrasound group and the ultrasound group, respectively, balancing the cut portion under an isothermal and isobaric ensemble, and applying a strain rate along the X-axis. In response to the strain reaching a preset percentage, the tensile strength, fracture strain, and fracture mode of the non-ultrasound group and the ultrasound group are obtained, and the ultrasound-assisted mechanical properties are obtained through failure mechanism analysis; S3015. Based on the ultrasonic-assisted structural evolution, stress changes, dislocation effects, and mechanical properties, the stress reduction attribution and the reduction effect are obtained.

9. The ultrasonic-assisted method for reducing residual stress in 3D printed aluminum-based composite materials according to claim 7, characterized in that: The S302 includes the following steps: S3021. Optimize the ultrasonic parameters using the single factor variable method based on the reduction effect, component thickness, and performance requirements to obtain the optimal parameter range; S3022. Based on the optimal parameter range, determine the initial ultrasonic parameter combination according to the residual stress index formula and the strength index formula; S3023. Based on the initial ultrasonic parameter combination, the composite material model is simulated using an orthogonal test to obtain an initial ultrasonic parameter model. The cutting conditions are set and the standard tensile specimens are cut to obtain the mixed characteristics of the specimen fracture surface. The smooth cleavage surface of the non-ultrasonic group is compared to obtain the interface bonding strength and plastic deformation capacity of the initial ultrasonic parameters. S3024. Based on the interface bonding strength and plastic deformation capacity of the initial ultrasonic parameters, and in combination with the use of low amplitude in ultrasonic assistance to refine grains through cavitation effect, and the use of high amplitude to fuse grains and migrate dislocations over long distances through enhanced acoustic streaming effect, the initial ultrasonic parameter combination is optimized based on the suitable structures of low amplitude and high amplitude to obtain the optimal ultrasonic parameters; S3025. Based on the optimal ultrasonic parameters, the simulated residual stress and mechanical property effects are verified through tensile tests.

10. The ultrasonic-assisted method for reducing residual stress in 3D printed aluminum-based composite materials according to claim 1, characterized in that: The S4 comprises the following steps: S401. Combine the reduction effect and the influence of mechanical properties, and map the optimal ultrasonic parameters to actual production according to the scale conversion formula to obtain the actual process parameters; S402. Based on actual production, an ultrasonic vibration module is installed in the laser powder bed fusion equipment. The vibration direction is perpendicular to the printed layer, and the piezoelectric ceramic transducer is used for vibration loading. In response to the completion of laser scanning, ultrasonic vibration is started and continued until interlayer cooling is completed, completing the actual ultrasonic parameter setting. S403, based on the actual ultrasonic parameter settings, setting a non-ultrasound group and an ultrasonic group, printing a standard part of an aluminum-based composite material reinforced with graphene, and measuring the actual 3D printed internal residual stress using X-ray diffraction to obtain the actual residual stress; S404. Based on the simulated residual stress and the actual residual stress, determine whether the deviation between the simulated residual stress and the actual residual stress is greater than a preset threshold. If so, establish a calibration iterative closed loop of simulation prediction, experimental verification, and parameter correction, adjust the actual ultrasonic parameters, and return to step S403. Otherwise, save the actual ultrasonic parameters to the ultrasonic-assisted process database to complete the ultrasonic-assisted reduction of residual stress in 3D-printed aluminum-based composite materials.

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