A method for inhibiting element segregation in the solidification process of additive magnesium-rare earth alloy by dual ultrasonic

Abstract

A method for inhibiting element segregation in the solidification process of additive manufacturing of magnesium-rare earth alloy by dual ultrasonic is provided. Different ultrasonic vibration modes are applied to both sides of the molten pool in stages. When the deposited height does not exceed 50 mm, longitudinal vibration mode or radial vibration mode is applied to both sides of the substrate. When the deposited height exceeds 50 mm, radial vibration mode is applied to both sides of the deposited layer wall. The two rolling ultrasonic tool heads move synchronously and in the same direction with the welding gun. The two rolling ultrasonic tool heads generate ultrasonic vibration of the same frequency at the same time. By reasonably designing the action positions of the two rolling ultrasonic tool heads on both sides of the molten pool, high-amplitude ultrasonic vibration is formed by superposition, which significantly improves the strength, adjustability and uniformity of the ultrasonic field in the molten pool, effectively reduces the solute element grain boundary segregation, and further improves the comprehensive mechanical properties of the magnesium-rare earth alloy produced by additive manufacturing, which has good application prospect.

Description

Technical Field

[0001] This invention belongs to the field of magnesium alloy arc additive manufacturing technology, specifically relating to a method for suppressing element segregation during the solidification process of arc additive magnesium rare earth alloys using dual ultrasound. Background Technology

[0002] Magnesium alloys have low density and high specific strength, making them promising for applications in the aerospace field. For the manufacture of large-size magnesium alloy structural components, arc additive manufacturing offers numerous advantages over traditional casting methods, such as fine grain size, absence of macroscopic segregation, near-net-shape forming of complex structures, and superior overall mechanical properties. In summary, the use of arc additive manufacturing technology to fabricate magnesium alloy structural components holds broad engineering application potential.

[0003] During the process of melting magnesium alloy welding wire layer by layer using an electric arc heat source, a molten pool is formed under the action of electric arc heat. Introducing high-energy ultrasonic vibration into the molten pool will improve the flow and solidification environment of the molten pool, and ultimately improve the comprehensive mechanical properties of magnesium alloys manufactured by electric arc additive manufacturing.

[0004] CN202110521112.1 discloses an arc additive manufacturing method featuring ultrasonic vibration and rolling characteristics during welding. An ultrasonic vibration rolling roller is installed behind the arc additive manufacturing welding torch, moving synchronously and in the same direction as the torch. This roller applies ultrasonic vibration and rolling to the arc additive manufacturing layer in its thermoplastic stage, promoting plastic deformation. Simultaneously, the ultrasonic vibration is transmitted to the molten pool. The combined effect of these two processes improves the microstructure and properties of the arc additive layer. While this application achieves the feature of synchronous movement between the ultrasonic vibration rolling roller and the welding torch, it is limited by the single ultrasonic vibration rolling roller. The energy and distribution of the ultrasonic field within the molten pool are uneven and cannot be flexibly controlled, making decoupling between the ultrasonic vibration effect and the rolling effect difficult.

[0005] CN201810464169.0 discloses a CMT-ultrasonic vibration composite additive manufacturing method, which performs ultrasonic vibration on a substrate simultaneously with CMT arc additive manufacturing. After applying ultrasonic vibration, a component with a fine and uniform non-dendritic structure can be obtained. This application directly applies a single ultrasonic impact gun to the substrate and moves synchronously with the CMT welding gun. This ultrasonic application method results in relatively low ultrasonic energy in the molten pool and a relatively uneven sound field distribution in the molten pool, with poor adjustability of the sound field distribution.

[0006] CN202411277389.4 discloses an apparatus and method for high-entropy alloy arc additive manufacturing based on double-sided ultrasonic rolling. In the process of additive manufacturing high-entropy alloys using tungsten inert gas welding, rolling ultrasonic rolling heads are symmetrically distributed on both sides of the high-entropy alloy additive body. The double-sided ultrasonic rolling technology makes the interlayer bonding of the high-entropy alloy additive body denser, improving the quality of high-entropy alloy arc additive manufacturing. However, this invention only emphasizes the symmetrical placement of ultrasonic rollers on both sides of the additive wall, without specifically describing the design strategy for the placement of the ultrasonic rolling heads. The focus is on using ultrasonic rollers to roll the additive manufacturing wall surface, rather than using ultrasonic rolling to control the magnitude of ultrasonic vibration energy within the molten pool and influence the microstructure of the molten pool after solidification.

[0007] Based on the above analysis, the following key issues remain unresolved in the existing technology for additive manufacturing of magnesium rare earth alloys using arc-fused wires:

[0008] (1) Magnesium alloys are different from other metal materials and have high damping characteristics. When mechanical vibrations propagate in magnesium alloys, the amplitude attenuation is large. When a single ultrasonic roller is applied to the magnesium alloy substrate or the side wall of the deposition area, the ultrasonic vibration amplitude is significantly attenuated in the magnesium alloy, resulting in weak ultrasonic energy in the magnesium alloy molten pool and insignificant changes in the microstructure of the arc-additive magnesium alloy.

[0009] (2) During the solidification process of magnesium rare earth alloys in arc additive manufacturing, the molten pool solidifies rapidly. The solubility of solute elements in the α-Mg solid solution decreases with decreasing temperature, and a large amount of solute elements are expelled to the solid-liquid interface front, eventually forming a large number of low-melting-point, high-hardness, and brittle Mg-RE intermetallic compounds at the grain boundaries. Severe element segregation and the resulting formation of a large number of Mg-RE intermetallic compounds at the grain boundaries have an adverse effect on the mechanical properties of magnesium rare earth alloys manufactured by arc additive manufacturing, weakening the solid solution strengthening effect of rare earth elements. At the same time, stress concentration is prone to occur near the Mg-RE intermetallic compounds, and cracks are prone to initiation and propagation at these locations. Summary of the Invention:

[0010] To address the existing technical problems in arc additive manufacturing of magnesium rare earth alloys, the present invention aims to provide a method for suppressing elemental segregation during the solidification process of arc additive manufacturing of magnesium rare earth alloys using dual ultrasound. This method employs a strong standing wave acoustic field formed by the superposition of dual ultrasound waves, which is then applied to the molten pool of the magnesium rare earth alloy. By designing the application position of the dual ultrasound waves and changing their amplitude and vibration mode, the ultrasonic energy and distribution within the molten pool during arc additive manufacturing of magnesium rare earth alloys can be effectively controlled. This ensures that the ultrasonic energy in the solid-liquid mixing zone is always at its maximum. The combined effects of acoustic cavitation, acoustic flow, and vibration-induced lattice distortion promote the forced migration of solute atoms into the solid magnesium matrix within the solid-liquid mixing zone, thereby increasing the solid solubility of solute elements, reducing the degree of grain boundary segregation of solute elements, decreasing the size of the eutectic phase at the grain boundaries, and dispersing its distribution. Finally, this comprehensively improves the strength and ductility of the arc additive manufactured magnesium rare earth alloy.

[0011] To address the problems in the existing technology, the technical solution adopted by this invention is as follows:

[0012] A method for suppressing elemental segregation during the solidification of arc-additive magnesium rare-earth alloys using dual ultrasound includes the following steps:

[0013] Step 1: Polish the surface of the magnesium alloy substrate to remove the oxide film and surface oil. Place the polished magnesium alloy substrate on the auxiliary heating stage, fix the magnesium alloy substrate with a clamp, turn on the auxiliary heating stage switch, and preheat the magnesium alloy substrate.

[0014] Step 2: Determine the relative positional relationship between the two sets of rolling ultrasonic tool heads on the surface of the magnesium alloy substrate and the molten pool, as well as the vibration mode of the rolling ultrasonic tool heads; place the magnesium rare earth alloy welding wire on the wire feeding mechanism and guide the welding wire out from the wire feeding nozzle of the welding gun; set the welding current, wire feeding speed, welding speed and shielding gas flow rate parameters.

[0015] Step 3: After the magnesium alloy substrate is preheated to the set temperature, two sets of rolling ultrasonic tool heads are applied to the designated positions on the surface of the magnesium alloy substrate and pressure is applied. At the same time, the ultrasonic vibration and electric arc additive manufacturing process are started. The two sets of rolling ultrasonic tool heads move synchronously and in the same direction with the welding gun at the same speed. The ultrasonic frequency is 20-50kHz and the ultrasonic power does not exceed 1500W. When the deposited height reaches 50mm, the first stage of additive manufacturing is completed. At the same time, the electric arc and ultrasonic vibration are turned off and the ultrasonic tool head is separated from the magnesium alloy substrate.

[0016] Step 4: After the first stage of arc additive manufacturing is completed, before proceeding to the second stage, determine the position of the rolling ultrasonic tool head on the sidewall of the deposited layer. Apply pressure to the designated positions on the sidewall of the magnesium alloy deposited layer using two sets of rolling ultrasonic tool heads. Simultaneously, start the ultrasonic vibration and arc additive manufacturing process. The two sets of rolling ultrasonic tool heads move synchronously and in the same direction as the welding torch at the same speed. The ultrasonic frequency is 20-50kHz, and the ultrasonic power does not exceed 1500W. The additive manufacturing process in the second stage is the same as in Step 3. At the end of each additive manufacturing pass, simultaneously shut off the arc and ultrasonic vibration, and separate the ultrasonic tool head from the sidewall of the deposited layer. In each subsequent additive manufacturing pass, the operation method is the same as the arc and ultrasonic operation in Step 4 until the set height is reached, at which point the additive manufacturing and ultrasonic processing are stopped. After the arc additive manufacturing is completed, shut off the arc and ultrasound, and adjust the welding torch and ultrasonic tool head to a suitable spatial position. Turn off the power to the auxiliary heating table. After the additive component has cooled naturally, remove the arc additive component.

[0017] As an improvement, the arc additive manufacturing process is carried out using an arc heat source fused wire additive manufacturing method. The arc heat source includes cold metal transfer welding (CMT), gas metal arc welding (MIG), or tungsten inert gas welding (TIG). When using cold metal transfer welding (CMT) or gas metal arc welding (MIG), the auxiliary heating temperature is 300-450℃; when using tungsten inert gas welding (TIG), the auxiliary heating temperature is 200-300℃, and the size of the magnesium alloy substrate is 220mm×220mm×30mm.

[0018] As an improvement, the magnesium rare earth alloy mentioned in step 2 includes, but is not limited to, Mg-Y-Nd series, Mg-Y-Nd-Gd series, Mg-Gd-Y series or Mg-Nd-Zn-Zr series, and the diameter of the welding wire is 1.2mm.

[0019] As an improvement, step 2 involves determining the relative positional relationship between the two sets of rolling ultrasonic tool heads on the magnesium alloy substrate surface and the molten pool, as well as the vibration mode of the rolling ultrasonic tool heads. The specific steps are as follows:

[0020] (1) Based on the actual size of the magnesium alloy substrate, a geometric model is established in the finite element simulation software, and the geometric model is consistent with the actual shape of the magnesium alloy substrate. During the geometric modeling process, different ultrasonic tool head action positions are set. The principle for setting the action position of the ultrasonic tool head is as follows: the center position of the molten pool is set to the centerline position of the upper surface of the magnesium alloy substrate. Two sets of rolling ultrasonic tool heads act on the magnesium alloy substrate surface on both sides of the center of the molten pool in a line contact manner. The radial distance between the action position of the ultrasonic tool head and the center of the molten pool is 5-35mm.

[0021] (2) Based on the actual magnesium alloy substrate material used, the accurate magnesium alloy substrate material is set in the finite element simulation software, and the boundary conditions and initial conditions are set. The elastic wave control equation and frequency domain solution method are adopted. Among them, the boundary conditions are as follows: each surface of the magnesium alloy substrate is set to a free vibration mode; the initial conditions are: the action pressure and ultrasonic amplitude are set at the action position of the two sets of rolling ultrasonic tool heads; the vibration mode of the two sets of rolling ultrasonic tool heads also needs to be set in the initial conditions. The vibration mode is either a longitudinal vibration mode with the ultrasonic vibration direction parallel to the surface of the magnesium alloy substrate or a radial vibration mode with the ultrasonic vibration direction perpendicular to the surface of the magnesium alloy substrate; the ultrasonic frequency is set in the frequency domain solver.

[0022] (3) The finite element mesh is generated using the tetrahedral mesh generation method, and the maximum mesh size must be less than 1 / 20 of the ultrasonic propagation wavelength in magnesium rare earth alloys;

[0023] (4) Finite element simulation was performed for cases with different vibration modes and action positions to simulate the amplitude distribution on the surface of the magnesium alloy substrate under different ultrasonic tool head action positions, and the action position of the rolling ultrasonic tool head with the maximum ultrasonic amplitude on the arc movement path was selected.

[0024] (5) Method for determining the positional relationship between the welding torch and the two sets of rolling ultrasonic tool heads: The welding torch is regarded as a point, and the position of the welding torch corresponds to the center position of the molten pool. According to step (4), the center position of the molten pool is set at the position with the largest ultrasonic amplitude on the magnesium alloy surface, and then the position between the welding torch and the two sets of rolling ultrasonic tool heads is determined. The dry extension of the welding wire is 12-15mm, and the tip of the welding wire is 1-2mm away from the surface of the magnesium alloy substrate.

[0025] A further improvement is that in step (1), the rolling ultrasonic tool head and the magnesium alloy substrate surface are in line contact, and the length of the contact area is 8-15mm; the vibration mode of the rolling ultrasonic tool head is either longitudinal vibration mode or radial vibration mode.

[0026] As an improvement, the pressure exerted by the rolling ultrasonic tool head on the substrate surface is controlled by controlling the air pressure intensity of the air compressor, with the air compressor pressure set to 0.15 MPa.

[0027] As an improvement, step 4, determining the effective position of the rolling ultrasonic tool head on the sidewall of the deposition layer, includes the following steps:

[0028] (1) Based on the actual size of the magnesium alloy substrate, a geometric model is established in the finite element simulation software. The geometric model is consistent with the actual geometric shape of the additive component after step 3. During the geometric modeling process, different ultrasonic tool head action positions are set. The principle for setting the ultrasonic tool head action positions is as follows: two sets of rolling ultrasonic tool heads act on the two sides of the additive wall in a line contact manner. The length of the line contact is 8-15mm. The ultrasonic tool head acts on the wall surface at a distance of 5-10mm from the upper surface of the wall.

[0029] (2) Based on the actual magnesium alloy substrate material used, the accurate magnesium alloy substrate material is set in the finite element simulation software, and the boundary conditions and initial conditions are set. The elastic wave control equation and frequency domain solution method are adopted. The boundary conditions are as follows: each surface of the magnesium alloy substrate is set to a free vibration mode; the initial conditions are: the action pressure and ultrasonic amplitude are set at the action position of the two sets of rolling ultrasonic tool heads; the vibration mode of the two sets of rolling ultrasonic tool heads also needs to be set in the initial conditions. The vibration mode is the radial vibration mode with the ultrasonic vibration direction perpendicular to the surface of the additively manufactured magnesium rare earth alloy wall; the ultrasonic frequency is set in the frequency domain solver.

[0030] (3) The finite element mesh is generated using the tetrahedral mesh generation method, and the maximum mesh size must be less than 1 / 20 of the ultrasonic propagation wavelength in magnesium rare earth alloys;

[0031] (4) Finite element simulation was performed for cases with different ultrasonic action positions to simulate the amplitude distribution on the surface of the magnesium rare earth alloy wall under different action positions of the ultrasonic tool head, and the action position of the rolling ultrasonic tool head with the maximum ultrasonic amplitude on the arc movement path was selected.

[0032] (5) Method for determining the positional relationship between the welding torch and the two sets of rolling ultrasonic tool heads: The welding torch is regarded as a point, and the position of the welding torch corresponds to the center position of the molten pool. According to the sound field simulation results, the center position of the molten pool is set at the position with the largest ultrasonic amplitude on the surface of the magnesium rare earth alloy deposition layer, and then the positional relationship between the welding torch and the two sets of rolling ultrasonic tool heads is determined. The wire extension is 12-15mm, and the tip of the welding wire is 1-2mm away from the surface of the magnesium alloy substrate.

[0033] This invention addresses the high damping characteristics of magnesium alloys by simultaneously applying a rolling ultrasonic toolhead to the surface of a magnesium alloy substrate and both sides of an arc-additive wall. The two ultrasonic beams superimpose within the magnesium alloy substrate and the additive wall to form a strong standing wave ultrasonic field. The strongest ultrasonic amplitude is applied to the solid-liquid mixing zone during the solidification process of the molten pool. The forced convection stirring of the high-temperature molten pool by the acoustic flow promotes the uniform distribution of solute elements within the melt. The high temperature and impact force generated by the ultrasonic cavitation effect at the solid-liquid interface during solidification enhance the migration kinetic energy of solute atoms. Ultrasonic vibration induces lattice distortion in the solid phase during the later stages of solidification within the solid-liquid mixing zone, creating vacancies and promoting the migration of solute atoms from the liquid phase to these defects in the solid phase. The ultrasonic distribution within the molten pool can be precisely adjusted by independently regulating the application position, amplitude, and phase of the two ultrasonic beams.

[0034] Beneficial effects:

[0035] Compared with existing technologies, this invention provides a method for suppressing elemental segregation during the solidification process of magnesium rare earth alloys manufactured by arc additive manufacturing using dual ultrasound. Specifically targeting the arc additive manufacturing process of high-damping magnesium rare earth alloys, two sets of rolling ultrasonic toolheads act in stages on the magnesium alloy substrate and the sidewalls of the deposition zone, moving synchronously and in the same direction as the welding torch. This enhances the ultrasonic intensity, uniformity, and controllability within the molten pool, thereby reducing elemental segregation, promoting the dispersion of eutectic phases at grain boundaries, and improving the overall mechanical properties of magnesium rare earth alloys manufactured by arc additive manufacturing. The advantages are as follows:

[0036] 1. The dual-ultrasonic-assisted method employed in this invention flexibly controls the acoustic field distribution within the magnesium alloy molten pool by independently adjusting the position and amplitude of two rolling ultrasonic tool heads acting on the magnesium alloy substrate and the sidewall of the deposition area. This significantly increases the ultrasonic energy within the magnesium alloy molten pool during arc additive manufacturing, effectively overcoming the adverse effects of the high damping characteristics of magnesium alloy on vibration attenuation and ensuring a more uniform ultrasonic distribution within the molten pool.

[0037] 2. In the process of producing magnesium rare earth alloys by electric arc additive manufacturing of the present invention, the solid solution of solute atoms into the α-Mg matrix is ​​promoted, which significantly reduces the degree of grain boundary segregation of solute elements and the size of low-melting-point Mg-RE eutectic phase at the grain boundary. This promotes the dispersed distribution of the Mg-RE eutectic phase at the grain boundary, and the strength and ductility are significantly higher than the mechanical properties of magnesium rare earth alloys produced by the original electric arc additive manufacturing, thus broadening the application of the material. Attached Figure Description

[0038] Figure 1 The simulation results show the ultrasonic field vibration distribution in the first stage of arc additive manufacturing.

[0039] Figure 2 The top view shows the position of the rolling ultrasonic tool head and the spatial relationship between the molten pool in the first stage of arc additive manufacturing.

[0040] Figure 3The simulation results show the ultrasonic field vibration distribution in the second stage of arc additive manufacturing.

[0041] Figure 4 The spatial relationship between the action position of the rolling ultrasonic tool head and the molten pool in the second stage of arc additive manufacturing (top view).

[0042] Figure 5 The distribution of solute elements in magnesium rare earth alloys manufactured by electric arc additive manufacturing under different treatments is shown in (a) for the original CMT electric arc additive manufacturing of ZM6 magnesium alloy, (b) for the CMT electric arc additive manufacturing of ZM6 magnesium alloy using the present invention, and (c) for the comparison of the size and content of precipitated phases in ZM6 magnesium alloy under the present invention and the original manufacturing process.

[0043] Figure 6 Changes in the mechanical properties of magnesium rare earth alloys prepared by electric arc additive manufacturing with different treatments. Detailed Implementation

[0044] The present invention will be further described in detail below with reference to schematic diagrams and specific embodiments.

[0045] This embodiment describes the arc additive manufacturing of ZM6 magnesium rare earth alloy (Mg-2.7Nd-0.58Zn-0.5Zr, wt%). The welding wire diameter is 1.2 mm, the substrate material is AZ31 magnesium alloy, and the substrate size is 220 mm × 220 mm × 30 mm. The ultrasonic amplitude is 30 μm, and the ultrasonic frequency is 28 kHz.

[0046] The arc additive manufacturing method used is the cold metal transfer (CMT) arc fuse additive manufacturing method, and the specific steps are as follows:

[0047] (1) The ultrasonic vibration distribution in the AZ31 magnesium alloy substrate during the first stage of arc additive manufacturing was simulated using finite element simulation software. The vibration mode of the rolling ultrasonic tool head was adopted as radial vibration mode. During the finite element simulation, the AZ31 magnesium alloy substrate was placed in a rectangular coordinate system, with the lower left corner of the magnesium alloy substrate at (0,0,0). The XYZ directions were as follows: Figure 1As shown, the movement direction of each layer of electric arc during the arc additive manufacturing process is parallel to the X-direction. In the Y-direction, the centerline of the magnesium alloy substrate is located at 110 mm on the Y-axis. The contact between the rolling ultrasonic tool head and the surface of the magnesium alloy substrate is a line contact (i.e., the contact area is a line segment with a length of 10 mm). During the modeling process, with the centerline of the magnesium alloy substrate as the line of symmetry, two rolling ultrasonic tool heads are symmetrically placed on both sides of the centerline. The coordinates of the rolling ultrasonic tool head acting on the AZ31 magnesium alloy substrate are calibrated by the two endpoints of the contact line segment. The coordinates of the two endpoints of the contact position between one rolling ultrasonic tool head and the substrate are (120, 90, 25) and (120, 100, 25), respectively. The coordinates of the two endpoints of the contact position between the other rolling ultrasonic tool head and the AZ31 magnesium alloy substrate are (120, 120, 25) and (120, 130, 25), respectively.

[0048] A geometric model was established based on the dimensions of the AZ31 magnesium alloy substrate and the location of the ultrasonic action. Material parameters were set, including the density, elastic modulus, sound velocity, and Poisson's ratio of the AZ31 magnesium alloy substrate. Reasonable boundary and initial conditions were set. The boundary conditions were as follows: each surface of the magnesium alloy substrate was set to a free vibration mode. Initial conditions: the applied pressure and ultrasonic amplitude were set at the action positions of the two sets of rolling ultrasonic tool heads; the vibration mode of the two sets of rolling ultrasonic tool heads was also set in the initial conditions, and the vibration mode was radial vibration mode. A tetrahedral meshing method was used to generate the finite element mesh, and the maximum mesh size needed to be less than 1 / 20 of the ultrasonic propagation wavelength in the magnesium rare earth alloy. A frequency domain solver was used for solving the problem, and the ultrasonic frequency was set in the frequency domain solver. The spatial relationship between the action position of the rolling ultrasonic tool head and the molten pool in the first stage of arc additive manufacturing was determined based on the sound field simulation results. The ultrasonic vibration simulation results of the magnesium alloy substrate surface are shown below. Figure 1 As shown, the coordinates of the location with stronger ultrasonic vibration amplitude on the center line of the magnesium alloy substrate (Y = 110 mm) are (94, 110, 25).

[0049] This simulation result can determine the spatial relationship between the positions of the two ultrasonic tool heads acting on the magnesium alloy substrate surface and the molten pool, such as... Figure 2 As shown. Along the X direction, the distance between the rolling ultrasonic tool head and the center of the molten pool (welding wire tip) is 26mm, and in the Y direction, the distance between the rolling ultrasonic tool head and the centerline of the magnesium alloy substrate is 10mm.

[0050] (2) Based on the simulation of the first stage of arc additive manufacturing, the ultrasonic vibration distribution in the ZM6 magnesium alloy additive wall of the second stage of arc additive manufacturing was simulated using finite element simulation software. The vibration modes of both sets of rolling ultrasonic tool heads adopted the radial vibration mode. For the second stage of arc additive manufacturing, the length of the additive wall was 140mm, the width was 10mm, and the height was 50mm during the finite element simulation. During the finite element simulation, the AZ31 magnesium alloy substrate was placed in a rectangular coordinate system, with the lower left corner coordinates of the magnesium alloy substrate being (0,0,0). The XYZ directions were as follows: Figure 3 As shown, the movement direction of each layer of electric arc during the arc additive manufacturing process is parallel to the X-direction. The contact between the rolling ultrasonic tool head and the ZM6 magnesium alloy wall surface is a line contact (i.e., the contact area is a line segment with a length of 10 mm). During the modeling process, two rolling ultrasonic tool heads are symmetrically placed on the two side walls of the wall. The coordinates of the rolling ultrasonic tool head acting on the side wall are calibrated using the two endpoints of the contact line segment. The coordinates of the two endpoints of the contact position between one rolling ultrasonic tool head and the wall are (120, 105, 60) and (120, 105, 70), respectively, and the coordinates of the two endpoints of the contact position between the other rolling ultrasonic tool head and the wall are (120, 115, 60) and (120, 115, 70), respectively.

[0051] Based on the actual magnesium alloy substrate material used, accurate magnesium alloy substrate material (including density, elastic modulus, sound velocity, and Poisson's ratio) was set in the finite element simulation software. Boundary conditions and initial conditions were set, and the elastic wave control equation was adopted using the frequency domain solution method. The boundary conditions are as follows: each surface of the magnesium alloy substrate is set to a free vibration mode. The initial conditions are: the applied pressure and ultrasonic amplitude are set at the action positions of the two sets of rolling ultrasonic tool heads; the vibration mode of the two sets of rolling ultrasonic tool heads is also set in the initial conditions, and the vibration mode is a radial vibration mode. For the radial vibration mode, the ultrasonic vibration direction is perpendicular to the surface of the additively manufactured magnesium rare earth alloy wall. The ultrasonic frequency (28kHz) is set in the frequency domain solver. The finite element mesh is generated using the tetrahedral meshing method, and the maximum mesh size must be less than 1 / 20 of the ultrasonic propagation wavelength in the magnesium rare earth alloy; the spatial positional relationship between the action position of the rolling ultrasonic tool head and the molten pool in the second stage of arc additive manufacturing is determined based on the sound field simulation results. The ultrasonic vibration simulation results of the ZM6 magnesium alloy wall surface are as follows. Figure 3 As shown in the simulation results, the strongest ultrasonic amplitude on the upper surface of the additive wall is located near the coordinates (138, 110, 75).

[0052] This simulation result can determine the spatial relationship between the positions of the two ultrasonic tool heads acting on the side surface of the ZM6 magnesium alloy wall and the molten pool, such as... Figure 4As shown. Along the X direction, the distance between the rolling ultrasonic tool head and the center of the molten pool (welding wire tip) is 18mm, and in the Z direction, the distance between the rolling ultrasonic tool head and the upper surface of the ZM6 magnesium alloy wall is 5mm.

[0053] (3) CMT Arc Wire Additive Manufacturing Parameters for ZM6 Magnesium Alloy: The substrate preheating temperature was set to 400℃. The CMT welding characteristic curve was selected as the magnesium alloy-specific characteristic curve. A unified welding mode was adopted, and the wire feed speed was automatically matched with the welding current and welding voltage. The wire feed speed of each layer during the arc additive manufacturing process remained consistent at 4.5m / min, the additive manufacturing speed (welding torch movement speed) was 16mm / s, and the average layer height was 1.7mm. A single-pass multi-layer additive manufacturing wall was planned, with a wall length of 140mm and a wall height of 70mm. The welding wire tip was located on the centerline of the magnesium alloy substrate. Argon gas with a purity of 99.99% was used as the shielding gas, and the shielding gas flow rate was 25L / min. The pressure of the rolling ultrasonic tool head acting on the substrate was controlled by an air compressor, and the air pressure was set to 0.15MPa. The rolling ultrasonic tool head moved synchronously and in the same direction with the welding torch, and the ultrasonic frequency of both sets of rolling ultrasonic tool heads was 28kHz.

[0054] (4) Grind the surface of the AZ31 magnesium alloy substrate according to conventional processing in the art to remove the oxide film and surface oil. Place the ground AZ31 magnesium alloy substrate on the auxiliary heating stage, fix the AZ31 magnesium alloy substrate with a clamp, turn on the auxiliary heating stage switch, and preheat the magnesium alloy substrate;

[0055] (5) Arc Additive Manufacturing Path Setting: Based on the dimensions of the wall to be added, the robot's walking path is programmed, adopting a single-pass reciprocating movement mode. The robot drives the welding torch to move along the single-pass reciprocating path, and the welding torch moving speed is 16mm / s. During each layer of additive manufacturing, when the robot drives the welding torch to move, the distance between the starting point and the ending point is equal to the length of the wall, which is 140mm.

[0056] (6) In the first stage of arc wire additive manufacturing (from the start of additive manufacturing to a cumulative additive height not exceeding 50mm), the two sets of rolling ultrasonic tool heads are positioned on the magnesium alloy substrate surface according to the method described in step (1). The spatial positions of the two sets of rolling ultrasonic tool heads and the welding wire tip in the CMT welding gun are determined according to... Figure 2 (a) or Figure 2(b) The correct placement is as shown below: In the X direction, the straight-line distance between the welding wire tip and the wheel-type ultrasonic tool head is 26 mm, and the welding wire tip is approximately 1-2 mm from the solid metal surface. Two sets of wheel-type ultrasonic tool heads are symmetrically placed on both sides of the substrate centerline, with the inner side of each wheel-type ultrasonic tool head 10 mm from the substrate centerline. After the preheating temperature of the magnesium alloy substrate surface reaches 400℃, the two sets of rolling ultrasonic tool heads are controlled by an air compressor to contact the magnesium alloy substrate surface, and the moving speed of the rolling ultrasonic tool heads is set to be the same as the additive speed (16 mm / s). The ABB welding robot is started to perform the first layer of arc additive manufacturing (along the positive x direction), while simultaneously controlling the two sets of rolling ultrasonic tool heads to move synchronously and in the same direction with the welding torch at the same moving speed. After the first layer of arc additive manufacturing is completed, the arc is extinguished, and the two sets of rolling ultrasonic tool heads are simultaneously controlled to separate from the magnesium alloy substrate. After a 60-second interval between layers, the second layer of arc additive manufacturing begins.

[0057] Ten seconds before starting the second layer of arc additive manufacturing, adjust the spatial positions of the two sets of rolling ultrasonic tool heads so that the spatial relationship between the two sets of rolling ultrasonic tool heads and the welding wire tip satisfies the following conditions along the arc movement direction. Figure 2 (a) or Figure 2 (b) Relationship. Two sets of rolling ultrasonic tool heads are controlled by an air compressor to contact the surface of the magnesium alloy substrate. The ABB welding robot is started to perform the second layer of arc additive manufacturing (along the negative x-direction, the end position of the first layer is used as the starting position of the second layer), while simultaneously controlling the two sets of rolling ultrasonic tool heads to move synchronously and in the same direction as the welding torch at the same speed. After the second layer of arc additive manufacturing is completed, the arc is extinguished, and the two sets of rolling ultrasonic tool heads are simultaneously controlled to separate from the magnesium alloy substrate. After a 60-second interval between layers, the third layer of arc additive manufacturing begins.

[0058] The process then proceeds by layering materials until the cumulative stacking height reaches 50mm, at which point the second stage of arc additive manufacturing begins.

[0059] (7) Taking the additive wall manufactured in the first stage of arc additive manufacturing as the object, the two sets of rolling ultrasonic tool heads are positioned on the side surface of the ZM6 magnesium alloy wall according to the method described in step (2). The spatial positions of the two sets of rolling ultrasonic tool heads and the welding wire tip in the CMT welding gun are determined according to... Figure 4 (a) or Figure 4(b) The correct placement is as follows: In the X direction, the straight-line distance between the welding wire tip and the wheeled ultrasonic tool head is 18 mm. The welding wire tip is approximately 1-2 mm from the solid metal surface. Two sets of wheeled ultrasonic tool heads act symmetrically on both sides of the additive wall, with the upper part of the wheeled ultrasonic tool heads approximately 5 mm from the surface of the deposited layer. During each layer of arc additive manufacturing, the two sets of rolling ultrasonic tool heads are controlled to move synchronously and in the same direction with the welding torch at the same speed. After each layer of additive manufacturing is completed, the arc is extinguished, and the two sets of rolling ultrasonic tool heads are simultaneously controlled to separate from the magnesium alloy wall. The interval between layers is 60 seconds before starting the next layer of arc additive manufacturing.

[0060] Ten seconds before starting the next layer of arc additive manufacturing, adjust the spatial positions of the two sets of rolling ultrasonic tool heads so that the spatial relationship between the two sets of rolling ultrasonic tool heads and the welding wire tip satisfies the following conditions along the arc movement direction. Figure 4 (a) or Figure 4 (b) Relationship. Two sets of rolling ultrasonic tool heads are controlled by an air compressor to contact the magnesium alloy wall surface. The ABB welding robot is started to execute the next layer of arc additive manufacturing (along the negative x-direction, the end position of the previous layer is used as the starting position of the next layer), while simultaneously controlling the two sets of rolling ultrasonic tool heads to move synchronously and in the same direction, following the welding torch at the same speed. After the current layer of arc additive manufacturing is completed, the arc is extinguished, and the two sets of rolling ultrasonic tool heads are simultaneously controlled to separate from the magnesium alloy substrate. After a 60-second interval between layers, the manufacturing of other layers of arc additive manufacturing begins.

[0061] Repeat the above steps for each layer of arc additive manufacturing until the height of the additive manufacturing reaches the set height (the height of the additive wall is 70mm). Turn off the arc and ultrasonic equipment, turn off the power to the auxiliary heating table, and remove the arc additive manufacturing component after it has cooled naturally.

[0062] Metallographic specimens and tensile mechanical property test specimens of the arc additive magnesium rare earth alloy prepared by the above method were cut by wire cutting. The content and distribution of the second phase at the grain boundary after the influence of dual ultrasonic vibration were observed by SEM. The room temperature tensile properties of the wall were tested by electronic universal testing machine with the tensile speed set to 1 mm / min, referring to GB / T228.1-2010 room temperature tensile test standard.

[0063] Figure 5The distribution of solute elements in magnesium rare earth alloys manufactured by arc additive manufacturing under different treatments is shown in the figures. (a) shows the microstructure of ZM6 magnesium alloy manufactured by the original CMT arc additive manufacturing process, (b) shows the microstructure of ZM6 magnesium alloy manufactured by CMT arc additive manufacturing using the present invention, and (c) shows the comparison of the size and content of precipitated phases in ZM6 magnesium alloy under the present invention and the original manufacturing process. As can be seen from the figures, the distribution of the intergranular second phase before and after the dual ultrasonic vibration treatment of the present invention is significantly reduced and the distribution of the intergranular eutectic phase in the ZM6 magnesium alloy manufactured by arc additive manufacturing is more dispersed under the dual ultrasonic vibration treatment.

[0064] Figure 6 The figure shows the changes in tensile strength and elongation after fracture of magnesium rare earth alloys prepared by arc additive manufacturing under different treatments. As can be seen from the figure, the strength and ductility of ZM6 magnesium alloys manufactured by arc additive manufacturing are significantly improved after the dual ultrasonic vibration treatment of the present invention. In particular, the increase in tensile strength and elongation after fracture of ZM6 magnesium alloys is relatively large in the longitudinal additive direction after dual ultrasonic vibration.

Claims

1. A method for suppressing elemental segregation during the solidification of arc-additive magnesium rare-earth alloys using dual ultrasound, characterized in that, Includes the following steps: Step 1: Polish the surface of the magnesium alloy substrate to remove the oxide film and surface oil. Place the polished magnesium alloy substrate on the auxiliary heating stage, fix the magnesium alloy substrate with a clamp, turn on the auxiliary heating stage switch, and preheat the magnesium alloy substrate. Step 2: Determine the relative positional relationship between the two sets of rolling ultrasonic tool heads on the magnesium alloy substrate surface and the molten pool, as well as the vibration mode of the rolling ultrasonic tool heads; place the magnesium rare earth alloy welding wire on the wire feeding mechanism and guide the welding wire out from the wire feeding nozzle of the welding torch; set the welding current, wire feeding speed, welding speed, and shielding gas flow rate parameters; wherein, the specific steps for determining the relative positional relationship between the two sets of rolling ultrasonic tool heads on the magnesium alloy substrate surface and the molten pool, as well as the vibration mode of the rolling ultrasonic tool heads, are as follows: (1) Based on the actual size of the magnesium alloy substrate, a geometric model is established in the finite element simulation software, and the geometric model is consistent with the actual shape of the magnesium alloy substrate. During the geometric modeling process, different ultrasonic tool head action positions are set. The principle for setting the action position of the ultrasonic tool head is as follows: the center position of the molten pool is set to the midline position of the upper surface of the magnesium alloy substrate. Two sets of rolling ultrasonic tool heads act on the magnesium alloy substrate surface on both sides of the center of the molten pool in a line contact manner. The length of the contact area is 8-15 mm. The vibration mode of the rolling ultrasonic tool head is either longitudinal vibration mode or radial vibration mode. The radial distance between the action position of the ultrasonic tool head and the center of the molten pool is 5-35 mm. (2) Based on the actual magnesium alloy substrate material used, the accurate magnesium alloy substrate material is set in the finite element simulation software, and the boundary conditions and initial conditions are set. The elastic wave control equation and frequency domain solution method are adopted. Among them, the boundary conditions are as follows: each surface of the magnesium alloy substrate is set to a free vibration mode; the initial conditions are: the action pressure and ultrasonic amplitude are set at the action position of the two sets of rolling ultrasonic tool heads; the vibration mode of the two sets of rolling ultrasonic tool heads also needs to be set in the initial conditions. The vibration mode is either a longitudinal vibration mode with the ultrasonic vibration direction parallel to the surface of the magnesium alloy substrate or a radial vibration mode with the ultrasonic vibration direction perpendicular to the surface of the magnesium alloy substrate; the ultrasonic frequency is set in the frequency domain solver. (3) The finite element mesh is generated using the tetrahedral mesh generation method, and the maximum mesh size must be less than 1 / 20 of the ultrasonic propagation wavelength in magnesium rare earth alloys; (4) Finite element simulation was performed for cases with different vibration modes and action positions to simulate the amplitude distribution on the surface of the magnesium alloy substrate under different ultrasonic tool head action positions, and the action position of the rolling ultrasonic tool head with the maximum ultrasonic amplitude on the arc movement path was selected. (5) Method for determining the positional relationship between the welding torch and the two sets of rolling ultrasonic tool heads: The welding torch is regarded as a point, and the position of the welding torch corresponds to the center position of the molten pool. According to step (4), the center position of the molten pool is set at the position with the largest ultrasonic amplitude on the magnesium alloy surface, and then the position between the welding torch and the two sets of rolling ultrasonic tool heads is determined. The dry extension of the welding wire is 12-15 mm, and the tip of the welding wire is 1-2 mm away from the surface of the magnesium alloy substrate. Step 3: After the magnesium alloy substrate is preheated to the set temperature, two sets of rolling ultrasonic tool heads are applied to the designated positions on the surface of the magnesium alloy substrate and pressure is applied. At the same time, the ultrasonic vibration and electric arc additive manufacturing process are started. The two sets of rolling ultrasonic tool heads move synchronously and in the same direction with the welding gun at the same speed. The ultrasonic frequency is 20-50 kHz and the ultrasonic power does not exceed 1500 W. When the deposited height reaches 50 mm, the first stage of additive manufacturing is completed. The electric arc and ultrasonic vibration are turned off synchronously, and the ultrasonic tool head is separated from the magnesium alloy substrate. Step 4: After the first stage of arc additive manufacturing is completed, before proceeding to the second stage, determine the position of the rolling ultrasonic tool head on the sidewall of the deposited layer. Apply pressure to the designated positions on the sidewall of the magnesium alloy deposited layer using two sets of rolling ultrasonic tool heads. Simultaneously, start the ultrasonic vibration and arc additive manufacturing process. The two sets of rolling ultrasonic tool heads move synchronously and in the same direction as the welding torch at the same speed. The ultrasonic frequency is 20-50 kHz, and the ultrasonic power does not exceed 1500W. The additive manufacturing process in the second stage is the same as in Step 3. At the end of each additive manufacturing pass, simultaneously shut off the arc and ultrasonic vibration, and separate the ultrasonic tool head from the sidewall of the deposited layer. In each subsequent additive manufacturing pass, the operation method is the same as the arc and ultrasonic operation in Step 4 until the set height is reached, at which point the additive manufacturing and ultrasonic processing are stopped. After the arc additive manufacturing is completed, shut off the arc and ultrasound, and adjust the welding torch and ultrasonic tool head to a suitable spatial position. Turn off the power to the auxiliary heating table. After the additive component has cooled naturally, remove the arc additive component.

2. The method for suppressing elemental segregation during the solidification process of arc-additive magnesium rare-earth alloys using dual ultrasound as described in claim 1, characterized in that, The arc additive manufacturing process employs an arc heat source fused wire additive manufacturing method. The arc heat source includes cold metal transfer welding, gas metal arc welding, or tungsten inert gas welding. When cold metal transfer welding or gas metal arc welding is used, the auxiliary heating temperature is 300-450 ℃; when tungsten inert gas welding is used, the auxiliary heating temperature is 200-300 ℃. The size of the magnesium alloy substrate is 220 mm × 220 mm × 30 mm.

3. The method for suppressing elemental segregation during the solidification of arc-additive magnesium rare-earth alloys using dual ultrasound as described in claim 1, characterized in that, The magnesium rare earth alloys mentioned in step 2 include, but are not limited to, Mg-Y-Nd series, Mg-Y-Nd-Gd series, Mg-Gd-Y series or Mg-Nd-Zn-Zr series, and the diameter of the welding wire is 1.2 mm.

4. The method for suppressing elemental segregation during the solidification of arc-additive magnesium rare-earth alloys using dual ultrasound as described in claim 1, characterized in that, The pressure exerted by the rolling ultrasonic tool head on the substrate surface is controlled by controlling the air pressure intensity of the air compressor, which is set to 0.15 MPa.

5. The method for suppressing elemental segregation during the solidification of arc-additive magnesium rare-earth alloys using dual ultrasound as described in claim 1, characterized in that, Step 4, determining the effective position of the rolling ultrasonic tool head on the sidewall of the deposition layer, includes the following steps: (1) Based on the actual size of the magnesium alloy substrate, a geometric model is established in the finite element simulation software. The geometric model is consistent with the actual geometric shape of the additive component after step 3. During the geometric modeling process, different ultrasonic tool head action positions are set. The principle for setting the ultrasonic tool head action positions is as follows: two sets of rolling ultrasonic tool heads act on the two sides of the additive wall in a line contact manner. The length of the line contact is 8-15 mm. The ultrasonic tool head acts on the wall surface at a distance of 5-10 mm from the upper surface of the wall. (2) Based on the actual magnesium alloy substrate material used, the accurate magnesium alloy substrate material is set in the finite element simulation software, and the boundary conditions and initial conditions are set. The elastic wave control equation and frequency domain solution method are adopted. The boundary conditions are as follows: each surface of the magnesium alloy substrate is set to a free vibration mode; the initial conditions are: the action pressure and ultrasonic amplitude are set at the action position of the two sets of rolling ultrasonic tool heads; the vibration mode of the two sets of rolling ultrasonic tool heads also needs to be set in the initial conditions. The vibration mode is the radial vibration mode with the ultrasonic vibration direction perpendicular to the surface of the additively manufactured magnesium rare earth alloy wall; the ultrasonic frequency is set in the frequency domain solver. (3) The finite element mesh is generated using the tetrahedral mesh generation method, and the maximum mesh size must be less than 1 / 20 of the ultrasonic propagation wavelength in magnesium rare earth alloys; (4) Finite element simulation was performed for cases with different ultrasonic action positions to simulate the amplitude distribution on the surface of the magnesium rare earth alloy wall under different action positions of the ultrasonic tool head, and the action position of the rolling ultrasonic tool head with the maximum ultrasonic amplitude on the arc movement path was selected. (5) Method for determining the positional relationship between the welding torch and the two sets of rolling ultrasonic tool heads: The welding torch is regarded as a point, and the position of the welding torch corresponds to the center position of the molten pool. According to the sound field simulation results, the center position of the molten pool is set at the position with the largest ultrasonic amplitude on the surface of the magnesium rare earth alloy deposition layer, and then the positional relationship between the welding torch and the two sets of rolling ultrasonic tool heads is determined. The wire extension is 12-15 mm, and the tip of the welding wire is 1-2 mm away from the surface of the magnesium alloy substrate.

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