Method for inhibiting element segregation in electric arc additive magnesium-rare earth alloy solidification process through double ultrasound

Abstract

The invention discloses a method for inhibiting element segregation in the solidification process of an electric arc additive magnesium rare earth alloy through double ultrasound. Ultrasonic vibration of different vibration modes is applied to the two sides of the molten pool in stages, when the deposited height does not exceed 50 mm, ultrasonic vibration of a longitudinal vibration mode or a radial vibration mode is symmetrically applied to base plates on the two sides of the molten pool, and when the deposited height exceeds 50 mm, ultrasonic vibration of the radial vibration mode is symmetrically applied to deposition layer walls on the two sides of the molten pool; and in the deposition process, the rolling type ultrasonic tool heads on the two sides synchronously move in the same direction along with the welding gun. The two rolling type ultrasonic tool heads generate ultrasonic vibration with the same frequency at the same time. The action positions of the two rolling type ultrasonic tool heads on the two sides of the molten pool are reasonably designed and stacked to form high-amplitude ultrasonic vibration, the strength, adjustability and uniformity of an ultrasonic field in the molten pool are remarkably improved, solute element grain boundary segregation is effectively reduced, then the comprehensive mechanical property of the magnesium rare earth alloy manufactured through electric arc additive manufacturing is improved, and the service life of the magnesium rare earth alloy is prolonged. Good application prospects are realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of arc additive manufacturing of magnesium alloys, and in particular relates to a method for suppressing element segregation during the solidification process of arc additive magnesium rare earth alloys by utilizing dual ultrasound. Background Art

[0002] Magnesium alloys, with their low density and high specific strength, hold broad application prospects in the aerospace sector. Arc additive manufacturing (AM) offers numerous advantages over traditional casting methods for the manufacture of large-scale magnesium alloy-related structural components, including fine grain size, lack of macrosegregation, near-net-shape formation of complex structures, and excellent overall mechanical properties. Overall, the use of arc AM technology to manufacture magnesium alloy structural components holds broad promise for engineering applications.

[0003] In the process of using arc heat source to melt magnesium alloy welding wire and stacking it layer by layer, a molten pool will be formed under the action of 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 arc additively manufactured magnesium alloy.

[0004] CN202110521112.1 discloses an arc additive manufacturing method with ultrasonic vibration and rolling characteristics during welding. An ultrasonic vibration rolling roller that can move synchronously with the arc additive manufacturing welding gun is arranged behind the arc additive manufacturing welding gun. The ultrasonic vibration rolling wheel ultrasonically vibrates and rolls the arc additive manufacturing layer in the thermoplastic stage to promote plastic deformation. At the same time, the ultrasonic vibration is transmitted to the molten pool. The combined effect of the two improves the organization and performance of the arc additive layer. Although this application realizes the characteristics of synchronous follow-up of the ultrasonic vibration rolling roller and the welding gun, it is limited by a single ultrasonic vibration rolling roller. The energy and distribution of the ultrasonic field in the molten pool are uneven and cannot be flexibly controlled. The decoupling between the ultrasonic vibration effect and the rolling effect is difficult.

[0005] CN201810464169.0 discloses a CMT-ultrasonic vibration composite additive manufacturing method, which performs ultrasonic vibration on a substrate while performing 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 low ultrasonic energy in the molten pool and a relatively uneven sound field distribution within the molten pool, resulting in poor adjustability of the sound field distribution.

[0006] CN202411277389.4 discloses a device and method for high-entropy alloy arc additive manufacturing assisted by double-sided ultrasonic rolling. In the process of additive manufacturing of high-entropy alloys using tungsten inert gas welding, the 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 more dense, thereby improving the quality of high-entropy alloy arc additive manufacturing. However, the 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 regulating the ultrasonic vibration energy in the molten pool through ultrasonic rolling to affect the microstructure after the molten pool solidifies.

[0007] Combined with the above analysis, it can be seen that the following key issues remain unresolved in the existing technology of arc fuse additive manufacturing of magnesium rare earth alloys:

[0008] (1) Magnesium alloy is different from other metal materials and has higher damping characteristics. The amplitude of mechanical vibration attenuates greatly when it propagates in magnesium alloy. When a single ultrasonic roller acts on 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 no significant changes in the microstructure of the arc-assisted magnesium alloy.

[0009] (2) During the arc additive solidification process of magnesium rare earth alloy, the solidification rate of the molten pool is fast. The solubility of the solute elements in the magnesium rare earth alloy in the α-Mg solid solution decreases with decreasing temperature. The solute elements are largely excluded from the solid-liquid interface front, and finally a large number of Mg-RE intermetallic compounds with low melting point, high hardness and high brittleness are formed 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 alloy manufactured by arc additive manufacturing, weakening the solid solution strengthening effect of rare earth elements. At the same time, stress concentration is likely to occur near the Mg-RE intermetallic compounds, and cracks are likely to initiate and expand here. Summary of the Invention

[0010] In response to the existing technical problems of arc additive manufacturing of magnesium rare earth alloys, the purpose of the present invention is to provide a method for suppressing element segregation during the solidification process of arc additive manufacturing of magnesium rare earth alloys by using dual ultrasound. The method adopts the dual ultrasound superposition to form a strong standing wave sound field to act on the magnesium rare earth alloy molten pool. By designing the action position of the dual ultrasound and changing the dual ultrasound amplitude and vibration mode, the ultrasonic energy and distribution position in the molten pool during the arc additive manufacturing of magnesium rare earth alloys are effectively regulated, so that the ultrasonic energy in the solid-liquid mixing zone is always at the maximum state. The combined action of acoustic cavitation, acoustic flow and vibration-induced lattice distortion is utilized to promote the forced migration of solute atoms in the solid-liquid mixing zone into the solid phase magnesium matrix, thereby increasing the solid solubility of the solute elements, reducing the degree of grain boundary segregation of the solute elements, reducing the size of the eutectic phase at the grain boundary and dispersing the distribution, and finally comprehensively improving the strength and ductility of the magnesium rare earth alloy manufactured by arc additive manufacturing.

[0011] In order to solve the problems of the prior art, the technical solution adopted by the present invention is:

[0012] A method for suppressing element segregation during arc-assisted magnesium-rare earth alloy solidification using dual ultrasound comprises 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 an auxiliary heating table, fix the magnesium alloy substrate with a clamp, turn on the auxiliary heating table switch, and preheat the magnesium alloy substrate;

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

[0015] Step 3: After the magnesium alloy substrate is preheated to the set temperature, two sets of rolling ultrasonic tool heads are respectively applied to the specified positions on the surface of the magnesium alloy substrate and pressure is applied. At the same time, the ultrasonic vibration and arc additive process are started. The two sets of rolling ultrasonic tool heads move synchronously with the welding gun at the same speed and in the same direction. 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. The arc and ultrasonic vibration are synchronously 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 the second stage of arc additive manufacturing is carried out, the action position of the rolling ultrasonic tool head at the side wall of the deposited layer is determined, and two sets of rolling ultrasonic tool heads are respectively applied to the specified positions of the side wall of the magnesium alloy deposited layer, and pressure is applied, and the ultrasonic vibration and arc additive process are started at the same time. The two sets of rolling ultrasonic tool heads move synchronously with the welding gun at the same speed and in the same direction. The ultrasonic frequency is 20-50kHz and the ultrasonic power does not exceed 1500W. The additive process of the second stage is the same as step 3. At the end of each additive process, the arc and ultrasonic vibration are synchronously turned off, and the ultrasonic tool head is separated from the side wall of the deposited layer. In each subsequent additive process, the operation method is the same as the arc and ultrasonic operation in step 4 until the set height is reached, and the additive and ultrasonic processing are stopped. After the arc additive process is completed, the arc and ultrasonic are turned off, and the welding gun and ultrasonic tool head are adjusted to a suitable spatial position; the auxiliary heating table power is turned off; after the additive component is naturally cooled, the arc additive component is removed.

[0017] As an improvement, the arc additive process adopts an arc heat source fuse additive method, and the arc heat source includes cold metal transfer welding (CMT), metal inert gas shielded welding (MIG) or tungsten inert gas welding (TIG). When cold metal transfer welding (CMT) or metal inert gas shielded welding (MIG) is used, the auxiliary heating temperature is 300-450°C; when tungsten inert gas welding (TIG) is used, the auxiliary heating temperature is 200-300°C, and the size of the magnesium alloy substrate is 220mm×220mm×30mm.

[0018] As an improvement, the magnesium rare earth alloy 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 1.2 mm.

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

[0020] (1) According to 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. Different ultrasonic tool head action positions are set during the geometric modeling process. 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, and two sets of rolling ultrasonic tool heads act on the magnesium alloy substrate surface on both sides of the molten pool center in a line contact manner. The radial distance between the ultrasonic tool head action position and the molten pool center is 5-35 mm;

[0021] (2) According to the actual magnesium alloy substrate material used, the accurate magnesium alloy substrate material is set in the finite element simulation software, the boundary conditions and initial conditions are set, and the elastic wave control equation and the frequency domain solution method are adopted; wherein, the boundary conditions are as follows: each surface of the magnesium alloy substrate is set to a free vibration mode; initial conditions: 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, and the vibration mode is a longitudinal vibration mode in which the ultrasonic vibration direction is parallel to the surface of the magnesium alloy substrate or a radial vibration mode in which the ultrasonic vibration direction is 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 divided using the tetrahedral meshing method, and the maximum mesh size must be less than 1 / 20 of the wavelength of ultrasonic propagation in magnesium rare earth alloys;

[0023] (4) Finite element simulation was performed on the conditions with different vibration modes and action positions to simulate the amplitude distribution on the surface of the magnesium alloy substrate 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 moving path was selected;

[0024] (5) Method for determining the positional relationship between the welding gun and the two sets of rolling ultrasonic tool heads: The welding gun is regarded as a point, and the position of the welding gun corresponds to the center of the molten pool. According to step (4), the center of the molten pool is set at the position where the ultrasonic amplitude on the surface of the magnesium alloy is the largest, and then the position between the welding gun and the two sets of rolling ultrasonic tool heads is determined. The dry extension length 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.

[0025] A further improvement is that in step (1), the rolling ultrasonic tool head is in line contact with the surface of the magnesium alloy substrate, and the length of the contact area is 8-15 mm; the vibration mode of the rolling ultrasonic tool head is a longitudinal vibration mode or a 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 of the air compressor, and the pressure of the air compressor is set to 0.15 MPa.

[0027] As an improvement, determining the action position of the rolling ultrasonic tool head at the side wall of the deposited layer in step 4 includes the following steps:

[0028] (1) According to 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 processing in step 3. Different ultrasonic tool head action positions are set during the geometric modeling process. The principle of setting the ultrasonic tool head action position 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, and the position where the ultrasonic tool head acts on the wall surface is 5-10 mm away from the upper surface of the wall;

[0029] (2) According to the actual magnesium alloy substrate material used, the accurate magnesium alloy substrate material is set in the finite element simulation software, the boundary conditions and initial conditions are set, and the elastic wave control equation and the frequency domain solution method are adopted, wherein the boundary conditions are as follows: each surface of the magnesium alloy substrate is set to a free vibration mode; initial conditions: 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, and the vibration mode is a radial vibration mode in which the ultrasonic vibration direction is 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 divided using the tetrahedral meshing method, and the maximum mesh size must be less than 1 / 20 of the wavelength of ultrasonic propagation in magnesium rare earth alloys;

[0031] (4) Finite element simulation was performed on the conditions 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 moving path was selected;

[0032] (5) Method for determining the positional relationship between the welding gun and the two sets of rolling ultrasonic tool heads: The welding gun is regarded as a point, and the position of the welding gun corresponds to the center of the molten pool. According to the sound field simulation results, the center of the molten pool is set at the position where the ultrasonic amplitude on the surface of the magnesium rare earth alloy deposition layer is the largest. Then, the positional relationship between the welding gun and the two sets of rolling ultrasonic tool heads is determined. The dry extension length 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.

[0033] The present invention addresses the high damping properties of magnesium alloys by simultaneously applying a rolling ultrasonic tool head to the surface of the magnesium alloy substrate and both sides of the arc-type additive wall. Two ultrasonic beams are superimposed 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. Forced convection stirring of the high-temperature melt in the molten pool by acoustic streaming promotes uniform distribution of solute elements within the melt. The high temperature and impact force generated by the ultrasonic cavitation effect at the leading edge of the solid-liquid interface during solidification increases the kinetic energy of solute atomic migration. Ultrasonic vibrations are used to induce lattice distortion in the solid phase of the late solidification phase within the solid-liquid mixing zone, forming vacancies and promoting the migration of solute atoms in the liquid phase to vacancy defects within the solid phase. By independently adjusting the action position, amplitude, and phase of the two ultrasonic beams, the ultrasonic distribution within the molten pool can be precisely adjusted.

[0034] Beneficial effects:

[0035] Compared with the existing technology, the present invention uses dual ultrasound to suppress element segregation during the solidification process of arc-added magnesium-rare earth alloys. Targeting the arc-added process of high-damping magnesium-rare earth alloys, two sets of rolling ultrasonic tool heads act on the magnesium alloy substrate and the sidewalls of the deposition area in stages, and move synchronously with the welding torch in the same direction, thereby improving the ultrasonic intensity, uniformity, and controllability in the molten pool, thereby reducing element segregation, promoting the dispersion of the eutectic phase at the grain boundaries, and improving the comprehensive 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 regulates 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 sidewalls of the deposition zone. This significantly increases the ultrasonic energy within the magnesium alloy molten pool during arc additive manufacturing, effectively overcoming the adverse effects of magnesium alloy's high damping properties on vibration attenuation and ensuring a more uniform ultrasonic distribution within the molten pool.

[0037] 2. During the process of arc additive manufacturing of the magnesium rare earth alloy of the present invention, the solid solution of solute atoms into the α-Mg matrix is ​​promoted, so that the degree of grain boundary segregation of solute elements and the size of the low-melting-point Mg-RE eutectic phase at the grain boundary are significantly reduced, and the dispersion distribution of the Mg-RE eutectic phase at the grain boundary is promoted. The strength and ductility are significantly higher than the mechanical properties of the magnesium rare earth alloy manufactured by the original arc additive manufacturing, which broadens the application effect of the material. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0039] Figure 2 This is the spatial relationship between the working position of the rolling ultrasonic tool head and the molten pool in the first stage of arc additive manufacturing (top view).

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

[0041] Figure 4 This is 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 Figure 3. Distribution of solute elements in arc additively manufactured magnesium rare earth alloys with different treatments. (a) shows the microstructure of the original CMT arc additively manufactured ZM6 magnesium alloy, (b) shows the microstructure of the CMT arc additively manufactured ZM6 magnesium alloy produced using the present invention, and (c) shows the comparison of the size and content of the precipitated phases in the ZM6 magnesium alloy produced using the present invention and the original manufacturing process.

[0043] Figure 6 Changes in mechanical properties of magnesium rare earth alloys prepared by arc additive manufacturing with different treatments. DETAILED DESCRIPTION

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

[0045] This example uses arc additive manufacturing of a ZM6 magnesium rare earth alloy (Mg-2.7Nd-0.58Zn-0.5Zr, wt%). The welding wire has a diameter of 1.2 mm and the substrate is made of AZ31 magnesium alloy, measuring 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. The specific steps are as follows:

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

[0048] According to the size of the AZ31 magnesium alloy substrate and the ultrasonic action position, a geometric model is established, and material parameters are set. The material parameters include the density, elastic modulus, sound velocity and Poisson's ratio of the AZ31 magnesium alloy substrate. Reasonable boundary conditions and initial conditions are set. The boundary conditions are as follows: each surface of the magnesium alloy substrate is set to a free vibration mode. Initial conditions: 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, and the vibration mode is a radial vibration mode. The finite element mesh is divided by the tetrahedral mesh division method, and the maximum mesh size must be less than 1 / 20 of the ultrasonic propagation wavelength in the magnesium rare earth alloy; the frequency domain solver is used for solution, and the ultrasonic frequency is set in the frequency domain solver; the spatial position relationship between the action position of the rolling ultrasonic tool head and the molten pool in the first stage of arc additive is determined according to the sound field simulation results. The ultrasonic vibration simulation results of the magnesium alloy substrate surface are shown as follows. Figure 1 As shown, on the center line of the magnesium alloy substrate (Y=110 mm), the coordinates of the position where the ultrasonic vibration amplitude is stronger are (94, 110, 25).

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

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

[0051] According to the actual magnesium alloy substrate material used, the accurate magnesium alloy substrate material (including density, elastic modulus, sound velocity and Poisson's ratio) is set in the finite element simulation software, the boundary conditions and initial conditions are set, and 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, among which 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, 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 divided by 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 position relationship between the action position of the rolling ultrasonic tool head and the molten pool in the second stage of arc additive is determined according to the sound field simulation results. The ultrasonic vibration simulation results of the ZM6 magnesium alloy wall surface are shown in the figure. Figure 3 As shown in the simulation results, it can be seen that the strongest ultrasonic amplitude on the upper surface of the additive wall is located near the coordinates (138,110,75).

[0052] The simulation results can be used to determine the spatial relationship between the position 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 in the figure, along the X direction, the distance between the rolling ultrasonic tool head and the center of the molten pool (the tip of the welding wire) is 18 mm, and in the Z direction, the distance between the rolling ultrasonic tool head and the upper surface of the ZM6 magnesium alloy wall is 5 mm.

[0053] (3) Determination of parameters for CMT arc fused wire additive manufacturing of ZM6 magnesium alloy: the substrate preheating temperature is set to 400℃, the CMT welding characteristic curve selects the special characteristic curve for magnesium alloy, and a unified welding mode is adopted, with the wire feed speed automatically matching the welding current and welding voltage. The wire feed speed of each layer in the arc additive process is consistent, all at 4.5m / min, the additive speed (welding gun movement speed) is 16mm / s, and the average layer height is 1.7mm. A single-pass multi-layer additive manufacturing wall is simulated, with a wall length of 140mm and a wall height of 70mm. The tip of the welding wire is located on the center line of the magnesium alloy substrate. Argon with a purity of 99.99% is used as the shielding gas, and the shielding gas flow rate is 25L / min. The pressure of the rolling ultrasonic tool head on the substrate is controlled by an air compressor, and the air pressure is set to 0.15MPa. The rolling ultrasonic tool head moves synchronously with the welding gun in the same direction, and the ultrasonic frequency of the two sets of rolling ultrasonic tool heads is 28kHz.

[0054] (4) According to conventional treatment in this field, the surface of the AZ31 magnesium alloy substrate is polished to remove the oxide film and surface oil. The polished AZ31 magnesium alloy substrate is placed on the auxiliary heating table, fixed with a clamp, and the auxiliary heating table switch is turned on to preheat the magnesium alloy substrate;

[0055] (5) Arc Additive Path Setting: The robot's path is programmed based on the size of the wall to be added. A single-pass reciprocating motion mode is used, with the robot driving the welding gun along a single-pass reciprocating path at a speed of 16 mm / s. During each layer of additive process, the distance between the starting point and the end point of the robot-driven welding gun movement is equal to the length of the wall, i.e., 140 mm.

[0056] (6) In the first stage of arc fuse additive manufacturing (from the start of additive manufacturing to the cumulative additive manufacturing height not exceeding 50 mm), the two sets of rolling ultrasonic tool heads are respectively positioned to act on the surface of the magnesium alloy substrate according to the method described in step (1). The spatial positions of the two sets of rolling ultrasonic tool heads and the tip of the welding wire in the CMT welding gun are determined according to the method described in step (1). Figure 2 (a) or Figure 2(b) is correctly positioned. The specific placement is described as follows: In the X-direction, the linear distance between the wire tip and the wheel ultrasonic tool head is 26 mm, and the wire tip is approximately 1-2 mm from the solid metal surface. The two sets of wheel ultrasonic tool heads are symmetrically placed on either side of the substrate's centerline, with the inner diameter of each wheel ultrasonic tool head 10 mm from the substrate's centerline. After the magnesium alloy substrate surface preheats to 400°C, an air compressor controls the two sets of rolling ultrasonic tool heads to contact the magnesium alloy substrate surface. The moving speed of the rolling ultrasonic tool heads is set to the same as the additive speed (16 mm / s). The ABB welding robot is activated to perform the first layer of arc additive fabrication (in the positive X-direction). Simultaneously, the two sets of rolling ultrasonic tool heads are controlled to move synchronously and in the same direction as the welding torch at the same speed. After the first layer of arc additive fabrication is completed, the arc is extinguished, and the two sets of rolling ultrasonic tool heads are controlled to separate from the magnesium alloy substrate. After a 60-second interval between layers, the second layer of arc additive fabrication begins.

[0057] 10 seconds before starting the second layer of arc additive manufacturing, adjust the spatial position of the two sets of rolling ultrasonic tool heads so that the spatial position relationship between the two sets of rolling ultrasonic tool heads and the welding wire tip meets the arc moving direction. Figure 2 (a) or Figure 2 (b) Relationship. Use an air compressor to control the two sets of rolling ultrasonic tool heads to contact the surface of the magnesium alloy substrate. Start the ABB welding robot 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 of additive manufacturing). At the same time, control the two sets of rolling ultrasonic tool heads to move synchronously with the welding gun at the same speed. After the second layer of arc additive manufacturing is completed, extinguish the arc, and control the two sets of rolling ultrasonic tool heads to separate from the magnesium alloy substrate. With an interval of 60s between layers, start the third layer of arc additive manufacturing.

[0058] Subsequently, the second stage of arc additive manufacturing is carried out by stacking layer by layer until the cumulative stacking height reaches 50mm.

[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 respectively determined to act 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 tip of the welding wire in the CMT welding gun are determined according to the method described in step (2). Figure 4 (a) or Figure 4(b) is correctly placed. The specific placement position is described as follows: in the X direction, the straight-line distance between the tip of the welding wire and the wheel ultrasonic tool head is 18 mm. The tip of the welding wire is about 1-2 mm away from the solid metal surface. The two sets of wheel ultrasonic tool heads act symmetrically on both sides of the additive wall, and the upper side of the wheel ultrasonic tool head is about 5 mm away 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 with the welding gun 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 controlled to separate from the magnesium alloy wall. The interval between layers is 60 seconds, and the next layer of arc additive manufacturing begins.

[0060] 10 seconds before starting the next layer of arc additive manufacturing, adjust the spatial position of the two sets of rolling ultrasonic tool heads so that the spatial position relationship between the two sets of rolling ultrasonic tool heads and the welding wire tip meets the arc moving direction. Figure 4 (a) or Figure 4 (b) Relationship. Use an air compressor to control the two sets of rolling ultrasonic tool heads to contact the surface of the magnesium alloy wall. Start the ABB welding robot 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 of additive manufacturing). At the same time, control the two sets of rolling ultrasonic tool heads to move synchronously with the welding gun at the same speed. After the arc additive manufacturing of this layer is completed, extinguish the arc, and control the two sets of rolling ultrasonic tool heads to separate from the magnesium alloy substrate. The interval between layers is 60s, and the arc additive manufacturing of other layers begins.

[0061] Repeat the above arc additive steps for each layer until the height of the additive reaches the set height (the additive wall height is 70mm), turn off the arc and ultrasound, turn off the auxiliary heating stage power, and remove the arc additive component after the additive component cools naturally.

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

[0063] Figure 5Figure 3 shows the distribution of solute elements in arc additively manufactured magnesium rare earth alloys with different treatments, where (a) is the microstructure of the original CMT arc additively manufactured ZM6 magnesium alloy, (b) is the microstructure of the CMT arc additively manufactured ZM6 magnesium alloy produced using the present invention, and (c) is a comparison of the size and content of the precipitated phases in the ZM6 magnesium alloy under the present invention and the original manufacturing process. It can be seen from the figure that the intergranular second phase distribution before and after the dual ultrasonic vibration of the present invention, the intergranular eutectic phase content of the ZM6 magnesium alloy manufactured by arc additively manufactured with the dual ultrasonic vibration is significantly reduced, and the distribution is more dispersed.

[0064] Figure 6 The graph shows the changes in tensile strength and elongation after fracture of magnesium-rare earth alloys produced using arc additive manufacturing with different treatments. The figure demonstrates that the strength and ductility of the ZM6 magnesium alloy produced using arc additive manufacturing significantly improves after dual ultrasonic vibration. In the longitudinal direction of the additive process, the increase in tensile strength and elongation after dual ultrasonic vibration is particularly significant.

Claims

1. A method for suppressing element segregation during the solidification process of arc-added magnesium-rare earth alloy using dual ultrasound, characterized in that: The following steps are involved: 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 an auxiliary heating table, fix the magnesium alloy substrate with a clamp, turn on the auxiliary heating table switch, and preheat the magnesium alloy substrate; Step 2: Determine the relative positional relationship between the two sets of rolling ultrasonic tool heads and the molten pool on the surface of the magnesium alloy substrate and the vibration mode of the rolling ultrasonic tool heads; place the magnesium rare earth alloy welding wire on the wire feeding mechanism, and lead the welding wire from the wire feeding nozzle of the welding gun, and set the welding current, wire feeding speed, welding speed and shielding gas flow parameters; Step 3: After the magnesium alloy substrate is preheated to the set temperature, two sets of rolling ultrasonic tool heads are respectively applied to the specified positions on the surface of the magnesium alloy substrate and pressure is applied. At the same time, the ultrasonic vibration and arc additive process are started. The two sets of rolling ultrasonic tool heads move synchronously with the welding gun at the same speed and in the same direction. 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. The arc and ultrasonic vibration are synchronously turned off, 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 the second stage of arc additive manufacturing is carried out, the action position of the rolling ultrasonic tool head at the side wall of the deposited layer is determined, and two sets of rolling ultrasonic tool heads are respectively applied to the specified positions of the side wall of the magnesium alloy deposited layer, and pressure is applied, and the ultrasonic vibration and arc additive process are started at the same time. The two sets of rolling ultrasonic tool heads move synchronously with the welding gun at the same speed and in the same direction. The ultrasonic frequency is 20-50kHz and the ultrasonic power does not exceed 1500W. The additive process of the second stage is the same as step 3. At the end of each additive process, the arc and ultrasonic vibration are synchronously turned off, and the ultrasonic tool head is separated from the side wall of the deposited layer. In each subsequent additive process, the operation method is the same as the arc and ultrasonic operation in step 4 until the set height is reached, and the additive and ultrasonic processing are stopped. After the arc additive process is completed, the arc and ultrasonic are turned off, and the welding gun and ultrasonic tool head are adjusted to a suitable spatial position; the auxiliary heating table power is turned off; after the additive component is naturally cooled, the arc additive component is removed.

2. The method of using dual ultrasound to suppress element segregation during arc-assisted magnesium-rare earth alloy solidification according to claim 1, characterized in that: The arc additive process adopts an arc heat source fuse additive method, and the arc heat source includes cold metal transfer welding, metal inert gas shielded welding or tungsten inert gas welding. When cold metal transfer welding or metal inert gas shielded welding is adopted, the auxiliary heating temperature is 300-450°C; when tungsten inert gas welding is adopted, the auxiliary heating temperature is 200-300°C. The size of the magnesium alloy substrate is 220mm×220mm×30mm.

3. The method of using dual ultrasound to suppress element segregation during arc-assisted magnesium-rare earth alloy solidification according to claim 1, characterized in that: The magnesium rare earth alloy 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 1.2 mm.

4. The method of using dual ultrasound to suppress element segregation during arc-assisted magnesium-rare earth alloy solidification according to claim 1, characterized in that: In step 2, the relative position relationship between the two sets of rolling ultrasonic tool heads and the molten pool on the surface of the magnesium alloy substrate and the vibration mode of the rolling ultrasonic tool heads are determined. The specific steps are as follows: (1) According to 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. Different ultrasonic tool head action positions are set during the geometric modeling process. 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, and two sets of rolling ultrasonic tool heads act on the magnesium alloy substrate surface on both sides of the molten pool center in a line contact manner. The radial distance between the ultrasonic tool head action position and the molten pool center is 5-35 mm; (2) According to the actual magnesium alloy substrate material used, the accurate magnesium alloy substrate material is set in the finite element simulation software, the boundary conditions and initial conditions are set, and the elastic wave control equation and the frequency domain solution method are adopted; wherein, the boundary conditions are as follows: each surface of the magnesium alloy substrate is set to a free vibration mode; initial conditions: 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, and the vibration mode is a longitudinal vibration mode in which the ultrasonic vibration direction is parallel to the surface of the magnesium alloy substrate or a radial vibration mode in which the ultrasonic vibration direction is 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 divided using the tetrahedral meshing method, and the maximum mesh size must be less than 1 / 20 of the wavelength of ultrasonic propagation in magnesium rare earth alloys; (4) Finite element simulation was performed on the conditions with different vibration modes and action positions to simulate the amplitude distribution on the surface of the magnesium alloy substrate 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 moving path was selected; (5) Method for determining the positional relationship between the welding gun and the two sets of rolling ultrasonic tool heads: The welding gun is regarded as a point, and the position of the welding gun corresponds to the center of the molten pool. According to step (4), the center of the molten pool is set at the position where the ultrasonic amplitude on the surface of the magnesium alloy is the largest, and then the position between the welding gun and the two sets of rolling ultrasonic tool heads is determined. The dry extension length 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.

5. The method of using dual ultrasound to suppress element segregation during arc-assisted magnesium-rare earth alloy solidification according to claim 4, characterized in that: In step (1), the rolling ultrasonic tool head is in line contact with the surface of the magnesium alloy substrate, and the length of the contact area is 8-15 mm; the vibration mode of the rolling ultrasonic tool head is a longitudinal vibration mode or a radial vibration mode.

6. The method of using dual ultrasound to suppress element segregation during arc-assisted magnesium-rare earth alloy solidification according to 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 of the air compressor, and the pressure of the air compressor is set to 0.15 MPa.

7. The method of using dual ultrasound to suppress element segregation during arc-assisted magnesium-rare earth alloy solidification according to claim 1, characterized in that: In step 4, determining the action position of the rolling ultrasonic tool head at the side wall of the deposited layer includes the following steps: (1) According to 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 processing in step 3. Different ultrasonic tool head action positions are set during the geometric modeling process. The principle of setting the ultrasonic tool head action position 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, and the position where the ultrasonic tool head acts on the wall surface is 5-10 mm away from the upper surface of the wall; (2) According to the actual magnesium alloy substrate material used, the accurate magnesium alloy substrate material is set in the finite element simulation software, the boundary conditions and initial conditions are set, and the elastic wave control equation and the frequency domain solution method are adopted, wherein the boundary conditions are as follows: each surface of the magnesium alloy substrate is set to a free vibration mode; initial conditions: 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, and the vibration mode is a radial vibration mode in which the ultrasonic vibration direction is 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 divided using the tetrahedral meshing method, and the maximum mesh size must be less than 1 / 20 of the wavelength of ultrasonic propagation in magnesium rare earth alloys; (4) Finite element simulation was performed on the conditions 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 moving path was selected; (5) Method for determining the positional relationship between the welding gun and the two sets of rolling ultrasonic tool heads: The welding gun is regarded as a point, and the position of the welding gun corresponds to the center of the molten pool. According to the sound field simulation results, the center of the molten pool is set at the position where the ultrasonic amplitude on the surface of the magnesium rare earth alloy deposition layer is the largest. Then, the positional relationship between the welding gun and the two sets of rolling ultrasonic tool heads is determined. The dry extension length 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.

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