CN113385820B - Double-magnetic-field and ultrasonic-wave cooperative auxiliary laser deep melting welding device - Google Patents
Double-magnetic-field and ultrasonic-wave cooperative auxiliary laser deep melting welding device Download PDFInfo
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- CN113385820B CN113385820B CN202110654742.6A CN202110654742A CN113385820B CN 113385820 B CN113385820 B CN 113385820B CN 202110654742 A CN202110654742 A CN 202110654742A CN 113385820 B CN113385820 B CN 113385820B
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K26/00—Working by laser beam, e.g. welding, cutting or boring
- B23K26/346—Working by laser beam, e.g. welding, cutting or boring in combination with welding or cutting covered by groups B23K5/00 - B23K25/00, e.g. in combination with resistance welding
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K26/00—Working by laser beam, e.g. welding, cutting or boring
- B23K26/70—Auxiliary operations or equipment
- B23K26/702—Auxiliary equipment
Abstract
The invention provides a double-magnetic-field and ultrasonic-wave cooperative auxiliary laser deep melting welding device which comprises a base, a workbench, a mechanical arm, a laser welding machine, a moving mechanism, a welding table, an ultrasonic vibrator, an alternating electromagnetic field coil, an alternating electromagnetic field power supply, a constant electromagnetic field coil and a constant electromagnetic field power supply, wherein the escape of gas in a molten pool is accelerated by utilizing the combined action of ultrasonic waves and an electromagnetic field, so that the defect of a gas hole is inhibited; meanwhile, the coupling effect of the ultrasonic impact force and the magnetic field electromagnetic force is utilized to break the intermetallic brittle compounds and the coarse grains, reduce the quantity of the intermetallic brittle compounds, refine the grains and improve the welding quality. A mathematical model of heat transfer and mass transfer of laser deep melting welding under the synergistic action of a magnetic field and ultrasonic waves is established, the heat transfer and flow rules of a molten pool in the welding process are disclosed, the influence of the ultrasonic waves and an alternating magnetic field on the floating rate of bubbles and the solidification rate of the molten pool by a stable magnetic field is researched, and the mechanism of reducing the pore defects is mainly analyzed.
Description
Technical Field
The invention relates to the technical field of laser welding, in particular to a double-magnetic-field and ultrasonic-wave cooperative auxiliary laser deep melting welding device.
Background
Energy conservation, consumption reduction and environmental pollution reduction become common problems facing human beings. The reduction of the weight of the transportation vehicle can effectively reduce the consumption and emission of fuel oil, so that more and more light metals (such as aluminum alloy, magnesium alloy and the like) are used on vehicles such as automobiles, aerospace and the like. Magnesium and aluminum are two metal elements widely distributed in the earth's crust at present, and the excellent performance of magnesium and aluminum is receiving more and more attention. The magnesium alloy has the advantages of light weight, high specific strength and specific stiffness, good shock resistance, radiation resistance, easy recovery and the like, and is known as a green engineering material in the new century. Similarly, aluminum alloy has been more and more widely used in transportation industry because of its advantages of light weight, good plasticity, strong corrosion resistance, excellent mechanical properties, relatively mature manufacturing process, etc.
Therefore, the problem of magnesium to aluminum bonding is becoming more and more of a concern. Welding is a widely used metal connection means at present. However, magnesium and aluminum have high chemical activity and thermal conductivity, and have poor weldability, so that the problems become technical difficulties and need to be solved for restricting the application of magnesium-aluminum alloy. At present, the main problems of magnesium-aluminum welding are summarized as follows:
(1) Oxidation, inclusions, underfloor welding and evaporation. Magnesium and aluminum are active in chemical property and are easy to combine with oxygen to generate MgO and Al 2 O 3 And the like. Due to MgO and Al 2 O 3 The oxides have high melting points, are not easy to melt in the welding process and are easy to form inclusion, thereby reducing the welding jointStrength; meanwhile, the melting points and boiling points of magnesium and aluminum are low, so that evaporation and even burning loss of alloy elements are easily caused in a high-power welding process, a welding line is easily collapsed, and the strength of a welding joint is obviously reduced.
(2) Coarse grain, thermal stress and cracks cause welding problems. The magnesium alloy and the aluminum alloy have high thermal conductivity, and when a high-power heat source is adopted for welding, the heat of a welding seam and the heat around the welding seam are too high, so that the crystal grains are coarse and the dendrite segregation phenomenon is easy to occur. In addition, the magnesium and the aluminum have larger thermal expansion coefficients, larger welding stress is easily generated in the welding process, the temperature of a brittle interval is wider, cracks are easily formed, and the mechanical property of a welding joint is further influenced.
(3) The formation of brittle intermetallic compounds. The magnesium and aluminum dissimilar metal is easy to form intermetallic brittle compounds during welding, and the mechanical property of the weld is seriously reduced by excessive intermetallic brittle compounds in the weld.
(4) The difference in solubility causes soldering problems. Magnesium and aluminum have low mutual solubility in a liquid state, and a fusion zone is difficult to form by the two metals. In addition, the gas has high solubility in magnesium aluminum at high temperature and low solubility in solid state, so that pores are easily generated, and the plasticity and toughness of a fusion area are reduced.
Therefore, the method for exploring a new welding method suitable for the magnesium-aluminum dissimilar metal, researching key technology and process problems has very important scientific research value and practical significance for thoroughly solving the technical bottleneck restricting the welding application of the magnesium-aluminum dissimilar metal, expanding the application scale of the light alloy in rail transportation vehicles and even in the aerospace field, and greatly reducing increasingly urgent environmental pollution and energy consumption pressure.
In order to solve the common welding problems in the magnesium-aluminum welding, the selection of a proper welding method is very important. Laser penetration welding is one such commonly used welding method. The laser welding has the advantages of concentrated heat, high energy density, easy control of heat input, small heat affected zone, high welding speed, small deformation, large depth-to-width ratio of welding line, easy automation realization and the like. At present, the researches on the laser welding of magnesium and aluminum by scholars at home and abroad mainly focus on the following two aspects: firstly, the process conditions are improved, and the joint quality is improved. Gao et al used the latest generation nanosecond pulse fiber laser to weld magnesium alloy and aluminum alloy, and the tensile strength of the joint reached 86MPa, which reached 75% of the strength of the aluminum alloy base material. Bannour et Al investigated the effect of Mg and Al alloy lap joint position on laser weld microstructure and hardness. Borrisutthekul et al comparatively analyzed the center lap and edge lap forms of laser welding magnesium and aluminum plates, and determined the appropriate welding mode in combination with a finite element model. Wang Gongyang [4] compared with magnesium aluminum dissimilar metal laser welding and traditional laser welding process, found that: the adoption of the magnesium-aluminum laser glue welding technology can improve the laser absorption rate of the aluminum alloy, increase the melting depth, reduce the thickness of intermetallic brittle compounds and reduce cracks, thereby improving the performance of the joint. And secondly, researching the influence of the intermetallic brittle compound on the performance of the joint. The main approach is to control the brittle compounds by adding filler materials, thereby increasing the tensile strength of the joint. Scherm et al, which uses a bifocal Nd: YAG laser and a ZnAl filler material to laser weld magnesium alloy and aluminum alloy, found that the aluminum content in the filler wire has a significant effect on the strength of the joint. Li Hui, et al, investigated the effect of intermetallic brittle compounds on the performance of AZ31B magnesium and 6061 aluminum alloy laser welded joints. Gao et al laser welded magnesium and aluminum with Ti as the intermediate layer and found that intermetallic brittle compounds were significantly suppressed. The hemp Ding Long et al adopt Zn as an intermediate layer to carry out laser welding on magnesium alloy and aluminum alloy, and study the influence mechanism of the Zn intermediate layer on joints.
However, in the case of laser welding of magnesium and aluminum dissimilar metals, the adverse effect of the brittle intermetallic compound on the weld joint performance can be reduced to some extent by improving the welding process or adding alloy elements, but the above measures are not effective in the welding problems such as the porosity defect, coarse crystal grains, and different laser absorption rates of magnesium and aluminum, which are easily generated in the welding of magnesium and aluminum dissimilar metals, and the brittle intermetallic compound is not easily controlled completely, and the porosity defect is even worsened when powder is added. How to inhibit the weld defects such as pores and coarse grains when dissimilar metals of magnesium and aluminum are welded and improve the welding quality needs further exploration.
In order to overcome the self limitation of single laser welding, the scholars at home and abroad propose ultrasonic-assisted laser welding, and two problems can be solved after ultrasonic is added on the basis of conventional laser welding: 1. inhibiting weld porosity defects: the proper ultrasonic loading mode, intensity and frequency are selected, so that the metal melt can be subjected to the driving force taking the 'external ultrasonic and force' as the leading factor, the flowing behavior, the alloy element distribution and the bubble movement behavior of liquid metal in a molten pool can be effectively interfered, meanwhile, the flow of the molten pool can be promoted by the acoustic flow effect, the cavitation effect, the mechanical effect and the thermal effect of ultrasonic waves, bubbles are forced to float upwards and escape to the maximum extent, in addition, the cavitation effect of the ultrasonic waves can also remove hydrogen in magnesium-based solution and aluminum-based solution, and the aim of eliminating the pore defects is finally achieved; 2. refining crystal grains, promoting the generation of equiaxed crystals and improving the microstructure: the mechanical vibration effect of the ultrasonic wave can strengthen the mass transfer process of the liquid metal, so that the temperature gradient and the stress gradient in the melt are reduced. In addition, the transmission of ultrasonic waves in liquid and solid media and the energy are in an attenuation form, so that unfused areas are eliminated, grains are refined, and the microstructure of a heat affected zone and a weld joint fusion zone is remarkably improved. The sound flow effect of the ultrasonic wave can play a certain stirring role on the medium, destroy the boundary layer, accelerate the heat and mass transfer rate, inhibit columnar crystals and promote the generation of isometric crystals. However, the ultrasonic action range generated by single application of ultrasonic wave is small, the molten pool cannot be fully stirred, and ultrasonic-assisted laser welding generally has a more remarkable inhibiting effect on the air holes only under the condition of low welding speed, because the molten pool stays for a longer time at high temperature when the welding speed is low, and the floating distance of bubbles is shortened by the profile of the rear wall of the molten pool with high gradient, which is beneficial to the escape of gas in the molten pool. Guo Tao studies showed: as the welding speed increases, the ability of the ultrasonic vibration to suppress the void defects decreases. However, the welding efficiency is affected by the reduction of the welding speed, and more seriously, the brittle compounds among magnesium and aluminum metals are increased along with the extension of the high-temperature time of the molten pool, meanwhile, the welding seam collapse is aggravated, and the joint strength is reduced. How to exert the beneficial effects of ultrasonic vibration (inhibiting pores and refining grains) to the maximum extent in ultrasonic-assisted laser welding, not sacrificing the welding efficiency and the performance of a welding joint due to reduction of the welding speed, and solving the problem of small action range of a single ultrasonic wave on a molten pool is a problem worthy of further research.
The auxiliary magnetic field applied in the laser deep melting welding process is generally divided into a stable magnetic field and an alternating magnetic field. The alternating magnetic field is added to stir the molten pool by utilizing the generated electromagnetic force, namely 'electromagnetic stirring'. The principle of electromagnetic stirring is as follows: 1. the conductive molten pool is cut by the alternating magnetic field at a certain speed, so that induced current is formed inside the molten pool; 2. the alternating current magnetic field cuts the conductive molten pool to generate electromagnetic force, and the electromagnetic force promotes the flow of liquid metal in the molten pool. Therefore, three problems can be solved by adding an alternating magnetic field on the basis of laser welding: 1. the flow of a molten pool is accelerated, the floating of bubbles is promoted, and the number of bubbles in the welding seam is reduced; 2. the superheat degree in the molten pool is reduced, a relatively uniform temperature field is formed, and the possibility of crack generation is reduced; 3. quickening the convection in the molten pool, being beneficial to refining crystal grains and improving the weld joint structure. The Lorentz magnetic force generated by adding the stable magnetic field is opposite to the flowing direction of the molten pool at any moment, so that the flowing of the molten pool can be inhibited, the effect of stirring the molten pool cannot be realized, and the method is generally used for improving the metallurgical quality. For high-power laser deep melting welding, the energy is concentrated, the temperature gradient of the welding center is large, the thermal capillary force is also large, and if a stable magnetic field is loaded at the position, the influence of the generated Lorentz magnetic force on the fluid is far less than that of the thermal capillary force, so that the action of the loading magnetic field is not obvious. Along with the progress of the welding process, the temperature of the rear edge of the molten pool is gradually reduced, the molten pool starts to enter a solidification stage, the temperature gradient is reduced, the thermal capillary force is also reduced, if a stable magnetic field is loaded at the position, the action of the magnetic field starts to appear, the flowing of the molten pool can be blocked, the movement of the molten pool is delayed, the solidification rate of the molten pool is reduced, the time of bubbles escaping from the molten pool is prolonged, and the defects of air holes are reduced.
It follows that the type and location of the auxiliary magnetic field loading during the welding process is critical. The loading magnetic field types are different, and the effects are quite different; the loading magnetic field has different positions and completely different action effects. However, in the existing magnetic field assisted laser welding research, only a single alternating magnetic field or a single steady magnetic field is loaded, and the aim of only increasing the floating rate of bubbles or reducing the solidification rate of a molten pool can be achieved. Obviously, the following conditions must be satisfied to suppress the pore defects: the bubble floating rate is greater than or equal to the solidification rate of the molten pool, which means that the bubble floating rate must be increased while the solidification rate of the molten pool is reduced during welding in order to suppress the blowhole defect. In addition, because the stirring time of the molten pool by the single alternating magnetic field is short, the refining effect on the welded structure is not obvious.
Disclosure of Invention
Technical problem to be solved
Aiming at the defects of the prior art, the invention provides a double-magnetic-field and ultrasonic-wave cooperative auxiliary laser deep melting welding device, which solves the problems in the background technology.
(II) technical scheme
In order to achieve the purpose, the invention is realized by the following technical scheme: the utility model provides a double-magnetic-field and ultrasonic wave assist laser deep melting welding set in coordination, includes base, workstation, arm, laser-beam welding machine, moving mechanism, welding bench, ultrasonic vibration machine, alternating electromagnetic field coil, alternating electromagnetic field power, invariable electromagnetic field coil, invariable electromagnetic field power, workstation, arm all set up on the base, moving mechanism sets up on the workstation, and can drive welding bench lateral shifting, be used for placing aluminum plate and magnesium board on the welding bench, the laser-beam welding machine sets up the tip at the arm and corresponding with the welding bench, ultrasonic vibration machine sets up on the workstation and corresponding with the welding bench, alternating electromagnetic field coil, invariable electromagnetic field coil transversely set gradually on the workstation and with the welding bench correspond from top to bottom, alternating electromagnetic field coil links to each other with the alternating electromagnetic field power, invariable electromagnetic field power links to each other with invariable electromagnetic field power.
Preferably, a magnetic field isolation plate is arranged between the alternating electromagnetic field coil and the constant electromagnetic field coil.
Preferably, the magnetic field isolation plate is made of silicon steel.
Preferably, the workbench is hollow.
Preferably, the worktable is provided with a clamping assembly for fixedly clamping the aluminum plate and the magnesium plate.
Preferably, the moving mechanism is a screw slide rail mechanism.
(III) advantageous effects
The invention provides a double-magnetic-field and ultrasonic-wave cooperative auxiliary laser deep melting welding device. The method has the following beneficial effects:
1. according to the double-magnetic-field and ultrasonic-wave cooperative auxiliary laser deep melting welding device, a constant magnetic field, an alternating magnetic field, a laser beam and an ultrasonic emitting head are fixed, and a magnesium plate and an aluminum plate on a welding table are driven to move through a moving mechanism to complete magnesium-aluminum welding; applying an alternating magnetic field and non-contact ultrasonic waves in a laser irradiation area, mutually coupling an electromagnetic stirring effect generated by the alternating magnetic field and an acoustic flow effect, a cavitation effect, a mechanical vibration effect and a thermal effect of the ultrasonic waves, and jointly accelerating the fluidity of liquid metal in a molten pool, so that the magnesium and aluminum can be fully and uniformly mixed, the floating rate of bubbles can be obviously improved, the time for the bubbles to escape is shortened, the time for the welding molten pool to be at high temperature is shortened, the formation of intermetallic brittle compounds is reduced, and in addition, the effect of the cooperative regulation and control on a welding tissue can be achieved by regulating various parameters of a composite field, so that the performance of a joint is further improved compared with that of a joint under the action of a single external energy field; and applying a constant magnetic field in a region which is irradiated by laser and waits for cooling, reducing the cooling rate of the molten pool, and prolonging the existence time of the molten pool at a relatively low temperature, so that the floating rate of bubbles is greater than or equal to the solidification rate of the molten pool, and the bubbles can be favorably and completely escaped.
2. According to the double-magnetic-field and ultrasonic-wave cooperative auxiliary laser deep melting welding device, a silicon steel with high magnetic permeability is inserted between a constant magnetic field and an alternating magnetic field to serve as a magnetic field isolation plate, so that the alternating magnetic field is prevented from stirring an action area of the constant magnetic field.
Drawings
FIG. 1 is an overall isometric view of the present invention;
FIG. 2 is a schematic view of a moving assembly of the present invention;
FIG. 3 is a view of the topography right above the molten pool of the single ultrasonic-assisted laser welding of magnesium and aluminum in accordance with the present invention;
FIG. 4 is a schematic diagram of the right upper side of a magnesium-aluminum single magnetic field assisted laser welding molten pool;
FIG. 5 is a view of the shape right above the molten pool of the laser welding assisted by the cooperation of the magnalium magnetic field and the ultrasonic wave.
In the figure: the device comprises a base 1, a workbench 2, a mechanical arm 3, a laser welding machine 4, a moving mechanism 5, a welding table 6, an ultrasonic vibrator 7, an alternating electromagnetic field coil 8, an alternating electromagnetic field power supply 9, a constant electromagnetic field coil 10, a constant electromagnetic field power supply 11, a magnetic field isolation plate 12, an aluminum plate 13 and a magnesium plate 14.
Detailed Description
The embodiment of the invention provides a double-magnetic-field and ultrasonic-wave cooperative auxiliary laser deep melting welding device, which comprises a base 1, a workbench 2, a mechanical arm 3, a laser welding machine 4, a moving mechanism 5, a welding table 6, an ultrasonic vibrator 7, an alternating electromagnetic field coil 8, an alternating electromagnetic field power supply 9, a constant electromagnetic field coil 10 and a constant electromagnetic field power supply 11, wherein the workbench 2 and the mechanical arm 3 are both arranged on the base 1, and the workbench 2 is hollowed. The moving mechanism 5 is arranged on the workbench 2 and can drive the welding table 6 to move transversely, and the moving mechanism 5 is a screw rod sliding rail mechanism. Be used for placing aluminum plate 13 and magnesium board 14 on the welding bench 6, be provided with the centre gripping subassembly that is used for fixed centre gripping aluminum plate 13, magnesium board 14 on the workstation 2, the centre gripping subassembly comprises a pair of elasticity splint. The laser welding machine 4 is arranged at the end part of the mechanical arm 3 and corresponds to the welding table 6, the ultrasonic vibrator 7 is arranged on the working table 2 and corresponds to the welding table 6, the alternating electromagnetic field coil 8 and the constant electromagnetic field coil 10 are transversely and sequentially arranged on the working table 2 and vertically correspond to the welding table 6, the alternating electromagnetic field coil 8 is connected with the alternating electromagnetic field power supply 9, and the constant electromagnetic field power supply 11 is connected with the constant electromagnetic field power supply 11.
A magnetic field isolation plate 12 is arranged between the alternating electromagnetic field coil 8 and the constant electromagnetic field coil 10. The magnetic field isolation plate 12 is made of silicon steel.
The constant magnetic field, the alternating magnetic field, the laser beam and the ultrasonic emitting head are fixed, and the magnesium plate 13 and the aluminum plate 14 on the welding table 6 are driven to move by the moving mechanism 5 to complete the welding of the magnesium and aluminum plate 14; an alternating magnetic field and non-contact ultrasonic waves are applied to a laser irradiation area, the electromagnetic stirring effect generated by the alternating magnetic field and the acoustic flow effect, cavitation effect, mechanical vibration effect and thermal effect of the ultrasonic waves are mutually coupled, so that the liquidity of liquid metal in a molten pool is jointly accelerated, the magnesium and aluminum can be fully and uniformly mixed, the floating rate of bubbles can be obviously improved, the time for escaping the bubbles is shortened, the time for the welding molten pool to be at high temperature is shortened, the formation of intermetallic brittle compounds is favorably reduced, in addition, the effect of the cooperative regulation and control on welding tissues can be achieved by regulating various parameters of a composite field, and the performance of a joint is further improved compared with the effect of a single external energy field; and applying a constant magnetic field in a region which is irradiated by laser and waits for cooling, reducing the cooling rate of the molten pool, and prolonging the existence time of the molten pool at a relatively low temperature, so that the floating rate of bubbles is greater than or equal to the solidification rate of the molten pool, and the bubbles can be favorably and completely escaped.
A silicon steel with high magnetic conductivity is inserted between the constant magnetic field coil 10 and the alternating magnetic field coil 8 to serve as a magnetic field isolation plate 12, so that the alternating magnetic field is prevented from stirring the action area of the constant magnetic field.
In addition, the addition of the magnetic field can increase the external pressure for preventing the generation of bubbles and increase the difficulty of bubble generation. Therefore, compared with the original ultrasonic-assisted laser deep melting welding, the double magnetic field and ultrasonic-assisted laser deep melting welding can reduce the air hole defects to a greater extent in the same time, so that the welding speed can be properly improved. After the welding speed is improved, the stability of the small holes can be enhanced, the possibility of generating small hole type air holes is reduced, the collapse of welding seams can be reduced, and the quantity of brittle compounds between magnesium and aluminum metals is reduced. In addition, the cavitation bubbles of the ultrasonic waves can collapse under the action of sound waves and generate shock waves with higher energy, and the shock waves are mutually coupled with electromagnetic force generated by a magnetic field, so that the capability of smashing thicker intermetallic brittle compounds and coarse crystal grains is remarkably increased, the thickness of the intermetallic brittle compounds is effectively reduced, the crystal grains are refined, the performance of joints is improved, and the welding quality is improved.
In conclusion, the invention aims to solve the welding problems of air hole defects, weld joint collapse, large crystal grains, thick and many intermetallic brittle compounds and the like in the magnesium-aluminum laser deep melting welding process by reasonably loading ultrasonic vibration and double magnetic fields, and finally obtain the high-quality and high-performance magnesium-aluminum welding joint.
The invention adopts a method of combining software simulation and experiment, firstly researches the flow condition of a molten pool, then researches the relation between ultrasonic waves and magnetic fields and the floating rate of bubbles and between a stable magnetic field and the solidification rate of the molten pool under the condition of ensuring that other process parameters are not changed, reveals the mechanism of reducing the defects of air holes, and mainly researches the influence of the ultrasonic waves and the magnetic fields on intermetallic brittle compounds, the sizes and the forms of crystal grains and optimizes welding process parameters. The research of the invention provides a new composite welding method for the high-quality welding of magnesium and aluminum dissimilar metals.
When the ultrasonic-assisted laser deep fusion welding technology is adopted to weld magnesium-aluminum dissimilar metals, the welding speed is improved, so that the inhibition effect of ultrasonic waves on air hole defects is weakened. Therefore, how to improve the welding speed and reduce the defects of pores and the like is the key for solving the problem of welding quality of the magnesium-aluminum dissimilar metal. In addition, more thick magnesium-aluminum intermetallic brittle compounds are generated in the melting welding process. How to reduce the thickness of the intermetallic brittle compounds and the amount of the intermetallic brittle compounds are also one of the welding difficulties of the magnesium-aluminum alloy.
The invention deeply develops the research of the double magnetic field and ultrasonic wave cooperative auxiliary laser deep melting welding method around the main problems of pore defects, intermetallic brittle compounds and the like existing in the welding of magnesium and aluminum dissimilar metals, and explores the action mechanism and influence rule of the ultrasonic wave and the magnetic field in the aspects of bubble generation, bubble escape, weld microstructure, intermetallic brittle compound formation and the like. The main contents are as follows:
(1) The research on the action mechanism of the coupling of the double magnetic field and the ultrasonic wave on the aspect of inhibiting the pore defects comprises the following steps: pores are easily generated in the magnesium-aluminum welding process, and the pores mainly comprise two types: 1. hydrogen pores (the solubility of hydrogen in the welding process is sharply reduced in the cooling process of the liquid molten pool, and the generated hydrogen bubbles do not have enough time to float upwards from the molten pool and escape to form hydrogen pores); 2. pinhole type pores (pores formed by unstable pinholes during welding). There are two main methods for reducing hydrogen hole defects: a. accelerating the escape of the bubbles, namely, the floating rate of the bubbles in the liquid metal is higher than the solidification rate of the liquid metal; b. preventing the formation of bubbles. a. The bubble escape is accelerated, an alternating magnetic field is applied to a laser irradiation area and can cut a molten pool at a certain speed, so that induced current is generated inside the conductive molten pool, lorentz force is generated under the interaction condition of the induced current and the alternating magnetic field, and the Lorentz force can play a non-contact stirring role on the molten pool. Meanwhile, the ultrasonic wave can generate a sound flow effect in the transmission of the liquid metal medium, and the sound flow effect can play a certain mechanical stirring role for the molten pool. When the ultrasonic waves are applied alone, the effect of the ultrasonic waves on the weld pool is reduced if the welding speed is high. When the alternating magnetic field and the ultrasonic wave are loaded simultaneously, the stirring effect of the molten pool can be enhanced in the same time, the internal flow of the molten pool is promoted, the internal temperature of the molten pool is increased, and the viscosity of the liquid metal is reduced. The floating rate of the bubbles in the liquid metal is influenced by factors such as the radius of the bubbles, the viscosity of the liquid metal, the density of gas in the bubbles and the like, and can be expressed by a Stocks formula:
v is the bubble floatation rate, R is the bubble radius, η is the liquid metal viscosity, ρ L Is the density of the liquid metal, p G Is the density of the gas in the bubbles. From Stocks formula, it can be known that the lower the viscosity of the liquid metal, the faster the bubble floating rate, and the less likely to form pores. Therefore, the alternating magnetic field applied on the basis of ultrasonic-assisted laser deep melting welding can be used for accelerating the floating rate of bubbles.
In the area behind the laser irradiation, the laser effect is very weak and can be ignored, and the distance from the laser center is far. At this time, the inside of the molten pool is always subjected to heat convection and heat conduction due to temperature unevenness, and heat exchange with the external environment exists. Along with the time, the temperature in the molten pool is slowly uniform, so that the temperature gradient is also slowly reduced, a stable magnetic field is applied to the region, the Lorentz magnetic force direction is opposite to the flow direction of the molten pool, the unstable flow of the molten pool in the solidification process can be prevented, the temperature of a melting area caused by thermal convection is reduced, the existence time of the molten pool is prolonged, the solidification rate of the molten pool is reduced, and bubbles are easier to escape.
The two aspects are combined to obtain: in the ultrasonic-assisted laser deep melting welding, the alternating magnetic field and the constant magnetic field are applied front and back, so that the floating rate of bubbles can be improved, the solidification rate of a molten pool is reduced, and the possibility of generating air hole defects is reduced.
b. Prevention of bubble formation
After the alternating magnetic field is added, lorentz magnetic force can be generated inside the molten pool, the flow of the molten pool can be accelerated by the Lorentz magnetic force, so that dynamic pressure can be generated randomly, external pressure generated by bubbles is prevented from being changed into dynamic pressure caused by the magnetic field on the original basis, the difficulty of bubble generation is increased, and the generation of pore defects is reduced.
In conclusion, compared with the original ultrasonic-assisted laser deep fusion welding, the dual magnetic field and ultrasonic-assisted laser deep fusion welding can reduce the air hole defects to a greater extent in the same time, so that the welding speed can be properly improved.
(2) The influence of the double magnetic field and the ultrasonic wave in cooperation with the auxiliary laser deep melting welding on the stability of the small hole;
the welding speed can be improved by increasing the magnetic field in the ultrasonic-assisted laser deep melting welding process, so that the position acted by the laser beam moves forwards, the generated recoil pressure only acts on the front wall of the small hole, the small hole is pushed to move forwards, and the rear wall of the small hole is free from the recoil pressure. Meanwhile, the liquidity of the liquid metal on the rear wall of the small hole is more stable, the radius of the small hole is increased, the external interference resistance is enhanced, the stability of the small hole and a molten pool is improved, and the generation of small hole type air holes is favorably prevented.
(3) The influence of the double magnetic field and the ultrasonic wave in cooperation with the auxiliary laser deep melting welding on the crystal grains and the intermetallic brittle compounds;
the shock wave generated by the ultrasonic cavitation effect and the Lorentz magnetic force generated by the magnetic field can jointly break up columnar crystals at a fusion line and coarse grains generated in the welding process. In addition, the sound flow effect and the mechanical stirring effect generated by the ultrasonic waves and the electromagnetic stirring effect generated by the magnetic field can enhance the fluidity of the molten pool together, so that the crystallized grains flow to the molten pool along with the liquid metal, and the refinement of the grains and the formation of isometric crystals are promoted. However, the energy of the ultrasonic wave is mainly concentrated near the probe, and the intensity of the ultrasonic wave is weakened with the increase of the distance, so that the effect on the molten pool is not obvious. In addition, the action time of the single magnetic field on the molten pool is short, and the refining effect on the welded structure is not obvious. Therefore, the defect of a single magnetic field or a single ultrasonic field can be made up by adding the magnetic field on the basis of the ultrasonic waves, and the thicker and larger intermetallic brittle compounds among magnesium and aluminum can be broken by the Lorentz force generated by the magnetic field and the shock waves generated by the ultrasonic cavitation effect, so that the thickness of the compound layer is reduced; meanwhile, due to the addition of the magnetic field, the welding speed can be increased, the overhigh heat input amount between magnesium and aluminum is prevented, the quantity of intermetallic brittle compounds is reduced, and the quality of a welding joint is finally improved.
(4) Optimizing parameters of the laser deep melting welding process by the aid of the magnesium/aluminum double magnetic field and ultrasonic waves;
the ultrasonic welding method mainly comprises the following steps of mainly exploring the ultrasonic power, frequency, alternating magnetic field strength, stable magnetic field strength, ultrasonic position (impact wave generated by ultrasonic cavitation effect of an ultrasonic emission head and a laser center and Lorentz force generated by the magnetic field can jointly break columnar crystals at a fusion line and coarse grains generated in the welding process).
Double-magnetic-field and ultrasonic-wave cooperative auxiliary laser deep melting welding test method
The method comprises the following steps: in order to allow the magnetic field to penetrate through the welding workpiece, a part of the clamping assembly needs to be hollowed out, and the alternating magnetic field coil 8 and the constant magnetic field coil 10 are controlled by the adjustable power supply. The ultrasonic vibrator 7 and the laser welder 4 are fixed right above the alternating magnetic field coil 8, and silicon steel (with good shielding magnetism) is used as a magnetic field isolation plate between the constant magnetic field and the alternating magnetic field to prevent mutual influence between the stable magnetic field and the alternating magnetic field. The magnesium plate 14 and the aluminum plate 13 each have a size of 100 x 40 x 2mm;
step two: simulation analysis of the intensity field and the flow field, namely establishing a double magnetic field and ultrasonic wave cooperative auxiliary laser deep melting welding heat source model and a flow model of the magnesium/aluminum dissimilar metal plate, and calculating a corresponding welding temperature field and a corresponding flow field.
Step three: the molten pool flow behavior test research comprises the steps of firstly adding a layer of copper foil with the thickness of about 0.2mm between a magnesium plate 14 and an aluminum plate 13, clamping the copper foil by the magnesium plate 14 and the aluminum plate 13 before welding to form a sandwich structure, and then welding the sandwich structure by adopting a double magnetic field and ultrasonic wave in cooperation with an auxiliary laser deep penetration welding method. And (3) carrying out SEM back-scattered electron imaging observation on the longitudinal section of the finally formed welding line and carrying out EDS analysis on the cross section of the welding line to obtain the distribution rule of the copper element, thereby obtaining the distribution rule of the flow of the molten pool. The test and the simulation are compared, the accuracy of a simulation model is verified, the flowing rule of the magnesium/aluminum dissimilar metal double magnetic field and the ultrasonic wave are found to assist the laser deep melting welding pool in a synergic mode, and a foundation is laid for the follow-up research of air hole defects and the optimization of process parameters.
Step four: the research on the flowing and bubble escape behaviors of the welding pool comprises the following steps: under the condition of ensuring other welding process parameters to be consistent, setting the following two groups of tests 1. Simultaneously loading laser and ultrasonic waves; 2. ultrasonic waves and an alternating magnetic field are simultaneously applied near the center of laser irradiation. And comparing the flow conditions of the two tests by using an element tracing method, detecting the temperatures of the surfaces of the two groups of molten pools by using a laser welding bicolor temperature system in the welding process, and deducing the change condition of the floating rate of the bubbles after the alternating magnetic field is loaded on the basis of ultrasonic waves according to the relation between the temperature and the viscosity and by combining a stocks formula. And then, increasing a certain welding speed for the group of experiments added with the alternating magnetic field, and comparing the welding speed with the quantity of bubbles at the section of the welding seam of the pure ultrasonic-assisted laser deep-fusion welding (by adopting a pore analysis method). In addition, the change conditions of the two groups of molten pools and the size of the uppermost small hole in the welding process are observed by using a high-speed camera, and the possibility of occurrence of the two groups of small hole type test holes is finally judged according to the behavior of the molten pools and the change conditions of the stability of the small holes after the magnetic field is added.
Step five: and (3) testing and analyzing the cooling rate of the welding pool: under the condition of ensuring other welding process parameters to be consistent, setting the following two groups of tests 1. Simultaneously loading ultrasonic waves and an alternating magnetic field near a laser irradiation center; 2. an ultrasonic wave and an alternating magnetic field are applied near the laser, while a constant magnetic field is applied to the rear cooling region. And measuring the temperature change conditions of the surface areas of the two groups of test low-temperature molten pools by using a laser welding bicolor temperature system, drawing a change curve of temperature and time, and comparing the cooling rates of the two groups of test molten pools according to the curve. And according to the change condition of the cooling rates of the two groups of low-temperature zone melting pools, deducing the influence on the cooling rate of the melting pool after the constant magnetic field is added.
Step six: pore formation mechanism study: the longitudinal section of the welding seam of three groups of tests (1. Loading laser and ultrasonic wave simultaneously; 2. Loading ultrasonic wave and alternating magnetic field simultaneously near the laser irradiation center; 3. Loading ultrasonic wave and alternating magnetic field near the laser, loading stable magnetic field simultaneously in the rear side cooling area) is scanned by a microscope, secondary processing and adjustment are carried out on the scanned picture, EDS energy spectrum analysis is adopted to carry out surface scanning on the pore wall, the type of pores is determined, meanwhile, the area of hydrogen pores and the area of small pore type pores on the longitudinal section of the welding seam are counted by combining with Image-Pro Plus software, and the sum of all the areas of hydrogen pores and the sum of the areas of small pore type pores on the longitudinal section of one welding seam and the total area of the longitudinal section of the welding seam are called as hydrogen porosity and small pore type porosity. And calculating hydrogen porosity and small pore type porosity of the three groups of experiments, performing comparative analysis, verifying the inference, and revealing a mechanism for reducing pore defects.
Step seven: pore defect inhibition study: the relation between the process parameters of the ultrasonic wave, the alternating magnetic field and the stable magnetic field and the number of bubbles is researched by adopting a controlled variable method, and the parameters of the ultrasonic wave, the alternating magnetic field and the stable magnetic field which can inhibit the pore defects optimally are obtained through a series of tests and simulation bases. The relation between the process parameters such as the ultrasonic power, the frequency, the strength and the direction of the alternating magnetic field and the stable magnetic field, the position of the ultrasonic wave (the distance between an ultrasonic transmitting head and a laser center), the positions of the alternating magnetic field and the stable magnetic field and the like and the gas hole number among welding seams is mainly explored.
Step eight: analyzing and detecting intermetallic brittle compounds: under the condition that other welding parameters are not changed, a series of welding experiments are carried out by changing ultrasonic parameters and magnetic induction intensity of a magnetic field, SEM or TEM scanning (observation of the thickness of an intermetallic compound layer) is carried out on a welding seam of a workpiece after welding is finished, EDS scanning and XRD analysis (determination of composition and distribution of the intermetallic compound) are carried out, comparison with pure magnetic field assisted laser deep melting welding is carried out, the relation between the magnetic field and ultrasonic waves and the brittle compound between magnesium and aluminum is obtained through contrast analysis, the parameters of the ultrasonic waves and the magnetic field are optimized finally, and the thickness and the quantity of the brittle compound between magnesium and aluminum are reduced.
Step nine: analyzing the structure performance of the welding seam: the method is characterized in that the influence of ultrasonic waves and a magnetic field system on the macroscopic appearance, the microscopic structure (paying attention to the size and the type of grains) and the mechanical property of a joint of the magnesium-aluminum laser deep melting welding is researched, an optical microscope and a scanning electron microscope are adopted to observe the appearance, the microscopic structure and the welding defects (cracks, holes and the like) of the welding joint, the mechanical property (tensile strength, microhardness, impact resistance, bending fatigue property and the like) of the welding joint is measured by a mechanical testing method, and in addition, the fracture mode is determined by the scanning electron microscope. And finally, all the influence factors are integrated, and all welding process parameters are optimized through an orthogonal test, so that the strength of the joint is highest.
A conclusion is drawn; (1) technology for inhibiting pores by the cooperation of double magnetic fields and ultrasonic waves: applying an alternating magnetic field and ultrasonic waves in a laser irradiation area, accelerating the flow of liquid metal in a molten pool by utilizing the electromagnetic stirring action of the alternating magnetic field and the coupling action of various effects of the ultrasonic waves, such as acoustic flow effect, cavitation effect, mechanical vibration effect, thermal effect and the like, and improving the escape speed of bubbles; and a stable magnetic field is applied to a region to be cooled at the rear part of the molten pool, so that the cooling rate of the molten pool is reduced, and the escape time of bubbles is prolonged. The defect of the air hole is effectively inhibited through the combined action of the double magnetic fields and the ultrasonic waves. (2) The technique for controlling the grain size and intermetallic brittle compounds by the cooperation of alternating magnetic field and ultrasonic wave comprises the following steps: by applying an alternating magnetic field and ultrasonic vibration in a laser irradiation area and utilizing the mutual coupling of the electromagnetic stirring effect generated by the alternating magnetic field and the acoustic flow effect, the mechanical vibration effect and the thermal effect of ultrasonic waves, the liquidity of liquid metal in a molten pool is jointly accelerated, the floating rate of bubbles is obviously improved, the time required by the bubbles to escape is reduced, and the time of a welding molten pool at high temperature is shortened, so that the aim of reducing intermetallic brittle compounds is fulfilled; in addition, the coupling effect of high-energy shock waves generated by collapse of the ultrasonic cavitation bubbles under the action of sound waves and electromagnetic force generated by a magnetic field is utilized to break thicker intermetallic brittle compounds and coarse crystal grains, so that the thickness of the intermetallic brittle compounds is reduced, and the crystal grains are refined.
In order to verify the feasibility of the project, the project depends on a unit to purchase required relevant laser processing equipment (a laser, a robot and the like), a set of double magnetic fields and ultrasonic wave cooperative auxiliary laser welding experimental device is designed and built in a project group, as shown in fig. 1, and partial early-stage research work is carried out by using the device. Firstly, a high-speed camera is used for respectively observing the shapes of the magnesium and aluminum right above a molten pool in single ultrasonic auxiliary laser welding, single magnetic field auxiliary laser welding and magnetic field and ultrasonic synergistic auxiliary laser welding, as shown in fig. 3, 4 and 5. From this it can be found that: in the welding process, the intensity of the flow in the molten pool of the single ultrasonic-assisted laser welding and the single magnetic-field-assisted laser welding is lower than that of the magnetic-field and ultrasonic-assisted laser welding, and the fact that the ultrasonic waves and the magnetic field are coupled can remarkably enhance the fluidity of the molten pool is proved.
Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.
Claims (6)
1. The utility model provides a two magnetic fields and ultrasonic wave assist laser deep melting welding set in coordination which characterized in that: the welding machine comprises a base (1), a workbench (2), a mechanical arm (3), a laser welding machine (4), a moving mechanism (5), a welding table (6), an ultrasonic vibrator (7), an alternating electromagnetic field coil (8), an alternating electromagnetic field power supply (9), a constant electromagnetic field coil (10) and a constant electromagnetic field power supply (11), wherein the workbench (2) and the mechanical arm (3) are both arranged on the base (1), the moving mechanism (5) is arranged on the workbench (2) and can drive the welding table (6) to transversely move, the welding table (6) is used for placing an aluminum plate (13) and a magnesium plate (14), the laser welding machine (4) is arranged at the end part of the mechanical arm (3) and corresponds to the welding table (6), the ultrasonic vibrator (7) is arranged on the workbench (2) and corresponds to the welding table (6), the alternating coil (8) and the constant electromagnetic field coil (10) are transversely arranged on the workbench (2) in sequence and correspond to the welding table (6) up and down, the alternating electromagnetic field coil (8) is connected to the constant electromagnetic field power supply (9), and the constant electromagnetic field power supply (11) is connected to the constant electromagnetic field power supply (11); applying an alternating magnetic field and ultrasonic waves in a laser irradiation area, accelerating the flow of liquid metal in a molten pool by utilizing the electromagnetic stirring action of the alternating magnetic field and the coupling action of the acoustic flow effect, the cavitation effect, the mechanical vibration effect and the thermal effect of the ultrasonic waves, and improving the escape speed of bubbles; and a stable magnetic field is applied to a region to be cooled at the rear part of the molten pool, so that the cooling rate of the molten pool is reduced, and the escape time of bubbles is prolonged.
2. The double-magnetic-field and ultrasonic-wave cooperative auxiliary laser deep melting welding device according to claim 1, characterized in that: a magnetic field isolation plate (12) is arranged between the alternating electromagnetic field coil (8) and the constant electromagnetic field coil (10).
3. The double-magnetic-field and ultrasonic-wave cooperative auxiliary laser deep melting welding device according to claim 2, characterized in that: the magnetic field isolation plate (12) is made of silicon steel.
4. The double-magnetic-field and ultrasonic-wave cooperative auxiliary laser deep melting welding device according to claim 1, characterized in that: the workbench (2) is hollow.
5. The double-magnetic-field and ultrasonic-wave cooperative auxiliary laser deep melting welding device according to claim 1, characterized in that: and the workbench (2) is provided with a clamping assembly for fixing and clamping the aluminum plate (13) and the magnesium plate (14).
6. The double-magnetic-field and ultrasonic-wave cooperative auxiliary laser deep melting welding device according to claim 1, characterized in that: the moving mechanism (5) is a screw rod sliding rail mechanism.
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