CN112975072A

CN112975072A - Method and system for assisting aluminum alloy/steel dissimilar metal melting and brazing by using additional alternating magnetic field

Info

Publication number: CN112975072A
Application number: CN202110377528.0A
Authority: CN
Inventors: 王林; 陈姬; 武传松
Original assignee: Shandong University
Current assignee: Shandong University
Priority date: 2021-04-08
Filing date: 2021-04-08
Publication date: 2021-06-18

Abstract

The invention relates to a method and a system for assisting aluminum alloy/steel dissimilar metal fusion brazing by an external alternating magnetic field. The method is that in the MIG welding and brazing process, an alternating magnetic field is applied along the direction parallel to the welding direction, and the alternating magnetic field interacts with the welding current. In the direction of MIG brazing parallel to the weld, an alternating magnetic field is applied, i.e. the direction of the magnetic field is parallel to the weld direction. The alternating magnetic field interacts with the welding current to generate additional alternating electromagnetic force, so that the periodic transverse swing of the electric arc and the molten drop is realized. The thickness of the intermetallic compound layer is controlled, and the wettability and the spreadability of the aluminum liquid on the surface of the steel are improved. The welding quality is improved.

Description

Method and system for assisting aluminum alloy/steel dissimilar metal melting and brazing by using additional alternating magnetic field

Technical Field

The invention belongs to the technical field of welding, and particularly relates to a method and a system for assisting aluminum alloy/steel dissimilar metal fusion brazing by an external alternating magnetic field.

Background

The information in this background section is only for enhancement of understanding of the general background of the invention and is not necessarily to be construed as an admission or any form of suggestion that this information forms the prior art that is already known to a person of ordinary skill in the art.

Energy conservation, emission reduction and environmental protection are the development directions of the current automobile industry and are also important problems related to human sustainable development. The lightweight design and manufacture of the automobile body are key ways for meeting the requirements of energy conservation and emission reduction. The aluminum alloy replaces part of steel, and the aluminum alloy/galvanized steel integrated vehicle body frame structure is adopted, so that the performance and advantages of the aluminum alloy and the galvanized steel can be fully exerted, the light weight, energy conservation and emission reduction of the automobile are realized, and the main trend of the development of the automobile manufacturing industry is formed.

The welding process is one of the core technologies for manufacturing the aluminum alloy/galvanized steel heterogeneous material structure, and the joint quality of the welding process has a significant influence on the performance and the service life of the product. However, the problems of small solubility, large difference of thermal physical properties (such as melting point, specific heat capacity, thermal conductivity and the like), easy formation of a large amount of Fe-Al brittle intermetallic compounds (IMC) at joints and the like exist between the aluminum alloy and the steel, and great challenges are provided for the welding process of the aluminum alloy/steel integrated vehicle body.

Researchers at home and abroad fully combine respective advantages of fusion welding and brazing process according to metallurgical characteristics of aluminum alloy/steel, and provide an aluminum alloy/steel MIG (metal-inert gas) arc fusion brazing process for melting filler metal and aluminum alloy base metal together and forming a high-strength brazing joint with the solid surface of steel base metal. Compared with welding processes such as brazing, diffusion welding, friction welding, high-energy beam fusion brazing (laser, electron beam and the like), the process has the advantages of low equipment cost, easiness in operation, wide applicability, difficulty in limitation of product structure and size and the like, and has wide application prospect in production of aluminum alloy/steel heterostructure. However, the MIG arc welding and brazing process also has a technical bottleneck that the heat input is difficult to accurately control, so that the arc energy output is easy to fluctuate, and the Fe-Al intermetallic compound layer of the joint is locally too thick or too thin (not brazed), and meanwhile, the spreading wettability of molten pool liquid metal aluminum on the steel surface is poor, so that the brazed joint surface is small, the tensile strength is low, the mechanical property of the joint is severely restricted, and the improvement of the welding quality is limited.

Disclosure of Invention

In view of the problems in the prior art, the invention aims to provide a method and a system for assisting aluminum alloy/steel dissimilar metal fusion brazing by an external alternating magnetic field. By using the alternating magnetic field, the accurate control of the heat input of the MIG welding and brazing welding is realized and the spreading and wetting of the molten metal are promoted.

In order to solve the technical problems, the technical scheme of the invention is as follows:

in a first aspect, an external alternating magnetic field assists a method for welding and brazing dissimilar metals of aluminum alloy/steel, which comprises the following steps: during MIG brazing an alternating magnetic field is applied in a direction parallel to the weld, which alternating magnetic field interacts with the welding current.

MIG welding and brazing is metal-inert gas welding (MIG welding) aiming at dissimilar metal aluminum and steel, namely filler metal and aluminum alloy base metal are jointly melted and form a high-strength brazing joint with the solid surface of the steel base metal. Both metals only melt aluminum and not steel. MIG welding is a welding method in which a meltable welding wire is used as an electrode and an arc generated by burning between a continuously fed welding wire and a workpiece to be welded is used as a heat source to melt the welding wire and a base metal.

MIG welding differs from existing TIG welders in that it uses an arc between a tungsten electrode and a workpiece to melt metal to form a weld. MIG welding has a major disadvantage over TIG welding in that it is not easy to control the heat input. The energy output fluctuation of electric arc is caused, the Fe-Al intermetallic compound layer of the joint is locally too thick or too thin (not brazed), and meanwhile, the spreading wettability of molten pool liquid metal aluminum on the surface of steel is poor, so that the brazed joint surface is small, the tensile strength is low, the mechanical property of the joint is severely restricted, and the improvement of the welding quality is limited.

In the prior art, a high-frequency magnetic field and TIG welding action are utilized, an electric arc is stabilized by the magnetic field, and the forming action is improved. However, during MIG brazing, the stabilizing arc does not have much effect on controlling the heat input profile of the MIG.

In the present invention, an alternating magnetic field is applied in the direction parallel to the weld direction of MIG brazing, i.e. the direction of the magnetic field is parallel to the weld direction. The alternating magnetic field interacts with the welding current to generate additional alternating electromagnetic force, so that the periodic transverse swing of the electric arc and the molten drop is realized. On one hand, the heat distribution of the electric arc and the molten drop acting on the aluminum alloy/steel base metal is accurately adjusted, the welding heat input size of the steel side is further controlled, the heated uniformity of the joint is improved, and the thickness consistency of the Fe-Al intermetallic compound layer of the joint is improved; on the other hand, the action force generated by the periodic swing of the electric arc and the molten drop is utilized to regulate and control the flow behavior of the molten pool, promote the transverse wetting and spreading of the liquid metal on the steel side and improve the surface forming of the welding seam; meanwhile, molten pool metal is stirred, gas escape is accelerated, pores in the welding seam are eliminated, and finally the mechanical property of the aluminum alloy/galvanized steel lap joint is improved.

In some embodiments of the invention, the MIG welding current is 50-80A and the welding voltage is 10-25V; further, MIG welding current is 55-75A, and welding voltage is 15-19V. The magnitude of the welding current is related to the material, thickness and the like of the aluminum alloy and the steel.

In some embodiments of the invention, the welding speed is 0.3 to 1 m/min; further 0.5-0.8 m/min.

In some embodiments of the invention, the wire feed speed is 2-4 m/min; further 2.5-3.3 m/min. The welding wire is conveyed by the welding gun, and the wire feeding speed represents the speed of the welding wire fed into the molten pool.

In some embodiments of the invention, the flow rate of the shielding gas is 10-20L/min; further 12-18L/min. The welding process needs to be carried out under the condition of protective gas.

In some embodiments of the present invention, the method for generating the alternating magnetic field is: and current is introduced into the two coils of the U-shaped iron core, and the two coils are alternately electrified and deenergized. One of the coils is energized, the energized magnetic head is an S pole, the other magnetic head is an N pole, and the direction of the magnetic field points to the S pole from the N pole. The reverse is true. This generates an alternating magnetic field, i.e. a magnetic field with a constantly changing magnetic field direction.

In some embodiments of the invention, the alternating magnetic field is generated with a current of 2 to 30A and a background current of 0. The magnetic field intensity of the alternating magnetic field is related to the current, the deflection degree, namely the deflection angle of the electric arc can be controlled by adjusting the magnitude of the current in the coil, on one hand, the heating area of the electric arc can be changed, so that the distribution of welding heat input is influenced, and the consistency of the thickness of the Fe-Al intermetallic compound layer is influenced finally; on the other hand the angle of deflection of the arc may affect the spreadability of the bath metal and thus the width of the braze interface.

In some embodiments of the invention, the pulse frequency is 1-40Hz and the two coil current waveforms are 180 ° out of phase. When one coil is energized, the other coil is de-energized, producing an alternating magnetic field. By adjusting the frequency of the pulsed current, the left and right deflection frequency of the arc can be varied. The arc deflection frequency can influence the residence time of the arc on two sides of the aluminum steel, so that the distribution of heat input is changed, and the consistency of the thickness of the Fe-Al intermetallic compound layer is influenced.

In the welding process, the deflection of electric arcs and molten drops is controlled by adjusting the conditions of current, pulse frequency, MIG welding current and voltage of an alternating magnetic field, the size of welding heat input of a steel side can be further controlled, meanwhile, the wettability and spreadability of molten aluminum can be influenced, and finally the surface forming and mechanical properties of a joint welding seam are influenced. The above parameter ranges can be applied to objects with different thicknesses and different materials. The adjustment of the condition may be made for different objects.

In a second aspect, the system for assisting the aluminum alloy/steel dissimilar metal melting and brazing by the aid of the additional alternating magnetic field comprises a magnetic generating device and an MIG (metal-inert gas) welding machine, wherein a magnetic field emitting end of the magnetic generating device is aligned with a position sprayed out by a welding gun nozzle of the MIG welding machine.

The magnetic field emitting end of the magnetic generator is aligned to the position sprayed out from the nozzle of the welding gun, so that the alternating magnetic field and the welding arc are interacted, an alternating electromagnetic force with a direction changing is generated in the arc, and the arc can periodically deflect left and right.

In some embodiments of the invention, the magnetic generating device comprises a U-shaped core and two coils wound around the core, the U-shaped core having two magnetic heads, the two magnetic heads being opposed and the opposed positions being aligned with the welding wire.

In some embodiments of the invention, a power source is further included, the power source being connected to the coil of the magnetic generating device.

In one embodiment, the power supply is a dual path excitation power supply.

One or more technical schemes of the invention have the following beneficial effects:

on one hand, the invention can regulate and control the heat input distribution of the workpiece through the periodic swing of the electric arc, thereby controlling the thickness of the intermetallic compound layer; on the other hand, the left-right swing of the electric arc can promote the transverse spreading of liquid metal in the molten pool, increase the area of a brazing interface, reduce a wetting angle, accelerate the flow of the molten pool, promote the escape of gas and reduce the generation of air holes. The tensile strength is improved compared to conventional MIG fusion soldered joints.

The invention can be matched with the traditional MIG welding equipment for welding production, does not need to change the original welding equipment or increase a composite heat source, has low cost and is easy to modify.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description, serve to explain the invention and not to limit the invention.

FIG. 1 is a structural diagram of an aluminum/steel dissimilar metal melting and brazing device assisted by an external alternating magnetic field according to the invention;

FIG. 2 is a structural view of a magnetic generating apparatus of the present invention;

FIG. 3 is a waveform diagram of the excitation current used by two coils of the present invention to generate an alternating magnetic field;

FIG. 4 is a schematic view of the arc stress under the action of an applied alternating magnetic field according to the present invention;

FIG. 5 is a cross-sectional view showing the formation of the weld surface in example 1 of the present invention;

FIG. 6 shows the weld surface formation and cross-section (without the assistance of an applied alternating magnetic field) of comparative example 1 in accordance with the present invention;

FIG. 7 is a comparison of the tensile strength of the joints of example 1 and comparative example 1.

The welding device comprises a MIG welding machine 1, a protective gas device 2, a welding gun 3, a magnetic generating device 4, a clamping device 5, a double-path excitation power supply 6, an aluminum plate workpiece 7, a steel plate workpiece 8, an iron core 9, a coil A10, a coil B11, a welding current direction I and a welding current direction I_e1The winding direction of coil A and the direction of the exciting current in coil A, I_e2The winding direction of coil B and the direction of the excitation current in coil B.

Detailed Description

It is to be understood that the following detailed description is exemplary and is intended to provide further explanation of the invention as claimed. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.

As introduced by the background art, the traditional MIG arc melting brazing process in the prior art is difficult to accurately control heat input, so that the arc energy output is easy to fluctuate, and the local part of a joint intermetallic compound layer is too thick or too thin (not brazed); the liquid metal in the molten pool has poor spreadability and weak fluidity, so that the brazed joint surface is small, and simultaneously, the problems of air hole defects and the like can be caused, the mechanical property of the joint is severely restricted, and the improvement of the welding quality is limited.

The invention will be further illustrated by the following examples

Example 1

Aiming at the problems that the joint strength is low and air holes are easily generated during aluminum/steel MIG welding and brazing, the invention provides an aluminum/steel MIG welding and brazing system assisted by an external alternating magnetic field. FIG. 1 is a diagram of an aluminum/steel MIG fusion welding system with the assistance of an additional alternating magnetic field, which comprises a magnetic generating device 4, a MIG welding machine 1 and a double-path excitation power supply 6, wherein the MIG welding machine 1 is connected with a protective gas device 2, and the protective gas is pure argon or helium. The magnetic generator 4 cooperates with the welding torch 3 of the MIG welder 1. The two-way excitation power supply 6 is connected to the coil of the magnetic generator 4.

In one embodiment, as shown in fig. 2, the magnetic generating device 4 includes a U-shaped iron core 9 and two coils, coil a10 and coil B11, respectively, wound around the iron core 9. The U-shaped iron core is provided with two magnetic heads which are opposite to each other, and the opposite positions of the two magnetic heads are aligned with the welding wire. The magnetic generator 4 is connected to the core by a clamping device 5, it being understood that the clamping device 5 may be two fixed plates or clamps connected by bolts. The two heads are head 1 and head 2, respectively. The magnetic head 1 and the magnetic head 2 are disposed oppositely.

In one embodiment, the U-shaped iron core is bent, part of the U-shaped iron core is fixedly connected with a welding gun, and part of the winding coil is connected with a power supply. This facilitates simultaneous connection to the welding gun and the power source.

During welding, the aluminum plate workpiece 7 is placed on the steel plate workpiece 8, and the welding gun is aligned to the welding position.

When the coil a in fig. 2 is energized, the magnetic head 1 is S-pole and the magnetic head 2 is N-pole, so that the magnetic field direction is directed from the magnetic head 2 to the magnetic head 1, and the direction of the electromagnetic force generated by the magnetic field is as shown in fig. 4(a), so that the arc can be deflected to the right. When the coil B in fig. 2 is energized, the magnetic head 1 is an N pole and the magnetic head 2 is an S pole, so that the magnetic field direction is directed from the magnetic head 1 to the magnetic head 2, and the direction of the electromagnetic force generated by the magnetic field is as shown in fig. 4(B), so that the arc can be deflected to the left. It can be seen that the magnetic fields generated when coil a10 and coil B11 are energized are in opposite directions, as are the directions of the electromagnetic forces generated in the arc. So that if the two coils are energized with the current waveform shown in FIG. 3, then t is the time₁At time, coil A is energized and coil B is not energized, at t₂When the coil B is electrified and the coil A is not electrified in time, a magnetic field with a direction changing, namely an alternating magnetic field, is generated periodically. Fig. 3 is a graph of current I versus time, in which the graph (a) in fig. 3 is a graph of coil a, and the graph (B) in fig. 3 is a graph of coil B.

Example 2

Step one, fixing an aluminum alloy plate and a steel plate to be welded, wherein the steel plate is arranged at the lower part, and the aluminum alloy plate is arranged at the upper part, as shown in figure 1.

And step two, starting an excitation power supply and setting excitation parameters. The waveforms of the exciting currents of the two coils are shown in fig. 3, the peak value of the exciting current is 2-30A, the base value current is 0, and the pulse frequency is 1-40 Hz.

And step three, selecting proper welding process parameters according to the plate thickness of the workpiece to be welded and the welding speed requirement, and starting welding.

The aluminum alloy of the welding workpiece adopts a 5052 aluminum alloy plate with the thickness of 1mm and a low-carbon steel galvanized steel plate with the thickness of 2 mm. And adjusting an MIG welding power supply, wherein the welding current is 71A, the wire feeding speed is 3.3m/min, the ER4043 welding wire with the diameter of 1.2mm is selected as the welding wire, the welding speed is 0.6m/min, the shielding gas is pure argon, and the gas flow is 16L/min. Welding was performed according to the previous steps.

Comparative example 1

The welding was performed using exactly the same welding workpiece and welding process parameters as in example 1, except that the excitation power was not turned on, i.e., the alternating magnetic field was not applied.

As shown in fig. 5 and 6, the width of the weld of example 1 of the present invention is wider and the wetting angle of the cross-section of the weld is smaller than that of comparative example 1, which indicates that the spreadability and fluidity of the liquid metal in the molten bath are enhanced and the brazed joint surface is widened.

Figure 7 compares the tensile strength of the joints of example 1 and comparative example 1, with example 1 producing a welded joint having a tensile strength significantly higher than that of the joint of comparative example 1.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. An additional alternating magnetic field assisted aluminum alloy/steel dissimilar metal fusion brazing method is characterized by comprising the following steps: during MIG brazing an alternating magnetic field is applied in a direction parallel to the weld, which alternating magnetic field interacts with the welding current.

2. The method for assisting the aluminum alloy/steel dissimilar metal melt brazing by the aid of the external alternating magnetic field according to claim 1, wherein the method comprises the following steps of: MIG welding current is 50-80A, and welding voltage is 10-25V; further, MIG welding current is 55-75A, and welding voltage is 15-19V.

3. The method for assisting the aluminum alloy/steel dissimilar metal melt brazing by the aid of the external alternating magnetic field according to claim 1, wherein the method comprises the following steps of: the wire feeding speed is 2-4 m/min; further 2.5-3.3 m/min.

4. The method for assisting the aluminum alloy/steel dissimilar metal melt brazing by the aid of the external alternating magnetic field according to claim 1, wherein the method comprises the following steps of: the flow rate of the protective gas is 10-20L/min; further 12-18L/min.

5. The method for assisting the aluminum alloy/steel dissimilar metal melt brazing by the aid of the external alternating magnetic field according to claim 1, wherein the method comprises the following steps of: the generation method of the alternating magnetic field comprises the following steps: and current is introduced into the two coils of the U-shaped iron core, and the two coils are alternately electrified and deenergized.

6. The method for assisting the aluminum alloy/steel dissimilar metal melt brazing by the aid of the external alternating magnetic field as claimed in claim 5, wherein the method comprises the following steps of: the current for generating the alternating magnetic field is 2-30A, and the base value current is 0.

7. The method for assisting the aluminum alloy/steel dissimilar metal melt brazing by the aid of the external alternating magnetic field as claimed in claim 5, wherein the method comprises the following steps of: the pulse frequency is 1-40Hz, and the phase difference of the current waveforms of the two coils is 180 degrees.

8. The system for assisting the melting and brazing of the aluminum alloy/steel dissimilar metal by the aid of the additional alternating magnetic field is characterized in that: the magnetic field emission end of the magnetic generator is aligned with the position sprayed out by a welding gun nozzle of the MIG welding machine.

9. The system for assisting the aluminum alloy/steel dissimilar metal melt brazing with the application of an alternating magnetic field according to claim 8, wherein: the magnetic generating device comprises a U-shaped iron core and two coils wound on the iron core, wherein the U-shaped iron core is provided with two magnetic heads, the two magnetic heads are opposite, and the opposite positions are aligned with the welding wire.

10. The system for assisting the aluminum alloy/steel dissimilar metal melt brazing with the application of an alternating magnetic field according to claim 8, wherein: the magnetic generator also comprises a power supply which is connected with the coil of the magnetic generator.