CN112192057B

CN112192057B - Butt-joint laser melting brazing method for aluminum/steel medium-thickness pipe

Info

Publication number: CN112192057B
Application number: CN202011039151.XA
Authority: CN
Inventors: 黄蓉蓉; 檀财旺; 陈波; 吴来军; 宋晓国; 冯吉才
Original assignee: Harbin Institute of Technology Weihai
Current assignee: Harbin Institute of Technology Weihai
Priority date: 2020-09-28
Filing date: 2020-09-28
Publication date: 2022-08-19
Anticipated expiration: 2040-09-28
Also published as: CN112192057A

Abstract

The invention relates to a method for welding an aluminum/steel medium-thick-wall pipeline, belonging to the technical field of welding. In order to solve the defect of poor strength of a welding structure obtained by the existing welding technology of aluminum/steel dissimilar materials, the invention provides a laser fusion brazing welding method for butt joint of aluminum/steel medium-thick-wall pipelines, which comprises the following specific steps: firstly, cleaning the surface of a base material to be welded; secondly, preparing the micro texture on the surface of the base metal of the steel to be welded: preparing a microtexture on the surface of the groove by adopting high-frequency pulse laser; thirdly, welding process: and adopting an aluminum-based welding wire or a zinc-based welding wire to carry out butt laser melting brazing welding on the steel pipeline and the pipeline to be welded with aluminum. The shape design of the micro-texture on the surface of the steel pipe groove improves the shape distribution of intermetallic compounds of an aluminum/steel interface, eliminates the defect of uneven thickness of the intermetallic compounds in the plate thickness direction, plays a role in blocking the expansion of cracks, and improves the joint strength of the butt joint of the aluminum/steel medium-thick-wall pipe.

Description

Butt-joint laser melting brazing welding method for aluminum/steel medium-thickness wall pipeline

Technical Field

The invention belongs to the technical field of welding, and particularly relates to a welding method of an aluminum/steel medium-thick-wall pipeline.

Background

In recent years, with the increase in energy consumption and the deterioration of the environment, the weight reduction technology has become the mainstream direction of the development of modern manufacturing industry. More and more light materials such as aluminum, magnesium, composite materials and the like are widely applied to the optimization design of materials and structures. The aluminum and the aluminum alloy have the advantages of small density, high strength, excellent cutting processing performance and the like, and the aluminum/steel composite structure is adopted, so that the use strength is ensured, and the weight reduction effect of the component can be greatly improved. The laser welding technology is a novel welding technology, has the advantages of high energy density, high welding efficiency, easiness in automation and the like, can realize accurate control of joint heat input by adopting laser welding, and is widely applied to aerospace aviation, automobile manufacturing, marine ships and pressure vessel manufacturing at present. At present, the connection of the aluminum/steel composite structure realized by adopting a laser welding technology has wide application prospect.

For welding of aluminum/steel dissimilar materials, the great difference of the physical properties and the chemistry of the aluminum/steel dissimilar materials brings great difficulty to metallurgical connection between the aluminum/steel dissimilar materials. Firstly, the difference of the melting points of aluminum/steel is large, the requirement on the precision of heat input during welding is high, otherwise, the burning loss of the base material is easily caused; because the solid solubility between Fe and Al is very low, the two meet each other to react to generate a large amount of brittle intermetallic compounds, thus deteriorating the performance of the joint. Wherein, the straight and thick appearance distribution of brittle phases leads to easy cracking of an aluminum/steel interface, and the bearing capacity damage to the dynamic load and the periodic load of the joint is great. In the thick plate welding process, due to uneven heating along the plate thickness direction, the residual stress of an aluminum/steel interface is larger, the thickness of an interface intermetallic compound layer is uneven, microcracks are easy to appear, the aluminum/steel interface performance is seriously reduced by the defects, and a joint always cracks along the interface intermetallic compound layer and rapidly expands to fail.

Disclosure of Invention

In order to solve the defect of poor strength of a welding structure obtained by the existing welding technology of the aluminum/steel dissimilar materials, the invention provides a butt laser fusion brazing welding method for an aluminum/steel medium-thick wall pipeline.

The technical scheme of the invention is as follows:

a butt laser fusion brazing welding method for aluminum/steel medium-thickness pipe comprises the following specific steps:

step one, cleaning the surface of a base material to be welded;

step two, preparing the surface microtexture of the base metal of the steel to be welded:

designing surface microtextures with different shapes and thickness distribution along the groove thickness direction, preparing the microtextures on the groove surface by adopting high-frequency pulse laser, and controlling the shapes of the microtextures by adjusting parameters of the pulse laser;

step three, welding process:

clamping the steel pipe subjected to surface treatment and the aluminum pipe to be welded onto a welding positioner, opening a laser and the welding positioner, carrying out butt laser fusion brazing welding on the steel pipe and the aluminum pipe to be welded by adopting an aluminum-based welding wire or a zinc-based welding wire with a certain single-channel laser power, a certain defocusing amount, a certain rotating speed, a certain optical wire spacing, a certain wire feeding speed, a certain wire feeding angle and a certain number of filling channels, slowly cooling after single filling, and carrying out next filling after a sample is cooled to room temperature; the laser always keeps the flat welding direction, and the welding positioner continuously rotates the base metal to be welded along with the welding process until the welding is finished.

Further, in the first step, the cleaning before welding of the groove surface of the steel pipe to be welded specifically comprises: scrubbing the surface of the parent material with acetone to remove oil stains, then adopting 5-10% HCL solution to perform acid cleaning for 2-4 min at room temperature, adopting flowing clean water to perform washing, and then performing air drying or low-temperature drying.

Further, in the second step, the adopted high-frequency pulse laser is any one of a nanosecond laser, a femtosecond laser or a picosecond laser.

Furthermore, in the second step, the laser power is 10-80W, the scanning speed is 200-2000mm/s, the pulse frequency is 20-1000kHZ, the scanning frequency is 5-100, and the surface microtexture depth is 10-150 μm.

Further, in the third step, the adopted laser is a fiber laser and CO ₂ A gas laser, a YAG solid laser, or a semiconductor laser.

Further, in the third step, the specific process parameters are as follows: the single-channel laser power is 2000-3500W, the defocusing amount is +25mm, the rotating speed is 0.2-0.5m/min, and the distance between optical fibers is 2-5 mm.

Further, in the third step, the wire feeding speed is 4-6m/min, and the wire is fed at an angle of 45 degrees ahead.

Furthermore, in the third step, the number of filling tracks is 1-20.

Further, in the third step, in the welding process, the welding line is subjected to side-blown protection behind the laser beam, the protective gas is pure Ar gas, and the flow of the protective gas is 15L/min.

Furthermore, the wall thickness of the steel pipe suitable for the method is 3-15mm, and the wall thickness of the aluminum pipe suitable for the method is 3-15 mm.

The invention has the beneficial effects that:

1. the invention provides a butt laser fusion brazing welding method for aluminum/steel medium-thickness wall pipelines, which adopts high-frequency pulse laser to realize the preparation of micro texture on the surface of a groove of a steel pipe to be welded, the preparation of the surface micro texture converts the flat groove surface into a rough structure with pits and bulges, a molten filling material can be filled into the pits to form tight connection and realize metallurgical reaction in the welding process, and the mechanical interlocking effect between aluminum and steel can be enhanced by the mutually-occluded interface morphology. The increase of the surface roughness of the steel groove effectively improves the aluminum/steel combination area, and the reason effectively improves the aluminum/steel interface strength in the aspects of physics and structure; in the aspect of metallurgical reaction, firstly, the straight and thick layered structure of an intermetallic compound between interfaces is damaged at the front edge of the reaction of a bent aluminum/steel interface, the appearance of the intermetallic compound generated on the surface of a micro-texture is changed along with the change of the texture appearance, and the rapid expansion of cracks along a brittle compound layer is effectively hindered by the rough-shaped, bent and discontinuous appearance distribution; secondly, the surface design on the groove surface along the depth direction can ensure that the reaction of molten metal and steel in different temperature intervals occurs on the surfaces with different appearances, thereby inhibiting the continuous formation and growth of interface intermetallic compounds under the high temperature condition, eliminating the metallurgical defects of uneven distribution of interface brittle phases along the groove direction and large thickness difference, reducing the interface residual stress and effectively improving the bearing capacity of the aluminum/steel interface. The shape design of the micro texture on the surface of the steel pipe groove provided by the invention improves the shape distribution of the intermetallic compound of the aluminum/steel interface, so that the straight and thick interface brittle intermetallic compound is converted into an intermittent bent shape, the defect of uneven thickness of the intermetallic compound in the plate thickness direction is eliminated, the expansion of cracks is effectively blocked, and the joint strength of butt joint of thick-wall pipes in aluminum/steel is improved.

2. According to the invention, the appearance control of an interface intermetallic compound layer is realized by preparing the microtexture of the aluminum/steel groove, so that the mechanical property of the butt joint of the aluminum/steel medium-thick-wall pipeline is improved, and the problems of non-fusion, difficult wetting, interface cracking and the like in the butt laser welding process of the aluminum/steel medium-thick-wall pipeline are solved. In the welding process, a melting and brazing mode that the steel base metal is not melted, the aluminum base metal and the welding wire are melted to fill the groove and metallurgical reaction occurs on the surface of the groove of the steel pipe is adopted, and the accurate control of heat input is realized by adjusting laser process parameters.

Drawings

FIG. 1 is a schematic view of a butt laser fusion brazing method for aluminum/steel medium-thickness pipes;

FIG. 2 is a schematic diagram of a process for preparing a micro-texture shape of the groove surface of a steel pipe to be welded;

FIG. 3 is a micro-texture shape of the groove surface of a steel pipe to be welded;

FIG. 4 is a metallographic micrograph of a butt joint for aluminum steel pipes prepared in example 1;

FIG. 5 is a metallographic micrograph of an aluminum-steel pipe butt joint prepared in comparative example 2;

in the figure, 1, a steel pipeline; 2. an aluminum alloy pipe; 3. a laser; 4. welding a positioner; 5. a laser beam; 6. an air supply pipe; 7. protective gas; 8. a wire feeding system; 9. the linear appearance of the groove; 10. and the grid shape of the groove.

Detailed Description

For a further understanding of the present invention, exemplary embodiments thereof will be described hereinafter with reference to the accompanying drawings. In the interest of clarity and conciseness, not all features of an actual implementation are described in the specification. It should be appreciated, however, that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another.

It should be noted that, in order to avoid obscuring the present invention with unnecessary details, only the device structures and/or processing steps closely related to the solution according to the present invention are shown in the drawings, and other details not so relevant to the present invention are omitted.

The invention provides a laser melting brazing welding method for butt joint of aluminum/steel medium-thickness wall pipelines, which mainly adopts the following technical principles: adopting high-frequency pulse laser to treat the cleaned surface of the steel plate to be welded so as to finish the preparation of the microtexture; the preparation of microtexture with different appearances at different positions in the depth direction of the groove is realized by changing the running track and the process parameters of the pulse laser; the welding mode of laser butt welding and brazing is adopted to realize the accurate control of the whole heat input, and in the welding process, the aluminum base metal and the filler metal are jointly melted and fill the groove and the texture of the surface of the groove; when the pipeline is welded, the pipeline is rotated at a constant speed through the positioner, and the laser is always kept at the flat welding position to ensure the welding stability.

The welding base metal needs to be cleaned before surface treatment and welding. For the surface of the groove of the steel pipe, firstly, the surface of the base material is scrubbed by acetone to remove oil stains, then, the acid cleaning is carried out for 2min to 4min by adopting 5 percent to 10 percent HCL solution at room temperature to remove the oxide film on the surface of the steel plate, and the steel plate is dried in the air or at low temperature after being washed by flowing clean water. For the aluminum pipe, the inner and outer pipe walls and the side walls are polished by an angle grinder to remove an oxide film on the surface of the aluminum plate, and the polished surface is wiped by acetone to remove oil stains. The wall thickness of the selected steel pipe 1 is 3-15mm, and the wall thickness of the selected aluminum pipe 2 is 3-15 mm. In the specific embodiment, the thickness of the adopted steel plate is 3-5mm, and the thickness of the aluminum plate is 3-5 mm.

In the process of preparing the surface microtexture, firstly, clamping and fixing the acid-washed steel pipe, specifically, placing the groove in the horizontal direction, and keeping the groove in the rotation process of preparing the microtexture all the time so as to ensure the stability of the diameters of pulse laser light spots acting on different positions of the groove; and opening a nanosecond laser to prepare the surface microtexture. The selected laser power is 20-80W, the scanning speed is 200-2000mm/s, the pulse frequency is 20-1000kHZ, the scanning frequency is 5-100, and the surface microtexture depth is 10-150 mu m. The design of the surface micro-texture in the direction along the thickness of the steel groove is mainly reflected in the appearance change of the micro-texture, including the change of the texture form (such as lattice arrangement, straight lines and the direction thereof, grids, spiral lines, concentric circles and the like) and the change of related parameters (such as single-point diameter, groove spacing, grid density, depth-to-width ratio and the like). The change of the surface appearance is realized by adjusting the scanning path and the process parameters of the pulse laser; the preparation process is schematically shown in figure one. In the process of pulse laser action, pure argon is used for side blowing protection, and after the preparation of the surface microtexture is finished, the protective gas atmosphere is kept until the sample is cooled to room temperature so as to prevent the oxidation of the groove.

After the groove is subjected to the surface treatment, the straight line shape 9 of the groove and the grid shape 10 of the groove are formed as shown in FIG. 3

Surface structure. After the surface treatment, the steel pipe with the micro texture and the aluminum material to be welded are clamped in a butt joint mode. Specifically, the steel pipe and the aluminum pipe to be welded are rotated at a constant speed in the same direction by using a welding positioner 4, wherein the groove gap is 0.5-2 mm.

And after the preparation work is finished, preparing to enter a laser melting brazing link. Laser welding can achieve accurate control over heat input, wherein factors such as laser power, welding speed, laser defocusing amount, laser offset and wire feeding speed jointly determine input of laser energy. In the laser melting brazing process, laser is directly irradiated on the filler metal to ensure that the filler metal is fully melted, the filler metal and an aluminum base metal are mixed through heat conduction, the filler metal and the aluminum base metal are wetted and spread on the microtexture of the groove surface, a metallurgical reaction occurs, and the non-melting of the steel base metal inhibits the mixing of iron and aluminum atoms to the maximum extent so as to inhibit the continuous formation and growth of Fe-Al brittle intermetallic compounds. In order to improve the stability of the welding process, the laser beam 5 always keeps the flat welding position, and the connection of the pipeline arrangement is realized through the rotation of the pipe. Considering the factors, the single-channel laser power of the aluminum/steel fusion brazing is 2000-3500W, the defocusing amount is +25mm, the rotating speed is 0.2-0.5m/min, the spacing between the optical wires is 2-5mm, the wire feeding angle is 45 degrees ahead, and laser spots are directly irradiated on the surface of the filler metal to ensure the sufficient melting of the welding wires; filling channels are 1-20 according to different pipe wall thicknesses, slowly cooling is carried out after single channel filling, and the next channel filling is carried out after the sample is cooled to room temperature; the filling metal is an aluminum-based welding wire or a zinc-based welding wire, the wire feeding speed of a wire feeding system 8 is 4-6m/min, the shielding gas is sent out through a gas feeding pipe 6, the shielding gas 7 is pure Ar gas, the flow of the shielding gas is 15L/min, and the shielding gas 7 performs side blowing protection on the welding seam behind the laser beam 5.

Example 1

Butt-joint laser melting brazing method for aluminum/steel medium-thickness pipe

Selecting a Q235 steel pipe with the wall thickness of 3mm and 6061 aluminum alloy with the wall thickness of 3mm as base materials, opening a 45-degree groove on one side of a steel plate, and cleaning the plate according to the method;

step two, preparing a surface microtexture of the steel plate by adopting high-frequency pulse laser, wherein the welding power is 60W, the welding speed is 500mm/s, the pulse frequency is 30kHZ, a straight line perpendicular to the direction of a welding seam is adopted, the interval is 0.5mm, the pulse laser scanning frequency at the upper part of the groove is 30 times, and the scanning frequency at the lower part is 10 times;

and step three, clamping the treated steel pipe and the aluminum pipe to be welded on a welding positioner in a butt joint mode, and carrying out fusion brazing on the steel pipe and the aluminum pipe to be welded by adopting an IPG-6kW optical fiber laser, wherein the laser power required by single-channel forming is 3kW, the rotating speed is 0.5m/min, the defocusing amount of laser is +25mm, a zinc-based welding wire is adopted, the wire feeding speed is 3m/min, and the groove gap is 1.2 mm.

The aluminum steel pipeline butt joint obtained by adopting the welding parameters is good in forming and free of obvious undercut and air hole defects. The interface was observed, and the observation results are shown in fig. 4, and it was found that the brittle phases of the aluminum/steel interface were relatively uniform in thickness along the thickness direction and distributed in a curved discontinuous manner, and the joint was subjected to a tensile test, and the joint strength was 238 MPa.

Example 2

step two, preparing a surface microtexture of the steel plate by adopting high-frequency pulse laser, wherein the welding power is 60W, the welding speed is 500mm/s, the pulse frequency is 30kHZ, a straight line vertical to the direction of a welding line is adopted at the upper part of the groove, the interval is 0.5mm, and the scanning frequency is 10; adopting a grid texture form at the lower part of the groove, wherein the interval is 0.5mm, and the scanning times are 10 times;

The aluminum steel pipeline butt joint obtained by adopting the welding parameters is good in forming and free of obvious undercut and air hole defects. And observing the interface, finding that the brittle phases of the aluminum/steel interface along the thickness direction have uniform thickness and are distributed in a bending discontinuous manner, and performing tensile test on the joint, wherein the joint strength is 220 MPa.

Comparative example 1

Compared with the embodiment 1, the cleaning process of the base metal is consistent with the fusion brazing method and parameters, and the difference is that the texture of the groove surface is not designed in appearance, is straight lines perpendicular to the direction of the welding seam, the interval is 0.5mm, and the scanning times are 10 times. It was observed that a difference in thickness of about 5 μm was present between brittle phases formed at the aluminum/steel interface in the thickness direction and microcracks were present at the upper part of the weld, and the joint was subjected to a tensile test and had a joint strength of 172 MPa.

Comparative example 2

Compared with the embodiment 1, the cleaning process of the parent metal is consistent with the melting brazing method and parameters, and the difference is that the groove surface is not prepared with texture and is a smooth plane. It was observed that a brittle phase generated at the aluminum/steel interface had a thickness difference of about 7.5 μm in the thickness direction, and the interface was observed, and as a result of the observation, as shown in fig. 5, the interface intermetallic compound was coarse and accompanied by a large number of micro cracks, and the joint was subjected to a tensile test, and the joint strength was 167 MPa.

Although the embodiments of the present invention have been described above, the contents thereof are merely embodiments adopted to facilitate understanding of the technical aspects of the present invention, and are not intended to limit the present invention. It will be apparent to persons skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. A butt laser fusion brazing welding method for aluminum/steel medium-thickness pipe is characterized by comprising the following specific steps:

selecting a steel pipe and an aluminum alloy pipe as parent metals, opening a 45-degree groove on one side of the steel pipe, and cleaning the parent metals to be welded;

step two, preparing a surface micro-texture of the steel pipeline by adopting high-frequency pulse laser, wherein the welding power is 60W, the welding speed is 500mm/s, the pulse frequency is 30kHZ, a straight line vertical to the direction of a welding seam is adopted at the upper part of the groove, the interval is 0.5mm, and the scanning frequency is 10; the lower part of the groove adopts a grid texture form, the distance is 0.5mm, and the scanning times are 10 times:

step three, welding process: clamping the treated steel pipe and an aluminum alloy pipe to be welded on a welding positioner in a butt joint mode, carrying out fusion brazing on the steel pipe and the aluminum alloy pipe by adopting an IPG-6kW optical fiber laser, carrying out laser fusion brazing on the steel pipe and the aluminum alloy pipe by adopting a zinc-based welding wire with the laser power of 3kW, the defocusing amount of +25mm and the rotation speed of 0.5m/min, the wire feeding speed of 3m/min and the groove gap of 1.2mm, carrying out laser fusion brazing on the steel pipe and the aluminum alloy pipe, slowly cooling after single filling, and carrying out next filling after a sample is cooled to room temperature; the laser always keeps the flat welding direction, and the welding positioner (4) continuously rotates the base metal to be welded along with the welding process until the welding is finished;

the wall thickness of the steel pipeline (1) is 3-15mm, and the wall thickness of the applicable aluminum alloy pipeline (2) is 3-15 mm.

2. The aluminum/steel medium-thick-wall pipeline butt-joint laser fusion welding and brazing method according to claim 1, wherein in the first step, the pre-welding cleaning of the groove surface of the steel pipeline (1) to be welded is specifically as follows: scrubbing the surface of the parent material with acetone to remove oil stains, then adopting 5-10% HCL solution to perform acid cleaning for 2-4 min at room temperature, adopting flowing clean water to perform washing, and then performing air drying or low-temperature drying.

3. The method for butt-joint laser fusion welding and brazing of the aluminum/steel medium-thickness pipeline according to claim 1, wherein in the second step, the adopted high-frequency pulse laser is any one of a nanosecond laser, a femtosecond laser or a picosecond laser.

4. The butt laser fusion brazing method for the aluminum/steel medium-thickness pipeline according to claim 3, wherein in the second step, the depth of the surface micro texture is 10-150 μm.

5. The butt laser fusion brazing method for the aluminum/steel medium-thickness pipe according to claim 4, wherein in the third step, the spacing between the optical fibers is 2-5 mm.

6. The method for butt-joint laser fusion brazing of aluminum/steel medium-thickness pipes according to claim 5, wherein in the third step, the wire feeding angle is 45 degrees ahead.

7. The butt laser fusion brazing method for the aluminum/steel medium-thickness pipe according to claim 6, wherein in the third step, the number of filling channels is 1-20.

8. The aluminum/steel medium-thick-wall pipe butt-joint laser fusion brazing welding method according to claim 7, characterized in that in the third step, in the welding process, the side blow protection is performed on the welding seam behind the laser beam, the protective gas (7) is pure Ar gas, and the protective gas flow is 15L/min.