CN118023710A - Steel/aluminum dissimilar metal welding method for reinforcing and toughening steel surface by adding short fibers - Google Patents

Abstract

The present invention discloses a steel/aluminum dissimilar metal welding method with short fiber implantation on the steel surface for reinforcement and toughening, and belongs to the technical field of dissimilar metal welding. The present invention adopts laser to remelt the steel surface, and during the movement of the laser, the short steel fiber is fed from the tail behind the molten pool, and the difference in melting point between the short steel fiber and the steel matrix and the dynamic solidification process of the surface molten pool are utilized to directly implant the short steel fiber into the surface of the steel matrix to form a high-roughness, short-fiber-shaped surface; further, brazing or melting brazing method is adopted to make the liquid aluminum alloy wet and spread on the surface of the short steel fiber to form a metallurgical bond, thereby obtaining a high-quality steel/aluminum transition joint. The method can effectively increase the bonding area between steel and liquid aluminum, relieve the residual stress of the joint, improve the toughness of the joint, obtain a joint with excellent mechanical properties and high strength, and facilitate popularization and application.

Description

A steel/aluminum dissimilar metal welding method for strengthening and toughening steel surface by implanting short fibers

Technical Field

The invention belongs to the technical field of dissimilar metal welding, and in particular relates to a steel/aluminum dissimilar metal welding method by implanting short fibers on the steel surface for reinforcement and toughening.

Background technique

Steel/aluminum dissimilar metal composite structures have a series of advantages such as light weight, low cost, good balance of structure and performance, and are widely used in the automotive, aerospace, shipbuilding and weapons industries. However, steel/aluminum dissimilar metals will inevitably produce intermetallic compounds during the welding process, resulting in high brittleness and low strength of the joint, which has become the main bottleneck restricting the application of this structure.

In response to the problem of brittle intermetallic compounds at the interface of steel/aluminum dissimilar metals, domestic and foreign researchers have conducted a lot of research on the interface reaction mechanism, metal compound growth regulation and process control during welding, trying to avoid or eliminate the formation of intermetallic compounds at the interface, but they can only control the scale and morphology. At present, it has become a consensus in the academic community that it is difficult to avoid intermetallic compounds at the interface during steel/aluminum dissimilar metal welding. Although the strength of steel/aluminum dissimilar metal welded joints can reach a good level after regulating the scale or morphology of intermetallic compounds, the fracture toughness of the interface is low, the mechanical properties of the joint are poorly stable, and the risk of automatic cracking is prone to occur under the action of welding residual stress. Therefore, the service capacity of steel/aluminum dissimilar metal welded joints is not reliable enough, especially in applications under impact loads and periodic pulsating loads. There are still great limitations. After years of efforts by domestic and foreign researchers, steel/aluminum dissimilar metal welding has made great progress, but intermetallic compounds at the interface are inevitable, and the brittleness of the joint has not been well solved. Therefore, some researchers have begun to try to perform micromachining on the steel surface, and various methods of preparing surface morphology include femtosecond laser, picosecond laser and nanosecond laser. On the one hand, this surface morphology can improve the wettability of liquid metal on the surface of the steel matrix, and on the other hand, it may improve the mechanical properties of steel/aluminum dissimilar metal welding joints. However, there are still some problems with the steel-aluminum interface microstructure prepared by this method. Because the grooves and micropits processed in the steel matrix are too shallow, or the height of the protrusions is too low, the intermetallic compounds are still close to the flat layer shape after the reaction with the liquid aluminum interface. From the perspective of fracture mechanics and mesomechanics, this interface structure will affect the improvement of strength and toughness.

Summary of the invention

In view of the above problems, the present invention provides a steel/aluminum dissimilar metal welding method by implanting short fibers on the steel surface for reinforcement and toughening. The prepared joint has the advantages of high strength, high toughness, and various workpiece sizes and specifications.

The present invention achieves the above object through the following technical solutions:

A steel/aluminum dissimilar metal welding method with short fiber implanted on the steel surface for reinforcement and toughening, firstly, steel with a short fiber surface is prepared. The contaminants on the steel surface are cleaned and dried, and a suspension of brazing flux and alcohol is evenly coated on the surface to enhance the wetting and spreading of aluminum liquid on the steel. The steel/aluminum dissimilar metal welding is performed by a laser-arc method.

The specific steps include:

1) Pre-welding treatment of steel plates and aluminum plates;

2) Perform short fiber additive manufacturing, use a laser to remelt the surface of the steel plate to be welded, use the laser head to guide the light and the nozzle of the powder feeder to deliver the steel short fiber particles to the tail of the molten pool, and control the laser according to the difference in melting points between the short fibers and the parent material. During the process of rapid solidification of the steel matrix remelting and melting of the short fibers, the morphology of the steel short fibers is retained on the re-solidified surface of the steel, and a steel plate with added short fibers is obtained;

3) Cooling the steel plate after short fiber implantation to room temperature, and then cleaning the surface;

4) Assemble and weld the steel plates and aluminum plates on which the short fibers have been implanted on the surface.

Furthermore, the steel plate described in step 1) is any one of stainless steel, galvanized steel and carbon steel.

Furthermore, the laser described in step 2) is any one of a YAG solid laser, a fiber laser and a semiconductor laser.

Furthermore, the implanted short fibers in step 2) are any one of steel wire and iron wire, and the size parameters of the short fibers are: length of 0.3-2 mm, diameter of 0.1-0.5 mm.

Furthermore, the technical parameters of controlling the laser in step 2) are: laser power is 800-3000W, scanning speed is 8-10mm/s, and the spot area of the laser on the workpiece surface is 1mm-5mm.

Furthermore, in step 2), the voltage of the powder feeder is 10-25V, and the gas flow rate is 10-15L/mi.

Furthermore, the additive manufacturing described in step 2) is to keep the laser and the powder feeder on the same axis, and adopt a movement mode in which the laser is in front and the powder feeder is in the back.

Furthermore, the surface cleaning treatment described in step 3) includes but is not limited to vacuum treatment, pickling, etc.; the pickling solution is 10%-15% dilute hydrochloric acid, and the pickling time is 30-40 minutes.

Furthermore, in the welding process described in step 4), it is necessary to improve the wettability and spreadability of the liquid aluminum metal on the surface of the short fiber steel, and the method used is but not limited to applying brazing flux or galvanizing on the surface of the steel plate to be welded.

Furthermore, the welding method described in step 4) includes but is not limited to any one of laser brazing, arc brazing, laser-arc hybrid brazing and various types of brazing.

Compared with the prior art, the present invention has the following advantages:

1. By preparing steel fibers perpendicular to the steel on the steel surface, a "pinning" structure can be formed at the interface, which is beneficial to improving the mechanical properties. At the same time, the molten aluminum can wet and spread the short fibers and the steel surface with the assistance of the brazing flux, thereby effectively increasing the bonding area and achieving high-strength and high-toughness welding of steel/aluminum dissimilar metals.

2. This process does not rely on complex operations or equipment such as explosion welding and stir friction welding. The operation of preparing transition joints is simple, the product sizes and specifications are diverse, and the scope of application is expanded.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 Schematic diagram of the surface short fiber laser augmentation process.

Among them, 1 is steel plate, 2 is laser head, 3 is powder feeder, 4 is steel short fiber, 5 is welding molten pool, and 6 is remelting zone.

Figure 2 Schematic diagram of the steel/aluminum transition joint with short fibers implanted on the steel surface to strengthen and toughen it.

Among them, 7 is steel plate, 8 is aluminum alloy plate, and 9 is weld.

Fig. 3 Surface morphology of the steel plate after implanting steel fibers.

Figure 4 Surface morphology of the steel/aluminum transition joint reinforced and toughened with short fibers implanted on the steel surface.

Figure 5 Cross-sectional morphology of the steel/aluminum transition joint reinforced and toughened with short fibers implanted on the steel surface.

Detailed ways

The present invention is described in detail below with reference to the accompanying drawings and embodiments.

The pre-welding treatment of the steel plate to be welded is to mechanically grind the surface to be welded flat; the pre-welding treatment of the aluminum plate to be welded is to use mechanical grinding method. After the side of the aluminum plate is grinded flat, the surface of the aluminum plate is cleaned with alcohol to remove stains, and then 10% to 15% NaOH solution is used for alkaline washing for 3 minutes, and then 10% to 15% _HNO3 solution is used for acid washing for 3 to 5 minutes, and then it is rinsed with running water and blown dry.

Example 1

This implementation is achieved through the following steps:

1. Select carbon steel plates with a thickness of 2 mm and 6061-T6 aluminum alloy plates, and perform pre-welding treatment on the steel plates and aluminum plates to be welded.

2. As shown in Figure 1, short fiber additive manufacturing is performed on the butt joint of the steel plate. The short fiber is iron wire with a diameter of 0.3mm and a length of 0.8mm. The laser power is 1000W, the scanning speed is 8mm/s, and the spot diameter is 2.5mm. The powder feeder voltage is 10-15V, the powder feeder protective gas is Ar gas, and the flow rate is 10-15L/min. Figure 3 is an ultra-depth microscope image of a steel plate with a short fiber surface prepared under the process parameters. It can be seen that a large number of fibers with different orientations are solidified on the surface of the steel plate, resulting in a large-scale roughness on the surface of the steel plate.

3. Use 10% dilute hydrochloric acid to pickle the surface of steel and short fibers, and then use an organic solvent to clean the surface of steel and steel fibers. The organic solvent is alcohol. After drying, vacuum seal and set aside.

4. The treated steel plate to be welded and the aluminum plate to be welded are butt-jointed and clamped with a fixture. Fiber laser and CMT welding machine are used for brazing. The welding wire is AlSi5, the laser power is 3.6KW, the scanning speed is 30mm/s, the defocus is +30mm, the spot offset is +0.5mm (the boundary of the aluminum plate welding surface is the origin, and the aluminum plate direction offset is the positive direction), the CMT wire feeding speed is 8m/min, the CMT voltage is 12V, the protective gas is Ar gas, and the flow rate is 10-15L/min.

Figure 2 is a schematic diagram of a steel/aluminum transition joint with short fiber reinforcement and toughening on the steel surface, and Figure 4 is a surface morphology of a steel/aluminum transition joint with short fiber reinforcement and toughening on the steel surface. It can be seen from the figure that there are no defects such as spatter and weld bumps on the steel plate surface, and the weld metal has a silvery white luster, indicating that the process parameter selection is relatively reasonable. Figure 5 is a SEM image of the cross section of the joint. It can be seen that the short fiber and the weld metal are well combined, the intermetallic compound layer is thin, and no defects such as cracks are found. When subjected to an external load, the introduction of short fibers will increase the effective bonding area and change the stress distribution state of the joint, thereby improving the service performance. Since short fibers only exist on the butt joint surface, in order to eliminate the influence of the excess height on the joint performance, mechanical grinding is used to remove the excess height during the mechanical property test. The tensile strength test of the joint shows that its tensile strength can reach 168.6MPa, which is significantly higher than the strength of the joint without surface short fiber implantation of 120.7MPa, and the strength is increased by 39.7%. The joint was subjected to a longitudinal bending test (the pressure head was perpendicular to the weld). When the bending angle reached 82.1°, the joint still had no cracks, while the joint without short fiber implantation on the surface had cracks when the bending angle reached 43.1°, and the toughness was greatly improved. In summary, it can be seen that the joint after short fiber implantation on the steel surface has the effect of strengthening and toughening.

Example 2

A steel/aluminum dissimilar metal welding method for strengthening and toughening steel surface by implanting short fibers

This implementation is achieved through the following steps:

1. Select 2mm thick galvanized steel plate and 6061-T6 aluminum alloy plate, and perform pre-welding treatment on the steel plate and aluminum plate to be welded.

2. Perform short fiber additive manufacturing on the butt surface of the steel plate. The short fiber is 304 stainless steel wire with a diameter of 0.5 mm and a length of 1 mm. The laser power is 1200 W, the scanning speed is 8 mm/s, and the spot diameter is 2.5 mm. The powder feeder voltage is 15-25 V, the powder feeder protective gas is Ar gas, and the flow rate is 10-15 L/min.

3. Use 10% dilute hydrochloric acid to pickle the surface of steel and short fibers, and then use an organic solvent to clean the surface of steel and steel fibers. The organic solvent is alcohol. After drying, vacuum seal and set aside.

4. The treated steel plate to be welded and the aluminum plate to be welded are butt-jointed, clamped with a fixture, and brazed with a fiber laser and a CMT welder. The welding wire is AlSi5, the laser power is 4KW, the scanning speed is 25mm/s, the defocus is +40mm, the spot offset is +0.5mm (the boundary of the aluminum plate welding surface is the origin, and the aluminum plate direction offset is the positive direction), the CMT wire feeding speed is 8m/min, the CMT voltage is 12V, the protective gas is Ar gas, and the flow rate is 10-15L/min. The tensile performance test of the joint after removing the excess height shows that the tensile strength of the joint is 155MPa, while the strength of the joint without surface short fiber implantation can reach 112.7MPa, which is an increase of 37.5%. The joint is subjected to a bending test, and the results show that no cracks appear when the bending angle of the joint reaches 70°, while the joint without surface short fiber implantation has cracks when the bending angle reaches 32.8°, and the toughness is also greatly improved.

Example 3

A steel/aluminum dissimilar metal welding method for strengthening and toughening steel surface by implanting short fibers

This implementation is achieved through the following steps:

1. Select stainless steel plates with a thickness of 2 mm and 6061-T6 aluminum alloy plates, and perform pre-welding treatment on the steel plates and aluminum plates to be welded.

2. Perform short fiber additive manufacturing on the butt joint of the steel plate. The short fiber is 304 stainless steel wire with a diameter of 0.3 mm and a length of 1.5 mm. The laser power is 1200 W, the scanning speed is 8 mm/s, and the laser spot diameter is 2.5 mm. The powder feeder voltage is 25-35 V, the powder feeder protective gas is Ar gas, and the flow rate is 10-15 L/min.

3. Use 10% dilute hydrochloric acid to pickle the surface of steel and short fibers, and then use an organic solvent to clean the surface of steel and steel fibers. The organic solvent is alcohol. After drying, vacuum seal and set aside.

4. The treated steel plate to be welded and the aluminum plate to be welded are butt-jointed, clamped with a fixture, and brazed with a fiber laser and a CMT welder. The welding wire is AlSi5, the laser power is 4.5KW, the scanning speed is 25mm/s, the defocus is +45mm, the spot offset is +0.5mm (the boundary of the aluminum plate welding surface is the origin, and the aluminum plate direction offset is the positive direction), the CMT wire feeding speed is 8m/min, the CMT voltage is 12V, the protective gas is Ar gas, and the flow rate is 10-15L/min. The tensile performance test of the joint after removing the excess height shows that the tensile strength of the joint is 158.5MPa, while the strength of the joint without surface short fiber implantation can reach 128.5MPa, which is an increase of 23.3%. The joint is subjected to a bending test, and the results show that no cracks appear when the bending angle of the joint reaches 68°, while the joint without surface short fiber implantation has cracks when the bending angle reaches 35.6°, and the toughness is still significantly improved.

The above description is only a preferred embodiment of the present invention, but the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements and improvements based on the technical solutions and inventive concepts of the present invention within the technical scope disclosed by the present invention, and all of these should be covered by the protection scope of the present invention.

Claims (10)

1. A steel/aluminum dissimilar metal welding method for reinforcing and toughening steel surface by adding short fibers is characterized by comprising the following steps:

1) Carrying out pre-welding treatment on the steel plate and the aluminum plate;

2) Remelting the surface to be welded of the steel plate by a laser, delivering steel staple fiber particles to the trailing part of a molten pool by utilizing a laser head to guide light and a nozzle of a powder feeder, and controlling the laser according to the difference of melting points of staple fibers and base materials, so that the morphology of the steel staple fibers is kept on the surface of the steel resolidified during the remelting and rapid solidification of a steel matrix and the melting of the staple fibers, thereby obtaining the steel plate after the staple fibers are planted;

3) Cooling the steel plate with the short fibers planted to room temperature, and cleaning the surface;

4) And assembling and welding the steel plate and the aluminum plate with the prepared surface embedded with the short fibers.

2. The method according to claim 1, wherein the steel sheet in step 1) is any one of stainless steel, galvanized steel, and carbon steel.

3. The method according to claim 1, wherein the laser in step 2) is any one of a YAG solid laser, a fiber laser, and a semiconductor laser.

4. The method according to claim 1, wherein the short fiber for increasing plant in the step 2) is any one of steel wire and iron wire, and the size parameters of the short fiber are: the length is 0.3-2mm, and the diameter is 0.1-0.5mm.

5. The method according to claim 1, wherein the technical parameters of controlling the laser in step 2) are: the laser power is 800-3000W, the scanning speed is 8-10mm/s, and the spot area of the laser on the surface of the workpiece is 1-5 mm.

6. The method according to claim 1, wherein the voltage of the powder feeder in the step 2) is 10-25V and the air flow rate is 10-15L/mi.

7. The method of claim 1, wherein the additive manufacturing in step 2) is to keep the laser and the powder feeder on the same axis and adopt a mode of movement of the laser in front and the powder feeding head in back.

8. The method according to claim 1, wherein the surface cleaning treatment in step 3) is vacuum treatment or acid washing; the pickling solution is 10-15% diluted hydrochloric acid, and the pickling time is 30-40min.

9. The method according to claim 1, wherein the welding in step 4) is performed by applying a flux or zinc plating on the surface to be welded of the steel sheet.

10. The method of claim 1, wherein the welding method in step 4) is one of laser brazing, arc brazing, laser-arc composite brazing, and any of various types of brazing.