CN113199163B - Welded joint of aluminum steel dissimilar metal - Google Patents
Welded joint of aluminum steel dissimilar metal Download PDFInfo
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- CN113199163B CN113199163B CN202110586941.8A CN202110586941A CN113199163B CN 113199163 B CN113199163 B CN 113199163B CN 202110586941 A CN202110586941 A CN 202110586941A CN 113199163 B CN113199163 B CN 113199163B
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- 239000010959 steel Substances 0.000 title claims abstract description 198
- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 197
- 229910052782 aluminium Inorganic materials 0.000 title claims abstract description 114
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 title claims abstract description 114
- 229910052751 metal Inorganic materials 0.000 title claims abstract description 33
- 239000002184 metal Substances 0.000 title claims abstract description 30
- 238000003466 welding Methods 0.000 claims abstract description 214
- 150000002739 metals Chemical class 0.000 claims abstract description 8
- 238000000034 method Methods 0.000 claims description 30
- 238000004519 manufacturing process Methods 0.000 claims description 19
- 238000004021 metal welding Methods 0.000 claims description 11
- 230000004927 fusion Effects 0.000 claims description 10
- 230000008569 process Effects 0.000 claims description 10
- 230000009471 action Effects 0.000 claims description 9
- 238000002844 melting Methods 0.000 claims description 7
- 230000008018 melting Effects 0.000 claims description 7
- 229910000838 Al alloy Inorganic materials 0.000 claims description 6
- 238000010438 heat treatment Methods 0.000 claims description 4
- 238000003825 pressing Methods 0.000 claims description 4
- 229910000881 Cu alloy Inorganic materials 0.000 claims description 3
- 238000007664 blowing Methods 0.000 claims description 2
- 238000010894 electron beam technology Methods 0.000 claims description 2
- 239000000463 material Substances 0.000 claims description 2
- 238000003672 processing method Methods 0.000 claims 1
- 238000010079 rubber tapping Methods 0.000 abstract 2
- 230000000052 comparative effect Effects 0.000 description 13
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- 229910000765 intermetallic Inorganic materials 0.000 description 4
- 230000035515 penetration Effects 0.000 description 4
- 230000007547 defect Effects 0.000 description 3
- 238000011161 development Methods 0.000 description 3
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- 238000007373 indentation Methods 0.000 description 3
- 238000001125 extrusion Methods 0.000 description 2
- 229910001234 light alloy Inorganic materials 0.000 description 2
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- 230000004048 modification Effects 0.000 description 2
- 238000007711 solidification Methods 0.000 description 2
- 230000008023 solidification Effects 0.000 description 2
- 229910000851 Alloy steel Inorganic materials 0.000 description 1
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 1
- 208000012868 Overgrowth Diseases 0.000 description 1
- 239000004411 aluminium Substances 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 238000005219 brazing Methods 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 239000012141 concentrate Substances 0.000 description 1
- 239000010949 copper Substances 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 238000004134 energy conservation Methods 0.000 description 1
- 239000000945 filler Substances 0.000 description 1
- 239000004519 grease Substances 0.000 description 1
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Classifications
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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
- B23K28/00—Welding or cutting not covered by any of the preceding groups, e.g. electrolytic welding
- B23K28/02—Combined welding or cutting procedures or apparatus
-
- 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
- B23K2103/00—Materials to be soldered, welded or cut
- B23K2103/18—Dissimilar materials
- B23K2103/20—Ferrous alloys and aluminium or alloys thereof
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- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Resistance Welding (AREA)
Abstract
A welded joint of aluminum-steel dissimilar metals is characterized in that a steel-tapping convex structure is manufactured on an aluminum-steel interface inside the spot-welding seam by changing a welding seam structure of the spot-welding seam of the aluminum-steel dissimilar metals, so that the steel-tapping convex structure is convexly extended from a steel workpiece to an aluminum workpiece to be embedded into the aluminum workpiece, and meanwhile, the joint is heated to obtain a metallurgically bonded aluminum-steel interface. The invention improves the integral mechanical property of the aluminum steel dissimilar metal spot welding seam by optimizing the joint structure of the spot welding seam.
Description
Technical Field
The invention belongs to the technical field of dissimilar metal material welding, and particularly relates to a welded joint of aluminum steel dissimilar metal.
Background
In order to achieve the effects of energy conservation and emission reduction, the automobile industry proposes an automobile lightweight development concept, so that an automobile body structure is optimized and more high-strength steel and light alloy are selected to manufacture an automobile body on the premise of ensuring the safety of a junction automobile body in the automobile structural design, wherein the aluminum alloy is used as the light alloy with the most wide application range, and is also increasingly popular in the manufacture of the automobile body. At present, aluminum-steel hybrid vehicle bodies are an important development direction of vehicle manufacture, and a large number of various types of steels and aluminum alloys are adopted in the vehicle body during the manufacture to achieve both the safety performance of a vehicle body structure and the light weight of the vehicle body, so that the problem of aluminum-steel dissimilar metal connection is inevitably faced in the manufacture of aluminum-steel hybrid vehicle bodies. Because aluminum steel dissimilar metal welded joints are too fragile to bear large loads, aluminum steel dissimilar metal is commonly connected by mechanical connection technologies such as self-piercing riveting and turning screws, but mechanical connection also has limitations such as high connection equipment in the riveting technology, weight increase of rivets on a vehicle body, high rivet cost, complexity and inefficiency of connection processes and the like, and in addition, as advanced high-strength steel applications are gradually increased, new challenges are also presented to mechanical connection of the advanced high-strength steel, such as failure of the rivets to pierce high-strength steel workpieces, failure of effective opening to form mechanical joggles or rivet upsets and other connection failure problems. However, for the welding technology, the self-connection cost and the equipment cost are low, the efficiency is high, and if the welding technology can be adopted to realize the aluminum-steel dissimilar metal connection, the method has profound significance for realizing the lightweight development of automobiles.
The aluminum steel dissimilar metal connection faces a great challenge so far and cannot be effectively solved, so that the application of the welding technology in the aluminum steel dissimilar metal connection is limited. Because of the greatly different physical properties of aluminum steel dissimilar metals, such as melting point, expansion coefficient, solidification shrinkage rate and the like, in the fusion welding with large heat input, a joint obtained by simultaneously fusing aluminum and steel two metals is easy to generate large deformation of a workpiece and large stress generated in the solidification process of a welding line so as to easily form cracks, and on the other hand, because the metallurgical compatibility of aluminum steel is poor, solid solution cannot be formed in the welding line, a large amount of brittle Fe-Al compound is formed in the welding line so as to cause extremely poor joint performance; if lower heat input is adopted, only the aluminum workpiece is melted, and the steel workpiece is welded in a non-melting strategy, namely a melting brazing method, the aluminum alloy is melted under the lower heat input, the molten aluminum metal is wetted and spread on the surface of the steel workpiece which is still in a solid state, and metallurgical bonding is formed through mutual diffusion of elements under the action of high temperature. On the one hand, the weld joint interface is generally flat, and on the other hand, a continuous Fe-Al brittle compound layer is formed on the interface between aluminum and steel, which results in very poor strength of the aluminum-steel joint.
In order to improve the mechanical properties of the aluminum-steel dissimilar metal joint, a great deal of current experimental research works aim at slowing down the generation of defects such as cracks and brittle compounds generated by the joint by precisely controlling welding heat input by optimizing technological parameters of different welding methods, however, the challenges of aluminum-steel dissimilar metal welding still cannot be effectively solved by optimizing the welding technological methods. In addition, a metal interlayer or filler metal is added into the aluminum-steel dissimilar metal joint to slow or prevent the formation of Fe-Al brittle compounds so as to improve the joint performance, but the metal element is added by a complex process, and the influence mechanism of different element components and contents on the joint still needs to be deeply explored, so that the current great challenges of aluminum-steel dissimilar metal welding limit the application of the aluminum-steel dissimilar metal welding joint.
Disclosure of Invention
The invention solves the technical problems: in order to overcome the defects of the existing aluminum steel dissimilar metal welding technology, the aluminum steel dissimilar metal welding joint is provided, and the mechanical property of the joint is improved by optimizing the spot welding structure of the aluminum steel dissimilar welding joint.
In order to achieve the above purpose, the technical scheme adopted by the invention is as follows: the welded joint of aluminum steel dissimilar metal is characterized in that the welded joint is a spot welding seam for connecting aluminum steel dissimilar metal workpieces stacked mutually, the spot welding seam is suitable for connecting steel workpieces with the thickness of 0.2-3.5 mm and aluminum workpieces, a steel convex structure is arranged in the spot welding seam and protrudes from the steel workpieces to the aluminum workpieces, the diameter D 1 of the steel convex structure is 2-7 v tmm, t is the thickness of the aluminum workpieces, the depth t 1 of the steel convex structure embedded into the aluminum workpieces from the aluminum steel interfaces is 0.1-0.8 times the thickness of the aluminum workpieces, the welded joint is a metallurgical bonding interface at the aluminum steel interfaces, the diameter D 2 of the metallurgical bonding surface is 3-9 v tmm (wherein t is the thickness of the aluminum workpieces), and the diameter D 2 of the metallurgical bonding surface is larger than the diameter D 1 of the steel convex structure;
The periphery of the steel convex structure is also provided with an annular welding seam, the inner diameter D 3 of the annular welding seam on the aluminum-steel interface is larger than the diameter D 1 of the steel convex structure, and the outer diameter D 4 of the annular welding seam on the aluminum-steel interface is smaller than 3.5 times of the diameter D 2 of the metallurgical bonding surface; the annular welding seam is penetrated into the aluminum workpiece from the surface of the steel workpiece, and the penetration t 2 in the aluminum workpiece is smaller than 0.6 times of the thickness of the aluminum workpiece.
The manufacturing method of the aluminum steel dissimilar metal welding joint is characterized by comprising the following steps of:
Step 1: heating the steel workpiece and the aluminum workpiece to a plastic state or a local melting state, and applying pressure to the surface of the steel workpiece to extrude the steel convex structure, so that the convex part of the steel convex structure is extruded into the aluminum workpiece, and metal elements of an aluminum-steel interface are mutually diffused under the action of high temperature to form a metallurgical bonding interface;
In the step, extrusion force is applied to the steel workpiece to form a steel convex structure, and the welding joint is heated to soften the steel workpiece to facilitate deformation to form the steel convex structure, and meanwhile, the high-temperature effect promotes the mutual diffusion of elements between aluminum-steel interfaces to form an aluminum-steel metallurgical bonding interface, so that the aluminum-steel metallurgical bonding interface can be manufactured by adopting a welding method such as resistance welding, friction welding and diffusion welding; when the extrusion force is applied to the surface of the steel workpiece to manufacture the steel convex structure, the depth of the concave indentation on the surface of the steel is controlled to be not more than 2.0 times of the thickness of the steel workpiece, and in addition, the surface of the aluminum workpiece is controlled to generate smaller deformation; the Fe-Al intermetallic compound layer exists in the metallurgical bonding interface of the aluminum steel, and the thickness of the Fe-Al intermetallic compound layer is controlled to be smaller than 10 mu m by controlling the heat input size and the high-temperature action time.
Step 2: and preparing an annular fusion welding seam in a region which is 3.5 times of the diameter of the metallurgical bonding surface and is arranged on the periphery of the steel convex structure by adopting a fusion welding method.
In this step, the manufacturing of the girth weld may be performed using a fusion welding method including laser welding, electron beam welding, arc welding, and the like, and the girth weld is preferably manufactured by blowing an inert shielding gas to prevent the weld from being oxidized; the annular welding seam is formed by one circle of annular welding seam or a plurality of circles of concentric annular welding seams with different diameters.
In order to make the welded joint and the manufacturing method easier and more efficient to manufacture, a method for manufacturing the aluminum steel dissimilar metal welded joint is provided, wherein the method is characterized in that resistance spot welding is adopted in step 1, and laser welding is adopted in step 2. The resistance spot welding in the step 1 adopts a special electrode, the resistance spot welding electrode comprises a steel electrode contacted with a steel workpiece and an aluminum electrode contacted with an aluminum workpiece, an annular groove is arranged on the welding surface of the steel electrode, the steel welding surface is divided into an inner welding surface and an outer welding surface by the annular groove, the height of the inner welding surface is larger than that of the outer welding surface, the height difference is 0.05-1.2 mm, and the bottom of the annular groove is lower than that of the outer welding surface, and the height difference is 0.1-1.5 mm; the center of the aluminum electrode welding surface is a concave arc surface, the maximum depth of the concave arc surface is 0.05-1.0 mm, at least one convex circular ring is arranged along the periphery of the concave arc surface, the height of the convex circular ring is 0.1-0.8 mm, the width of the convex circular ring is 0.2-0.8 mm, and the diameter of the convex circular ring of the aluminum electrode is larger than the diameter of the welding surface in the steel electrode. The steel electrode and the aluminum electrode are made of the same material, and are preferably copper alloy.
The specific implementation process is as follows:
And step1, placing aluminum-steel dissimilar metal workpieces stacked with each other between a steel electrode and an aluminum electrode of resistance spot welding, wherein the steel workpiece is arranged on one side of the steel electrode, and the aluminum workpiece is arranged on one side of the aluminum electrode.
Step 2, resistance spot welding is started, a welding electrode applies pressure to stacked aluminum steel workpieces, welding current is connected at the same time, under the action of pressure and resistance heat, the inner welding surface of the steel electrode extrudes the steel workpieces to obtain a steel convex structure of an aluminum steel interface, and under the action of resistance heat, aluminum alloy contacted with steel is melted to wet the surfaces of the steel workpieces spread in welding spots to form a metallurgically bonded connecting interface;
In the step, since the inner welding surface of the steel electrode is higher than the outer welding surface, the inner welding surface of the steel electrode is firstly contacted with the steel workpiece to receive a large welding acting force and concentrate all welding current, so that the heating effect of the inner welding surface on the workpiece is remarkable, the steel workpiece is heated and softened, and meanwhile, the inner welding surface of the steel electrode is extruded towards the steel workpiece to form a concave indentation on the steel surface and form a steel convex structure on a steel-aluminum interface to be embedded into the aluminum workpiece; after the inner welding surface of the steel electrode is pressed into the steel workpiece, the outer welding surface is contacted with the steel workpiece, so that the inner welding surface is limited to be pressed into the steel workpiece continuously, welding current is dispersed to the outer welding surface, the heated area of spot welding is enlarged, and the aluminum-steel metallurgical bonding surface is further enlarged to the peripheral area of the steel convex structure. The central area of the welding surface of the aluminum electrode is a concave arc surface, so that the peripheral area of the aluminum electrode and the convex circular ring can attract welding current to be dispersed to the peripheral area of the aluminum electrode, the temperature field of the spot welding seam is more uniform, the problem of overgrowth of Fe-Al intermetallic compounds caused by overconcentration of the temperature of the central area of the welding spot is avoided, the thickness of the Fe-Al intermetallic compounds is controlled below 10 mu m, and the interface bonding performance is improved.
Step 3, finishing the resistance spot welding process, and removing the resistance spot welding electrode which is in contact with the workpiece;
and 4, starting laser welding, wherein a laser beam acts on the surface of the steel workpiece, and controlling the laser beam to scan along the circular welding path to obtain the circular welding seam around the periphery of the steel convex structure.
In the step, parameters such as welding speed, welding power and the like of laser welding are controlled, excessive welding heat input is avoided, and then the penetration t 2 of the laser welding seam in the aluminum workpiece is controlled to be smaller than 0.6 times of the thickness of the aluminum workpiece, and t 2 is controlled to be 0.05-0.55 mm preferentially.
The beneficial effects of the invention are as follows:
(1) Besides forming metallurgical bonding interface, the aluminum steel dissimilar metal welding joint also has a steel convex structure which is convex and embedded into the aluminum workpiece, the contact area of the steel convex structure with the aluminum workpiece is increased, the metallurgical bonding interface which is smooth in traditional aluminum steel resistance spot welding is changed, the mutual embedding locking effect with the aluminum workpiece is achieved, and the interface bonding performance is further improved.
(2) When the spot welding seam is loaded, the stress is highly concentrated in the peripheral area of the welding spot, the peripheral area of the spot welding seam is usually a weak connection area, so that cracks are quickly started by the edge of the welding spot and quickly spread towards the center of the spot welding seam along a welding seam interface, the annular welding seam on the periphery of the steel convex structure strengthens the connection strength of the periphery of the spot welding seam on the one hand, and on the other hand, the initial initiated cracks can be prevented or changed from spreading towards the center of the welding seam along an aluminum-steel interface, and the loading capacity of the periphery of the spot welding seam is further improved.
(3) The steel convex structure and the circular weld joint in the welding joint are mutually matched, and the steel workpiece is tightly meshed with the aluminum workpiece like the root part of pinning, so that the integral mechanical properties of the aluminum steel dissimilar metal welding joint, such as tensile shearing property and cross tensile property, are improved.
Drawings
Fig. 1 is a schematic cross-sectional view of a welded joint of the present invention.
Fig. 2 is a three-dimensional schematic view of a welded joint according to the present invention.
FIG. 3 is a schematic cross-sectional view of a steel electrode for resistance spot welding used to make a weld joint of the present invention.
FIG. 4 is a schematic cross-sectional view of an aluminum electrode for resistance spot welding used to make the weld joint of the present invention.
FIG. 5 is a schematic diagram of resistance spot welding using a steel electrode and an aluminum electrode in an embodiment of the invention.
Fig. 6 is a schematic view of laser welding in an embodiment of the invention.
Fig. 7 is a cross-sectional view of a weld joint in an embodiment of the invention.
FIG. 8 is an interface microstructure view of a cross-sectional center area of a weld joint in an embodiment of the invention.
FIG. 9 is a microstructure view of a laser weld in a welded joint at an aluminum-steel interface in an embodiment of the invention.
Fig. 10 is a cross-sectional view of a welded joint in the examples and comparative examples of the present invention.
FIG. 11 is a graph of weld joint tensile shear load versus displacement for an embodiment of the present invention.
FIG. 12 is a cross tensile load-displacement curve of a weld joint in an embodiment of the present invention.
FIG. 13 is a graph of macroscopic topography of a side fracture of a steel workpiece after tensile shear and cross-draw testing of a welded joint in examples and comparative examples of the present invention.
Detailed Description
The present invention will be better understood by the following detailed description of the invention with reference to the drawings. It should be understood that the detailed description is presented by way of example only and is not intended to limit the invention.
When the aluminum steel dissimilar metal welding joint is implemented, an advanced high-strength steel Q & P1180 with the thickness of 1.2mm is selected as a steel workpiece 1, and a 6N16 aluminum alloy with the thickness of 1.6mm is selected as an aluminum workpiece 2, and residual grease and impurities are removed by wiping the surface of the welding workpiece with alcohol before welding; in the mechanical property test of the welded joint, the specification of a sample in a tensile shear test is 127.0 multiplied by 38.1mm, and the specification of a lap joint area is 38.1 multiplied by 38.1mm; the specification of the sample for the cross tensile test is 150×50mm, and the lap joint area is 50×50mm; 3 specimens for each test were manufactured to obtain an average value of the load of the welded joint, and the mechanical properties of the joint were tested by using a universal tensile tester, and the tensile speed was set to 1mm/min at the time of the test.
The method for manufacturing the aluminum steel dissimilar metal welded joint of the invention by adopting the steel workpiece 1 and the aluminum workpiece 2 specifically comprises the following steps:
step 1: heating the steel workpiece to a plastic state or a local melting state, applying pressure to the surface of the steel workpiece to extrude the steel convex structure 4, extruding the steel convex structure 4 into the aluminum workpiece 2, and mutually diffusing metal elements of an aluminum-steel interface under the action of high temperature to form a metallurgical bonding interface 5;
In this step, the electrode spot welding method is used to manufacture the steel convex structure 4 and the metallurgically bonded interface 5 of the aluminum steel dissimilar metal welding joint, the steel electrode 7 and the aluminum electrode 8 adopting the invention are used in welding, and the welding schematic diagram of the resistance spot welding is shown in fig. 5. The steel electrode 7 and the aluminum electrode 8 are made of Cr-Zr-Cu copper alloy, and the diameter of the electrode body is 16mm.
The steel electrode 7 has an inner welding surface 73 with an end surface diameter of 5.2mm, an end surface shape of a spherical surface and a spherical radius of 35mm, as shown in fig. 3. The height difference between the inner welding surface 73 and the outer welding surface 71 is 5.5mm, the width of the outer welding surface 71 is an annular plane of 1.5mm, and the maximum diameter of the outer welding surface 71 is 11mm; a groove 72 is arranged between the outer welding surface 71 and the inner welding surface 73, and the height difference between the groove and the outer welding surface is 0.3mm
As shown in FIG. 4, the depth of the concave cambered surface 81 of the aluminum electrode 8 is 0.25mm, and the width of the concave cambered surface is 0.65mm; the diameter and the height of the raised circular ring 82 are 8.2mm and 0.2mm respectively, the cross section of the raised circular ring 82 is of an isosceles trapezoid structure, and the widths of the upper bottom and the lower bottom are 0.2mm and 0.4mm respectively.
During welding, the steel workpiece 1 is lapped on the aluminum workpiece 2, and the steel electrode 7 and the aluminum electrode 8 are respectively extruded to the steel workpiece 1 and the aluminum workpiece 2, and the welding pressure is set to 5600N. The welding parameters of the resistance spot welding are set as follows: the welding time is 190ms, the welding current is 19kA, the number of welding pulses is 3, the pre-pressing time is 300ms, and the pressure maintaining time is 100ms; when the inner welding surface 73 of the steel electrode 7 is pressed onto the surface of the steel workpiece 1, the outer welding surface 71 is not in contact with the steel workpiece 1, current is concentrated on the inner welding surface of the steel electrode, after the steel workpiece 1 is heated and softened by resistance heat, the inner welding surface 73 presses the steel workpiece 1 to deform, a steel convex structure 4 is formed at an aluminum-steel interface and extends into the aluminum workpiece 2, and at this time, the inner welding surface 73 also presses a deeper indentation 3 on the surface of the steel workpiece 1, as shown in fig. 5. As the resistance heat increases, the aluminum work piece 2 on the aluminum-steel contact interface melts and wets and spreads to the surface of the steel work piece 1, and the elements mutually diffuse at high temperature to form the metallurgical bonding layer 5, and furthermore, due to the higher electric resistance and lower heat conductivity of the steel work piece 1, there is also a steel local melting inside the steel convex structure 4 to form the steel nugget 9, and after the welding is finished, the welded joint solidifies and cools to present the steel nugget 9 and the aluminum nugget 10, as shown in fig. 5 and 7.
In the welding process, after the inner welding surface 73 of the steel electrode 7 is extruded to the steel workpiece 1, the outer welding surface 71 of the steel electrode 7 is in contact with the steel workpiece 1, so that part of welding current is diffused to the outer welding surface 71 to enlarge the spot welding area; since the current generally selects the shortest path with lower path resistance to pass through, the center of the aluminum electrode 8 is a concave arc surface 81, the welding surface at the periphery of the concave arc surface 81 and the convex circular ring 82 have closer distance to the steel electrode 7, in addition, the convex circular ring 82 can cut off the oxide film insulated on the surface of the aluminum workpiece 3 to reduce the contact resistance between the aluminum electrode 8 and the aluminum workpiece 2, so that the peripheral welding surface of the concave arc surface 81 of the aluminum electrode 8 and the convex circular ring 82 can attract part of the welding current to be distributed towards the periphery of the welding spot, the welding current is distributed more uniformly on the aluminum workpiece, and the thickness of the aluminum-steel interface metallurgical bonding layer 5 in the central area of the welding joint is more uniform and is not more than 10 mu m, as shown in fig. 8.
Step 2: an annular fusion welding seam 6 is prepared by adopting a fusion welding method in a region which is 3.5 times of the diameter of the metallurgical bonding surface 5 and the periphery of the steel convex structure 4.
In this step, a laser welding method is used to manufacture an annular weld 6 of the aluminum-steel dissimilar metal joint; the laser welding system is started to emit a laser beam 11, the laser beam 11 is enabled to act on the surface of the steel workpiece 1, the speed of the laser beam 11 is controlled, and the annular path is scanned, so that the laser beam 11 prepares the annular welding seam 6 on the welding joint. In the step, setting the laser power to 1114W, the welding speed to 2m/min, and the welding path to two concentric rings with the diameters of 8mm and 9mm respectively, wherein the welding sequence is from the inner ring to the outer ring, and the welding schematic diagram is shown in FIG. 6; in this embodiment the laser welding process parameters are controlled to control the penetration t 2 of the laser weld into the aluminum workpiece to about 0.2 to about 0.45mm, as shown in fig. 9.
Comparative example 1 embodiment
Adopt the same specification steel work piece 1 and aluminium work piece 2 to its resistance spot welding that adopts, select traditional spherical welding electrode during the welding, the body diameter of electrode is 16mm, spherical electrode's spherical radius be 100mm, its welded surface diameter is 11mm, select the welding parameter welding of preferred after optimizing, the welding parameter who adopts is: the welding pressure is 5600N, the welding current is 17kA, the welding time is 100ms, 5 pulse currents are adopted, the interval between the pulse currents is 20ms, and the welding time is 300ms after welding.
Comparative example 2 embodiment
In the embodiment, a laser welding is adopted to weld laser welding seams of a steel workpiece 1 and an aluminum workpiece 2 which are stacked and clamped mutually, a laser path is set to be spiral, the number of turns is 6, the outermost ring of the spiral path is sealed to be annular, the diameter of the outermost ring is 8.5mm, the laser power is set to be 1750W, the welding speed is linearly increased from 3m/min to 5m/min at the center of a welding spot, the welding direction is clockwise, and the welding sequence is welded outwards from the center of the welding spot.
The welded joint interface structure of the present invention is significantly different from the joint interface structure of comparative examples 1 and 2 in terms of the welded joint cross sections of the present invention and comparative examples. The joint interface of the comparative example 1 is relatively straight, a larger air hole exists in the center, and an aluminum nugget in the aluminum workpiece is melted through the aluminum steel interface to the surface of the aluminum workpiece in the center area of a welding spot; the joint of comparative example 2 had a large number of cracks in the weld due to a large heat input, and a pit appeared in the center aluminum side of the weld due to a severe reaction of aluminum in the weld with steel, as shown in fig. 10. The central steel convex structure 4 and the laser welding seam 6 of the welding joint are embedded into an aluminum workpiece, and the interface structure is fluctuated and changeable. Because the aluminum-steel interface is tightly combined after the resistance spot welding, the gap between the steel workpiece 1 and the aluminum workpiece 2, which are applied with the laser welding seam area, is eliminated, the forming of the laser welding seam 6 is facilitated, and in addition, the penetration t 2 of the laser welding seam 6 in the aluminum workpiece 2 is controlled in a small range, so that the defects of air holes, cracks and the like in the laser welding seam are avoided as shown in figure 9. After tensile shear mechanical property testing, the welded joint of the present invention was significantly better in tensile shear load and cross tensile load than the joints of comparative examples 1 and 2, and the statistical results are shown in table 1 below. In the tensile shear load and cross tensile load test process of the joint, the displacement of the welded joint is more than 3 times of that of the welded joint in comparative examples 1 and 2, and the stability of the mechanical properties of the joint is better, as shown in fig. 11 and 12; in addition, in the testing process of the tensile shear load and the cross tensile load of the welded joint, the failure modes are button pull-out fracture modes, as shown in fig. 13, which further proves that the connection performance of the welded joint is obviously improved.
Table 1: mechanical Properties of the welded joints of the invention in examples and the welded joints of comparative examples 1 and 2
| Project | Average tensile shear load (N) | Average cross tensile load (N) |
| The joint of the invention | 5358.93 | 1968.67 |
| Comparative example 1 | 3652.94 | 378.54 |
| Comparative example 2 | 3041.86 | 671.33 |
The foregoing is merely a preferred embodiment of the present invention, and it should be noted that modifications could be made by those skilled in the art without departing from the method of the present invention, and such modifications should also be considered as being within the scope of the present invention.
Claims (5)
1. The manufacturing method of the aluminum steel dissimilar metal welding joint is characterized by comprising the following steps of:
Step 1: heating the steel workpiece and the aluminum workpiece to a plastic state or a local melting state, and applying pressure to the surface of the steel workpiece to extrude the steel convex structure, so that the convex part of the steel convex structure is extruded into the aluminum workpiece, and metal elements of an aluminum-steel interface are mutually diffused under the action of high temperature to form a metallurgical bonding interface;
Step 2: preparing an annular fusion welding seam in a region which is 3.5 times of the diameter of the metallurgical bonding interface and is arranged on the periphery of the steel convex structure by adopting a fusion welding method;
the processing method adopted in the step 1 is resistance welding, and after welding spots are formed, the surface of the aluminum workpiece only generates small deformation;
The resistance welding adopts resistance spot welding, the resistance welding adopts a special electrode, the electrode comprises a steel electrode contacted with a steel workpiece and an aluminum electrode contacted with an aluminum workpiece, an annular groove is arranged on the welding surface of the steel electrode, the steel welding surface is divided into an inner welding surface and an outer welding surface by the annular groove, the height of the inner welding surface is larger than that of the outer welding surface, the height difference is 0.05-1.2 mm, the bottom of the annular groove is lower than that of the outer welding surface, and the height difference is 0.1-1.5 mm; the center of the aluminum electrode welding surface is a concave arc surface, the maximum depth of the concave arc surface is 0.05-1.0 mm, at least one convex circular ring is arranged along the periphery of the concave arc surface, the height of the convex circular ring is 0.1-0.8 mm, the width of the convex circular ring is 0.2-0.8 mm, and the diameter of the convex circular ring of the aluminum electrode is larger than the diameter of the welding surface in the steel electrode.
2. The method for manufacturing a welded joint of dissimilar metals of aluminum steel as claimed in claim 1, wherein the fusion welding method employed in step 2 comprises laser welding, electron beam welding or arc welding.
3. The method for manufacturing the welded joint of aluminum steel dissimilar metals according to claim 1, wherein the thicknesses of the steel workpiece and the aluminum workpiece are 0.2-3.5 mm, and the welding seam is prevented from being oxidized by blowing inert shielding gas when the annular welding seam is manufactured by adopting a fusion welding method in the step 2.
4. The method for manufacturing a welded joint of dissimilar metals of aluminum steel according to claim 1 or 2, wherein said step 1 uses resistance spot welding, and said step 2 uses laser welding, specifically as follows:
Step 1, placing mutually stacked aluminum-steel dissimilar metal workpieces between two welding electrodes of resistance spot welding, wherein the steel workpieces are arranged on one side of the steel electrodes, and the aluminum workpieces are arranged on one side of the aluminum electrodes;
Step 2, resistance spot welding is started, a welding electrode applies pressure to stacked aluminum steel workpieces, welding current is connected at the same time, under the action of pressure and resistance heat, the inner welding surface of the steel electrode extrudes the steel workpieces to obtain a steel convex structure of an aluminum steel interface, and under the action of resistance heat, aluminum alloy contacted with steel is melted to wet the surfaces of the steel workpieces spread in welding spots to form a metallurgically bonded connecting interface;
step 3, finishing the resistance spot welding process, and removing the resistance spot welding electrode which is in contact with the workpiece;
and 4, starting laser welding, wherein a laser beam acts on the surface of the steel workpiece, and controlling the laser beam to scan along the circular welding path to obtain the circular welding seam around the periphery of the steel convex structure.
5. The method of manufacturing a welded joint of dissimilar metals of aluminum and steel according to claim 4, wherein said steel electrode and said aluminum electrode are made of the same material and are made of copper alloy.
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