Composite joining method of aluminum alloy and steel by brazing-friction stir welding and riveting

Abstract

The present invention discloses a brazing-stirring friction welding and riveting composite connection method for aluminum alloy and steel. The steel plate and the aluminum alloy plate are welded by selecting tungsten inert gas welding combined with stir friction welding. A groove is prefabricated on the surface of the steel plate before welding. When welding, the tungsten inert gas welding torch is first started to fill the prefabricated groove on the surface of the steel plate with welding wire. When the weld metal is in a semi-solid state, the stirrer of the stir friction welding is intervened, and the tungsten inert gas welding torch and the stirrer of the stir friction welding are synchronously moved forward to complete the welding. Through the above technical scheme, the thickness of the intermetallic compound layer of the weld is reduced, and its morphology is changed, and the residual stress of the joint is effectively released; through the prefabricated groove combined with tungsten inert gas welding and stir friction welding, the macro-microscopic welding and riveting composite connection of the steel plate and the aluminum alloy plate is realized, and the mechanical properties of the joint are significantly improved.

Description

Technical Field

[0001] The invention belongs to the technical field of material connection, and particularly relates to a composite connection method of aluminum alloy and steel by brazing-friction stirring welding and riveting. Background Art

[0002] The widespread application of lightweight concepts has promoted the technological innovation and sustainable development of the automotive and aerospace industries. Aluminum alloys are often connected with steel to form composite structures due to their excellent properties such as low density, good corrosion resistance, and good plasticity, thereby achieving lightweight design. However, aluminum and steel have low solid solubility and large differences in thermal expansion coefficients. After welding, the joints are prone to produce a large amount of brittle Fe-Al intermetallic compounds and large residual stresses, which seriously deteriorate the joint performance. Therefore, it is difficult to obtain a good connection using conventional single fusion brazing methods, such as laser welding and TIG welding.

[0003] The literature "Effects of preheat treatment on microstructure evolution and properties of brazed-fusion welded joint of aluminum alloy to steel, H.Ma, G.Qin, L.Wang, et al., Materials and Design, 2016 90: 330-339." reported the growth behavior of intermetallic compounds during the fusion brazing process of aluminum alloy and stainless steel. The formation of the intermetallic compound layer indicates that the aluminum alloy and stainless steel have undergone metallurgical bonding. However, when the compound layer is too thick, the joint strength is too low, which may cause the joint to spontaneously fracture, seriously deteriorating the joint performance.

[0004] The invention patent with application number CN202210035908.0 discloses a transition layer welding wire for the preparation of aluminum-steel composite structures and a preparation and arc surfacing method. The formation of intermetallic compounds in the aluminum-steel joint is suppressed by designing the composition of the transition layer welding wire. The Ag element is used to lower the melting point and improve the wettability and spreadability of the matrix. However, the design cost of the welding wire is increased. In addition, the method does not involve a solution to the problem of residual stress inside the weld.

[0005] As an efficient solid-phase connection technology, friction stir welding has the advantages of low welding temperature, small deformation, few welding defects, and easy to obtain high-strength joints. However, for aluminum-steel welding, due to the large differences in hardness, melting point, etc. between the two, the direct use of friction stir welding method places stringent requirements on the stirring head material, resulting in poor welding ability and increased operating costs. In addition, aluminum-steel joints prepared by a single friction stir welding method are prone to low-stress cracking during service under extreme working conditions, greatly increasing safety hazards.

[0006] The paper “Gas tungsten arc welding assisted hybrid friction stir welding of dissimilar materials Al6061-T6 aluminum alloy and STS304 stainless steel, H.Bang, H.Bang, G.Jeon, et al., Materials and Design, 2012 37:48-55.” reported a hybrid welding method of Al6061-T6 aluminum alloy and STS304 stainless steel. This method preheats the stainless steel surface by GTAW and uses an additional heat source to enhance the plastic flow of the stainless steel material, which can effectively reduce the damage to the stirring head. However, it should be pointed out that the arc only provides an auxiliary heat source in this method, and the residual stress of the joint is still unevenly distributed, and the risk of low stress cracking is not eliminated.

[0007] It can be seen that in order to reduce the harm of intermetallic compounds in aluminum-steel joints (reduce thickness or change shape), release residual stress in the joints, and improve the strength of welded joints, it is urgent to develop a low-cost, simple-to-operate, and practical new process method to improve the performance of aluminum-steel joints and achieve high-performance connection of heterogeneous metal joints of aluminum alloy and steel. Summary of the invention

[0008] In view of this, the present invention discloses a composite connection method of aluminum alloy and steel by brazing-friction stir welding and riveting, and the specific scheme is as follows:

[0009] A method for composite connection of aluminum alloy and steel by brazing-stirring friction welding and riveting comprises the following steps:

[0010] S1. Grind the surface of steel plate and aluminum alloy plate;

[0011] S2. The aluminum alloy plate and the steel plate are fixed so that the welded joint is in the form of a butt joint, the aluminum alloy plate is provided with a groove, and the upper surface of the steel plate is provided with a prefabricated groove;

[0012] S3. A TIG welding gun is arranged above the prefabricated groove, and a stirring head of a friction stir welding is arranged above the area between the steel plate and the aluminum alloy plate. During welding, the TIG welding gun is first started, and the liquid metal after the welding wire melts fills the prefabricated groove and then flows into the area between the steel plate and the aluminum alloy plate to form a filler metal. When the filler metal between the steel plate and the aluminum alloy plate is in a semi-solid state, the stirring head of the friction stir welding intervenes from the starting point of the area between the aluminum alloy plate and the steel plate to complete the welding of the steel plate and the aluminum alloy plate. During the welding process, the stirring head of the friction stir welding and the TIG welding gun move in the same direction at the same speed.

[0013] S4. After welding is completed, first turn off the TIG welding gun, then withdraw the stirring head of the friction stir welding, and turn off the friction stir welding machine.

[0014] As a supplement to the technical solution of the present invention, the shoulder of the friction stir welding stirring head covers the prefabricated groove and the groove on the aluminum alloy plate.

[0015] As a supplement to the technical solution of the present invention, in step S1, the specific structure of the prefabricated groove is a dovetail groove structure.

[0016] As a supplement to the technical solution of the present invention, the specific structure of the prefabricated groove is a continuous and uninterrupted dovetail groove structure.

[0017] As a supplement to the technical solution of the present invention, in step S2, the angle of the groove formed on the aluminum alloy plate is 30°-40°.

[0018] As a supplement to the technical solution of the present invention, in step S3, the welding process parameters of TIG welding are specifically as follows: the distance between the tungsten electrode tip of the TIG welding gun and the horizontal plane of the steel plate is 0.5-2.5 mm, the argon shielding gas flow rate is 18-22 L / min, the welding current is 20-200 A, the welding speed is 1.5-4 mm / s, and the wire feeding speed is 10-28 mm / s.

[0019] As a supplement to the technical solution of the present invention, in step S3, the specific welding process parameters of the friction stir welding are: rotation speed 400-1500r / min, shoulder pressure 0.1mm, welding speed 1.5-4mm / s, stirring needle inclination angle 2°-2.5°.

[0020] As a supplement to the technical solution of the present invention, in step S3, the friction stir welding adopts static shoulder friction stir welding.

[0021] Beneficial effects:

[0022] 1. The present invention uses TIG welding and stir friction welding riveting to achieve composite connection, breaking through the limitation of a single welding method and having a novel concept.

[0023] 2. Through the prefabricated groove of the steel plate, TIG welding is used in conjunction with stir friction welding, so that the liquid metal formed after the TIG welding wire melts fills the prefabricated groove and then flows into the area between the steel plate and the aluminum alloy plate, forming a macroscopic welding and riveting composite connection.

[0024] 3. When the weld metal is in a semi-solid state, the stirring head of the friction stir welding intervenes, and the large deformation is used to break the brittle phases such as the intermetallic compounds, thereby achieving the effect of thinning the compound thickness and refining the grain structure. In addition, the broken interface intermetallic compound layer exists in a serrated form, forming a microscopic welding and riveting composite connection in situ.

[0025] 4. After the stirring head of the friction stir welding is involved, the static shoulder of the stirring head reduces the peak temperature of the weld metal, improves the weld formation, and releases the residual stress inside the weld. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a structural schematic diagram of the present invention;

[0027] Figure 2 It is a schematic diagram of the side structure of the steel plate and the aluminum alloy plate;

[0028] In the figure: 1. TIG welding gun, 2. welding wire, 3. workbench, 4. stirring head, 5. welding direction, 6. steel plate, 7. forming groove, 8. aluminum alloy plate, 9. prefabricated groove. DETAILED DESCRIPTION

[0029] In the description of the present invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0030] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection, an electrical connection, or communication with each other; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0031] like Figure 1 , Figure 2 As shown, the aluminum alloy and steel brazing-stir friction welding and riveting composite connection method comprises the following steps:

[0032] S1. Select aluminum alloy and steel plates of consistent thickness, and clean the plates by mechanical grinding to keep their surfaces flat and clean.

[0033] S2. Fix the aluminum alloy plate and the steel plate by a clamp. The welding joint is a butt joint. To ensure sufficient metallurgical reaction on the aluminum alloy plate side, a 30°-40° groove is opened on the aluminum alloy plate. A prefabricated groove is provided on the surface of the steel plate. The groove on the aluminum alloy plate and the prefabricated groove on the surface of the steel plate are wiped with alcohol. The position of the prefabricated groove is located near the edge of the area to be welded on the steel plate.

[0034] S3. A TIG welding gun is arranged above the prefabricated groove area of ​​the steel plate, with the tungsten electrode tip of the TIG welding gun being 0.5-2.5 mm away from the horizontal plane of the steel plate. A stirring head for friction stir welding is arranged above the area between the steel plate and the aluminum alloy plate, with the shoulder of the stirring head covering the prefabricated groove and the groove on the aluminum alloy plate.

[0035] The friction stir welding adopts static shoulder friction stir welding in which only the friction of the stirring needle generates heat to deform the material. The static shoulder friction stir welding is used to reduce the friction heat generated between the stirring head and the weld metal, reduce the peak temperature of the weld metal, improve the weld formation, and release the residual stress inside the weld.

[0036] During welding, the TIG welding gun is first started to allow the welding wire to fill the prefabricated groove on the surface of the steel plate. The liquid metal after the welding wire is melted fills the prefabricated groove and then flows into the area between the steel plate and the aluminum alloy plate to form filler metal. When the filler metal between the steel plate and the aluminum alloy plate is in a semi-solid state, the stirring head of the stir friction welding intervenes from the starting point of the area between the aluminum alloy plate and the steel plate to complete the welding of the steel plate and the aluminum alloy plate. During the welding process, the stirring head of the stir friction welding and the TIG welding gun move at the same speed and in the same direction.

[0037] The distance between the TIG welding gun and the stirring head of the stir friction welding is 20-80mm, which can enable the liquid metal after the welding wire is melted to fill the prefabricated groove and then flow into the area between the steel plate and the aluminum alloy plate to form filler metal. When the filler metal between the steel plate and the aluminum alloy plate is in a semi-solid state, stir friction welding at this time can reduce the damage of the stirring needle and improve the welding quality.

[0038] When the shoulder of the stirring head of the friction stir welding covers the prefabricated groove, during the friction stir welding process, the static shoulder on the stirring head compacts the metal in the prefabricated groove of the steel plate to ensure that the prefabricated groove on the steel plate is fully filled. At the same time, the stirring needle can release the stress of the metal in the prefabricated groove on the steel plate to solve the problem of stress concentration. Secondly, during the processing of the weld joint, the stirring needle can make the metal flow, disperse it more evenly, achieve a dispersed distribution effect, break up the intermetallic compounds of the weld joint, and reduce the thickness of the intermetallic compounds.

[0039] The semi-solid state specifically means that the weld metal is between solid and liquid, and contains part of the liquid phase, but the overall structure is still solid.

[0040] In the above welding process, the specific welding process parameters of TIG are: argon shielding gas flow rate 18-22L / min, welding current 20-200A, welding speed 1.5-4mm / s, wire feeding speed 10-28mm / s, to ensure that the welding wire is fully melted and undergoes metallurgical reaction with the base material.

[0041] The specific welding process parameters of stir friction welding are: rotation speed 400-1500r / min, shoulder pressure 0.1mm, welding speed 1.5-4mm / s, stirring needle inclination angle 2°-2.5°.

[0042] S4. After welding is completed, first turn off the TIG welding gun, then withdraw the stirring head of the friction stir welding, and turn off the friction stir welding machine.

[0043] As a supplement to the technical solution of the present invention, the prefabricated groove on the steel plate is specifically a groove body opened on the upper surface of the steel plate. The groove body can be discontinuous or continuous, preferably continuous, because the use of a continuous groove body can increase the macroscopic welding and riveting composite connection area and improve the overall strength of the welded joint. The specific structure of the prefabricated groove can be any shape, preferably a dovetail groove structure, such as Figure 2 As shown in FIG. 1 , the corner position in the dovetail groove is set to a rounded structure so that the TIG welding wire can fully fill the dovetail groove after melting. In addition, in order to achieve that the liquid metal after the TIG welding wire melts fills the dovetail groove and can smoothly flow into the area between the steel plate and the aluminum alloy plate, as shown in FIG. Figure 2 As shown, the height of the upper end surface of the steel plate located on the left side of the dovetail groove is higher than the height of the upper end surface of the steel plate located on the right side of the dovetail groove.

[0044] The present invention adopts TIG welding combined with stir friction welding to achieve welding and riveting composite connection. Through the prefabricated groove of the steel plate, the liquid metal after the welding wire melts by TIG welding fills the prefabricated groove and then flows into the area between the steel plate and the aluminum alloy plate. After welding, the metal in the prefabricated groove is connected with the metal in the weld area to form a macro welding and riveting composite connection, thereby improving the strength of the welded joint.

[0045] When the weld metal is in a semi-solid state, the friction stir treatment is used to break the brittle phases such as intermetallic compounds by large deformation, thereby reducing the thickness of the compound and refining the grain structure. In addition, the broken intermetallic compound layer on the interface exists in a serrated form, forming a microscopic weld-riveted composite connection in situ. After the friction stir treatment is used, the static shoulder of the stirring head reduces the peak temperature of the aluminum alloy plate and the steel plate, improves the weld formation, and releases the residual stress inside the weld.

[0046] In summary, the present invention innovatively proposes a new method of brazing-stir friction welding and riveting composite connection, which reduces the thickness of the intermetallic compound layer and changes its morphology, effectively releasing the residual stress of the joint; in addition, large deformation drives plastic flow to prompt the weld metal to fill the macro-mechanical prefabricated groove and form micro-interlocking in situ, ultimately achieving macro-micro mechanical bite and significantly improving the mechanical properties of the joint.

[0047] In the present invention, "melting brazing" is a welding method in which the interface of the high melting point side of the heterogeneous metal (such as steel, titanium, copper) is brazed, and the interface of the low melting point side (such as aluminum) is fusion welding. The welding method can be MIG, TIG, laser welding, or laser + TIG, laser + MIG or other welding methods, and is not limited to the TIG welding disclosed in the present invention. Its main purpose is to melt the welding wire.

[0048] To facilitate the understanding of the technical solution, the present invention provides the following embodiments, specifically, 5A06 grade is selected from the aluminum alloy for welding, but it is not limited to the above grade aluminum alloy, and the welding method disclosed in the present invention is also applicable to the welding of other grades of aluminum alloy and steel. In the embodiment of the present invention, the steel plate is selected from stainless steel plate, and the welding method disclosed in the present invention is also applicable to other steel plates, such as low alloy steel plate, carbon steel plate, alloy steel plate and stainless steel plate.

[0049] Embodiment 1:

[0050] S1. Select 5A06 aluminum alloy plate and stainless steel plate of the same thickness, clean the plates by mechanical grinding to keep their surfaces flat and clean.

[0051] S2. Fix the 5A06 aluminum alloy plate and the stainless steel plate by a clamp. The welding joint is a butt joint. To ensure sufficient metallurgical reaction on the aluminum alloy plate side, a 40° groove is opened on the 5A06 aluminum alloy plate, and a prefabricated groove of a dovetail groove structure is opened on the surface of the steel plate. The groove on the 5A06 aluminum alloy plate and the prefabricated groove on the surface of the steel plate are wiped with alcohol.

[0052] S3. A TIG welding gun is arranged above the prefabricated groove area of ​​the stainless steel plate, with the tungsten electrode tip of the TIG welding gun being 1 mm away from the horizontal plane of the steel plate; a stirring head for friction stir welding is arranged above the prefabricated groove and the area between the stainless steel plate and the aluminum alloy plate, with the shoulder of the stirring head covering the groove on the prefabricated groove and the aluminum alloy plate. The friction stir welding adopts static shoulder friction stir welding in which only the friction of the stirring needle generates heat to deform the material.

[0053] The distance between the TIG welding gun and the stirring head of the stir friction welding is 30 mm. In the above welding process, the specific welding process parameters of TIG are: argon shielding gas flow rate 20 L / min, welding current 90 A, welding speed 2 mm / s, and wire feeding speed 18 mm / s.

[0054] The specific welding process parameters of friction stir welding are: rotation speed 900r / min, shoulder pressure 0.1mm, welding speed 2mm / s, and stirring needle inclination angle 2°.

[0055] S4. After welding is completed, first turn off the TIG welding gun, then withdraw the stirring head of the friction stir welding, and turn off the friction stir welding machine.

[0056] S5. The tensile strength of the aluminum-steel welded riveted joint was tested using a universal tensile testing machine, and the average strength of the aluminum-steel welded riveted joint was about 192 MPa.

[0057] Comparative Example 1:

[0058] S1. Select 5A06 aluminum alloy plate and stainless steel plate of the same thickness, clean the plates by mechanical grinding to keep their surfaces flat and clean.

[0059] S2. Fix the 5A06 plate and the stainless steel plate with a clamp. The welding joint is a butt joint. A 40° groove is opened on the 5A06 plate and the stainless steel. The grooves on the 5A06 plate and the stainless steel are wiped with alcohol.

[0060] S3. Set the TIG welding gun just above the gap between the stainless steel plate and the 5A06 plate, with the distance between the tungsten tip of the TIG welding gun and the horizontal plane of the steel plate being 1 mm;

[0061] S4. During the formal welding, the TIG welding gun is started to fill the groove of the aluminum alloy plate and the stainless steel plate with welding wire. The welding process parameters of TIG welding are the same as those in Example 1.

[0062] S5. Welding is finished and the TIG welding gun is turned off.

[0063] S6. The tensile strength of the aluminum-steel brazing joint was tested using a universal tensile testing machine. The average strength of the aluminum-steel brazing joint was about 115 MPa.

[0064] By comparing Implementation 1 with Comparative Example 1, the aluminum-steel joint was prepared by the brazing-friction stir welding and riveting composite connection method of the present invention, and the tensile strength of the joint was increased by about 70%.

[0065] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical solutions and inventive concepts of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. Aluminum alloy and steel brazing-stir friction welding and riveting composite connection method, characterized in that: The following steps are involved: S1. Grinding the surface of steel plate and aluminum alloy plate; S2. The aluminum alloy plate and the steel plate are fixed so that the welded joint is in the form of a butt joint, the aluminum alloy plate is provided with a groove, the upper surface of the steel plate is provided with a prefabricated groove; the prefabricated groove is located near the edge of the steel plate to be welded; S3. A TIG welding gun is arranged above the prefabricated groove, and a friction stir welding stirring head is arranged above the area between the steel plate and the aluminum alloy plate, wherein the shoulder of the friction stir welding stirring head covers the prefabricated groove and the groove on the aluminum alloy plate; during welding, the TIG welding gun is first started, and the liquid metal after the welding wire melts fills the prefabricated groove and then flows into the area between the steel plate and the aluminum alloy plate to form a filler metal; when the filler metal between the steel plate and the aluminum alloy plate is in a semi-solid state, the friction stir welding stirring head intervenes from the starting point of the area between the aluminum alloy plate and the steel plate to complete the welding of the steel plate and the aluminum alloy plate; during the welding process, the friction stir welding stirring head and the TIG welding gun move in the same direction at the same speed; S4. After welding is completed, first turn off the TIG welding gun, then withdraw the stirring head of the friction stir welding, and turn off the friction stir welding machine.

2. The aluminum alloy and steel brazing-friction stir welding and riveting composite connection method according to claim 1 is characterized in that: In the step S1, the specific structure of the prefabricated groove is a dovetail groove structure.

3. The aluminum alloy and steel brazing-friction stir welding and riveting composite connection method according to claim 2 is characterized in that: The specific structure of the prefabricated groove is a continuous and uninterrupted dovetail groove structure.

4. The aluminum alloy and steel brazing-friction stir welding and riveting composite connection method according to claim 1 is characterized in that: In the step S2, the angle of the groove formed on the aluminum alloy plate is 30°-40°.

5. The aluminum alloy and steel brazing-friction stir welding and riveting composite connection method according to claim 1 is characterized in that: In step S3, the welding process parameters of TIG welding are specifically as follows: the distance between the tungsten electrode tip of the TIG welding gun and the horizontal plane of the steel plate is 0.5-2.5 mm, the argon shielding gas flow rate is 18-22 L / min, the welding current is 20-200 A, the welding speed is 1.5-4 mm / s, and the wire feeding speed is 10-28 mm / s.

6. The aluminum alloy and steel brazing-friction stir welding and riveting composite connection method according to claim 1 is characterized in that: In step S3, the specific welding process parameters of the friction stir welding are: rotation speed 400-1500 r / min, shoulder pressure 0.1 mm, welding speed 1.5-4 mm / s, and stirring needle inclination angle 2°-2.5°.

7. The aluminum alloy and steel brazing-friction stir welding and riveting composite connection method according to claim 1 is characterized in that: In step S3, the friction stir welding adopts static shoulder friction stir welding.

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