An aluminum-steel composite part, its preparation method and application

Abstract

The present invention relates to the technical field of metal composite materials, and in particular, to an aluminum-steel composite part, a preparation method and an application thereof. The aluminum-steel composite part comprises an aluminum alloy part and a coated steel part which are connected to each other through a connecting piece and / or through metallurgical bonding; when the aluminum alloy part and the coated steel part are connected through a connecting piece, the connecting piece comprises at least one of a steel bolt and a composite bolt; when the aluminum alloy part and the coated steel part are connected through at least a steel bolt, the head of the steel bolt is arranged inside the aluminum alloy part, and a filling layer is arranged between the head of the steel bolt and the aluminum alloy part. The aluminum-steel composite part has the advantages of stable quality, high bonding strength, and not being prone to loosening at the joint.

Description

Technical Field

[0001] The present invention relates to the technical field of metal composite materials, and in particular, to an aluminum-steel composite part, a preparation method thereof, and an application thereof. Background Art

[0002] Steel materials and aluminum alloy materials have the characteristics of high strength and excellent formability, and are currently the two most widely used metal materials in industrial applications. However, whether it is steel materials or aluminum alloy materials, single metal materials always have certain limitations in terms of physical, chemical, and mechanical properties. The mixed use of aluminum and steel can meet the development trends of lightweight, high performance, and low cost in the transportation industry, and is increasingly widely used.

[0003] Bolt connection is a common mechanical connection method for aluminum and steel, which has the advantages of convenient connection, easy disassembly, and low cost. In the threaded connection combined structure, due to the structural characteristics of the threaded connection, problems such as stress concentration and uneven load distribution on the thread teeth often occur, and stress concentration mainly occurs at the root of the thread, especially obvious at the root of the first thread, which to a certain extent affects the strength and reliability of the bolt connection. Aluminum alloy materials are sensitive to temperature and will creep under low temperature and external load. The aluminum-steel threaded connection combined structure is relatively easy to creep and relax, resulting in a reduction in the reliability of the threaded connection. Especially when the connection force between aluminum and steel is insufficient, there will be a large gap between the aluminum alloy part and the steel plate, and the intrusion of the electrolyte will cause crevice corrosion. Under the conditions of impact, vibration, especially transverse vibration, problems such as loosening, detachment, and dropping of the threaded connection often occur.

[0004] Moreover, when using traditional steel bolts or screws to connect aluminum parts, due to the inconsistent thermal expansion coefficients of the steel bolts and the aluminum connected parts, when the temperature changes, it will cause additional stress in the threaded connection pair, increasing the creep risk of the aluminum alloy and weakening the ability to maintain the preload. And aluminum bolts have poor toughness and are prone to fatigue fracture under stress-strain conditions.

[0005] In view of this, the present invention is specifically proposed. Summary of the Invention

[0006] The first object of the present invention is to provide an aluminum-steel composite part, which has stable quality, high bonding strength, is not easy to loosen at the joint, does not have gaps, and avoids corrosion caused by the intrusion of the electrolyte into the gaps.

[0007] The second object of the present invention is to provide a preparation method of the aluminum-steel composite part.

[0008] The third object of the present invention is to provide an application of the aluminum-steel composite part in transportation tools and building materials.

[0009] In order to achieve the above objects of the present invention, the following technical solutions are specifically adopted:

[0010] The present invention provides an aluminum-steel composite part, and the aluminum-steel composite part includes a connected aluminum alloy part and a plated steel part. Among them, the aluminum alloy part and the plated steel part are tightly connected through a connecting part, and / or, the aluminum alloy part and the plated steel part are permanently connected through metallurgical bonding.

[0011] As Figure 1 shown is a schematic cross-sectional view of a partial structure of the aluminum-steel composite part in one solution (the aluminum alloy part and the plated steel part are tightly connected through a connecting part). As Figure 5 shown is a schematic cross-sectional view of a partial structure of the aluminum-steel composite part in another solution (the aluminum alloy part and the plated steel part are permanently connected through metallurgical bonding), and it is also a schematic cross-sectional view of a partial structure of the aluminum-steel composite part filled with a metal filling rod after heating.

[0012] Among them, the plated steel part includes a steel layer and a plating layer provided on the outer surface of the steel layer.

[0013] In some specific embodiments of the present invention, when the aluminum alloy part and the plated steel part are connected through metallurgical bonding, the aluminum alloy part is connected (in contact) with the plating layer of the plated steel part.

[0014] When there is no metallurgical bonding between the aluminum alloy part and the plated steel part, the aluminum alloy part can be connected with the plating layer of the plated steel part, which can reduce electrochemical corrosion; the aluminum alloy part can also be connected with the steel layer of the plated steel part, that is, not in contact with the plating layer.

[0015] Among them, the shape of the aluminum alloy part can adopt any conventional shape, such as flat plate shape, block shape, cuboid shape, polyhedron shape, etc., but not limited thereto. The shape of the plated steel part can be the same as or different from the shape of the aluminum alloy part, such as flat plate shape, block shape, cuboid shape, polyhedron shape, etc., but not limited thereto. However, the connection part between the plated steel part and the aluminum alloy part needs to be fitted, such as by edge fitting or by fitting through a side surface.

[0016] In some specific embodiments of the present invention, the aluminum-steel composite part can include, for example, a steel-aluminum (composite) joint for a gearbox, and an aluminum-steel composite plate used as a train floor, but not limited thereto.

[0017] In some specific embodiments of the present invention, the steel layer in the plated steel part can adopt any conventional steel material, such as No. 45 steel, Q195 steel, Q215 steel, Q235 steel, Q255 steel, and Q275 steel, etc., but not limited thereto.

[0018] In some specific embodiments of the present invention, the material of the aluminum alloy part may include, for example, 1050 aluminum alloy, 1060 aluminum alloy, 1100 aluminum alloy, 3003 aluminum alloy, 3004 aluminum alloy, 3A21 aluminum alloy, etc., but is not limited thereto.

[0019] The coating in the coated steel part includes at least one of an aluminum alloy layer, a metallic zinc layer, and a zinc alloy layer.

[0020] The connecting part includes at least one of a steel bolt and a composite bolt.

[0021] Among them, the material of the steel bolt is mainly steel, and any conventional steel bolt that can be purchased can be used. In some specific embodiments of the present invention, the outer surface of the steel bolt is also provided with a coating of at least one of an aluminum alloy layer, a metallic zinc layer, and a zinc alloy layer.

[0022] The composite bolt includes an aluminized steel shell and an aluminum core disposed inside the aluminized steel shell; as Figure 2 shown is a schematic cross-sectional view of the composite bolt. Among them, the aluminized layer in the aluminized steel shell includes a metallic aluminum coating and / or an aluminum alloy coating; the aluminum core includes a metallic aluminum core and / or an aluminum alloy core. Among them, the steel used for the aluminized steel shell can be any conventional steel type, such as 45 steel, Q195 steel, Q215 steel, Q235 steel, Q255 steel, Q275 steel, etc., but is not limited thereto.

[0023] The composite bolt provided by the present invention for the aluminum-steel composite part has good toughness, is difficult to loosen under stress and vibration conditions, and its anti-deformation and anti-vibration capabilities are greatly enhanced. Moreover, compared with traditional steel bolts, the composite bolt has an aluminized surface and an aluminum core, which reduces the weight, and the aluminum-steel joint is not prone to electrochemical corrosion.

[0024] When the aluminum alloy part and the coated steel part are connected at least through the steel bolt, see Figure 3 , the head of the steel bolt is disposed inside the aluminum alloy part (a part of the screw rod of the steel bolt penetrates through the aluminum alloy part, and the other part of the screw rod penetrates through the coated steel part), and a filling layer is disposed between the head of the steel bolt and the aluminum alloy part, and the filling layer is mainly formed by a coated metal. Among them, the coated metal includes at least one of an aluminum alloy, a metallic zinc, and a zinc alloy.

[0025] Among them, the zinc alloy may include, for example, Zn98Al2, Zn95Al5, Zn90Al10, Zn85Al15, Zn78Al22, etc., but is not limited thereto.

[0026] The aluminum-steel composite provided by the present invention is difficult to loosen under creep, stress, and vibration conditions, and its anti-deformation and anti-vibration capabilities are greatly enhanced. Moreover, the aluminum-steel composite is beautifully formed without exposed nuts, bolts, etc.

[0027] The aluminum alloy part and the coated steel part are metallurgically bonded, making the gap between the aluminum alloy and the coated steel part zero, and improving the connection strength.

[0028] Among them, when the coating in the coated steel part is a metal zinc layer or a zinc alloy layer, a low melting temperature zinc or zinc alloy layer (below 420 °C) is used as the connection interface. When heated, the interface temperature is relatively low (below 500 °C), which can avoid direct contact between aluminum and steel, reduce the formation of brittle compounds at the steel-aluminum interface, and improve the bonding strength of the aluminum-steel composite.

[0029] When the coating in the coated steel part is an aluminum alloy layer without metallurgical bonding, aluminizing can reduce electrochemical corrosion at the steel-aluminum interface.

[0030] The aluminum-steel composite provided by the present invention has the advantages of stable quality, light weight, high bonding strength, not easy to loosen at the joint, no gap will appear, and avoiding corrosion of the gap.

[0031] Preferably, the number of the connecting pieces is not less than 4 per square meter 2 . That is, at least 4 connecting pieces are included on each square meter of the aluminum-steel composite.

[0032] In some specific embodiments of the present invention, the distance between each connecting piece is not less than 10 mm.

[0033] The present invention adopts the method of fastening with closely arranged bolts and uniform heating by heat conduction, which can reduce the deformation of the plate during the heating process, and is particularly suitable for the preparation of large-area aluminum-steel composites.

[0034] Preferably, the thickness of the coating in the coated steel part is 20-100 μm, including but not limited to the point values of 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm or the range values between any two of them.

[0035] Preferably, the thickness of the aluminized steel shell in the composite bolt is 0.5-2 mm, including but not limited to the point values of 0.7 mm, 0.9 mm, 1.0 mm, 1.2 mm, 1.5 mm, 1.8 mm or the range values between any two of them.

[0036] Preferably, the aluminum alloy core in the composite bolt includes at least one of an aluminum-silicon alloy core, an aluminum-copper alloy, an aluminum-manganese alloy, and an aluminum-magnesium-silicon alloy, and more preferably an aluminum-silicon alloy core.

[0037] Preferably, a brazing flux is also added during the formation of the filling layer. The brazing flux includes the following components by mass: 30-40 parts of ethanol, 10-60 parts of KF-AlF3 brazing flux, and 10-60 parts of CsF-AlF3 brazing flux.

[0038] Among them, the mass parts of the ethanol include, but are not limited to, any point value of 31 parts, 32 parts, 33 parts, 34 parts, 35 parts, 36 parts, 37 parts, 38 parts, 39 parts or the range value between any two of them. The mass parts of the KF-AlF3 brazing flux (potassium fluoroaluminate eutectic aluminum brazing flux, eutectic point temperature is 565 °C) include, but are not limited to, any point value of 15 parts, 20 parts, 25 parts, 30 parts, 35 parts, 40 parts, 15 parts, 50 parts, 55 parts or the range value between any two of them. The mass parts of the CsF-AlF3 brazing flux (cesium fluoroaluminate eutectic aluminum brazing flux, eutectic point temperature is 471 °C) include, but are not limited to, any point value of 15 parts, 20 parts, 25 parts, 30 parts, 35 parts, 40 parts, 15 parts, 50 parts, 55 parts or the range value between any two of them.

[0039] In some specific embodiments of the present invention, the mass fraction of the ethanol is 30% - 40%, preferably 35%.

[0040] Preferably, the preparation method of the composite bolt includes the following steps:

[0041] Thread rolling treatment is performed on a steel shell in the shape of a bolt with a cavity inside, so that threads are formed on the rod part of the steel shell; the thread-rolled steel shell is subjected to hot dip aluminizing treatment to form an aluminized layer on the outer surface of the steel shell, and an aluminized steel shell is obtained.

[0042] In some specific embodiments of the present invention, during the hot dip aluminizing treatment, part of the aluminum melt will penetrate into the inner layer, and the inner layer will be aluminized, which is more conducive to the formation of an aluminum core.

[0043] After applying the brazing flux in the cavity of the aluminized steel shell, metal aluminum and / or aluminum alloy are placed in the cavity and heated to melt the metal aluminum and / or aluminum alloy to form an aluminum core, and then cooled to obtain the composite bolt.

[0044] The preparation method of the composite bolt provided by the present invention realizes the integrated production of composite and heat treatment, which is convenient for energy saving and improves production efficiency.

[0045] In some specific embodiments of the present invention, the preparation method of the steel shell in the shape of a bolt with a cavity inside includes: subjecting a steel pipe to internal high-pressure forming to form a hollow pipe with a hexagonal step in the middle; cutting along the normal at the midline of the hexagonal step to form two steel shells in the shape of a bolt with a hexagonal step and a cavity inside; and performing thread rolling on the rod part (the area except the hexagonal step) of the steel shell to form threads on the rod part of the steel shell.

[0046] In some specific embodiments of the present invention, the shape of the metal aluminum and / or aluminum alloy is the same (adapted) as the shape of the cavity of the aluminized steel shell, so that the metal aluminum and / or aluminum alloy can fully fill the cavity.

[0047] In some specific embodiments of the present invention, during the process of placing the metal aluminum and / or aluminum alloy in the cavity and heating, the heating method includes heating in an induction coil. Preferably, it is heated to 820 - 840 °C, held for a period of time, and heating is stopped after the metal aluminum and / or aluminum alloy is completely melted.

[0048] Preferably, the temperature of the aluminum melt used in the hot-dip aluminizing process is 690 - 740 °C, including but not limited to the point values of any one of 700 °C, 710 °C, 720 °C, 730 °C or the range values between any two of them.

[0049] The dipping time in the hot-dip aluminizing process is 30 - 50 s, including but not limited to the point values of any one of 35 s, 40 s, 45 s or the range values between any two of them.

[0050] Preferably, a flux is covered on the surface of the aluminum melt.

[0051] Preferably, the flux includes the following components by mass parts: 20 - 40 parts of NaCl, 20 - 40 parts of KCl, 10 - 20 parts of NaAlF6, and 10 - 20 parts of Na2SiF6.

[0052] Among them, the mass parts of the NaCl include but not limited to the point values of any one of 25 parts, 30 parts, 35 parts or the range values between any two of them. The mass parts of the KCl include but not limited to the point values of any one of 25 parts, 30 parts, 35 parts or the range values between any two of them. The mass parts of the NaAlF6 include but not limited to the point values of any one of 13 parts, 15 parts, 18 parts or the range values between any two of them. The mass parts of the Na2SiF6 include but not limited to the point values of any one of 13 parts, 15 parts, 18 parts or the range values between any two of them.

[0053] The present invention also provides a method for preparing the aluminum-steel composite part as described above, which includes the following steps:

[0054] A stepped hole is formed by counterboring the aluminum alloy part, and a through hole with a thread is formed by drilling and tapping the coated steel part; a steel bolt is sequentially inserted into the stepped hole and the through hole to complete the connection between the aluminum alloy part and the coated steel part; then, a brazing flux is filled in the gap between the head of the steel bolt and the aluminum alloy part. After the brazing flux is heated and melted, the brazing flux will penetrate into the interface between the aluminum alloy and the coated steel part along the gap formed by the bolt and the counterbore, the coating melts, and the aluminum alloy is combined with the coated steel part. Then, a coating metal is added and melted (and the liquid level of the mixed molten liquid is in the same plane as the upper surface of the aluminum alloy part), and then it is cooled to obtain the aluminum-steel composite part. Wherein, the brazing flux includes the following components by mass parts: 30-40 parts of ethanol, 10-60 parts of KF-AlF3 brazing flux, and 10-60 parts of CsF-AlF3 brazing flux.

[0055] In some preferred embodiments of the present invention, the material of the coating in the coated steel part is the same as the material of the aluminum alloy part, and the coating in the coated steel part is made to fit the aluminum alloy part during the connection process. The steel used for the steel bolt is the same as the steel used in the coated steel part. By using aluminum alloy with the same material as the aluminum alloy part as the composite connection interface, the aluminum alloy part and the coated steel part are metallurgically bonded, making the gap between the aluminum alloy and the steel plate zero, and improving the connection strength; at the same time, the steel bolt is metallurgically bonded with the aluminum alloy part and the steel plate, further improving the connection strength.

[0056] And / or, a stepped hole is formed by counterboring the aluminum alloy part, and a through hole with a thread is formed by drilling and tapping the coated steel part; a composite bolt is sequentially inserted into the stepped hole and the through hole to complete the connection between the aluminum alloy part and the coated steel part, and the aluminum-steel composite part is obtained.

[0057] And / or, a stepped hole is formed by counterboring the aluminum alloy part, and a through hole with a thread is formed by drilling and tapping the coated steel part; a fixing bolt is sequentially inserted into the stepped hole and the through hole, and a brazing flux is added to the gap formed between the head of the fixing bolt and the stepped hole, heated until completely melted, and then the heating is stopped, so that a metallurgical bond is formed between the aluminum alloy part and the coated steel part to connect them to each other. Subsequently, the fixing bolt is taken out to obtain the aluminum-steel composite part. At this time, a metallurgical bond has occurred between the aluminum alloy part and the galvanized steel part, forming a permanent connection.

[0058] Optionally (either optional or not), after removing the fixing bolt, it further includes the steps of filling a metal filling rod into the stepped hole and the through hole, then heating for hole filling, and then cooling. Wherein, the metal filling rod includes an integrally connected aluminum alloy area and a steel area, the aluminum alloy area includes a head and a non-threaded screw rod connected thereto, and the steel area is a threaded screw rod.

[0059] Specifically, during the filling, the steel area is placed in the through hole, and the aluminum alloy area is placed in the stepped hole. The material of the aluminum alloy area includes aluminum alloy, and the steel area includes steel (steel material) and a coating metal provided on the outer surface of the steel. Wherein, the coating metal includes at least one of aluminum alloy, metallic zinc, and zinc alloy.

[0060] Since holes will be left on the aluminum alloy part and the galvanized steel part after the fixing bolt is removed, for the sake of aesthetics and convenience of subsequent processing such as rolling, and to reduce surface defects of the plate, a metal filling rod can be filled in the holes. Wherein, the metal filling rod includes an integrally connected aluminum alloy area and a steel area, that is, the aluminum alloy area and the steel area form an integral bolt structure, the aluminum alloy area includes a head and a non-threaded screw rod, and the steel area is a threaded screw rod. Preferably, the inner diameter of the stepped hole is larger than the diameter of the head of the aluminum alloy area for easy assembly; at the same time, in order to completely fill the gap between the head of the aluminum alloy area and the stepped hole, it is preferred that the head is higher than the upper plane (top surface) of the stepped hole.

[0061] During the process of heating for hole filling, after the metal filling rod is heated, the head and the non-threaded screw rod of the aluminum alloy area are completely fused with the aluminum alloy part to form an integral body; the steel in the steel area does not melt, while the coating melts and forms a metallurgical connection with the steel part.

[0062] Among them, for the partial cross-sectional schematic diagram of the aluminum-steel composite part with a metal filling rod before heating (i.e., before heating), see Figure 4 ; for the partial cross-sectional schematic diagram after heating, see Figure 5 , it can be seen that after heating, the head and the non-threaded screw rod of the aluminum alloy area are completely fused with the aluminum alloy part.

[0063] In some preferred embodiments of the present invention, the heating method includes conduction heating and / or laser heating.

[0064] Among them, conduction heating acts on the coated steel part and / or the aluminum alloy part, and can form a metallurgical bond. This heating method can precisely control the temperature and has uniform heating, and can avoid deformation of the plate during the heating process. Preferably, the heat conduction device used for conduction heating is a constant-temperature heating plate, which is mainly composed of a steel workbench, heating tubes, and a temperature control system.

[0065] The laser heating acts on the head of the steel bolt. The laser heating is local heating, which melts the brazing flux to fill the gap, thereby promoting the melting and filling of the metal and the melting connection of the coating metal. Preferably, the laser power of the laser heating is 350 - 3000 W, and the spot diameter is 2 - 8 mm.

[0066] When complete chemical metallurgical bonding between the aluminum and steel layers is required, conduction heating is selected; when partial chemical metallurgical bonding between the aluminum and steel layers is required, laser heating is selected.

[0067] It is possible to select a combination of the above two heating methods simultaneously for better results.

[0068] The preparation method of the aluminum - steel composite part can adopt any one of the above methods, or a combination of two, or a combination of all three simultaneously.

[0069] The preparation method of the aluminum - steel composite part provided by the present invention can prevent joint loosening, the appearance of gaps at the joint, and the corrosion of the gaps. Moreover, the process is simple, the production is flexible, the cost is low, it can be mass - produced, and the production efficiency is high.

[0070] The present invention also provides the application of the aluminum - steel composite part as described above in transportation tools and building materials.

[0071] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0072] (1) The composite bolt for the aluminum - steel composite part provided by the present invention has good toughness, is difficult to loosen under stress and vibration conditions, and its anti - deformation and anti - vibration capabilities are greatly enhanced. At the same time, compared with the traditional steel bolt, the surface of this composite bolt is aluminized and the core is aluminum, which reduces the weight, and the aluminum - steel joint is not prone to electrochemical corrosion.

[0073] (2) The aluminum - steel composite part provided by the present invention is difficult to loosen under creep, stress and vibration conditions, and its anti - deformation and anti - vibration capabilities are greatly enhanced.

[0074] (3) The aluminum - steel composite part provided by the present invention has the advantages of stable quality, light weight, high bonding strength, not easy to loosen at the joint, and not easy to generate gaps.

[0075] (4) The preparation method of the aluminum - steel composite part provided by the present invention can prevent joint loosening, the appearance of gaps at the joint, and the corrosion of the gaps. Moreover, the method is simple, the production cost is low, and the production efficiency is high. Description of the Drawings

[0076] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0077] Figure 1 It is a partial cross-sectional view of an aluminum-steel composite part provided by the present invention when an aluminum alloy part and a plated steel part are tightly connected through a connecting piece;

[0078] Figure 2 It is a cross-sectional view of a composite bolt provided by the present invention;

[0079] Figure 3 It is a partial cross-sectional view of an aluminum-steel composite part provided by the present invention when an aluminum alloy part and a plated steel part are connected by a steel bolt;

[0080] Figure 4 It is a partial cross-sectional view of an aluminum-steel composite part filled with a metal filling rod before heating provided by the present invention;

[0081] Figure 5 It is a partial cross-sectional view of an aluminum-steel composite part filled with a metal filling rod after heating provided by the present invention. Specific Embodiments

[0082] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the drawings and specific embodiments. However, those skilled in the art will understand that the following described embodiments are some embodiments of the present invention, not all embodiments, and are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention. For those conditions not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. For the reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0083] Figure 1 It is a partial cross-sectional view of an aluminum-steel composite part provided by the present invention when an aluminum alloy part and a plated steel part are tightly connected through a connecting piece. Figure 2 It is a cross-sectional view of a composite bolt provided by the present invention. Figure 3 It is a partial cross-sectional view of an aluminum-steel composite part provided by the present invention when an aluminum alloy part and a plated steel part are connected by a steel bolt. Figure 4 It is a partial cross-sectional view of an aluminum-steel composite part filled with a metal filling rod before heating provided by the present invention. Figure 5Schematic diagram of a partial cross-section of the aluminum-steel composite filled with a metal filling rod provided by the present invention after heating, and also a schematic diagram of a partial cross-section of the aluminum-steel composite filled with a metal filling rod after heating.

[0084] In the following embodiments of the present invention, the material of the aluminum alloy part is 1050 aluminum alloy, and the thickness is 30 mm.

[0085] In the following embodiments of the present invention, the material of the steel layer in the plated steel part is Q195 steel, and the thickness is 15 mm.

[0086] Embodiment 1

[0087] The preparation method of the aluminum-steel composite provided in this embodiment (specifically a steel-aluminum joint for a gearbox) includes the following steps:

[0088] (1) Prepare a composite bolt: perform internal high-pressure forming on a 45# steel pipe to form a hollow pipe with a hexagonal step in the middle; saw along the normal direction at the midline of the hexagonal step to form two hollow steel shells with hexagonal steps, in the shape of bolts (with a thickness of 1 mm); and perform thread rolling on its rod part (the area except the hexagonal step) so that the rod part of the steel shell forms threads. Then perform hot-dip aluminizing (aluminum-silicon alloy plating) on the thread-rolled steel shell: a fluxing agent covers the surface of the aluminum-silicon alloy melt, dip it in the melt at 700 °C for 40 s and then take it out, blow off the excess aluminum-silicon alloy melt on the surface with an air knife and then cool it to form an aluminized layer on the outer surface of the steel shell, obtaining an aluminized steel shell.

[0089] Brush a paste-like non-corrosive brazing flux into the cavity of the aluminized steel shell, then insert an aluminum-silicon alloy filling rod with the same shape and volume as the cavity, and place it in an induction coil for heating; when the induction heating temperature rises to 830 °C, keep it warm until the aluminum-silicon alloy filling rod is completely melted to form an aluminum core, then stop heating, and quickly spray water onto the outer surface of the aluminized steel shell to cool it, obtaining the composite bolt, and its cross-sectional schematic diagram is shown in Figure 2 .

[0090] Among them, the fluxing agent includes the following components by mass: 35 parts of NaCl, 35 parts of KCl, 15 parts of NaAlF6, and 15 parts of Na2SiF6.

[0091] (2) Prepare the aluminum-steel composite: perform counterboring on the aluminum alloy part to obtain a stepped hole. Perform drilling and tapping on the plated steel part to obtain a through hole with threads. Insert the composite bolt into the stepped hole of the aluminum alloy part and the through hole of the plated steel part in sequence to tightly connect the aluminum alloy part and the plated steel part (without gaps), obtaining the aluminum-steel composite.

[0092] The aluminum-steel composite provided in this embodiment is a steel-aluminum joint for a gearbox, which includes a connected aluminum alloy part and a plated steel part, and the aluminum alloy part and the plated steel part are connected by a connecting piece; the plating layer in the plated steel part is an aluminum alloy of the same material as the aluminum alloy part. The connecting piece is the composite bolt prepared above, and the number of them is 4 pieces / m 2 , and the composite bolt includes an aluminized steel shell (the aluminized layer therein is an aluminum-silicon alloy plating layer) and an aluminum-silicon alloy core arranged inside the aluminized steel shell.

[0093] Embodiment 2

[0094] The preparation method of the aluminum-steel composite provided in this embodiment (specifically, a steel-aluminum joint for a gearbox) includes the following steps:

[0095] Perform close-packed counterbore treatment on the aluminum alloy part. The step surface of the counterbore is provided with grooves to obtain a stepped hole. Punch and thread the aluminized steel part (the aluminized layer thereof is of the same material as the aluminum alloy part) according to the reference of the close-packed counterbore of the aluminum alloy part to obtain a through hole with threads. Use a hexagonal steel bolt with an aluminum alloy plating layer (of the same material as the aluminum alloy part) on the rod part (the steel used in the bolt is of the same material as the steel used in the aluminized steel part) to pass through the stepped hole of the aluminum alloy part and penetrate into the through hole of the aluminized steel part for threaded connection, so that the aluminized steel part and the aluminum alloy part are tightly connected without gaps. Apply a paste-like non-corrosive brazing flux to the gap between the hexagonal head of the steel bolt and the counterbore, and use a laser to emit a laser beam (the laser power is 2000W, and the spot diameter is 5mm) to conductively heat the hexagonal head of the steel bolt (the laser heating acts on the head of the steel bolt, and the laser heating is local heating, and no chemical metallurgical bonding is formed at the aluminum alloy-steel interface); after the non-corrosive brazing flux at the counterbore (i.e., the stepped hole) is completely melted, continuously fill in an aluminum alloy wire of the same material as the aluminum alloy part until the liquid level of the mixed melt is flush with the upper surface of the aluminum alloy part, stop heating, and cool to obtain the aluminum-steel composite.

[0096] Among them, the thickness of the aluminized layer in the aluminized steel part is 50μm. The paste-like non-corrosive brazing flux includes the following components by mass: 30 parts of ethanol, 40 parts of KF-AlF3 brazing flux, and 30 parts of CsF-AlF3 brazing flux. The power of the laser is 2000W, and the spot diameter is 5mm. The diameter of the aluminum alloy wire is 1.5mm.

[0097] The aluminum-steel composite provided in this embodiment is a steel-aluminum joint for a gearbox, which includes a connected aluminum alloy part and an aluminized steel part, and the aluminum alloy part and the aluminized steel part are connected by a connecting piece; the aluminized layer in the aluminized steel part is an aluminum alloy layer of the same material as the aluminum alloy part. The connecting piece is a hexagonal steel bolt with an aluminum alloy plating layer on the rod part, and the number of them is 4 pieces / m 2, the head of the steel bolt is arranged inside the aluminum alloy part, and a filling layer is arranged between the head of the steel bolt and the aluminum alloy part, and the filling layer is aluminum alloy.

[0098] Example 3

[0099] The preparation method of the aluminum-steel composite part (specifically an aluminum-steel composite plate) provided in this embodiment includes the following steps:

[0100] Perform close-packed counterbore treatment on the aluminum alloy part (in the shape of a flat plate). The step surface of the counterbore is provided with grooves to obtain a stepped hole. Punch and tap the galvanized steel part (the material of its galvanized layer is metallic zinc, and this galvanized steel part is in the shape of a flat plate, hereinafter simply referred to as "galvanized steel plate") according to the reference of the close-packed counterbore of the aluminum alloy part to obtain a through hole with threads. Use a hexagonal steel bolt (the material of the bolt is the same as the steel used in the galvanized steel plate) to pass through the stepped hole of the aluminum alloy part (the distance between the screw rod of the steel bolt and the stepped hole is 0.1 mm), and penetrate into the through hole of the galvanized steel plate and be threadedly connected with the galvanized steel plate, so that the galvanized steel plate and the aluminum alloy part are tightly connected without gaps. Apply a paste-like non-corrosive flux to the gap between the hexagonal head of the steel bolt and the counterbore, and then use a heat conduction device (constant temperature heating plate) to conductively heat the connected steel-aluminum plate (the conductive heating acting on the connected steel-aluminum plate can cause chemical metallurgical bonding at the aluminum alloy-steel interface); after the non-corrosive flux at the counterbore (i.e., the stepped hole) is completely melted, continuously fill in metallic zinc wire inward until the liquid level of the mixed melt is flush with the upper surface of the aluminum alloy part, stop heating, and cool to obtain the aluminum-steel composite part.

[0101] Among them, the thickness of the galvanized layer in the galvanized steel plate is 80 μm. The paste-like non-corrosive flux includes the following components by mass fraction: 40 parts of ethanol, 10 parts of KF-AlF3 flux, and 50 parts of CsF-AlF3 flux. The heat conduction device is a constant temperature heating plate, which consists of a steel workbench, heating tubes and a temperature control system. The diameter of the metallic zinc wire is 1 mm.

[0102] The aluminum-steel composite part provided in this embodiment is an aluminum-steel composite plate used as a train floor, which includes a connected aluminum alloy part (aluminum alloy plate) and a galvanized steel plate (i.e., the galvanized steel part). The aluminum alloy part and the galvanized steel plate are connected not only by a connecting piece but also by metallurgical bonding; the galvanized layer in the galvanized steel plate is metallic zinc (i.e., zinc element). The connecting piece is a steel bolt, and the number of them is 4 pieces / m 2 , the head of the steel bolt is arranged inside the aluminum alloy part, and a filling layer is arranged between the head of the steel bolt and the aluminum alloy part, and the filling layer is formed by metallic zinc.

[0103] Example 4

[0104] The preparation method of the aluminum-steel composite part (specifically, an aluminum-steel composite plate) provided in this embodiment includes the following steps:

[0105] Perform close-packed counterbore treatment on the aluminum alloy part (in the shape of a flat plate, i.e., an aluminum alloy plate). The stepped surface of the counterbore is provided with a groove to obtain a stepped hole. Punch and tap the galvanized steel plate (the material of its galvanized layer is zinc alloy Zn98Al2, and this galvanized steel part is in the shape of a flat plate, hereinafter simply referred to as "galvanized steel plate") according to the reference of the close-packed counterbore of the aluminum alloy part to obtain a through hole with threads. Insert the fixing bolts into the stepped hole and the through hole in sequence, fasten and connect the aluminum alloy part and the galvanized steel plate, and apply a paste-like non-corrosive flux to the gap position between the head of the fixing bolt and the stepped hole. Use a heat conduction device (constant temperature heating plate) to conduct heat on the connected steel-aluminum plate. After the non-corrosive flux at the counterbore (i.e., the stepped hole) is completely melted, stop heating and take out the fixing bolts after natural cooling. At this time, metallurgical bonding has occurred between the aluminum alloy part and the galvanized steel part, forming a permanent connection. Since holes will be left on the aluminum alloy part and the galvanized steel part after the fixing bolts are taken out, for the sake of beauty and convenience of subsequent processing such as rolling and reducing surface defects on the plate, a metal filling rod is filled into the holes after the fixing bolts are taken out. Among them, the metal filling rod includes an aluminum alloy area and a steel area integrally connected. The aluminum alloy area includes a head and a non-threaded screw rod connected thereto. The material of the aluminum alloy area is the same aluminum alloy as that of the aluminum alloy part; the steel area is a threaded screw rod, the material of the steel in the steel area is the same as the material of the steel used in the galvanized steel plate, and the material of the zinc alloy coating in the steel area is the same as the material of the zinc alloy plated on the galvanized steel plate. When filling, place the steel area of the metal filling rod in the through hole and the aluminum alloy area in the stepped hole; the inner diameter of the stepped hole is larger than the diameter of the head of the aluminum alloy area, and the head is higher than the upper plane (top surface or upper surface) of the stepped hole.

[0106] After filling the metal filling rod into the stepped hole and the through hole, heat for hole filling. During the heating process, use laser heating to remelt the aluminum alloy area. Stop laser heating after the aluminum alloy area is completely melted. After the metal filling rod is heated, the head and the non-threaded screw rod of the aluminum alloy area are completely fused with the aluminum alloy part to form an integral body; the steel in the steel area does not melt, while the coating metal melts (the zinc alloy melts) to fill the gap and form a metallurgical connection with the steel part. Then cool naturally and mill and remove the laser heating riser to obtain the aluminum-steel composite part.

[0107] Among them, the thickness of the galvanized layer in the galvanized steel plate is 30μm. The paste-like non-corrosive flux includes the following components by mass: 30 parts of ethanol, 20 parts of KF-AlF3 flux, and 50 parts of CsF-AlF3 flux. The heat conduction device is a constant temperature heating plate, which consists of a steel workbench, a heating tube, and a temperature control system. The power of the laser is 1000W, and the spot diameter is 5mm.

[0108] The aluminum-steel composite provided in this embodiment is an aluminum-steel composite plate used as a train floor, which includes an aluminum alloy part and a galvanized steel plate connected by metallurgical bonding (the aluminum alloy part and the galvanized steel plate are connected by metallurgical bonding, and the filling rod only serves to fill the holes); the galvanized layer in the galvanized steel plate is a zinc alloy. The connecting piece is a metal filling rod, and the number thereof is 4 pieces / m 2 .

[0109] Comparative Example 1

[0110] The preparation method of the aluminum-steel composite provided in this comparative example is basically the same as that of Example 1, except that the composite bolt is replaced with a commercially available hexagon bolt Q235, and its specifications are M12*1.75*40.

[0111] Comparative Example 2

[0112] The preparation method of the aluminum-steel composite plate provided in this comparative example is basically the same as that of Example 2, except that the paste-like non-corrosive brazing flux is not fully coated and the aluminum alloy wire is not filled.

[0113] Experimental Example 1

[0114] Through the transverse vibration experiment, the anti-loosening performance of the aluminum-steel composites (steel-aluminum joints) prepared in Examples 1-2 and Comparative Examples 1-2 was detected. The initial pre-tightening forces were 12 KN and 20 KN respectively, the vibration frequency was 10 Hz, the vibration period was 3000 cycles, and the transverse vibration amplitude was ±1.0 mm. The detection results are shown in Table 1.

[0115] Among them, the experimental equipment was a Junker transverse vibration testing machine. To avoid errors, each transverse vibration experiment was performed 3 times, and then the average value was taken.

[0116] Table 1 Detection results of the anti-loosening performance of the aluminum-steel composite (steel-aluminum joint)

[0117]

[0118] As can be seen from Table 1, the anti-loosening performance of Examples 1 and 2 is significantly better than that of Comparative Examples 1 and 2. It can be seen that the aluminum-steel composite (steel-aluminum joint) provided by the present invention is difficult to loosen, and its anti-deformation and vibration capabilities are greatly enhanced.

[0119] Experimental Example 2

[0120] The T-peel test was carried out on the bonding strength of the aluminum-steel composite parts obtained in Example 4. The equipment used for the test was a SHIMADZU AG-X universal testing machine, and the experiment was carried out at a tensile speed of 10 mm / min according to the ASTM D1876-08 standard. The specimens with a width of 10 mm and a length of 100 mm were cut along the rolling direction of the plate by wire cutting. After the two sides of the specimens (perpendicular to the width direction) were polished smoothly with 600# sandpaper, one end of the specimen was peeled off with a clamp, and the peeling length was 15 mm to facilitate clamping on the testing machine. Three specimens were prepared for each type of plate under each condition, and their average values were taken to ensure the accuracy of the measurement results. The peeling strength was calculated using the formula: Peeling strength = F / W. Where F is the tensile force of the testing machine (N), W is the width of the specimen (10 mm), and the unit of the peeling strength is N / mm.

[0121] Meanwhile, the T-peel test was carried out on the aluminum-steel composite parts obtained by explosion welding, diffusion welding, rolling method, and continuous casting and rolling method respectively according to the above method. The test results are shown in Table 2.

[0122] Table 2 Detection results of the peeling strength of the aluminum-steel composite parts obtained by various composite methods

[0123] Composite method Explosion welding Diffusion welding Rolling method Continuous casting and rolling method Example 4 Peel strength (N / mm) 11.2 14.1 9.6 13.6 16.4

[0124] It can be seen that the peeling strength of the aluminum-steel composite parts obtained in Example 4 is significantly higher than that of the aluminum-steel composite parts obtained by conventional explosion welding, diffusion welding, rolling method, and continuous casting and rolling method.

[0125] Although the present invention has been illustrated and described with reference to specific embodiments, it should be realized that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; those of ordinary skill in the art should understand that: without departing from the spirit and scope of the present invention, the technical solutions described in the foregoing embodiments can be modified, or some or all of the technical features can be equivalently replaced; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such replacements and modifications within the scope of the present invention are included in the appended claims.

Claims

1. A preparation method of an aluminum-steel composite part, characterized in that, The aluminum-steel composite part includes an aluminum alloy part and a coated steel part that are connected to each other through a connecting piece and metallurgical bonding; wherein, the coating in the coated steel part includes at least one of an aluminum alloy layer, a metallic zinc layer, and a zinc alloy layer; The connecting piece includes at least one steel bolt and at least one composite bolt; wherein, the composite bolt includes an aluminized steel shell and an aluminum core disposed inside the aluminized steel shell; the aluminized layer in the aluminized steel shell includes a metallic aluminum coating and / or an aluminum alloy coating; the aluminum core includes a metallic aluminum core and / or an aluminum alloy core; When the aluminum alloy part and the coated steel part are connected at least through the steel bolt, the head of the steel bolt is disposed inside the aluminum alloy part, and a filling layer is disposed between the head of the steel bolt and the aluminum alloy part, and the filling layer is mainly formed by a coating metal; Wherein, the coating metal includes at least one of an aluminum alloy, metallic zinc, and a zinc alloy; The preparation method of the aluminum-steel composite part includes: Performing counterboring on the aluminum alloy part to obtain a stepped hole 1, and performing drilling and tapping on the coated steel part to obtain a through hole 1 with a thread; sequentially passing the steel bolt through the stepped hole 1 and the through hole 1 to complete the connection of the aluminum alloy part and the coated steel part; then filling a brazing flux in the gap between the head of the steel bolt and the aluminum alloy part, heating the brazing flux to melt it, then adding a coating metal thereto and melting it, and then cooling to obtain the aluminum-steel composite part; Performing counterboring on the aluminum alloy part to obtain a stepped hole 2, and performing drilling and tapping on the coated steel part to obtain a through hole 2 with a thread; sequentially passing the composite bolt through the stepped hole 2 and the through hole 2 to complete the connection of the aluminum alloy part and the coated steel part to obtain the aluminum-steel composite part; Performing counterboring on the aluminum alloy part to obtain a stepped hole 3, and performing drilling and tapping on the coated steel part to obtain a through hole 3 with a thread; sequentially passing a fixing bolt through the stepped hole 3 and the through hole 3, and adding a brazing flux into the gap formed between the head of the fixing bolt and the stepped hole 3, heating to completely melt it, then stopping heating, so that the aluminum alloy part and the coated steel part are connected to each other through metallurgical bonding, and then taking out the fixing bolt to obtain the aluminum-steel composite part; after taking out the fixing bolt, it further includes the steps of filling a metal filling rod into the stepped hole 3 and the through hole 3, heating for hole filling, and then cooling, wherein, the metal filling rod includes an aluminum alloy area and a steel area that are integrally connected, the aluminum alloy area includes a head and a screw rod without a thread, and the steel area is a screw rod with a thread.

2. The preparation method of the aluminum-steel composite part according to claim 1, characterized in that The number of the connecting pieces is not less than 4 pieces / m 2 .

3. The preparation method of the aluminum-steel composite part according to claim 1, characterized in that, The thickness of the coating in the coated steel part is 20 - 100 μm.

4. The preparation method of the aluminum-steel composite part according to claim 1, characterized in that, The thickness of the aluminized steel shell in the composite bolt is 0.5 - 2 mm.

5. The preparation method of the aluminum-steel composite part according to claim 1, characterized in that, The aluminum alloy core in the composite bolt includes at least one of an aluminum-silicon alloy core, an aluminum-copper alloy, an aluminum-manganese alloy, and an aluminum-magnesium-silicon alloy.

6. The preparation method of the aluminum-steel composite part according to claim 1, characterized in that, A brazing flux is further added during the formation of the filling layer, and the brazing flux includes the following components by mass parts: 30 - 40 parts of ethanol, 10 - 60 parts of KF-AlF3 brazing flux, and 10 - 60 parts of CsF-AlF3 brazing flux.

7. The preparation method of the aluminum-steel composite part according to claim 1, characterized in that The preparation method of the composite bolt comprises the following steps: Thread rolling treatment is carried out on a steel shell in the shape of a bolt with a cavity inside, so that threads are formed on the rod part of the steel shell; the steel shell after the thread rolling treatment is subjected to hot dip aluminizing treatment to form an aluminized layer on the outer surface of the steel shell, and an aluminized steel shell is obtained; After a flux is coated in the cavity of the aluminized steel shell, metallic aluminum and / or aluminum alloy are placed in the cavity and heated to melt the metallic aluminum and / or aluminum alloy to form an aluminum core, and then it is cooled to obtain the composite bolt.

8. The preparation method of the aluminum-steel composite part according to claim 7, characterized in that, In the process of the hot dip aluminizing treatment, the temperature of the aluminum melt used is 690-740 °C, and the dipping time is 30-50 s.

9. The preparation method of the aluminum-steel composite part according to claim 8, characterized in that, A fluxing agent is covered on the surface of the aluminum melt.

10. The preparation method of the aluminum-steel composite part according to claim 9, characterized in that, The fluxing agent comprises the following components by mass parts: 20-40 parts of NaCl, 20-40 parts of KCl, 10-20 parts of NaAlF6 and 10-20 parts of Na2SiF6.

11. Application of the aluminum-steel composite part prepared by the preparation method of the aluminum-steel composite part according to any one of claims 1 to 10 in transportation tools and building materials.

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