Friction stir welding preparation method of carbon nanotube reinforced aluminum steel composite plate and composite plate

Abstract

The invention discloses a friction stir welding preparation method of a carbon nanotube reinforced aluminum steel composite plate and the composite plate. The friction stir welding preparation method comprises the following steps: welding an aluminum alloy base material and a steel base material by adopting friction stir welding; before friction stir welding, steps are machined on the upper end face and the lower end face of the butt joint face of an aluminum alloy base material and the butt joint face of a steel base material in advance respectively, the butt joint face is machined to be in a sawtooth shape, the aluminum alloy base material and the steel base material form the complete steps, and the butt joint face of the aluminum alloy base material and the butt joint face of the steel base material are tightly meshed. Carbon nanotube coatings are respectively laid on an upper complete step and a lower complete step formed by the aluminum alloy base material and the steel base material in advance; a stirring needle of a friction stir welding tool adopted by the friction stir welding technology is machined into a sawtooth shape matched with the butt joint face in advance. The composite board has higher performance in the aspects of connection strength, toughness and the like, and when the composite board prepared through the method is applied to shipbuilding and ocean platform construction, hidden danger of safety construction can be avoided, and the construction efficiency is improved.

Description

Technical Field

[0001] The invention relates to the technical field of manufacturing heterogeneous metal composite materials, and in particular to a friction stir welding preparation method for a carbon nanotube reinforced aluminum-steel composite plate and the composite plate. Background Art

[0002] Replacing steel with aluminum in marine engineering and shipbuilding is an important way to achieve low carbon and environmental protection. For example, in shipbuilding and offshore platform construction, aluminum alloy is used for superstructure and steel plate is used for substructure, so as to reduce the overall structural weight and reduce fuel consumption during the life cycle of the ship.

[0003] This brings about the connection problem between the aluminum alloy superstructure and the steel substructure. Due to the obvious differences in the thermal physical properties of aluminum alloy and steel, common TIG, MIG, MAG, and laser welding all have problems with low connection joint quality and substandard weld performance.

[0004] At present, the prevention of aluminum-steel layered composite transition joints is prepared by explosive welding. Due to the limitations of explosive welding itself, the connection strength of the above aluminum-steel layered composite joints is low, generally not exceeding 100MPa, and it is easy to crack during use. At the same time, when welding the actual ship / platform with the upper aluminum building and the lower steel structure, the welding process and heat input requirements are strict. The high welding temperature (above 300℃) will seriously damage the strength of the composite joint prepared by explosive welding, resulting in a rapid decline in its performance, which brings great safety hazards to ships / offshore platforms. At the same time, the production process of explosive welding has very strict requirements on safety, and its production process is difficult to automate.

[0005] Friction stir welding is a solid-state welding method invented in 1991. It is suitable for welding light alloys, especially aluminum alloys. For the welding of ferrous metals such as steel and aluminum alloys, studies have shown that intermetallic compounds will be generated at the connection interface. The right amount of intermetallic compounds is conducive to improving the performance of aluminum-steel friction stir welds. However, when there are more of these compounds, the essential characteristics of their embrittlement will cause brittle fractures in the welds. At the same time, due to the uneven heat input on the upper and lower sides of the welded plate, the deformation is large and requires shape correction, which increases the cost. Severe deformation will lead to the scrapping of the weld.

[0006] Carbon nanotubes are a one-dimensional quantum material with a special structure. Their radial dimensions are in the nanometer range, and their axial dimensions are in the micrometer range. They are coaxial circular tubes composed of several to dozens of layers of carbon atoms arranged in a hexagonal pattern. Since their discovery in 1991, they have shown broad application prospects due to their unique structure and excellent mechanical, electrical and chemical properties. Their tensile strength can reach 50 to 200 GPa, which is 100 times that of steel, and their density is only 1 / 6 of that of steel. They have good flexibility, and their aspect ratio can reach over 1000:1, so they are called "super fibers." Summary of the invention

[0007] The purpose of the present invention is to solve the above problems and to provide a friction stir welding preparation method for carbon nanotube reinforced aluminum-steel composite plates.

[0008] To achieve the above purpose, the technical solution provided by the present invention is:

[0009] A friction stir welding preparation method for a carbon nanotube reinforced aluminum-steel composite plate, wherein the aluminum alloy base material and the steel base material are welded by friction stir welding;

[0010] Before the friction stir welding, the first steps are respectively processed on the upper and lower end surfaces of the butt joint surface of the aluminum alloy base material, and the butt joint surface is processed into a first serrated shape. The second steps are respectively processed on the upper and lower end surfaces of the butt joint surface of the steel base material, and the butt joint surface is processed into a second serrated shape. The first step and the second step have the same height, so that the aluminum alloy base material and the steel base material form a complete step. The second serrated shape matches the first serrated shape, so that the butt joint surface of the aluminum alloy base material and the butt joint surface of the steel base material are closely meshed.

[0011] The carbon nanotube coating is pre-laid on the upper and lower complete steps formed by the aluminum alloy parent material and the steel parent material, respectively. The carbon nanotube coating is pre-processed into a long strip shape that matches the shape of the complete step formed by the aluminum alloy parent material and the steel parent material, so that the carbon nanotube coating can be embedded in the step cavity to form an integral structure with the aluminum alloy parent material and the steel parent material.

[0012] The stirring pin of the friction stir welding tool used in the friction stir welding technology is pre-processed into a sawtooth shape, and the sawtooth shape of the stirring pin corresponds to the first sawtooth shape and the second sawtooth shape of the butt joint surface.

[0013] The aluminum alloy parent material is 5xxx or 6xxx aluminum alloy; the thickness tolerance of the aluminum alloy parent material and the steel parent material is within ±0.05mm, the thickness range is 5 to 20mm, and the width is 30 to 100mm.

[0014] To optimize the above technical solutions, the specific measures taken also include:

[0015] The carbon nanotube coating is a single-layer or multi-layer carbon nanotube structure; the upper and lower steps of the parent metal are 0.3mm-1mm deep and 3mm-10mm wide respectively; the upper and lower steps of the carbon nanotube coating and the parent metal are interference fit, the thickness of the carbon nanotube coating is 0.1mm-0.3mm greater than the step depth, and the width is the same as the step width.

[0016] The sawtooth parameters of aluminum alloy and steel base materials include the angle of the sawtooth and the side length of the sawtooth. The angle of the sawtooth is 30-50°, and the side length of the sawtooth is 1 / 5-1 / 3 of the thickness of the composite plate to be welded. 板厚 .

[0017] The friction stir welding tool used in the friction stir welding technology is a double-shoulder friction stir welding tool, and the parameters are as follows:

[0018] The length of the stirring needle l 针长 and the thickness of the composite plate to be welded h 板厚 The relationship is l 针长 ≈h 板厚 -(0.2~0.3)mm; its upper shoulder diameter D 上轴肩 and the diameter D of the lower shoulder 下轴肩 is the plate thickness h 板厚 2-3 times;

[0019] The serration parameters of the stirring needle are the same as those of the aluminum alloy base material and the steel base material;

[0020] The diameter of the stirring needle D 针直径 ≈ the thickness of the composite plate to be welded h 板厚 ; The parameters of the thread on the stirring needle include the thread depth d 螺纹深度 、Thread width w 螺纹 , thread length l 螺纹 , the distance between two adjacent threads d 螺纹距离 ; Among them, when l 针长 When d is 4.7~10mm, 螺纹深度 0.3~0.8mm, l 针长 When d is 10~15mm, 螺纹深度 0.8~2mm, l 针长 >15mm, d 螺纹深度 2~4mm; thread width w 螺纹 =0.8~1d 螺纹深度 , thread pitch d 螺纹距离 1.5~3d 螺纹深度 .

[0021] The upper part and the lower part of the stirring pin of the friction stir welding tool are both provided with threads, and the thread directions of the upper thread and the lower thread of the stirring pin are opposite.

[0022] During the friction stir welding process, the aluminum alloy base material is located on the forward side; during the friction stir welding process, the center line of the stirring needle is biased towards the aluminum alloy base material side, and the offset range is 2 to 5 mm.

[0023] The rotation speed of the friction stir welding tool is generally 200 to 1500 rpm, and the feed speed is generally 100 to 1000 mm / min.

[0024] The angle of the thread on the stirring needle of the friction stir welding tool is between 10 and 40 degrees, the thread depth on the stirring needle is generally between 1 and 4 mm, and the diameter D of the stirring needle is 针直径 ≈ the thickness of the composite plate to be welded h 板厚 .

[0025] The friction stir welding preparation method of the carbon nanotube reinforced aluminum-steel composite plate specifically comprises the following steps:

[0026] The aluminum alloy base metal and the steel base metal to be welded are pre-milled to form upper and lower end face steps and saw teeth of the butt joint surface;

[0027] Determine the diameter of the upper and lower shoulders of the double-shouldered friction stir welding tool and the size parameters of the stirring needle according to the thickness of the aluminum alloy parent material and the steel parent material to be welded;

[0028] According to the sawtooth shape of the butt surface processed between the aluminum alloy base material and the steel base material, the corresponding shape of the stirring pin sawtooth is determined, and according to the size of the stirring pin, the morphology parameters of the thread on it are determined;

[0029] According to the steps of the upper and lower end surfaces of the aluminum alloy parent material and the steel parent material, the carbon nanotube coating is processed to match the integral step cavity formed by the upper and lower end surfaces of the aluminum alloy parent material and the steel parent material;

[0030] Assembling and fastening the milled aluminum alloy base material, steel base material and carbon nanotube cladding;

[0031] The double-shoulder friction stir welding tool is driven by the external welding execution structure to enter from the side of the butt joint surface and perform double-shoulder welding operation on the butt joint surface to be welded according to the set rotation speed, feed speed and offset parameters, and ensure that the aluminum alloy base material is located on the forward side during welding;

[0032] At the end of welding, the double-shoulder friction stir welding tool leaves the weld from the other side of the butt surface, completing the entire welding operation.

[0033] The present invention also protects the composite plate prepared by the friction stir welding preparation method of the carbon nanotube reinforced steel composite plate.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] The present invention replaces the traditional three-layer composite plate structure of aluminum-aluminum-steel or aluminum-titanium-steel using explosive welding, and adopts direct aluminum-steel butt welding. The sum of the width of the aluminum plate + the width of the steel plate before butt welding is the thickness index of the final product, which can save a lot of materials.

[0036] The present invention solves the problem that when the traditional explosion welding technology is used in the construction of shipbuilding and offshore platforms, the welding temperature of the explosion-welded composite plate is limited, and the temperature at the composite joint needs to be monitored at all times, which affects the construction process. The thickness of the composite plate structure prepared by the traditional explosion welding technology is limited. During construction welding, if the welding temperature exceeds more than 300 degrees, the performance of the explosion-welded composite plate structure will be seriously affected, which poses a great safety hazard. Therefore, during construction, it is necessary to monitor the temperature at the composite explosion-welded composite plate structure at all times, and continuous welding operations cannot be performed in order to control the temperature, which affects the construction process. The composite plate prepared by the method of the present invention is not limited to the size limited by the explosion welding technology, so it has no effect on the composite plate when construction is carried out at the welding distance, which can avoid safety hazards and ensure normal construction.

[0037] The present invention pre-processes steps on the upper and lower end faces of the butt joint of the aluminum alloy parent material and the steel parent material before friction stir welding, processes the butt joint into a sawtooth shape, forms a complete step between the aluminum alloy parent material and the steel parent material, and achieves tight meshing between the butt joint of the aluminum alloy parent material and the steel parent material. In addition, carbon nanotube coatings are pre-laid on the upper and lower complete steps formed between the aluminum alloy parent material and the steel parent material, and the carbon nanotube coatings are pre-processed into long strips matching the shape of the steps. The carbon nanotube coatings can be embedded in the step cavity to form an integral structure with the aluminum alloy parent material and the steel parent material. The stirring needle of the friction stir welding tool used in the friction stir welding technology is also pre-processed into a sawtooth shape. The shape of the stirring needle is matched with the serrated shape of the butt joint surface of the aluminum alloy parent material and the steel parent material, thereby increasing the stirring effect of the butt joint surface material and promoting the full stirring and fragmentation of the intermetallic compound (IMC) formed during welding; the high strength and high toughness of the carbon nanotube coating are matched, thereby enhancing the fluidity of the parent metal material during welding, inhibiting the formation of intermetallic compounds, and eliminating defects such as holes formed by the mismatch of the fluidity of the aluminum alloy parent material and the steel parent material; at the same time, the dispersed carbon nanotubes serve as nano-scale particle reinforcement items to enhance the connection strength and toughness of the connection joint; the performance of the composite plate of the present invention can reach 2-3 times the performance of the explosive welding composite plate.

[0038] Preferably, the friction stir welding tool used in the friction stir welding technology of the present invention is a double-shouldered friction stir welding tool. The upper and lower shoulders generate heat simultaneously on the upper and lower surfaces during welding, which optimizes the heat input in the thickness direction of the joint, so that the welding deformations of the upper and lower surfaces can almost offset each other, reducing the post-weld deformation of the component; furthermore, during welding, the carbon nanotube coating and the upper and lower shoulders of the stirring tool are in direct contact, and the heat generation and temperature in this area are the largest, which reduces the welding temperature of the aluminum alloy base material and the steel base material at the upper and lower shoulders, which is beneficial to controlling the formation of intermetallic compounds.

[0039] The upsetting force in the floating double-shoulder friction stir welding process adopted by the present invention is zero, which reduces the rigidity requirement for the welding actuator, is beneficial to the subsequent assembly, and further the configuration and cost of the corresponding welding equipment can be greatly reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 : Schematic diagram of the processing structure of the friction stir welding preparation method of the carbon nanotube reinforced aluminum-steel composite plate of the present invention.

[0041] Figure 2 : Schematic diagram of the processing structure of the double-shoulder friction stir welding tool.

[0042] In the figure: 101 upper shaft shoulder; 103 lower shaft shoulder; 2 aluminum alloy base material; 3 steel base material; 401 upper carbon nanotube coating; 402 lower carbon nanotube coating; 102 serrated stirring needle; 1021 upper thread; 1022 lower thread. DETAILED DESCRIPTION

[0043] The above contents of the present invention are further described in detail below in the form of embodiments, but this should not be understood as the scope of the above subject matter of the present invention being limited to the following embodiments, and all technologies realized based on the above contents of the present invention belong to the scope of the present invention.

[0044] The present invention provides a method for preparing a carbon nanotube reinforced aluminum-steel composite plate by friction stir welding and the composite plate. Figure 1 As shown, the aluminum alloy base material 2 and the steel base material 3 are welded by friction stir welding;

[0045] Before the friction stir welding, the first steps are respectively processed on the upper and lower end faces of the butt joint surface of the aluminum alloy base material 2, and the butt joint surface is processed into a first serrated shape. The second steps are respectively processed on the upper and lower end faces of the butt joint surface of the steel base material 3, and the butt joint surface is processed into a second serrated shape. The first step and the second step have the same height, so that the aluminum alloy base material 2 and the steel base material 3 form a complete step. The second serrated shape matches the first serrated shape, so that the butt joint surface of the aluminum alloy base material 2 and the butt joint surface of the steel base material 3 are closely meshed.

[0046] In addition, carbon nanotube coatings are preliminarily laid on the upper and lower complete steps formed by the aluminum alloy base material 2 and the steel base material 3, respectively, to form an upper carbon nanotube coating 401 and a lower carbon nanotube coating 402. The carbon nanotube coatings are preliminarily processed into a long strip shape that matches the shape of the complete step formed by the aluminum alloy base material 2 and the steel base material 3, so that the carbon nanotube coatings can be embedded in the step cavity to form an integral structure with the aluminum alloy base material 2 and the steel base material 3.

[0047] The stirring pin of the friction stir welding tool used in the friction stir welding technology is pre-processed into a serrated shape, and the serrated shape of the stirring pin corresponds to the first serrated shape and the second serrated shape of the butt surface.

[0048] In some embodiments, the friction stir welding tool used in the friction stir welding technique is a double-shoulder friction stir welding tool.

[0049] In some embodiments, the aluminum alloy base material 2 uses 5xxx or 6xxx aluminum alloy; the thickness tolerance of the aluminum alloy base material 2 and the steel base material 3 is within ±0.05mm, and the thickness range is 5 to 20mm; the width is 30 to 100mm; and the length can be 3 to 10m without excessive restrictions.

[0050] The carbon nanotube coating can be produced by arc discharge method or chemical vapor deposition method, and its purity is generally higher than 95%.

[0051] The carbon nanotube coating is a single-layer or multi-layer carbon nanotube structure; the upper and lower steps of the base metal are 0.3mm-1mm deep and 3mm-10mm wide respectively; the upper and lower steps of the carbon nanotube coating and the base metal are interference fit, the thickness of the carbon nanotube coating is 0.1mm-0.3mm greater than the step depth, and the width is the same as the step width.

[0052] The sawtooth parameters of aluminum alloy and steel base materials include the angle of the sawtooth and the side length of the sawtooth. The angle of the sawtooth is 30-50°, and the side length of the sawtooth is 1 / 5-1 / 3 of the thickness of the composite plate to be welded. 板厚 .

[0053] In some embodiments, Figure 2 As shown, the friction stir welding tool used in the friction stir welding technology is a double-shoulder friction stir welding tool, and the parameters are as follows:

[0054] The length of the stirring needle l 针长 and the thickness of the composite plate to be welded h 板厚 The relationship is l 针长 ≈h 板厚 -(0.2~0.3)mm; its upper shoulder diameter D 上轴肩 and the diameter D of the lower shoulder 下轴肩 is the plate thickness h板厚 2-3 times;

[0055] The serration parameters of the stirring needle are the same as those of the aluminum alloy base material and the steel base material;

[0056] The diameter of the stirring needle D 针直径 ≈ the thickness of the composite plate to be welded h 板厚 ; The parameters of the thread on the stirring needle include the thread depth d 螺纹深度 、Thread width w 螺纹 , thread length l 螺纹 , the distance between two adjacent threads d 螺纹距离 ; Among them, when l 针长 When d is 4.7~10mm, 螺纹深度 0.3~0.8mm, l 针长 When d is 10~15mm, 螺纹深度 0.8~2mm, l 针长 >15mm, d 螺纹深度 2~4mm; thread width w 螺纹 =0.8~1d 螺纹深度 , thread pitch d 螺纹距离 1.5~3d 螺纹深度 .

[0057] The upper shaft shoulder 101, the lower shaft shoulder 102 and the stirring needle are generally made of tungsten-rhenium alloy, polycrystalline cubic boron nitride (PCBN), precipitation-strengthened nickel-based high-temperature alloy, high-hardness hot-working die steel and other materials.

[0058] In some embodiments, both the upper and lower portions of the stirring pin of the friction stir welding tool are provided with threads, and the thread directions of the upper thread 1021 and the lower thread 1022 of the stirring pin are opposite.

[0059] During the friction stir welding process, the aluminum alloy base material 2 is located on the forward side; during the friction stir welding process, the center line of the stirring needle is biased towards the aluminum alloy base material 2, and the offset range is 2 to 5 mm.

[0060] The rotation speed of the friction stir welding tool is 200 to 1500 rpm, and the feed speed is 100 to 1000 mm / min.

[0061] The friction stir welding preparation method of the carbon nanotube reinforced aluminum-steel composite plate and the composite plate specifically include the following steps:

[0062] The aluminum alloy base material 2 and the steel base material 3 to be welded are pre-milled to form upper and lower end face steps and saw teeth of the butt joint surface;

[0063] The diameters of the upper shoulder 101 and the lower shoulder 102 of the double-shouldered friction stir welding tool and the length parameters of the stirring needle are determined according to the thicknesses of the aluminum alloy base material 2 and the steel base material 3 to be welded;

[0064] According to the sawtooth parameters of the butt surface processed between the aluminum alloy base material 2 and the steel base material 3, the corresponding morphological parameters on the stirring needle are determined, including the shape and size of the sawtooth, the angle and depth of the thread;

[0065] According to the upper and lower end surface steps of the aluminum alloy base material 2 and the steel base material 3, the carbon nanotube coating is processed to match the integral step cavity formed by the upper and lower end surfaces of the aluminum alloy base material 2 and the steel base material 3;

[0066] Assembling and fastening the milled aluminum alloy base material 2, the steel base material 3 and the carbon nanotube coating;

[0067] The double-shoulder friction stir welding tool is driven by the external welding execution structure to enter from the side of the butt joint surface and perform double-shoulder welding operation on the butt joint surface to be welded according to the set rotation speed, feed speed and offset parameters, and ensure that the aluminum alloy base material 2 is located on the forward side during welding;

[0068] At the end of welding, the double-shoulder friction stir welding tool leaves the weld from the other side of the butt surface, completing the entire welding operation.

[0069] The present invention is further described in detail below in conjunction with specific embodiments:

[0070] Example 1

[0071] Take 8mm5083 aluminum alloy + 8mmCCSB steel as an example:

[0072] The diameter D of the upper shoulder 101 of the floating double shoulder is determined according to the thickness of the welded 8mm5083 aluminum alloy plate and 8mmCCSB steel plate. 上轴肩101 18mm, D 下轴肩102 is 18mm, the length of the stirring needle is l 针长 The diameter of the stirring needle is 5.75mm and the root diameter of the stirring needle is 8mm.

[0073] The sawtooth angle of the butt joint surface of the aluminum alloy plate and the steel plate is 45°, the sawtooth side length is 2 mm, the sawtooth stirring pin 102 has the same sawtooth shape, and the thread parameters on the stirring pin 102 are: thread depth d 螺纹深度 is 0.4mm, the thread width is 0.35mm, and the thread spacing d 螺纹距离 The thread is 1mm, the upper part is right-handed and the lower part is left-handed.

[0074] According to the parameters of the steps and tooth shapes of the upper and lower end surfaces of the aluminum alloy base material 2 and the steel base material 3, the upper and lower end surfaces and the butt surfaces of the aluminum alloy plate, the steel plate, etc. are milled using CNC equipment to machine steps with a depth of 0.5 mm and a width of 4 mm on the upper and lower end surfaces, and the butt surfaces are machined with corresponding serrated shapes.

[0075] According to the stepped shape of the upper and lower end surfaces of the aluminum alloy mother material 2 and the steel mother material 3, the carbon nanotube coating is processed by CNC equipment with a depth of 0.6mm and a length of 4mm, so that the steps at the upper and lower end surfaces of the aluminum alloy mother material 2 and the steel mother material 3 are interference fit.

[0076] The aluminum alloy plate base material, the steel base material 3 and the cladding metal plate that have been milled are assembled and fastened.

[0077] Driven by the external welding execution structure, the floating double-shoulder welding tool enters from the side of the butt joint and applies double-shoulder welding operation to the butt joint to be welded according to the set parameters such as rotation speed 750rpm, feed speed 450mm / min, offset (biased towards aluminum alloy 3.5mm), etc., ensuring that the steel base material 3 is located on the forward side during welding.

[0078] The floating dual-shoulder stirring tool leaves the weld from the other side of the butt joint to complete the entire welding operation.

[0079] Example 2

[0080] Take 12mm6061 aluminum alloy + 12mm304 stainless steel as an example:

[0081] The diameter D of the upper shoulder 101 of the floating double shoulder is determined according to the thickness of the 12mm6061 aluminum alloy plate and the 12mm304 stainless steel plate to be welded. 上轴肩101 26mm, D 下轴肩102 is 26mm, the length of the stirring needle is l 针长 The diameter of the stirring needle is 11.75mm and the root diameter of the stirring needle is 12mm.

[0082] The sawtooth angle of the butt joint surface of the aluminum alloy plate and the steel plate is 35°, the sawtooth side length is 3mm, the sawtooth stirring pin 102 has the same sawtooth shape, and the thread parameters on the stirring pin 102 are: thread depth d 螺纹深度 is 0.9mm, thread width is 0.8mm, thread pitch d 螺纹距离 The thread is 1.8 mm, with the upper part being right-handed and the lower part being left-handed.

[0083] According to the parameters of the steps and tooth shapes of the upper and lower end surfaces of the aluminum alloy base material 2 and the steel base material 3, the upper and lower end surfaces and the butt surfaces of the aluminum alloy plate, the steel plate, etc. are milled using CNC equipment to machine steps with a depth of 0.7mm and a width of 8mm on the upper and lower end surfaces, and the butt surfaces are machined with corresponding serrated shapes.

[0084] According to the step shape of the upper and lower end surfaces of the aluminum alloy mother material 2 and the steel mother material 3, the carbon nanotube coating is processed using CNC equipment with a depth of 0.8mm and a length of 8mm to match the steps at the upper and lower end surfaces of the aluminum alloy mother material 2 and the steel mother material 3 after being matched.

[0085] The aluminum alloy plate base material, the steel base material 3 and the cladding metal plate that have been milled are assembled and fastened.

[0086] Driven by the external welding execution structure, the floating double-shoulder welding tool enters from the side of the butt joint and applies double-shoulder welding operation to the butt joint to be welded according to the set parameters such as rotation speed of 350rpm, feed speed of 200mm / min, offset (biased towards aluminum alloy 4.2mm), etc., ensuring that the steel base material 3 is located on the forward side during welding.

[0087] The floating dual-shoulder stirring tool leaves the weld from the other side of the butt joint to complete the entire welding operation.

[0088] Comparative Example 1

[0089] The main method of this comparative example is the same as that of Example 1, except that: the stirring needle has serrations but no oblique threads. After welding, it can be found that the butt surfaces of the aluminum and steel can be connected, but the mutual stirring and fusion effect of the two materials at the welding joint is not as good as that of Example 1. This is mainly because the oblique threads can improve the fluidity of the materials. During the welding process, the materials of the upper and lower parts can be transported to the middle part of the joint through the oblique threads, thereby improving the fluidity of the materials and improving the performance of the joint.

[0090] Comparative Example 2

[0091] The main method of this comparative example is the same as that of Example 1, except that the stirring needle has no serrations but has oblique threads. After welding, it can be found that defects are prone to occur at the joint of aluminum and steel. This is because there is no serration morphology on the stirring needle corresponding to the butt surface. During the welding process, the aluminum and steel materials in some areas are not stirred by the stirring needle, and will not move with the rotation of the stirring needle, resulting in material shortage in the joint, which is prone to defects such as holes or tunnels, reducing the performance of the joint.

[0092] Comparative Example 3

[0093] The main method of this comparative example is the same as that of Example 1, except that the stirring needle has no serrations and no oblique threads. After welding, it can be found that the joints at the aluminum-steel joints are more likely to have defects such as holes and tunnels. This is because the stirring needle does not have a serrated morphology corresponding to the butt surface. During the welding process, the aluminum and steel materials in some areas are not stirred by the stirring needle, and will not move with the rotation of the stirring needle, resulting in material shortage in the joints, which makes it easy for defects such as holes or tunnels to appear. At the same time, the lack of oblique threads leads to poor stirring of the materials in the upper and lower parts during welding, and defects such as holes are easy to appear in the center of the welded joint.

[0094] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any technician familiar with the profession, without departing from the scope of the technical solution of the present invention, according to the technical essence of the present invention, any simple modification, equivalent replacement and improvement made to the above embodiment still falls within the protection scope of the technical solution of the present invention.

Claims

1. A friction stir welding preparation method for carbon nanotube reinforced aluminum-steel composite plates, characterized in that: The aluminum alloy base metal and the steel base metal are welded by friction stir welding; Before the friction stir welding, the first steps are respectively processed on the upper and lower end surfaces of the butt joint surface of the aluminum alloy base material, and the butt joint surface is processed into a first serrated shape. The second steps are respectively processed on the upper and lower end surfaces of the butt joint surface of the steel base material, and the butt joint surface is processed into a second serrated shape. The first step and the second step have the same height, so that the aluminum alloy base material and the steel base material form a complete step. The second serrated shape matches the first serrated shape, so that the butt joint surface of the aluminum alloy base material and the butt joint surface of the steel base material are closely meshed. The carbon nanotube coating is pre-laid on the upper and lower complete steps formed by the aluminum alloy parent material and the steel parent material, respectively. The carbon nanotube coating is pre-processed into a long strip shape that matches the shape of the complete step formed by the aluminum alloy parent material and the steel parent material, so that the carbon nanotube coating can be embedded in the step cavity to form an integral structure with the aluminum alloy parent material and the steel parent material. The stirring pin of the friction stir welding tool used in the friction stir welding technology is pre-processed into a sawtooth shape, and the sawtooth shape of the stirring pin corresponds to the first sawtooth shape and the second sawtooth shape of the butt joint surface.

2. The friction stir welding preparation method for carbon nanotube reinforced aluminum-steel composite plate according to claim 1, characterized in that: The aluminum alloy parent material is 5xxx or 6xxx aluminum alloy; the thickness tolerance of the aluminum alloy parent material and the steel parent material is within ±0.05mm, the thickness range is 5 to 20mm, and the width is 30 to 100mm.

3. The friction stir welding preparation method of carbon nanotube reinforced aluminum-steel composite plate according to claim 1, characterized in that: The carbon nanotube coating is a single-layer or multi-layer carbon nanotube structure; the upper and lower steps of the parent metal are 0.3mm-1mm deep and 3mm-10mm wide respectively; the upper and lower steps of the carbon nanotube coating and the parent metal are interference fit, the thickness of the carbon nanotube coating is 0.1mm-0.3mm greater than the step depth, and the width is the same as the step width.

4. The friction stir welding preparation method of carbon nanotube reinforced aluminum-steel composite plate according to claim 1, characterized in that: The sawtooth parameters of aluminum alloy and steel base materials include the angle of the sawtooth and the side length of the sawtooth. The angle of the sawtooth is 30-50°, and the side length of the sawtooth is 1 / 5-1 / 3 of the thickness of the composite plate to be welded. 板厚 .

5. The friction stir welding preparation method of carbon nanotube reinforced aluminum-steel composite plate according to claim 1, characterized in that: The friction stir welding tool used in the friction stir welding technology is a double-shoulder friction stir welding tool, and the parameters are as follows: The length of the stirring needle l 针长 and the thickness of the composite plate to be welded h 板厚 The relationship is l 针长 ≈h 板厚 -(0.2~0.3)mm; its upper shoulder diameter D 上轴肩 and the diameter D of the lower shoulder 下轴肩 is the plate thickness h 板厚 2-3 times; The serration parameters of the stirring needle are the same as those of the aluminum alloy base material and the steel base material; The diameter of the stirring needle D 针直径 ≈ the thickness of the composite plate to be welded h 板厚 ; The parameters of the thread on the stirring needle include the thread depth d 螺纹深度 、Thread width w 螺纹 , thread length l 螺纹 , the distance between two adjacent threads d 螺纹距离 ; Among them, when l 针长 When d is 4.7~10mm, 螺纹深度 0.3~0.8mm, l 针长 When d is 10~15mm, 螺纹深度 0.8~2mm, l 针长 >15mm, d 螺纹深度 2~4mm; thread width w 螺纹 =0.8~1d 螺纹深度 , thread pitch d 螺纹距离 1.5~3d 螺纹深度 .

6. The friction stir welding preparation method of carbon nanotube reinforced aluminum-steel composite plate according to claim 1, characterized in that: The friction stir welding preparation method for carbon nanotube reinforced aluminum-steel composite plates according to claim 1 is characterized in that the upper and lower parts of the stirring needle of the friction stir welding tool are both provided with threads, and the thread directions of the upper thread of the stirring needle are opposite to those of the lower thread.

7. The friction stir welding preparation method of carbon nanotube reinforced aluminum-steel composite plate according to claim 1, characterized in that: During the friction stir welding process, the aluminum alloy base material is located on the forward side; during the friction stir welding process, the center line of the stirring needle is biased towards the aluminum alloy base material side, and the offset range is 2 to 5 mm.

8. The friction stir welding preparation method for carbon nanotube reinforced aluminum-steel composite plate according to claim 1, characterized in that: The rotation speed of the friction stir welding tool is 200 to 1500 rpm, and the feed speed is 100 to 1000 mm / min.

9. The friction stir welding preparation method for carbon nanotube reinforced aluminum-steel composite plate according to claim 1, characterized in that: The following steps are involved: The aluminum alloy base metal and the steel base metal to be welded are pre-milled to form upper and lower end face steps and saw teeth of the butt joint surface; Determine the diameter of the upper and lower shoulders of the double-shouldered friction stir welding tool and the size parameters of the stirring needle according to the thickness of the aluminum alloy parent material and the steel parent material to be welded; According to the sawtooth shape of the butt surface processed between the aluminum alloy base material and the steel base material, the corresponding shape of the stirring pin sawtooth is determined, and according to the size of the stirring pin, the morphology parameters of the thread on it are determined; According to the steps of the upper and lower end surfaces of the aluminum alloy mother material and the steel mother material, the carbon nanotube coating is processed to match the integral step cavity formed by the upper and lower end surfaces of the aluminum alloy mother material and the steel mother material; Assembling and fastening the milled aluminum alloy base material, steel base material and carbon nanotube cladding; The double-shoulder friction stir welding tool is driven by the external welding execution structure to enter from the side of the butt joint surface and perform double-shoulder welding operation on the butt joint surface to be welded according to the set rotation speed, feed speed and offset parameters, and ensure that the aluminum alloy base material is located on the forward side during welding; At the end of welding, the double-shoulder friction stir welding tool leaves the weld from the other side of the butt surface, completing the entire welding operation.

10. A composite plate prepared by the friction stir welding preparation method for a carbon nanotube reinforced aluminum-steel composite plate according to any one of claims 1 to 9.

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