Foamed aluminum filled hollow metal tube with metallurgical bonding interface and manufacturing method thereof

Abstract

The invention discloses a foamed aluminum filled hollow metal tube with a metallurgical bonding interface and a manufacturing method thereof, and belongs to the technical field of foamed aluminum filling materials. According to the method, the surface of the metal outer pipe is subjected to modified aqueous solution assisted plating, liquid metal filling and foaming are conducted, the metal inner pipe is positioned and placed, ultrasonic treatment is conducted on liquid foamed aluminum, further foaming is conducted, metallurgical bonding can be achieved between the outer wall of the metal pipe and the core layer, and the mechanical property stability of the foamed aluminum filled composite structure is improved. Meanwhile, ultrasonic vibration is applied to the interface between the foamed aluminum melt and the metal pipe, interface element diffusion is promoted, the interface bonding strength is improved, the hollow metal pipe filled with the foamed aluminum is prepared in a low-cost and short-process mode, and the application scene of the foamed aluminum composite structure is widened.

Description

Technical Field

[0001] The invention belongs to the technical field of foam aluminum filling materials, and in particular relates to a foam aluminum filled hollow metal tube with a metallurgical bonding interface and a preparation method thereof. Background Art

[0002] Thin-walled metal tubes filled with foam materials are a type of highly efficient impact-resistant, energy-absorbing and shock-absorbing components, with the characteristics of light weight, high specific strength, and large damping and energy absorption. In recent years, domestic and foreign scholars have proposed foam-filled tubes with various composite structures such as round tubes, square tubes, double round tubes and multi-cell tubes in the study of thin-walled metals filled with foam materials. Foam-filled materials include foamed aluminum, foamed steel, foamed alloy, foamed concrete and polyurethane foam. Among them, the structural forms of foamed aluminum are diverse, such as open-cell foamed aluminum, closed-cell foamed aluminum, gradient-distributed foamed aluminum, and polyurethane-filled foamed aluminum.

[0003] Recently, foam sandwich structures have become a hot topic in the research of foam aluminum filled composite structures due to their excellent resistance to explosion loads, and have been widely used in aerospace, military and other fields. The excellent performance of this type of structure is mainly due to the porous structure characteristics of the foam core, which can effectively enhance its load-bearing and energy absorption capacity. In addition, traditional explosion-proof devices usually have the disadvantages of low energy absorption efficiency and heavy weight, which is particularly insufficient when facing modern safety challenges. The demand for lightweight and more powerful explosion-proof containers is growing. In this context, sandwich tubes have gradually attracted attention as a new type of structural design. It can not only enhance the explosion resistance of explosion-proof containers, but also effectively protect personnel or equipment from the impact of internal explosions. Compared with integral explosion-proof tubes, foam sandwich tubes can undergo extreme plastic deformation under nearly constant platform stress due to their unique sandwich structure, thereby providing better energy absorption performance.

[0004] At present, the preparation method of hollow metal tubes filled with foam aluminum in industry is mainly through gluing, that is, foam aluminum is made into a large billet, processed into the required size and shape, pressed into the hollow tube, and the core layer and the outer tube are connected by gluing. Although the gluing method has a simple process flow, it has strict requirements on the service environment of the filling tube and cannot be used in a humid and high temperature environment, which limits the use scenarios of foam aluminum sandwich metal tubes. Summary of the invention

[0005] In view of the above technical problems, the purpose of the present invention is to provide a hollow metal tube filled with foam aluminum having a metallurgical bonding interface and a preparation method thereof, wherein the surface is modified with an aqueous solution to assist plating, and liquid metal filling, foaming, metal inner tube positioning and ultrasonic treatment are performed to achieve metallurgical bonding of the foam aluminum with the metal inner tube and the metal outer tube respectively, while achieving near-forming and continuous production of the hollow metal tube filled with foam aluminum.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] A method for preparing a hollow metal tube filled with foamed aluminum having a metallurgical bonding interface, specifically comprising the following steps:

[0008] S1: Preprocessing

[0009] S1.1 Treatment of the metal outer tube: after removing the oxide on the inner wall of the metal outer tube, the metal outer tube is assisted in plating with a surface modifier aqueous solution and then dried to obtain a metal outer tube to be filled; wherein the metal outer tube is one of a steel tube, an aluminum tube, and an aluminum alloy tube;

[0010] S1.2 Preheating: Preheat the metal outer tube, metal inner tube, mold and ultrasonic probe to be filled respectively and keep them ready for use; the preheating temperature of the metal outer tube is 150℃~200℃, and the insulation time is ≥10min; the preheating temperature of the metal inner tube is 590℃~700℃, and the insulation time is ≥15min; the preheating temperature of the mold is 650℃~750℃; the preheating temperature of the ultrasonic probe is 600℃~700℃;

[0011] S1.3 Melting of the aluminum foam to be foamed: melting the aluminum foam melt raw material and then keeping it warm to obtain the aluminum melt to be foamed;

[0012] S2: Filling of molten aluminum

[0013] Add the aluminum melt to be foamed into the preheating mold, and then place the preheated metal outer tube in the preheating mold to ensure that the aluminum melt to be foamed fills the metal outer tube, and keep it warm for 5 minutes to 10 minutes to achieve a metallurgical bonding interface between the aluminum melt and the metal outer tube;

[0014] S3: Foaming

[0015] Adding a viscosity enhancer Ca to the aluminum melt to be foamed, and continuously stirring the aluminum melt to obtain a uniformly stirred metal melt;

[0016] Adding a foaming agent TiH2 to the uniformly stirred metal melt, stirring and dispersing the metal melt uniformly, and then keeping the temperature for 30s to 120s to obtain a metal tube filled with liquid foam aluminum; wherein the foaming temperature is maintained at 590°C to 700°C;

[0017] S4: Positioning of the metal inner tube

[0018] The preheated metal inner tube is fixed at the target position inside the metal outer tube by a self-made mold;

[0019] S5: Sonication

[0020] Inserting a circular ultrasonic probe into liquid aluminum foam for ultrasonic treatment to promote the formation of a metallurgical bonding interface between the aluminum foam and the metal inner tube, the ultrasonic frequency being 19.5kHz to 20.3kHz;

[0021] S6: Post-processing

[0022] The metal double tube filled with foam aluminum is cooled to the solidus temperature of the foam aluminum, and the excess foam aluminum is cut off to obtain a foam aluminum filled hollow metal tube with a metallurgical bonding interface.

[0023] In the method, the time from the addition of TiH2 to the end of ultrasonication should be completed within 8 minutes to 10 minutes.

[0024] In the method, when the metal outer tube is an aluminum alloy tube, after the aluminum melt to be foamed is added to the preheating mold, the viscosity enhancer is first added to the aluminum melt to be foamed and stirred evenly, and after the temperature is lowered to 590°C to 610°C, the metal outer tube is placed in the preheating mold.

[0025] In step S1.1, the surface modifier is selected from one or more chlorides or fluorides, preferably one or more of zinc chloride, ammonium chloride, potassium chloride, potassium fluoride, and potassium fluorozirconate; the plating assist temperature is 70°C to 90°C, and the plating assist time is 5min to 15min.

[0026] In step S1.2, the ultrasonic probe is a ring-shaped ultrasonic probe;

[0027] In the above-mentioned S1.3, the raw material of the foamed aluminum melt is pure aluminum or aluminum alloy, the melting temperature is 700° C. to 750° C., and the insulation time is 20 min to 30 min.

[0028] In step S2, the temperature of the aluminum melt to be foamed is stably controlled at 590°C to 720°C, and the metal outer tube and the aluminum melt to be foamed are metallurgically bonded;

[0029] In step S3, the continuous stirring process after adding the thickener is as follows: inserting a stirring paddle into the metal outer tube for stirring, the stirring speed is 700 r / min to 1500 r / min, and the stirring time is 5 min to 15 min;

[0030] In step S3, the amount of the viscosity enhancer Ca added is 1% to 3% by mass of the foamed aluminum melt raw material used;

[0031] In step S3, the amount of TiH2 added is 1.0% to 2.0% of the mass percentage of the metal melt, and the particle size is 10μm to 50μm; TiH2 needs to be oxidized, and the treatment method is to oxidize TiH2 in air at 400℃ to 500℃ for 1h to 4h.

[0032] In step S3, stirring and dispersing uniformly is performed by inserting a stirring paddle into the metal tube for stirring, with a stirring speed of 1500 r / min to 3000 r / min and a stirring time of 1 min to 4 min.

[0033] In step S4, the metal inner tube is a steel tube or an aluminum tube with a bottom seal;

[0034] In step S5, the temperature of the liquid aluminum foam is stably controlled at a temperature within the range of 590°C to 700°C; the temperature of the ultrasonic probe is 0 to 30°C higher than the temperature of the liquid aluminum foam;

[0035] Furthermore, in step S5, the ultrasonic treatment power is 500W to 1500W; and the ultrasonic treatment time is 0.5min to 3min.

[0036] The method must be carried out strictly in accordance with the above steps.

[0037] A hollow metal tube filled with foamed aluminum and having a metallurgical bonding interface is prepared by the method.

[0038] When the double-layer metal tube is filled with foamed aluminum, the present invention adopts a hot-dip plating process to make the outer tube and the aluminum liquid metallurgically bonded, and then adds a foaming agent for heat preservation and foaming. In order to achieve the metallurgical bonding of the metal inner tube and the foamed aluminum, ultrasound is applied during the foaming process. High-intensity ultrasound will produce strong cavitation and acoustic streaming effects, that is, the formation, growth, pulsation and collapse of microbubbles in the metal melt under the action of cyclic high-intensity ultrasound (thousands of microbubbles will be formed, expanding during the negative pressure cycle and collapsing during the positive pressure cycle). At the end of a cavitation cycle, the implosion and collapse of the microbubbles will produce transient micro "hot spots", the pressure of which can be as high as about 1000atm, and the heating and cooling rates exceed 1010K / s. Transient cavitation can generate a sufficiently strong implosion impact force to promote the diffusion of atoms at the solid-liquid interface and enhance the wettability of the foamed aluminum melt to the metal of the tube body. At the same time, the oxide film on the metal tube wall will hinder the wetting of the melt to the metal of the tube body, as well as the diffusion of elements in the liquid-solid composite process. In order to prevent the ultrasonic wave from affecting the stability of the foamed aluminum during the violent foaming, so as to prevent the problem that the ultrasonic wave is too strong to destroy the pore structure and cannot foam, and the ultrasonic wave is too weak to cause the interface to fail to metallurgically bond, the ultrasonic frequency of the ultrasonic wave is controlled to be 19.5kHz-20.3kHz, and the ultrasonic power is 500W-1500W, so as to ensure the atomic diffusion between the foam core and the pipe without destroying the stability of the foam structure; the ultrasonic time is 0.5min-3min, so as to ensure the expansion of the foamed aluminum and promote the interface bonding, so as to complete the metallurgical bonding of the inner pipe and the core layer.

[0039] The modifier used in the present invention is selected from one or more of chlorides or fluorides, preferably one or more of zinc chloride, ammonium chloride, potassium chloride, and potassium fluoride. The surface modifier aqueous solution used in the present invention has good cleaning, wetting, activation, and the ability to prevent the surface of the steel part from reoxidation. At the same time, it also plays a role in reducing the surface tension of the aluminum liquid and reducing the generation of aluminum slag.

[0040] Compared with the prior art, the present invention is beneficial in that:

[0041] (1) The present invention prepares a hollow metal tube filled with foamed aluminum by surface-modifying the metal outer tube with an aqueous solution-assisted plating, and then performing liquid metal filling, foaming, positioning and placing of the metal inner tube, and ultrasonic treatment. The outer wall and the core layer of the hollow metal tube can achieve metallurgical bonding, thereby improving the mechanical property stability of the composite structure filled with foamed aluminum and broadening the application scenarios of the composite structure filled with foamed aluminum.

[0042] (2) Applying ultrasonic vibration to the interface between the foam aluminum melt and the metal tube promotes the diffusion of interface elements to form a metal compound layer, which is beneficial to improving the interface bonding strength.

[0043] (3) The hollow metal tube filled with foamed aluminum can be prepared at low cost and in a short process, which is suitable for industrial continuous production. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a macroscopic cross-sectional view of a hollow metal tube (eccentric) filled with foamed aluminum having a metallurgical bonding interface prepared in Comparative Example 1 of the present invention;

[0045] Figure 2 is a macroscopic cross-sectional view of a hollow metal tube (eccentric) filled with foamed aluminum having a metallurgical bonding interface obtained in Example 1 of the present invention;

[0046] Figure 3 This is a SEM image of the metal outer tube / core layer interface of the hollow metal tube filled with foamed aluminum having a metallurgical bonding interface prepared in Example 1 of the present invention;

[0047] Figure 4 This is a SEM image of the metal inner tube / core layer interface of a hollow metal tube filled with foam aluminum having a metallurgical bonding interface prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0048] The metal inner tube used in the embodiment of the present invention is a steel tube or an aluminum tube with a bottom seal; the metal outer tube is one of a steel tube, an aluminum tube, and an aluminum alloy tube. When the metal outer tube is an aluminum alloy tube, after adding the foamed aluminum metal melt to be foamed into the preheating mold, first add the tackifier to the foamed aluminum metal melt to be foamed, stir evenly, cool to 590°C to 610°C, and then place the metal outer tube in the preheating mold.

[0049] In the embodiment of the present invention, a BN coating is coated on the outer wall of the metal outer tube, thereby reducing the adhesion of the foamed aluminum liquid on the outer wall of the metal outer tube.

[0050] In the embodiment of the present invention, the metal inner tube used is a steel tube or an aluminum tube with a bottom seal.

[0051] In the embodiment of the present invention, when the viscosity enhancer is added to the foam aluminum raw material, the temperature of the foam aluminum raw material is 660° C. to 720° C. When the temperature of the foam aluminum raw material is lower than 660° C., calcium cannot be effectively melted into the melt; when the temperature is too high, the melt will be oxidized.

[0052] The method for preparing the hollow metal tube filled with foam aluminum having a metallurgical bonding interface provided by the present invention must be carried out strictly according to the steps in each embodiment.

[0053] The present invention is further described in detail below in conjunction with specific embodiments and drawings.

[0054] Example 1

[0055] A method for preparing a composite structure of a hollow metal tube filled with foamed aluminum having a metallurgical bonding interface is carried out according to the following steps:

[0056] No. 20 steel was selected as the material of the metal outer tube. After removing the oxide film on the inner wall of the metal outer tube, a mixed solution of NH4Cl and ZnCl2 with a mass concentration of 15wt.% was used as a surface modifier aqueous solution. The metal outer tube was placed in the surface modifier aqueous solution and immersed for 5 minutes at 80°C to assist plating of the inner wall of the metal outer tube. It was then dried to obtain a steel tube to be filled.

[0057] The preheating temperature of the mold in the heating furnace is controlled at 750℃, the preheating temperature of the steel pipe to be filled is controlled at 150℃, and the preheating and heat preservation time is controlled at 15min; 6061 aluminum alloy is selected as the metal inner tube material, the preheating temperature of the inner tube is controlled at 590℃, and the preheating and heat preservation time is controlled at 18min; the annular ultrasonic probe is preheated at 620℃. The outer tube, inner tube, mold, and annular ultrasonic probe are preheated separately and set aside.

[0058] AlSi10 was used as the foam matrix, and after being melted at 750°C and kept warm for 30 minutes, the aluminum melt to be foamed was obtained.

[0059] Add the aluminum melt to be foamed into the preheated mold, and then place the preheated metal outer tube into the preheated mold to ensure that the steel tube is filled with the aluminum melt to be foamed. Keep it warm for 5 minutes. At this time, the temperature of the aluminum melt should be stably controlled at 720°C.

[0060] Add calcium, a viscosity enhancer, to the aluminum melt, with calcium accounting for 2.0% of the mass percentage of AlSi10 used. Continue to stir the calcium evenly (speed 700r / min, time 10min), and add the foaming agent TiH2 after the temperature drops to 660℃, and stir and disperse evenly at a stirring speed of 1500r / min and a stirring time of 1min. Add titanium hydride, which accounts for 1.2% of the mass percentage of the sum of the mass of AlSi10 and Ca, with a particle size of 48μm. Titanium hydride TiH2 needs to be oxidized in air at 400℃ for 1h before being added to the aluminum melt. Keep the foam melt in the mold warm and foam it, and control the temperature at 690℃ for 1min.

[0061] The metal inner tube is fixed at an eccentric position inside the outer tube by a homemade mold.

[0062] Then, the preheated annular ultrasonic probe was inserted into the aluminum melt to ensure that the ultrasonic treatment temperature of the melt was 600°C, and then the ultrasonic generator was automatically searched to stabilize the frequency at 20.2kHz. The aluminum melt was ultrasonically treated for 0.5 minutes at a power of 1500W.

[0063] The semi-finished hollow metal tube filled with foam aluminum is taken out from the mold; the excess foam aluminum layer at both ends of the semi-finished hollow metal tube filled with foam aluminum is cut off to obtain a foam aluminum filled hollow metal tube (eccentric) with a metallurgical bonding interface. Figure 2 The metallurgical interface of steel / aluminum (i.e. outer tube / core layer) and aluminum / aluminum (i.e. inner tube / core layer) are as follows: Figure 3 , Figure 4 As shown. Figure 3 It can be seen that the foam aluminum structure and the metal outer tube 20 steel are metallurgically bonded to form a metallurgical bonding compound layer of a certain thickness.

[0064] from Figure 4 It can be seen that a large number of needle-shaped Al-Si phases are distributed on one side of the foam aluminum, which is consistent with the foam core layer composition of AlSi10. The interface between the inner tube and the foam aluminum is smooth, complete and seamless, effectively achieving metallurgical bonding.

[0065] Example 2

[0066] A method for preparing a composite structure of a hollow metal tube filled with foamed aluminum having a metallurgical bonding interface is carried out according to the following steps:

[0067] Select No. 20 steel as the material of the metal outer tube, prepare a surface modifier aqueous solution with 15wt.% NH4Cl+20wt.% ZnCl2 and the remainder deionized water, place the metal outer tube in the surface modifier aqueous solution, set the immersion temperature to 78°C, and the immersion time is 5 minutes to assist plating on the inner wall of the metal outer tube, and then dry to obtain a steel tube to be filled.

[0068] The preheating temperature of the mold in the heating furnace is controlled at 730℃, the preheating temperature of the steel pipe to be filled is controlled at 160℃, and the preheating and heat preservation time is controlled at 21min; No. 20 steel is selected as the metal inner tube material, the preheating temperature of the inner tube is controlled at 680℃, and the preheating and heat preservation time is controlled at 20min; the annular ultrasonic probe is preheated at 710℃. The outer tube, inner tube, mold, and annular ultrasonic probe are preheated separately and put into use.

[0069] Pure aluminum is used as the foam matrix, and after melting at 720°C and keeping the temperature for 20 minutes, an aluminum melt to be foamed is obtained.

[0070] Add the aluminum foam metal melt to be foamed into the preheated mold, and then place the preheated metal outer tube into the preheated mold to ensure that the steel tube is filled with aluminum melt to be foamed, and keep it warm for 6 minutes. At this time, the temperature of the aluminum melt should be stably controlled at 690°C. Add the viscosity enhancer calcium into the aluminum melt, and the mass percentage of calcium is 2.5% of the aluminum used. Continue to stir the calcium evenly (speed 1500r / min, time 5min), and add the foaming agent TiH2 after the temperature drops to 680°C, stir and disperse evenly, the stirring speed is 2600r / min, and the stirring time is 4min. Add titanium hydride with a mass percentage of 1.0% of the sum of the mass of pure aluminum and Ca, and a particle size of 45μm. Titanium hydride TiH2 needs to be oxidized in air at 480°C for 2h before adding it, and then added to the aluminum melt. Keep the foam melt in the mold warm and foam, control the temperature at 680°C, and keep it warm for 90s.

[0071] The metal inner tube is fixed at an eccentric position inside the outer tube by a homemade mold.

[0072] Then, the preheated annular ultrasonic probe was inserted into the aluminum melt to ensure that the ultrasonic treatment temperature of the melt was 690°C, and then the ultrasonic generator was automatically searched to stabilize the frequency at 20.2kHz. The aluminum melt was ultrasonically treated for 1 minute at a power of 1000W.

[0073] The semi-finished hollow metal tube filled with foam aluminum is taken out from the mold; the excess foam aluminum layer at both ends of the semi-finished hollow metal tube filled with foam aluminum is cut off to obtain a composite structure of the foam aluminum filled metal tube with a metallurgical bonding interface.

[0074] Example 3

[0075] A method for preparing a composite structure of a hollow metal tube filled with foamed aluminum having a metallurgical bonding interface is carried out according to the following steps:

[0076] Select No. 20 steel as the material of the metal outer tube, prepare a surface modifier aqueous solution with 25wt.% NH4Cl+20wt.% ZnCl2 and the remainder deionized water, place the metal outer tube in the surface modifier aqueous solution, set the immersion temperature to 85°C, and the immersion time is 5 minutes to assist plating on the inner wall of the metal outer tube, and then dry to obtain a steel tube to be filled.

[0077] The mold preheating temperature in the heating furnace is controlled at 700℃, the preheating temperature of the steel pipe to be filled is controlled at 170℃, and the preheating and heat preservation time is controlled at 25min; No. 45 steel is selected as the metal inner tube material, the preheating temperature of the inner tube is controlled at 670℃, and the preheating and heat preservation time is controlled at 25min; the annular ultrasonic probe is preheated at 700℃. The outer tube, inner tube, mold, and annular ultrasonic probe are preheated separately and put into use.

[0078] AlSi10 was used as the foam matrix, and after being melted at 700°C and kept warm for 30 minutes, the aluminum melt to be foamed was obtained.

[0079] Add the aluminum melt to be foamed into the preheated mold, and then place the preheated metal outer tube into the preheated mold to ensure that the steel tube is filled with the aluminum melt to be foamed. Keep it warm for 7 minutes. At this time, the aluminum melt temperature should be stably controlled at 700℃.

[0080] Add calcium, a viscosity enhancer, to the aluminum melt, with calcium accounting for 2.0% of the mass percentage of the aluminum used. Continue to stir the calcium evenly (speed 1200r / min, time 15min), and add the foaming agent TiH2 after the temperature drops to 650℃, and stir and disperse evenly at a stirring speed of 3000r / min and a stirring time of 2min. Add titanium hydride, which accounts for 1.5% of the mass percentage of the sum of the mass of AlSi10 and Ca, with a particle size of 35μm. Titanium hydride TiH2 needs to be oxidized in air at 440℃ for 2h before being added to the aluminum melt. Keep the foam melt in the mold warm and foam it, and control the temperature at 670℃ for 50s.

[0081] The metal inner tube is fixed at an eccentric position inside the outer tube by a homemade mold.

[0082] Then, the preheated annular ultrasonic probe was inserted into the aluminum melt to ensure that the ultrasonic treatment temperature of the melt was 670°C, and then the ultrasonic generator was automatically searched to stabilize the frequency at 20.0kHz. The aluminum melt was ultrasonically treated for 3 minutes at a power of 1200W.

[0083] The semi-finished hollow metal tube filled with foam aluminum is taken out from the mold; the excess foam aluminum layer at both ends of the semi-finished hollow metal tube filled with foam aluminum is cut off to obtain a composite structure of the foam aluminum filled metal tube with a metallurgical bonding interface.

[0084] Example 4

[0085] A method for preparing a composite structure of a hollow metal tube filled with foamed aluminum having a metallurgical bonding interface is carried out according to the following steps:

[0086] Select 304 stainless steel as the material of the metal outer tube, prepare a surface modifier aqueous solution with 25wt.% NH4Cl+25wt.% ZnCl2 and the remainder deionized water, place the metal outer tube in the surface modifier aqueous solution, set the immersion temperature to 75°C, and the immersion time for 10 minutes to assist plating the inner wall of the metal outer tube, and then dry it to obtain a steel tube to be filled.

[0087] The preheating temperature of the mold in the heating furnace is controlled at 680℃, the preheating temperature of the steel pipe to be filled is controlled at 180℃, and the preheating and heat preservation time is controlled at 20min; No. 45 steel is selected as the metal inner tube material, the preheating temperature of the inner tube is controlled at 650℃, and the preheating and heat preservation time is controlled at 20min; the annular ultrasonic probe is preheated at 670℃. The outer tube, inner tube, mold, and annular ultrasonic probe are preheated separately and put into use.

[0088] With AlSi2 as the foam matrix, the aluminum melt to be foamed is obtained after melting at 730°C and keeping warm for 25 minutes.

[0089] Add the aluminum foam metal melt to be foamed into the preheated mold, and then place the preheated metal outer tube into the preheated mold to ensure that the steel tube is filled with aluminum melt to be foamed. Keep it warm for 9 minutes. At this time, the temperature of the aluminum melt should be stably controlled at 660°C. Add the viscosity enhancer calcium into the aluminum melt, and the mass percentage of calcium is 2.0% of the aluminum used. Continue to stir the calcium evenly (speed 800r / min, time 15min), and add the foaming agent TiH2 after the temperature drops to 640°C. Stir and disperse evenly, the stirring speed is 2200r / min, and the stirring time is 3min. Add titanium hydride with a mass percentage of 2.0% of the sum of the mass of AlSi2 and Ca, and the particle size is 25μm. Titanium hydride TiH2 needs to be oxidized in air at 500°C for 3h before adding it, and then added to the aluminum melt. Keep the foam melt in the mold warm and foam, control the temperature at 640°C, and keep it warm for 80s.

[0090] The metal inner tube is fixed at an eccentric position inside the outer tube by a homemade mold.

[0091] Then, the preheated annular ultrasonic probe was inserted into the aluminum melt to ensure that the ultrasonic treatment temperature of the melt was 650°C, and then the ultrasonic generator was automatically searched to stabilize the frequency at 20.0kHz. The aluminum melt was ultrasonically treated for 2 minutes with a power of 800W.

[0092] The semi-finished hollow metal tube filled with foam aluminum is taken out from the mold; the excess foam aluminum layer at both ends of the semi-finished hollow metal tube filled with foam aluminum is cut off to obtain a composite structure of the foam aluminum filled metal tube with a metallurgical bonding interface.

[0093] Example 5

[0094] A method for preparing a composite structure of a hollow metal tube filled with foamed aluminum having a metallurgical bonding interface is carried out according to the following steps:

[0095] Select 6061 aluminum as the material of the metal outer tube, prepare a surface modifier aqueous solution with 10wt.% K2ZrF6 and the remainder deionized water, place the metal outer tube in the surface modifier aqueous solution, set the immersion temperature to 75°C, and immerse for 10 minutes to assist plating the inner wall of the metal outer tube, and then dry it to obtain a steel tube to be filled.

[0096] The mold preheating temperature in the heating furnace is controlled at 650℃; the preheating temperature of the steel pipe to be filled is controlled at 200℃, and the preheating and heat preservation time is controlled at 25min; 6061 aluminum alloy is selected as the metal inner tube material, the preheating temperature of the inner tube is controlled at 595℃, and the preheating and heat preservation time is controlled at 25min; the annular ultrasonic probe is preheated at 600℃. The outer tube, inner tube, mold, and annular ultrasonic probe are preheated separately and put into use.

[0097] AlSi7 was used as the foam matrix, and after melting at 710°C and keeping warm for 20 minutes, the aluminum melt to be foamed was obtained.

[0098] Add calcium, a viscosity enhancer, to the aluminum melt in the graphite crucible, with calcium accounting for 2.5% of the mass percentage of the aluminum to be foamed. Continue to stir the calcium evenly (speed 1500r / min, time 8min), then add the aluminum foam metal melt to be foamed to the mold in the heating furnace, and then place the preheated metal outer tube in the preheating mold to ensure that the aluminum foam metal melt to be foamed fills the metal tube to be filled, and keep warm for 10min. At this time, the temperature of the aluminum melt should be stably controlled at 590℃. Add the foaming agent TiH2, stir and disperse evenly, the stirring speed is 1800r / min, and the stirring time is 2min. Add titanium hydride with a mass percentage of 1.0% of the sum of the mass of AlSi7 and Ca, and a particle size of 12μm. Titanium hydride TiH2 needs to be oxidized in air at 450℃ for 4h before adding it, and then added to the aluminum melt. The foam melt in the mold is insulated and foamed, and the temperature is controlled at 640℃ for 50s.

[0099] The metal inner tube is fixed at an eccentric position inside the outer tube by a homemade mold.

[0100] Then, the preheated annular ultrasonic probe was inserted into the aluminum melt to ensure that the ultrasonic treatment temperature of the melt was 595°C, and then the ultrasonic generator was automatically searched to stabilize the frequency at 20.0kHz. The aluminum melt was ultrasonically treated for 1min20s, and the power of the ultrasonic treatment was 500W.

[0101] The semi-finished hollow metal tube filled with foam aluminum is taken out from the mold; the excess foam aluminum layer at both ends of the semi-finished hollow metal tube filled with foam aluminum is cut off to obtain a composite structure of the foam aluminum filled metal tube with a metallurgical bonding interface.

[0102] Comparative Example 1

[0103] No. 20 steel was selected as the material for the metal outer tube. After removing the oxide film on the inner wall of the metal outer tube, a mixed solution of NH4Cl and ZnCl2 with a mass concentration of 15wt.% was used as a surface modifier aqueous solution. The metal outer tube was placed in the surface modifier aqueous solution and immersed for 5 minutes at 80°C to assist plating of the inner wall of the metal outer tube, and then dried.

[0104] With AlSi10 as the foam matrix, aluminum melt was obtained after melting at 750°C and keeping warm for 30 minutes.

[0105] The preheating temperature of the mold in the heating furnace is controlled at 750℃, the preheating temperature of the steel pipe to be filled is controlled at 150℃, and the preheating and heat preservation time is controlled at 15min. Then, the aluminum melt to be foamed is added to the mold in the heating furnace, and then the preheated metal outer tube is placed in the preheating mold to ensure that the steel pipe is filled with the aluminum melt to be foamed. The heat preservation is carried out for 5min, at which time the aluminum melt temperature should be stably controlled at 720℃.

[0106] Add calcium, a viscosity enhancer, to the aluminum melt, with calcium accounting for 2.0% of the mass percentage of the aluminum alloy used. Continue to stir the calcium evenly (speed 700r / min, time 10min), and add the foaming agent TiH2 after the temperature drops to 660℃, and stir and disperse evenly, with a stirring speed of 1500r / min and a stirring time of 1min. Add titanium hydride, which accounts for 1.2% of the mass percentage of the sum of the mass of AlSi10 and Ca, with a particle size of 48μm. Titanium hydride TiH2 needs to be oxidized in air at 400℃ for 1h before being added to the aluminum melt. Keep the foam melt in the mold warm and foam it, and control the temperature at 690℃ for 1min.

[0107] 6061 is selected as the material of the metal inner tube, wherein the preheating temperature of the inner tube is controlled at 590°C, and the preheating and insulation time is controlled at 18 minutes; the metal inner tube is fixed at an eccentric position inside the outer tube by a homemade mold.

[0108] The semi-finished hollow metal tube filled with foam aluminum is taken out from the mold; the excess foam aluminum layer at both ends of the semi-finished hollow metal tube filled with foam aluminum is cut off to obtain a foam aluminum filled hollow metal tube (eccentric) with a metallurgical bonding interface. Figure 1 .

[0109] In the hollow tubes prepared without applying ultrasonic treatment ( Figure 1 ), there is an obvious gap between the foam aluminum and the 6061 aluminum tube (inner tube). Figure 2 ), during the liquid-solid composite process, the oxide film on the surface of 6061 is destroyed by ultrasonic vibration and cavitation, and is carried away by ultrasonic convection, achieving seamless bonding between the inner tube and the foamed aluminum. Therefore, ultrasonic treatment can promote the contact and wetting between the liquid foamed aluminum and the metal tube, thereby forming a metallurgical bonding interface.

Claims

1. A method for preparing a hollow metal tube filled with foamed aluminum having a metallurgical bonding interface, characterized in that: The specific steps include: S1: Pre-processing: S1.1 Treatment of metal outer tube: after removing the oxide on the inner wall of the metal outer tube, the metal outer tube is assisted with plating using a surface modifier aqueous solution and then dried to obtain a metal outer tube to be filled; S1.2 Preheating: Preheat the metal outer tube, metal inner tube, mold, and ultrasonic probe to be filled and set them aside; S1.3 Melting of the aluminum foam to be foamed: melting the aluminum foam melt raw material and then keeping it warm to obtain the aluminum melt to be foamed; S2: Filling of aluminum liquid: Add the aluminum melt to be foamed into the preheating mold, and then place the preheated metal outer tube in the preheating mold to ensure that the aluminum melt to be foamed fills the metal outer tube, and keep it warm for 5 minutes to 10 minutes to achieve a metallurgical bonding interface between the aluminum melt to be foamed and the metal outer tube; S3: Foaming: Adding a viscosity enhancer to the aluminum melt to be foamed, and continuously stirring to obtain a metal melt; Adding a foaming agent TiH2 into the metal melt, stirring and dispersing it evenly, and then keeping it warm for 30s to 120s to obtain a metal tube filled with liquid foam aluminum; wherein the foaming temperature is maintained at 590°C to 700°C; S4: Positioning of the metal inner tube: The preheated metal inner tube is fixed at a target position inside the metal outer tube by a self-made mold; the metal inner tube is a steel tube or aluminum tube with a bottom seal; S5: Ultrasonication: Inserting a circular ultrasonic probe into liquid aluminum foam for ultrasonic treatment to promote the formation of a metallurgical bonding interface between the aluminum foam and the metal inner tube; wherein the ultrasonic frequency is 19.5kHz to 20.3kHz, the ultrasonic treatment power is 500W to 1500W, and the ultrasonic treatment time should be controlled to be 0.5min to 3min; S6: Post-processing The metal double tube filled with foam aluminum is cooled to the solidus temperature of the foam aluminum, and the excess foam aluminum is cut off to obtain a foam aluminum sandwich double tube with a metallurgical bonding interface; In the method, the timing starts from the addition of TiH2 to the end of ultrasonication within 8 minutes to 10 minutes.

2. The method for preparing a hollow metal tube filled with foamed aluminum having a metallurgical bonding interface according to claim 1, characterized in that: In S1.1, the metal outer tube is one of a steel tube, an aluminum tube, and an aluminum alloy tube; When the metal outer tube is an aluminum alloy tube, after adding the aluminum melt to be foamed into the preheating mold, first add the viscosity enhancer into the aluminum melt to be foamed, stir evenly, cool to 590°C to 610°C, and then place the metal outer tube in the preheating mold; In S1.1, the surface modifier is selected from one or more of chlorides or fluorides; the plating temperature is 70°C to 90°C, and the plating time is 5min to 15min.

3. The method for preparing a hollow metal tube filled with foamed aluminum having a metallurgical bonding interface according to claim 2, characterized in that: The surface modifier is one or more of zinc chloride, ammonium chloride, potassium chloride, potassium fluoride, and potassium fluorozirconate.

4. The method for preparing a hollow metal tube filled with foamed aluminum having a metallurgical bonding interface according to claim 1, characterized in that: In S1.2, the preheating temperature of the metal outer tube is 150℃~200℃, and the holding time is ≥10min; the preheating temperature of the metal inner tube is 590℃~700℃, and the holding time is ≥15min; the preheating temperature of the mold is 650℃~750℃; the preheating temperature of the ultrasonic probe is 600℃~700℃; The ultrasonic probe is a ring-shaped ultrasonic probe.

5. The method for preparing a hollow metal tube filled with foamed aluminum having a metallurgical bonding interface according to claim 1, characterized in that: In S1.3, the raw material of the foamed aluminum melt is pure aluminum or aluminum alloy, the melting temperature is 700°C to 750°C, and the holding time is 20min to 30min.

6. The method for preparing a hollow metal tube filled with foamed aluminum having a metallurgical bonding interface according to claim 1, characterized in that: In S2, the temperature of the aluminum melt to be foamed is stably controlled at 590°C to 720°C, and the metal outer tube and the aluminum melt to be foamed are metallurgically bonded.

7. The method for preparing a hollow metal tube filled with foamed aluminum having a metallurgical bonding interface according to claim 1, characterized in that: In S3, the amount of TiH2 added is 1.0% to 2.0% of the mass percentage of the metal melt, and the particle size is 10μm to 50μm; TiH2 needs to be oxidized, and the treatment method is to oxidize TiH2 in air at 400℃ to 500℃ for 1h to 4h.

8. The method for preparing a hollow metal tube filled with foamed aluminum having a metallurgical bonding interface according to claim 1, characterized in that: In S3, the viscosity enhancer is Ca, and the amount of the viscosity enhancer added is 1% to 3% by mass of the foamed aluminum melt raw material used; The stirring and dispersion are uniformly performed by inserting a stirring paddle into the metal tube for stirring at a stirring speed of 1500 r / min to 3000 r / min and a stirring time of 1 min to 4 min.

9. The method for preparing a hollow metal tube filled with foamed aluminum having a metallurgical bonding interface according to claim 1, characterized in that: In S5, the temperature of the liquid aluminum foam is stably controlled at a temperature within the range of 590°C to 700°C; The temperature of the ultrasonic probe is 0-30° C. higher than the temperature of the liquid foam aluminum.

10. A hollow metal tube filled with foamed aluminum having a metallurgical bonding interface, produced by the method according to any one of claims 1 to 9.

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