Multilayer aluminum alloy material for aluminum jacket, method for manufacturing the same, and all-aluminum heat exchanger

Abstract

The present invention relates to an aluminium tube, wherein the aluminium tube comprises an aluminium alloy composite material comprising a core material, a brazing layer and optionally one or more corrosion protection layers. The present invention further relates to the aluminium tube material solution and a method for its production, as well as a heat exchanger using the aluminium tube as a tube.

Description

Technical Field

[0001] This invention relates to the field of aluminum sleeves and heat exchangers, specifically to an aluminum sleeve material scheme for connecting aluminum tubes and its manufacturing method, as well as a heat exchanger using the aluminum sleeve. Background Technology

[0002] Under the dual pressure of the "Green and Efficient Cooling Action Plan" and the goal of "carbon neutrality," achieving energy conservation and environmental protection has become an inevitable path for the development of the HVAC industry. As an important component of HVAC systems, reducing the cost of heat exchangers has always been a key research topic in the HVAC industry.

[0003] Currently, air conditioner heat exchangers are mainly copper tube and aluminum fin heat exchangers. Taking a 4-row copper tube fin heat exchanger as an example, copper accounts for approximately 69% of the total cost. In recent years, copper prices have soared, and industry insiders even predict that global copper inventories are at a low level. Especially for my country, copper resources are relatively scarce, while aluminum resources are abundant. Therefore, promoting "aluminum replacing copper" in the air conditioning industry can effectively alleviate raw material pressure and give air conditioning companies stronger control over the entire industrial chain. Current copper tube and aluminum fin heat exchanger designs mainly consist of copper tubes, aluminum fins, and end plates (made of steel). During recycling, the copper tubes, fins, and end plates need to be disassembled separately. Due to the tight mechanical expansion joints, the separation of aluminum and copper materials during recycling is complex, requiring significant manpower and resources, resulting in low recycling efficiency and resource waste. Promoting "aluminum replacing copper" and further promoting the all-aluminum transformation of heat exchanger components can greatly simplify the heat exchanger recycling process and promote the low-carbon development of the air conditioning industry.

[0004] Currently, all-aluminum heat exchangers are not widely used, and they mainly fall into two categories: one is the brazed parallel flow microchannel heat exchanger, and the other is the extruded aluminum tube and aluminum fin heat exchanger. Because parallel flow heat exchangers use flat tubes, condensate is not easily discharged, and this type of heat exchanger is not yet in mass production for outdoor heat exchangers in heating conditions or evaporators in cooling conditions.

[0005] Extruded aluminum tubes have poor corrosion resistance, and in environments where high corrosion resistance is required, extruded aluminum tube finned heat exchangers cannot replace copper tube heat exchangers on a large scale.

[0006] Heat exchange tubes are the main components of a heat exchanger. CN201527144 proposes an air conditioning heat exchanger using aluminum alloy U-shaped tubes, which can reduce the refrigerant charge while achieving the same heat exchange performance as copper tube heat exchangers. CN112254563A proposes a long-life aluminum alloy with high corrosion resistance and a spiral grooved tube produced from this alloy. This heat exchange tube uses existing extrusion processes, and its corrosion resistance is improved through alloy composition design.

[0007] High-frequency welded aluminum tubes are made of composite aluminum alloy materials, which have higher corrosion resistance and overcome the shortcomings of poor corrosion resistance of extruded tubes. High-frequency welded aluminum tube finned heat exchangers can replace existing copper tube finned heat exchangers, meeting corrosion resistance requirements while reducing heat exchanger costs. Furthermore, they facilitate the recycling of the entire heat exchanger core, demonstrating promising market prospects.

[0008] The inventor (see CN115537608B) proposed an aluminum tube with internal threads manufactured by high-frequency induction welding of multi-layer composite materials. It has good strength (pressure resistance) and corrosion resistance, and can effectively reduce costs by replacing the heat exchange tube of copper tube heat exchanger.

[0009] To connect the heat exchange tubes, existing copper-tube aluminum-fin heat exchangers require two mechanical cold-working processes: "cupping" and "flaring" the ends of longer heat exchange tubes, such as U-shaped ones, before inserting a shorter, U-shaped connecting bend into the flared heat exchange tube. However, this method results in a large diameter variation at the flared end of the heat exchange tube, requiring high elongation of the material. If heat exchangers using high-frequency welded aluminum tubes still employ this existing bend connection method, the heat exchange tube ends are prone to cracking, reducing the yield of the heat exchanger.

[0010] Furthermore, existing patent documents CN203349579U and CN212620240U both involve brazed aluminum tube and finned heat exchangers that do not require mechanical cold processing steps such as "flaring the rim" and "expanding the rim". However, although the processing technology of these heat exchangers avoids the damage to the heat exchange tube ends caused by the flaring process in traditional production methods, the increased number of welded joints increases the risk of leakage, reduces assembly efficiency, and requires the entire unit to pass through a welding furnace, resulting in high energy consumption during production.

[0011] Therefore, there is an urgent need in this field for novel all-aluminum heat exchangers and methods for connecting heat exchange tubes. Summary of the Invention

[0012] In one aspect, the present invention provides an aluminum tube, wherein the aluminum tube comprises an aluminum alloy composite material, the aluminum alloy composite material comprising a core material, a brazing layer, and optionally one or more anti-corrosion layers, wherein the alloy of the core material comprises: <0.8 wt% Si, 1.0-1.7 wt% Mn, <0.7 wt% Fe, 0.05-0.8 wt% Cu, <0.1 wt% Mg, <0.25 wt% Zn, <0.2 wt% Ti, with the balance being Al and unavoidable impurities; the brazing layer is a layer of aluminum alloy matrix containing flux particles, the aluminum alloy of the brazing layer comprising: 10-15 wt% Si, < The alloy comprises: 0.2 wt% Mn, <0.5 wt% Fe, <2.0 wt% Cu, <0.03 wt% Mg, <5.0 wt% Zn, 0.5-6 wt% K, with the balance being Al and unavoidable impurities; and when the anti-corrosion layer is present, its alloy comprises: <0.5 wt% Si, <0.5 wt% Mn, <0.50 wt% Fe, <0.1 wt% Cu, <0.1 wt% Mg, 0.5-3 wt% Zn, with the balance being Al and unavoidable impurities; the solidus temperature of the core alloy of the aluminum alloy composite material is more than 40°C higher than the liquidus temperature of the brazing layer alloy.

[0013] In one aspect, the present invention provides a sleeve made of the aluminum tube of the present invention, wherein two aluminum alloy round tubes are respectively inserted into and welded to both ends of the sleeve so that the two aluminum alloy round tubes are connected to each other; the sleeve has an anti-corrosion layer, and the potential difference between the outer side of the anti-corrosion layer and the core material of the sleeve is 50-200mV, for example 70mV or 100mV.

[0014] In another aspect, the present invention provides a heat exchanger comprising the sleeve of the present invention.

[0015] In another aspect, the present invention provides a method for preparing the aluminum alloy composite material of the present invention, comprising the following steps: 1) casting ingots of a core alloy and an optional anti-corrosion layer alloy respectively; and preparing a brazing layer alloy; 2) homogenizing the core alloy with heat treatment; 3) milling the core alloy, brazing layer alloy ingot and optional anti-corrosion layer alloy ingot; 4) preparing a plate-shaped brazing layer alloy and optional anti-corrosion layer alloy by hot rolling; 5) laminating a thick plate of brazing layer alloy of a certain thickness on one side of the core alloy; laminating a thick plate of anti-corrosion layer alloy of a certain thickness on the other side of the core alloy to obtain a composite; 6) preheating the composite obtained in step 5), then hot rolling and coiling it; 7) cold rolling to the finished thickness to obtain a composite coil; 8) annealing the composite coil obtained in step 7).

[0016] In another aspect, the present invention provides a method for preparing the aluminum tube or the sleeve of the present invention, comprising preparing the aluminum tube or sleeve from the aluminum alloy composite material aluminum tube of the present invention by high frequency induction welding. Attached Figure Description

[0017] Figure 1a , Figure 1b : A schematic diagram of the structure of the aluminum alloy composite material of the present invention (A: core material; B: brazing layer; C: anti-corrosion layer).

[0018] Figure 2a , Figure 2b The flux distribution diagram in the aluminum alloy composite material of the present invention is shown, wherein the pure black part is the background.

[0019] Figure 3 : A perspective view of one embodiment of the all-aluminum heat exchanger of the present invention; wherein the aluminum sleeve of the present invention is used to connect the heat exchange tube to the connecting tube, the input tube or the output tube.

[0020] Figure 4 : Figure 3 A three-dimensional schematic diagram of the connection position between the heat exchange tube and the connecting bend in the all-aluminum heat exchanger.

[0021] Figure 5 : Figure 4 A cross-sectional view of the all-aluminum heat exchanger at the connection point between the heat exchange tubes and the connecting bend.

[0022] Figure 6 : Schematic diagram of the potential distribution near the connection points of the bushing and the aluminum alloy round tubes inserted at both ends of the bushing. Wherein, A is the outer surface of the bushing; B is the outer surface of the round tube; C is the brazing layer of the bushing; D is the end face of the bushing (the bushing core material).

[0023] Figure 7 A cross-section along the length of a handmade sample after flame brazing of the sleeve and the aluminum alloy round tubes inserted into both ends of the sleeve.

[0024] Figure 8 Micrographs of the cross-sectional structure along the length of a hand-made sample after flame brazing of the sleeve and the aluminum alloy round tubes inserted at both ends of the sleeve. The aluminum alloy round tubes have internal threads. Detailed Implementation

[0025] The following specific embodiments illustrate the technical content of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention through the content disclosed in the specification. The present invention can also be implemented or applied through other different specific embodiments. Those skilled in the art can make various modifications and changes without departing from the spirit of the present invention.

[0026] definition

[0027] Unless otherwise defined below, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. The term "technique" as used herein refers to techniques commonly understood in the art, including variations and equivalent substitutions that are obvious to one of ordinary skill in the art. While it is believed that the following terms will be readily understood by one of ordinary skill in the art, the following definitions are set forth to better illustrate the invention. When a trade name appears herein, it refers to the corresponding product or its active ingredient. All patents, published patent applications, and publications cited herein are incorporated herein by reference.

[0028] Unless otherwise stated, all percentages, parts, proportions, etc. are by weight.

[0029] When a quantity, concentration, or other numerical value or parameter is described as a range, preferred range, or preferred upper or lower limit, it should be understood as equivalent to specifically disclosing any range formed by combining any upper or preferred value with any lower or preferred value, whether or not the range is explicitly stated. Unless otherwise stated, the numerical ranges listed herein are intended to include the endpoints of the range as well as all integers and fractions (decimals) within the range.

[0030] When used with a numerical variable, the terms "about" or "approximately" usually mean that the value of the variable and all values ​​of the variable are within the experimental error (e.g., within a 95% confidence interval for the mean) or within ±10% of the specified value, or a wider range.

[0031] Unless the context clearly specifies otherwise, the singular forms such as “a kind” and “the kind” include the plural forms. The expressions “a kind or more” or “at least one” can mean 1, 2, 3, 4, 5, 6, 7, 8, 9, or more. In one embodiment, “at least one” means 1, 2, 3, or 4.

[0032] The terms “optional” or “optional” mean that the events described below may occur but are not guaranteed to occur, and the description includes the possibility that the events or situations described therein may or may not occur.

[0033] Unless otherwise stated, the terms "combination thereof" and "mixture thereof" refer to a multi-component mixture of the elements, such as two, three, four, and up to the maximum possible multi-component mixture.

[0034] Furthermore, if the number of components or parts of the present invention is not previously specified, it indicates that there is no limitation on the number of times a component or part may appear (or be present). Therefore, it should be interpreted as including one or at least one, and the singular form of a component or part also includes the plural, unless the value clearly indicates a singular number.

[0035] The expressions “comprising,” “including,” “having,” “containing,” or “involving,” and their other variations herein, are inclusive or open-ended and do not exclude other unlisted elements or method steps. Those skilled in the art will understand that the foregoing terms such as “comprising” encompass the meaning of “consisting of.” The expression “consisting of” excludes any unspecified elements, steps, or components. The expression “substantially constitutes” means that the scope is limited to the specified elements, steps, or components, as well as optional elements, steps, or components that do not materially affect the essential and novel features of the claimed subject matter. It should be understood that the expression “comprising” includes both the expressions “substantially constitutes” and “consisting of.”

[0036] The term “selected from…” means one or more elements from the groups listed below, selected independently, and may include combinations of two or more elements.

[0037] The aluminum alloy designations “AA3xxx” and “AA4xxx” refer to the general alloy designations used by the Aluminum Association (AA).

[0038] The term "unavoidable impurities" refers to other elemental components that were not intentionally added or included during the manufacture of the alloy, and which were introduced as unavoidable impurities. Among these other elements, the content of any single element is ≤0.05% by weight, and the total elemental content is ≤0.15% by weight.

[0039] The terms "flux", "soldering flux" or "soldering flux" refer to a brazing flux, which is a substance that, directly or in the form of its reaction products, helps to break down or dissolve the oxide film on the surface to be brazed during brazing.

[0040] In this article, the term "composite ratio" refers to the proportion of the thickness of each layer to the total thickness of the aluminum alloy composite material. Taking the core material as an example, the core material composite ratio is the proportion of the core material thickness to the total thickness of the aluminum alloy composite material.

[0041] In this document, the term "high-frequency induction welding" has the meaning as commonly understood by those skilled in the art, referring to a welding process that uses the skin effect and proximity effect generated by high-frequency current to butt-join materials (such as aluminum). Typically, the frequency of high-frequency welding can be approximately 300-450 kHz.

[0042] Aluminum tubes and aluminum sleeves

[0043] In one aspect, the present invention relates to an aluminum tube comprising an aluminum alloy composite material, the aluminum alloy composite material comprising a core material, a brazing layer and optionally one or more anti-corrosion layers.

[0044] The aluminum tube can be round or elliptical. In one embodiment, the aluminum tube is a round aluminum tube.

[0045] With mature processing and manufacturing techniques, aluminum tubes can be used in circular tube heat exchangers as sleeves connecting aluminum alloy circular tubes. Therefore, in one aspect, this invention relates to a sleeve made of the composite aluminum material of this invention.

[0046] In one embodiment, two aluminum alloy round tubes are respectively inserted into and welded to both ends of a sleeve, so that the two aluminum alloy round tubes are interconnected. These aluminum alloy round tubes are, for example, heat exchanger tubes, connecting tubes, inlet tubes, or outlet tubes of a heat exchanger. In one embodiment, one end of the sleeve is a flared section into which a heat exchanger tube (e.g., an expanded long U-tube) can be inserted, and the other end of the sleeve is an unflared section into which a heat exchanger connecting tube (e.g., a short U-tube), inlet tube, or outlet tube can be inserted. See also one embodiment of the sleeve. Figure 4 The sleeve 40 includes a flared first section 41 and an unflared second section 42, both with approximately the same axial length. The inner diameter of the first section 41 is slightly larger than the inner diameter of the second section 42. See the cross-sectional view for details. Figure 5 .

[0047] In one embodiment, the aluminum tube or sleeve of the present invention can be welded under flame brazing or induction welding conditions. The welding, for example, involves the following process: the brazing layer melts and wets the surface to be brazed, forming a joint (brazed joint). Preferably, the joint is defect-free or has few defects.

[0048] Aluminum alloy composite materials

[0049] The aluminum tube is made of aluminum alloy composite material. The aluminum alloy composite material can be in the form of sheet or strip. In one embodiment, the aluminum alloy composite material is an aluminum alloy composite strip.

[0050] In one embodiment, the aluminum alloy composite material comprises a core material and a brazing layer. Depending on the requirements, the aluminum alloy composite material may also include additional layers to achieve different functions. For example, it may also include an anti-corrosion layer, an intermediate layer, etc.

[0051] The core material is one of the main structures of aluminum alloy composite materials, and its properties (such as hardness, strength, toughness, etc.) affect the performance of the composite material.

[0052] In the aluminum alloy composite material of the present invention, based on the total weight of the core material, the core material comprises: <0.8 wt% Si, 1.0-1.7 wt% Mn, <0.7 wt% Fe, 0.05-0.8 wt% Cu, <0.1 wt% Mg, <0.25 wt% Zn, <0.2 wt% Ti; the balance being Al and unavoidable impurities.

[0053] Si in the core material has a significant impact on the properties of composite materials. In the core, Si, together with Fe and Mn, forms AlFeMnSi compounds, which provide dispersion strengthening. Si can react with Mg to form Mg₂Si compounds, thereby improving the strength of the composite material. Furthermore, Si can be dissolved in the core matrix, enhancing the material's strength through solid solution strengthening. The Si content also affects corrosion resistance.

[0054] In one embodiment, the alloy of the core material contains <0.8% by weight of Si. In one embodiment, the alloy of the core material contains <0.6% by weight of Si. In one embodiment, the alloy of the core material contains ≤0.4% by weight of Si.

[0055] In one embodiment, the alloy of the core material contains 0.1-0.8% by weight of Cu.

[0056] In one embodiment, the alloy of the core material contains 0.05-0.2% by weight Ti.

[0057] Including an appropriate amount of Mn in the core material helps improve the material's strength, brazing properties, corrosion resistance, and electrical potential.

[0058] Fe can combine with other elements, such as Mn and Si, to form casting crystalline phases. These crystalline phases can become intermetallic compounds of recrystallization nucleus size, thus lowering the recrystallization temperature.

[0059] Cu can improve the strength of the core material and increase its potential through solid solution strengthening.

[0060] Mg can significantly improve the strength of alloys, either through solid solution strengthening or by precipitating Mg2Si.

[0061] An appropriate amount of Zn can reduce the potential of the core material.

[0062] Ti enhances its strength and corrosion resistance through solid solution strengthening.

[0063] The brazing layer is a layer of aluminum alloy matrix containing flux particles.

[0064] The brazing layer contains flux, thus avoiding the use of solder rings or solder pads or additional flux application, further reducing manufacturing steps and improving welding quality, reducing problems such as poor welding caused by flux residue.

[0065] The flux can be any substance that, either directly during brazing or in the form of its reaction products, helps to break down the oxide film on the surface to be brazed. The liquidus temperature of the flux is preferably lower than the solidus temperature of the aluminum alloy matrix of the brazed layer. In one embodiment, the flux is potassium fluoroaluminate (KAlF4).

[0066] The flux is preferably present as particles in the aluminum alloy matrix of the solder layer. In one embodiment, the equivalent spherical diameter of the flux particles is from about 1 nm to about 10 μm. In another embodiment, the equivalent spherical diameter of the flux particles is from about 1 nm to about 5 μm. In one embodiment, the flux is insoluble in the aluminum alloy matrix of the solder layer.

[0067] Based on the total weight of the aluminum alloy in the brazing layer, the aluminum alloy in the brazing layer contains: 10-15 wt% Si, <0.2 wt% Mn, <0.5 wt% Fe, <2.0 wt% Cu, <0.03 wt% Mg, <5.0 wt% Zn, 0.5-6 wt% K; the balance being Al and unavoidable impurities.

[0068] The flux in the solder layer can be distributed in a suitable manner. In one embodiment, the flux particles are unevenly distributed in the solder layer. In a particular embodiment, the distribution is as follows: Figure 2a As shown. In one embodiment, flux particles are uniformly distributed in the solder layer. In a particular embodiment, their distribution is as follows: Figure 2b As shown. Figure 2a and Figure 2b In the middle, the brazing layer is closer to the black background than the core material; the flux distributed in it is darker in color than the aluminum alloy matrix.

[0069] The flux content in the brazing layer has a significant impact on the brazing performance of aluminum alloy composite materials. In one embodiment, the flux content in the brazing layer is approximately 5 g / m². 2 Approximately 30g / m 2 Preferred concentration: approximately 10g / m 2 Approximately 20g / m 2 In one embodiment, the flux content in the solder layer is approximately 10 g / m². 2 15g / m 2 or about 20g / m 2 Especially about 20g / m 2 In one embodiment, the flux content in the brazing layer is relative to the inner surface of the sleeve material (i.e., the surface of the brazing layer away from the core material).

[0070] The material of the brazing layer (i.e., the "brazing layer alloy") used in the aluminum alloy composite material of the present invention can be prepared by any suitable method for obtaining a matrix of aluminum or aluminum alloy containing flux particles. Possible methods include obtaining the material body by spray forming as described in WO2008 / 110808A1, or by subjecting aluminum or aluminum alloy powder and flux particles to high pressure, such as hot isostatic pressing (HIP), as described in EP552567A1 or FR2855085A1. Other possible methods are thermal spraying, such as flame spraying or plasma spraying, or additive manufacturing techniques such as 3D metal printing. Depending on the size and geometry of the resulting body, it can be extruded or processed in any other suitable manner to obtain a slab or plate, which can be hot-rolled and / or cold-rolled to the desired thickness if desired.

[0071] The aluminum alloy composite material of the present invention can be provided with an anti-corrosion layer to further improve the corrosion resistance of the material at the casing.

[0072] Based on the total weight of the anti-corrosion coating, the anti-corrosion coating contains: <0.5 wt% Si, <0.5 wt% Mn, <0.50 wt% Fe, <0.1 wt% Cu, <0.1 wt% Mg, 0.5-3 wt% Zn; the balance is Al and unavoidable impurities.

[0073] In one embodiment, when the anti-corrosion coating is present, its alloy contains 0.5-3% by weight of Zn. In another embodiment, when the anti-corrosion coating is present, its alloy contains 1-2% by weight of Zn. In yet another embodiment, when the anti-corrosion coating is present, its alloy contains 1-1.5% by weight of Zn.

[0074] Zinc (Zn) acts as a sacrificial anode. Through diffusion during brazing, a corrosion potential gradient is created, mitigating the risk of corrosion from the outer side of the anti-corrosion layer (the side furthest from the core material). The Zn content of the anti-corrosion layer affects the corrosion resistance and strength of the aluminum tube. Excessive Zn content leads to increased corrosion rates and shortens product lifespan.

[0075] The brazing ratio of the brazing layer in an aluminum alloy composite material has a significant impact on its brazing performance. In one embodiment, the brazing ratio of the brazing layer in the aluminum alloy composite material is about 10% to about 30%, preferably about 10% to about 20%, more preferably about 15% to about 20%, for example about 10%, about 15%, or about 20%, particularly about 20%.

[0076] There are no particular restrictions on the composite ratio of the optional anti-corrosion layer in the aluminum alloy composite material, but it should be such that the target thickness of the aluminum alloy composite material can be obtained. In one embodiment, the aluminum alloy composite material has an anti-corrosion layer, and the composite ratio of the anti-corrosion layer is from about 5% to about 30%, for example, 10% or 15%.

[0077] This invention achieves excellent brazing performance and corrosion resistance of aluminum tubes through the combination of core alloy, brazing layer and optional anti-corrosion layer.

[0078] Using aluminum alloys with low or no Mg content in the brazing layer can avoid the poisoning effect of Mg on F-Al-K flux and improve brazing quality.

[0079] During brazing, magnesium reacts with F-Al-K flux (such as KAlF4 and K3AlF6) to produce MgF2, KMgF3, and K2MgF4. These compounds have melting points exceeding 900 degrees Celsius, making it impossible to effectively remove the oxide film on the aluminum surface at normal brazing temperatures. Therefore, the addition of magnesium poisons the F-Al-K flux, reducing the effective fluxing agent dosage. Furthermore, these high-melting-point substances act as inclusions in the brazed joint, compromising the joint strength and integrity.

[0080] In the aluminum tube of this invention, the Mg content is controlled in both the core material and the brazing layer. The inventors surprisingly discovered that good brazing performance can be ensured by also controlling the Mg content in the core material. This may be due to preventing the diffusion of Mg from the core material into the brazing layer, but is not limited to this theory.

[0081] The difference between the solidus temperature of the core alloy and the liquidus temperature of the brazing layer alloy in an aluminum alloy composite material has a significant impact on the flame brazing effect. In one embodiment, the solidus temperature of the core alloy of the aluminum alloy composite material is about 40°C higher than the liquidus temperature of the brazing layer alloy, preferably about 50°C higher. In another embodiment, the solidus temperature of the core alloy of the aluminum alloy composite material is about 40°C to about 60°C, 40°C to about 50°C, or about 50°C to about 60°C, particularly about 50°C to about 60°C, higher than the liquidus temperature of the brazing layer alloy. In yet another embodiment, the solidus temperature of the core alloy of the aluminum alloy composite material is about 40°C, about 50°C, or about 60°C, particularly about 60°C, higher than the liquidus temperature of the brazing layer alloy.

[0082] The potential of the anti-corrosion layer in the aluminum tube needs to be lower than that of the core material in order to give the aluminum tube excellent corrosion resistance.

[0083] The sleeve of this invention can be welded to the outside of the connection position between two aluminum alloy round tubes by high-temperature flame welding or induction welding to achieve the connection between the two. The potential distribution near the joint after connection is as follows: Figure 6The potentials, from lowest to highest, are: the outer side of the sleeve (A) (the anti-corrosion layer in the sleeve of this invention), the outer surface of the connected aluminum round tube (B), the brazed layer of the sleeve (C), and the core material of the sleeve (D). During the use of a heat exchanger employing this welded component, the outer side of the sleeve (A), with the lowest potential, will corrode preferentially, thereby protecting other areas and preventing premature leakage at the end face and joints of the round tube or sleeve.

[0084] In some aspects, the corrosion potential (Ecorr) of the core material can be about -700 mV or higher; for example, about -699 mV or higher, about -692 mV or higher, or about -678 mV or higher; particularly about -699 mV, about -692 mV, or about -678 mV. In some aspects, the corrosion potential of the protective coating can be about -760 mV or lower; for example, about -805 mV or lower, or about -840 mV or lower; particularly about -760 mV, about -805 mV, or about -840 mV. In one embodiment, the corrosion potential is tested according to ASTM G69 standard.

[0085] In one embodiment, the potential difference between the outer side of the casing's anti-corrosion layer and the core material is approximately 50 to approximately 200 mV. In another embodiment, the potential difference between the outer side of the casing's anti-corrosion layer and the core material is approximately 70 mV. In yet another embodiment, the potential difference between the outer side of the casing's anti-corrosion layer and the core material is approximately 100 mV.

[0086] Manufacturing method of aluminum alloy composite materials

[0087] This invention also relates to a method for manufacturing the aluminum alloy composite material of this invention, comprising:

[0088] 1) Cast ingots of the core alloy and the optional anti-corrosion layer alloy separately; and prepare the brazing layer alloy;

[0089] 2) The core alloy is homogenized by heat treatment;

[0090] 3) Milling;

[0091] 4) Prepare a plate-shaped brazing layer alloy and an optional anti-corrosion layer alloy;

[0092] 5) Composite;

[0093] 6) Preheating and hot rolling;

[0094] 7) Cold rolling;

[0095] 8) Annealing;

[0096] The casting method in step 1) can be selected from methods known in the art. In one embodiment, the casting method in step 1) is DC casting (direct water-cooled semi-continuous casting) or continuous casting thin ingot method or thin strip method.

[0097] In one embodiment, the homogenization heat treatment in step 2) is performed at a temperature of about 550°C to about 620°C for a time of about 5-20 hours.

[0098] Typically, the brazing alloy and the optionally present anti-corrosion alloy are optionally homogenized. In one embodiment, neither the brazing alloy nor the optionally present anti-corrosion alloy requires homogenization.

[0099] In one embodiment, in step 3), for example, 5-20 mm is milled off each side of the core alloy. In another embodiment, in step 3), for example, 5-20 mm is milled off each side of the brazing layer alloy. Optionally, a sawing step may be included before the milling in step 3).

[0100] In one embodiment, step 4) includes heating the milled brazing alloy and optionally present corrosion-resistant alloy in a furnace, and then rolling them into a sheet of specified thickness using a rolling mill to obtain a plate-shaped brazing alloy and a plate-shaped corrosion-resistant alloy. In one embodiment, the heating includes holding the milled brazing alloy and optionally present corrosion-resistant alloy in a heating furnace at about 450°C to about 520°C for 5-20 hours. In one embodiment, the rolling is hot rolling.

[0101] In one embodiment, step 5) includes laminating a thick plate of a brazing layer alloy of a certain thickness to one side of the core alloy; and laminating a thick plate of an anti-corrosion layer alloy of a certain thickness to the other side of the core alloy to obtain a composite, wherein the thickness of the brazing layer alloy is about 4% to about 20% of the thickness of the composite, and the thickness of the anti-corrosion layer alloy is about 5% to about 25% of the thickness of the composite.

[0102] In one embodiment, the preheating in step 6) includes heating the composite obtained in step 5) between about 400°C and about 520°C before hot rolling. In one embodiment, the preheating time is 1-25 hours. In one embodiment, the hot rolling in step 6) includes hot rolling the heated composite from an initial thickness of about 2 mm to about 6 mm using a hot rolling mill and then coiling it.

[0103] In one embodiment, the cold rolling in step 7) includes rolling the hot-rolled coil obtained in step 6) on a cold rolling mill to a finished thickness, for example, 0.5 mm to 3 mm, to obtain a composite coil.

[0104] In one embodiment, the annealing in step 8) includes placing the composite roll obtained in step 7) in an annealing furnace for finished product annealing at an annealing temperature of about 250°C to 450°C for about 1-3 hours to obtain the aluminum alloy composite material of the present invention.

[0105] The target dimensions (such as thickness, size, etc.) of aluminum alloy composite materials can be reasonably selected according to the dimensions of the aluminum tube.

[0106] Manufacturing methods for aluminum tubes and aluminum sleeves

[0107] The present invention also relates to a method for manufacturing the aluminum tube and sleeve of the present invention.

[0108] In one embodiment, the aluminum tube of the present invention is manufactured by using a coiled aluminum alloy composite strip, through a tube-making device, and by high-frequency induction welding.

[0109] In one embodiment of the sleeve of the present invention, the aluminum tube of the present invention manufactured above is used as the sleeve.

[0110] In one embodiment, the sleeve of the present invention is made of the aluminum alloy composite material of the present invention by high-frequency induction welding.

[0111] In one embodiment, the sleeve of the present invention is made of the aluminum tube of the present invention.

[0112] In another embodiment of the sleeve of the present invention, the inner diameter of a section of the aluminum tube of the present invention is enlarged by a flaring tool to form a flared section, thereby producing a sleeve containing a flared section and an unflared section.

[0113] heat exchanger

[0114] In another aspect, the present invention also relates to a heat exchanger comprising heat exchange tubes and a jacket, and optionally including an inlet tube, an outlet tube, and a connecting tube; wherein,

[0115] (i) The sleeve is the sleeve of the present invention; and

[0116] (ii) Aluminum alloy round tubes a and b are respectively inserted into and welded to both ends of the sleeve, so that aluminum alloy round tubes a and b are connected to each other; wherein

[0117] Aluminum alloy round tube a is a heat exchange tube, and aluminum alloy round tube b is a connecting tube, input tube, or output tube;

[0118] and

[0119] The welding is flame brazing.

[0120] In a preferred embodiment, the sleeve includes a flared first section 41 and an unflared second section 42 of approximately the same axial length; aluminum alloy round tube a is an expanded long U-tube, inserted and welded to the first section 41 of the sleeve; and aluminum alloy round tube b is a short U-tube, inserted and welded to the second section 42 of the sleeve. In a more preferred embodiment, two adjacent heat exchange tubes are connected to each other by a short U-tube, wherein one connecting end of each of the two heat exchange tubes is connected to the two connecting ends of a short U-tube by being inserted and welded to the respective flared first sections 41 and 41' of the two sleeves as described above.

[0121] In one implementation, the heat exchanger is an all-aluminum heat exchanger.

[0122] Heat exchangers also typically include fins. Through the rational design of the fins, heat exchange tubes, and their connections, the corrosion resistance of the heat exchanger in corrosive environments can be enhanced while ensuring strength (pressure resistance). Therefore, in another aspect, the present invention relates to the application of the sleeve of the present invention in heat exchangers, particularly for connecting heat exchange tubes to connecting pipes, inlet pipes, or outlet pipes.

[0123] In one implementation, the heat exchanger is an assembled aluminum tube and aluminum fin heat exchanger.

[0124] Figure 3 An embodiment of an all-aluminum heat exchanger is shown. Figure 4 The connection positions of the heat exchange tubes and connecting bends are shown. In the illustrated all-aluminum heat exchanger embodiment, each heat exchange tube 20 is constructed as a U-shaped tube (i.e., a "longer U-shaped tube" or "long U-tube") and includes two first connecting ends 21; each connecting bend 30 is also constructed as a U-shaped tube (i.e., a "shorter U-shaped tube" or "short U-tube") and includes two second connecting ends 31; wherein the two second connecting ends 31 of the connecting bend 30 are respectively connected to the first connecting ends 21 of two adjacent heat exchange tubes 20 by means of a sleeve 40 (i.e., the sleeve of the present invention), so that the two adjacent heat exchange tubes 20 are in communication with each other. Furthermore, the input pipe 50 (i.e., the "coolant inlet pipe") includes a third connecting end 51; the output pipe 60 (i.e., the "coolant outlet pipe") includes a fourth connecting end 61; the third connecting end 51 of the input pipe 50 is connected to the first connecting end 21 of the heat exchange pipe 20 at the starting end (i.e., the "uppermost") through the sleeve 40, and the fourth connecting end 61 of the output pipe 60 is connected to the first connecting end 21 of the heat exchange pipe 20 at the end (i.e., the "lowermost") through the sleeve 40, so that the input pipe 50, each heat exchange pipe 20 and the connecting bend pipe 30, and the output pipe 60 are sequentially connected to form a cooling circuit.

[0125] Among them, such as Figure 4As shown, in the sleeve 40, the inner diameter of the first flared section 41 is slightly larger than the inner diameter of the unflared second section 42. Therefore, the first connecting end 21 of the expanded heat exchange tube 20 can be inserted into and welded to the first section 41, and the second connecting end 31 of the connecting bend 30 can be inserted into and welded to the second section 42.

[0126] In one embodiment, after the overall assembly of the heat exchanger is completed, flame brazing is performed at the location of each sleeve of the present invention to complete the welding of the heat exchanger.

[0127] In one embodiment, the flame brazing temperature is 590-630°C, and the heating time is less than or equal to 2 minutes.

[0128] Beneficial effects

[0129] The aluminum tube of this invention is made from a composite aluminum alloy strip via high-frequency induction welding. The composite aluminum alloy material of this invention achieves excellent technical effects through a combination of a core material, a brazing layer, and an optional anti-corrosion layer, and through optimized alloy element ratios. The aluminum tube prepared from this material exhibits excellent brazing performance and corrosion resistance. The aluminum tube of this invention can be made into a sleeve. The aluminum tube or sleeve of this invention can be welded under flame brazing or induction welding conditions; wherein, flame brazing further offers the advantages of simple operation and low cost. The all-aluminum heat exchanger using the sleeve of this invention to connect the heat exchange tubes significantly reduces costs compared to copper tube heat exchangers. Furthermore, by welding the sleeve to the outside of the connection point between the heat exchange tube and the connecting bend, the "cupping" and "flaring" processes at the heat exchange tube ends during manufacturing are eliminated. This avoids cracking at the high-frequency welded heat exchange tube ends, improves the yield rate of the heat exchanger, and enhances the corrosion resistance of the weld, ensuring the heat exchanger's maximum pressure resistance and optimal corrosion resistance. In addition, during manufacturing, simple welding can be performed only at the sleeve location, eliminating the need for the entire heat exchanger to pass through a welding furnace, thus reducing production energy consumption. Aluminum tube and aluminum fin heat exchangers produced using conventional "cupping" and "flaring" processes are prone to leakage near the cupping end of the long U-tube during burst pressure tests. The sleeve connection method further improves the strength at the joint between the long and short U-tubes.

[0130] Example

[0131] To more clearly illustrate the objectives and technical solutions of this invention, the invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Specific experimental methods not mentioned in the following embodiments were performed according to conventional experimental methods.

[0132] Core alloy and anti-corrosion alloy ingots with specific compositions are cast separately. A brazing alloy is then prepared. The core alloy undergoes homogenization heat treatment at 550-620°C. The core alloy, brazing alloy ingot, and optionally anti-corrosion alloy ingot are milled. The milled brazing alloy and optionally anti-corrosion alloy are held in a furnace at 450-520°C for 5-20 hours, and then hot-rolled to prepare plate-shaped brazing alloy and optionally anti-corrosion alloy. A thick plate of brazing alloy of a certain thickness is laminated to one side of the core alloy; a thick plate of anti-corrosion alloy of a certain thickness is laminated to the other side of the core alloy to obtain a composite, wherein the thickness of the brazing alloy is 4% to 20% of the composite thickness, and the thickness of the anti-corrosion alloy is 5% to 25% of the composite thickness. The composite material is preheated at 400-520℃ for 1-25 hours, then hot-rolled to 2-6 mm and coiled; the hot-rolled coil is further cold-rolled to the finished thickness. The finished thickness of the composite aluminum material is annealed at 250-450℃ for 1-3 hours to obtain the composite materials of each embodiment and comparative example.

[0133] The alloy composition for preparing the core material is shown in Table 1, the alloy composition for preparing the brazing layer is shown in Table 2, and the alloy composition for preparing the anti-corrosion layer is shown in Table 3. The balance is Al and unavoidable impurities.

[0134] Table 1

[0135]

[0136] Table 2

[0137]

[0138] Table 3

[0139]

[0140] Aluminum alloy composite strip wound into coils is used to manufacture aluminum tubes via high-frequency induction welding using tube-making equipment. The composite ratio and flux content of the brazing layers in the examples and comparative examples are shown in Table 4.

[0141] The welding slag inside the aluminum tube is removed, and the inner diameter of one section of the aluminum tube is enlarged using a flaring tool to form a flared section, thus obtaining a sleeve. An expanded aluminum alloy round tube is inserted into the flared section at one end of the sleeve, and an aluminum alloy round tube is inserted into the unflared section at the other end of the sleeve to obtain a test piece. The aluminum alloy round tube is the internally threaded aluminum tube described in CN115537608B.

[0142] Experimental Example

[0143] The melting point difference between the core alloy and the brazing layer alloy of the evaluated examples and comparative examples was determined. The corrosion potential of the core alloy and the anti-corrosion layer alloy was measured using an electrochemical workstation; the test was conducted according to standard ASTM-G69, with a standard calomel electrode (SCE) as the reference electrode; then the potential difference between the anti-corrosion layer and the core material was evaluated. A sleeve was then prepared as described above, and an aluminum alloy round tube was inserted into it to obtain a test piece. The test piece was flame brazed to obtain a welded test piece; then the welding condition was evaluated, and the corrosion resistance of the welded test piece was assessed; the evaluation results are shown in Table 4.

[0144] Figure 7 , Figure 8 The image shows a cross-section along the length of a hand-made sample of an aluminum sleeve and aluminum alloy round tubes inserted at both ends of the sleeve after flame brazing, along with a microstructure photograph. The aluminum alloy round tubes have internal threads. It can be seen that the sleeve of the present invention, when welded to the aluminum alloy round tube under flame brazing conditions, can form a satisfactory brazed joint.

[0145] Table 4

[0146]

[0147] As can be seen from Table 4, the sleeve of the present invention has excellent brazing performance, and the welded test piece has excellent corrosion resistance.

Claims

1. An aluminum tube, wherein the aluminum tube comprises an aluminum alloy composite material, the aluminum alloy composite material comprising a core material, a brazing layer, and optionally one or more anti-corrosion layers, wherein... (i) The alloy of the core material comprises: <0.8% by weight of Si, 1.0-1.7% by weight of Mn, <0.7% by weight of Fe, 0.05-0.8% by weight of Cu, <0.1% by weight of Mg, <0.25% by weight of Zn, <0.2% by weight of Ti, The balance consists of Al and unavoidable impurities; The brazing layer is a layer of aluminum alloy matrix containing flux particles. (ii) The aluminum alloy of the brazing layer comprises: 10-15% by weight of Si, <0.2% by weight of Mn, <0.5% by weight of Fe, <2.0% by weight of Cu, <0.03% by weight of Mg, <5.0% by weight of Zn, 0.5-6% by weight of K, The balance is Al and unavoidable impurities; and (iii) When the anti-corrosion layer is present, its alloy comprises: <0.5% by weight of Si, <0.5% by weight of Mn, <0.50% by weight of Fe, <0.1% by weight of Cu, <0.1% by weight of Mg, 0.5-3% by weight of Zn, The balance consists of Al and unavoidable impurities; The solidus temperature of the core alloy of the aluminum alloy composite material is more than 40°C higher than the liquidus temperature of the brazing layer alloy.

2. The aluminum tube of claim 1, wherein The solidus temperature of the core alloy of the aluminum alloy composite material is more than 50°C higher than the liquidus temperature of the brazing layer alloy, more preferably 50°C to 60°C higher, especially 60°C.

3. The aluminum tube of claim 1 or 2, wherein The alloy of the core material contains <0.6% by weight, preferably ≤0.4% by weight, of Si; and / or When the anti-corrosion layer is present, its alloy contains 1-2% by weight, preferably 1-1.5% by weight, of Zn.

4. The aluminum tube according to any one of claims 1-3, wherein The flux content in the brazing layer of the aluminum alloy composite material is 5g / m 2 Up to 30g / m 2 10g / m 2 Up to 20g / m 2 ; and / or The flux is potassium fluoroaluminate (KAlF4).

5. The aluminum tube according to any one of claims 1-4, wherein The brazing layer in the aluminum alloy composite material has a composite ratio of 10% to 30%, preferably 15% to 20%, and particularly 20%. and / or The anti-corrosion layer in the aluminum alloy composite material has a composite ratio of 5% to 30%, preferably 10% or 15%.

6. A sleeve made of an aluminum tube according to any one of claims 1-5, wherein The sleeve allows two aluminum alloy round tubes to be inserted into and welded to both ends of the sleeve, so that the two aluminum alloy round tubes can be connected to each other. The sleeve has an anti-corrosion layer, and the potential difference between the outer side of the anti-corrosion layer and the core material of the sleeve is 50-200mV, for example, 70mV or 100mV.

7. The sleeve of claim 6, wherein The sleeve includes a flared first section (41) and an unflared second section (42) of approximately the same axial length.

8. A heat exchanger comprising heat exchange tubes and a jacket, and optionally including an inlet tube, an outlet tube, and a connecting tube, wherein... (i) the sleeve is the sleeve of claim 6 or 7; and (ii) Aluminum alloy round tubes a and b are respectively inserted into and welded to both ends of the sleeve, so that aluminum alloy round tubes a and b are connected to each other; wherein The aluminum alloy round tube a is a heat exchange tube, and the aluminum alloy round tube b is a connecting tube, an input tube, or an output tube. Preferably, the sleeve comprises a first section (41) with a flared end and a second section (42) with an unflared end, both having approximately the same axial length; the aluminum alloy round tube a is a long U-shaped tube after expansion, inserted into and welded to the first section (41) of the sleeve; and the aluminum alloy round tube b is a short U-shaped tube, inserted into and welded to the second section (42) of the sleeve; and Preferably, the welding temperature is 590-630℃ and the heating time is less than or equal to 2 minutes.

9. A method for preparing the aluminum alloy composite material according to any one of claims 1-5, comprising the following steps: 1) Cast ingots of the core alloy and the optional anti-corrosion layer alloy separately; and prepare the brazing layer alloy; 2) The core alloy is subjected to homogenization heat treatment, wherein the homogenization heat treatment temperature is 550°C to 620°C and the homogenization heat treatment time is 5-20 hours. 3) Mill the surfaces of the core material, brazing layer alloy ingot, and optional anti-corrosion layer alloy ingot; 4) Place the milled brazing alloy and the optional anti-corrosion alloy in a heating furnace at 450℃ to 520℃ for 5-20 hours, and then prepare plate-shaped brazing alloy and optional anti-corrosion alloy by hot rolling. 5) A thick plate of a brazing layer alloy of a certain thickness is laminated on one side of the core alloy; a thick plate of an anti-corrosion layer alloy of a certain thickness is laminated on the other side of the core alloy to obtain a composite, wherein the thickness of the brazing layer alloy is 4% to 20% of the thickness of the composite, and the thickness of the anti-corrosion layer alloy is 5% to 25% of the thickness of the composite. 6) Preheat the composite obtained in step 5) at 400°C to 520°C for 1 to 25 hours, then hot roll it to 2 to 6 mm and roll it into a coil; 7) Cold roll to the finished thickness to obtain composite coil; 8) Place the composite roll obtained in step 7) into an annealing furnace for finished product annealing. The annealing temperature is 250℃ to 450℃ and the annealing time is 1 to 3 hours.

10. A method for preparing an aluminum tube according to any one of claims 1-5 or a sleeve according to claim 6 or 7, comprising preparing the aluminum tube or the sleeve by high-frequency induction welding from an aluminum alloy composite material as defined in any one of claims 1-5.

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