CN115537608B

CN115537608B - Aluminum pipe, manufacturing method thereof and all-aluminum heat exchanger

Info

Publication number: CN115537608B
Application number: CN202211211734.5A
Authority: CN
Inventors: 张萍; 王浩红; 高凤华; 池武; 万小峰
Original assignee: Granges AB
Current assignee: Granges AB
Priority date: 2021-11-18
Filing date: 2022-09-30
Publication date: 2023-07-14
Anticipated expiration: 2042-09-30
Also published as: CN115537608A; WO2023087957A1

Abstract

The invention relates to an aluminum pipe with internal threads, wherein the aluminum pipe is made of a multi-layer composite material, the multi-layer composite material comprises a core material and a composite layer, and an alloy of the core material comprises: 0.5 to 2.0 wt% Si,0.5 to 1.5 wt% Mn,0.06 to 0.60 wt% Fe,0.1 to 1.0 wt% Cu, <0.5 wt% Mg, <1.0 wt% Zn, <0.2 wt% Ti, <0.2 wt% Zr, a single element of not more than 0.05 wt% and not more than 0.15 wt% total content, the balance being aluminum; the alloy of the composite layer comprises: <1.0 wt% Si, <1.5 wt% Mn, <0.5 wt% Fe, <0.25 wt% Cu, <0.25 wt% Mg,0.01-2 wt% Zn, <0.1 wt% Ti, <0.1 wt% Zr, other elements having a single content of 0.05 wt% or less and a total content of 0.15 wt% or less, and the balance being aluminum; wherein the depth of diffusion of the elements in the composite layer to the core material is 10-100 mu m; the diffusion depth of the element in the core material into the composite layer is more than 10 mu m. The invention also relates to a preparation method of the aluminum pipe and a heat exchanger comprising the aluminum pipe.

Description

Aluminum pipe, manufacturing method thereof and all-aluminum heat exchanger

Technical Field

The invention relates to the field of aluminum pipes and heat exchangers, in particular to an aluminum pipe with internal threads, a manufacturing method thereof and a heat exchanger using the aluminum pipe.

Background

The realization of energy conservation and environmental protection has become a necessary path for the development of the heating ventilation air conditioning industry. The heat exchanger is used as an important part in a heating ventilation air conditioning system, so that the efficiency of the heat exchanger is improved, the cost of the heat exchanger is reduced, and the refrigerant filling amount is reduced. With the great increase in the price of copper pipe materials, the call for cost reduction by using aluminum instead of copper is increasing.

At present, a refrigeration air conditioner heat exchanger mainly takes copper pipe aluminum fins (RTPF), and a refrigerant in a pipe exchanges heat with outside air through pipe walls and fins. The application of the all-aluminum heat exchanger is less, and the two types of the all-aluminum heat exchanger are mainly: one is a brazed parallel flow micro-channel heat exchanger, and the other is an extruded aluminum tube aluminum fin heat exchanger. The parallel flow heat exchanger adopts flat pipes, so that condensed water is not easy to drain, and the heat exchanger is not applied to mass production in the application of an outdoor heat exchanger in a heating working condition or an evaporator in a refrigerating working condition. The extruded tube of the extruded aluminum tube aluminum fin heat exchanger is limited by a production process, so that the corrosion resistance of the tube is poor, the internal enhanced heat transfer threads are difficult to process, and the product with high corrosion resistance and high heat exchange efficiency is difficult to obtain.

The heat transfer pipe is a main component of the heat exchanger, the weight of the heat transfer pipe accounts for 30% -50% of the heat exchanger, and the cost of the heat transfer pipe accounts for more than 40% of the heat exchanger. The traditional heat transfer tube adopts copper as raw material, and the price of the traditional heat transfer tube rises due to the shortage of copper resources. The aluminum heat exchange tube has rich aluminum resources on the earth, so that the aluminum heat exchange tube with good heat transfer performance, excellent corrosion resistance and easy processing is adopted, the production cost of the air conditioner industry can be reduced, the full heat exchanger is convenient to recycle, and the carbon emission of the whole life cycle of the heat exchanger is reduced.

CN201527144 proposes an air-conditioning heat exchanger employing an aluminum alloy U-shaped tube, which can reduce the refrigerant charge amount in the case of the same heat exchange performance as a copper tube heat exchanger. CN112254563a proposes a long-life aluminum alloy with high corrosion resistance and a spiral groove pipe produced from the alloy, and the flat pipe adopts the existing extrusion process, and the corrosion resistance of the flat pipe is improved through the design of alloy components.

Disclosure of Invention

In one aspect, the present invention relates to an aluminum pipe with internal threads, wherein the aluminum pipe is made of a multi-layer composite material, the multi-layer composite material comprises a core material and a composite layer, and an alloy of the core material comprises: 0.5 to 2.0 wt% Si,0.5 to 1.5 wt% Mn,0.06 to 0.60 wt% Fe,0.1 to 1.0 wt% Cu, <0.5 wt% Mg, <1.0 wt% Zn, <0.2 wt% Ti, <0.2 wt% Zr, a single element of not more than 0.05 wt% and not more than 0.15 wt% total content, the balance being aluminum; the alloy of the composite layer comprises: <1.0 wt% Si, <1.5 wt% Mn, <0.5 wt% Fe, <0.25 wt% Cu, <0.25 wt% Mg, 0.01-2 wt% Zn, <0.1 wt% Ti, <0.1 wt% Zr, other elements having a single content of 0.05 wt% or less and a total content of 0.15 wt% or less, and the balance being aluminum; wherein the depth of diffusion of the elements in the composite layer to the core material is 10-100 mu m; the diffusion depth of the element in the core material into the composite layer is more than 10 mu m.

In one embodiment, the depth of diffusion of the elements in the composite layer into the core material in the aluminum tube is 20-80 μm. In another embodiment, the diffusion depth of the element in the core material into the composite layer in the aluminum pipe is 20 μm or more.

In one embodiment, the composite layer in the aluminum tube includes at least an outer composite layer located on the outer surface of the core material. In an optional embodiment, the composite layer further comprises an inner composite layer located on the inner surface of the core material.

In one embodiment, the thickness of the outer and inner composite layers in the aluminum tube is 5% -20% of the thickness of the multilayer composite, respectively. In a preferred embodiment, the thickness of the outer and inner composite layers in the aluminum tube is 10% -15% of the thickness of the multilayer composite, respectively.

In one embodiment, the aluminum tube has a high frequency weld with a height less than or equal to the tooth height of the internal threads.

In one embodiment, the aluminum tube has a high frequency weld, and the aluminum tube has a width of the high frequency weld that is less than or equal to the tooth width of the internal threads.

In one embodiment, the potential of the composite layer in the aluminum tube is from-850 mV to-730 mV and the potential of the core material is from-730 mV to-600 mV.

In another aspect, the present invention also relates to a heat exchanger comprising the aluminum tube heat exchange tube of the present invention.

In yet another aspect, the present invention is also directed to a method of manufacturing an aluminum pipe, which may include at least the steps of: step 1: obtaining a multilayer composite of a target size; step 2: installing the composite material on pipe making equipment for uncoiling, and pressing an internal thread structure on the multilayer composite material through a thread die to obtain the multilayer composite material with internal threads; step 3: performing high-frequency induction welding on the multi-layer composite material with the internal threads obtained in the step 2 to form an aluminum pipe with the height of the inner welding rib of the high-frequency welding line being smaller than or equal to the tooth height of the internal threads; step 4: and (3) winding the aluminum pipe obtained in the step (3) into a disc and carrying out annealing treatment.

Drawings

Fig. 1: the aluminum pipe is schematically shown;

fig. 2: the production process flow of the aluminum pipe comprises the following steps of;

fig. 3: the type of thread on the composite material of the invention;

fig. 4: (a) a schematic structural view of the internal thread of the present invention;

(b) Another internal thread structure schematic diagram of the invention;

fig. 5: metallographic microscope pictures of high-frequency welding seam positions of the elliptic aluminum pipe and the aluminum pipe;

fig. 6: the structural schematic diagram of the composite material of the aluminum pipe;

fig. 7: the corrosion resistance mechanism of the composite material of the aluminum pipe;

Fig. 8: a partial schematic of the heat exchanger of the present invention;

fig. 9: the heat exchanger of the invention is compared with the cost of a heat exchange tube of a copper tube heat exchanger;

fig. 10: element diffusion between the composite layer and the core material;

fig. 11: influence of Zn content in the composite layer on performance;

fig. 12: the effect of Mn content in the core material on performance;

fig. 13: after 30 days of corrosion testing, (a) results of the heat exchanger of the present invention (b) cross-sectional view of the aluminum tube at the finless protected location;

fig. 14: after 90 days of corrosion test, the result diagram of the heat exchanger of the invention;

fig. 15: after 30 days corrosion testing, (a) photographs of heat exchangers using prior art extruded aluminum tubes (b) cross-sectional view of extruded aluminum tubes at finless protected locations

Fig. 16: results of heat exchangers using copper tubing after 30 days of corrosion testing.

Detailed Description

General definitions and terms

All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety, if not indicated otherwise.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In the event of a conflict, the definitions provided herein will control.

All percentages, parts, ratios, etc. are by weight unless otherwise specified.

When an amount, concentration, or other value or parameter is given as either a range, preferred range or upper and lower limit or a particular value, this is to be understood as specifically disclosing all ranges formed from any pair of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether ranges are separately disclosed. When numerical ranges are recited herein, unless otherwise stated, the stated ranges are meant to include the endpoints thereof, and all integers and fractions within the range. The scope of the invention is not limited to the specific values recited when defining the scope. For example, "1-8" encompasses 1, 2, 3, 4, 5, 6, 7, 8 and any subrange comprised of any two values therein, e.g., 2-6, 3-5.

The terms "about", "about" when used in conjunction with a numerical variable generally refer to the value of the variable and all values of the variable being within experimental error (e.g., within a confidence interval of 95% for the average) or within + -10% of the specified value, or more broadly.

The terms "comprising," "including," "having," "containing," or "involving," and other variations thereof herein, are inclusive or open-ended and do not exclude additional unrecited elements or method steps. Those skilled in the art will appreciate that such terms as "comprising" encompass the meaning of "consisting of …". The expression "consisting of …" excludes any element, step or ingredient not specified. The expression "consisting essentially of …" means that the scope is limited to the specified elements, steps, or components, plus any elements, steps, or components that are optionally present that do not materially affect the basic and novel characteristics of the claimed subject matter. It should be understood that the expression "comprising" encompasses the expressions "consisting essentially of …" and "consisting of …".

The term "selected from …" means that one or more elements in the group listed below are independently selected and may include a combination of two or more elements.

When numerical values or range endpoints are described herein, it is to be understood that the disclosure includes the specific value or endpoint cited.

The terms "one or more" or "at least one" as used herein mean one, two, three, four, five, six, seven, eight, nine or more.

Furthermore, the number of components or groups of components of the present invention not previously indicated is not limiting with respect to the number of occurrences (or existence) of components or groups of components. Thus, the singular forms of a component or a constituent should be interpreted to include one or at least one, and the plural unless the numerical value clearly indicates the singular.

The term "optional" or "optionally" as used herein means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where said event or circumstance occurs and instances where it does not.

The term "aluminum tube interior" as used herein refers to a tubular cavity within an aluminum tube.

The term "core outer surface" refers to the surface of the core material that is adjacent to the outside of the aluminum tube. The "core material inner surface" means a core material surface on the side of the inner cavity of the aluminum pipe.

In one aspect, the invention relates to an aluminum tube with internal threads, wherein the aluminum tube is made of a multi-layer composite material, and the multi-layer composite material comprises a core material and a composite layer.

The aluminum tube may be circular or elliptical in shape. In one embodiment, the aluminum tube is a round aluminum tube. Through the mature processing and manufacturing technology, the aluminum round tube can be used in the heat exchanger to manufacture the round tube heat exchanger. In another embodiment, the aluminum tube is an aluminum oval tube. Compared with an aluminum round tube, the elliptical structure can reduce the pressure drop of the air side of the heat exchanger using the aluminum tube and reduce the energy consumption of an air conditioning system using the heat exchanger.

Internal thread

In the present invention, the "internal thread" means a thread structure on the inner cavity side of the aluminum pipe. The internal thread can increase the contact area between the aluminum pipe and the heat exchange medium, and can also enable the heat exchange medium to be in a turbulent state when flowing in the aluminum pipe, thereby being beneficial to improving the heat exchange efficiency.

An aluminum pipe having internal threads can be obtained by rolling threads on a multilayer composite material and then by the method for manufacturing an aluminum pipe of the present invention (described in the subsequent specification). The threads on the multi-layer composite may be obtained by any suitable method. In one embodiment, the threads on the multilayer composite are obtained by roll forming.

The type of thread can be selected according to actual needs, and different types of internal thread forms can be pressed on the multi-layer composite material by flexibly replacing different internal thread rollers, for example, see fig. 3. The aluminium tube obtained by the subsequent process also has corresponding different types of internal threads.

The specific structure of the internal thread can be selected according to the actual situation. Fig. 4 (a) shows a schematic view of the structure of an internal thread, in which the internal thread form 1 in fig. 3 is pressed in a single-screw structure on a material web. The external diameter of the internally threaded aluminum pipe is 5mm to 15mm, preferably 5mm to 9mm. The bottom wall thickness is 0.3mm to 1.0mm, preferably 0.3mm to 0.5mm. The tooth height is 0.05 mm-0.5. 0.5mm, preferably 0.1mm-0.25mm. The number of teeth is 20-70. The tooth tip angle alpha is 10 deg. -70 deg., preferably 20 deg. -50 deg.. The helix angle is 0 ° to 40 °, preferably 10 ° to 30 °.

Fig. 4 (b) shows another internal thread structure, which is formed by pressing the internal thread pattern 3 of fig. 3 onto a material web. The internal thread comprises 2 internal threads with different helix angles, which are alternately pressed on a material belt, so that the threads are difficult to produce in a conventional drawing mode, and can be prepared by the preparation method of the invention through flexible adjustment of an internal thread roller. The external diameter of the internally threaded tube is 5mm-15mm, preferably 5mm-9mm. The bottom wall thickness is 0.3mm-1.0mm, preferably 0.3-mm mm-0.5mm. The tooth height is 0.05mm to 0.5mm, preferably 0.1mm to 0.25mm. The total number of teeth is 20-70. The tooth tip angle alpha is 10 deg. -70 deg., preferably 20 deg. -50 deg.. The helix comprises both left-handed and right-handed and has an angle of 0 ° -40 °, preferably 10 ° -30 °.

High frequency weld

An aluminum pipe having a high-frequency weld was obtained by high-frequency induction welding. Herein, the term "high frequency induction welding" has a meaning as generally understood by those skilled in the art, and may refer to a welding process for joining materials (e.g., aluminum materials) using the skin effect and proximity effect generated by a high frequency current. Typically, the frequency of the high frequency welding may be about 300-450kHz. The structure of the high frequency weld is shown in the metallographic micrograph of FIG. 5. The aluminum pipe can have more excellent mechanical properties by controlling the height and width of the weld. By adjusting the height and width of the welding seam, the aluminum pipe can have lower cracking rate of the expanded pipe, and the finished product rate is higher when the prepared aluminum pipe is used for a heat exchanger. The height of the high-frequency welding line refers to the height of the welding rib of the high-frequency welding line on the inner side of the aluminum pipe.

In one embodiment, the weld height is less than or equal to the internal thread tooth height. The high frequency weld may have a height of 50% to 100%, preferably 75% to 100%, more preferably 85% to 100%, for example about 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 89%, 90%, 95%, 100%, etc. of the internal thread tooth height.

In one embodiment, the weld width is less than or equal to the internal thread tooth width. The width of the high frequency weld may be 50% -100%, preferably 75% -100%, more preferably 85% -100%, for example about 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 95%, 100%, etc. of the tooth width.

The aluminum pipe is also subjected to a tube expansion operation for use in a heat exchanger. Therefore, the high-frequency welding seam needs to have certain mechanical strength, so that the high-frequency welding seam has better manufacturability in the subsequent expansion process, and the cracking of the pipe wall is avoided.

Multilayer composite material

The aluminum pipe is made of a multi-layer composite material. The multilayer composite may be in the form of a sheet or strip. In one embodiment, the multilayer composite is a multilayer composite tape.

The multilayer composite comprises a core material and a composite layer. The composite layer is used as a sacrificial anode protective layer to improve the corrosion resistance of the aluminum pipe. The core material has high strength to meet the requirements of strength and formability of the aluminum pipe.

In one embodiment, the multilayer composite is comprised of a core material and a composite layer. The multi-layer composite may also include additional layers to achieve different functions, as desired. For example, a braze layer may also be included.

The current electrolytic aluminum has higher energy consumption, which is unfavorable for environmental protection. According to the invention, the raw materials of the aluminum pipe are obtained by remelting and casting waste materials in production and aluminum alloy materials recovered from a heat exchanger. Compared with electrolytic aluminum, the method provided by the invention can reduce energy consumption, reduce carbon emission in the production process of aluminum pipe materials, and is more environment-friendly.

The composite layer may be a single layer composite layer. In one embodiment, the multi-layer composite is comprised of a core material and an outer composite layer located on the outer surface of the core material, in which case the composite layer is the outer composite layer. The aluminum pipe is obtained through the subsequent process, the outer side of the aluminum pipe is a composite layer, the inner cavity side of the aluminum pipe is a core material, and the inner surface of the core material is provided with internal threads.

The composite layer may be a two-layer composite layer. In one embodiment, the multi-layer composite is comprised of a core material, an outer composite layer located on an outer surface of the core material, and an inner composite layer located on an inner surface of the core material. The aluminum pipe is obtained through the subsequent process, the outer side of the aluminum pipe is an outer composite layer, the inner cavity side of the aluminum pipe is an inner composite layer, a core material is arranged between the outer composite layer and the inner composite layer, and the surface, close to the inner cavity of the aluminum pipe, of the inner composite layer is provided with an inner thread.

The ratio of the respective thicknesses of the outer composite layer and the inner composite layer to the thickness of the multilayer composite material is maintained within a certain range. When the thickness ratio is too high, the strength and formability of the aluminum pipe are deteriorated. The thickness of the composite layer is too low, and the effect of protecting the core material by sacrificing the composite layer is poor, so that the corrosion resistance of the product is poor. In one embodiment, the thickness of the outer composite layer is 5-20%, preferably 5% -15%, such as 10%, 15% of the thickness of the multilayer composite. In one embodiment, the thickness of the inner composite layer is 5-20%, preferably 5% -15%, of the thickness of the multilayer composite, for example: 15%.

The potential of the composite layer in the aluminum tube needs to be lower than the potential of the core material so that the aluminum tube has excellent corrosion resistance. In one embodiment, the composite layer has a potential of-850 mV to-730 mV and the core has a potential of-730 mV to-600 mV.

The composition of the core alloy affects the potential of the aluminum pipe core. Therefore, it is necessary to reasonably control the composition of the core alloy so that the core has a higher potential than the composite layer so that the composite layer can act as a protective layer to avoid corrosion of the core.

The alloy of the core material comprises:

0.5 to 2.0% by weight of Si,

0.5 to 1.5 wt% of Mn,

0.06 to 0.60% by weight of Fe,

0.1 to 1.0 wt% Cu

<0.5 wt% Mg,

<1.0 wt% Zn,

<0.2 wt.% Ti,

<0.2 wt% Zr,

The content of single element is less than or equal to 0.05 weight percent, the total content is less than or equal to 0.15 weight percent, and the balance is aluminum.

The alloy of the core material includes:

0.005% by weight or more of Mg,

0.01 wt% or more of Zn,

0.002 wt% or more of Ti,

0.002 wt% or more of Zr.

When preparing a multilayer composite material, the Mn content in the core alloy has a significant influence on the potential distribution, mechanical strength, and the like of the obtained multilayer composite material, and thus the corrosion resistance, strength, and the like of the aluminum pipe are further affected. When the Mn content in the core alloy is 1.5 wt% or more, the material is easily in a large particle state during casting, which is unfavorable for obtaining a proper uniform potential gradient distribution, and thus the corrosion resistance of the material is reduced. In an embodiment of the invention, the core alloy comprises less than 1.5 wt.% Mn, preferably comprises 0.5-1.5 wt.% Mn, e.g. comprises 1.21 wt.% or 1.13 wt.% Mn.

In one embodiment, an alloy for preparing a core material comprises: 0.72 wt% Si, 1.21 wt% Mn, 0.45 wt% Fe, 0.51 wt% Cu, 0.02 wt% Mg, 0.03 wt% Zn, 0.14 wt% Ti, 0.01 wt% Zr, the balance being aluminum, it being understood that it is also possible to contain other elements in an amount of 0.05 wt% or less and in an amount of 0.15 wt% or less in total. In another embodiment, the alloy composition for preparing the core material is: 1.37 Si in weight%, mn in weight% 1.13%, fe in weight% 0.36%, cu in weight% 0.43%, mg in weight% 0.16%, zn in weight% 0.24%, ti in weight% 0.08%, zr in weight% 0.04% and the balance aluminum, it being understood that it is also possible to contain other elements in a single content of 0.05% by weight or less and in a total content of 0.15% by weight or less.

The composition of the composite layer alloy affects the potential of the aluminum tube composite layer. Therefore, it is necessary to reasonably control the composition of the composite layer alloy so that the composite layer has a lower potential relative to the core material, which can act as a protective layer, whereby the aluminum pipe has a corrosion-resistant effect.

The alloy of the composite layer comprises:

<1.0 wt% Si,

<1.5 wt.% Mn,

<0.5 wt% Fe,

<0.25 wt% Cu,

<0.25 wt% Mg,

0.01-2 wt% of Zn,

<0.1 wt.% Ti,

<0.1 wt% Zr,

The alloy of the composite layer comprises:

si in an amount of 0.01 wt% or more,

mn in an amount of 0.001 wt% or more,

0.005 wt% or more of Fe,

0.0025 wt% or more of Cu,

0.0025 wt% or more of Mg,

0.001 wt% or more of Ti,

0.001 wt% or more of Zr.

In one embodiment, an alloy for preparing a composite layer comprises: 0.08 wt% Si, 0.02 wt% Mn, 0.26 wt% Fe, 0.01 wt% Cu, 0.01 wt% Mg, 0.01 wt% Zn, 0.01 wt% Ti, <0.1 wt% Zr, and the balance aluminum, it being understood that it is also possible to contain other elements in an amount of 0.05 wt% or less and in an amount of 0.15 wt% or less in total. In another embodiment, the alloy composition for making the composite layer is: 0.18 wt% Si, 0.05 wt% Mn, 0.32 wt% Fe, 0.02 wt% Cu, 0.01 wt% Mg, 1.15 wt% Zn, 0.02 wt% Ti, <0.1 wt% Zr, and the balance aluminum, it being understood that it is also possible to contain other elements in an individual content of 0.05 wt% or less and in a total content of 0.15 wt% or less. In yet another embodiment, the alloy composition for preparing the composite layer is: 0.7 wt% Si, 1.2 wt% Mn, 0.25 wt% Fe, 0.03 wt% Cu, 0.02 wt% Mg, 0.7 wt% Zn, 0.02 wt% Ti, 0.02 wt% Zr, the balance being aluminum, it being understood that it is also possible to contain other elements in an amount of 0.05 wt% or less and in an amount of 0.15 wt% or less in total.

The alloy of the composite layer contains elements in suitable amounts to give the aluminum pipe excellent properties.

The alloy of the composite layer comprises less than 1.0 wt% Si. Preferably, the alloy of the composite layer contains 0.01 wt% or more and less than 1.0 wt% Si.

The alloy of the composite layer comprises less than 0.5 wt% Fe. Preferably, the alloy of the composite layer contains 0.005 wt% or more and less than 0.5 wt% of Fe.

The alloy of the composite layer comprises less than 0.25 wt.% Cu. Preferably, the alloy of the composite layer comprises 0.0025 wt% or more and less than 0.25 wt% Cu.

The alloy of the composite layer comprises less than 0.25 wt% Mg. Preferably, the alloy of the composite layer comprises 0.0025 wt% or more and less than 0.25 wt% Mg,

the alloy of the composite layer comprises less than 0.1 wt.% Ti. Preferably, the alloy of the composite layer contains 0.001 wt% or more and less than 0.1 wt% Ti.

The alloy of the composite layer comprises less than 0.1 wt% Zr. Preferably, the alloy of the composite layer contains Zr in an amount of 0.001 wt% or more and less than 0.1 wt%.

In the alloy for preparing the composite layer, the Zn content affects the corrosion resistance, strength, etc. of the aluminum pipe. When the Zn content exceeds 2 wt%, the Zn content in the composite layer is too high, which results in an increase in the corrosion rate of the material and a reduction in the service life of the product. In an embodiment of the invention the alloy of the composite layer comprises 0.01-2 wt.% Zn, preferably 0.01-1.5 wt.% Zn, e.g. 0.01 wt.%, 1.15 wt.%, or 0.7 wt.% Zn.

On the basis of the structure of the composite layer and the core material, the self-corrosion and galvanic corrosion performances of the material can be further improved by controlling the grain structure collocation of the composite layer and the core material and controlling the element interdiffusion between the composite layer and the core material. The depth of interdiffusion of the elements in the composite layer and the core material needs to be controlled within a suitable range so that the aluminum pipe attains desired properties. Such a diffusion process may be achieved, for example, by a preparation process.

As shown in fig. 7, when a material is locally corroded for some reason, a loss in depth occurs, and potential 1, potential 2, and potential 3 form potential differences due to differences in concentration of elements at different depths. In the present invention, potential 1> potential 2> potential 3. At this time, the position 3 (the outer surface of the composite layer) having the lowest potential is preferentially corroded, thereby protecting the positions 2 and 1, and then the corroded position 2 protects 1. Therefore, the missing position 3 which appears earlier can not continuously form a pit downwards, but extend towards the parallel direction, thus avoiding perforation leakage caused by rapid corrosion of the aluminum pipe and achieving the corrosion resistance effect.

The element diffusion can be generally determined by the distribution of the elements (e.g., si, mn, fe, cu, mg, zn, ti and/or Zr, etc.). Element diffusion conditions between the composite layer and the core material are determined through element distribution of the composite layer and the core material obtained by a scanning electron microscope. Those skilled in the art will appreciate that when referring to the depth of diffusion of an element, it is determined by the element under consideration. When more than one element is considered, the diffusion range referred to is determined by the element that diffuses the deepest and the element that diffuses the shallowest. In one embodiment, the elements used are Cu and/or Zn.

The details are described below with reference to fig. 10, wherein the total thickness of the tube wall material of the aluminum tube is 700 μm, and wherein the thickness of the composite layer is 80 μm. When the Zn element contained in the composite layer was diffused into the core material and the Zn content in the core material was stable (the position having a difference of about 130 μm from the outer surface of the aluminum pipe in FIG. 10), the diffusion distance was the diffusion depth of the Zn element from the composite layer to the core material, and the diffusion depth of the Zn element from the composite layer to the core material was about 50 μm in FIG. 10, depending on the thicknesses of the core material and the composite layer. When the Cu content in the composite layer is stable (the position having a distance of about 70 μm from the outer surface of the aluminum pipe in fig. 10), the Cu element contained in the core layer diffuses into the composite layer at a distance of about 10 μm from the composite layer, which is the diffusion depth of the Cu element from the composite layer to the core material, and similarly, the diffusion depth of the Cu element from the composite layer to the core material in fig. 10 is known to be about 10 μm.

In one embodiment, the depth of diffusion of the elements (e.g., si, mn, fe, cu, mg, zn, ti and/or Zr, etc.) into the core material in the composite layer is 10-100 μm, preferably 20-80 μm, e.g., 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, 100 μm. The diffusion depth of elements in the composite layer to the core material is too large, the overall potential gradient of the material is small, and a better sacrificial anode cannot be formed to protect the core material. The depth is too small, the composite layer and the core material have obvious element distribution limit, and the effect of protecting the core material by the sacrificial anode from outside to inside cannot be formed. In an exemplary embodiment, the element of diffusion of the composite layer into the core material is Cu and/or Zn. In yet another embodiment, the depth of Cu and/or Zn diffusion into the core material is 10-100 μm, preferably 20-80 μm, e.g. 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, 100 μm.

In one embodiment, the diffusion depth of the element (e.g., si, mn, fe, cu, mg, zn, ti and/or Zr, etc.) in the core material into the composite layer is 10 μm or more, preferably 20 μm or more, e.g., 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 100 μm, 200 μm, 500 μm, etc. If the diffusion depth of the elements in the core material to the composite layer is too small, the composite layer and the core material will generate obvious element distribution limit, and the sacrificial anode from outside to inside cannot be formed to protect the core material effect. The elements in the core material may diffuse throughout the composite layer. In one exemplary embodiment, the element of diffusion of the core material into the composite layer is Cu and/or Zn. In yet another embodiment, the diffusion depth of Cu and/or Zn of the elements in the core material into the composite layer is 10 μm or more, preferably 20 μm or more, for example 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 100 μm, 200 μm, 500 μm, etc.

Through reasonable collocation of the structures, components and the like of the core material and the composite layer and proper process control, the aluminum pipe has higher strength (pressure resistance) and excellent corrosion resistance.

Heat exchanger

In another aspect, the invention also relates to a heat exchanger, wherein the heat exchange tube included in the heat exchanger is the aluminum tube of the invention. The heat exchanger also typically includes fins (as shown in fig. 8), and by reasonable design of the fins and aluminum tubes, the potential of the heat exchanger is: the fin < aluminum pipe outer surface < aluminum pipe core material can strengthen the corrosion resistance of the heat exchanger in a corrosive environment.

In one embodiment, the heat exchanger fins have a potential of-850 mV to-740 mV.

The composition of the fin is an important factor affecting its potential. Materials useful in the present invention for the fins include, but are not limited to, AA8011, AA3102, AA1100. In one embodiment, the material of the fins is AA8011.

Method for manufacturing aluminum pipe

In another aspect, the present invention also relates to a method of manufacturing the aluminum pipe of the present invention, comprising the steps of: obtaining a multilayer composite of a target size; installing the multilayer composite material in pipe making equipment, and pressing an internal thread structure on the multilayer composite material through a thread die to obtain the multilayer composite material with internal threads; performing high-frequency induction welding on the multi-layer composite material with the internal threads to form an aluminum pipe; the aluminum tube was wound into a disc and annealed.

The multilayer composite may be composed of a suitable composite layer prepared from the composite layer alloy as described above and a core material prepared from the core material alloy as described above.

The multi-layer composite may be composed of a single layer composite layer and a core material, such as shown in the left-hand view of fig. 6. The multi-layer composite may be composed of a two-layer composite and a core material, wherein the core material is located between an outer composite layer and an inner composite layer, such as shown in the right-hand view of fig. 6.

The process of preparing a multi-layer composite material generally comprises a series of steps of alloy casting, rolling into a plate, hot rolling into a plate or strip rolled to a certain thickness after compounding, and the like.

In one embodiment, the multilayer composite is prepared by the following method: casting of aluminum ingots, wherein the proportion of different elements is optimized; sawing; special homogenization; milling the surface; compounding; hot rolling; cogging and cold rolling; special heat treatment; finish rolling to a target thickness (e.g., 0.7 mm). In the whole process, the element proportion of the alloy is optimized, the content of Si, cu, mn, ti and the like is further optimized and adjusted on the basis of the conventional AA3003, and the core material is combined with the corrosion-resistant composite layer to obtain the high-strength corrosion-resistant composite material.

The target dimensions (e.g., thickness, size, etc.) of the multi-layer composite may be reasonably selected based on the dimensions of the aluminum tube and the dimensions of the internally threaded rollers. The multi-layer composite material is generally obtained in a larger size during the preparation process, and then the composite material with the target size is obtained by adopting an online mechanical cutting mode.

In one embodiment, an aluminum alloy strip wound into a roll is used, which is composed of a core material and a corrosion-resistant layer, and has a width of typically 15mm to 50mm and a thickness of typically 0.3 to 1.0mm. And (3) after the aluminum alloy coiled material is installed in pipe making equipment, uncoiling is sequentially carried out. And then leveling the aluminum alloy strip so as to facilitate subsequent internal thread pressing.

Different internal thread rollers are flexibly selected, and different types of internal thread structures can be pressed on the multilayer composite material, so that the manufactured aluminum pipe has different types of internal threads, for example, as shown in fig. 3.

The step of pressing the internal thread of the present invention is performed during the tubing process. In one embodiment, the internal threads are pressed on a tubing machine. Specifically, the composite material is mounted on a pipe making device and uncoiled, and an internal thread structure is pressed on the multilayer composite material through a thread die. The method can reduce the cost of the die, has higher flexibility, and simultaneously avoids the multi-layer composite material with the internal threads from being segmented, so that the integrity of the threads can be maintained.

A multi-layer composite material with internal threads obtained by high frequency induction welding may be used. In one embodiment, a multi-layer composite material having internal threads is subjected to high frequency induction welding to obtain an aluminum tube having a high frequency weld. The pipe making mode adopting the high-frequency induction welding process has the technical advantages of high production efficiency and good yield, the production efficiency can reach 100-150 m/min, and the yield is higher than 92%. The whole pipe making process is carried out in an oil-free and chip-free mode, and the cleanliness of the inside of the aluminum pipe is high.

Fig. 2 shows a basic production flow of the aluminum pipe of the invention. The aluminum alloy coiled material is sequentially uncoiled after being installed in tubing equipment, is formed by internal thread rolling, is subjected to high-frequency induction welding, and is finally coiled into a disc for annealing, so that the refrigeration tube capable of being used for a heat exchanger is prepared. The aluminum pipe forming method has the advantages of large pipe diameter range, capability of pressing different types of thread structures (shown in figure 3 for example) on the composite aluminum belt by flexibly replacing different internal thread rollers, high production efficiency and yield, low cost, good pipe making cleanliness and convenience in manufacturing of subsequent heat exchangers.

Advantageous effects

According to the high-corrosion-resistance high-frequency welded aluminum pipe, through the material design of the multi-layer composite aluminum alloy, the aluminum pipe has good corrosion resistance, and the corrosion resistance of a finless protected part (such as a elbow and the like) can be improved, so that the use of an anti-corrosion coating is reduced or avoided, and the high-corrosion-resistance high-frequency welded aluminum pipe has the advantages of low carbon and environmental protection. Meanwhile, the coordination and balance of the strength (pressure resistance) and the corrosion resistance of the aluminum pipe are realized through the matching and combination of the core material and the composite layer.

The invention adopts the multilayer composite material to roll the screw thread on line, and overcomes the defects of single material, poor wall thickness uniformity, limited internal thread form and the like of the existing extruded tube by high-frequency induction welding. The high-frequency welding pipe making mode has the technical advantages of high production efficiency and good yield. The whole pipe making process is carried out in an oil-free and chip-free mode, and the internal cleanliness is high.

Examples

The following describes the aspects of the invention in further detail with reference to specific examples.

The following examples are given for the purpose of clearly illustrating the technical aspects of the present invention, and are not to be construed as limiting the present invention. Other variations or modifications of the above description will be apparent to those of ordinary skill in the art, and it is not necessary or exhaustive of all embodiments, and obvious variations or modifications of the invention are intended to be within the scope of the invention. The instrumentation and reagent materials used herein are commercially available unless otherwise indicated.

The alloy composition of the core material is shown in table 1, the alloy composition of the composite layer is shown in table 2, and the balance is Al.

TABLE 1

TABLE 2

Examples 1-6 were prepared according to the preparation method of the present invention by selecting a multi-layer composite aluminum alloy tape whose core material, the alloy composition of the composite layer are shown in table 3.

Example 1:

core-1 is selected as Core material alloy, clad-A is selected as composite layer alloy, the Core material and a single-layer composite layer are subjected to hot rolling and compositing to prepare the aluminum alloy strip wound into the coil, the width of the aluminum alloy strip is 21.8mm, the thickness of the aluminum alloy strip is 0.7mm, and the thickness of the composite layer accounts for 10% of the total thickness of the strip.

And (3) after the aluminum alloy strip is installed in pipe making equipment and is uncoiled and leveled in sequence, a roller with an internal thread form 1 (see figure 3) is selected, and the internal thread is formed on the surface of a core material of the strip by rolling.

And then forming a pipe by high-frequency induction welding, sizing and finishing to form an aluminum round pipe with the outer diameter of 7mm, wherein the internal thread is positioned on the inner cavity side of the aluminum round pipe, and the height of the high-frequency welding seam does not exceed the tooth height of the internal thread and the width of the high-frequency welding seam does not exceed the tooth width of the internal thread. The aluminum pipe of example 1 was obtained by winding into a disc and then annealing.

Examples 2 to 4

The preparation method is the same as in example 1, except that the core alloy, the clad alloy and the clad thickness ratio are different. As shown in table 3.

Example 5:

the Core-1 is selected as the Core material alloy, the Clad-A is selected as the alloy of the outer composite layer, and the Clad-B is selected as the alloy of the inner composite layer. The core material and the double-layer composite layer are subjected to hot rolling and compositing, wherein the core material is positioned between an outer composite layer (Clad-A) and an inner composite layer (Clad-B) to prepare the aluminum alloy strip wound into the coil, the thickness of the outer composite layer accounts for 10% of the total thickness of the strip, and the thickness of the inner composite layer accounts for 15% of the total thickness of the strip.

Subsequently, an aluminum pipe of example 5 was produced in the same manner as in example 1.

Example 6

The preparation was the same as in example 5, except that Core-2 was used as the Core alloy.

Example 7

And then forming a tube by high-frequency induction welding, sizing and finishing to form an aluminum round tube with the outer diameter of 7mm and the wall thickness of 0.45 and mm, wherein the internal thread is positioned on the inner cavity side of the aluminum round tube, and the tooth height of the internal thread is as follows: 0.18mm, internal thread tooth width: 0.35mm; height of high frequency weld: width of high frequency weld of 0.16 mm: 0.32mm. The aluminum pipe of example 7 was obtained by winding a coil and then annealing.

Comparative example 1:

an aluminum pipe with AA3102, internal threads and an outer diameter of 7mm was prepared by extrusion. Comparative example 1 was obtained by the following method: and continuously extruding the aluminum alloy round pipe, wherein the aluminum material is continuously extruded into a die cavity due to the friction force between the aluminum pipe and an extrusion wheel groove, and coating and filling the thread core head under the high-pressure and high-temperature state, so that the internal thread aluminum pipe which is matched with the thread core head is formed.

Comparative example 2:

copper pipe with material C11000, internal thread and external diameter of 7mm is prepared by extrusion. Comparative example 2 was obtained by the following method: the copper ingot is rolled, pulled in a dual way, pulled in a disc way, annealed on line, formed by internal threads, horizontally wound, annealed in a disc way and the like in sequence, and then the copper tube for the air conditioner heat exchanger is formed.

Comparative example 3

And then forming a tube through high-frequency induction welding, sizing and finishing to form an aluminum round tube with the outer diameter of 7mm, wherein the internal thread is positioned on the inner cavity side of the aluminum round tube, and the tooth height of the internal thread is as follows: 0.18mm, internal thread tooth width: 0.35mm; height of high frequency weld: width of high frequency weld of 0.25 mm: 0.9mm. After being wound into a disc, the aluminum tube of comparative example 3 was annealed.

Experimental example

Element diffusion: and determining the element diffusion condition between the composite layer and the core material by combining the element distribution of the composite layer and the core material obtained by the scanning electron microscope. For example, as described in detail with reference to fig. 10, the total thickness of the tube wall material of the aluminum tube is 700 μm, and the thickness of the composite layer is 80 μm. When the Zn content in the core material is stable (the position with a difference of about 130 μm from the outer surface of the aluminum pipe in FIG. 10), the diffusion distance in the core material is the diffusion depth of Zn element from the composite layer to the core material, and the diffusion depth of Zn element from the composite layer to the core material in FIG. 10 is about 50. Mu.m. When the Cu content in the composite layer is stable (the position having a distance of about 70 μm from the outer surface of the aluminum pipe in fig. 10), the Cu element contained in the core layer diffuses into the composite layer at a distance of about 10 μm from the composite layer, i.e., the diffusion depth of the Cu element into the core material from the composite layer in fig. 10.

According to the above measurement method, it was measured that in examples 1 to 4, the diffusion depth of the elements Zn and Cu in the composite layer toward the core material was 20 to 65 μm; the diffusion depth of Zn and Cu elements in the core material to the composite layer is 20-40 mu m.

In examples 5 to 6, the diffusion depth of the outer composite layer (Clad A) element into the core material is 20 to 45 μm of the thickness of the core material; the diffusion depth of the element of the inner composite layer (Clad B) to the core material is 25-40 mu m; the diffusion depth of the core material element to the composite layer is 15-35 mu m. The diffusion depth of the core material element to the outer composite layer is 15-30 mu m; the diffusion depth of the core element into the inner composite layer is 13-27 μm.

The potential, mechanical properties, percent core material waste were measured by the following methods for examples and comparative examples, and the results are shown in tables 3 to 4. The method for measuring the mechanical properties of the material comprises the following steps: the national standard GB/T228-2002 metallic material room temperature tensile test method. Core scrap consumption%scrap weight used to make core/total alloy weight used to make core x 100%. Wherein recovered waste in% = weight of waste from recovery/weight of total waste used x 100%.

TABLE 3 Table 3

TABLE 4 Table 4

	Mechanical properties MPa	Core material consumption waste material percentage%	The recovery waste material accounts for%
				Example 1	142	63％	100％
Example 2	145	63％	100％
				Example 3	155	100％	100％
Example 4	160	100％	100％
				Example 5	135	63％	100％
Example 6	146	100％	100％
				Comparative example 1	95	<10％	<10％
Comparative example 2	225	-	-

The data in Table 4 shows that examples 1-6 have tensile strengths of 135MPa-160 MPa, which are about 42% -78% higher than the prior art extruded aluminum tube comparative example 1. This shows that the aluminum pipe of the invention has higher strength and better pressure resistance than the aluminum pipe of the prior art produced by extrusion.

The corrosion resistance test method comprises the following steps: standard ASTM-G85-A3

The composite materials comprising composite layers of different Zn content and core material were subjected to corrosion resistance tests, the results are shown in fig. 11. The results show that for a composite material with an initial thickness of 600 μm, for a composite material with a Zn content in the composite layer exceeding 2 wt.%, the main elemental composition of the composite layer is: 0.29 wt% Si,0.20 wt% Fe, 2.5 wt% Zn, the thickness of the composite remained 259.3 μm after 70 days of corrosion resistance test; for the composite material with the Zn content below 2 wt% in the composite layer, wherein the composite layer is Clad B, after 120 days of testing, the thickness of the composite material remains 474.3 mu m. From the above results, the Zn content has a significant effect on the corrosion resistance of the material, and the composite layer contains Zn with a proper content, which is beneficial to improving the corrosion resistance.

Effect of Mn content in core alloy on performance

Casting a composite material containing Mn in an amount of 1.5 wt% or more, wherein the core alloy has a main elemental composition of: a metallographic microscope photograph of 0.31 wt% Si,0.25 wt% Fe,0.46 wt% Cu,1.68 wt% Mn, and the material is shown in fig. 12. The results show that the material has a large particle structure (see the structure indicated by the circles in fig. 12), and the material in the state of large particles cannot obtain a proper uniform potential gradient distribution, and the corrosion resistance of the material is poor.

Influence of high-frequency weld on aluminum tubes

The size and strength of the high frequency weld affects the practical application of the aluminum pipe. As shown in table 5 below, the aluminum pipe of example 7 was good in workability, low in cracking rate of the expanded pipe, and high in yield when applied to a heat exchanger. The bursting pressure of the aluminum pipe of the embodiment 7 is more than 17.5MPa, so that the practical application, such as a heat exchanger used in the field of refrigeration and air conditioning, is satisfied. Compared with example 7, comparative example 3 has poorer processability, is more prone to cracking of the expanded tube, and has lower yield when applied to a heat exchanger. The experimental data show that the high-frequency welded aluminum pipe obtained by controlling the height of the high-frequency welded joint to be smaller than the tooth height and the width to be smaller than the tooth width has better performance.

TABLE 5

Tube expansion cracking rate in the verification stage of aluminum round tube products: refers to the proportion of the cracking condition of the aluminum pipe after the pipe expanding operation: 5% below: low; 5% -10%: medium; 10% -15%: higher; 15% or more: high.

Heat exchanger yield in the aluminum round tube product verification stage: 85% or less: low; 85% -90%: medium; 90% -95%: higher; 95% or more: high.

Aluminum heat exchanger

The aluminum pipe of the invention is adopted to prepare the corrosion-resistant aluminum heat exchanger. Wherein the fin is made of AA8011. The potential ranges of the respective positions are measured as shown in table 6 below.

TABLE 6

Potential value	Fin type	Aluminum pipe composite layer	Aluminum pipe core material
				Aluminum heat exchanger	-850mV to-740 mV	-850mV to-730 mV	-730mV to-600 mV

The electric potential of the fins of the prepared aluminum heat exchanger is lower than the electric potential of the outer surface of the aluminum pipe (namely the outer surface of the aluminum pipe composite layer), the electric potential of the aluminum pipe core material is higher than the electric potential of the outer surface of the aluminum pipe, and according to the corrosion resistance result, the corrosion condition of the aluminum pipe at the places without fin protection is reduced due to the protection effect of the fins. Finally, the corrosion resistance of the heat exchanger in a corrosive environment is enhanced while the use of an anti-corrosion coating is avoided.

As shown in fig. 9, for the 1.5P outdoor unit condenser of the home air conditioner, the cost of the aluminum pipe of the present invention was compared with that of the conventional copper pipe condenser, and both condensers had the same heat exchanging performance. The cost of the aluminum tube is 33% of the cost of the copper tube, and the cost difference brought by the manufacturing process is reduced by 20% -30% compared with that of the copper tube condenser.

The testing method for the corrosion resistance of the heat exchanger comprises the following steps: standard ASTM-G85-A3

The aluminum tubes of the present invention of examples 1 to 6, the extruded aluminum tube of comparative example 1, and the copper tube of comparative example 2 were used as heat exchanger cores, respectively, to prepare the obtained heat exchangers. The heat exchanger prepared was tested for corrosion performance using ASTM G85 Annex A3 corrosion test method. The test results are shown in table 7 below.

TABLE 7

The aluminum tubes of examples 1-6 of the present invention are used as aluminum heat exchangers made of heat exchanger cores, and have excellent corrosion resistance. After 30 days of corrosion test, the aluminum tubes of examples 1 to 6 were not corroded, no through hole leakage was observed, and the fins were not corroded.

Fig. 13 shows a state of an aluminum heat exchanger using the aluminum pipe of example 1 after 30 days of corrosion test. It can be seen from fig. 13 (a) that no corrosion of the aluminum tubes and fins of the aluminum heat exchanger occurs, and fig. 13 (b) shows a cross-sectional view of the aluminum tubes (within the circles of fig. 13 (a)) at the finless protected locations, and that the aluminum tubes are intact and not corroded.

Fig. 14 shows a state of a heat exchanger using the aluminum pipe of example 1 after 90 days of corrosion test. As can be seen from fig. 14, the aluminum tube of the aluminum heat exchanger is not corroded, no perforation is leaked, the fins are only slightly corroded, the fins are not separated, and the actual service performance of the aluminum heat exchanger is not affected.

The heat exchanger using the extruded aluminum tube of comparative example 1, as shown in fig. 15, was subjected to corrosion test for 30 days, and the extruded aluminum tube was severely corroded, and perforation leakage occurred.

As shown in FIG. 16, after 30 days of corrosion test, the copper tube heat exchanger manufactured by the copper tube of the comparative example 2 has no corrosion and no perforation leakage phenomenon, but the fins have serious corrosion and fin falling off, so that the copper tube heat exchanger fails and the actual service performance of the heat exchanger is affected.

The aluminum pipe provided by the invention not only can improve corrosion resistance, but also can strengthen heat exchange in the pipe and improve heat exchange efficiency by combining different internal threads. The aluminum pipe can replace the copper pipe for the heat exchanger in the application fields of the existing household/commercial air conditioner, refrigeration/refrigeration and the like, reduces the cost of the heat exchanger on the premise of meeting the requirements of heat exchange performance and corrosion resistance of the product, and is convenient for the integral recycling of the product at the end of use.

Claims

1. An aluminum pipe with internal threads, wherein the aluminum pipe is made of a multi-layer composite material, the multi-layer composite material comprises a core material and a composite layer,

the alloy of the core material comprises:

0.5 to 2.0 wt% Si,

0.5 to 1.5 wt% Mn,

0.06 to 0.60 wt% Fe,

0.1 to 1.0 wt% Cu,

< 0.5% by weight of Mg,

< 1.0% by weight of Zn,

< 0.2% by weight of Ti,

<0.2 wt% Zr,

the content of single element is less than or equal to 0.05 weight percent, the total content of other elements is less than or equal to 0.15 weight percent, and the balance is aluminum;

the alloy of the composite layer comprises:

< 1.0% by weight of Si,

<1.5 wt% of Mn,

< 0.5% by weight of Fe,

<0.25 wt% of Cu,

< 0.25% by weight of Mg,

0.01 to 2 wt% of Zn,

< 0.1% by weight of Ti,

<0.1 wt% Zr,

the content of single element is less than or equal to 0.05 weight percent, the total content of other elements is less than or equal to 0.15 weight percent, and the balance is aluminum; wherein,,

the diffusion depth of the elements in the composite layer to the core material is 10-100 mu m;

the diffusion depth of the element in the core material into the composite layer is more than 10 mu m.

2. The aluminum pipe as recited in claim 1, wherein,

the alloy of the core material comprises:

0.005% by weight or more of Mg,

0.01 wt% or more of Zn,

0.002 wt% or more of Ti,

0.002 wt% or more of Zr;

the alloy of the composite layer comprises:

si in an amount of 0.01 wt% or more,

mn in an amount of 0.001 wt% or more,

0.005 wt% or more of Fe,

0.0025 wt% or more of Cu,

0.0025 wt% or more of Mg,

0.001 wt% or more of Ti,

0.001 wt% or more of Zr.

3. The aluminum pipe as recited in claim 1 or 2, wherein,

the diffusion depth of the elements in the composite layer to the core material is 20-80 mu m; and/or

The diffusion depth of the element in the core material to the composite layer is more than 20 mu m.

4. The aluminum pipe as recited in claim 1 or 2, wherein,

the composite layer at least comprises an outer composite layer positioned on the outer surface of the core material,

optionally, the composite layer further comprises an inner composite layer located on the inner surface of the core material.

5. The aluminum pipe as recited in claim 4, wherein,

the thickness of the outer composite layer and the thickness of the inner composite layer are respectively 5% -20% of the thickness of the multilayer composite material.

6. The aluminum pipe as recited in claim 5, wherein,

the thickness of the outer composite layer and the thickness of the inner composite layer are respectively 10% -15% of the thickness of the multilayer composite material.

7. The aluminum pipe as recited in claim 1 or 2, wherein,

the potential of the composite layer is-850 mV to-730 mV, and the potential of the core material is-730 mV to-600 mV.

8. The aluminum pipe as recited in claim 1 or 2, wherein,

the aluminum tube has a high frequency weld, wherein,

the height of the high-frequency welding seam is smaller than or equal to the tooth height of the internal thread; and/or

The width of the high-frequency welding seam is smaller than or equal to the tooth width of the internal thread.

9. A heat exchanger includes a heat exchange tube, wherein,

the heat exchange tube is an aluminum tube according to any one of claims 1 to 8.

10. A method of manufacturing the aluminum pipe of any one of claims 1-8, wherein the method comprises the steps of:

obtaining a multilayer composite of a target size;

installing the composite material on pipe making equipment for uncoiling, and pressing an internal thread structure on the multilayer composite material through a thread die to obtain the multilayer composite material with internal threads;

Performing high-frequency induction welding on the multi-layer composite material with the internal threads to form an aluminum pipe with the height of a welding rib on the inner side of the high-frequency welding seam being smaller than or equal to the tooth height of the internal threads;

the aluminum tube was wound into a disc and annealed.