Heat exchanger and method of processing thereof

Abstract

This application provides a heat exchanger and its processing method. The heat exchanger includes a heat exchange tube and fins. The heat exchange tube is made of aluminum or an aluminum alloy. The fins are also made of aluminum or an aluminum alloy. The fins are welded to the heat exchange tube. The Si concentration at the grain boundaries of the heat exchange tube is a first concentration, and the Si concentration within the grains of the heat exchange tube is a second concentration. The depth of the heat exchange tube where the first concentration is greater than twice the second concentration does not exceed 40 μm. This application can extend the corrosion resistance life of aluminum heat exchangers and improve their reliability.

Description

Technical Field

[0001] This application relates to the field of heat exchanger technology, and in particular to a heat exchanger used in refrigeration, heating, ventilation and air conditioning systems and its processing method. Background Technology

[0002] In the field of refrigeration, heating, ventilation, and air conditioning (HVAC), aluminum heat exchangers have gained increasingly widespread use due to their advantages such as lightweight, ease of processing, and high cost-effectiveness. Furthermore, the heat exchange tubes and fins of aluminum heat exchangers are connected by welding, eliminating air thermal resistance and thus improving heat exchange capacity. However, during use, localized corrosion can easily occur at the welded joints between the heat exchange tubes and fins, resulting in poor corrosion resistance. Corrosion of the heat exchange tubes can also lead to leakage risks, affecting the reliability of the heat exchanger. Summary of the Invention

[0003] This application provides a heat exchanger and its processing method to extend the corrosion resistance life of aluminum heat exchangers and improve their reliability.

[0004] The first aspect of this application provides a heat exchanger comprising: a heat exchange tube and fins, wherein the heat exchange tube is made of aluminum or an aluminum alloy; the fins are made of aluminum or an aluminum alloy; the fins are welded to the heat exchange tube; the Si concentration at the grain boundaries of the heat exchange tube is a first concentration, the Si concentration within the grains of the heat exchange tube is a second concentration, and the depth of the heat exchange tube when the first concentration is greater than twice the second concentration does not exceed 40 μm.

[0005] The technical solution provided in this application can achieve the following beneficial effects:

[0006] The heat exchanger provided in this application includes heat exchange tubes and fins. The heat exchange tubes are made of aluminum or aluminum alloy, and the fins are also made of aluminum or aluminum alloy. The fins and heat exchange tubes are connected to each other by welding. The Si concentration at the grain boundaries of the heat exchange tubes is a first concentration, and the Si concentration within the grains of the heat exchange tubes is a second concentration. The depth of the heat exchange tubes where the first concentration is greater than twice the second concentration does not exceed 40 μm. When the first concentration is greater than twice the second concentration, Si-rich phases are easily generated at the grain boundaries. These Si-rich phases are prone to causing localized corrosion. The Si-rich phases are mainly formed within a depth of 40 μm on the surface of the heat exchange tubes to reduce the adverse effects of Si diffusion on the corrosion resistance of the heat exchange tubes. This allows the interior of the heat exchange tubes to maintain high corrosion resistance, thereby preventing corrosion penetration and leakage, effectively extending the corrosion resistance life of the heat exchanger, and improving its reliability.

[0007] The second aspect of this application provides a heat exchanger processing method, the processing method comprising the following steps: extruding aluminum alloy material into a heat exchange tube blank; forming a heat exchange tube from the heat exchange tube blank to a specified length, wherein the thickness variation of the heat exchange tube relative to the heat exchange tube blank is 1.5% to 13.5%; and welding fins and the heat exchange tube.

[0008] The technical solution provided in this application can achieve the following beneficial effects:

[0009] The heat exchanger processing method provided in this application includes the following steps: extruding aluminum alloy material into a heat exchanger tube blank; forming a heat exchanger tube from the heat exchanger tube blank to a specified length, wherein the thickness variation of the heat exchanger tube relative to the heat exchanger tube blank is 1.5% to 13.5%; and welding fins and heat exchanger tubes. By reasonably controlling the deformation of the heat exchanger tube, the grain size inside the heat exchanger tube is increased, thereby reducing the diffusion of Si into the heat exchanger tube during the welding process. This maintains high corrosion resistance inside the heat exchanger tube, thus preventing corrosion penetration and leakage, effectively extending the corrosion resistance life of the heat exchanger, and improving the reliability of the heat exchanger.

[0010] It should be understood that the above general description and the following detailed description are merely exemplary and do not limit this application. Attached Figure Description

[0011] Figure 1 This is a partial structural schematic diagram of a heat exchanger provided in an embodiment of this application;

[0012] Figure 2 A schematic cross-sectional view of the heat exchange tube provided in an embodiment of this application;

[0013] Figure 3 for Figure 1 A magnified view of a portion of the image;

[0014] Figure 4 Figure 3 A partial metallographic diagram is shown.

[0015] Figure 5 The gradient distribution diagram of Zn on the surface of the heat exchange tube provided in the embodiments of this application.

[0016] Figure label:

[0017] 1-Heat exchange tube;

[0018] 2-Manifold;

[0019] 3-Fin;

[0020] 4-Weld;

[0021] 5-Grain;

[0022] 6-Grain boundary.

[0023] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0025] In the description of this application, unless otherwise expressly specified and limited, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance; unless otherwise specified or explained, the term "multiple" refers to two or more; the terms "connected," "fixed," etc., should be interpreted broadly. For example, "connected" can be a fixed connection, a detachable connection, an integral connection, or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0026] In the description of this specification, it should be understood that the directional terms such as "upper" and "lower" used in the embodiments of this application are used to describe the angles shown in the accompanying drawings and should not be construed as limiting the embodiments of this application. Furthermore, in the context, it should also be understood that when it is mentioned that an element is connected "upper" or "lower" to another element, it can be directly connected to the other element "upper" or "lower," or indirectly connected to the other element "upper" or "lower" through an intermediate element.

[0027] like Figures 1-5 As shown in the figure, this application provides a heat exchanger, which includes heat exchange tubes 1, manifolds 2, and fins 3. The interior of the heat exchange tubes 1 is used for the flow of the heat exchange medium, and the material of the heat exchange tubes 1 is aluminum or aluminum alloy. The heat exchange tubes 1 are arranged at intervals along their own thickness direction, and their ends are interconnected through the manifolds 2. Fins 3 are disposed between adjacent heat exchange tubes 1 to increase the heat dissipation area of ​​the heat exchange tubes 1, and the material of the fins 3 is aluminum or aluminum alloy. The fins 3 are welded to the heat exchange tubes 1 to eliminate the air thermal resistance between the fins 3 and the heat exchange tubes 1, thereby improving the heat exchange capacity of the heat exchanger. The heat exchange tubes 1 can adopt any form of tubular structure; in the embodiments of this application, only the use of microchannel flat tubes as an example is described in detail. The thickness of the heat exchange tube 1 refers to the distance between two opposite outer surfaces of the heat exchange tube 1, denoted as W; the wall thickness of the heat exchange tube 1 refers to the distance between the outer surface and the inner surface of the heat exchange tube 1, denoted as H.

[0028] Specifically, Al-Si alloy is used as the solder between the fins 3 and the heat exchange tube 1 to achieve a brazing connection. During the brazing process, the Al-Si alloy melts and fills the space between the fins 3 and the heat exchange tube 1 to form a weld 4, thereby forming a metallurgical bond between the heat exchange tube 1 and the fins 3, and achieving a brazing connection between the heat exchange tube 1 and the fins 3.

[0029] The internal structure of heat exchange tube 1 and fin 3 each has multiple grains 5, and the interface region between adjacent grains 5 is a grain boundary 6. During the brazing process, the diffusion rate of elements such as Si at the grain boundary 6 is much higher than that inside the grains 5. Therefore, Si easily forms a Si-rich phase at the grain boundary 6 where heat exchange tube 1 and fin 3 are connected. The Si-rich phase has a higher potential relative to the aluminum matrix, resulting in a large potential difference between the Si-rich phase and the aluminum matrix. Under the action of electrochemical corrosion, corrosion easily starts from the grain boundary 6, and further corrosion of the grain boundary 6 causes the blockage cell to accelerate corrosion, forming a narrow corrosion channel extending along the grain boundary 6, causing localized corrosion such as pitting corrosion or intergranular corrosion in fin 3 and heat exchange tube 1. The corrosion resistance of heat exchange tube 1 determines the service life of the heat exchanger. That is to say, when corrosion penetrates heat exchange tube 1, the heat exchange medium inside heat exchange tube 1 leaks, affecting the normal use of the heat exchanger.

[0030] Furthermore, at a depth h in the wall thickness direction of the heat exchanger tube 1, the Si concentration at the grain boundary 6 is the first concentration, and the Si concentration within the grain 5 is the second concentration. The depth of the heat exchanger tube 1 where the first concentration is greater than twice the second concentration does not exceed 40 μm. That is, when the first concentration is greater than twice the second concentration, h ≤ 40 μm. For example, h can be 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, or 40 μm. In other words, the Si-rich phase mainly forms within a depth of 40 μm on the surface of the heat exchanger tube 1 to reduce the adverse effects of Si diffusion on the corrosion resistance of the heat exchanger tube 1, maintain high corrosion resistance inside the heat exchanger tube 1, prevent corrosion penetration of the heat exchanger tube 1 leading to leakage, effectively extend the corrosion resistance life of the heat exchanger, and improve the reliability of the heat exchanger.

[0031] Specifically, during the brazing process, Si in the fins diffuses into the heat exchange tube 1. This diffusion alters the composition of the heat exchange tube 1, negatively impacting its corrosion resistance. The diffusion rate of Si at grain boundaries 6 is much higher than at grains 5. Therefore, the first concentration is significantly higher than the second concentration, leading to the formation of a Si-rich phase at grain boundaries 6 and consequently, poor corrosion resistance in the heat exchange tube 1. When the depth h of the heat exchange tube 1 exceeds 40 μm, the difference between the first and second concentrations is smaller, meaning the difference in Si concentration between the grain boundaries and the grain interior is smaller, resulting in a smaller potential difference. Consequently, less Si diffuses at each grain boundary 6, maintaining high corrosion resistance inside the heat exchange tube 1. The corrosion spreads more slowly inside the heat exchange tube 1, thus extending the corrosion resistance life of the heat exchanger.

[0032] Furthermore, the average grain size 5 of the heat exchanger tube 1 after welding is greater than 60 μm. For example, the average grain size 5 of the heat exchanger tube 1 after welding can be 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, or 150 μm, etc. Without changing the shape and size of the heat exchanger tube 1, the larger grain size 5 of the heat exchanger tube 1 results in a smaller number of grains 5 within the heat exchanger tube 1, thus reducing the number of grain boundaries 6 within the heat exchanger tube 1, thereby reducing corrosion originating from the grain boundaries 6 and improving the corrosion resistance of the heat exchanger tube 1. Specifically, under normal circumstances, the average grain size 5 of the heat exchanger tube 1 after welding is about 50 μm. In this embodiment, by reasonably controlling the processing parameters of the heat exchanger tube 1 and the welding parameters of the heat exchanger, the average grain size 5 of the heat exchanger tube 1 after welding is increased to more than 60 μm, thereby reducing the number of grains 5 within the heat exchanger tube 1.

[0033] Furthermore, after welding, the heat exchange tube 1 has an average number of grains 5 of less than 6 in its wall thickness direction. For example, the average number of grains 5 in the wall thickness direction of the heat exchange tube 1 after welding can be 5, 4, 3, 2, or 1. Without changing the shape and size of the heat exchange tube 1, the heat exchange tube 1 has fewer grains 5 along its own thickness direction. After reducing the number of grains, corrosion starting from the grain boundaries 6 can be reduced, thereby improving the corrosion resistance of the heat exchange tube 1.

[0034] The fins 3 can be made of composite plates or single-layer plates. The specific structural form of the fins 3 can be serrated, porous, straight or corrugated, etc., as long as it can increase the heat dissipation area and improve the heat dissipation effect.

[0035] Furthermore, when the fin 3 is made of composite material, the average grain size 5 of the fin 3 after welding is greater than 300 μm. For example, the average grain size 5 of the fin 3 can be 300 μm, 350 μm, 400 μm, 450 μm, 500 μm, 550 μm, 600 μm, 650 μm, 700 μm, 750 μm, 800 μm, 850 μm, 900 μm, 950 μm, or 1000 μm, etc. Without changing the shape and size of the fin 3, the larger grain size 5 of the fin 3 results in a smaller number of grains 5 within the fin 3. Therefore, the number of grain boundaries 6 of the corresponding fin 3 per unit area of ​​the heat exchange tube 1 can be reduced. Within the effective weld length 4, there is at most one grain boundary 6, which can reduce corrosion starting from the grain boundary 6 and reduce the phenomenon of accelerated corrosion of the closed cell caused by the corrosion of the grain boundary 6, thereby improving the corrosion resistance of the heat exchange tube 1.

[0036] Furthermore, the surface of heat exchange tube 1 includes a Zn layer. Specifically, Zn is pre-deposited on the surface of heat exchange tube 1 through methods such as arc spraying or pre-coating with zinc-containing paint. During brazing, the pre-deposited Zn on the surface of heat exchange tube 1 diffuses inward from the surface, thus forming a Zn layer on the surface of heat exchange tube 1. Since the potential of Zn is lower than that of Al, adding Zn to the surface of heat exchange tube 1 can reduce the potential of the surface of heat exchange tube 1, creating a potential difference between the surface and the interior of heat exchange tube 1. This allows the material on the surface of heat exchange tube 1 to act as a sacrificial shield, slowing the spread of corrosion into the interior of heat exchange tube 1 and preventing the generation or spread of localized corrosion such as intergranular corrosion. Specifically, when electrochemical corrosion occurs, the metal with the lower potential (i.e., the material on the surface of heat exchange tube 1) corrodes preferentially, thus protecting the metal with the higher potential (i.e., the material inside heat exchange tube 1) from corrosion, thereby extending the corrosion resistance life of the heat exchanger.

[0037] Furthermore, the Zn content on the surface of heat exchanger tube 1 is not less than 1% by mass. For example, the Zn content on the surface of heat exchanger tube 1 can be 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 2.5%, 3%, 3.4%, 3.6%, or 3.8%, etc., to effectively reduce the potential and increase the potential difference between the surface of heat exchanger tube 1 and the interior of heat exchanger tube 1. Specifically, when the Zn content on the surface of heat exchanger tube 1 is 1% or higher, it can be ensured that the Zn content on the surface of heat exchanger tube 1 is higher than the Zn content inside heat exchanger tube 1, which in turn ensures that the potential on the surface of heat exchanger tube 1 is lower than the potential inside heat exchanger tube 1. This ensures that the surface material of heat exchanger tube 1 plays a sacrificial protective role, slows down the spread of corrosion into the interior of heat exchanger tube 1, and extends the corrosion resistance life of the heat exchanger. It should be noted that the Zn content on the surface of heat exchange tube 1 is generally no more than 4% by mass percentage. When the Zn content on the surface of heat exchange tube 1 is above 4%, the corrosion rate of the surface material of heat exchange tube 1 is too fast, which will lead to a shorter corrosion resistance life of the heat exchanger.

[0038] Specifically, heat exchange tube 1 itself forms a reasonable potential distribution, and heat exchange tube 1 corrodes in the order of surface corrosion first and then internal corrosion. Therefore, before the surface material of heat exchange tube 1 corrodes and peels off, the surface material of heat exchange tube 1 always protects the internal material. The electrochemical corrosion between the surface and the interior of heat exchange tube 1 only damages the surface material of heat exchange tube 1, and does not lead to the destruction of the internal material of heat exchange tube 1. This can reduce the influence of Si diffusion inside heat exchange tube 1 and prevent the generation or spread of local corrosion such as intergranular corrosion.

[0039] Furthermore, after welding, the Zn layer forms a gradient diffusion from the outside to the inside of heat exchange tube 1 (reference). Figure 5 As shown in Table 1, the Zn content gradient decreases from the outside to the inside of heat exchanger tube 1, resulting in layer-by-layer corrosion on the surface of heat exchanger tube 1 from the outside to the inside, ensuring that the material on the surface of heat exchanger tube 1 can fully exert its sacrificial protection function. Since Zn has a high solid solubility in Al, besides reacting with alloying elements to form a second phase, Zn usually exists in Al alloys in solid solution form. If the concentration of dissolved Zn decreases from the outside to the inside of heat exchanger tube 1, it will cause the corrosion potential distribution of heat exchanger tube 1 to increase from the outside to the inside. This distribution can effectively improve the resistance of aluminum alloy to pitting corrosion and intergranular corrosion. A specific Zn layer gradient is shown in Table 1, where every 10 μm depth from the surface of the heat exchanger tube inwards is considered a gradient. That is, pt1 is the depth of 0-10 μm from the surface of the heat exchanger tube inwards, pt2 is the depth of 10-20 μm from the surface of the heat exchanger tube inwards, and so on, with pt10 being the depth of 90-100 μm from the surface of the heat exchanger tube inwards. The Zn content in pt1 is slightly reduced due to surface volatilization and other reasons, while the Zn content gradient from pt2 to pt11 decreases.

[0040] Table 1

[0041] Depth (μm) Zn-K pt1 0～10 2.20 pt2 10～20 2.64 pt3 20～30 2.42 pt4 30～40 2.32 pt5 40～50 1.93 pt6 50～60 1.40 pt7 60～70 1.13 pt8 70～80 0.78 pt9 80～90 0.67 pt10 90～100 0.41 pt11 100～110 0.06

[0042] Furthermore, the depth where the Zn content is not less than 0.1% is defined as the Zn diffusion depth, and the Zn diffusion depth on the surface of heat exchanger tube 1 is not less than 80 μm. For example, the Zn diffusion depth on the surface of heat exchanger tube 1 can be 80 μm, 82 μm, 85 μm, 88 μm, 90 μm, 93 μm, 95 μm, 98 μm, or 100 μm, etc., to maximize the Zn diffusion depth on the surface of heat exchanger tube 1, allowing more material on the surface of heat exchanger tube 1 to play a sacrificial protective role, thereby further improving the corrosion resistance life of the heat exchanger. A specific Zn diffusion depth is shown in Table 1. The Zn content of pt1-pt10 is all greater than 0.1%, and the Zn content of pt11 is all less than 0.1%. Therefore, the depth corresponding to pt10 is the Zn diffusion depth on the surface of heat exchanger tube 1, and this depth is not less than 80 μm.

[0043] Furthermore, the Zn content of fin 3 is not less than 1.3% by mass percentage, specifically ranging from 1.3% to 3%. For example, the Zn content of fin 3 can be 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 1.8%, 1.9%, or 2%, etc. The Zn content of fin 3 is higher than that of the surface of heat exchange tube 1, resulting in a lower potential of fin 3 than that of the surface of heat exchange tube 1. This creates a potential difference between heat exchange tube 1 and fin 3, allowing the material of fin 3 to act as a sacrificial shield, slowing the spread of corrosion to heat exchange tube 1.

[0044] Specifically, a reasonable potential distribution is formed between the heat exchange tube 1 and the fins 3. The corrosion of the heat exchange tube 1 and the fins 3 occurs in the order of first corroding the fins 3 and then corroding the surface of the heat exchange tube 1. Therefore, before the fins 3 corrode and fall off, the fins 3 always protect the heat exchange tube 1. The electrochemical corrosion between the fins 3 and the heat exchange tube 1 will only damage the fins 3, and the heat exchange tube 1 will not be corroded. This can prevent the corrosion of the heat exchange tube 1 for a certain period of time and extend the corrosion resistance life of the heat exchanger.

[0045] In some embodiments, the heat exchange tube 1 is made of aluminum alloy. For example, the heat exchange tube 1 may be made of 1-series aluminum alloy (e.g., 1100 aluminum alloy or 1197 aluminum alloy, etc.) or 3-series aluminum alloy (e.g., 3102 aluminum alloy or 3103 aluminum alloy, etc.).

[0046] Furthermore, the composition of heat exchanger tube 1 includes Mn, Al, and unavoidable impurities, with each impurity element having a mass percentage not exceeding 0.05%, and the sum of the mass percentages of all impurity elements not exceeding 0.15%. Mn is added to the material of heat exchanger tube 1. At room temperature, Mn has low solid solubility in aluminum alloys and typically exists as the Al6Mn second phase. The dispersed Al6Mn particles can effectively improve the strength of heat exchanger tube 1. Moreover, since the corrosion potential of Al6Mn is close to that of pure Al, the added Mn element improves the strength of heat exchanger tube 1 without affecting its corrosion resistance.

[0047] Furthermore, the mass percentage of Mn in heat exchanger tube 1 is no greater than 1.50%. For example, the mass percentage of Mn in heat exchanger tube 1 can be 0.20%, 0.30%, 0.40%, 0.50%, 0.60%, 0.70%, 0.80%, 0.90%, 1.00%, 1.10%, 1.20%, 1.30%, 1.40%, or 1.50%, etc., to ensure the forming quality of heat exchanger tube 1. Specifically, when the mass percentage of Mn in heat exchanger tube 1 is greater than 1.50%, the excessive Mn content reduces the extrusion processing performance of the aluminum alloy material, affecting the extrusion processing of heat exchanger tube 1.

[0048] Furthermore, the heat exchange tube 1 is composed of Fe and Si. Fe and Si are the main impurity elements in electrolytic aluminum raw materials (the upper limits of Fe and Si content in remelted aluminum ingot Al99.70 are 0.10% and 0.20%, respectively), and are also the main alloying and strengthening elements of 1-series aluminum alloys. Specifically, Fe has very low solid solubility in Al. When Fe exists alone in Al, it usually exists in the form of intermetallic compounds such as Al3Fe, which has a good strengthening effect on the alloy; a small amount of Si exists in Al in solid solution form, which has a certain solid solution strengthening effect on Al.

[0049] Furthermore, the mass percentage of Mn in heat exchanger tube 1 is not less than 0.20%, that is, the mass percentage of Mn in heat exchanger tube 1 is 0.20% to 1.50%. For example, the mass percentage of Mn in heat exchanger tube 1 can be 0.20%, 0.30%, 0.40%, 0.50%, 0.60%, 0.70%, 0.80%, 0.90%, 1.00%, 1.10%, 1.20%, 1.30%, 1.40%, or 1.50%, etc., to reduce the adverse effects of excessive Fe and Si elements on the corrosion resistance of heat exchanger tube 1. Specifically, Al3Fe has a large difference in corrosion potential from the Al matrix, which easily induces pitting corrosion; Si is an element that increases the corrosion potential of Al alloys, and excessive Si will reduce the corrosion resistance of aluminum alloys; a certain amount of Mn element forms an Al-Mn-Fe-Si phase with Fe and Si, which can reduce the adverse effects of Fe and Si on the corrosion resistance of heat exchange tube 1.

[0050] Furthermore, considering the purity grade of the electrolytic aluminum raw materials and their impact on the alloy's corrosion resistance and extrusion performance, the mass percentage of Fe in heat exchanger tube 1 is 0.08%–0.25%, and the mass percentage of Si is 0.03%–0.12%. For example, the mass percentage of Fe in heat exchanger tube 1 can be 0.08%, 0.10%, 0.12%, 0.15%, 0.16%, 0.18%, 0.19%, 0.20%, 0.22%, 0.24%, or 0.25%, etc.; and the mass percentage of Si can be 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.10%, 0.11%, or 0.12%, etc. When the mass percentage of Fe in heat exchanger tube 1 is less than 0.08%, or the mass percentage of Si is less than 0.03%, the process of producing electrolytic aluminum raw materials is difficult and the production cost is too high. When the mass percentage of Fe in heat exchanger tube 1 is greater than 0.25%, or the mass percentage of Si is greater than 0.12%, the corrosion resistance of heat exchanger tube 1 is poor, and the strength of heat exchanger tube 1 is too high, which affects the extrusion processing and forming of heat exchanger tube 1.

[0051] Furthermore, the heat exchange tube 1 comprises Ti, with the mass percentage of Ti in the heat exchange tube 1 ranging from 0.01% to 0.25%. For example, the mass percentage of Ti in the heat exchange tube 1 may be 0.01%, 0.02%, 0.05%, 0.08%, 0.10%, 0.15%, 0.18%, 0.20%, or 0.25%, etc., to form a layered potential difference within the heat exchange tube 1, thereby improving the corrosion resistance of the heat exchange tube 1.

[0052] In some embodiments, the fins 3 are made of a composite plate, which includes a core material layer and a solder layer located on at least one side of the core material layer. That is, the core material layer may have a solder layer on only one side, or the core material layer may have solder layers on both sides. The core material is a 3-series aluminum alloy with a certain amount of Zn, and the solder layer is a low-melting-point 4-series aluminum alloy (i.e., Al-Si alloy, such as 4343 aluminum alloy or 4045 aluminum alloy). When the heat exchange tube 1 and the fins 3 are brazed together, the solder layer melts and connects the heat exchange tube 1 to the core material layer, thereby forming a metallurgical bond between the heat exchange tube 1 and the fins 3, realizing the brazing connection between the heat exchange tube 1 and the fins 3.

[0053] Furthermore, the core layer comprises, by mass percentage: Mn: 0.9%–1.8%, Fe: 0.08%–0.25%, Si: 0.03%–0.7%, Ti: 0.08%–0.25%, Zn: 1.0%–3.0%, Al, and unavoidable impurities, with each impurity element having a mass percentage not exceeding 0.05%, and the sum of the mass percentages of all impurity elements not exceeding 0.15%. For example, the mass percentage of Mn in the core layer can be 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, or 1.8%, etc.; the mass percentage of Fe can be 0.08%, 0.1%, 0.15%, 0.18%, 0.2%, 0.22%, or 0.25%, etc.; the mass percentage of Si can be 0.03%, 0.1%, 0.15%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, or 0.7%, etc.; the mass percentage of Ti can be 0.08%, 0.1%, 0.15%, 0.18%, 0.2%, 0.22%, or 0.25%, etc.; and the mass percentage of Zn can be 1.0%, 1.5%, 2.0%, 2.5%, or 3.0%, etc.

[0054] The core layer material incorporates manganese (Mn). At room temperature, Mn has low solid solubility in aluminum alloys and typically exists as the Al6Mn second phase. Dispersed Al6Mn particles effectively improve the strength of the core layer. Furthermore, since the corrosion potential of Al6Mn is close to that of pure Al, the added Mn improves the core layer's strength without affecting its corrosion resistance. In addition, a certain amount of Mn forms an Al-Mn-Fe-Si phase with elements such as Fe and Si, thereby reducing the adverse effects of Fe and Si on the core layer's corrosion resistance. Ti is added to the core layer material to create a layered potential difference within the core layer, further enhancing its corrosion resistance.

[0055] Furthermore, the solder layer comprises, by mass percentage: Mn: 0.01%–0.15%, Fe: 0.02%–0.2%, Si: 6%–10%, Zn: 0.01%–2.0%, Al, and unavoidable impurities, with each impurity element having a mass percentage not exceeding 0.05%, and the sum of the mass percentages of all impurity elements not exceeding 0.15%. For example, the mass percentage of Mn in the solder layer can be 0.01%, 0.05%, 0.1%, 0.11%, 0.12%, 0.13%, 0.14%, or 0.15%, etc.; the mass percentage of Fe can be 0.02%, 0.1%, 0.15%, 0.18%, or 0.2%, etc.; the mass percentage of Si can be 6%, 6.5%, 7%, 8%, 9%, or 10%, etc.; and the mass percentage of Zn can be 0.01%, 0.05%, 0.1%, 0.5%, 0.8%, 0.9%, 1.0%, 1.5%, or 2.0%, etc. The Si in the solder layer enables the welding of the fins to the heat exchanger tubes.

[0056] In some embodiments, the fin 3 is made of a single-layer plate. When the fin 3 is a single layer, the single-layer plate material of the fin 3 contains Si, and the Si content is required to be low. This allows the Si content of the fin 3 to be reduced while achieving welding, thereby reducing the diffusion of Si to the heat exchange tube 1 during the welding process and thus reducing intergranular corrosion.

[0057] Furthermore, the mass percentage of Si in the single-layer plate is 2.0% to 4.0%. For example, the mass percentage of Si in the single-layer plate is 2.0%, 2.2%, 2.5%, 2.7%, 3.0%, 3.3%, 3.5%, 3.7%, or 4.0%, etc., to ensure a reliable welding effect between the fins 3 and the heat exchange tube 1. When the mass percentage of Si in the single-layer plate is less than 2%, the liquidus fraction on the surface of the fins 3 is insufficient, and an effective metallurgical bond cannot be formed; when the mass percentage of Si in the single-layer plate exceeds 4%, the liquidus fraction on the surface of the fins 3 is too high, resulting in a significant reduction in the thickness and strength of the fins 3 themselves, making it difficult to meet the structural strength and operational requirements of the heat exchanger.

[0058] Furthermore, the components of the single-layer board, by mass percentage, include: Mn: 0.20%–1.20%, Fe: 0.08%–0.25%, Si: 2.0%–4.0%, Zn: 1.0%–3.0%, Ti: 0.08%–0.25%, Al, and unavoidable impurities, with each impurity element having a mass percentage not exceeding 0.05%, and the sum of the mass percentages of all impurity elements not exceeding 0.15%. For example, the mass percentage of Mn in a single-layer plate can be 0.20%, 0.40%, 0.50%, 0.60%, 0.80%, 1.00%, 1.10%, or 1.20%, etc.; the mass percentage of Fe can be 0.08%, 0.1%, 0.15%, 0.18%, 0.2%, 0.22%, or 0.25%, etc.; the mass percentage of Si can be 2.0%, 2.2%, 2.5%, 2.7%, 3.0%, 3.3%, 3.5%, 3.7%, or 4.0%, etc.; the mass percentage of Zn can be 1.0%, 1.5%, 2.0%, 2.5%, or 3.0%, etc.; and the mass percentage of Ti can be 0.08%, 0.1%, 0.15%, 0.18%, 0.2%, 0.22%, or 0.25%, etc.

[0059] The single-layer sheet material incorporates manganese (Mn). At room temperature, Mn has low solid solubility in aluminum alloys and typically exists as the Al6Mn second phase. Dispersed Al6Mn particles effectively improve the strength of the single-layer sheet. Furthermore, since the corrosion potential of Al6Mn is close to that of pure Al, the added Mn improves the strength of the single-layer sheet without affecting its corrosion resistance. In addition, a certain amount of Mn forms an Al-Mn-Fe-Si phase with elements such as Fe and Si, thereby reducing the adverse effects of Fe and Si on the corrosion resistance of the single-layer sheet. Ti is also added to the single-layer sheet material to create a layered potential difference within the sheet, further enhancing its corrosion resistance.

[0060] This application provides a heat exchanger processing method, which includes the following steps: extruding aluminum alloy material into a heat exchanger tube blank; cutting the heat exchanger tube blank to length to form a heat exchanger tube 1; and welding fins 3 and the heat exchanger tube 1. The thickness variation of the heat exchanger tube 1 relative to the heat exchanger tube blank is 1.5% to 13.5%, for example, the thickness variation of the heat exchanger tube 1 relative to the heat exchanger tube blank can be 1.5%, 2.0%, 3.0%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 7.5%, 8.0%, 9.0%, 10.0%, 11.5%, 12.5%, or 13.5%, etc. By reasonably controlling the deformation of the heat exchanger tube 1, the number of grains 5 inside the heat exchanger tube 1 is increased, thereby reducing the diffusion of Si into the heat exchanger tube 1 during welding. This maintains high corrosion resistance inside the heat exchanger tube 1, thus preventing corrosion penetration and leakage, effectively extending the corrosion resistance life of the heat exchanger, and improving the reliability of the heat exchanger.

[0061] Specifically, the thickness of the heat exchange tube 1 is reduced relative to the thickness of the heat exchange tube blank, and the reduction is 1.5% to 13.5% of the thickness of the heat exchange tube blank. The size of the grain 5 depends on the number of crystal nuclei and the relative magnitude of the grain growth rate of the grain 5. When the deformation is less than 1.5% or greater than 13.5%, the grains 5 will become finer and the grain boundaries 6 will increase, thereby increasing the diffusion depth of Si during the subsequent welding process.

[0062] Furthermore, when the Zn content of fin 3 is not less than 1.3% by mass, after the heat exchange tube blank is cut to length to form heat exchange tube 1, the process further includes: forming a Zn layer on the surface of heat exchange tube 1, with the Zn content on the surface of heat exchange tube 1 being not less than 1% by mass. On the one hand, the Zn content on the surface of heat exchange tube 1 is lower than the Zn content of fin 3, resulting in a potential difference between fin 3 and the surface of heat exchange tube 1. This allows the material of fin 3 to act as a sacrificial protectant, slowing the spread of corrosion to heat exchange tube 1. On the other hand, a Zn content of 1% or more on the surface of heat exchange tube 1 ensures that the Zn content on the surface of heat exchange tube 1 is higher than the Zn content inside heat exchange tube 1. This also ensures that the potential on the surface of heat exchange tube 1 is lower than the potential inside heat exchange tube 1, thus ensuring that the surface material of heat exchange tube 1 acts as a sacrificial protectant, slowing the spread of corrosion to the interior of heat exchange tube 1, and extending the corrosion resistance life of the heat exchanger.

[0063] The method for forming the Zn layer on the surface of heat exchanger tube 1 can be any method, such as arc zinc spraying, pre-coating with zinc, or roller coating. There are no restrictions on the method used. The surface of the heat exchanger tube can be treated with zinc spraying at a rate of 8±2 g / m² to achieve a Zn content of 1% to 4% by mass on the surface of heat exchanger tube 1.

[0064] Furthermore, when the fins are made of composite sheets, the amount of processing during the fin composite plate processing or the temperature control during the heat treatment process can be used to form fins with grains larger than 300 μm. Without changing the shape and size of the fins 3, the larger grain size of the fins 3 results in fewer grains 5 within the fins 3. This reduces the number of grain boundaries 6 of the corresponding fins 3 per unit area of ​​the heat exchange tube 1. Within the effective weld length 4, there is at most one grain boundary 6, which reduces corrosion starting from the grain boundary 6 and reduces the phenomenon of accelerated corrosion of the closed cell caused by the corrosion of the grain boundary 6, thereby improving the corrosion resistance of the heat exchange tube 1.

[0065] To illustrate the corrosion resistance of the heat exchanger provided in this application embodiment, a comparative test is conducted between the heat exchanger provided in this application embodiment and an existing heat exchanger. The test results are detailed in Table 2.

[0066] Each embodiment or comparative example represents a group of sample heat exchangers, and the test results are statistical results of the test results of that group of sample heat exchangers. Except for the differences listed in Table 2 (i.e., the amount of Zn injected into the heat exchange tube and the fin material), all other parameters (e.g., the shape, size, thickness, and forming process of the heat exchange tube, and the shape, size, thickness, and forming process of the fins, etc.) of each group of sample heat exchangers are exactly the same, and the remaining test conditions are also exactly the same.

[0067] It should be noted that in the embodiments and comparative examples in Table 2, the heat exchanger tubes and fins are connected by brazing. The heat exchanger tubes are made of materials one and two, and the fins are made of materials three, four, or five. The specific structures and compositions of materials one, two, three, four, and five are as follows:

[0068] The components of Material 1 and Material 2, by mass percentage, are as follows: Mn: 0.20%–1.50%, Fe: 0.08%–0.25%, Si: 0.03%–0.12%, with the balance being Al and unavoidable impurities. The mass percentage of each impurity element does not exceed 0.05%, and the sum of the mass percentages of all impurity elements does not exceed 0.15%. The average grain size of Material 1 after welding is 70 μm, and the average grain size of Material 2 after welding is 40 μm.

[0069] Material 3 is a fin made of a single-layer plate. The composition of Material 3 by mass percentage is as follows: Mn: 0.20%~1.20%, Fe: 0.08%~0.25%, Si: 2.0%~4.0%, Ti: 0.08%~0.25%, with the balance being Al and unavoidable impurities. The mass percentage of each impurity element does not exceed 0.05%, and the sum of the mass percentages of all impurity elements does not exceed 0.15%.

[0070] Materials 4 and 5 are fins made of composite plates. Both materials 4 and 5 include a core layer and solder layers on both sides (the thickness of each solder layer is 8% to 12% of the total thickness). The average grain size of material 4 after welding is greater than 300 μm, while the average grain size of material 5 after welding is less than 300 μm. The composition of the core layer by mass percentage is as follows: Mn: 0.9% to 1.8%, Fe: 0.08% to 0.25%, Si: 0.03% to 0.7%, Ti: 0.08% to 0.25%, Zn: 1.0% to 3.0%, with the balance being Al and unavoidable impurities. The mass percentage of each impurity element does not exceed 0.05%, and the sum of the mass percentages of all impurity elements does not exceed 0.15%. The composition of the solder layer by mass percentage is as follows: Mn: 0.01% to 0.15%, Fe: 0.02% to 0.2%, Si: 6% to 10%, Zn: 0.01% to 2.0%, with the balance being Al and unavoidable impurities. The mass percentage of each impurity element shall not exceed 0.05%, and the sum of the mass percentages of all impurity elements shall not exceed 0.15%.

[0071] Table 2

[0072] heat exchanger heat exchanger tube fins Zn injection rate in heat exchanger tubes Si-rich depth Leakage time Example 1 Material 1 Material 3 8±2g / m2 0-25μm 200-300 days Example 2 Material 1 Material 4 8±2g / m2 0-25μm 200-250 days Example 3 Material 2 Material 4 8±2g / m2 10-30μm 100-130 days Comparative Example 1 Material 1 Material 5 8±2g / m2 40-45μm 50-90 days

[0073] According to the test results in Table 2, the leakage time of Examples 1, 2, and 3 is all over 100 days, while the leakage time of Comparative Example 1 is all less than 90 days. The corrosion resistance life of the heat exchanger provided in this application is significantly higher than that of existing heat exchangers. Therefore, the heat exchanger provided in this application has better corrosion resistance. Furthermore, comparing the Si-rich depth of Examples 1, 2, 3, and Comparative Example 1 shows that reducing the Si-rich depth can effectively extend the corrosion resistance life of the heat exchanger. Comparing the heat exchange tube materials of Examples 2 and 3 shows that increasing the average grain size of the heat exchange tube can reduce the Si-rich depth of the heat exchange tube. Comparing the fin materials of Examples 2 and Comparative Example 1 shows that increasing the average grain size of the fins can reduce the Si-rich depth of the heat exchange tube.

[0074] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A heat exchanger, characterized in that, include: The heat exchange tubes are made of aluminum or aluminum alloy; the fins are made of aluminum or aluminum alloy. The fins are welded to the heat exchange tube; the Si concentration at the grain boundary of the heat exchange tube is a first concentration, the Si concentration within the grain of the heat exchange tube is a second concentration, and the depth of the heat exchange tube where the first concentration is greater than twice the second concentration does not exceed 40 μm.

2. The heat exchanger according to claim 1, characterized in that, After welding, the average grain size of the heat exchange tube is greater than 60 μm, and / or the average number of grains in the heat exchange tube in its wall thickness direction is less than 6.

3. The heat exchanger according to claim 1, characterized in that, The heat exchange tube comprises, by mass percentage: Mn: 0.20%–1.50%, Fe: 0.08%–0.25%, Si: 0.03%–0.12%, Al, and unavoidable impurities.

4. The heat exchanger according to claim 1, characterized in that, The fins are made of a composite plate, which includes a core layer and a solder layer located on at least one side of the core layer, and the average grain size of the fins is greater than 300 μm.

5. The heat exchanger according to claim 4, characterized in that, The core material layer comprises, by mass percentage: Mn: 0.9%–1.8%, Fe: 0.08%–0.25%, Si: 0.03%–0.7%, Ti: 0.08%–0.25%, Zn: 1.0%–3.0%, Al, and unavoidable impurities; And / or, the solder layer comprises, by mass percentage: Mn: 0.01% to 0.15%, Fe: 0.02% to 0.2%, Si: 6% to 10%, Zn: 0.01% to 2.0%, Al, and unavoidable impurities.

6. The heat exchanger according to claim 1, characterized in that, The fins are made of a single-layer plate, the components of which, by mass percentage, include: Mn: 0.20%–1.20%, Fe: 0.08%–0.25%, Si: 2.0%–4.0%, Zn: 1.0%–3.0%, Ti: 0.08%–0.25%, Al, and unavoidable impurities.

7. The heat exchanger according to any one of claims 1-6, characterized in that, The surface of the heat exchange tube includes a Zn layer, and the Zn content on the surface of the heat exchange tube is not less than 1% by mass percentage.

8. The heat exchanger according to claim 7, characterized in that, The Zn layer forms a gradient diffusion from the outside to the inside of the heat exchange tube. The depth at which the Zn content is not less than 0.1% is defined as the diffusion depth of Zn, and the diffusion depth of Zn on the surface of the heat exchange tube is not less than 80 μm.

9. The heat exchanger according to claim 7, characterized in that, The Zn content of the fins is not less than 1.3% by mass percentage.

10. A method for processing a heat exchanger, characterized in that, The processing method includes the following steps: Aluminum alloy material is extruded into heat exchange tube blanks; The heat exchange tube blank is cut to length to form a heat exchange tube, and the thickness variation of the heat exchange tube relative to the heat exchange tube blank is 1.5% to 13.5%. Welding fins and the heat exchange tube.

11. The heat exchanger processing method according to claim 10, characterized in that, The Zn content of the fins is not less than 1.3% by mass. After the heat exchange tube blank is cut to length to form a heat exchange tube, the method further includes: forming a Zn layer on the surface of the heat exchange tube, wherein the Zn content on the surface of the heat exchange tube is not less than 1% by mass.

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