JP2013221204A - Clad tube made of aluminum alloy for braze-joining and heat exchanger to which the clad tube made of aluminum alloy is applied - Google Patents

Abstract

PROBLEM TO BE SOLVED: To disclose a clad tube made of an aluminum alloy for braze-joining that can achieve both the corrosion resistance of a tube and the corrosion resistance of a joint, and is excellent in hairpin bendability.SOLUTION: In a clad tube made of an aluminum alloy for braze-joining that includes a core material made of an aluminum alloy and a skin material made of an aluminum alloy clad on the outer surface of the core material, and is joined with other members by brazing, the core material is composed of an aluminum alloy containing 0.8-1.8% by mass Mn, 0.4-0.8% by mass Cu and 0.2% by mass or less Si, the balance being aluminum and inevitable impurities, and the skin material is composed of an aluminum alloy containing 0.5-1.5% by mass Zn, the balance being aluminum and inevitable impurities. Further, the clad tube made of an aluminum alloy for braze-joining is characterized in that the average cross-sectional crystal grain size of the core material is 150 μm or less.

Description

  The present invention relates to an aluminum alloy clad tube joined to another member by brazing. In particular, the present invention relates to an aluminum alloy clad tube for brazing joining, which is suitable for a heat transfer tube of a cross fin type heat exchanger used for a domestic air conditioner, a commercial air conditioner, a heat pump type hot water heater or the like.

  Aluminum fins are joined in cross fin type heat exchangers (also called fin-and-tube heat exchangers) commonly used in home air conditioners, commercial air conditioners, heat pump water heaters, etc. Heat transfer tubes are used. When manufacturing this heat transfer tube with aluminum heat radiation fins, insert the heat transfer tube into the open hole of the aluminum heat radiation fin, expand the diameter of the heat transfer tube, and use the outer surface of the heat transfer tube as the insertion hole of the aluminum heat radiation fin. It is in close contact. This tube expansion process is generally a step of pushing a tube expansion mandrel having an outer diameter larger than its inner diameter into the heat transfer tube. After that, the heat transfer tube integrated with the aluminum radiation fin is bent into a hairpin shape, and a heat transfer tube (U-shaped tube) bent into a U-shape is joined by torch brazing to make the main part of the heat exchanger Completed. Details of the manufacturing process of the above cross fin type heat exchanger are described in Non-Patent Document 1.

  Conventionally, copper-based materials such as copper and copper alloys have been used for heat transfer tubes used in cross-fin type heat exchangers, but aluminum and aluminum have been used to meet demands for reducing material costs and weight. The use of aluminum-based materials such as alloys (hereinafter referred to as aluminum alloys) has been studied.

  When aluminum alloy is applied to a heat transfer tube for a cross fin heat exchanger, attention should be paid to improvement of its corrosion resistance. Since aluminum alloys are inferior in corrosion resistance compared to copper-based materials, improvement in corrosion resistance is first required from the viewpoint of ensuring the durability and reliability of heat transfer tubes. As a measure for improving the corrosion resistance of the aluminum alloy heat transfer tube, the application of a clad tube has been proposed. For example, in Patent Documents 1 and 2, the heat transfer tube has a two-layer structure, an Al-Mn alloy is used for the core material that is the inner layer of the tube, and the outer surface layer of the core material is Al-Zn as a skin material. A clad tube clad with an alloy is proposed. In this aluminum alloy clad tube, the skin material acts as a sacrificial anticorrosion layer, and suppresses the corrosion of the core material.

  However, if the improvement of corrosion resistance as a heat transfer tube for a heat exchanger is pursued, in addition to the corrosion resistance of the material (base material) of the clad tube, the possibility of a decrease in the corrosion resistance of the brazed joint should be considered. As described above, in manufacturing the heat exchanger, the heat transfer tube is often brazed and joined to another member. In the brazed joint, the clad tube is heated to a high temperature, and compositional variation due to contact with the brazing material may occur, thereby impairing corrosion resistance. The conventional aluminum alloy clad tube has not been sufficiently considered for ensuring the corrosion resistance of the joint.

  Further, as described above, the heat transfer tube of the cross fin type heat exchanger is subjected to hairpin bending after the fins are brought into close contact with each other. Accordingly, workability is required in addition to corrosion resistance. The conventional aluminum alloy clad pipe has not been sufficiently examined about the workability, and sometimes breaks at the bending portion during the processing. As a prior art for improving the workability of an aluminum alloy clad pipe, Patent Document 3 discusses improvement of pipe expansion workability by using an alloy obtained by adding Zn to JIS3003 as a skin material. However, this prior art relates to the improvement of pipe expansion workability and does not consider the corrosion resistance of the joint.

JP 2011-85290 A JP 1998-46312 A JP 2008-267714 A

“Involved in the development of heat transfer promotion tubes” Masaaki Ito: Heat transfer, 42, 174 (2003), p31-40, published by The Japan Heat Transfer Society

  The present invention has been made in view of the above circumstances, and for an aluminum alloy clad tube to be brazed, both the corrosion resistance of the material (base material) and the corrosion resistance of the joint can be achieved, and further, hairpin bending, etc. It aims at providing the thing which was excellent in workability at the time of processing.

  The present inventors have made various studies on an aluminum alloy clad tube, and in order to improve the hairpin bending workability of the core material, the material has excellent workability by making the alloy component a specific type and content. Found that can be provided. Then, considering the alloy component of the core material, the corrosion resistance of the pipe material and the corrosion resistance of the joint can be made compatible by making the Zn distribution of the skin material serving as the sacrificial anticorrosive layer into a specific range. Invented.

  That is, the present invention comprises a core material made of an aluminum alloy and a skin material made of an aluminum alloy clad on the outer surface of the core material, and is joined to other members by brazing. In the clad tube, the core material contains Mn: 0.8 to 1.8 mass%, Cu: 0.4 to 0.8 mass%, Si: 0.2 mass% or less, and the balance aluminum and inevitable impurities. It is made of an aluminum alloy, and the skin material is made of an aluminum alloy containing Zn: 0.5 to 1.5 mass%, the balance being aluminum and inevitable impurities, and the core material has a cross-sectional average crystal grain size of 150 μm or less. It is a clad tube made of aluminum alloy for brazing joining, characterized by being.

  Hereinafter, the core material and the skin material constituting the aluminum alloy clad pipe according to the present invention will be described in detail. In the present specification, “%” indicating the alloy composition means mass% (mass%).

  As described above, the core material is an aluminum alloy made of the remaining aluminum with the contents of Mn, Cu, and Si within a predetermined range. First, Mn is a main additive element for improving strength in a 3000 series alloy (Al-Mn series alloy), and has an effect of precipitating a part while being dissolved in aluminum and imparting strength. If the amount of Mn added is less than 0.8%, the strength as a heat transfer tube will be insufficient. On the other hand, if it exceeds 1.8%, the effect of improving the strength is saturated, and the amount of coarse intermetallic compound increases, so that defects such as cracks are likely to occur in the manufacturing process of the tube. Therefore, the amount of Mn added is in the range of 0.8 to 1.8%. A more preferable range is 1.0 to 1.5%.

  Cu is an element that has an effect of further improving strength by solid solution in aluminum and does not impair workability. Further, Cu serves to make the electrode potential noble. Here, in the clad tube provided with an aluminum alloy containing Zn as a skin material as in the present invention, the presence of Cu in the core material can increase the pitting corrosion potential difference between the skin material and the core material, The sacrificial anticorrosive action for the core material can be enhanced. When Cu is added in an amount less than 0.3%, the strength is insufficient and the crushing of the groove cannot be prevented during the tube expansion process, and the sacrificial anticorrosive action is lowered due to insufficient pitting potential. . On the other hand, if the Cu content is more than 0.8%, not only the extrudability and drawability at the time of pipe production deteriorate, but also the corrosion resistance of the material decreases. Therefore, the Cu addition amount is set to a range of 0.3 to 0.8%. A more preferable range is 0.4 to 0.6%.

  When Si is contained in an Al-Mn-Cu alloy, it forms an Al-Mn-Si-based or Al-Mn-Si-Cu-based intermetallic compound, and has the effect of improving strength. On the other hand, these intermetallic compounds have a role of inhibiting recrystallization, and tend to coarsen crystal grains during recrystallization. And when the addition amount of Si exceeds 0.2%, this crystal grain coarsening is likely to occur, and there is a possibility of exceeding the upper limit (150 μm) of the average crystal grain size described later, and rough skin during the hairpin bending process. Cause breakage. Therefore, the addition amount of Si is set to 0.2% or less. A preferable Si concentration range is 0.1% or less. In addition, about the lower limit of Si content, it is preferable to set it as 0.02%. Since Si is an element that is unavoidably present in the aluminum alloy, restricting it to less than 0.02% takes into consideration the adverse effect on industrial mass production, which is an increase in material manufacturing cost.

  Impurities for the aluminum alloy as the core material include Fe, Mg, Zn, etc., but these are Fe: 0.6% or less, Mg: 0.2% or less, and Zn: 0.3% or less. The effect of the present invention is not inhibited.

  Further, Ti, Cr, and Zr may be contained because they have an effect of uniformly refining the ingot structure. However, if the content of these exceeds 0.2%, a giant intermetallic compound is formed or the extrudability is lowered. Therefore, the content is preferably 0.2% or less. If it is this range, the effect of the heat exchanger tube in this embodiment will not be inhibited. This content may be 0 to 0.1% or 0 to 0.05%.

  The core material made of the aluminum alloy having the composition range described above needs to have an average crystal grain size of 150 μm or less in the cross-sectional structure. The reason for defining the crystal grain size of the core material is to prevent rough skin and breakage during hairpin bending. In addition, coarse crystal grains cause stress corrosion cracking. Regarding the control of the crystal grain size of the core material, in addition to the regulation of the Si content (0.2% or less) as described above, it is necessary to set the reduction until the annealing softening process described later to 90% or more. is there. The average crystal grain size is preferably measured based on two directions of the tube thickness direction and the circumferential direction by observing the cross-sectional structure and using the intersection method.

  Next, the skin material of the clad pipe made of aluminum alloy according to the present invention will be described. The skin material is applied with an Al-Zn alloy with a regulated Zn content, has a pitting corrosion potential lower than that of the core material, exerts a sacrificial anticorrosive action, prevents the core material, and has an effect of improving the durable life of the pipe material. .

  Here, Zn lowers the natural electrode potential of the aluminum alloy serving as a skin material (base) and acts as a sacrificial anode to improve the corrosion resistance of the heat transfer tube. If the amount added is less than 0.5%, the potential difference from the core material is insufficient and the effect of sacrificial corrosion protection cannot be obtained, so 0.5% or more of Zn is required. On the other hand, if it exceeds 1.5%, Zn is concentrated at the joint and the corrosion resistance of the joint is deteriorated. Therefore, the Zn addition amount is in the range of 0.5 to 1.5%. A more preferable range is 0.7 to 1.0%.

  Examples of impurities in the aluminum alloy used as a skin material include Si, Fe, Cu, and Mn. These are Si: 0.5% or less, Fe: 0.6% or less, Cu: 0.2% or less, Mn : If it is 0.8% or less, the effect of this invention is not inhibited.

  As in the case of the core material, the aluminum alloy Ti, Cr, Zr as the skin material may be contained because it has the effect of uniformly refining the ingot structure. In other words, the content is preferably 0.2% or less. If it is this range, the effect of the heat exchanger tube in this embodiment will not be inhibited. This content may be 0 to 0.1% or 0 to 0.05%.

  There are no essential conditions regarding the cross-sectional structure of the aluminum alloy as the skin material, unlike the core material, but the skin material preferably has an average crystal grain size of 50 μm or more. This is because if the average crystal grain size of the skin material is as fine as less than 50 μm, the skin material is significantly eroded by the molten brazing at the time of brazing joining, and the thickness of the skin material is locally reduced, leading to a decrease in pressure strength.

  The thickness of the skin material is not particularly limited, but is preferably 5 to 30% with respect to the total thickness of the clad tube. This is because the skin material is a consumable region called a sacrificial anticorrosive layer, and if it is less than 5%, the effective period that can be used as a heat exchanger becomes insufficient. On the other hand, if the thickness of the skin material is set to exceed 30% with respect to the total thickness of the clad tube, the strength of the heat transfer tube becomes low.

  As a heat exchanger tube for a heat exchanger that is suitable for application of the present invention, for example, a U-shaped tube of a heat exchanger for an air conditioner for general households can be cited. The dimensions are, for example, a small-diameter thin tube having an outer diameter of φ4.0 to φ9.54 mm and a bottom thickness of about 0.3 to 0.6 mm. Therefore, when manufacturing such a small-diameter thin-walled cladding tube, among various aluminum alloys, an alloy having an appropriate strength and relatively excellent workability for processing into a small-diameter thin-walled tube (for example, It is preferable to select an Al-Mn-based A3003 alloy (Al-1.0 to 1.5% Mn-0.05 to 0.20% Cu alloy) as a base and adjust the additive elements. By doing in this way, refinement | miniaturization and the intensity | strength of a crystal grain can be improved, and the crack at the time of a hairpin bending process can be prevented. A suitable aluminum alloy clad tube can be obtained by optimizing the concentration of the Al—Zn alloy as the sacrificial anticorrosive layer.

  Next, the manufacturing method of the aluminum alloy clad pipe according to the present invention will be described. The aluminum alloy clad pipe manufacturing method according to the present invention includes an aluminum alloy (Al-Mn-Cu alloy) cylindrical billet as a core material and an aluminum alloy (Al-Zn alloy) as a skin material. A step of producing a two-layer hollow billet by combining cylindrical billets and extruding the cylindrical billet to obtain a two-layer clad extruded tube and appropriately processing it may be mentioned.

  For example, a billet made of aluminum alloy plate material, which is a skin material, is bent outside the cylindrical billet of aluminum alloy, which is a core material, and is heated to 350-600 ° C in a heating furnace to homogenize. The treatment is performed to produce a two-layer hollow billet. Thereafter, the billet is extruded by an indirect extruder or the like to obtain a two-layer clad extruded tube. Next, the two-layer clad tube according to the present invention can be manufactured by drawing the two-layer clad extruded tube to a predetermined outer diameter and thickness. The drawing process preferably uses a draw block type continuous drawing machine with high productivity.

  Further, after manufacturing a two-layer hollow billet obtained by heating an aluminum alloy cylindrical billet as a skin material to 350 to 600 ° C. and shrink-fitting an aluminum alloy cylindrical billet inside as a core material Alternatively, a two-layer clad extruded tube may be obtained by extrusion. Then, the two-layer clad tube according to the present invention can be manufactured by drawing in the same manner.

  Furthermore, in addition to the process of manufacturing through the above two-layer clad extruded tube, the aluminum alloy clad tube according to the present invention can be manufactured by welding the sheet material. In this case, a two-layer clad sheet obtained by clad rolling an aluminum alloy sheet serving as a skin material on one side of an aluminum alloy sheet serving as a core material is manufactured. Is welded to form a two-layer clad electro-sewn tube, the two-layer clad tube according to the present invention can be manufactured.

  The two-layer clad tube formed by the above methods is subjected to annealing softening for the purpose of adjusting the mechanical characteristics. In that case, it is industrially preferable that the annealing temperature is 300 to 400 ° C. and the time is 2 to 8 hours. And it is necessary to set the reduction before the stage of cold drawing to annealing softening to 90% or more. As described above, in the present invention, the average crystal grain size of the core material is required to be 150 μm or less, which is the influence of reduction (processing rate) due to cold working until the final annealing in addition to the composition of the core material. Because it receives. However, if the reduction before annealing exceeds 99.995%, the crystal grain size of the skin material may become too fine.

  The clad tube made of aluminum alloy for brazing according to the present invention can suppress the occurrence of cracking during hairpin bending and is excellent in workability. And it also has the effect that it is excellent in the corrosion resistance of both pipe | tube itself and the corrosion resistance of a junction part.

  The aluminum alloy clad tube according to the present invention is suitable as a heat transfer tube which is a member for a heat exchanger, is excellent in workability and can be joined to other members. The heat exchanger is a device having a flow path for circulating a refrigerant therein, and a heat exchanger having excellent corrosion resistance and reliability is obtained by applying the joined body obtained as described above to the flow path. be able to.

  Embodiments of the present invention will be described below. In the present embodiment, as the aluminum alloy used as the skin material and the core material, alloys of various compositions were set to produce a two-layer clad tube, and its workability, strength, and corrosion resistance were evaluated.

  First, an aluminum alloy plate having the composition shown in Table 1 was cast as a skin material by continuous casting. On the other hand, an aluminum alloy cylindrical billet having a composition shown in Table 2 was prepared as a core material. And the combination billet was produced by the combination of Table 3, and the two-layer clad extruded tube with an outer diameter of 47 mm and a wall thickness of 3.5 mm was obtained by an indirect extrusion method. Next, the two-layer clad extruded tube is subjected to drawing by a draw block type continuous drawing machine, subjected to annealing softening treatment at 360 ° C. for 2 hours, and an aluminum alloy having an outer diameter of 5 to 10 mm and a wall thickness of 0.1 to 2 mm. A clad tube was completed. Table 2 shows the reduction of each aluminum alloy clad pipe from drawing to pre-annealing softening.

  Two of these clad tubes are cut out to 100 mm, one is subjected to a hairpin bending process, which will be described later, and then joined to the other tube, and joined by torch brazing using an Al-12% Si ring brazing. Finished the material. And in order to evaluate a characteristic about the manufactured aluminum alloy clad pipe of each example and a comparative example, the following measurement and a test were done.

(A) Measurement of average crystal grain size With respect to the aluminum alloy clad tube, a specimen for microstructural observation was cut out from the non-heat-affected zone of brazing, and the average crystal grain size was measured. Measurement of the average crystal grain size was carried out in two directions of the tube thickness direction and the circumferential direction using an intersection method, and the average value was obtained.

(B) Evaluation of hairpin bending workability An aluminum alloy clad tube with a diameter of 10 mm was subjected to hairpin bending work with a bending pitch of 16 mm. The surface after bending was visually observed to confirm the presence or absence of surface cracking. At this time, 10 clad tubes were prepared and evaluated according to the following criteria. ○: No cracks occurred in all 10 pieces. Δ: Only 1 to 9 cracks are not generated. X: Cracking occurred in all 10 pieces.

(C) Tensile strength measurement In order to measure the strength of the aluminum alloy clad tube assembly, a tensile test was carried out in accordance with JIS Z2241, and the tensile strength was measured. The strength measured here is the lower of the strength of the tube itself and the strength of the joint.

(D) Evaluation of corrosion resistance In order to evaluate corrosion resistance, a CASS test was conducted for 1500 hours in accordance with JIS Z8681 for aluminum alloy clad pipe joined bodies. After the test, the surface corrosion products of the test material were removed and the corrosion status of the tube was observed. This observation was made for both corrosion and joints of the clad tube. At this time, 10 aluminum alloy clad pipe assemblies were prepared for each, and evaluated according to the following criteria. Corrosion of clad tube straight portion and clad tube bent portion, ○: There are no through holes in all 10 pieces. (Triangle | delta): There is no through-hole only 2-9 pieces. X: There are 9 to 10 through holes. Corrosion of joints, ○: Preferential corrosion does not occur in all 10 pieces. Δ: Preferential corrosion does not occur for only 2 to 9 pieces. X: Preferential corrosion occurred in 9 to 10 pieces.

  Table 4 shows the results obtained for the above various measurement results and evaluation results.

  The evaluation results shown in Table 4 will be described. Although C1-C16 which is an Example is a thing with the composition of the aluminum alloy which is a core material and a skin material in the range of this invention, it is excellent in all in hairpin bending workability, the intensity | strength of a joined body, and corrosion resistance.

  Then, considering the results of the comparative example in detail, first, regarding the composition of the aluminum alloy as the core material, C19 is deficient in Mn and C22 is deficient in Cu relative to the component range defined in the present invention. To do. For this reason, the strength of the clad tube is low. Further, C20 is excessive in Mn, and C21 is excessive in Cu. For this reason, the workability deteriorated and a drawing break occurred during the drawing process, and the tube could not be manufactured.

  Further, regarding the composition of the aluminum alloy as the skin material, C17 had a lower Zn concentration than the component range defined in the present invention, and a through-hole was generated in the cladding tube. Further, since C18 has a high Zn concentration, preferential corrosion of the joint occurred.

  Further, regarding the crystal grain size of the core material, C23 has a high Si concentration in the core material, and the average crystal grain size exceeds 150 μm. Therefore, cracks occurred during the hairpin bending process. Furthermore, when the crack portion was removed and the corrosion resistance was evaluated, the corrosion resistance was inferior because penetration due to stress corrosion cracking occurred.

  In C24, since the reduction from drawing to annealing was small, the average crystal grain size exceeded 150 μm, and cracking occurred during hairpin bending. Further, when this cracked portion was removed and the corrosion resistance was evaluated, the corrosion resistance was inferior because penetration due to stress corrosion cracking occurred.

  From the above examination, it can be said that in order to ensure both corrosion resistance and workability, it is necessary to strictly define the composition of the aluminum alloy that constitutes both the core material and the skin material. C16 has fine core crystal grains and does not generate cracks during hairpin bending and has good corrosion resistance. However, since the amount of Si is extremely low, the production cost is high to produce this. Is concerned. However, since it can be confirmed from other examples that sufficient workability and strength can be obtained without reducing the Si amount so far and making the crystal grains finer, the composition range of the core material is defined in the scope of the present invention. If it is within, it can be said that it can be freely controlled according to the cost.

The aluminum alloy clad tube for brazing joint according to the present invention has excellent workability and suppresses the occurrence of cracks in hairpin bending during the production of heat transfer tubes. Moreover, the corrosion resistance is also good, and the corrosion resistance is also secured at the joint. INDUSTRIAL APPLICABILITY The present invention is suitable for heat transfer tubes of cross fin type heat exchangers used for home and commercial air conditioners and the like, and it is possible to ensure the life and reliability of these refrigerant flow paths.

Claims (4)

In a clad pipe made of aluminum alloy for brazing, which is composed of a core material made of an aluminum alloy and a skin material made of an aluminum alloy clad on the outer surface of the core material, and is joined by brazing to other members.
The core material is made of an aluminum alloy containing Mn: 0.8 to 1.8 mass%, Cu: 0.4 to 0.8 mass%, Si: 0.2 mass% or less, and the balance aluminum and inevitable impurities,
The skin material contains Zn: 0.5 to 1.5 mass%, and is made of an aluminum alloy composed of the balance aluminum and inevitable impurities,
Furthermore, the aluminum alloy clad tube for brazing joining, wherein the core material has a cross-sectional average crystal grain size of 150 μm or less.   The clad tube made of aluminum alloy for brazing according to claim 1, wherein the skin material has an average crystal grain size of 50 µm or more.   A joined body using the aluminum alloy clad tube for brazing joining according to claim 1 or 2. It is a heat exchanger provided with the tubular flow path through which a refrigerant | coolant distribute | circulates, Comprising: The heat exchanger using the conjugate | zygote of Claim 3 for at least one part of the said tubular flow path.