JP2019045091A - Heat exchanger - Google Patents

Abstract

To provide a heat exchanger which is excellent in the corrosion resistance of a heat exchange pipe.SOLUTION: A capacitor being a heat exchanger comprises a plurality of aluminum-extrusion shape material heat exchange pipes, and aluminum bare material fins which are arranged between the adjacent heat exchange pipes, and joined to the heat exchange pipes by brazing materials. A pipe wall 30 of the heat exchange pipe is composed of a main body part 31 composed of an Al alloy for forming an aluminum-extrusion shape material, and a coating layer 32 composed of an AI-Si-Zn alloy, and covering an outer face of the main body part 31. A diffusion layer 33 in which Zn and Si in the Al-Ai-Zn alloy for forming the coating layer 32 are diffused is formed at an outer surface layer part of the main body part 31 of the pipe wall 30. In a range between an outermost face of the pipe wall 30 of the heat exchange pipe, and the deepest part of the diffusion layer 33, there exist a low-potential portion in which natural potential in the range is the lowest, and a high-potential portion in which natural potential in the range becomes higher than the low-potential portion by 60 mV or higher so that the low-potential portion is located at the outermost face of the pipe wall 30.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a heat exchanger, and more particularly to a heat exchanger used as a condenser of a car air conditioner mounted on a vehicle such as a car.

  In this specification and claims, the term "aluminum" includes aluminum alloys in addition to pure aluminum. Moreover, the material represented by the elemental symbol means a pure material, and the term "Al alloy" means an aluminum alloy.

  Further, in this specification, the "natural potential" means the electrode potential of the material for the saturated calomel electrode (SCE) as a standard electrode in an aqueous solution of 5% NaCl, pH 3 (acidic). It is.

  As heat exchangers used for condensers for car air conditioners, a plurality of flat aluminum extrusions are arranged at intervals in the thickness direction with the longitudinal direction oriented in the same direction and the width direction oriented in the ventilation direction A heat exchange pipe, a header tank disposed on both ends in the longitudinal direction of the heat exchange pipe with the longitudinal direction oriented in the direction in which the heat exchange pipes are aligned, and adjacent heat exchange with the header tank to which both ends of the heat exchange pipe are connected Aluminum corrugated fins arranged between the tubes and outside the heat exchange tubes at both ends and brazed to the heat exchange tubes, and aluminum side plates arranged outside the fins at both ends and brazed to the fins And the header tank is formed into a tubular shape by brazing an aluminum brazing sheet having a brazing material layer on both sides to braze a butt portion between both side edges. A cylindrical aluminum tank main body which is open at both ends and opened, and an aluminum closing member which is brazed to both ends of the tank main body to close the opening at both ends, And a plurality of tube insertion holes, each of which is an elongated hole, directed at a distance in the longitudinal direction of the tank body, and an end of the heat exchange tube is inserted into the tube insertion hole and brazed to the tank body Things are widely known.

As a method of manufacturing the heat exchanger described above, the applicant previously contained 0.2 to 0.3% by mass of Mn, 0.05% by mass or less of Cu, 0.2% by mass or less of Fe, and the balance Al and unavoidable impurities. And an aluminum extruded heat exchanger tube having a wall thickness of 200 μm or less, and a brazing sheet comprising an aluminum core material and an aluminum brazing material covering both surfaces of the aluminum core material. Preparing a fin formed by the following method, a dispersion obtained by dispersing and mixing a flux powder and a Zn powder having an average particle diameter of 3 to 5 μm and a maximum particle diameter of less than 10 μm in a binder, the outer surface of the heat exchange tube by vaporizing the liquid component in the dispersion as well as applied to the outer surface of the heat exchange tubes, Zn powder deposition amount 1 to 3 g / m ^2, the flux powder coating weight of 15 g / m ² Adhere Zn powder and flux powder such that the ratio of flux powder adhesion amount to Zn powder adhesion amount (flux powder adhesion amount / Zn powder adhesion amount) is 1 or more, and combine heat exchange tubes and fins Heat and braze the heat exchange tube and fins using flux powder and fin skins attached to the outer surface of the heat exchange tube and melt the Zn powder attached to the outer surface of the heat exchange tube A method was proposed that proposed forming a Zn diffusion layer in the outer surface layer portion of the heat exchange tube by diffusing Zn in the outer surface layer portion of the heat exchange tube (see Patent Document 1).

  The heat exchange pipe and the fins of the heat exchanger manufactured by the method described in Patent Document 1 are joined by the brazing material melted from the skin of the brazing sheet forming the fins.

  In the heat exchanger manufactured by the method described in Patent Document 1, in order to further improve the corrosion resistance of the fins, it is considered to use an aluminum bear fin instead of the aluminum brazing sheet fin. In this case, in the manufacturing method described above, Al is added to the Zn powder to adhere the Si powder to the outer surface of the heat exchange tube to form an aluminum extruded section to be the heat exchange tube, and Al before bonding It is conceivable to join the heat exchange tube and the fin by a brazing material composed of Si and Si powder that has been attached to the surface of the exchange tube.

  However, in the heat exchanger manufactured by such a method, the corrosion resistance of the heat exchange pipe may be insufficient.

JP, 2014-238209, A

  An object of the present invention is to solve the above-mentioned problems and to provide a heat exchanger excellent in the corrosion resistance of the heat exchange pipe.

  The present invention comprises the following aspects in order to achieve the above object.

1) A plurality of extruded aluminum material heat exchange tubes, and an aluminum bear material fin disposed between adjacent heat exchange tubes and joined to the heat exchange tubes with a brazing material,
A tube wall of a heat exchange tube comprising: a main body portion made of an Al alloy forming the aluminum extruded section; and a covering layer made of an Al-Si-Zn alloy and covering the outer surface of the main body portion A diffusion layer in which Zn and Si in the Al-Si-Zn alloy forming the covering layer are diffused is formed in the outer surface layer portion of the main body of the wall, and the outermost surface of the tube wall of the heat exchange tube and the deepest portion of the diffusion layer The low potential part where the natural potential is lowest in the range and the high potential part where the natural potential is higher by 60 mV or more than the low potential part within the range A heat exchanger that exists on the outer side.

  2) In the range between the outermost surface of the tube wall of the heat exchange tube and the deepest portion of the diffusion layer, the natural potential decreases from the outermost surface of the tube wall toward the main portion to reach the low potential portion; The heat exchanger according to the above 1), wherein the high potential portion is reached as it goes from the low potential portion toward the main body.

  3) The brazing material for joining the heat exchange tube and the fin is formed of Al in the Al alloy forming the aluminum extruded profile and Si of Si powder deposited on the surface of the heat exchange tube before joining. The heat exchanger according to the above 1) or 2), which is configured.

  4) The Al-Si-Zn alloy which is the coating layer of the heat exchange tube is adhered to the surface of the heat exchange tube before bonding and Al in the Al alloy forming the aluminum extruded section The heat exchanger according to any one of the above 1) to 3), which is constituted by Si of Si powder and Zn of Zn powder deposited on the surface of the heat exchange tube before bonding.

  According to the heat exchangers of the above 1) to 4), since the fins are made of an aluminum bear material, the corrosion resistance of the fins is improved as compared with the heat exchanger provided with the fins formed of an aluminum brazing sheet.

  Further, the heat exchange pipe comprises a pipe wall of the heat exchange pipe, a main body made of an Al alloy forming the aluminum extruded section, and a covering layer made of an Al-Si-Zn alloy and covering the outer surface of the main body. A diffusion layer in which Zn and Si in the Al-Si-Zn alloy forming the covering layer are diffused is formed in the outer surface layer portion of the main body portion of the main body, and the outermost surface of the tube wall of the heat exchange tube and the deepest portion of the diffusion layer In the range between the low potential portion where the natural potential is the lowest in the range, and the high potential portion where the natural potential is higher by 60 mV or more than the low potential portion, the low potential portion is the outermost surface of the tube wall As it is present on the side, corrosion from the outer surface of the tube wall of the heat exchange tube will stop at the high potential portion. Therefore, the corrosion depth can be made shallow, and the corrosion resistance of the heat exchange tube is improved. As a result, it is possible to reduce the thickness of the tube wall of the heat exchange tube, and to reduce the weight of the heat exchange tube, and further to reduce the weight of the heat exchanger using the heat exchange tube.

FIG. 1 is a perspective view showing an entire configuration of a condenser for a car air conditioner to which a heat exchanger of the present invention is applied. It is sectional drawing which expanded a part of pipe | tube wall of the heat exchange pipe | tube of the capacitor | condenser of FIG. It is a graph which shows the natural potential of a different depth position from the tube wall outermost surface in one heat exchange tube brazed with a fin in an experiment example.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. This embodiment is an application of the heat exchanger of the present invention to a condenser for a car air conditioner.

  FIG. 1 shows the overall configuration of a car air conditioner condenser to which the heat exchanger of the present invention is applied, and FIG. 2 shows the configuration of the main part thereof.

  In the following description, upper and lower and right and left in FIG. 1 are referred to as upper and lower and left and right.

  In FIG. 1, the condenser (1) for a car air conditioner has an interval in the vertical direction (thickness direction of the heat exchange pipe (2)) with the longitudinal direction directed to the left and right and the width direction directed to the ventilation direction. Between the heat exchange tubes (2) adjacent to each other and between the heat exchange tubes (2) adjacent to each other, and the heat exchange tubes (2) at the upper and lower ends. Space between the aluminum bear material corrugated fins (3) brazed to the heat exchange pipe (2) and the longitudinal direction in the vertical direction (the direction in which the heat exchange pipes (2) are aligned) A pair of aluminum header tanks (4) and (5) to which the left and right ends of the heat exchange pipe (2) are connected and the corrugated fins (3) at the upper and lower ends are disposed (3) is equipped with an aluminum brazing sheet side plate (6) brazed to FIG. The wind flows in the direction indicated by the arrow W in FIG.

  The left header tank (4) is divided into two upper and lower header parts (4a) (4b) by the partition plate (7) above the central part in the height direction, and the right header tank (5) is in the height direction The upper and lower two header portions (5a, 5b) are partitioned by a partition plate (7) below the central portion of the head. A refrigerant inlet (not shown) is formed in the upper header portion (4a) of the left header tank (4), and an aluminum inlet member (8) having an inflow path (8a) communicating with the refrigerant inlet is formed in the upper header portion (4a) It is brazed. In addition, a refrigerant outlet (not shown) is formed in the lower header portion (5b) of the right header tank (5), and an aluminum outlet member (9) having an outflow passage (9a) communicating with the refrigerant outlet is the lower header portion (5b) Brazed to). Then, the refrigerant that has flowed into the upper header portion (4a) of the left header tank (4) through the inflow path (8a) of the inlet member (8) is greater than the partition plate (7) of the left header tank (4). It flows to the right in the heat exchange pipe (2) located at the upper side, flows into the upper part in the upper header part (5a) of the right header tank (5), and flows downward in the upper header part (5a) The left header tank (4) flows in the heat exchange pipe (2) at the height position between the partition plate (7) of the header tank (4) and the partition plate (7) of the right header tank (5). 4) A heat exchange pipe (flowing into the upper part in the lower header part (4b), flowing downward in the lower header part (4b) and located below the partition plate (7) of the right header tank (5) 2) Flows to the right inside and flows into the lower header part (5b) of the right header tank (5), and flows out of the condenser (1) through the outlet (9a) of the outlet member (9) .

  The left and right header tanks (4) and (5) are formed of an aluminum pipe having a brazing material layer at least on the outer surface, for example, a base plate made of an aluminum brazing sheet having a brazing material layer on both sides And a tank body (11) comprising a plurality of tube bodies partially overlapped and brazed to each other and having a plurality of long tube insertion holes in the longitudinal direction, and brazed to both ends of the tank body (11) It consists of an aluminum closing member (12) closing its both end opening. The detailed illustration of the header tank body (11) is omitted. Further, the header tank body (11) may be made of an aluminum extruded tube having a brazing material sprayed on the outer peripheral surface.

  The heat exchange pipe (2) is made of an extruded section formed of an Al alloy containing, for example, 0.4 to 0.5 mass% of Cu, 0.1 to 0.3 mass% of Mn, and the balance Al and unavoidable impurities. Is preferred. The Al alloy is one commonly used to form extruded shape heat exchange tubes.

  As shown in FIG. 2, the tube wall (30) of the heat exchange tube (2) comprises a main body (31) made of an Al alloy forming the aluminum extruded section, an Al-Si-Zn alloy, and a main body A coating layer (32) covering the outer surface of the part (31), and forming a coating layer (32) on the outer surface layer portion of the main portion (31) of the tube wall (30) in Al-Si-Zn alloy A diffusion layer (33) in which Zn and Si are diffused is formed.

  The wall thickness of the tube wall (30) of the heat exchange tube (2) is preferably 200 μm or less. Here, the wall thickness of the pipe wall (30) of the heat exchange pipe (2) is not entirely the same but may be partially different, but the wall thickness of the pipe wall (30) is 200 μm or less, It means that the thickness of the thickest portion of the tube wall (30) is 200 μm or less.

  In a range between the outermost surface of the tube wall (30) of the heat exchange tube (2) and the deepest portion of the diffusion layer (33), a low potential portion (34) having the lowest natural potential in the range; The high potential portion where the natural potential is higher by 60 mV or more than the low potential portion exists such that the low potential portion is on the outermost surface of the tube wall. For example, in the range between the outermost surface of the tube wall (30) and the deepest portion of the diffusion layer (33), the natural potential gradually decreases from the outermost surface of the tube wall (30) toward the main body (31) And reaches the low potential portion, and increases from the low potential portion toward the main body (31) to reach the high potential portion.

  Cu in the alloy forming the aluminum extruded heat exchanger tube (2) has the effect of improving the corrosion resistance of the main portion (31) of the heat exchanger tube (2), but is less than 0.4% by mass This effect can not be obtained, and when it exceeds 0.5% by mass, the sacrificial corrosion effect on the main portion (31) of the diffusion layer (33) is reduced. That is, for the purpose of forming a sacrificial corrosion layer for the main body (31), a diffusion layer (33) in which Zn is diffused, which has an effect of reducing the natural potential, is formed. When the content is more than% by mass, the effect of Zn is insufficient, and the natural potential of the diffusion layer (33) can not be sufficiently reduced. Therefore, it is preferable to make Cu content into 0.4-0.5 mass%. In addition, Mn in the alloy forming the aluminum extruded shape heat exchange tube has a property to improve the strength of the heat exchange tube, but this effect can be obtained when the Mn content is less than 0.1 mass%. However, since extrusion processability will fall when it exceeds 0.3 mass%, it is preferable to make Mn content into 0.1-0.3 mass%.

  In addition, in the alloy which forms the aluminum extruded shape material heat exchange pipe (2), as an unavoidable impurity, Si 0.2 mass% or less, Fe 0.2 mass% or less, Mg 0.05 mass% or less, Cr 0.05 mass % Or less, Zn 0.05 mass% or less, Ti 0.05 mass% or less may be contained. The content of these unavoidable impurities may be zero. When the content of Si and Fe is too large, the corrosion resistance of the heat exchange pipe (2) is reduced, and when the content of Zn is too large, the natural potential of the heat exchange pipe (2) is degraded and the surrounding area If the potential balance with the parts is changed and the Ti content is too high, the cost becomes high. Furthermore, unavoidable impurities other than Si, Fe, Mg, Cr, Zn, and Ti have an individual content of 0.05% by mass or less (including 0% by mass) and a total content of 0.15% by mass or less It may be included to be

  The corrugated fin (3) is preferably made of, for example, an Al alloy containing 1.0 to 1.5% by mass of Mn, 1.2 to 1.8% by mass of Zn, and the balance Al and unavoidable impurities. The Al alloy that forms the corrugated fins (3) is an alloy that is usually used as a fin made of a bare material.

  Mn in the alloy forming the corrugated fin (3) has the property of improving the strength of the corrugated fin (3), but this effect can not be obtained when the Mn content is less than 1.0 mass%, 1 If the content is more than 5% by mass, the processability is reduced, so the Mn content is made 1.0 to 1.5% by mass.

  In addition, Zn in the alloy forming the corrugated fin (3) has a property of maintaining the potential balance with the heat exchange tube (2) properly, but this effect is achieved when the Zn content is less than 1.2% by mass If the content exceeds 1.8% by mass, the corrugate fin (3) becomes strongly corroded, so the Zn content is set to 1.2 to 1.8% by mass.

  In the Al alloy forming the corrugated fin (3), 0.6 mass% or less of Si, 0.5 mass% or less of Fe, 0.05 mass% or less of Cu, 0.12 mass% or less of Cr are contained as unavoidable impurities Sometimes. The content of these unavoidable impurities may be zero. If the contents of Si, Fe and Cu are too high, the corrosion rate of the corrugated fin (3) will be fast. Furthermore, the unavoidable impurities other than Si, Fe, Cu, and Cr are such that the individual content is 0.05 mass% or less (including 0 mass%) and the total content is 0.15 mass% or less May be included.

  The capacitor (1) is manufactured by the method described below.

  First, a heat exchange pipe (2) made of an extruded section formed of the above-mentioned Al alloy, a corrugated fin (3) made of the above-mentioned Al alloy, a side plate (6), a partition member (7) A pair of cylindrical aluminum header tank body material having a material layer, a closing member (12), an inlet member (8), and an outlet member (9) are prepared. A plurality of pipe insertion holes are formed in the header tank body material.

Also, a binder was dispersed and mixed with a flux powder, a Zn powder having an average particle diameter of 3 to 5 μm and a maximum particle diameter of less than 10 μm, and an Si powder having an average particle diameter of 2 to 6 μm and a maximum particle diameter of less than 10 μm. Prepare a dispersion. Here, as the flux powder, for example, one composed of a fluoride-based non-corrosive flux mainly composed of a mixture of KAlF ₄ and KAlF ₅ is used. As the binder, for example, one comprising an acrylic resin dissolved in 3-methoxy-3-methyl-1-butanol is used. In addition, the diluent which consists of 3-methoxy- 3-methyl- 1-butanol, for example in order to adjust the viscosity of a binder to a dispersion liquid is added.

Next, the dispersion is applied to the outer surface of the heat exchange tube (2) and the liquid component in the dispersion is vaporized to deposit an amount of Zn powder of 4 to 6 g / m on the outer surface of the heat exchange tube (2). ^2. Zn powder, Si powder and flux powder are attached such that the amount of Si powder is 3 to 6 g / m ² and the amount of flux powder is 6 to 24 g / m ² . As a method of depositing Zn powder, Si powder and flux powder on the outer surface of the heat exchange pipe (2), the dispersion liquid is applied to the outer surface of the heat exchange pipe (2) by the spray method, and then the heat exchange pipe (2) By heating and drying the liquid component in the dispersion to deposit Zn powder, Si powder and flux powder on the outer surface of the heat exchange tube (2), and preheating the outer surface of the heat exchange tube (2) In the above state, the dispersion is applied to the outer surface of the heat exchange pipe (2) by a roll coating method, and then the heat exchange pipe (2) is heated and dried to vaporize the liquid components in the dispersion, thereby exchanging heat. There is a method of depositing Zn powder, Si powder and flux powder on the outer surface of the tube (2).

  When Zn powder, Si powder and flux powder are attached to the outer surface of the heat exchange tube (2), a flux powder layer containing Zn powder and Si powder is formed on the outer surface of the heat exchange tube (2). In the flux powder layer, Zn powder and Si powder are uniformly dispersed and held.

  Next, a pair of header tank body materials having a tube insertion hole is disposed at an interval, and closing members (12) are disposed at both ends of both header tank body materials, and further partition members (both header tank body materials) 7) Arrange the header tank material. Further, the heat exchange tubes (2) and the fins (3) are alternately arranged, and both ends of the heat exchange tube (2) are inserted into the tube insertion holes of the header tank material. Further, the side plate (6) is disposed outside the fins (3) at both ends, and the inlet member (8) and the outlet member (9) are disposed.

  Next, a header tank material comprising a header tank body material, a closing member (12) and a partition member (7), a heat exchange pipe (2), fins (3), side plates (6), an inlet member (8) and an outlet Temporarily fix the member (9) to make a temporarily fixed body.

  Next, the temporary fixing body is placed in the brazing furnace, and the temporary fixing body is heated to a predetermined temperature and heated in the brazing furnace. In addition, the flux is applied to parts other than the heat exchange pipe (2) according to a known method such as brush coating, if necessary.

  At the time of temperature rise of the temporary fixing body, the flux powder forming the flux powder layer is first melted, and the oxide film on the outer surface of the heat exchange tube (2), the oxide film on the corrugated fin (3) surface, the oxide film on the Si powder surface and The oxide film on the surface of the Zn powder is destroyed. Then, Si and Zn diffuse into the outer surface layer portion of the heat exchange pipe (2) to form a brazing material made of Al-Si-Zn alloy having a low melting point in the outer surface layer portion of the heat exchange pipe (2). The material brazes the heat exchange pipe (2) and the corrugated fins (3). Moreover, while the thing which was not used for brazing among the said brazing materials becomes a coating layer (32), Zn and Si in the Al-Si-Zn alloy which becomes a coating layer (32) are diffused, and a diffusion layer (33) is formed. At the same time, the molten flux of the outer surface of the heat exchange pipe (4) flows and spreads simultaneously, and the molten Zn also flows and spreads, and Zn diffuses to the outer surface layer portion of the heat exchange pipe (4) to form a Zn diffusion layer. Thus, the capacitor (1) is manufactured.

  In the heat exchange tube (2) of the manufactured capacitor (1), the tube wall (30) is, as described above, the body portion (31), the covering layer (32), and the outer side of the body portion (31) And a diffusion layer (33) formed in the surface layer. And, in the range between the outermost surface of the tube wall (30) of the heat exchange tube (2) and the deepest portion of the diffusion layer (33), the low potential portion having the lowest natural potential in the range and the low potential The high potential portion where the natural potential is higher by 60 mV or more than the potential portion exists so that the low potential portion is on the outermost surface side of the tube wall.

  In the heat exchange pipe (2), in the range between the outermost surface of the pipe wall (30) of the heat exchange pipe (2) and the deepest part of the diffusion layer (33) The fact that the potential part and the high potential part where the natural potential is higher by 60 mV or more than the low potential part is limited so that the low potential part is on the outermost surface of the tube wall is as follows: Based on the experimental results described in

  Cu: 0.42% by mass, Mn: 0.16% by mass, Si: 0.12% by mass, Fe: 0.11% by mass, Ti: 0.01% by mass, and the balance Al and the inevitable impurities An extruded heat exchanger tube made of an alloy, Si: 0.77% by mass, Fe: 0.24% by mass, Mn: 1.68% by mass, Zn: 1.60% by mass, Zr: 0.. A bare corrugated fin made of an Al alloy containing 11% by mass, the balance Al and unavoidable impurities was prepared. In addition to Si, Fe, and Ti, inevitable impurities having an individual content of 0.05% by mass or less are contained in total of 0.15% by mass or less in the Al alloy forming the heat exchange tube. Further, the wall thickness of the heat exchange pipe is 180 μm, and the wall thickness of the corrugate fin is 70 μm.

Further, a fluoride non-corrosive flux powder containing 90% by mass or more of a mixture of KAlF ₄ and KAlF ₅ (the amount of KAlF ₅ in the mixture is 10 to 40 mass%), and an average particle diameter of 3 to 5 μm And Zn powder having a maximum particle size of less than 10 μm (5% by mass of the total weight of the Zn powder is zinc oxide), Si powder having an average particle size of 2 to 6 μm and a maximum particle size of less than 10 μm, and acrylic resin Prepare a binder consisting of a solution of 3-methoxy-3-methyl-1-butanol and a diluent consisting of 3-methoxy-3-methyl-1-butanol; Zn powder, Si powder and non-corrosiveness The flux powder was dispersed and mixed in a binder and a diluent to obtain a dispersion. The weight ratio of all the components in the dispersion is Zn powder: Si powder: non-corrosive flux powder: binder: diluent, 14.1 parts by weight: 10.6 parts by weight: 21.1 parts by weight: 9.2 Parts by weight: 45.0 parts by weight.

Then, the dispersion is applied to the outer surface of the heat exchange tube by a spraying method, and then dried in a dryer to evaporate the liquid components in the dispersion, whereby the amount of Zn powder deposited on the outer surface of the heat exchange tube is 4 to 6 g / m ^2, Si powder coating weight of 3 to 6 g / m ^2, so that the flux powder deposition amount becomes 24 g / m ² or less, was deposited Zn powder, Si powder and the flux powder.

  Thereafter, a plurality of heat exchange tubes and a plurality of corrugated fins are alternately combined and stacked, the heat exchange tubes and the corrugated fins are heated in a furnace having a nitrogen gas atmosphere, and the heat exchange tubes and the corrugated fins are brazed did. During heating of the heat exchange tubes and the corrugated fins, the heat exchange tubes were heated and held for 6.3 minutes so that the substantial temperature of the heat exchange tubes was 580 ° C. or more and the maximum temperature was 600.7 ° C.

  One heat exchange pipe was cut out from the heat exchange pipe and the brazed body of the fins, and the natural potentials at different depth positions from the outermost surface of the pipe wall (30) were measured. The results are as shown in FIG. The thickness of the tube wall (30) was 180 μm. In FIG. 3, the low potential portion having the lowest natural potential in the range between the outermost surface of the tube wall (30) and the deepest portion of the diffusion layer (33) is the position shown by the straight line A, ie 7 μm from the outermost surface. It was in the depth position. Also, the depth position of the deepest part of the diffusion layer (33) was 100 μm from the outermost surface of the tube wall (30). From the results shown in FIG. 3, it is found that the low potential portion having the lowest natural potential and the low potential portion are at least 60 mV higher in the range between the outermost surface of the tube wall (30) and the deepest portion of the diffusion layer (33). It has been found that a high potential portion having a natural potential is present such that the low potential portion is on the outermost surface side of the tube wall (30).

  Furthermore, after conducting a CCT test for 240 days about brazing of a heat exchange pipe and a fin, one heat exchange pipe was cut out, and the corrosion depth from the outermost surface of the pipe wall (30) of the heat exchange pipe was measured, The maximum corrosion depth was 53.0 μm, and it was found that the corrosion was stopped at the high potential portion present in the diffusion layer (33). In addition, it was found that the residual thickness of the tube wall (30) of the heat exchange tube after the CCT test is 100 μm or more, and it has sufficient corrosion resistance.

  From the above-described experimental results, the low potential portion having the lowest natural potential in the range within the range between the outermost surface of the tube wall (30) of the heat exchange tube (2) and the deepest portion of the diffusion layer (33) And the high potential portion where the natural potential is higher by 60 mV or more than the low potential portion is limited so that the low potential portion is located on the outermost surface side of the tube wall.

  The heat exchange pipe according to the present invention is suitably used as a condenser for a car air conditioner.

(1): Condenser (heat exchanger)
(2): Flat heat exchange pipe
(3): Corrugated fin
(30): Tube wall
(31): Core layer
(32): Coating layer
(33): Diffusion layer

Claims (4)

A plurality of aluminum extruded heat exchange tubes, and an aluminum bear fin disposed between adjacent heat exchange tubes and joined to the heat exchange tubes by a brazing material;
A tube wall of a heat exchange tube comprising: a main body portion made of an Al alloy forming the aluminum extruded section; and a covering layer made of an Al-Si-Zn alloy and covering the outer surface of the main body portion A diffusion layer in which Zn and Si in the Al-Si-Zn alloy forming the covering layer are diffused is formed in the outer surface layer portion of the main body of the wall, and the outermost surface of the tube wall of the heat exchange tube and the deepest portion of the diffusion layer The low potential part where the natural potential is lowest in the range and the high potential part where the natural potential is higher by 60 mV or more than the low potential part within the range A heat exchanger that exists on the outer side. In the range between the outermost surface of the tube wall of the heat exchange tube and the deepest portion of the diffusion layer, the natural potential decreases from the outermost surface of the tube wall toward the main body to reach the low potential portion, The heat exchanger according to claim 1, wherein the high potential portion is reached as it goes from the potential portion toward the body portion. The brazing material for joining the heat exchange tube and the fin is composed of Al in the Al alloy forming the aluminum extruded profile and Si of Si powder deposited on the surface of the heat exchange tube before joining. The heat exchanger according to claim 1 or 2. The Al--Si--Zn alloy which is the covering layer of the heat exchange tube is the Al powder in the Al alloy forming the aluminum extruded profile and the Si powder deposited on the surface of the heat exchange tube before bonding The heat exchanger according to any one of claims 1 to 3, wherein the heat exchanger is constituted of Si and Zn of Zn powder deposited on the surface of the heat exchange tube before bonding.

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