JP6066299B2 - Aluminum heat exchanger - Google Patents

Description

  The present invention relates to an aluminum heat exchanger. Here, aluminum means to include an aluminum alloy, and the same applies to the following.

  In general, as an aluminum heat exchanger, a heat exchange tube made of a plurality of flat extruded shapes parallel to each other is arranged in a horizontal direction between a pair of opposing header pipes, and further, a corrugated fin is interposed between these heat exchange tubes. A parallel flow type heat exchanger in which these are joined and joined by brazing is widely used.

  In this type of heat exchanger, as a general method for improving corrosion resistance, the electrochemical natural potential of the heat exchange tube and corrugated fin is adjusted, and the natural potential of the corrugated fin is reduced to heat exchange. By making the natural potential of the tube noble, the corrugated fins are preferentially corroded, the corrosion of the heat exchange tube is delayed, and the surface of the heat exchange tube is sprayed with Zn to form a Zn diffusion layer during brazing. The sacrificial anti-corrosion layer is preferentially corroded to prevent corrosion (pitting corrosion) in the depth direction of the tube and to corrode parallel to the outer surface of the heat exchange tube (surface corrosion). (See, for example, Patent Document 1).

Japanese Patent No. 4431361

  However, regarding the potential adjustment of the heat exchange tube and corrugated fin, the natural potential of the tube is made noble by adding Cu to the aluminum used for the heat exchange tube, and the aluminum used for the corrugated fin, more precisely the corrugated fin, is used. A general method is to reduce the natural potential of the corrugated fin by adding Zn to the constituting skin material (brazing material) and the core material, but there is a problem that Cu is likely to cause intergranular corrosion if the amount of Cu added is large. there were.

  In addition, regarding the formation of the sacrificial anticorrosive layer on the surface of the heat exchange tube, it is difficult to control the Zn spraying performed to form the sacrificial anticorrosive layer, and the amount of Zn is excessive, leading to the consumption of the sacrificial anticorrosive layer and causing the fins to fall off. Further, there is a problem that the amount of Zn becomes too small and the sacrificial anticorrosion layer is not sufficiently constructed, and the necessary corrosion resistance cannot be obtained.

  The present invention has been made in view of the above circumstances, and the amount of Cu added and the natural potential are optimized. In addition, aluminum that causes corrosion due to corrosion without using a Zn diffusion layer is used for a heat exchange tube. Thus, an object of the present invention is to provide an aluminum heat exchanger that can maintain long-term corrosion resistance without performing Zn spraying on the heat exchange tube.

In order to achieve the above object, the invention according to claim 1 includes a plurality of flat heat exchange tubes made of an aluminum extruded profile having a plurality of heat medium flow paths and a plurality of aluminum corrugated fins arranged in parallel, An aluminum heat exchanger in which both ends of the flat heat exchange tube are connected in communication with a pair of opposing aluminum header pipes and integrally brazed with a fluoride-based flux, wherein the flat heat exchange tube is Fe is 0.05 to 0.20 mass%, Si is 0.10 mass% or less, Cu is 0.15 to 0.32 mass%, Mn is 0.08 to 0.15 mass%, and Zr is 0.00. 02 to 0.05% by mass, Ti is 0.06 to 0.15% by mass, V is 0 to 0.05% by mass , Cr is 0.01 to 0.03% by mass , and the balance is Al and Consisting of inevitable impurities Has formed, and, on the surface of the flat heat exchange tubes, anticorrosion not been Zn is applied for the purpose of, the corrugated fins, a core, surface material is clad on both surfaces of said cardiac member It consists of a brazing sheet, the core material contains 1.3 to 2.2% by mass of Zn, the balance is made of Al and inevitable impurities, and the skin material is 0.7 to 1.3% by mass of Zn. And the balance is made of Al and inevitable impurities.

The invention according to claim 2 is the aluminum heat exchanger according to claim 1 , wherein the fluoride flux is a non-corrosive potassium fluoroaluminate flux.

By configuring in this way, the natural potential difference in the corrugated fin core material, skin material (brazing material), and flat heat exchange tube is within an appropriate range for the anticorrosion effect, and Zn diffuses on the surface of the flat heat exchange tube. It is possible to establish an anticorrosion method that does not depend on sacrificial anticorrosion by layers. Specifically, Fe (0.05 to 0.20 mass%), Si (0.10 mass% or less), Cu (0.15 to 0.15%), which is an alloy having a relatively high natural potential as a flat heat exchange tube material. 0.32 mass%), Mn (0.08 to 0.15 mass%), Zr (0.02 to 0.05 mass%), Ti (0.06 to 0.15 mass%), V ( 0 0.05 mass% ) and Cr ( 0.01-0.03 mass% ) are selected. Further, the corrugated fin is composed of a core material and a brazing sheet in which a skin material is clad on both sides of the core material, the core material contains 1.3 to 2.2% by mass of Zn, and the balance is Al and inevitable impurities. Al-Mn based aluminum alloy (JIS A 3003 material) having a composition consisting of Zn is used, and the skin material contains 0.7 to 1.3% by mass of Zn, with the balance being Al and inevitable impurities. An Al—Si based aluminum alloy (JIS A 4343 material) having a composition is used.

  In addition, a heat exchanger core including a flat heat exchange tube and a corrugated fin is integrally brazed by an in-furnace brazing method using a non-corrosive potassium fluoroaluminate flux such as KAlF4 and K3AlF6 as a fluoride flux. can do.

  According to the present invention, the amount of Cu added to the aluminum used in the heat exchange tube is suppressed, the corrosion is controlled to become a surface corrosion tendency, and it is not necessary to spray the heat exchange tube with Zn, so that it can be stably performed over a long period of time. Corrosion resistance can be maintained. Further, since the sacrificial anticorrosive layer need not be taken into consideration, the thickness of the heat exchange tube can be reduced to contribute to weight reduction, and the cost can be reduced by not performing the Zn spraying.

It is a schematic front view which shows an example of the aluminum heat exchanger which concerns on this invention. It is a perspective view which shows a part of said heat exchanger in a cross section. It is an expanded sectional view of the flat heat exchange tube in this invention. It is an expanded sectional view which shows the brazing state of the flat heat exchange tube and fin in this invention. It is a graph which shows the relationship between Zn content and a natural potential. It is a graph which shows the relationship between the test time and the corrosion depth in the salt spray test of a Zn thermal spray flat heat exchange tube and a flat heat exchange tube without Zn thermal spray.

  EMBODIMENT OF THE INVENTION Below, the form for implementing this invention is demonstrated in detail based on an accompanying drawing.

  As shown in FIG. 1, an aluminum heat exchanger 1 (hereinafter referred to as a heat exchanger 1) according to the present invention includes a pair of header pipes 2 a and 2 b that are made of aluminum (including an aluminum alloy) and that face each other. These header pipes 2a and 2b are disposed between a plurality of flat heat exchange tubes 3 (hereinafter referred to as heat exchange tubes 3) which are arranged in parallel and connected in parallel in the horizontal direction and between adjacent heat exchange tubes 3. Corrugated fins 4 (hereinafter referred to as fins 4) are brazed. In this case, as will be described later, the fin 4 is formed of a core material 4a and a brazing sheet in which a skin material 4b is clad on both surfaces of the core material 4a (see FIG. 4).

  The heat exchange tube 3 is formed with a plurality of divided heat medium passages 3a. Also, aluminum side plates 5 are brazed to the upper outer side and the lower open side of the fins 4 at the upper and lower ends, respectively. An end cap 6 made of aluminum is brazed to the upper and lower opening ends of the header pipes 2a and 2b.

  An inlet pipe 7a for a heat medium (hereinafter referred to as refrigerant) is connected to the upper part of one of the header pipes 2a and 2b (left side in FIG. 1), and the upper part of the header pipe 2a is connected to the upper part of the header pipe 2a. The first partition plate 8a is arranged at a position of about 1/3. A refrigerant outflow pipe 7b is connected to the lower part of the other header pipe 2b (right side in FIG. 1), and a second partition plate 8b is arranged at about 1/3 of the lower side of the header pipe 2b. Yes.

  In the heat exchanger 1 configured as described above, the refrigerant flows into the header pipe 2a defined by the first partition plate 8a via the inflow pipe 7a, and then flows through the heat exchange tube 3. It flows to the upper side in the header pipe 2b partitioned by the second partition plate 8b, and then flows into the lower side in the header pipe 2a partitioned by the first partition plate 8a via the heat exchange tube 3, After that, it flows to the outside through the outflow pipe 7b.

  Below, the composition of the heat exchange tube 3, the fin 4, and the brazing method will be described.

<Composition of heat exchange tube>
In the heat exchange tube 3 formed of a thin and small extruded flat tube having the fine heat medium flow path 3a in the present invention, durability and productivity from an industrial standpoint are problems. Generally, JIS A 1000 series pure aluminum material and JIS A 3000 series Al-Mn series material are used as extruded flat tubes, but pure aluminum materials have problems from the standpoint of corrosion resistance, while Al-Mn In the case of a system material, there is a problem in productivity in terms of thinness and small extrusion property. Therefore, in the present invention, an alloy excellent in terms of extrudability and corrosion resistance of the alloy itself is used. The characteristics will be described below. In addition, all the addition amounts of the following elements are mass%.

Fe: 0.05-0.20%
Fe has the effect of improving the strength of a pure aluminum alloy, and also has the effect of preventing cracking during casting and refining the cast structure. This effect is exhibited when the content is 0.05% or more. However, if the content exceeds 0.20%, an Al-Fe compound is produced at the grain boundaries during casting, and pitting corrosion resistance, The upper limit of Fe is set to 0.20% because there is a possibility that the corrosion may be adversely affected and the extrudability may be deteriorated due to stuffiness or cracking during extrusion.

Si: 0.10% or less Si is an inevitable impurity mixed in from the Al base material, but in order to suppress the formation of Al-Fe-Si compounds that adversely affect workability, and excessive Si particles are pit-like In order to become a starting point of corrosion and to generate compounds such as additive elements such as Mn and Zr and reduce their effects, the upper limit value was made 0.10%.

Cu: 0.15-0.32%
Cu is an element effective for suppressing deep pitting corrosion of Al ground. The effect is recognized when the content is 0.15% or more. However, when the content increases, the Al—Cu compound CuAl2 is formed at the grain boundary, and the grain boundary segregation cannot be completely eliminated by the homogenization treatment, and the grain boundary corrosion is promoted. In order to increase the extrusion pressure, the Cu content was set to 0.15 to 0.32%.

Mn: 0.08 to 0.15%
Mn has the effect of improving corrosion resistance and strength, particularly high temperature strength. These effects are manifested by inclusion of 0.030% or more, but in order to improve the potential of the Al matrix and stably suppress corrosion propagation, 0.08% or more of Mn addition is preferable. In order to increase the strength at high temperatures, there is a significant role in maintaining the rigidity of the structure without significant softening during brazing. On the other hand, since the high temperature strength is high, the processing pressure at the time of extrusion becomes large and the extrudability is lowered. Further, an Al—Mn-based intermetallic compound Al 6 Mn is formed along the crystal grain boundary, which may adversely affect the intergranular corrosion resistance. Therefore, the upper limit of the Mn content is 0.15%.

-Zr: 0.02-0.05%
Zr increases the high-temperature strength of the material by a combined effect with Mn and the like even when added in a small amount, and it alone has an effect at 0.02% or more, and when it exceeds 0.05%, it forms a compound with other elements. Influencing and reducing the effect and increasing the extrusion pressure when extruding thin-walled materials. Further, the addition of 0.02 to 0.05% Zr makes the matrix noble and has the effect of reducing intergranular corrosion as well as pitting corrosion.

Ti: 0.06-0.15%
Ti refines the cast structure, and the distribution state of the Ti element has the effect of suppressing intergranular corrosion of the extruded material. This effect is effectively exhibited when the content is 0.06% or more. However, when the content is increased, a coarse intermetallic compound TiAl3 is produced to deteriorate the extrudability and increase the non-uniformity of Ti distribution, so the upper limit was made 0.15%.

V: 0.05% or less V and V compounds crystallized at the time of casting have a function of preventing the progress of intergranular corrosion by dispersing in a layer form by extrusion, and are contained as necessary. However, as the content increases, the extrudability deteriorates, so the upper limit was made 0.05%. The combined effect of Ti and V increases the effect of suppressing intergranular corrosion. However, if the Ti and V contents are excessively increased, the extrudability deteriorates, so the upper limit of the total amount of Ti and V is 0.15%. It was.

-Cr: 0.03% or less Cr has an action of suppressing the coarsening of the extruded structure. This effect is effectively expressed by the content of 0.03% or less, but if it is contained in a large amount, the extrudability deteriorates, so the upper limit was made 0.03%.

  The remaining balance is Al and inevitable impurities.

<Fin composition>
The fin 4 is a brazing sheet in which a core material 4a and a skin material 4b, which is a brazing material, are clad on both sides, and it is desirable to use a standard alloy having versatility in consideration of industrial viewpoint and cost.

  In this invention, an alloy in which 1.3 to 2.2% by mass of Zn element is added to JIS A 3000 alloy as core material 4a from core material 4a and skin material 4b (brazing material) standardized in JIS Z 3263-2002. Standard name 3N03), brazing material specified an alloy (standard name 4N43) in which 0.7 to 1.3 mass% of Zn element was added to JIS A 4343 alloy.

The amount of Zn added to the core material 4a and the skin material 4b (brazing material) is such that, after brazing, the natural potential relationship with the heat exchange tube 3 is as shown in FIG. In this order, the potential difference can be maintained between 50 ± 20 mV in an appropriate range for the anticorrosion effect (see FIG. 5 and Table 1). ). Here, the reason why the range appropriate for the anticorrosion effect is 50 ± 20 mV is that in a long-term atmospheric exposure test, if there is a potential difference exceeding 70 mV, the promotion of sacrificial corrosion is accelerated, and if the potential is less than 30 mV, corrosion occurs. This is because there is a risk of corrosion becoming unstable at each site.

<Brazing method>
As described above, vacuum brazing methods that do not use flux and in-furnace brazing methods that use flux are widely used as brazing methods for aluminum products. In any case, depending on the difference in the method of removing the oxide film on the aluminum surface, which is essential in aluminum brazing, in the case of vacuum brazing, brazing heating in an atmosphere with a vacuum degree of about 1 × 10 ⁻² Pa or less Along with this, the Mg element added to a part of the constituent material evaporates, so that the oxide film on the surface is destroyed and bonding becomes possible.

  On the other hand, the flux brazing method enables bonding by removing the oxide film on the aluminum surface by the action of the molten flux during heating. A typical flux is a fluoride-based flux of KAlF4 and K3AlF6, and in this case, it is performed under an N2 gas atmosphere under almost atmospheric pressure.

  As described above, in the fin material of the brazing sheet having the material structure of the present invention, an aluminum alloy in which an appropriate range of Zn element is added to the core material 4a and the skin material 4b, that is, the core material 4a is made of JIS A 3000 alloy with Zn. Al-Mn alloy containing 1.3 to 2.2% by mass of element, Al-Si system containing 0.7 to 1.3% by mass of Zn element in JIS A 4343 alloy as skin material 4b (brazing material) Use an alloy.

  This makes it possible to minimize the decrease due to evaporation in the furnace brazing method. On the other hand, in the vacuum brazing method, since the added Zn metal evaporates in the vacuum, the mechanism of corrosion protection cannot be maintained, so the fluoride flux brazing method is effective as a brazing method selection. It is.

  According to the aluminum heat exchanger according to the embodiment configured as described above, it is possible to establish a corrosion prevention method that does not depend on sacrificial corrosion prevention by the Zn diffusion layer on the surface of the heat exchange tube 3.

  Moreover, Fe (0.05-0.20 mass%), Si (0.10 mass% or less), Cu (0.15-0.32) which are alloys with a comparatively high natural potential as a material of the heat exchange tube 3 Mass%), Mn (0.08 to 0.15 mass%), Zr (0.02 to 0.05 mass%), Ti (0.06 to 0.15 mass%), V (0.05 mass%) ), Cr (0.03% by mass or less), and the fin 4 is composed of a core material 4a and a brazing sheet in which a skin material 4b (brazing material) is clad on both sides of the core material 4a. Uses an Al-Mn-based aluminum alloy (JIS A 3003 material) having a composition comprising 1.3 to 2.2% by mass of Zn and the balance being Al and inevitable impurities, and the skin material 4b (the brazing material) Material) contains 0.7 to 1.3% by mass of Zn, with the balance being Al and inevitable impurities? In-furnace brazing method using non-corrosive potassium fluoroaluminate flux such as KAlF4 and K3AlF6 as a fluoride flux using an Al-Si aluminum alloy (JIS A 4343 material) having the following composition Thus, the heat exchanger core including the flat heat exchange tube and the corrugated fin can be brazed integrally.

  The items required as a heat exchanger include, as described above, mass production of the heat exchange tube (extrusion and strength), productivity of the heat exchanger (brazing), and finally as a heat exchanger. It is necessary to satisfy the corrosion resistance.

  Below, mass productivity (extrusion property, strength) of a heat exchange tube, productivity (brazing property) of a heat exchanger, and verification of corrosion resistance as a heat exchanger will be described.

(Verification of heat exchange tube)
About the heat exchange tube, the extrudability and the strength were verified for various aluminum alloys (invention alloys 1 to 17 and comparative alloys 18 to 25) having chemical compositions shown in Table 2.

  First, various aluminum alloys having the chemical composition shown in Table 2 (invention alloys 1 to 17 and comparative alloys 18 to 25) were melted, and the diameter was 7 inches (7 × 2.54 = 17.78 cm) and the length was 2 m. A cast body (billet) was prepared.

  The cast body is homogenized under conditions of holding at 550 to 590 ° C. for 5 to 6 hours, then heated to 460 to 550 ° C., and extruded with a thin-walled die having an extrusion ratio of 30 to 1000. did. As shown in FIG. 3, the cross-sectional shape of the heat exchange tube in this case is 13.85 mm in width (W), 1.93 mm in thickness (H), and 0.35 mm in thickness (T).

  The extrusion speed of a pure aluminum material (JIS A 1050 material), which is usually excellent in extrudability, was taken as 100, where ◎ was up to 10% reduction, ○ was up to 20% reduction, and x was less than 20%.

  The surface condition is judged by the surface defects (mushy, rough skin, internal defects) of the heat exchange tube, ◎ if there are no surface defects, ○ if there are slight but no problems in use, many surface defects Those that cannot be used were marked with x.

  The strength was determined based on the room temperature strength of the annealed material. Based on the pure aluminum material of 65 MPa, the strength exceeding 90 MPa was rated as ◎, the 60 to 90 MPa level as ○, and the strength below 60 MPa as ×.

  As a comprehensive evaluation, an acceptable product that can be used as a flat heat exchange tube was evaluated as ◯, and an unacceptable product that was not usable was evaluated as ×.

(Verification of heat exchanger)
Next, the tube material with a comprehensive evaluation of ○ in the heat exchange tube verification, the corrugated fin and header pipe processed with brazing sheet are assembled and brazed to produce a heat exchanger as shown in FIG. Corrosion resistance was evaluated by a spray test (JIS-Z2371). Table 2 shows the configurations and evaluation results of various heat exchangers.

Production of heat exchanger ・ Core size: 300H × 400Lmm
・ Heat exchange tube: 13.85W × 1.93Hmm
Corrugated fin: brazing sheet, 7.9H × 14Wmm, thickness 0.85mm
・ Flux: Nocolok flux (potassium fluoroaluminate flux)
Coating amount Approx. 5g / unit Brazing: N2 gas atmosphere mesh belt type continuous brazing furnace
Brazing temperature 600 ℃
For brazing, 98% or more of all the joint surfaces of the fin and heat exchange tube were evaluated as ◯ and less than 98% as x.

  As for corrosion resistance, the presence or absence of intergranular corrosion and the degree of progress are evaluated by observation of the microstructure after the corrosion test by a salt spray test (JIS-Z2371) for 5000 hours, and the corrosion depth is 150 μm or less and the fins are not peeled off. ○, where the fins were partially peeled at a corrosion depth of 150 μm or less, ○, and those where the corrosion depth exceeded 200 μm were rated as x.

As a comprehensive evaluation, an acceptable product that has good brazing and corrosion resistance and can be used as a heat exchanger was rated as ◯, and an unacceptable product that could not satisfy any of the evaluations was rated as x.

  The relationship between test time (hr) and maximum corrosion depth (μm) was investigated by the salt spray test (JIS-Z2371) using the same material and method in this invention compared with the sample with or without Zn coating on the heat exchange tube. As a result, a result as shown in FIG. 6 was obtained.

  As a result of this salt spray test, it was confirmed that the Zn diffusion layer had a tendency to corrode early in the heat exchange tube sprayed with Zn, and that the corrosion rate could be reduced in the heat exchange tube without Zn spraying.

DESCRIPTION OF SYMBOLS 1 Heat exchanger 2a, 2b Header pipe 3 Heat exchange tube 4 Corrugated fin 4a Core material 4b Skin material (brazing material)
4c Fillet (joint)

Claims (2)

A flat heat exchange tube made of an aluminum extruded shape having a plurality of heat medium flow paths and a plurality of aluminum corrugated fins are arranged in parallel, and a pair of aluminum products facing both ends of the flat heat exchange tube An aluminum heat exchanger connected to the header pipe and integrally brazed with a fluoride-based flux,
In the flat heat exchange tube, Fe is 0.05 to 0.20 mass%, Si is 0.10 mass% or less, Cu is 0.15 to 0.32 mass%, and Mn is 0.08 to 0.15. Mass%, Zr is 0.02 to 0.05 mass%, Ti is 0.06 to 0.15 mass%, V is 0 to 0.05 mass% , Cr is 0.01 to 0.03 mass% , And the balance is composed of Al and inevitable impurities, and the surface of the flat heat exchange tube is not coated with Zn for anticorrosion, and the corrugated fin is composed of a core material and The core material is composed of a brazing sheet having a skin material clad on both sides of the core material, the core material contains 1.3 to 2.2% by mass of Zn, and the balance is composed of Al and inevitable impurities. Contains 0.7 to 1.3% by mass of Zn, the balance being Al and inevitable impurities Having Ranaru composition, aluminum heat exchanger, characterized in that. The aluminum heat exchanger according to claim 1 ,
An aluminum heat exchanger, wherein the fluoride flux is a non-corrosive potassium fluoroaluminate flux.

Images