Aluminum alloy heat exchanger and method of producing refrigerant tube used for the heat exchanger

Abstract

An aluminum alloy heat exchanger is produced by applying a coating material that is prepared by adding a binder to a mixture of an Si powder and a Zn-containing compound flux powder to a surface of an aluminum alloy refrigerant tube, assembling a bare fin that is formed of an AlMnZn alloy with the refrigerant tube, and brazing the refrigerant tube and the bare fin by heating in an atmosphere-controlled furnace, the refrigerant tube being an extruded product of an aluminum alloy that comprises 0.5 to 1.7% (mass %, hereinafter the same) of Mn, less than 0.10% of Cu, and less than 0.10% of Si, with the balance being Al and unavoidable impurities.

Claims

1. A method of producing an aluminum alloy refrigerant tube that is used in the manufacture of an aluminum alloy heat exchanger, comprising the steps of: providing an ingot of an aluminum alloy comprising 0.5-1.7 mass % of Mn, less than 0.10% of Cu and less than 0.10% of Si, with the balance being Al and unavoidable impurities; subjecting the ingot of the aluminum alloy to a homogenization heat treatment that holds the ingot at a temperature of from 400-650 C. for 4 hours or more; and hot-extruding the ingot to produce the aluminum alloy refrigerant tube.

2. The method of claim 1, wherein the homogenization heat treatment includes a first-stage heat treatment that holds the ingot at 570-650 C. for 2 hours or more, followed by cooling the ingot to 200 C. or less, and a second-stage heat treatment that holds the ingot at 400-550 C. for 3 hours or more.

3. The method of claim 1, wherein the homogenization heat treatment includes a first-stage heat treatment that holds the ingot at 570-650 C. for 2 hours or more and a second-stage heat treatment that holds the ingot at 400-550 C. for 3 hours or more.

4. The method of claim 3, wherein the aluminum alloy refrigerant tube has an aluminum alloy bare fin made of an AlMnZn alloy brazed thereto, the AlMnZn alloy further comprising at least one of 0.001 to 0.10 mass % of In and 0.001 to 0.10 mass % of Sn.

5. The method of claim 4, wherein the homogenization heat treatment includes the first-stage heat treatment, followed by cooling the ingot to 200 C. or less, and the second-stage heat treatment.

Description

DESCRIPTION OF EXEMPLARY EMBODIMENTS

(1) The effects and the reasons for limitations of the alloy components of the extruded product of the aluminum alloy that forms the refrigerant tube of the aluminum alloy heat exchanger according to the present invention are described below.

(2) Mn:

(3) Mn is dissolved in the matrix after brazing the heat exchanger so that the strength of the aluminum alloy can be increased as compared with a pure aluminum alloy that has been used to form a multi-port extruded tube for automotive heat exchangers. The addition of Mn decreases extrudability (particularly the critical extrusion rate) to only a small extent as compared with the case of adding the same amount of Si, Cu, or Mg. When adding an identical amount of Mn, Si, Cu, or Mg to obtain an identical strength, a decrease in critical extrusion rate is a minimum when adding Mn so that high strength and high extrudability (i.e., productivity) can be achieved in combination. The Mn content is preferably 0.5 to 1.7%. If the Mn content is less than 0.5%, an increase in strength may occur to only a small extent. If the Mn content exceeds 1.7%, extrudability may decrease. The Mn content is more preferably 0.6 to 1.5%.

(4) Si:

(5) The Si content is limited to less than 0.10%. This achieves the following effects. The Si powder applied to the surface of the refrigerant tube diffuses into the refrigerant tube during brazing, forms an AlMnSi intermetallic compound with Mn included in the aluminum alloy that forms the refrigerant tube, and precipitates. The solid solubility of Mn and Si in the Si diffusion layer of the refrigerant tube decreases due to precipitation, so that the potential of the Si diffusion layer becomes lower than that of an area deeper than the Si diffusion layer (i.e., an area in which Si is not diffused). As a result, an area of the refrigerant tube from the surface to the bottom of the Si diffusion layer serves as a sacrificial anode layer for an area that is deeper than the Si diffusion layer, so that the corrosion perforation life in the depth direction can be improved.

(6) If the Si content is 0.10% or more, since an AlMnSi metal compound is initially present in the aluminum alloy that forms the refrigerant tube, the solid solubility of Mn in the alloy decreases. In this case, even if the Si powder applied to the surface diffuses into the alloy during brazing, precipitation of AlMnSi intermetallic compounds decreases, so that the effect of lowering the potential of the Si diffusion layer decreases. Therefore, an area of the refrigerant tube from the surface to the bottom of the Si diffusion layer does not serve as a sacrificial anode layer (i.e., the corrosion perforation life is not improved). The Si content is more preferably 0.05% or less in order to reliably achieve the above effect.

(7) Cu:

(8) The Cu content is limited to less than 0.10%. This achieves the following effects (1) to (3). (1) Intergranular corrosion can be suppressed during use of a brazed automotive heat exchanger (particularly at a high temperature). If the Cu content is 0.10% or more, the operating temperature of a heat exchanger increases to about 150 C. particularly when using CO.sub.2 as a refrigerant, so that precipitation of Cu or the like significantly occurs at the grain boundary. As a result, the intergranular corrosion susceptibility increases. (2) The addition of Cu significantly decreases extrudability as compared with Mn. It is also necessary to limit the amount of Cu taking account of a decrease in extrudability. (3) It is known that a potential decreases due to the addition of Zn, and increases due to the addition of Cu. The inventors found that the potential-increasing effect of Cu predominantly occurs when Zn coexists with Cu (particularly when the Zn content is low). In the present invention, a Zn diffusion layer formed during brazing with the Zn-containing flux powder has a low surface Zn concentration as compared with a Zn diffusion layer formed during brazing by Zn thermal spraying, etc. Therefore, if the refrigerant tube contains 0.10% or more of Cu, the potential-decreasing effect of the Zn diffusion layer formed by the Zn-containing flux powder is counterbalanced by the potential-increasing effect of Cu. In this case, the potential of the surface of the refrigerant tube does not decrease in spite of the presence of the Zn diffusion layer, so that a potential gradient cannot be formed such that the surface has a lower potential and the deep area has a higher potential in the thickness direction of the refrigerant tube. This makes it difficult to protect the deep area from corrosion by utilizing the surface as a sacrificial anode to improve the perforation life. An Si diffusion layer is present in the surface of the refrigerant tube due to the applied Si powder, and increases the potential of the surface. When the Cu content is high, the potential-increasing effect of Cu becomes completely predominant over the potential-decreasing effect of the Zn diffusion layer, so that a potential gradient is formed such that the surface has a higher potential and the deep area has a lower potential in the thickness direction of the refrigerant tube along with the potential-increasing effect of the Si diffusion layer. In this case, since the deep area serves as an anode with respect to the surface of the refrigerant tube, perforation corrosion occurs at an early stage. The surface Zn concentration may be increased by increasing the deposition amount of the Zn-containing flux powder. However, this increases the thickness of the resulting film. In this case, the thickness of the film decreases during brazing due to melting of Si and the flux so that the distance between the refrigerant tube and the fin material decreases. Since the above phenomenon occurs over the entire core, the outer dimension of the core decreases. When the Cu content is limited to less than 0.10%, the potential of the surface of the refrigerant tube decreases due to the low-concentration Zn diffusion layer. Therefore, a potential distribution in the thickness direction can be formed such that the surface has a lower potential and the deep area has a higher potential. This protects the deep area against corrosion by utilizing the surface of the refrigerant tube as a sacrificial anode. The Cu content is more preferably less than 0.05%, and still more preferably 0.03% or less.
Ti, Sr, and Zr:

(9) Ti forms a high-Ti-concentration area and a low-Ti-concentration area in the alloy. These areas are alternately distributed in layers in the direction of the thickness of the material. Since the low-Ti-concentration area is preferentially corroded as compared with the high-Ti-concentration area, corrosion occurs in a layered manner. Therefore, corrosion does not proceed in the thickness direction of the material, so that pitting corrosion resistance and intergranular corrosion resistance are improved. Moreover, the strength of the material at room temperature and a high temperature is improved by adding Ti. The Ti content is preferably 0.30% or less. If the Ti content exceeds 0.30%, coarse crystallized products may be produced during casting. This may make it difficult to produce a sound refrigerant tube.

(10) Sr causes the Si powder applied to the surface of the refrigerant tube to react with Al in the matrix during brazing to produce an AlSi alloy liquid filler metal, and causes the crystallized eutectic structure to be refined and dispersed during solidification due to cooling. When the eutectic structure that serves as an anode site on the surface of the material is dispersed, corrosion is uniformly dispersed, so that a planar corrosion configuration is obtained. This improves corrosion resistance. The Sr content is preferably 0.10% or less. If the Sr content exceeds 0.10%, an AlSiSr compound may be crystallized, so that the eutectic structure may not be refined.

(11) Zr increases the size of recrystallized grains when the alloy that forms the refrigerant tube recrystallizes during brazing. This reduces the grain boundary density of the matrix, suppresses a phenomenon in which the AlSi alloy liquid filler metal produced by the Si powder applied to the surface of the refrigerant tube penetrates the grain boundaries of the matrix, and suppresses preferential intergranular corrosion. The Zr content is preferably 0.30% or less. If the Zr content exceeds 0.30%, coarse crystallized products may be produced during casting. This may make it difficult to produce a sound refrigerant tube. The effects of Ti, Sr, and Zr can be obtained in combination by adding Ti, Sr, and Zr in combination.

(12) The extruded product of the aluminum alloy that forms the refrigerant tube of the aluminum alloy heat exchanger according to the present invention is preferably produced as follows. An aluminum alloy having the above composition is melted, and cast to obtain an ingot. The ingot is subjected to a homogenization treatment that holds the ingot at 400 to 650 C. for 4 hours or more, and hot-extruded. The homogenization treatment causes coarse crystallized products formed during casting and solidification to be decomposed, or granulated, so that a non-uniform texture (e.g., segregation layer) produced during casting can be homogenized. When coarse crystallized products or a non-uniform texture (e.g., segregation layer) produced during casting remain during hot extrusion, extrudability may decrease, or the surface roughness of the extruded product may decrease. If the homogenization temperature is less than 400 C., the above effects may not be obtained. The above effects are more easily obtained as the homogenization temperature increases. If the homogenization temperature is more than 650 C., melting may occur. The homogenization temperature is more preferably 430 to 620 C. The homogenization time is preferably 10 hours or more in order to achieve a sufficient effect. The effect of the homogenization treatment may be saturated (i.e., uneconomical) even if the homogenization treatment is performed for more than 24 hours. Therefore, the homogenization time is preferably 10 to 24 hours.

(13) The ingot may be subjected to a high-temperature homogenization treatment and a low-temperature homogenization treatment in combination. This further improves hot-extrudability, and reduces aluminum refuse. The term aluminum refuse refers to a defect wherein aluminum pieces accumulated in the die during extrusion are discharged from the die when a given size is reached, and adhere to the surface of the refrigerant tube aluminum extruded product. The high-temperature homogenization treatment (first-stage heat treatment) holds the ingot at 570 to 650 C. for 2 hours or more. This treatment causes coarse crystallized products formed during casting and solidification to be decomposed, granulated, or redissolved. If the treatment temperature is less than 570 C., redissolution may proceed to only a small extent. It is effective to employ a high homogenization temperature. However, melting may occur if the homogenization temperature is too high. Therefore, the homogenization temperature is set to be 650 C. or less. The homogenization temperature is more preferably 580 to 620 C. The homogenization time is preferably 5 to 24 hours. The effect of the homogenization treatment may be saturated (i.e., uneconomical) even if the homogenization treatment is performed for more than 24 hours.

(14) When performing a homogenization treatment (second-stage heat treatment) after the high-temperature homogenization treatment (first-stage heat treatment) at a temperature lower than that of the high-temperature homogenization treatment, Mn dissolved in the matrix precipitates, so that the solid solubility of Mn decreases. This reduces deformation resistance during the subsequent hot extrusion, so that extrudability can be improved. The temperature of the low-temperature homogenization treatment (second-stage heat treatment) is preferably 400 to 550 C. If the temperature of the low-temperature homogenization treatment (second-stage heat treatment) is less than 400 C., since only a small amount of Mn precipitates, the effect of reducing the deformation resistance may be insufficient. If the temperature of the low-temperature homogenization treatment (second-stage heat treatment) exceeds 550 C., precipitation may occur to only a small extent, so that the effect of reducing the deformation resistance may be insufficient. The low-temperature homogenization treatment (second-stage heat treatment) is performed for 3 hours or more. If the treatment time is less than 3 hours, precipitation may not sufficiently occur, so that the effect of reducing the deformation resistance may be insufficient. The effect of the low-temperature homogenization treatment (second-stage heat treatment) may be saturated (i.e., uneconomical) even if the homogenization treatment is performed for more than 24 hours. The low-temperature homogenization treatment (second-stage heat treatment) is preferably performed for 5 to 15 hours. The above two-stage homogenization treatment is designed so that Mn that has been sufficiently and homogeneously dissolved by the first-stage heat treatment is precipitated by the second-stage heat treatment. The first-stage heat treatment and the second-stage heat treatment need not necessarily be performed consecutively. Specifically, the second-stage heat treatment may be performed immediately after the first-stage heat treatment, or may be performed after cooling the ingot subjected to the first-stage heat treatment to 200 C. or less.

(15) Mixture of Si Powder, Zn-Containing Compound Flux Powder, and Binder

(16) When brazing the aluminum alloy heat exchanger according to the present invention, a coating material that is prepared by adding a binder to a mixture of an Si powder and a Zn-containing compound flux powder is applied to the surface of the refrigerant tube. The following effects are achieved by applying the coating material. Specifically, the Si powder reacts with Al of the matrix of the refrigerant tube during brazing to produce an AlSi filler metal, so that a fin material or a header material can be bonded to the refrigerant tube. The Zn-containing flux decomposes into the flux and Zn during brazing. The flux enables brazing, and Zn diffuses into the refrigerant tube to form a Zn diffusion layer. A potential gradient can thus be formed so that the surface of the refrigerant tube has a lower potential and the deep area of the refrigerant tube has a higher potential. Therefore, the deep area can be protected against corrosion by utilizing the surface area as a sacrificial anode. The binder improves adhesion when causing the mixed powder to adhere to the refrigerant tube. The particle size of the Si powder included in the mixture of the Si powder and the Zn-containing compound flux powder is preferably 100 m or less, more preferably 30 m or less, and still more preferably 15 m or less. The fluidity of the AlSi liquid filler metal produced during brazing is improved as the particle size of the Si powder decreases. Moreover, erosion of the matrix is suppressed as the particle size of the Si powder decreases. It is preferable that the Zn-containing compound flux powder have an average particle size of about 5 m. For example, KZnF.sub.3 is used as the Zn-containing compound flux powder.

(17) The mixing ratio of the Si powder to the Zn-containing compound flux powder is preferably 10:90 to 40:60. If the mixing ratio is less than 10:90 (i.e., the amount of the Si powder is less than 10%), a sufficient liquid filler metal may not be produced during brazing, so that bonding failure may occur. If the mixing ratio is more than 40:60 (i.e., the amount of the Si powder is more than 40%), the amount of Zn diffused into the refrigerant tube may be insufficient. Moreover, brazability may deteriorate due to a decrease in the amount of flux.

(18) When applying the mixture to the surface of the refrigerant tube, adhesion is improved by applying the mixture as a coating material that is prepared by adding a binder (e.g., a resin that volatilizes during heating for brazing) to the mixture. For example, an acrylic resin is used as the binder. The binder is used in an amount of 5 to 40% based on the total amount of the coating material. If the amount of the binder is less than 5% based on the total amount of the coating material, the mixture may easily separate from the surface of the refrigerant tube. If the amount of the binder is more than 40% based on the total amount of the coating material, brazability may deteriorate.

(19) The mixture of the Si powder and the Zn-containing compound flux powder is preferably applied in an amount of 5 to 30 g/m.sup.2. If the amount of the mixture applied is less than 5 g/m.sup.2, the amount of Zn that adheres to the surface of the refrigerant tube may be insufficient. If the amount of the mixture applied is more than 30 g/m.sup.2, the amount of filler metal produced may increase, so that melting or dissolution of the fin or the matrix may easily occur. Moreover, since the thickness of the film between the refrigerant tube and the fin material increases, the dimensions of the entire core may decrease if the film is melted during brazing and is reduced in thickness. The mixture may be applied to the refrigerant tube by roll coating.

(20) Potential Difference Between the Surface and Deep Area of Refrigerant Tube and Relationship with Potential of Fin Material

(21) In the aluminum alloy heat exchanger according to the present invention, the surface of the refrigerant tube has a potential lower than that of an area of the refrigerant tube that is deeper than a diffusion depth of Si and Zn by 20 to 200 mV, and the potential of the fin is lower than that of the deep area of the refrigerant tube. Therefore, the surface of the refrigerant tube serves as a sacrificial anode with respect to the deep area so that the deep area can be cathodically protected. If the potential difference is smaller than 20 mV, a sufficient sacrificial anode effect may not be obtained. If the potential difference is larger than 200 mV, the corrosion rate of the surface area increases, so that the sacrificial anode may be quickly exhausted. It is also important that the potential of the fin be lower than that of the deep area of the refrigerant tube. If the potential of the fin is higher than that of the deep area of the refrigerant tube, the fin serves as a cathode with respect to the refrigerant tube, so that corrosion of the refrigerant tube is promoted. Therefore, the potential of the fin must be lower than that of the deep area of the refrigerant tube.

(22) When producing a heat exchanger using the refrigerant tube according to the present invention, defective brazing that may occur at a joint between the refrigerant tube and a header material can be suppressed. Specifically, the refrigerant tube and the header material are mainly bonded via a filler metal applied to the header material. However, the Si powder adheres to the surface of the refrigerant tube, and the joint is covered with a liquid filler metal that is produced by the Si powder and the surface area of the refrigerant tube that are melted during brazing. Therefore, the filler metal of the header material communicates with the liquid filler metal on the surface of the refrigerant tube (i.e., flows freely). The refrigerant tube is bonded to the fin on the side opposite to the header, and the filler metal of the header material moves along the surface of the refrigerant tube, and reaches the joint with the fin due to surface tension. Therefore, the amount of filler metal becomes insufficient at the joint between the header and the refrigerant tube, so that defective brazing occurs. In particular, defective brazing occurs when using a refrigerant tube formed of a pure aluminum alloy or an alloy produced by adding Cu to a pure aluminum alloy. On the other hand, when forming a refrigerant tube using the aluminum alloy according to the present invention, defective brazing does not occur at the joint between the refrigerant tube and the header material even when the header material is provided with the same amount of filler metal as in the case of using the refrigerant tube formed of the above alloy. Specifically, since an AlMn precipitate (resistance) is present on the surface of the refrigerant tube aluminum alloy according to the present invention, the wettability of the liquid filler metal with the surface of the aluminum alloy can be suppressed as compared with a pure aluminum alloy or an alloy produced by adding Cu to a pure aluminum alloy. This makes it possible to prevent a situation in which the filler metal of the header material moves along the surface of the refrigerant tube and flows into the joint with the fin. In the present invention, since the refrigerant tube is bonded to the fin material through the mixture of the Si powder and the Zn-containing flux that is applied to the surface of the refrigerant tube, it is possible to reduce the Zn concentration of the fillet at the joint with the fin material as compared with the case of applying Zn to the surface of the refrigerant tube by thermal spraying or the like. Therefore, preferential corrosion of the fillet at the joint with the fin can be suppressed, so that removal of the fin can be prevented.

(23) The effects and the reasons for limitations of the alloy components of the aluminum alloy that forms the bare fin material of the aluminum alloy heat exchanger according to the present invention are described below.

(24) Mn:

(25) Mn improves the strength of the fin material. The Mn content is preferably 0.1 to 1.8%. If the Mn content is less than 0.1%, the effect may be insufficient. If the Mn content exceeds 1.8%, coarse crystallized products may be produced during casting. This may make it difficult to produce a sound fin material. The Mn content is more preferably 0.8 to 1.7%.

(26) Zn:

(27) Zn decreases the potential of the fin material. The Zn content is preferably 0.8 to 3.0%. If the Zn content is less than 0.8%, a sufficient potential-decreasing effect may not be obtained. If the Zn content exceeds 3.0%, the potential of the fin material is sufficiently decreased, but the self-corrosion resistance of the fin material may decrease. Moreover, since the potential difference between the fin and the deep area of the refrigerant tube increases, the fin (anode) may be consumed at an early stage due to corrosion in an environment in which the material is always exposed to a high-conductivity liquid. The Zn content is more preferably 1.0 to 2.5%.

(28) Si, Fe, Cu, Mg, Cr, Zr, and Ti:

(29) Si improves the strength of the fin material. The Si content is preferably 0.1 to 1.2%. If the Si content is less than 0.1%, the effect may be insufficient. If the Si content exceeds 1.2%, the melting point of the fin material may decrease, so that local melting may occur during brazing. The Si content is more preferably 0.2 to 0.6%.

(30) Fe improves the strength of the fin material. The Fe content is preferably 0.01 to 0.8%. If the Fe content is less than 0.01%, the effect may be insufficient. If the Fe content exceeds 0.8%, the amount of AlFe compounds produced may increase, so that the self-corrosion resistance of the fin material may decrease. The Fe content is more preferably 0.1 to 0.7%.

(31) Mg improves the strength of the fin material. The Mg content is preferably 0.05 to 0.5%. If the Mg content is less than 0.05%, the effect may be insufficient. If the Mg content exceeds 0.5%, Mg reacts with a fluoride flux to produce magnesium fluoride during brazing in an inert gas atmosphere using a fluoride flux. As a result, brazability may decrease, and the appearance of the brazed area may deteriorate. The Mg content is more preferably 0.05 to 0.3%, and still more preferably 0.05 to 0.15%.

(32) Cu improves the strength of the fin material. The Cu content is preferably 0.3% or less. If the Cu content exceeds 0.3%, the potential of the fin material may increase, so that the corrosion resistance of the refrigerant tube may be impaired. Moreover, the self-corrosion resistance of the fin material may decrease.

(33) Cr and Zr increase the grain size after brazing, and reduce buckling of the fin during brazing. The Cr content and the Zr content are preferably 0.3% or less. If the Cr content or the Zr content exceeds 0.3%, coarse crystallized products may be produced during casting. This may make it difficult to produce a sound fin material.

(34) Ti forms a high-Ti-concentration area and a low-Ti-concentration area in the alloy. These areas are alternately distributed in layers in the direction of the thickness of the material. Since the low-Ti-concentration area is preferentially corroded as compared with the high-Ti-concentration area, corrosion occurs in a layered manner. Therefore, corrosion does not proceed in the thickness direction of the material. As a result, pitting corrosion resistance and intergranular corrosion resistance are improved. Moreover, the strength of the material at room temperature and a high temperature is improved by adding Ti. The Ti content is preferably 0.3% or less. If the Ti content exceeds 0.3%, coarse crystallized products may be produced during casting. This may make it difficult to produce a sound fin material.

(35) In and Sn:

(36) In and Sn decrease the potential of the fin material with a small amount of addition. In and Sn exhibit a sacrificial anode effect for the refrigerant tube, and prevent pitting corrosion of the refrigerant tube. The In content and the Sn content are preferably 0.001 to 0.1%. If the In content or the Sn content is less than 0.001%, the effect may be insufficient. If the In content or the Sn content exceeds 0.1%, the self-corrosion resistance of the fin material may decrease.

(37) The heat exchanger according to the present invention may be produced by assembling the refrigerant tube and the fin material having the above composition, and brazing the refrigerant tube and the fin material by a normal method. The production method is not particularly limited. The heat exchanger according to the present invention exhibits an excellent corrosion resistance, and exhibits excellent durability, even when installed in an automobile that is subjected to a severe corrosive environment, for example. The heating method and the structure of the heating furnace used when subjecting the aluminum alloy that forms the refrigerant tube to the homogenization treatment are not particularly limited. The shape of the aluminum alloy extruded product that forms the refrigerant tube is not particularly limited. The extrusion shape is determined depending on the application (e.g., the shape of the heat exchanger). Since the material has excellent extrudability, the material may be extruded using a multi-cavity die having a hollow shape. For example, the refrigerant tube for heat exchangers is normally assembled with another member (e.g., fin material or header material), followed by brazing. The brazing atmosphere, heating temperature, heating time, and brazing method are not particularly limited. The fin material is normally produced by producing an ingot by semi-continuous casting, and subjecting the ingot to hot rolling, cold rolling, process annealing, and cold rolling. Note that process annealing may be omitted. A hot-rolled sheet may be directly obtained from a molten metal by continuous casting and rolling, and may be cold-rolled.

EXAMPLES

(38) An aluminum alloy extruded product for a refrigerant tube was produced as follows. A billet of an aluminum alloy (Alloys A to L) having a composition shown in Table 1 or an aluminum alloy (Alloys M to T) having a composition shown in Table 2 was cast. Alloy T has been widely used. The resulting billet was subjected to the following tests 1, 2, and 3. In Table 2, a value that does not meet the requirements of the present invention is underlined.

(39) Test 1

(40) The cast billet was homogenized at 600 C. for 10 hours, and hot-extruded to obtain a multi-port tube. The critical extrusion rate ratio (relative ratio with respect to the critical extrusion rate of Alloy T) during extrusion was determined. The results are shown in Tables 3 and 4. A case where the critical extrusion rate ratio was more than 1.0 was evaluated as Good, and a case where the critical extrusion rate ratio was less than 1.0 was evaluated as Bad (extrudability evaluation).

(41) Test 2

(42) The multi-port tube extruded in Test 1 was brazed. The multi-port tube was heated to 600 C. in a nitrogen gas atmosphere at an average temperature increase rate of 50 C./min, held for 3 minutes, and cooled to room temperature. The multi-port tube was then subjected to a tensile test at room temperature. The results (tensile strength) are shown in Tables 3 and 4. A case where the tensile strength was higher than that of Alloy T was evaluated as Good, and a case where the tensile strength was lower than that of Alloy T was evaluated as Bad (evaluation of strength after brazing).

(43) Test 3

(44) The billets of Alloys C and D were homogenized under conditions shown in Tables 5 and 6, and hot-extruded to obtain multi-port tubes. The critical extrusion rate ratio (relative ratio with respect to the critical extrusion rate of Alloy T) was determined. The temperature increase rate was 50 C./h. The temperature decrease rate when successively performing the first-stage heat treatment and the second-stage heat treatment was 25 C./h. The billet was allowed to cool after the second-stage heat treatment. The results (critical extrusion rate ratio) are shown in Tables 5 and 6. A case where the critical extrusion rate ratio was more than 1.0 was evaluated as Good, and a case where the critical extrusion rate ratio was less than 1.0 was evaluated as Bad (extrudability evaluation).

(45) TABLE-US-00001 TABLE 1 Composition (mass %) Alloy Si Fe Cu Mn Ti Sr Zr A 0.05 0.15 0 0.5 0 0 0 B 0.05 0.15 0 1.7 0 0 0 C 0.05 0.15 0 1.0 0 0 0 D 0.05 0.15 0 0.7 0 0 0 E 0.05 0.15 0 0.7 0.15 0 0 F 0.05 0.15 0 0.7 0 0.03 0 G 0.05 0.15 0 0.7 0 0 0.15 H 0.05 0.15 0 0.7 0.15 0.03 0 I 0.05 0.15 0 0.7 0 0.03 0.15 J 0.05 0.15 0 0.7 0.15 0 0.15 K 0.05 0.15 0 0.7 0.15 0.03 0.15 L 0.05 0.15 0.03 0.7 0 0 0

(46) TABLE-US-00002 TABLE 2 Composition (mass %) Alloy Si Fe Cu Mn Ti Sr Zr M 0.05 0.15 0 04 0 0 0 N 0.05 0.15 0 1.8 0 0 0 O 0.05 0.15 0 0.7 0.35 0 0 P 0.05 0.15 0 0.7 0 0.20 0 Q 0.05 0.15 0 0.7 0 0 0.35 R 0.05 0.15 0.15 0.7 0 0 0 S 0.05 0.15 0.01 0.01 0 0 0 T 0.05 0.15 0.4 0.1 0 0 0

(47) TABLE-US-00003 TABLE 3 Extrudability Brazability Critical extrusion Tensile strength Strength Alloy rate ratio Evaluation after brazing (MPa) after brazing A 1.41 Good 75 Good B 1.00 Good 115 Good C 1.17 Good 100 Good D 1.33 Good 80 Good E 1.29 Good 83 Good F 1.29 Good 80 Good G 1.29 Good 80 Good H 1.15 Good 84 Good I 1.15 Good 81 Good J 1.15 Good 84 Good K 1.10 Good 84 Good L 1.30 Good 82 Good

(48) TABLE-US-00004 TABLE 4 Extrudability Brazability Critical extrusion Tensile strength Strength Alloy rate ratio Evaluation after brazing (MPa) after brazing M 1.42 Good 70 Bad N 0.90 Bad 120 Good O 0.95 Bad 90 Good P 0.95 Bad 85 Good Q 0.95 Bad 85 Good R 0.95 Bad 87 Good S 1.58 Good 60 Bad T 1.00 75

(49) TABLE-US-00005 TABLE 5 First-stage Cooling to room Second-stage heat treatment temperature before heat treatment Extrudability Temperature Time second-stage heat Temperature Critical extrusion Alloy (C.) (h) treatment (C.) Time (h) rate ratio Evaluation C 600 10 1.17 Good D 600 10 1.33 Good C 600 10 None 500 10 1.25 Good C 600 10 Cooled 500 10 1.27 Good D 600 10 None 500 10 1.45 Good

(50) TABLE-US-00006 TABLE 6 First-stage heat Cooling to room Second-stage treatment temperature before heat treatment Extrudability Temperature second-stage heat Temperature Critical extrusion Alloy (C.) Time (h) treatment (C.) Time (h) rate ratio Evaluation C 600 2 0.95 Bad C 350 10 0.90 Bad C 600 1 None 500 2 0.85 Bad C 500 10 None 450 10 0.90 Bad T 600 10 1.00

(51) As shown in Table 3 and 4, Alloys A to L according to the present invention exhibited excellent extrudability and brazability. On the other hand, Alloys M to S that do not meet the requirements of the present invention exhibited inferior extrudability or brazability.

(52) When homogenizing Alloys C and D according to the present invention under the conditions shown in Tables 5 and 6, excellent extrudability was obtained when homogenizing the alloy under the conditions (conditions shown in Table 5) according to the present invention. On the other hand, inferior extrudability was obtained when homogenizing the alloy under conditions that do not meet the requirements of the present invention.

(53) As an aluminum alloy for a fin material, a slab of an aluminum alloy (Alloys a to 1) having a composition shown in Table 7 or an aluminum alloy (Alloys m to x) having a composition shown in Table 8 was cast. The slab was homogenized, hot-rolled, and cold-rolled to obtain a fin material having a thickness of 0.1 mm. The fin material was then corrugated (fin pitch: 3 mm, fin height: 7 mm). In Tables 7 and 8, a value that does not meet the requirements of the present invention is underlined.

(54) TABLE-US-00007 TABLE 7 Composition (mass %) Alloy Si Fe Cu Mn Zn Others a 0.05 0.15 0 1.2 0.8 b 0.05 0.15 0 1.2 3.0 c 0.05 0.15 0 1.2 1.0 d 0.05 0.15 0.15 1.2 2.5 e 0.5 0.15 0 1.2 1.0 f 0.5 0.15 0.15 1.2 2.5 g 0.05 0.15 0 1.2 1.0 Mg: 0.1 h 0.05 0.15 0 1.2 1.0 Cr: 0.15 i 0.05 0.15 0 1.2 1.0 Zr: 0.15 j 0.05 0.15 0 1.2 1.0 Ti: 0.15 k 0.05 0.15 0 1.2 1.0 In: 0.05 l 0.05 0.15 0 1.2 1.0 S,: 0.05

(55) TABLE-US-00008 TABLE 8 Composition (mass %) Alloy Si Fe Cu Mn Zn Others m 0.05 0.15 0 1.2 0.3 n 0.05 0.15 0 1.2 3.5 o 1.3 0.15 0 1.2 1.0 P 0.05 0.15 0 2.0 1.0 q 0.05 1.0 0 1.2 1.0 r 0.05 0.15 0 1.2 1.0 Mg: 0.6 s 0.05 0.15 0.5 1.2 1.0 t 0.05 0.15 0 1.2 1.0 Cr: 0.35 u 0.05 0.15 0 1.2 1.0 Zr: 0.35 v 0.05 0.15 0 1.2 1.0 Ti: 0.35 w 0.05 0.15 0 1.2 1.0 In: 0.15 x 0.05 0.15 0 1.2 1.0 Sn: 0.15

(56) A coating material was prepared by adding an acrylic resin binder to a mixture of an Si powder and a KZnF.sub.3 powder (the mixing ratio is shown in Tables 9 and 10). The coating material was applied to the surface of the above multi-port tube (aluminum alloy multi-port extruded tube for refrigerant tube) (indicated by the alloy reference symbol in Tables 9 and 10) by roll coating in an amount shown in Tables 9 and 10. The multi-port tube and the corrugated fin (indicated by the alloy reference symbol in Tables 9 and 10) were assembled (see Tables 9 and 10), and brazed to obtain a heat exchanger core.

(57) A case where the heat exchanger core was produced without any problem was evaluated as Good, and a case where a problem occurred when producing the heat exchanger core was evaluated as Bad (evaluation of heat exchanger core production). The results are shown in Table 9 and 10. The multi-port tube was homogenized at 600 C. for 10 hours. When brazing the multi-port tube and the fin, the multi-port tube and the fin were heated to 600 C. in a nitrogen gas atmosphere at an average temperature increase rate of 50 C./min, held for 3 minutes, and cooled to room temperature. The resulting heat exchanger core was subjected to the following tests 4, 5, 6, and 7.

(58) TABLE-US-00009 TABLE 9 Heat Refrigerant Coating Core exchange tube Si KZnF.sub.3 Acrylic resin Amount Fin material Problem during core production core No. Alloy (%) (%) binder (%) (/m.sup.3) Alloy production state 1 A 20 60 20 13 c None Good 2 B 20 60 20 13 c None Good 3 C 20 60 20 13 c None Good 4 D 20 60 20 13 c None Good 5 E 20 60 20 13 c None Good 6 F 20 60 20 13 c None Good 7 G 20 60 20 13 c None Good 8 H 20 60 20 13 c None Good 9 I 20 60 20 13 c None Good 10 J 20 60 20 13 c None Good 11 K 20 60 20 13 c None Good 12 L 20 60 20 13 c None Good 13 D 20 60 20 13 a None Good 14 D 20 60 20 13 b None Good 15 D 20 60 20 13 d None Good 16 D 20 60 20 13 e None Good 17 D 20 60 20 13 f None Good 18 D 20 60 20 13 g None Good 19 D 20 60 20 13 h None Good 20 D 20 60 20 13 i None Good 21 D 20 60 20 13 j None Good 22 D 20 60 20 13 k None Good 23 D 20 60 20 13 l None Good 24 D 20 60 10 13 c None Good

(59) TABLE-US-00010 TABLE 10 Heat Refrigerant Coating Fin Core exchange tube Si KZnF.sub.3 Acrylic resin Amount material Problem during production core No. Alloy (%) (%) binder (%) (g/m.sup.3) Alloy core production state 25 D 20 60 20 13 m None Good 26 D 20 60 20 13 n None Good 27 D 20 60 20 13 o Fin was melted Bad during brazing 28 D 20 60 20 13 p Fin broke during forming Bad 29 D 20 60 20 13 q None Good 30 D 20 60 20 13 r Fin was not bonded Bad during brazing 31 D 20 60 20 13 s None Good 32 D 20 60 20 13 t Fin broke during forming Bad 33 D 20 60 20 13 u Fin broke during forming Bad 34 D 20 60 20 13 v Fin broke during forming Bad 35 D 20 60 20 13 w None Good 36 D 20 60 20 13 x None Good 37 D 20 60 20 4 c Fin was not bonded Bad during brazing 38 D 20 60 20 25 c Core dimensions decreased Bad 39 D 24 73 3 13 c Coating separation Bad 40 D 16 49 35 13 c Defective brazing Bad 41 D 5 75 20 13 c Fin was not bonded Bad during brazing 42 D 45 35 20 13 c Defective brazing Bad 43 T 20 60 20 13 c None Good 44 T 10 85 5 20 c None Good
Test 4

(60) The heat exchanger core was subjected to a leakage test to determine the presence or absence of leakage due to defective brazing at the joint between the header and the refrigerant tube. The results are shown in Tables 11 and 12.

(61) Test 5

(62) The heat exchanger core was heated at 150 C. for 120 hours (high-temperature usage simulation), and subjected to an intergranular corrosion test in accordance with ISO 11846 (Method B). The results are shown in Tables 13 and 14.

(63) Test 6

(64) The Zn concentration and the Zn diffusion depth of the surface of the refrigerant tube of the heat exchanger core, the potentials of the surface and the deep area of the refrigerant tube, the potential difference between the surface and the deep area of the refrigerant tube, the potential of the fin material, the potential difference between the surface of the refrigerant tube and the fin material, and the potential difference between the deep area of the refrigerant tube and the fin material were measured. The Zn concentration and the Zn diffusion depth of the surface of the refrigerant tube were determined by filling the cross section of the core with a resin, and calculating the Zn concentration and the Zn diffusion depth from the EPMA line analysis results in the thickness direction. A depth at which the Zn concentration was 0.01% was taken as the Zn diffusion depth. The potential of the surface of the refrigerant tube and the potential of the surface of the fin material were measured directly after brazing. The potential of the deep area of the refrigerant tube was determined by facing the refrigerant tube to a depth of 150 m from the surface, and measuring the potential of an area in which Zn diffusion did not occur. When measuring the potential of the material, the material was immersed in a 5% NaCl aqueous solution (the pH was adjusted to 3 using acetic acid) for 24 hours. The average value of stable measured values obtained after immersing the material for 10 hours or more was employed. A saturated calomel electrode was used as a reference electrode. The results are shown in Tables 15 and 16.

(65) Test 7

(66) The heat exchanger core was subjected to the SWAAT test and the CCT test specified by ASTM-G85-Annex A3 for 1000 hours. In the CCT test, a 5% salt solution (the pH was adjusted to 3 using acetic acid) was used as a test solution. After spraying the test solution onto the heat exchanger core at 35 C. (atmospheric temperature) for 2 hours, the heat exchanger core was dried at 60 C. for 4 hours, and wetted at 50 C. for 2 hours at a relative humidity of 95% or more. The above cycle was repeated. The maximum corrosion depth of the refrigerant tube (tube) and the corrosion state of the fin after the test are shown in Tables 17 and 18. A case where the maximum corrosion depth of the refrigerant tube was 0.05 mm or less was evaluated as Excellent, a case where the maximum corrosion depth of the refrigerant tube was more than 0.05 mm and 0.10 mm or less was evaluated as Good, a case where the maximum corrosion depth of the refrigerant tube was more than 0.10 mm and 0.20 mm or less was evaluated as Fair, and a case where the maximum corrosion depth of the refrigerant tube was more than 0.20 mm was evaluated as Bad. A case where the fin was corroded to only a small extent was evaluated as Excellent, a case where the fin was slightly corroded was evaluated as Good, a case where the fin was corroded to some extent was evaluated as Fair, and a case where the fin was significantly corroded was evaluated as Bad.

(67) TABLE-US-00011 TABLE 11 Refrigerant Coating Leakage at Heat exchange tube Si KZnF.sub.3 Acrylic resin Amount Fin material header/refrigerant core No. Alloy (%) (%) binder (%) (g/m.sup.3) Alloy tube joint 1 A 20 60 20 13 c None 2 B 20 60 20 13 c None 3 C 20 60 20 13 c None 4 D 20 60 20 13 c None 5 E 20 60 20 13 c None 6 F 20 60 20 13 c None 7 G 20 60 20 13 c None 8 H 20 60 20 13 c None 9 I 20 60 20 13 c None 10 J 20 60 20 13 c None 11 K 20 60 20 13 c None 12 L 20 60 20 13 c None 13 D 20 60 20 13 a None 14 D 20 60 20 13 b None 15 D 20 60 20 13 d None 16 D 20 60 20 13 e None 17 D 20 60 20 13 f None 18 D 20 60 20 13 g None 19 D 20 60 20 13 h None 20 D 20 60 20 13 i None 21 D 20 60 20 13 j None 22 D 20 60 20 13 k None 23 D 20 60 20 13 l None 24 D 20 60 10 13 c None

(68) TABLE-US-00012 TABLE 12 Heat exchange Refrigerant tube Coating Leakage at core Si KZnF.sub.3 Acrylic resin Amount Fin material header/refrigerant No. Alloy (%) (%) binder (%) (g/m.sup.3) Alloy tube joint 25 D 20 60 20 13 m None 26 D 20 60 20 13 n None 27 D 20 60 20 13 o None 28 D 20 60 20 13 p None 29 D 20 60 20 13 q None 30 D 20 60 20 13 r None 31 D 20 60 20 13 s None 32 D 20 60 20 13 t None 33 D 20 60 20 13 u None 34 D 20 60 20 13 v None 35 D 20 60 20 13 w None 36 D 20 60 20 13 x None 37 D 20 60 20 4 c None 38 D 20 60 20 25 c None 39 D 24 73 3 13 c None 40 D 16 49 35 13 c None 41 D 5 75 20 13 c None 42 D 45 35 20 13 c None 43 T 20 60 20 13 c Presence 44 T 10 85 5 20 c Presence

(69) TABLE-US-00013 TABLE 13 Heat exchange Coating core Refrigerant tube Si KZnF.sub.3 Acrylic resin Amount Fin material Intergranular No. Alloy (%) (%) binder (%) (g/m.sup.3) Alloy corrosion 1 A 20 60 20 13 c None 2 B 20 60 20 13 c None 3 C 20 60 20 13 c None 4 D 20 60 20 13 c None 5 E 20 60 20 13 c None 6 F 20 60 20 13 c None 7 G 20 60 20 13 c None 8 H 20 60 20 13 c None 9 I 20 60 20 13 c None 10 J 20 60 20 13 c None 11 K 20 60 20 13 c None 12 L 20 60 20 13 c None 13 D 20 60 20 13 a None 14 D 20 60 20 13 b None 15 D 20 60 20 13 d None 16 D 20 60 20 13 e None 17 D 20 60 20 13 f None 18 D 20 60 20 13 g None 19 D 20 60 20 13 h None 20 D 20 60 20 13 i None 21 D 20 60 20 13 j None 22 D 20 60 20 13 k None 23 D 20 60 20 13 l None 24 D 20 60 10 13 c None

(70) TABLE-US-00014 TABLE 14 Heat Refrigerant Coating exchange tube Si KZnF.sub.3 Acrylic resin Amount Fin material Intergranular core No. Alloy (%) (%) binder (%) (g/m.sup.3) Alloy corrosion 25 D 20 60 20 13 m None 26 D 20 60 20 13 n None 27 D 20 60 20 13 o None 28 D 20 60 20 13 p None 29 D 20 60 20 13 q None 30 D 20 60 20 13 r None 31 D 20 60 20 13 s None 32 D 20 60 20 13 t None 33 D 20 60 20 13 u None 34 D 20 60 20 13 v None 35 D 20 60 20 13 w None 36 D 20 60 20 13 x None 37 D 20 60 20 4 c None 38 D 20 60 20 25 c None 39 D 24 73 3 13 c None 40 D 16 49 35 13 c None 41 D 5 75 20 13 c None 42 D 45 35 20 13 e None 43 T 20 60 20 13 c Significant 44 T 10 85 5 20 c Significant

(71) TABLE-US-00015 TABLE 15 Tube Refrigerant Refrigerant tube surface/ Tube deep Heat Coating tube Zn potential Fin fin area/fin ex- Refrig- Acrylic Fin Surface Diffu- Deep material material material change erant resin mate- concen- sion Surface area Potential potential potential potential core tube Si KZnF.sub.3 binder Amount rial tration depth (mV vs. (mV vs. difference (mV vs. difference difference No. Alloy (%) (%) (%) (g/m.sup.3) Alloy (mass %) (m) SCE) SCE) (mV) SCE) (mV) (m/V) 1 A 20 60 20 13 c 1.5 100 845 750 95 780 65 30 2 B 20 60 20 13 c 1.5 100 815 720 95 780 35 60 3 C 20 60 20 13 c 1.5 100 825 730 95 780 45 50 4 D 20 60 20 13 c 1.5 100 835 740 95 780 55 40 5 E 20 60 20 13 c 1.5 100 835 740 95 780 55 40 6 F 20 60 20 13 c 1.5 100 835 740 95 780 55 40 7 G 20 60 20 13 c 1.5 100 835 740 95 780 55 40 8 H 20 60 20 13 c 1.5 100 835 740 95 780 55 40 9 I 20 60 20 13 c 1.5 100 835 740 95 780 55 40 10 J 20 60 20 13 c 1.5 100 835 740 95 780 55 40 II K 20 60 20 13 c 1.5 100 835 740 95 780 55 40 12 L 20 60 20 13 c 1.5 100 830 730 100 780 50 50 13 D 20 60 20 13 a 1.5 100 835 740 95 760 75 20 14 D 20 60 20 13 b 1.5 100 835 740 95 900 65 160 15 D 20 60 20 13 d 1.5 100 835 740 95 800 35 60 16 D 20 60 20 13 c 1.5 100 835 740 95 770 65 30 17 D 20 60 20 13 f 1.5 100 835 740 95 790 45 50 18 D 20 60 20 13 g 1.5 100 835 740 95 780 55 40 19 D 20 60 20 13 h 1.5 100 835 740 95 780 55 40 20 D 20 60 20 13 i 1.5 100 835 740 95 780 55 40 21 D 20 60 20 13 j 1.5 100 835 740 95 780 55 40 22 D 20 60 20 13 k 1.5 100 835 740 95 820 15 80 23 D 20 60 20 13 l 1.5 100 835 740 95 820 15 80 24 D 20 60 10 13 c 1.5 100 835 740 95 780 55 40

(72) TABLE-US-00016 TABLE 16 Tube Tube deep Refrigerant surface/ area/ Heat Coating tube Zn Refrigerant tube potential Fin fin fin ex- Refrig- Acrylic Fin Surface Diffu- Deep material material material change erant resin mate- concen- sion Surface area Potential potential potential potential core tube Si KZnF.sub.3 binder Amount rial tration depth (mV vs. (mV vs. difference (mV vs. difference difference No. Alloy (%) (%) (%) (g/m.sup.3) Alloy (mass %) (m) SCE) SCE) (mV) SCE) (mV) (mV) 25 D 20 60 20 13 m 1.5 100 835 740 95 730 105 10 26 D 20 60 20 13 n 1.5 100 835 740 95 950 115 210 27 D 20 60 20 13 o 1.5 100 835 740 95 750 85 10 28 D 20 60 20 13 p 1.5 100 835 740 95 720 115 20 29 D 20 60 20 13 q 1.5 100 835 740 95 780 55 40 30 D 20 60 20 13 r 1.5 100 835 740 95 780 55 40 31 D 20 60 20 13 s 1.5 100 835 740 95 700 135 40 32 D 20 60 20 13 t 1.5 100 835 740 95 780 55 40 33 D 20 60 20 13 u 1.5 100 835 740 95 780 55 40 34 D 20 60 20 13 v 1.5 100 835 740 95 780 55 40 35 D 20 60 20 13 w 1.5 100 835 740 95 820 15 80 36 D 20 60 20 13 x 1.5 100 835 740 95 820 15 80 37 D 20 60 20 4 c 0.2 45 760 740 20 780 20 40 38 D 20 60 20 25 c 2.4 140 880 740 140 780 100 40 39 D 24 73 3 13 c 1.7 105 845 740 105 780 65 40 40 D 16 49 35 13 c 1.0 80 780 740 40 780 0 40 41 D 5 75 20 13 c 1.8 110 850 740 110 780 70 40 42 D 45 35 20 13 c 0.5 60 770 740 30 780 10 40 43 T 20 60 20 13 c 1.5 100 710 710 0 780 70 70 44 T 10 85 5 20 c 2.5 145 720 710 10 780 60 70

(73) TABLE-US-00017 TABLE 17 Refrigerant Coating Fin SWAAT-Ioooh CCT-loooh Heat exchange tube Si KZnF.sub.3 Acrylic resin Amount material Maximum corrosion Corrosion Maximum corrosion Corrosion core No. Alloy (%) (%) binder (%) (g/m.sup.3) Alloy depth of tube (mm) of fin depth of tube (mm) of fin 1 A 20 60 20 13 c 0.05 Excellent Excellent 0.05 Excellent Excellent 2 B 20 60 20 13 c 0.05 Excellent Excellent 0.05 Excellent Excellent 3 C 20 60 20 13 c 0.05 Excellent Excellent 0.05 Excellent Excellent 4 D 20 60 20 13 c 0.05 Excellent Excellent 0.05 Excellent Excellent 5 E 20 60 20 13 c 0.03 Excellent Excellent 0.03 Excellent Excellent 6 F 20 60 20 13 c 0.03 Excellent Excellent 0.03 Excellent Excellent 7 G 20 60 20 13 c 0.04 Excellent Excellent 0.04 Excellent Excellent 8 H 20 60 20 13 c 0.03 Excellent Excellent 0.03 Excellent Excellent 9 I 20 60 20 13 c 0.03 Excellent Excellent 0.03 Excellent Excellent 10 J 20 60 20 13 c 0.03 Excellent Excellent 0.03 Excellent Excellent 11 K 20 60 20 13 c 0.03 Excellent Excellent 0.03 Excellent Excellent 12 L 20 60 20 13 c 0.05 Excellent Excellent 0.05 Excellent Excellent 13 D 20 60 20 13 a 0.05 Excellent Excellent 0.05 Excellent Excellent 14 D 20 60 20 13 b 0.05 Excellent Good 0.05 Excellent Excellent 15 D 20 60 20 13 d 0.05 Excellent Excellent 0.05 Excellent Excellent 16 D 20 60 20 13 e 0.05 Excellent Excellent 0.05 Excellent Excellent 17 D 20 60 20 13 f 0.05 Excellent Excellent 0.05 Excellent Excellent 18 D 20 60 20 13 g 0.05 Excellent Excellent 0.05 Excellent Excellent 19 D 20 60 20 13 h 0.05 Excellent Excellent 0.05 Excellent Excellent 20 D 20 60 20 13 i 0.05 Excellent Excellent 0.05 Excellent Excellent 21 D 20 60 20 13 j 0.05 Excellent Excellent 0.05 Excellent Excellent 22 D 20 60 20 13 k 0.05 Excellent Excellent 0.05 Excellent Excellent 23 D 20 60 20 13 l 0.05 Excellent Excellent 0.05 Excellent Excellent 24 D 20 60 10 13 c 0.05 Excellent Excellent 0.05 Excellent Excellent

(74) TABLE-US-00018 TABLE 18 Refrigerant Coating Fin SWAAT-loooh CCT-loooh Heat exchange tube Si KZnF.sub.3 Acrylic resin Amount material Maximum corrosion Corrosion Maximum corrosion Corrosion core No. Alloy (%) (%) binder (%) (g/m.sup.3) Alloy depth of tube (mm) of fin depth of tube (mm) of fin 25 D 20 60 20 13 m 0.30 Bad Excellent 0.30 Bad Excellent 26 D 20 60 20 13 n 0.05 Excellent Bad 0.05 Excellent Bad 27 D 20 60 20 13 o 0.05 Excellent Excellent 0.05 Excellent Excellent 28 D 20 60 20 13 p 0.30 Bad Excellent 0.30 Bad Excellent 29 D 20 60 20 13 q 0.05 Excellent Bad 0.05 Excellent Bad 30 D 20 60 20 13 r 0.05 Excellent Excellent 0.05 Excellent Excellent 31 D 20 60 20 13 s 0.30 Bad Bad 0.30 Bad Bad 32 D 20 60 20 13 t 0.05 Excellent Excellent 0.05 Excellent Excellent 33 D 20 60 20 13 u 0.05 Excellent Excellent 0.05 Excellent Excellent 34 D 20 60 20 13 v 0.05 Excellent Excellent 0.05 Excellent Excellent 35 D 20 60 20 13 w 0.05 Excellent Bad 0.05 Excellent Bad 36 D 20 60 20 13 x 0.05 Excellent Bad 0.05 Excellent Bad 37 D 20 60 20 4 c 0.11 Fair Good 0.30 Bad Good 38 D 20 60 20 25 c 0.05 Excellent Excellent 0.05 Excellent Excellent 39 D 24 73 3 13 c 0.05 Excellent Excellent 0.05 Excellent Excellent 40 D 16 49 35 13 c 0.05 Excellent Good 0.21 Bad Good 41 D 5 75 20 13 c 0.05 Excellent Excellent 0.05 Excellent Excellent 42 D 45 35 20 13 c 0.08 Good Good 0.30 Bad Good 43 T 20 60 20 13 c 0.30 Bad Good 0.30 Bad Good 44 T 10 85 5 20 c 0.22 Bad Good 0.30 Bad Good

(75) The results of Tests 4 to 7 were as follows. The heat exchanger cores No. 1 to 24 produced according to the present invention showed no leakage at the joint between the header and the refrigerant tube when subjected to the leakage test after brazing. On the other hand, the heat exchanger cores No. 43 and 44 using Alloy T having a low Mn content as the refrigerant tube aluminum alloy showed leakage.

(76) The heat exchanger cores No. 1 to 24 produced according to the present invention showed no intergranular corrosion. On the other hand, the heat exchanger cores No. 43 and 44 using Alloy T containing Cu as the refrigerant tube aluminum alloy showed significant intergranular corrosion.

(77) In the heat exchanger cores No. 1 to 24 produced according to the present invention, a sufficient Zn diffusion layer was formed in the surface of the refrigerant tube. Therefore, the surface of the refrigerant tube had a potential lower than that of the deep area of the refrigerant tube. The potential difference between the surface and the deep area of the refrigerant tube was 95 to 100 mV. The potential of the fin material was also lower than that of the deep area of the refrigerant tube. A sufficient Zn diffusion layer was not formed in the surface of the refrigerant tube in some of the heat exchanger cores No. 25 to 44 produced under conditions that do not meet the requirements of the present invention. In this case, a sufficient potential difference was not obtained between the surface and the deep area of the refrigerant tube. In the heat exchanger cores No. 43 and 44 using Alloy T containing Cu as the refrigerant tube aluminum alloy, since the potential-decreasing effect of Zn was counterbalanced, the surface of the refrigerant tube had a potential equal to or slightly lower than that of the deep area of the refrigerant tube, although a sufficient Zn diffusion layer was formed.

(78) When subjecting the heat exchanger cores No. 1 to 24 produced according to the present invention to the SWAAT test, the maximum corrosion depth was small (i.e., excellent corrosion resistance was obtained) since a sufficient potential difference was obtained between the surface and the deep area of the refrigerant tube. In the SWAAT test, since the fin exhibits a sacrificial anode effect, corrosion of the fin material differs depending on the potential difference between the surface of the refrigerant tube and the fin material. In the heat exchanger cores No. 1 to 24 produced according to the present invention, the fin material was corroded to no or only a small extent due to an appropriate potential difference between the surface of the refrigerant tube and the fin material. Moreover, the potential of the fin material was lower than that of the deep area of the refrigerant tube. Therefore, the fin material did not accelerate corrosion of the refrigerant tube as a cathode.

(79) With regard to the heat exchanger cores No. 25 to 44 produced under conditions that do not meet the requirements of the present invention, the maximum corrosion depth was large in the heat exchanger cores No. 25, 28, 31, 37, 43, and 44 in which a sufficient potential difference was not obtained between the surface and the deep area of the refrigerant tube, or the potential of the fin material was higher than that of the deep area of the refrigerant tube. The fin of Heat exchanger core No. 26 using Alloy n having a high Zn content as the fin material showed significant corrosion since the potential of the fin material was significant lower than that of the surface of the refrigerant tube. In the heat exchanger cores No. 29, 31, 35, and 36 using Alloy q having a high Fe content, Alloy s having a high Cu content, Alloy w having a high In content, or Alloy x having a high Sn content as the fin material, the fin showed significant corrosion due to inferior self-corrosion resistance.

(80) When subjecting the heat exchanger cores No. 1 to 24 produced according to the present invention to the CCT test (the CCT test is similar to the actual environment due to the drying step; however, the fin may not exhibit a sacrificial anode effect), the maximum corrosion depth of the refrigerant tube was small (i.e., excellent corrosion resistance was obtained) since a sufficient potential difference was obtained between the surface and the deep area of the refrigerant tube. The fin material was corroded to no or only a small extent. Regarding the heat exchanger cores No. 25 to 44 produced under conditions that do not meet the requirements of the present invention, the maximum corrosion depth of the refrigerant tube was large when the potential difference between the surface and the deep area of the refrigerant tube was insufficient. The same tendency as that of the SWAAT test was observed for corrosion of the fin material. The heat exchanger cores No. 27, 30, 32-34, 38, 39, and 41 showed excellent corrosion resistance results. However, a problem occurred when producing the heat exchanger core (see Table 12).

(81) Obviously, numerous modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.