ALUMINUM ALLOY FIN MATERIAL AND HEAT EXCHANGER

Abstract

An aluminum alloy fin material and a heat exchanger having excellent moldability, strength, resistance to brazing erosion and durability are provided. The aluminum alloy fin material has a composition comprising Mn: 1.8 to 2.5%, Si: 0.7 to 1.3%, Fe: 0.05 to 0.3%, Cu: 0.14 to 0.30%, Zn: 1.3 to 3.0%, with the balance being Al and inevitable impurities, wherein a ratio Mn/Si in terms of content is in a range of 1.5 to 2.9, and the aluminum alloy fin material has a solidus temperature of 610 C. or more, a tensile strength before brazing of 220 to 270 MPa, has a crystal grain structure before brazing of a non-recrystallized grain structure, and has a tensile strength after brazing of 160 MPa or more, an electrical conductivity after brazing of 40% IACS or more and an average crystal grain size in a rolled surface after brazing of 300 m to 2,000 m.

Claims

1. An aluminum alloy fin material having a composition comprising, in % by mass, Mn: 1.8 to 2.5%, Si: 0.7 to 1.3%, Fe: 0.05 to 0.3%, Cu: 0.14 to 0.30%, Zn: 1.3 to 3.0%, with the balance being Al and inevitable impurities, wherein a ratio of Mn/Si in terms of content is in a range of 1.5 to 2.9, and the aluminum alloy fin material has a solidus temperature of 610 C. or more, a tensile strength before brazing of 220 to 270 MPa, and has a crystal grain structure before brazing of a non-recrystallized grain structure, a tensile strength after brazing of 160 MPa or more, an electrical conductivity after brazing of 40% IACS or more, and an average crystal grain size in a rolled surface after brazing of 300 m to 2,000 m.

2. The aluminum alloy fin material according to claim 1, wherein, particles having a circle-equivalent diameter of 400 nm or less among second phase particles distributed in matrix before brazing, have an average diameter in a range of 40 to 90 nm, and a number density thereof is within a range of 6 to 13 particles/m.sup.2.

3. The aluminum alloy fin material according to claim 1, wherein, particles having a circle-equivalent diameter of 400 nm or less among second phase particles distributed in matrix after brazing, have an average diameter in a range of 50 to 100 nm, and a number density thereof is 5 particles/m.sup.2 or more.

4. The aluminum alloy fin material according to claim 2, wherein, particles having a circle-equivalent diameter of 400 nm or less among second phase particles distributed in matrix after brazing, have an average diameter in a range of 50 to 100 nm, and a number density thereof is 5 particles/m.sup.2 or more.

5. A heat exchanger prepared by brazing the aluminum alloy fin material according to claim 1 and an aluminum material.

6. A heat exchanger prepared by brazing the aluminum alloy fin material according to claim 2 and an aluminum material.

7. A heat exchanger prepared by brazing the aluminum alloy fin material according to claim 3 and an aluminum material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0063] The advantages and features provided by one or more embodiments of the invention will become more fully understood from the detailed description given hereinbelow and the appended drawings which are given by way of illustration only, and thus are not intended as a definition of the limits of the present invention:

[0064] FIG. 1 shows a perspective view illustrating a heat exchanger for an automobile made of aluminum according to an embodiment of the present invention; and

[0065] FIG. 2 shows a view illustrating a model for evaluating brazing in Examples of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0066] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. However, the scope of the invention is not limited to the disclosed embodiments.

[0067] Provided is an aluminum alloy having a composition comprising, in % by mass, Zr: 0.04% or less, Mn: 1.8 to 2.5%, Si: 0.7 to 1.3%, Fe: 0.05 to 0.3%, Cu: 0.14 to 0.30%, Zn: 1.3 to 3.0%, with the balance being inevitable impurities, wherein a ratio of Mn/Si is in the range of 1.5 to 2.9.

[0068] An aluminum alloy fin material can be produced by casting the above alloy by continuous casting rolling (CC process) using, for example, a twin roll caster, subjecting the cast sheet to homogenizing treatment and cold rolling. It is desirable that the cooling rate in casting is adjusted to the range of 50 to 400 C./second.

[0069] When the cooling rate in casting is less than 50 C./second, the supersaturated solid solution amount of elements such as Mn, Si and Fe to the matrix is reduced, making it difficult to control the dispersion state of second phase particles of 400 nm or less to the desired state in the subsequent heating treatment. In contrast, when the cooling rate in casting is more than 400 C./second, the amount of supersaturated solid solution is excessively increased, also making it difficult to control the dispersion state.

[0070] The cast sheet obtained is preferably subjected to cold rolling at 5 to 30% and then subjected to the first heat-treatment. Introduction of strain in the material by cold rolling facilitates precipitation when the heat treatment, making it easy to control the dispersion state. Then the first heat treatment is carried out. In the first heat treatment, the maintaining temperature is set to the range of 350 to 550 C. and the maintaining time is set to 3 to 40 hours, and the second phase particles are precipitated finely and homogeneously at high density.

[0071] When the maintaining temperature is less than 350 C., the size of dispersed particles to be precipitated is excessively fine. In contrast, when the maintaining temperature is more than 550 C., the size of dispersed particles to be precipitated becomes excessively coarse.

[0072] Furthermore, when the maintaining time is less than 3 hours, the amount of precipitation is insufficient. When the maintaining time is more than 40 hours, dispersed particles grow and cause a non-homogeneous distribution.

[0073] Subsequently, cold rolling is performed at 70% or more, and then the second heat treatment is performed. Since second phase particles have been homogeneously and finely distributed in the first heat treatment, and the size of the second phase particles is increased while maintaining the homogeneity of the second phase particles which have been precipitated in the first heat treatment, due to strain introduced by cold rolling, this provides the desired dispersion state useful for improving properties. If the second heat treatment is omitted, a homogeneous and fine distribution of second phase particles is unlikely to be obtained, and the cold rolling ratio until temper annealing is increased, therefore the tensile strength before brazing is increased, causing a reduction in moldability.

[0074] It is desirable that the maintaining temperature is 370 to 530 C. and the maintaining time is 1 to 20 hours in the second heat treatment.

[0075] When the maintaining temperature is less than 370 C., dispersed particles cannot grow, and thus their size is excessively fine. When the maintaining temperature is more than 530 C., the size of dispersed particles to be precipitated becomes excessively coarse, and besides, only particular particles are likely to grow, causing a non-homogeneous distribution.

[0076] When the maintaining time is less than 1 hour, dispersed particles do not grow completely and thus the desired state cannot be obtained. When the maintaining time exceeds 20 hours, dispersed particles grow too much, causing a non-homogeneous distribution.

[0077] After the second heat treatment, the sheet goes through the process of cold rolling, temper annealing and the final cold rolling to be produced as an H1n material. For the temperature of temper annealing, temper annealing is preferably carried out at a temperature equal to or lower than the second heat treatment temperature so as to not destroy the dispersion state which has been adjusted until the second heat treatment. This condition is not particularly limited, and normally the maintaining temperature is in the range of 200 to 500 C. and the maintaining time is in the range of 2 to 8 hours.

[0078] Strength before brazing can be further reduced by adding heat treatment of low temperature after the final rolling. However, when the temperature is excessively high, elongation is increased as the strength is reduced, and burr is likely to be formed in the molding of a fin. Furthermore, when the temperature is excessively low, the desired effect cannot be obtained. Thus, the suitable temperature range is 100 to 250 C. and the suitable time is 1 to 10 h.

[0079] It is desirable that cold rolling is performed at a rolling ratio of 40 to 80% after the second heat treatment. When the rolling ratio is excessively low, the amount of strain stored in the material reduces, and a fin of H1n temper is not completely recrystallized in brazing, and thus is significantly eroded. Conversely, when the rolling ratio is excessively high, the strength before brazing excessively increases.

[0080] It is desirable that the maintaining temperature is 180 to 250 C. and the maintaining time is 2 to 10 hours in temper annealing. When the maintaining temperature is high, a non-crystallized structure cannot be obtained. When the maintaining temperature is low, strength before brazing is excessively increased.

[0081] It is desirable that the rolling ratio in the final cold rolling is set to 5 to 20%. When the rolling ratio in the final cold rolling is less than 5%, rolling is difficult, and when the final cold rolling is more than 20%, strength before brazing is excessively increased.

[0082] The sheet thickness is preferably formed to 0.04 to 0.06 mm by performing the final cold rolling. However, the final sheet thickness is not particularly limited in the present invention.

[0083] A fin material for a heat exchanger can be obtained by the above process.

[0084] The resulting fin material has excellent strength, conductivity, corrosion resistance and brazing properties.

[0085] In particular, the fin material has a non-recrystallized grain structure and a solidus temperature of 610 C. or more before brazing. The fin material has a tensile strength before brazing of 220 to 270 MPa and has excellent strength, conductivity and corrosion resistance.

[0086] Furthermore, it is desirable that, before brazing, particles having a circle-equivalent diameter of 400 nm or less among the second phase particles distributed in matrix have an average diameter in the range of 40 to 90 nm, and the number density thereof is in the range of 6 to 13 particles/m.sup.2.

[0087] The resulting fin material is, for example, corrugated to form a fin, and the fin is combined with an aluminum member for a heat exchanger, such as a header, a tube and a side plate and joined by brazing, thus a heat exchanger can be produced. The composition of the aluminum alloy material to be brazed with the fin material is not particularly limited, and an aluminum material having a suitable composition can be used. The aluminum material includes pure aluminum in addition to aluminum alloy materials.

[0088] Conditions and methods of heat treatment in brazing (e.g., brazing temperature, atmosphere, presence of flux, types of brazing materials) are not particularly limited in the present invention. Brazing can be performed by the desired method.

[0089] The fin material has a tensile strength of 160 MPa or more, an electrical conductivity of 40% IACS or more, and an average crystal grain size in the rolled surface of 300 m to 2,000 m, after brazing. Heat treatment conditions of brazing are assumed according to those properties, which are to increase temperature from room temperature to 600 C. within about 6 minutes and then without maintaining the temperature, cool the material to room temperature at 100 C./minute. Brazing conditions are not particularly limited and can be appropriately determined in the present invention.

[0090] It is desirable that, particles having a circle-equivalent diameter of 400 nm or less among the second phase particles distributed in matrix after brazing have an average diameter in the range of 50 to 100 nm, and the number density is 5 particles/m.sup.2 or more.

[0091] The heat exchanger obtained is equipped with the fin material according to the present embodiment, and thus has excellent brazing joining properties, and excellent strength, conductivity and corrosion resistance.

[0092] FIG. 1 shows heat exchanger 1 produced by assembling tube 3, header 2 and side plate 5 in the fin 4 of the present embodiment and then brazing.

[0093] The present embodiment can provide an aluminum alloy fin material for a heat exchanger and a heat exchanger having excellent strength, conductivity, corrosion resistance and brazing properties.

[0094] In the present embodiment, Mn was added by an amount larger than that in conventional materials, other components were appropriately adjusted, and the dispersion state before and after brazing of second phase particles having a predetermined or smaller size was controlled at high accuracy. More specifically, for the size of second phase particles, the impact of the size of second phase particles on the strength before and after brazing was investigated. It has been found that the larger the size of second phase particles, the strength before brazing is decreased; by contrast, regarding the strength after brazing, the smaller the size of second phase particle, the strength after brazing is increased, but the strength after brazing is substantially saturated when the size reaches a predetermined size or less. Thus, both a reduction of strength before brazing and an improvement of strength after brazing, which are contrary to each other, are achieved by suitably dispersing second phase particles having a pre-determined size.

Example 1

[0095] An aluminum alloy having the composition shown in Table 1 (the balance being Al and inevitable impurities) was produced by a twin roll casting method. The cooling rate was 200 C./second.

[0096] The aluminum alloy cast sheet obtained was sequentially subjected to cold rolling, the first heat treatment, cold rolling, the second heat treatment, and the final cold rolling, as shown in Table 2.

[0097] After the second heat treatment, cold rolling, temper annealing and the final cold rolling were performed to obtain an aluminum alloy fin material having a desired plate thickness. The final rolling ratio in the final cold rolling is shown in the table.

[0098] Cold rolling after the first heat treatment was performed at 98%, cold rolling after the second heat treatment was performed at 50%, and temper annealing was performed at 250 C.5 hours, and then the resultant was rolled at the final rolling ratio. Some materials were subjected to a heat treatment of low temperature after the final rolling.

[0099] Subsequently, with respect to the obtained aluminum alloy fin material, the tensile strength, the crystal grain structure, the melting point and the dispersion state of second phase particles of the resulting aluminum alloy fin material were measured by the method described below.

[0100] The aluminum alloy fin material was also braze-heated in the condition described below, and the tensile strength, the electrical conductivity, the crystal grain size in the rolled surface and the dispersion state of second phase particles were measured after braze-heating. The results of the measurement are shown in Table 2.

[0101] Furthermore, resistance to erosion brazing, corrugation moldability and corrosion resistance were evaluated by the method described below. Then, the results of measurement and the results of evaluation were comprehensively assessed.

[0102] The results of the evaluation are shown in Table 3.

<Tensile Strength Before Brazing>

[0103] Before brazing a sample was cut parallel to the rolling direction to prepare a JIS No. 13 B shaped test piece. A tensile test was performed to measure tensile strength. The speed of tensile was set to 3 mm/minute.

<Crystal Grain Structure Before Brazing>

[0104] Before brazing, a cross section parallel to the rolling direction is processed by a cross section polisher and then OIM measurement is performed by SEM-EBSD at a magnification of 5,000 times to determine the presence of subgrains based on the boundary map. The area of the visual field is 1020 m and the step size is 0.05 m, and 10 visual fields are measured. Structures in which a subgrain structure accounts for more than 50% of the visual field measured are determined as a non-recrystallized structure. A region surrounded by grain boundaries with a misorientation of 2 or more in the EBSD measurement is defined as a subgrain.

<Melting Point (Solidus Temperature)>

[0105] The solidus temperature of the fin material prepared was measured by DTA with a usual method. The rate of temperature increase at the time of measurement was set by 20 C./minute from room temperature to 500 C., and by 2 C./minute in the range of 500 to 600 C. Alumina was used as a reference. The results are shown in the column of melting point.

<Dispersion State (Average Particle Diameter, Number Density) of Second Phase Particles Before Brazing>

[0106] Before brazing, a cross section parallel to the rolling direction was processed by a cross section polisher and then 10 visual fields were observed with FE-SEM at a magnification of 30,000 times. Subsequently, the dispersion state was quantified by using an image analysis software to calculate the average particle diameter (m) and the number density (particles/m.sup.2) of particles having an particle diameter of 400 nm or less.

<Heat Treatment Equivalent to Brazing>

[0107] In the heat treatment equivalent to brazing, the temperature was increased from room temperature to 600 C. in 6 minutes and then the material was cooled to room temperature at 100 C./minute without maintaining the temperature.

<Tensile Strength after Brazing>

[0108] After brazing, a sample was cut parallel to the rolling direction to prepare a JIS No. 13 B shaped test piece. A tensile test was performed to measure tensile strength. The speed of testing tensile was 3 mm/minute.

<Dispersion State (Average Particle Diameter, Number Density) of Second Phase Particles after Brazing>

[0109] After brazing, a cross section parallel to the rolling direction was processed by a cross section polisher and then 10 visual fields were observed with FE-SEM at a magnification of 30,000 times. Subsequently, the dispersion state was quantified by using an image analysis software to calculate the average particle diameter (m) and the number density (particles/m.sup.2) of particles having an particle diameter of 400 nm or less.

<Crystal Grain Size in Rolled Surface after Brazing>

[0110] After brazing, the crystal grain size in the rolled surface was measured with a stereomicroscope.

[0111] For the method of measurement, the fin material prepared was subjected to heat treatment equivalent to brazing, then immersed in a DAS solution for a predetermined time, and was etched until the crystal grain structure in the rolled surface can be clearly seen. Then the crystal grain structure in the rolled surface was observed with a stereomicroscope. The standard magnification of observation was 20 times and the magnification of observation was accordingly changed depending on the size of crystal grains when crystal grains were significantly coarse or fine. The crystal grain structure of 5 visual fields was photographed, and the material was cut parallel to the rolling direction and the size of the crystal grain (m) was measured by a cutting method.

<Electrical Conductivity>

[0112] After brazing, electrical conductivity (% IACS) was measured by the measuring method for conductivity described in JIS H-0505 at room temperature with a double bridge type conductivity meter.

<Resistance to Brazing Erosion>

[0113] As shown in FIG. 2, fin 11 was assembled to form a joint shape of fin 11/tube 12 with a JIS A4045/A3003 one-side brazing material having a sheet thickness of 0.20 mm (cladding ratio of brazing material being 10%), and, then was subjected to brazing. A cross section of mini-core 10 prepared by brazing was observed to determine the presence of buckling and erosion.

[0114] Those in which erosion penetrating though the sheet thickness and buckling occurred in 15% or less of the portions joined were rated as , and those in which erosion penetrating though the sheet thickness and buckling occurred in more than 15% of the portions were rated as x.

<Moldability>

[0115] A corrugation molding machine was adjusted so that fins had a width of 20 mm, a fin height of 5 mm and a fin pitch (between ridges) of 3 mm. Then, 50 ridges were formed for each of fin ridges and the height of the respective ridges was measured to evaluate variation in the ridge height. Those having 10 or more ridges with a ridge height of 5 mm10% or more were rated as x, those having ridges in the range of 5 to 9 were rated as and those having ridges less than 5 were rated as .

<Corrosion Resistance>

[0116] As shown in FIG. 2, corrugated fin 11 was assembled to form a joint shape of fin 11/tube 12 with a JIS A4045/A3003 one-side brazing material having a sheet thickness of 0.20 mm (cladding ratio of brazing material being 10%), and then was subjected to brazing to produce mini-core 10. This mini-core was exposed to SWAAT for 30 days. Those in which corrosion having a depth of 0.10 mm or more occurred in the tube were rated as x, and those in which corrosion having a depth of less than 0.10 mm occurred in the tube were rated as .

<Comprehensive Evaluation>

[0117] Those having an electrical conductivity of 41% IACS or more, a melting point of 610 C. or more, whose moldability alone was rated as , and having a strength after brazing of 160 MPa or more were determined as .

[0118] Those having an electrical conductivity of 41% IACS or more, a melting point of 610 C. or more, whose all properties were rated as , and having a strength after brazing of 160 MPa or more were determined as .

[0119] Those having an electrical conductivity of 41% IACS or more, a melting point of 610 C. or more, whose all properties were rated as , and having a strength after brazing of 170 MPa or more were determined as .

[0120] Furthermore, those any of whose properties is rated as x or having a strength after brazing of less than 160 MPa were determined as x.

TABLE-US-00001 TABLE 1 Test material chemical component (% by mass) Test material No. Mn Si Fe Cu Zn Zr Mn/Si Comperative example 1 1.6 0.8 0.15 0.15 1.6 0.01 2.00 Present example 2 1.8 0.8 0.15 0.15 1.6 0.01 2.25 Present example 1 2.3 0.8 0.15 0.15 1.6 0.01 2.88 Comperative example 4 2.7 0.8 0.15 0.15 1.6 0.01 3.38 Comperative example 5 2.0 0.5 0.15 0.15 1.6 0.01 4.00 Present example 6 2.0 0.7 0.15 0.15 1.6 0.01 2.86 Present example 7 2.0 1.3 0.15 0.15 1.6 0.01 1.54 Comperative example 8 2.0 1.5 0.15 0.15 1.6 0.01 1.33 Comperative example 9 2.0 0.8 0.01 0.15 1.6 0.01 2.50 Present example 10 2.0 0.8 0.05 0.15 1.6 0.01 2.50 Present example 11 2.0 0.8 0.30 0.15 1.6 0.01 2.50 Comperative example 12 2.0 0.8 0.60 0.15 1.6 0.01 2.50 Comperative example 13 2.0 0.8 0.15 0.10 1.6 0.01 2.50 Present example 14 2.0 0.8 0.15 0.14 1.6 0.01 2.50 Present example 15 2.0 0.8 0.15 0.30 1.8 0.01 2.50 Comperative example 16 2.0 0.8 0.15 0.50 1.8 0.01 2.50 Comperative example 17 2.0 0.8 0.15 0.15 1.2 0.01 2.50 Present example 18 2.0 0.8 0.15 0.15 1.4 0.01 2.50 Present example 19 2.0 0.8 0.15 0.15 2.9 0.01 2.50 Comperative example 20 2.0 0.8 0.15 0.15 3.5 0.01 2.50 Comperative example 21 2.0 0.8 0.15 0.15 1.6 0.10 2.50 Comperative example 22 1.0 0.5 0.15 0.15 1.6 0.01 2.00 Present example 23 1.8 0.8 0.15 0.15 1.6 0.01 2.25 Present example 24 2.2 1.3 0.15 0.25 1.6 0.01 1.69 Comperative example 25 2.2 1.3 0.15 0.25 1.6 0.01 1.69 Present example 26 2.0 1.3 0.15 0.15 1.6 0.01 1.54 Present example 27 2.0 1.3 0.15 0.15 1.6 0.01 1.54 Present example 28 2.0 1.3 0.15 0.15 1.6 0.01 1.54 Present example 29 2.0 1.3 0.15 0.15 1.6 0.01 1.54 Present example 30 2.0 1.3 0.15 0.15 1.6 0.01 1.54 Comperative example 31 2.2 1.3 0.15 0.25 1.6 0.01 1.69 Present example 32 2.2 1.3 0.15 0.25 1.6 0.01 1.69 Present example 33 2.0 1.3 0.15 0.15 1.6 0.01 1.54 Comperative example 34 2.0 1.3 0.15 0.15 1.6 0.01 1.54 Present example 35 2.0 1.3 0.15 0.15 1.6 0.01 1.54 Present example 36 2.0 1.3 0.15 0.15 1.6 0.01 1.54 Present example 37 2.0 1.3 0.15 0.15 1.6 0.01 1.54 Comperative example 38 1.8 1.3 0.15 0.15 1.6 0.01 1.38 Comperative example 39 2.5 0.7 0.15 0.20 1.8 0.01 3.57 Present example 40 2.2 1.3 0.15 0.25 1.6 0.01 1.69 Present example 41 2.0 1.3 0.15 0.15 1.6 0.01 1.54 Present example 42 2.2 1.3 0.15 0.25 1.6 0.01 1.69

TABLE-US-00002 TABLE 2 Final Heat Strength Strength Before brazing After brazing 1st 2nd rolling treatment at before after Melting Electrical Average Average Crystal heat heat ratio low brazing brazing point conductivity particle Number particle Number grain Test material No. treatment treatment (%) temperature (MPa) (MPa) ( C.) (% IACS) diameter density diameter density Crystal grain structure size Comperative example 1 425 C. 12 h 430 C. 7 h 20 None 225 154 625 43 75 8.5 85 5.5 non-recrystallized 600 Present example 2 425 C. 12 h 430 C. 7 h 20 None 231 161 627 42 76 9.1 86 6.1 non-recrystallized 650 Present example 3 425 C. 12 h 430 C. 7 h 20 None 252 177 634 41 80 11.2 90 8.2 non-recrystallized 800 Comperative example 4 425 C. 12 h 430 C. 7 h 20 None 258 158 636 39 82 11.8 92 8.8 non-recrystallized 400 Comperative example 5 425 C. 12 h 430 C. 7 h 20 None 225 155 641 41 75 8.5 85 5.5 non-recrystallized 600 Present example 6 425 C. 12 h 430 C. 7 h 20 None 233 162 633 41 77 9.3 87 6.3 non-recrystallized 650 Present example 7 425 C. 12 h 430 C. 7 h 20 None 257 182 612 41 81 11.7 91 8.7 non-recrystallized 800 Comperative example 8 425 C. 12 h 430 C. 7 h 20 None 265 190 601 41 83 12.5 93 9.5 non-recrystallized 900 Comperative example 9 425 C. 12 h 430 C. 7 h 20 None 235 159 629 41 77 9.5 87 6.5 non-recrystallized 900 Present example 10 425 C. 12 h 430 C. 7 h 20 None 236 161 629 41 77 9.6 87 6.6 non-recrystallized 800 Present example 11 425 C. 12 h 430 C. 7 h 20 None 241 166 629 42 78 10.1 88 7.1 non-recrystallized 600 Comperative example 12 425 C. 12 h 430 C. 7 h 20 None 244 157 629 42 79 10.4 89 7.4 non-recrystallized 450 Comperative example 13 425 C. 12 h 430 C. 7 h 20 None 235 156 631 42 77 9.5 87 6.5 non-recrystallized 700 Present example 14 425 C. 12 h 430 C. 7 h 20 None 237 162 630 41 77 9.7 87 6.7 non-recrystallized 700 Present example 15 425 C. 12 h 430 C. 7 h 20 None 243 168 626 41 79 10.3 89 7.3 non-recrystallized 600 Comperative example 16 425 C. 12 h 430 C. 7 h 20 None 251 176 621 41 80 11.1 90 8.1 non-recrystallized 550 Comperative example 17 425 C. 12 h 430 C. 7 h 20 None 237 162 629 41 77 9.7 87 6.7 non-recrystallized 600 Present example 18 425 C. 12 h 430 C. 7 h 20 None 237 162 629 41 77 9.7 87 6.7 non-recrystallized 600 Present example 19 425 C. 12 h 430 C. 7 h 20 None 237 162 629 41 77 9.7 87 6.7 non-recrystallized 600 Comperative example 20 425 C. 12 h 430 C. 7 h 20 None 237 162 629 41 77 9.7 87 6.7 non-recrystallized 600 Comperative example 21 425 C. 12 h 430 C. 7 h 20 None 237 162 629 39 77 9.7 87 6.7 non-recrystallized 700 Comperative example 22 425 C. 12 h 430 C. 7 h 10 None 195 120 631 45 69 6.1 79 4.0 non-recrystallized 1500 Present example 23 425 C. 12 h 430 C. 7 h 10 None 222 172 627 42 76 9.1 86 6.1 non-recrystallized 1800 Present example 24 425 C. 12 h 430 C. 7 h 25 None 267 192 614 41 83 12.7 93 9.7 non-recrystallized 500 Comperative example 25 425 C. 12 h 430 C. 7 h 35 None 280 192 614 41 83 12.7 93 9.7 non-recrystallized 200 Present example 26 425 C. 12 h None 20 None 269 178 612 41 30 22.0 87 8.6 non-recrystallized 1600 Present example 27 445 C. 9 h 410 C. 2 h 20 None 265 177 612 41 45 16.0 90 8.5 non-recrystallized 1500 Present example 28 425 C. 12 h 500 C. 7 h 20 None 240 170 612 41 90 6.0 100 5.5 non-recrystallized 600 Present example 29 425 C. 12 h 550 C. 7 h 20 None 230 163 612 41 130 4.0 150 4.5 non-recrystallized 400 Present example 30 425 C. 12 h 430 C. 7 h 20 None 257 182 612 41 81 11.7 91 8.7 non-recrystallized 650 Comperative example 31 425 C. 12 h 430 C. 7 h 50 None 267 192 614 41 83 12.7 93 9.7 recrystallized 800 Present example 32 425 C. 12 h 430 C. 7 h 25 None 267 192 614 41 83 12.7 93 9.7 non-recrystallized 700 Present example 33 425 C. 12 h 430 C. 7 h 20 None 257 182 612 41 81 11.7 91 8.7 non-recrystallized 800 Comperative example 34 425 C. 12 h None 20 None 268 178 609 41 38 17.2 48 8.4 recrystallized 1500 Present example 35 475 C. 5 h None 20 None 230 163 612 41 110 4.9 142 4.8 non-recrystallized 580 Present example 36 525 C. 10 h None 20 None 230 165 612 41 121 5.7 142 5.1 non-recrystallized 580 Present example 37 590 C. 10 h None 20 None 228 162 612 41 132 3.9 152 4.4 non-recrystallized 400 Comperative example 38 425 C. 12 h 430 C. 7 h 20 None 252 177 608 41 82 11.4 92 8.1 non-recrystallized 750 Comperative example 39 425 C. 12 h 430 C. 7 h 20 None 255 156 627 40 77 10.5 87 6.6 non-recrystallized 600 Present example 40 425 C. 12 h 430 C. 7 h 25 200 C. 4 h 259 192 614 41 83 12.7 93 9.7 non-recrystallized 500 Present example 41 445 C. 9 h 410 C. 2 h 20 200 C. 8 h 253 177 612 41 45 16.0 90 8.5 non-recrystallized 1500 Present example 42 425 C. 12 h 430 C. 7 h 25 220 C. 4 h 250 192 614 41 83 12.7 93 9.7 non-recrystallized 700

TABLE-US-00003 TABLE 3 Resistance to Corrosion Comprehensive Test material No. brazing erosion Corrugation moldability resistance evaluation Comparative example 1 (2 or less fin ridges for NG) X Present example 2 (2 or less fin ridges for NG) Present example 3 (2 or less fin ridges for NG) Comparative example 4 (2 or less fin ridges for NG) X Comparative example 5 (2 or less fin ridges for NG) X Present example 6 (2 or less fin ridges for NG) Present example 7 (2 or less fin ridges for NG) Comparative example 8 X X Comparative example 9 (2 or less fin ridges for NG) X Present example 10 (2 or less fin ridges for NG) Present example 11 (2 or less fin ridges for NG) Comparative example 12 (2 or less fin ridges for NG) X Comparative example 13 (2 or less fin ridges for NG) X Present example 14 (2 or less fin ridges for NG) Present example 15 (2 or less fin ridges for NG) Comparative example 16 (2 or less fin ridges for NG) X X Comparative example 17 (2 or less fin ridges for NG) X X Present example 18 (2 or less fin ridges for NG) Present example 19 (2 or less fin ridges for NG) Comparative example 20 (2 or less fin ridges for NG) X X Comparative example 21 (2 or less fin ridges for NG) X Comparative example 22 X X Present example 23 (2 or less fin ridges for NG) Present example 24 (4 fin ridges for NG).sup. Comparative example 25 X X X Present example 26 Present example 27 (4 fin ridges for NG).sup. Present example 28 (2 or less fin ridges for NG) Present example 29 (2 or less fin ridges for NG) Present example 30 (2 or less fin ridges for NG) Comparative example 31 X X Present example 32 (4 fin ridges for NG).sup. Present example 33 (2 or less fin ridges for NG) Comparative example 34 X X Present example 35 (2 or less fin ridges for NG) Present example 36 (2 or less fin ridges for NG) Present example 37 (2 or less fin ridges for NG) Comparative example 38 X (2 or less fin ridges for NG) X Comparative example 39 (2 or less fin ridges for NG) X Present example 40 (4 fin ridges for NG).sup. Present example 41 (4 fin ridges for NG).sup. Present example 42 (4 fin ridges for NG).sup.

[0121] As shown in Table 3, all of the present Examples which satisfy the definitions of the present invention marked a comprehensive evaluation of or more with excellent results of strength, resistance to brazing erosion, moldability and corrosion resistance. By contrast, no good results were obtained in Comparative Examples which do not satisfy one or more definitions of the present invention.

[0122] Although embodiments of the present invention have been described and illustrated in detail, the disclosed embodiments are made for purposes of illustration and example only and not limitation. The scope of the present invention should be interpreted by terms of the appended claims.