Aluminum alloy fin material for heat exchanger excellent in strength, electrical conductivity, and brazeability, method for manufacturing aluminum alloy fin material for heat exchanger, and heat exchanger comprising aluminum alloy fin material for heat exchanger

Abstract

An aluminum alloy fin material for a heat exchanger in the present invention comprises an aluminum alloy having a composition containing Mn: 1.2 to 2.0%, Cu: 0.05 to 0.20%, Si: 0.5 to 1.30%, Fe: 0.05 to 0.5%, and Zn: 1.0 to 3.0% by mass and a remainder comprising Al and an unavoidable impurity, further containing one or two or more of Ti: 0.01 to 0.20%, Cr: 0.01 to 0.20% and Mg: 0.01 to 0.20% by mass as desired, and, after heating in brazing, has a tensile strength of 140 MPa or more, a proof stress of 50 MPa or more, an electrical conductivity of 42% IACS or more, an average grain diameter of 150 μm or more and less than 700 μm, and a potential of −800 mV or more and −720 mV or less.

Claims

1. An aluminum alloy fin material for a heat exchanger comprising an aluminum alloy having a composition containing Mn: 1.2 to 2.0%, Cu: 0.05 to 0.20%, Si: 0.5 to 1.30%, Fe: 0.05 to 0.35%, and Zn: 1.0 to 3.0% in terms of % by mass and a remainder comprising Al and an unavoidable impurity, wherein, after brazing-equivalent heating, the aluminum alloy fin material has a tensile strength of 140 MPa or more, a proof stress of 50 MPa or more, an electrical conductivity of 42% IACS or more, an average grain diameter of 150 μm or more and less than 700 μm, and a potential in a range of −800 mV to −720 mV, wherein the aluminum alloy fin material has an electrical conductivity of 45% IACS or more before brazing, and wherein, in the aluminum alloy fin material before brazing, less than 5.0×10.sup.4/mm.sup.2 of crystallized products having an equivalent circular diameter of 1.0 μm or more and 5.0×10.sup.4/mm.sup.2 or more of Al—Mn—based, Al—Mn—Si-based, and Al—Fe—Si-based second-phase particles having an equivalent circular diameter of 0.01 to 0.10 μm are present.

2. The aluminum alloy fin material for a heat exchanger according to claim 1, wherein the aluminum alloy further contains at least one of Ti: 0.01 to 0.20%, Cr: 0.01 to 0.20%, and Mg: 0.01 to 0.20% in terms of % by mass.

3. The aluminum alloy fin material for a heat exchanger according to claim 1, wherein after the brazing-equivalent heating, the aluminum alloy fin material has, at 115° C., a tensile strength of 90 MPa or more and a proof stress of 40 MPa or more.

4. The aluminum alloy fin material for a heat exchanger according to claim 1, wherein, after the brazing-equivalent heating, 1.0×10.sup.4/mm.sup.2 or more of Al—Mn—based, Al—Mn—Si-based, and Al—Fe—Si-based second-phase particles having an equivalent circular diameter of 0.01 to 0.10 μm are present.

5. The aluminum alloy fin material for a heat exchanger according to claim 1, having a plate thickness of 80 μm or less.

6. The aluminum alloy fin material for a heat exchanger according to claim 1, having a recrystallization start temperature and a recrystallization end temperature in a range of 350° C. to 550° C., during heating for brazing.

7. A heat exchanger comprising the aluminum alloy fin material for a heat exchanger according to claim 1.

8. A method for manufacturing the aluminum alloy fin material for a heat exchanger according to claim 1, the method comprising: casting, by a semicontinuous casting method, a molten aluminum alloy having a composition containing Mn: 1.2 to 2.0%, Cu: 0.05 to 0.20%, Si: 0.5 to 1.30%, Fe: 0.05 to 0.35%, and Zn: 1.0 to 3.0% in terms of % by mass and a remainder comprising Al and an unavoidable impurity; subjecting an ingot obtained in the casting to homogenization treatment at a treatment temperature of 350° C. to 480° C. for a treatment time of 1 to 10 hours; and carrying out soaking treatment with the temperature and treatment time of the homogenization treatment or less before hot rolling.

9. A method for manufacturing the aluminum alloy fin material for a heat exchanger according to claim 2, the method comprising: casting, by a semicontinuous casting method, a molten aluminum alloy having a composition containing Mn: 1.2 to 2.0%, Cu: 0.05 to 0.20%, Si: 0.5 to 1.30%, Fe: 0.05 to 0.35%, and Zn: 1.0 to 3.0% in terms of % by mass, at least one of Ti: 0.01 to 0.20%, Cr: 0. 01 to 0.20%, and Mg: 0.01 to 0.20% in terms of % by mass, and a remainder comprising Al and an unavoidable impurity; subjecting an ingot obtained in the casting to homogenization treatment at a treatment temperature of 350° C. to 480° C. for a treatment time of 1 to 10 hours; and carrying out soaking treatment with the temperature and treatment time of the homogenization treatment or less before hot rolling.

Description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(1) One embodiment of the present invention will be described below.

(2) The fin material of the present invention can be manufactured, for example, by an ordinary method, and an aluminum alloy is ingoted after preparation with the composition of the present invention. The ingotting is performed by a semicontinuous casting method. The obtained aluminum alloy ingot is subjected to homogenization treatment under predetermined conditions. In other words, the homogenization treatment conditions are a treatment temperature of 350° C. to 480° C. and a treatment time of 1 to 10 hours. Then, a fin material (specimen material) having a plate thickness of 80 μm or less and a temper of H14 can be obtained through soaking treatment, hot rolling, cold rolling, and the like. The soaking treatment conditions are the temperature and treatment time of the homogenization treatment or less, desirably a temperature of 350 to 480° C. and a holding time of 1 to 10 hours. In the cold rolling, it is possible to perform cold rolling at 75% or more, perform intermediate annealing at a temperature of 300 to 400° C., and then perform final rolling at a rolling rate of 20 to 45%. The intermediate annealing need not be performed.

(3) The fin material obtained by the above cold rolling and the like can then be subjected to corrugation processing and the like as needed. The corrugation processing can be performed by passing the fin material between two rotating dies, which allows good processing and provides excellent moldability.

(4) The fin material obtained above, as a constituent member of a heat exchanger, is subjected to brazing in combination with other constituent members (tubes, headers, and the like). The conditions in the brazing (the brazing temperature, the atmosphere, whether a flux is used or not, the type of the brazing material, and the like) are not particularly limited, and the brazing can be performed by an ordinary method.

(5) The heat exchanger fabricated above is used in applications such as automobiles. The fin portions of the heat exchanger use the fin material obtained above and therefore have both high strength and high thermal conductivity though being thinned.

Examples

(6) Examples of the present invention will be described below compared with Comparative Examples.

(7) An aluminum alloy brazing material having a composition shown in Table 1 (the remainder Al+unavoidable impurities) was melted and cast by a semicontinuous casting method. The cooling rate of the slag was 0.5 to 3.5° C./s. Further, the obtained ingot was subjected to homogenization treatment under conditions shown in Table 2 (the temperature increase rate was 25 to 75° C./h, and the cooling rate was 20 to 50° C./h). Then, soaking treatment was performed under conditions shown in Table 2 (the temperature increase rate was 25 to 75° C./h, and the cooling rate was 20 to 50° C./h), and treatment was performed in the order of hot rolling and cold rolling.

(8) In the cold rolling step, cold rolling was performed at 75% or more, then intermediate annealing was performed at 350° C. for 6 hours, and then final rolling at a rolling rate of 40% was performed to obtain a plate material (specimen material) having a plate thickness of 0.06 μm and a temper of H14. For the obtained specimen material, conductivity and the number density of crystallized products having an equivalent circular diameter of 1.0 μm or more and second-phase particles having an equivalent circular diameter of 0.01 to 0.10 μm were calculated by methods shown below and are shown in Table 2. In addition, brazing-equivalent heating was performed under conditions shown below, and for the fin material after the heating, tensile strength, proof stress, conductivity, grain diameter, potential, elevated temperature tensile strength, high temperature proof stress, and the number density of second-phase particles having an equivalent circular diameter of 0.01 to 0.10 μm were evaluated by methods shown below.

(9) (Brazing Treatment)

(10) Brazing-equivalent heating was performed under the conditions of heat treatment in which the temperature was increased from room temperature to 600° C. at an average temperature increase rate of 40° C./min, held at 600° C. for minutes, and then decreased for cooling at a temperature decrease rate of 100° C./min.

(11) (Electrical Conductivity)

(12) The electrical conductivity was measured before brazing and after brazing by a double bridge type electrical conductivity meter by the electrical conductivity measurement method described in JIS H-0505.

(13) (Distributed State of Compounds of Material)

(14) For the specimen material before and after brazing, the number density (number/μm.sup.2) of crystallized products (having an equivalent circular diameter of 1.0 μm or more) and second-phase particles (having an equivalent circular diameter of 0.01 to 0.10 μm) was measured by a transmission electron microscope (TEM). The measurement method was as follows. Before brazing, the material was subjected to salt bath annealing at 400° C. for 15 seconds to remove deformation strain to make compounds easy to observe, and then a thin film was fabricated by mechanical polishing and electrolytic polishing by a usual method. Photographs of crystallized products and second-phase particles were taken at 3000 magnification and 30000 magnification respectively by a transmission electron microscope. The photographs at 3000 magnification were taken with a field of view of 50 μm×50 μm for a total of 50 fields of views, and the photographs at 30000 magnification were taken with a field of view of 5 μm×5 μm for a total of 5 fields of views. The size and number density of dispersed particles were measured by image analysis.

(15) (Recrystallization Temperature)

(16) Assuming heating in brazing, the temperature was increased from ordinary temperature to about 600° C. at a constant rate of 100° C./min, and after each temperature was reached, cooling to ordinary temperature was performed. Then, a JIS No. 5 test piece was fabricated, a tensile test was carried out, and the proof stress was measured. The tensile rate was 15 mm/min. The temperature at which the proof stress value started to decrease by 20% or more compared with proof stress before brazing was taken as recrystallization start temperature, and the temperature at which the proof stress value started to decrease to within +20% compared with proof stress after heating in brazing was taken as recrystallization end temperature. They are shown in Table 2.

(17) (Strength after Brazing)

(18) A sample was cut from the specimen material subjected to brazing-equivalent heating parallel to the rolling direction, and a test piece having the shape of JIS No. 13 B was fabricated. A tensile test was carried out at ordinary temperature, and the tensile strength and proof stress were measured. The tensile rate was 3 mm/min. Also for high temperature strength, similarly, using a sample subjected to the brazing treatment, a tensile test was carried out at a test temperature of 115° C., and the tensile strength and proof stress were measured. The tensile rate during the elevated temperature tensile test was 1 mm/min.

(19) (Natural Potential)

(20) A sample for potential measurement was cut from the fin material subjected to brazing-equivalent heat treatment, immersed in a 5% NaOH solution heated to 50° C. for 30 seconds, then immersed in a 30% HNO.sub.3 solution for seconds, further washed with tap water and ion-exchanged water, and immersed in a 5% NaCl solution (adjusted to pH 3 with acetic acid) at 25° C. for 60 min as it was without drying. Then, the natural potential (the reference electrode was a silver-silver chloride electrode (saturated)) was measured.

(21) (Grain Diameter)

(22) For the specimen material subjected to brazing-equivalent heat treatment, a sample surface was etched with a mixed liquid of hydrochloric acid, hydrofluoric acid, and nitric acid to expose grains, and using a surface grain texture photograph taken, the grain diameter was measured by a straight line cutting method.

(23) TABLE-US-00001 TABLE 1 Chemical components (% by mass) No. Mn Si Cu Fe Zn Ti Cr Mg Examples 1 1.22 1.00 0.15 0.30 2.00 — — — 2 1.97 1.00 0.12 0.30 2.00 — — — 3 1.60 0.51 0.15 0.30 2.00 — — — 4 1.60 1.28 0.09 0.30 2.00 — — — 5 1.60 0.90 0.05 0.30 2.00 — — — 6 1.60 0.90 0.19 0.20 2.00 — — — 7 1.50 0.90 0.10 0.05 2.00 — — — 8 1.50 0.90 0.10 0.48 2.00 — — — 9 1.50 0.90 0.12 0.30 1.01 — — — 10 1.50 0.90 0.12 0.30 2.98 — — — 11 1.30 0.90 0.15 0.30 1.50 0.01 — — 12 1.30 0.90 0.15 0.30 1.50 0.18 — — 13 1.60 0.60 0.10 0.40 2.00 — 0.01 — 14 1.60 0.60 0.10 0.40 2.00 — 0.18 — 15 1.60 1.00 0.08 0.20 2.00 — — 0.01 16 1.60 1.00 0.08 0.20 2.00 — — 0.18 Com- 1 1.15 0.70 0.10 0.30 1.50 — — — parative 2 2.08 0.70 0.10 0.30 1.50 — — — Examples 3 1.50 0.47 0.10 0.30 1.50 — — — 4 1.50 1.32 0.10 0.30 1.50 — — — 5 1.50 0.90 0.04 0.20 2.00 — — — 6 1.50 0.90 0.21 0.20 1.50 — — — 7 1.60 0.60 0.15 0.02 1.50 — — — 8 1.60 0.60 0.15 0.53 1.50 — — — 9 1.60 0.80 0.15 0.30 0.97 — — — 10 1.60 1.00 0.05 0.30 3.06 — — — 11 1.60 0.90 0.10 0.30 2.00 — — — 12 1.75 1.10 0.12 0.48 2.00 — — — 13 1.60 0.90 0.10 0.20 2.00 — — — 14 1.30 0.90 0.15 0.30 2.50 — — 0.02

(24) TABLE-US-00002 TABLE 2 After brazing Elevated temperature High Tensile Proof Electrical Grain tensile temperature No. strength stress conductivity diameter Potential strength proof stress Exam- 1 143 MPa 52 MPa 43.0%IACS 410 μm −755 mV  93 MPa  45 MPa ples 2 157 MPa 57 MPa 42.6%IACS 340 μm −751 mV  98 MPa  46 MPa 3 143 MPa 52 MPa 42.4%IACS 380 μm −757 mV  93 MPa  45 MPa 4 159 MPa 59 MPa 43.1%IACS 320 μm −753 mV 100 MPa  48 MPa 5 144 MPa 53 MPa 43.2%IACS 420 μm −772 mV  92 MPa  43 MPa 6 152 MPa 58 MPa 42.4%IACS 280 μm −732 mV 105 MPa  50 MPa 7 144 MPa 53 MPa 42.8%IACS 420 μm −756 mV  95 MPa  45 MPa 8 148 MPa 54 MPa 42.5%IACS 210 μm −755 mV 107 MPa  49 MPa 9 144 MPa 53 MPa 44.2%IACS 420 μm −721 mV  95 MPa  45 MPa 10 144 MPa 53 MPa 42.1%IACS 420 μm −780 mV  95 MPa  45 MPa 11 143 MPa 53 MPa 43.0%IACS 380 μm −738 mV  94 MPa  44 MPa 12 145 MPa 54 MPa 42.2%IACS 270 μm −736 mV  95 MPa  45 MPa 13 143 MPa 53 MPa 43.4%IACS 330 μm −755 mV  94 MPa  44 MPa 14 145 MPa 54 MPa 42.2%IACS 220 μm −750 mV  95 MPa  45 MPa 15 145 MPa 54 MPa 42.7%IACS 350 μm −754 mV  95 MPa  45 MPa 16 147 MPa 55 MPa 42.2%IACS 240 μm −752 mV  96 MPa  46 MPa Com- 1 138 MPa 48 MPa 43.2%IACS 580 μm −742 mV  91 MPa  42 MPa parative 2 — — — — — — — Exam- 3 137 MPa 50 MPa 43.2%IACS 420 μm −746 mV  90 MPa  42 MPa ples 4 — — — — — — — 5 143 MPa 52 MPa 43.5%IACS 450 μm −748 mV  87 MPa  41 MPa 6 153 MPa 58 MPa 41.9%IACS 240 μm −716 mV 108 MPa  51 MPa 7 142 MPa 52 MPa 42.6%IACS 520 μm −750 mV  89 MPa  39 MPa 8 157 MPa 55 MPa 42.5%IACS 170 μm −748 mV 116 MPa  51 MPa 9 145 MPa 53 MPa 44.6%IACS 350 μm −712 mV  95 MPa  45 MPa 10 142 MPa 52 MPa 43.2%IACS 380 μm −812 mV  92 MPa  42 MPa 11 135 MPa 47 MPa 42.3%IACS 180 μm −756 mV  87 MPa  38 MPa 12 141 MPa 51 MPa 42.4%IACS 130 μm −750 mV  90 MPa  41 MPa 13 136 MPa 48 MPa 42.3%IACS 220 μm −756 mV  88 MPa  40 MPa 14 141 MPa 51 MPa 41.8%IACS 130 μm −754 mV  91 MPa  41 MPa Recrystallization Before brazing Compounds temperature Manufacturing process Electrical Compounds Compounds after brazing Start End Homogenization Soaking No. conductivity 1.0 μm or more 0.01~0.1 μm 0.01~0.1 μm temperature temperature treatment treatment Exam- 1 46.5%IACS 2.0 × 10.sup.4 7.8 × 10.sup.4 3.3 × 10.sup.4 400 500 450° C. × 8 h 430° C. × 4 h ples 2 45.6%IACS 4.2 × 10.sup.4 2.3 × 10.sup.5 7.9 × 10.sup.4 400 500 450° C. × 8 h 430° C. × 4 h 3 46.5%IACS 2.0 × 10.sup.4 2.4 × 10.sup.5 8.2 × 10.sup.4 400 500 450° C. × 8 h 450° C. × 4 h 4 45.6%IACS 4.2 × 10.sup.4 2.3 × 10.sup.5 7.9 × 10.sup.4 400 500 450° C. × 8 h 450° C. × 4 h 5 46.1%IACS 2.3 × 10.sup.4 2.6 × 10.sup.5 7.3 × 10.sup.4 400 500 450° C. × 8 h 450° C. × 4 h 6 45.4%IACS 1.7 × 10.sup.4 3.3 × 10.sup.5 1.1 × 10.sup.5 400 500 450° C. × 8 h 450° C. × 4 h 7 45.8%IACS 8.9 × 10.sup.3 3.1 × 10.sup.5 9.7 × 10.sup.4 430 530 400° C. × 10 h 400° C. × 4 h 8 45.6%IACS 4.6 × 10.sup.4 1.9 × 10.sup.5 5.4 × 10.sup.4 430 530 400° C. × 10 h 400° C. × 4 h 9 47.7%IACS 2.2 × 10.sup.4 2.1 × 10.sup.5 7.7 × 10.sup.4 430 530 400° C. × 10 h 400° C. × 4 h 10 45.8%IACS 2.4 × 10.sup.4 2.4 × 10.sup.5 7.5 × 10.sup.4 430 530 450° C. × 8 h 400° C. × 4 h 11 46.1%IACS 2.1 × 10.sup.4 1.2 × 10.sup.5 6.5 × 10.sup.4 430 530 450° C. × 8 h 400° C. × 4 h 12 45.3%IACS 2.0 × 10.sup.4 1.6 × 10.sup.5 6.6 × 10.sup.4 380 480 380° C. × 10 h 380° C. × 6 h 13 46.0%IACS 4.0 × 10.sup.4 7.5 × 10.sup.4 3.5 × 10.sup.4 380 480 380° C. × 10 h 380° C. × 6 h 14 45.4%IACS 3.9 × 10.sup.4 7.3 × 10.sup.4 3.4 × 10.sup.4 380 480 470° C. × 4 h 450° C. × 4 h 15 45.7%IACS 2.2 × 10.sup.4 2.5 × 10.sup.5 8.2 × 10.sup.5 440 510 470° C. × 4 h 450° C. × 4 h 16 45.3%IACS 2.4 × 10.sup.4 2.4 × 10.sup.5 7.8 × 10.sup.5 440 510 430° C. × 6 h 420° C. × 4 h Com- 1 46.2%IACS 1.2 × 10.sup.4 6.7 × 10.sup.4 1.4 × 10.sup.4 400 510 430° C. × 6 h 420° C. × 4 h parative 2 — — — — — — — — Exam- 3 46.2%IACS 2.2 × 10.sup.4 2.0 × 10.sup.5 7.7 × 10.sup.4 400 510 450° C. × 8 h 430° C. × 4 h ples 4 44.8%IACS 2.4 × 10.sup.4 2.1 × 10.sup.5 — 400 510 450° C. × 8 h 430° C. × 4 h 5 46.5%IACS 2.2 × 10.sup.4 2.6 × 10.sup.5 7.2 × 10.sup.4 400 510 450° C. × 8 h 450° C. × 4 h 6 44.8%IACS 1.8 × 10.sup.4 3.3 × 10.sup.5 1.2 × 10.sup.5 400 510 470° C. × 4 h 450° C. × 4 h 7 45.6%IACS 8.7 × 10.sup.3 3.1 × 10.sup.5 9.4 × 10.sup.4 400 510 470° C. × 4 h 450° C. × 4 h 8 45.5%IACS 4.4 × 10.sup.4 2.0 × 10.sup.5 5.2 × 10.sup.4 400 510 450° C. × 10 h 450° C. × 4 h 9 47.6%IACS 2.3 × 10.sup.4 2.2 × 10.sup.5 8.2 × 10.sup.4 450 550 400° C. × 10 h 400° C. × 4 h 10 46.2%IACS 2.2 × 10.sup.4 2.4 × 10.sup.5 7.4 × 10.sup.4 450 550 400° C. × 10 h 400° C. × 4 h 11 45.4%IACS 2.6 × 10.sup.4 4.8 × 10.sup.4 8.4 × 10.sup.3 260 340 520° C. × 10 h 520° C. × 4 h 12 45.4%IACS 5.2 × 10.sup.4 4.7 × 10.sup.4 1.1 × 10.sup.4 330 440 450° C. × 10 h 520° C. × 4 h 13 45.4%IACS 2.8 × 10.sup.4 5.2 × 10.sup.4 8.2 × 10.sup.3 330 440 550° C. × 10 h 450° C. × 4 h 14 45.1%IACS 5.6 × 10.sup.4 4.5 × 10.sup.4 8.6 × 10.sup.3 260 340 550° C. × 12 h 550° C. × 10 h

(25) All the Examples of the present invention exhibited high strength, high conductivity, and high brazeability compared with the Comparative Examples, whereas the Comparative Examples could not satisfy all of high strength, high conductivity, and high brazeability. In Comparative Example 2, a fin material could not be manufactured, and in Comparative Example 4, the fin material melted locally when brazing-equivalent heating was performed, and could not be evaluated.

(26) The present invention has been described above based on the above embodiment and Examples. Appropriate changes can be made in the above embodiment and the above Examples without departing from the scope of the present invention.