High corrosion-resistant aluminum alloy brazing sheet, method of manufacturing such sheet, and corrosive-resistant heat exchanger using such sheet

Abstract

An aluminum alloy brazing sheet having a good brazing property that prevents diffusion of molten filler material in a core material of the aluminum alloy brazing sheet during a brazing process and which has a superior corrosion resistance to an exhaust gas condensate water after the brazing process is disclosed. A method of manufacturing of the aluminum alloy brazing sheet also is disclosed. A high corrosion-resistant heat exchanger that employs the aluminum alloy brazing sheet also is disclosed.

Claims

1. A method of manufacturing a high corrosion-resistant aluminum alloy brazing sheet, wherein the brazing sheet comprises: a core material composed of an aluminum alloy; a sacrificial anode material cladded on one surface of said core material; and a filler material composed of an Al/Si-based alloy and cladded on another surface of said core material, wherein said sacrificial anode material comprises an aluminum alloy which contains Si falling within a range of about 2.5-about 7.0 mass %, Zn falling a range of about 1.0-about 5.5 mass %, Fe falling within a range of about 0.05-about 1.0 mass %, and optionally contains at least one element selected from the group consisting of Ti falling within a range of about 0.05-about 0.3 mass %, Zr falling within a range of about 0.05-about 0.3 mass %, Cr falling within a range of about 0.05-about 0.3 mass %, and V falling within a range of about 0.05-about 0.3 mass %, and further contains the balance Al and the inevitable impurities, and wherein a clad thickness of said sacrificial anode material falling within a range of about 25-about 80 m, wherein the method comprises the steps of: casting each of said core material, said sacrificial anode material and selectively said filler material composed of an Al/Si-based alloy, separately from each other; heating said casted sacrificial anode material and selectively said casted filler material composed of an Al/Si-based alloy, separately from each other; and hot-rolling said heated sacrificial anode material and selectively said heated filler material composed of an Al/Si-based alloy, separately from each other; wherein during the casting step of said sacrificial anode material, a cooling rate V ( C./s) for an ingot of said sacrificial anode material and a content Sic of Si satisfies the following formula (2):
VSic/5(2) wherein in the heating step of said sacrificial anode material, the ingot of said sacrificial anode material is heated and held at a temperature falling within a range of about 300-about 500 C. for a time period falling within a range of about 1-about 10 hrs.; and wherein in the hot-rolling step of said heated sacrificial anode material, a temperature of said sacrificial anode material is at most 350 C. at an end of the hot rolling process.

2. The method of manufacturing a high corrosion-resistant aluminum alloy brazing sheet according to claim 1, wherein the method further comprises the steps of: combining said core material, sacrificial anode material and selectively said filler material composed of an Al/Si-based alloy with each other, thereby producing a composite material; heating an ingot of said composite material; hot-rolling said heated composite material; cold-rolling said hot-rolled composite material; and annealing said composite material during the cold-rolling step or after the cold-rolling step; wherein in the heating step of said composite material, an ingot of said composite material is heated and held at a temperature falling within about 400 about 500 C. for a time period falling within a range of about 1-about 10 hrs. after the combining step; and wherein in the hot rolling step of said composite material, a rolling time for rolling said composite material is at most 40 min after the heating step, and in which a temperature of said composite material is at most 300 C. at the end of the hot rolling step.

3. The method of manufacturing a high corrosion-resistant aluminum alloy brazing sheet according to claim 2, wherein an existence density of Si particles having a projected area diameter of at least 1.0 m is at most 5,000/mm.sup.2 in a matrix of said sacrificial anode material.

4. The method of manufacturing a high corrosion-resistant aluminum alloy brazing sheet according to claim 3, wherein an existence density of Si particles having a projected area diameter of at least 5.0 m is at most 500/mm.sup.2 in the matrix of said sacrificial anode material.

5. The method of manufacturing a high corrosion-resistant aluminum alloy brazing sheet according to claim 4, wherein an average crystallized grain diameter in the thickness direction of said sacrificial anode material is at least 80% of the clad thickness of said sacrificial anode material after the high corrosion-resistant aluminum alloy brazing sheet is heated and brazed.

6. The method of manufacturing a high corrosion-resistant aluminum alloy brazing sheet according to claim 5, wherein the high corrosion-resistant aluminum alloy brazing sheet is utilized as a tube member of a heat exchanger into which an exhaust gas of an automobile flows.

7. The method of manufacturing a high corrosion-resistant aluminum alloy brazing sheet according to claim 6, wherein the high corrosion-resistant aluminum alloy brazing sheet is used in the corrosion environment in which pH is less than pH 3, and in which the density of chloride ions is more than 5 ppm.

8. A method of manufacturing a high corrosion-resistant aluminum alloy brazing sheet, wherein the brazing sheet comprises: a core material composed of an aluminum alloy; and sacrificial anode materials cladded on both surfaces of said core material, respectively; wherein said sacrificial anode material contains an aluminum alloy which contains Si falling within a range of about 2.5-about 7.0 mass %, Zn falling a range of about 1.0-about 5.5 mass %, Fe falling within a range of about 0.05-about 1.0 mass %, and optionally contains at least one element selected from the group consisting of Ti falling within a range of about 0.05-about 0.3 mass %, Zr falling within a range of about 0.05-about 0.3 mass %, Cr falling within a range of about 0.05-about 0.3 mass %, and V falling within a range of about 0.05-about 0.3 mass %, and further contains the balance Al and the inevitable impurities, and wherein a clad thickness of said sacrificial anode material falls within a range of about 25-about 80 m; wherein the method comprises the steps of: casting said core material; casting said sacrificial anode material to form an ingot of said sacrificial anode material; heating said ingot of said cast sacrificial anode material to form heated sacrificial anode material; and hot-rolling said heated sacrificial anode material to form a hot-rolled sacrificial anode material; wherein during the casting step of said sacrificial anode material, a cooling rate V ( C./s) for an ingot of said sacrificial anode material and a content Sic of Si satisfies the following formula (2):
VSic/5(2) wherein in the heating step of said ingot of said cast sacrificial anode material, the ingot of said cast sacrificial anode material is heated and held at a temperature falling within a range of about 300-about 500 C. over a time period falling within a range of about 1-about 10 hrs.; and wherein in the hot-rolling step of said heated sacrificial anode material, a temperature of said hot-rolled sacrificial anode material is at most 350 C. at an end of the hot rolling process.

9. The method of manufacturing a high corrosion-resistant aluminum alloy brazing sheet according to claim 8, wherein the method further comprises the steps of: combining said cast core material and said hot-rolled sacrificial anode material with each other, thereby producing a composite material; heating said composite material to form heated composite material; hot-rolling said heated composite material to form hot-rolled composite material; cold-rolling said hot-rolled composite material; and annealing said composite material during the cold-rolling step or after the cold-rolling step; wherein in the heating step of said composite material, an ingot of said composite material is heated and held at a temperature falling within about 400-about 500 C. for a time period falling within a range of about 1-about 10 hrs. after the combining step; and wherein in the hot rolling step of said composite material, a rolling time for rolling said composite material is at most 40 min after the heating step, and in which a temperature of said composite material is at most 300 C. at the end of the hot rolling step.

10. The method of manufacturing a high corrosion-resistant aluminum alloy brazing sheet according to claim 9, wherein an existence density of Si particles having a projected area diameter of at least 1.0 m is at most 5,000/mm.sup.2 in a matrix of said sacrificial anode material.

11. The method of manufacturing a high corrosion-resistant aluminum alloy brazing sheet according to claim 10, wherein an existence density of Si particles having a projected area diameter of at least 5.0 m is at most 500/mm.sup.2 in the matrix of said sacrificial anode material.

12. The method of manufacturing a high corrosion-resistant aluminum alloy brazing sheet according to claim 11, wherein an average crystallized grain diameter in the thickness direction of said sacrificial anode material is at least 80% of the clad thickness of said sacrificial anode material after the high corrosion-resistant aluminum alloy brazing sheet is heated and brazed.

13. The method of manufacturing a high corrosion-resistant aluminum alloy brazing sheet according to claim 12, wherein the high corrosion-resistant aluminum alloy brazing sheet is utilized as a tube member of a heat exchanger into which an exhaust gas of an automobile flows.

14. The method of manufacturing a high corrosion-resistant aluminum alloy brazing sheet according to claim 13, wherein the high corrosion-resistant aluminum alloy brazing sheet is used in the corrosion environment in which pH is less than pH 3, and in which the density of chloride ions is more than 5 ppm.

Description

EXAMPLES

(1) Although the present invention will be further explained in detail based on examples below, the present invention cannot be limited to these examples.

(2) Sacrificial anode material alloys composed of components as shown in Table 1 and core material alloys composed of components as shown in Table 2 were cast by respective DC casting processes, and then each of the cast alloys was machined and finished so that both surfaces thereof were shaved. At this time, the ingots for the sacrificial anode material alloys and the ingots for the core material alloys had a thickness of 500 mm. In each of the casting processes, a cooling rate and a value of Sic/5 are shown in Table 1. Also, in addition to the sacrificial anode materials, for filler materials, JIS 4045 alloys were used, and the sacrificial anode materials and the filler materials were subjected to heating processes and hot rolling processes, respectively, so that each of the materials was rolled so as to have a predetermined thickness. The conditions on the heating processes and the hot rolling processes are shown in Table 3.

(3) TABLE-US-00001 TABLE 1 Cooling Rate At Alloy Casting Refer- Alloy Composition (mass %) Process ences Si Zn Fe Ti Zr Cr V Al V( C./s) Sic/5 Examples of A1 2.5 2.0 0.05 0.05 Balance 0.7 0.5 Invention A2 2.5 3.0 0.1 0.3 Balance 0.5 0.5 A3 4.5 3.8 0.2 0.05 Balance 1.2 0.9 A4 4.5 2.0 0.4 0.3 Balance 0.9 0.9 A5 5.5 4.0 0.6 0.05 Balance 1.5 1.1 A6 5.5 1.0 0.8 0.3 Balance 1.2 1.1 A7 6.0 5.5 1.0 0.05 Balance 1.5 1.2 A8 7.0 3.0 0.2 0.3 Balance 1.7 1.4 A9 2.5 3.5 0.2 0.1 0.1 Balance 0.7 0.5 A10 2.5 4.5 0.2 0.1 0.1 Balance 0.8 0.5 A11 3.5 5.0 0.2 Balance 1.0 0.7 A12 2.5 3.0 0.2 0.1 Balance 0.4 0.5 A13 4.5 3.0 0.2 0.1 Balance 0.6 0.9 A14 6.0 3.0 0.2 0.1 Balance 1.1 1.2 Comparative A15 7.5 3.0 0.2 0.1 Balance 1.6 1.5 Examples A16 5.0 7.0 0.2 0.1 Balance 1.0 1.0 A17 5.0 0.5 0.2 0.1 0.1 Balance 1.0 1.0 A18 5.0 3.0 1.1 0.1 Balance 1.0 1.0 A19 2.0 3.0 0.1 Balance 0.5 0.4

(4) TABLE-US-00002 TABLE 2 Alloy Refer- Alloy Composition (mass %) ences Si Fe Cu Mn Mg Ti Zr Cr V Al B1 0.8 0.2 0.4 1.5 0.05 0.05 Balance B2 0.5 0.4 0.8 1.1 0.05 0.05 Balance B3 0.1 0.6 0.5 0.8 0.4 0.3 Balance B4 0.6 0.8 1.0 1.1 0.3 Balance B5 1.0 1.0 0.5 1.8 Balance

(5) TABLE-US-00003 TABLE 3 Combined Materials Sacrificial Anode Materials Combining/Material Hot Rolling Process Hot Rolling Process Heating Process Temperature At Heating Process Temperature At Process Temperature Time End Of Rolling Temperature Time Time End Of Rolling References ( C.) (hrs) ( C.) ( C.) (hrs) (min) ( C.) C1 400 2 250 450 2 30 250 C2 500 8 350 500 10 40 300 C3 400 2 250 450 2 10 250 C4 520 2 300 450 2 30 250 C5 400 15 250 450 2 30 250 C6 400 2 450 450 2 30 250 C7 400 2 250 520 2 30 250 C8 400 2 250 450 15 30 250 C9 400 2 250 450 2 50 250 C10 400 2 250 450 2 30 350

(6) With using the alloys, each of the core materials was combined with a sacrificial anode material as shown in Table 2 and either the same sacrificial anode material or a filler material comprising JIS 4045 alloy, so that the sacrificial anode material was applied to one surface of the core material as a cladding 1, and so that either the same sacrificial anode material or the JIS 4045 alloy filler material was applied to the other surface of the core material as a cladding 2, resulting in production of composite materials. Each of the combined composite materials was subjected to a heating process and a combining/material hot rolling process, to thereby produce a 3-play clad material having a thickness of 3.5 mm. Then, the 3-play clad material was subjected to an intermediate annealing process (at a temperature 450 C. over 5 hrs) and a final cold rolling process, so that a plate material exhibiting a H1n refining and having a thickness of 0.5 mm was produced as a sample.

(7) As shown in Table 4, in the examples of the present invention and the comparative examples, the sacrificial anode materials defined as the claddings 1 and shown in Table 1, either the same sacrificial anode material or the JIS 4045 alloy filler materials defined as the claddings 2 and shown in Table 1, the core materials shown in Table 2, and the processes shown in Table 3 were combined.

(8) TABLE-US-00004 TABLE 4 Sacrificial Sacrificial Anode Material Anode Material Alloys Or Brazing Core Pro- Alloys Material Alloys Material duction (Cladding 1) (Cladding 2) Alloys Process Examples 1 A1 A1 B1 C1 Of 2 A2 A2 B2 C1 Invention 3 A3 A3 B3 C1 4 A4 A4 B4 C1 5 A5 A5 B5 C1 6 A6 A6 B1 C1 7 A7 A7 B1 C1 8 A8 A8 B1 C1 9 A9 A9 B1 C1 10 A10 A10 B1 C1 11 A11 A11 B1 C1 12 A12 A12 B1 C1 13 A13 A13 B1 C1 14 A14 A14 B1 C1 Compar- 15 A15 4045 B1 C1 ative 16 A16 4045 B1 C1 Examples 17 A17 4045 B1 C1 18 A18 4045 B1 C1 19 A19 4045 B1 C1 20 A4 A4 B4 C1 21 A4 A4 B4 C1 Examples 22 A4 4045 B1 C1 Of 23 A4 4045 B1 C2 Invention 24 A4 4045 B1 C3 25 A4 4045 B1 C4 26 A4 4045 B1 C5 27 A4 4045 B1 C6 28 A4 4045 B1 C7 29 A4 4045 B1 C8 30 A4 4045 B1 C9 31 A4 4045 B1 C10
G: Evaluation

(9) In the samples produced as sated above, thicknesses of the sacrificial anode materials and thickness of the filler materials were measured, and values of X of the above-mentioned formula (1) were calculated. Also, in each of the sacrificial anode materials, an existence density of Si particles having a projected area diameter of at least 1.0 m and an existence density of Si particles having a projected area diameter of at least 0.5 m were measured. Further, each of the samples was subjected to a heating process for brazing, and an average crystallized grain diameter measured thickwise in the sacrificial anode material, a corrosion resistance and a brazing property were evaluated.

(10) G-1: Thickness Measurement of Sacrificial Anode Material and Filler Material

(11) In each of the sample, an L-ST face was exposed by a polishing process, and was etched by a Keller's corrective liquid. Then, thicknesses of the sacrificial anode materials and thicknesses of the JIS 4045 alloy filler materials were measured by observing contrasts based on differences between alloy compositions, using a microscope.

(12) G-2: Measurement of Existence Density of Si Particles

(13) The existence densities of Si particles having the projected area diameter of at least 1.0 m and the projected area diameter of at least 0.5 m were measured by observing a cut face of a sacrificial anode material of each of the samples which is etched with the aforesaid Keller's corrective liquid. Note, in the samples in which the respective sacrificial anode materials are applied to both the surfaces of each of the core materials, a cladding 1 was selected as a surface to be measured.

(14) G-3: Measurement of Average Crystallized Grain Diameter after Brazing

(15) After each of the samples was subjected to a heating process for brazing as a plate-like material, an L-ST face was exposed by a polishing process, was anode-oxidized using a barker's corrosive liquid, and was then observed by a microscope through a polarization filter, so that an average crystallized grain diameter was measured thickwise in the sacrificial anode material. The microscope had a 100-power in observation, and a total of crystallized grain diameters in three view fields of the sacrificial anode material was averaged in three view fields. Note, in the samples in which the respective sacrificial anode materials are applied to both the surfaces of each of the core materials, a cladding 1 was selected as a surface to be measured.

(16) G-4: Measurement of Corrosion Resistance

(17) After each of the samples was subjected to a heating process for brazing as a plate-like material, it was cut into sample pieces having a size of 50 mm50 mm. In each of the pieces, the surface of the cladding 2 was masked with a resin, and the surface of the sacrificial anode material which is cladded as the cladding 1 on the core material was defined as a test surface. For the immersion test, the sample pieces were immersed in the aqueous solutions composed of components as shown in Table 5 at a temperature of 50 C. over a time period of 1,000 hrs. After the immersion test is finished, corrosion products were removed from the sample pieces, using a concentrated nitric acid solution. Then, depths of corrosions produced in the surface of the sacrificial anode material were measured, using a focal depth method, and the maximum depth was defined as a corrosion depth. In evaluation with the aqueous solutions A, B, C and D, when the sample pieces had a corrosion depth of less than 150 m in all of the aqueous solutions, they were evaluated as being acceptable (). When the sample pieces had a corrosion depth of at least 150 m, they were evaluated as being unacceptable (x).

(18) TABLE-US-00005 TABLE 5 Chloride Ion Density (ppm) pH Aqueous Solution A 10 2.3 Aqueous Solution B 300 1.8 Aqueous Solution C 2 2.3 Aqueous Solution D 10 4.0
G-5: Evaluation of Brazing Property

(19) JIS 3003 alloy was corrugated and shaped into a fin, and was combined with the surface of the sacrificial anode material of each of the samples. Then, the combined sample was immersed in an aqueous solution containing 5% fluoride flux, and was subjected to a heating process for brazing at a temperature of 80 C. over a time period of 3 min. In this core sample, when a fin joining rate was at least 95%, and when no melting occurred in the sample, a brazing property was evaluated as being sufficient (). When a fin joining rate was less than 95%, and when a melting occurred in the sample, a brazing property was evaluated as being insufficient (x).

(20) The results of the measured thicknesses of the sacrificial anode materials, the measured thicknesses of the filler materials, the calculated values of X, the measured existence densities of Si particles having the projected area diameter of at least 1.0 m and the projected area diameter of at least 0.5 m in the sacrificial anode materials, the measured average crystallized grain diameters thickwise in the sacrificial anode materials after the brazing, the measured corrosion depths, and the evaluated brazing properties shown in Table 6.

(21) TABLE-US-00006 TABLE 6 Sacrificial Sacrificial Anode Density Of Density Of Average Crystalized Anode Material Thickness Si particles Si particles Grain Diameter Measured Material Or Brazing Material having At having At Thickwise In Sacrificial Thickness (m) Thickness (m) Least 1.0 m Least 5.0 m Anode Material <Cladding 1> <Cladding 2> X Value (number/mm.sup.2) (number/mm.sup.2) (m) Examples Of 1 60 50 102 2100 301 58 Invention 2 25 51 64 3200 350 23 3 25 48 62 3600 362 23 4 42 49 55 2500 311 39 5 60 50 132 2700 309 57 6 29 50 16 3800 364 27 7 52 53 143 2200 321 48 8 26 53 31 3200 340 24 9 53 48 158 2200 304 50 10 80 50 306 2500 309 76 11 70 52 263 2100 303 65 12 51 51 130 7100 580 35 13 70 52 137 6300 550 50 14 26 53 39 6900 545 20 Comparative 15 48 50 50 2900 310 45 Examples 16 50 50 210 2500 320 48 17 50 51 15 2500 311 47 18 53 51 95 2400 310 49 19 42 50 113 1200 300 40 20 20 52 26 2300 308 19 21 85 51 111 2600 323 80 Examples Of 22 48 51 62 2500 303 45 Invention 23 51 51 66 2300 307 48 24 40 41 52 2500 316 38 25 50 52 65 5600 411 42 26 50 51 65 6000 423 43 27 53 50 69 5500 441 44 28 50 50 65 5200 417 43 29 51 53 66 5300 419 42 30 52 48 68 5800 426 43 31 49 47 64 5600 429 45 Corrosion Resistance Corrosion Depth (m) Aqueous Aqueous Aqueous Aqueous Brazing Solution A Solution B Solution C Solution D Evalution Property Examples Of 1 52 62 42 30 Invention 2 78 85 65 51 3 75 88 63 51 4 60 70 49 51 5 56 68 55 43 6 78 89 70 52 7 51 63 43 32 8 97 92 90 71 9 109 132 100 72 10 108 136 102 73 11 110 131 101 71 12 115 133 100 73 13 112 131 102 70 14 110 133 105 72 Comparative 15 155 182 130 101 X Examples 16 163 190 129 109 X 17 158 181 133 113 X 18 159 178 131 111 X 19 51 60 41 32 X 20 100 126 92 78 X 21 53 65 42 48 X Examples Of 22 62 85 55 43 Invention 23 65 86 53 41 24 51 75 43 38 25 114 135 101 71 26 113 138 101 75 27 113 138 102 72 28 112 131 103 73 29 111 134 107 74 30 118 132 101 73 31 115 134 106 72

(22) Examples 1 to 14, and 22 to 31 of the present invention satisfied the requirements regulated by the present invention, and were acceptable in both the corrosion resistance and the brazing property. Especially, in Examples 1 to 8, and 22 to 24 of the present invention satisfied the formula (1) and the existence densities of Si particles having the projected area diameter of at least 1.0 m and the projected area diameter of at least 0.5 m, all of the corrosion depths were less than 100 m in the corrosion test, and thus these examples were very superior in the corrosion resistance.

(23) Comparative Example 15 deteriorated in the corrosion resistance due to the fact that the Si component was too large in the sacrificial anode material.

(24) Comparative Example 16 deteriorated in the corrosion resistance due to the fact that the Zn component was too large in the sacrificial anode material.

(25) Comparative Example 17 deteriorated in the corrosion resistance due to the fact that the Zn component was too small in the sacrificial anode material.

(26) Comparative Example 18 deteriorated in the corrosion resistance due to the fact that the Fe component was too large in the sacrificial anode material.

(27) Comparative Example 19 deteriorated in the brazing property due to the fact that the Si component was too small in the sacrificial anode material.

(28) Comparative Example 20 deteriorated in the brazing property due to the fact that the thickness of the sacrificial anode material was too thin.

(29) Comparative Example 21 deteriorated in the brazing property due to the fact that the thickness of the sacrificial anode material was too thick.

INDUSTRIAL APPLICABILITY

(30) In the aluminum alloy clad material according to the present invention, not only can the uniform corrosion deriving from the lowness of pH of the corrosion liquid be restrained, but also it is possible to suppress occurrence and development of pitting corrosion deriving from the existence of chloride ions in the corrosion liquid. Thus, for example, the aluminum alloy clad material can be suitably utilized as a corrosion-resistant material for a fluid passage forming member of a heat exchanger for an automobile and so forth.