JP2003082428A - Aluminum alloy brazing sheet having excellent corrosion resistance in weld zone - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aluminum alloy brazing sheet which has excellent corrosion resistance in a weld zone, and is useful for various structural members such as a tube for a heat exchanger. SOLUTION: The brazing sheet 3 having excellent corrosion resistance in a weld zone 5 is obtained by coating one side or both sides of a core material 1 containing, by mass, 0.1 to 0.5% Cu, 0.05 to 0.3% Ti and 0.3 to 1.5% Mn, <=0.2% Si, Fe and Mg, and the balance Al with inevitable impurities with an aluminum alloy brazing filler metal 2 in a cladding ratio of 10 to 20% per one side. The crystal grain diameter L in a rolling direction in the longitudinal face of the core material 1 is 150 to 200 μm, the diffusion depth D of Cu in the weld zone 5 when subjected to brazing heating after welding is >=100 μm, and the potential difference S between the surface of the brazing filler metal 2 in the weld zone 5 and the position at the inside by 100 μm from the surface of the brazing filler metal 2 is >=50 mV.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy brazing sheet which is useful for various structural members such as tubes for heat exchangers and which has excellent corrosion resistance at welds. [0002] Automotive heat exchangers (radiators, etc.)
As shown in FIG. 3, a core 9 in which a header 7 for connecting the tube 6 and a radiation fin 8 are brazed to the tube 6.
The main part is configured. In FIG. 3, reference numeral 10 denotes a skin material. For example, as shown in FIG. 4, the tube 6 is made of a brazing material 3 coated with a brazing material 2 on one side of a core material 1 and a skin material 10 on another side, and a brazing material 2.
Is roll-formed into a cylindrical shape with the outside facing, induction heating by a high-frequency coil 11, and welding by pressing the molten end face by a pressure roll 12 to produce a weld. [0003] By the way, pitting corrosion occurs in the tube 6, and when it penetrates, liquid leakage occurs, so that the corrosion resistance of the tube 6 is extremely important. The corrosion resistance of tube 6 is tube 6
The radiating fins 8 or the skin material 10 to be brazed are maintained as a sacrificial corrosive material, but the thickness of the tube 6 has been reduced as a part of the recent reduction in the weight of automobiles. It became so. In order to improve the corrosion resistance of the core material 1, Cu is added to the core material 1, and the Cu is diffused into the brazing material 2 to corrode the tube in a planar shape by a potential gradient formed in the core material, thereby causing pitting corrosion. (JP-A-64-83396),
A method of adding Ti to the core material 1 and distributing the Ti in a layered manner in the length direction (rolling direction) of the core material 1 to form a local battery between the thick and thin layers of Ti to prevent pitting corrosion (Japanese Patent Laid-Open No. -283
No. 891) has been proposed. [0005] However, in the method of adding Cu, since the brazing material is melted once in a welded portion such as the tube to form a solidified structure and Cu is hardly diffused, The diffusion depth D (the distance from the surface of the brazing material to the start of the decrease in the concentration of Cu in the core material) becomes shallow, and the effect of preventing the pitting corrosion due to the potential gradient of Cu cannot be obtained sufficiently. In the method of distributing Ti in a layered manner, Ti diffuses along a crystal grain boundary at the time of welding to form a thickened layer of Ti at a joint interface, and pitting corrosion proceeds along the thickened layer of Ti. There was a problem of doing. For this reason, the present inventors have studied the corrosion resistance of the welded portion of the aluminum alloy brazing sheet, and have found that the two problems can be solved by defining the crystal grain size of the core material. Thus, the present invention has been completed. An object of the present invention is to provide an aluminum alloy brazing sheet having excellent corrosion resistance at a welded portion. Means for Solving the Problems The invention according to claim 1 is:
0.1 to 0.5 mass% of Cu and 0.05 to 0.3 of Ti
mass%, Mn containing 0.3 to 1.5 mass%, Si, F
e, Mg is regulated to 0.2 mass% or less, and the rest is a brazing sheet in which aluminum alloy brazing material is coated on one or both sides of a core material composed of Al and unavoidable impurities at a cladding rate of 10 to 20% per side. And the crystal grain size in the rolling direction in the longitudinal section of the core material is 150 to 2
The diffusion depth D of Cu from the brazing filler metal surface at the time of brazing and heating after welding is 100 μm or more.
An aluminum alloy brazing sheet excellent in corrosion resistance of a welded part, wherein a potential difference S from an inner position of 0 μm is 50 mV or more. DETAILED DESCRIPTION OF THE INVENTION The present invention, as shown in FIG.
A brazing sheet 3 in which a brazing material 2 is coated on one surface of an aluminum alloy core material 1 containing appropriate amounts of u, Mn, and Ti, and regulating the amounts of Si, Fe, and Mg. (Cross section) the grain size L in the rolling direction is 1
By defining the thickness to be 50 to 200 μm, FIG.
As shown in (b), the diffusion depth D of Cu from the surface of the brazing material 2 in the welded portion 5 after the brazing is heated is increased to 100 μm or more to form a gentle potential gradient in the core material 1, and Ti Is suppressed at the welding interface 4 and the potential difference S
This is a brazing sheet in which the (potential difference between the surface of the brazing material 2 and an internal position of 100 μm from the surface of the brazing material 2) is set to 50 mV or more, thereby improving the corrosion resistance of the welded portion 5. In the present invention, the welded portion 5 refers to a region including a portion melted by welding heat. Hereinafter, the alloy composition of the core material of the brazing sheet of the present invention will be described. Cu forms a solid solution by heating at the time of brazing (600 ° C. × 3 to 4 minutes) to increase the strength of the core material 1 and diffuses into the brazing material as shown in FIG. A gentle potential gradient is formed from the surface of the material 2 toward the inside, thereby improving the corrosion mode from a pitting type that progresses in the thickness direction to a surface type that spreads in the surface direction. If the Cu content is less than 0.1 mass%, the above effect cannot be sufficiently obtained. If the Cu content exceeds 0.5 mass%, Al-Cu intermetallic compounds are precipitated at the crystal grain boundaries, and the intergranular corrosion susceptibility is lowered. It becomes large and the corrosion resistance decreases. For this reason, the content of Cu is regulated to 0.1 to 0.5 mass%. Especially 0.1 ~
0.3 mass% is desirable. Further, in the present invention, the diffusion depth D of Cu in the welded portion (distance from the surface of the brazing material until the concentration of Cu in the core material starts to decrease: see FIG. 2B) is set to 100 μm or more. In order to increase the diffusion depth D of Cu to 100 μm or more, the grain size L in the rolling direction in the longitudinal section of the core material is adjusted.
(See FIG. 1) must be set to 200 μm or less to promote Cu diffusion. In the present invention, the potential difference S between the surface of the brazing material at the welded portion and the position 100 μm from the surface of the brazing material of the core material is defined to be 50 mV or more, and the corrosion mode is set to a surface corrosion type. In the present invention, Ti contained in the core material precipitates in a layer parallel to the surface of the core material to suppress pitting corrosion, and also shifts the potential of the core material noble to enhance the corrosion resistance of the core material. If the content of Ti is less than 0.05 mass%, the above effect cannot be sufficiently obtained. If the content exceeds 0.3 mass%, the above effect is saturated, and a coarse compound is formed to lower processability. . For this reason, Ti is defined as 0.05 to 0.3 mass%. In particular, 0.05 to 0.2 mass% is desirable. In the present invention, the enrichment of Ti at the bonding interface is prevented by setting the crystal grain size L to 150 μm or more to suppress the diffusion of Ti. Crystal grain size L is 200μ
If it exceeds m, a gradual concentration gradient of Cu cannot be obtained as described above, and microcracks occur during welding, resulting in a decrease in the strength of the welded portion. The crystal grain size L can be controlled by selecting a cold working rate, an intermediate annealing condition, and the like of the aluminum alloy brazing sheet. Intermediate annealing temperature is 36
Around 0 ° C. is appropriate. Mn enhances the corrosion resistance, weldability and strength of the core material. If the content of Mn is less than 0.3 mass%, the above effect cannot be sufficiently obtained, and if it exceeds 1.5 mass%, a coarse intermetallic compound is formed and the workability is reduced. For this reason, the content of Mn is specified to be 0.3 to 1.5 mass%. Especially 0.
3 to 1.2 mass% is desirable. [0015] Si forms an intermetallic compound with Fe to increase the strength of the core material. However, when the amount is large, a noble compound is formed and the corrosion resistance of the matrix is reduced. Therefore, Si is 0.2
Restrict to mass% or less. Especially 0.02 to 0.2 mass%
Is desirable. As described above, Fe forms an intermetallic compound with Si to increase the strength of the core material and to reduce the crystal grain size L to 2%.
It is refined to 50 μm or less and further enhances the weldability of the core material. However, when the amount is large, the corrosion resistance of the core material is reduced.
For this reason, Fe is restricted to 0.2 mass% or less. In particular, 0.02 to 0.2 mass% is desirable. [0017] Mg increases the strength of the core material, but if the amount is large, the brazing property decreases in the Nocolok brazing method using a fluoride-based flux. Therefore, Mg is 0.2 ma.
Restrict to ss% or less. In particular, 0.1 mass% or less is desirable. In the present invention, the cladding ratio of the brazing material is set to 1
The reason for defining the range from 0 to 20% is that if it is less than 10%, the brazing properties with the fins decrease, and if it exceeds 20%, the residual thickness of the core material becomes thin when the brazing material soaks into the core material. This is because a heat exchanger having a skeleton may cause fatigue fracture due to external force. Although any aluminum alloy brazing material can be used as the brazing material, an Al—Si alloy brazing material is desirable because it can stably provide good brazing properties. The brazing sheet of the present invention includes a core material having both surfaces coated with a brazing material, a core material having one surface coated with a brazing material, another surface coated with a brazing material, and a core material having one surface coated with a brazing material. What was just done. The present invention will be described below in more detail with reference to examples. (Example 1) 4045 alloy brazing material (Si1
0.5 mass%, Fe 0.05 mass%, Cu 0.05 mass
%, 0.01 mass% of Ti, and the balance of Al), and hot-rolled to a thickness of 35 mm, then cold-rolled, intermediately annealed,
Cold rolling is performed in this order to obtain a 3.5 mm thick plate,
Further, the sheet was repeatedly subjected to cold rolling and intermediate annealing to produce an H14 aluminum alloy brazing sheet having a thickness of 0.4 mm. Cladding rate of brazing material is 10-20%
Were variously changed within the range. The crystal grain size of the core material is 150 to 200 μm by controlling the cold rolling rate and the intermediate annealing temperature.
Was controlled within the range. Comparative Example 1 An aluminum alloy brazing sheet was manufactured in the same manner as in Example 1, except that an aluminum alloy having a composition outside the range specified in the present invention shown in Table 2 was used as a core material. (Comparative Example 2) An aluminum alloy brazing sheet was manufactured in the same manner as in Example 1 except that the clad ratio of the brazing material was outside the range specified in the present invention. A test piece was cut out from each of the brazing sheets produced in Example 1 and Comparative Examples 1 and 2, and (1)
Brazing properties, (2) tensile strength, (3) fatigue resistance properties,
(4) The corrosion resistance was examined and evaluated by the following method. The results are shown in Tables 1 and 2. (1) A brazing property drop test was carried out by a conventional method to obtain a fluidity coefficient. A fluidity coefficient of 60% or more was judged to be acceptable. (2) Brazing conditions (600 ° C) for tensile strength test piece (JIS No. 5 test piece)
× 3.5 minutes) and leave it at room temperature for one week.
A tensile test was performed according to H.241. Tensile strength is 140N /
mm ² or more was determined to be acceptable. (3) Brazing conditions (600 ° C. × 3.
5 minutes) and leave it at room temperature for 1 week, then JISZ2273
In accordance with to determine the fatigue strength at 10 ⁷ times by adding a repeated bending stress. The bending was a double swing at a frequency of 15 Hz, and the applied stress was changed according to the length of the test piece. The amplitude was constant. A fatigue strength of 30 MPa or more was considered acceptable. (4) After heating a corrosion resistance test piece (width 30 mm, length 120 mm) under brazing conditions (600 ° C. × 3.5 minutes), the end portion was masked with an insulating tape, and a CASS test was performed for 750 hours according to JIS H8601. After the test, corrosion products were removed, and the pit depth was measured by a depth of focus method using an optical microscope.
A pit depth of 170 μm or less was accepted. [Table 1] [Table 2] As is clear from Tables 1 and 2, No. 1 of the present invention example. All of Nos. 1 to 18 were excellent in brazing property, tensile strength, fatigue resistance and corrosion resistance. In contrast, N of the comparative example
o. Nos. 19, 20, and 22 each contain a large amount of Si, Fe, and Cu. 21, 24 and 26 are Cu and M, respectively.
Since both n and Ti were small, the corrosion resistance was inferior. No.
In Nos. 21 and 24, the strength also decreased. No. 23 is Mg of the core material
Because there are many, No. 28 had low brazing properties because of low cladding ratio. No. No. 25 is inferior in rollability due to a large amount of Mn. No. 27 was inferior in electric resistance workability due to a large amount of Ti. No. Nos. 29 and 30 were inferior in fatigue strength due to a large cladding ratio. In addition, the brazing sheet of the present invention was confirmed to be satisfactorily brazed by other atmosphere brazing, flux brazing, vacuum brazing, etc., through a test and investigation conducted separately. (Example 2) No. 2 shown in Table 1 The aluminum alloy core material of No. 11 was overlaid with 4045 alloy brazing material on one side, hot-rolled to a thickness of 35 mm, and then cold-rolled.
Intermediate annealing (360 ° C. × 2 hours) and cold rolling were performed in this order to produce a 3.5 mm-thick plate. In the sheet material, the crystal grain size L was controlled within the specified value of the present invention by changing the cold rolling reduction and the intermediate annealing temperature. (Comparative Example 3) A cold rolling reduction and an intermediate annealing temperature were selected so that the crystal grain size L was outside the specified value of the present invention.
A plate was manufactured in the same manner as in Example 2. A test piece (width: 100 mm, length: 30 mm) was cut out from each of the plate members produced in Example 2 and Comparative Example 3, and the test piece was subjected to direct current (DC) pad welding to determine the number of microcracks in the welded section. The crack occurrence rate R (R
= [Number of welding times microcracking occurred / total number of welding times] × 10
0) was determined. In addition, the CASS test was performed for 750 hours in accordance with JIS 8601 in the same manner as in Example 1 to check the corrosion resistance of the welded portion. If no pitting occurred on the welded portion, the corrosion resistance was good (O), and if it did, it was poor (X).
It was determined. Table 3 shows the results. In direct current (DC) bad welding, an external force acts in a semi-molten state during welding, as in the case of high-frequency induction welding. [Table 3] As is apparent from Table 3, N of the present invention example
o. All of Nos. 31 to 33 were excellent in weldability and corrosion resistance of a welded portion. On the other hand, in Comparative Example No. In No. 34, since the crystal grain size L of the core material was large, cracks were easily generated. In No. 35, the corrosion resistance of the welded portion was inferior because the crystal grain size L of the core material was small. Here, a 3.5 mm-thick plate material was used as the test piece, but it was confirmed by another experiment that the same result was obtained even with a thin brazing sheet. (Example 3) No. 3 shown in Table 1 Using the alloy No. 15, an H14 brazing sheet having a thickness of 0.4 mm was produced in the same manner as in Example 1, and this brazing sheet was processed into a tube by the electric resistance welding method shown in FIG. The conditions (high frequency welding conditions) of the electric resistance welding method were a frequency of 400 kHz, a current of 3.7 mA, a voltage of 6.7 kV, an upset amount of 200 μm, and a pipe-making speed of 90 m / min. Under the above conditions, the diffusion depth D and the potential difference S of Cu in the welded portion of the tube satisfied the specified values of the present invention. The welding condition (fillet shape) and dimensional accuracy of the tube were both good. (Comparative Example 4) The tube was subjected to ERW by the same method as in Example 3 except that the conditions of the high-frequency welding method were changed so that the diffusion depth D and the potential difference S of Cu were outside the specified values of the present invention. did. A radiator core shown in FIG. 3 was prepared using each of the tubes manufactured in Example 3 and Comparative Example 4, and the corrosion resistance of the welded portion of the tube was evaluated and evaluated in the same manner as in Example 2. Those in which pitting corrosion did not occur in the welded portion were determined to have good corrosion resistance (○), and those in which pitting corrosion occurred were determined to be poor (x). The radiator core was assembled so that the radiation fins were sandwiched between the tubes, and a flux for Nokoloc was spray-coated on the assembled body in an amount of 3 g / m ^2. After drying, the dew point was −40 ° C., the oxygen concentration was 300 ppm, and the temperature was 600
Heating was performed in an atmosphere at a temperature of 5 ° C. for 5 minutes, and a radiation fin was brazed to the tube. A good fillet was formed at the connection between the tube and the fin. Table 4 shows the results. Table 4 also shows the Cu diffusion depth D (see FIG. 2B) and the potential difference S. The diffusion depth D of Cu was determined by a quantitative line analysis method using EPMA. The potential difference S is measured by using a reference electrode Ag / AgCl in 5% NaCl using a reference electrode Ag / AgCl in measuring the potential a on the brazing material surface and the potential b on the polished surface 100 μm inside from the brazing material surface. Indicated by value. [Table 4] As is clear from Table 4, N of the present invention example
o. No. 36 showed good corrosion resistance, but no. Three
No. 7 has a low potential difference S, and No. 38 has a shallow Cu diffusion depth D, and Numeral 39 indicates a shallow diffusion depth D and a potential difference S
, The corrosion resistance of the welds was inferior. As described above, the brazing sheet of the present invention contains appropriate amounts of Cu, Ti, and Mn and contains Si,
Brazing sheet in which aluminum alloy brazing material is coated on one or both sides of a core material in which Fe and Mg are restricted to a small amount at a cladding ratio of 10 to 20% per one side, brazing properties, tensile strength, fatigue resistance properties, corrosion resistance And other properties required for a heat exchanger tube and the like. Further, the crystal grain size L in the rolling direction in the longitudinal section of the core material is set to 150 to 200.
μm, C in the weld when brazing and heating after welding
The diffusion depth D of u is set to 100 μm or more, and the potential difference S between the brazing sheet surface of the welded portion and the position 100 μm from the surface is set to 50 mV or more. Therefore, a remarkable industrial effect is achieved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram of a crystal grain size in a core material of a brazing sheet of the present invention. 2A is an explanatory view of a welded portion of the brazing sheet of the present invention, and FIG. 2B is a diffusion depth D and a potential difference S of Cu.
FIG. FIG. 3 is a partial explanatory view of a radiator core. FIG. 4 is an explanatory diagram of an electric resistance sewing method. [Description of Signs] 1 core material 2 brazing material 3 brazing sheet 4 welding interface 5 welded portion 6 tube 7 header 8 radiating fin 9 core 10 skin material 11 high frequency coil 12 pressure roll

Claims (1)

[Claim 1] 0.1 to 0.5 mass% of Cu, 0.05 to 0.3 mass% of Ti, and 0.3 to 1.5 mass% of Mn.
The content of Si, Fe, and Mg is regulated to 0.2 mass% or less, respectively, and the balance is made of aluminum alloy brazing material on one or both sides of a core material consisting of Al and unavoidable impurities.
A brazing sheet coated with a cladding ratio of 0 to 20%, wherein a crystal grain size in a rolling direction in a longitudinal section of the core material is 150 to 200 μm, and a brazing material surface at a welded portion when heated by brazing after welding. Cu diffusion depth D
Is equal to or more than 100 μm, and the potential difference S between the surface of the brazing material of the welded portion and a position 100 μm inside from the surface of the brazing material is 50 mV.
An aluminum alloy brazing sheet having excellent corrosion resistance at a welded portion, characterized in that: