JP2015199993A - Production method of aluminum alloy fin material for heat exchanger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method of aluminum alloy fin material for heat exchanger, excellent in corrugate molding property and intensity after brazing heating, and having freedom degree of a heat gain during annealing.SOLUTION: An aluminum alloy casting mass is formed by using an aluminum alloy comprising Si:1.0-1.8%, Fe:0.3-0.9%, Mn:1.0-1.8%, Zn:0.5-2.0%, by mass% and balance formed of Al and inevitable impurities and casting. To the aluminum alloy casting mass, at least once or more times of annealing and once or more times of cold rolling are performed and a heat gain Ai(°C.h) per once of annealing at i-th time is 10 or more and 40000 or less, and a final rolling ratio in the cold rolling is 20-50%.

Description

  The present invention relates to a method for producing an aluminum alloy fin material for a heat exchanger that is excellent in corrugate formability and strength after brazing heating.

  Aluminum alloys are suitable for heat exchangers such as radiators, heater cores, condensers, and intercoolers because they are lightweight and have excellent strength and thermal conductivity. The heat exchanger is assembled, for example, by brazing and joining aluminum alloy fins shaped into corrugations by corrugation molding to other members. As an alloy of the aluminum alloy fin material, a pure aluminum alloy such as JIS1050 alloy excellent in thermal conductivity and an Al-Mn alloy such as JIS3003 alloy excellent in strength and buckling resistance have been generally used.

  By the way, in recent years, demands for weight reduction, size reduction, and high performance have been increasing for heat exchangers. Accordingly, the aluminum alloy fin material to be brazed and joined is also desired to be thin and excellent in properties such as strength after brazing heating, thermal conductivity and corrosion resistance. In particular, as the fin material becomes thinner, further improvement in strength after brazing and heating is required. However, generally, when the strength after brazing heating is improved, the strength before brazing heating is improved at the same time, and thus the corrugated formability is lowered. For this reason, it was difficult to achieve both strength after brazing heating and corrugate formability.

  As an aluminum alloy fin material, Patent Document 1 describes a high-strength aluminum alloy fin material having a thickness of 40 to 200 μm, which is cast by a twin belt type continuous casting and rolling method, and the metal structure before brazing heating is a fiber structure. Has been. However, recrystallization is not performed during intermediate annealing, and the metal structure before brazing heating is a fiber structure, which increases the amount of strain in the raw material state. As a result, the material strength is increased, and when corrugating a thin fin material, a predetermined dimensional accuracy cannot be obtained, and the performance of the heat exchanger may be deteriorated.

  In Patent Document 2, casting is performed by a twin belt type continuous casting method, the first intermediate annealing is performed at a temperature of 250 to 550 ° C., the second intermediate annealing is performed at a temperature of 360 to 550 ° C., and the final thickness is 40 to 200 μm. An aluminum alloy fin material for a heat exchanger is disclosed. However, the metal structure before brazing heating is not specified, the material strength before brazing heating is high, and corrugate formability may be reduced.

  Patent Document 3 discloses an aluminum alloy material excellent in erosion resistance, cast by a continuous casting and rolling method, first annealed at a temperature of 450 to 600 ° C. for 1 to 10 hours, and having a final thickness of 0.1 mm or less. The manufacturing method of this is proposed. However, since the intermediate annealing is performed at a high temperature, as described above, the second phase particles become coarse and have a sparse distribution during annealing, and the strength after brazing heating decreases. In addition, the crystal grain size after brazing heating is expected to be fine, and there is a possibility that brazing properties cannot be ensured.

  Patent Document 4 describes an aluminum alloy fin material for a heat exchanger which is cast by a semi-continuous casting method and has excellent corrosion resistance by containing Ni. However, since a compound containing Ni has a large potential difference from the matrix and is likely to be a starting point of corrosion, the self-corrosion resistance is low, which is insufficient practically. Further, in the semi-continuous casting method, the size of a compound generated during casting is larger than that in the continuous casting rolling method, and since many compounds that are the starting points of corrosion are likely to proceed, corrosion is inferior.

JP 2007-31778 A JP 2008-38166 A JP 2008-307661 A JP 2003-147466 A

  As described above, no conventional heat exchanger fin material has been developed that has both the corrugate formability and the strength after brazing heating, and the processing conditions during annealing are strictly regulated. And there was no degree of freedom in heat input.

  The present invention has been made in view of such problems, and is a method for producing an aluminum alloy fin material for a heat exchanger that is excellent in corrugated formability and strength after brazing heating, and is free from heat input during annealing. It aims at providing the manufacturing method which has a degree.

  As a result of studying the above problems, the present inventors have found that the above problems can be solved by adjusting the heat input amount during annealing and the final rolling rate for an aluminum alloy having a specific alloy composition, and complete the present invention. It came to.

That is, the method for producing an aluminum alloy fin material for a heat exchanger according to the present invention is characterized by the following (1) to (3).
(1) In mass%, Si is 1.0 to 1.8%, Fe is 0.3 to 0.9%, Mn is 1.0 to 1.8%, Zn is 0.5 to 2.0%, An aluminum alloy composed of Al and inevitable impurities is used as the balance.

(2) An aluminum alloy ingot cast using the above aluminum alloy is subjected to at least one annealing and one or more cold rollings, and per i-th annealing calculated by the following formula 1. The amount of heat input Ai (° C. · h) is 10 or more and 40000 or less.

(3) The final rolling reduction in cold rolling is set to a range of 20 to 50%.

Moreover, it is preferable that the total heat input T calculated by the following formula 2 is 10 or more and 60000 or less.

  According to the production method of the present invention, it is possible to provide an aluminum alloy fin material for a heat exchanger that is excellent in corrugated formability and strength after brazing heating while giving a degree of freedom in heat input during annealing.

It is a figure which shows the temperature chart at the time of annealing, and the calculation method of heat input. It is a figure which shows an example of the temperature chart for calculating the heat gain.

  Hereinafter, the manufacturing method of the aluminum alloy fin material for heat exchangers of the present invention will be described in detail.

[1. Composition of aluminum alloy fins]
The composition of the aluminum alloy fin material of the present invention is mass%, Si is 1.0 to 1.8%, Fe is 0.3 to 0.9%, Mn is 1.0 to 1.8%, Zn is It contains 0.5 to 2.0%, and the balance is Al and inevitable impurities. Hereinafter, the reason for adding the component elements and the reason for limiting the content range will be described.

(Si: 1.0% to 1.8%)
Si is an essential element for improving the strength of the material. Si forms an Al-Fe-Si-based, Al-Mn-Si-based, Al-Fe-Mn-Si-based compound together with Al, Fe, and Mn, thereby causing dispersion strengthening or by dissolving in a matrix. Increases strength by causing solid solution strengthening. In the present invention, the Si content range is 1.0 to 1.8%, preferably 1.2 to 1.5%. If the content is less than 1.0%, dispersion strengthening and solid solution strengthening are not sufficient, and the strength after brazing heating is lowered. On the other hand, if the content exceeds 1.8%, the solidus temperature is lowered and the fins may be melted during brazing.

(Fe: 0.3% to 0.9%)
Fe is an essential element for improving the strength of the material. Since Fe is formed as an Al-Fe-based, Al-Fe-Si-based, Al-Fe-Mn-based, Al-Fe-Mn-Si-based fine compound during twin-roll continuous casting and rolling, dispersion strengthening is performed. Wake up to improve the strength of the material. Moreover, since these fine compounds suppress recrystallization nuclei during brazing, the crystal grain size after brazing is coarsened and brazing diffusion to the fin material is suppressed. In the present invention, the Fe content range is 0.3 to 0.9%, preferably 0.4 to 0.7%. If the content is less than 0.3%, the above effects cannot be obtained sufficiently. On the other hand, if the content exceeds 0.9%, a coarse crystallized product is formed at the time of casting, so that the plastic deformability is lowered, and the rollability and the corrugated formability are lowered. Moreover, since the cathode site by a fine compound increases, there exists a possibility that a corrosion start point may increase and self-corrosion resistance may fall.

(Mn: 1.0% to 1.8%)
Mn is an essential element for improving the strength of the material. Mn causes dispersion strengthening by forming Al—Fe—Mn, Al—Mn—Si, and Al—Fe—Mn—Si compounds together with Al, Fe, and Si, or dissolves in the matrix. Increases strength by causing solid solution strengthening. In addition, Mn combines with solute Si to reduce the amount of solute Si in the matrix, thereby improving the melting point of the material and preventing melting during brazing. In the present invention, the Mn content is 1.0 to 1.8%, preferably 1.2 to 1.5%. If the content is less than 1.0%, the above effect cannot be obtained sufficiently. On the other hand, if the content exceeds 1.8%, a coarse crystallized product is formed at the time of casting, so that the plastic deformability is lowered, and the rollability and the corrugated formability are lowered. In addition, the amount of Mn solid solution in the matrix increases and the thermal conductivity tends to decrease.

(Zn: 0.5% to 2.0%)
Zn lowers the natural potential of the material and contributes to the improvement of the sacrificial anticorrosive effect. In the present invention, the Zn content is 0.5 to 2.0%, preferably 1.0 to 1.5%. If the content is less than 0.5%, the above effect cannot be obtained sufficiently. On the other hand, if it exceeds 2.0%, the self-corrosion rate increases and the self-corrosion resistance decreases.

  In addition to the above elements, basically, Al and inevitable impurities may be used, but other elements usually added to the aluminum alloy are allowed within a range that does not greatly affect the characteristics. For example, if Ti and B added as a finer during casting are 0.1% or less and 0.01% or less, respectively, there is no problem, and Cr or V that may be added for strength improvement , Zr is not particularly problematic as long as it is 0.1% or less.

[2. Manufacturing process]
Next, in the embodiment of the present invention, the molten aluminum alloy having the above composition is made into an aluminum alloy plate ingot by a twin roll continuous casting and rolling method, and at least once for the aluminum alloy plate ingot. Annealing and at least one cold rolling. Hereinafter, it demonstrates for every process.

(Twin roll continuous casting and rolling method)
First, a molten aluminum alloy having the above composition is formed into a plate-shaped ingot by a twin roll continuous casting and rolling method. In the twin-roll continuous casting and rolling method, the cooling rate of the molten aluminum alloy at the time of casting is 100 to 1000 ° C./second, and the cooling rate is faster than 20 to 100 ° C./second of the general DC (Direct Hill) method. . Therefore, intermetallic compounds such as Al—Fe, Al—Fe—Mn, and Al—Fe—Mn—Si are easily finely dispersed during casting. Since the finely dispersed intermetallic compound promotes the precipitation of Si, Fe, and Mn dissolved in the matrix, the strength is easily improved by dispersion strengthening, and the thermal conductivity is also easily improved. Moreover, since there are many fine compounds, there is little abrasion of a corrugated shaping | molding die.

  In the twin-roll continuous casting and rolling method, the molten metal temperature is preferably maintained at 680 to 800 ° C. Here, the molten metal temperature is the temperature of the head box immediately before the hot water supply nozzle. If the molten metal temperature is too low, coarse crystals are easily formed during casting, and the plastic deformability of the material is lowered. In the worst case, the plate may be broken during the subsequent cold rolling. On the other hand, if the molten metal temperature is too high, the molten metal does not solidify during casting, and a plate-shaped ingot cannot be obtained.

(Annealing)
Subsequently, the obtained plate-shaped ingot is annealed at least once before reaching the final thickness. Here, the amount of heat input during annealing is different from the amount of heat generally calculated. In general, the amount of heat can be determined by the product of current, voltage, and time. However, even if current and voltage are defined in industrial annealing, it is not a meaningful numerical value. In the present invention, in the i-th annealing per time, the product of temperature, coefficient corresponding to each temperature and time is defined as heat input A _i (° C. · h), and heat input A _i by annealing per time Is defined as a range of 10 ≦ A _i ≦ 40000. The amount of heat input A _i is calculated by Equation 3.

As shown in Table 1, the coefficient α _{k in} Equation 3 differs in each annealing temperature region, and is an index indicating the influence on the metal structure in each annealing temperature region.

As shown in Table 1, the coefficient α _{k in} Equation 3 is, for example, 0.01 at 250 ° C. or higher and lower than 300 ° C., 0.05 at 300 ° C. or higher and lower than 350 ° C., and 10, 400 ° C. at 350 ° C. or higher and lower than 400 ° C. 20 at less than 450 ° C. and 30 at 450 ° C. or more.

In the present embodiment, the temperature to be heat input is set to an annealing temperature of 250 ° C. or higher. When the annealing temperature is less than 250 ° C., there is little influence on the metal structure of the material, and it does not make much sense to perform annealing for a long time. In general, when the annealing temperature is high, the amount of solid solution of elements in the matrix of the crystallized product at the time of casting decreases, and the intermetallic compound precipitates coarsely and loosely. The coefficient α _k is a degree indicating the degree, and the larger the value, the stronger the degree. On the other hand, when the annealing temperature is low, the amount of solid solution of elements in the matrix remains high and the intermetallic compound precipitates finely and densely.

A _{i in} Formula 3 is 10 to 40,000. If A _i is less than 10, since the heat input amount is small, the strength after brazing heating is high, but the material is not sufficiently softened and the strength before brazing heating is high, so that the corrugated formability is poor. On the other hand, when A _i exceeds 40000, the strength before brazing heating is low and the corrugated formability is not impaired, but the strength after brazing heating is greatly reduced, so the durability of the final heat exchanger is reduced. Resulting in.

In FIG. 1, the schematic diagram of the temperature chart at the time of annealing is shown.
The amount of heat input A per annealing in this temperature chart is:
A = a ₁ + a ₂ + a ₃ + a ₄ + a ₅
= Α ₁ × S ₁ + α ₂ × S ₂ + α ₃ × S ₃ + α ₄ × S ₄ + α ₅ × S ₅ (Expression 4).

Here, a _{k is the} amount of heat input in each temperature region, α _{k is} the coefficient of each temperature region, and S _{k is} the area (temperature × time) of each temperature region.

(Calculation example of heat input A)
An example in which the heat input A is calculated based on the temperature flowchart shown in FIG.
The temperature flow chart of the figure shows the case where the heating rate and the cooling rate are both 50 ° C./h and annealing is performed at 430 ° C. for 2 hours. The coefficients shown in Table 1 and the area of each region (= product of temperature and time, this In this case, the amount of heat input A is calculated as follows.
Heat input A = α ₄ × S ₄ (area from 430 ° C. to 400 ° C.) + Α ₃ × S ₃ (area from 400 ° C. to 350 ° C.) + Α ₂ × S ₂ (area from 350 ° C. to 300 ° C.) + Α ₁ × S ₁ (area from 300 ° C to 250 ° C)
= 20 × (430 ° C.-400 ° C.) × (2h + 3.2h) / 2
+ 10 × (400 ° C.-350 ° C.) × (3.2 h + 5.2 h) / 2
+ 0.05 × (350 ° C.-300 ° C.) × (5.2 h + 7.2 h) / 2
+ 0.01 × (300 ° C.−250 ° C.) × (7.2 h + 9.2 h) / 2
= 3680 (℃ ・ h)

  The above is a calculation example when assuming the case of annealing in a batch furnace. In order to facilitate calculation, the heat input area is trapezoidal, but even if the temperature rises rapidly (temperature chart approximates a rectangle) as in a salt bath, etc. The same performance can be obtained. Furthermore, in actual machines, the temperature chart generally draws a curve, but even in this case, if the curve is integrated, the area can be obtained, and if the heat input satisfies the range specified in the present invention, it is for a heat exchanger with good performance. A fin material can be obtained. If the heat input is within the specified range, the temperature and time can be freely selected. In any case, heat exchange is excellent in corrugating formability, strength after brazing heating, corrosion resistance and brazing. A fin material can be obtained.

で表すことができる。焼鈍全回数の合計の入熱量Ｔは、以下の実施例の結果を参酌して１０〜６００００とすることが好ましい。 (Total heat input T of all annealing times)
Furthermore, the total heat input T of all times when annealing is performed a plurality of times,

Can be expressed as The total heat input T of the total number of annealing is preferably 10 to 60000 in consideration of the results of the following examples.

(rolling)
In this manufacturing method, the final rolling reduction in cold rolling is specified as 20 to 50%. If the final rolling rate is less than 20%, the driving force for recrystallization during brazing heating is reduced, and erosion may occur without sufficient recrystallization. On the other hand, if the final rolling ratio exceeds 50%, the strength before brazing heating becomes high, and there is a possibility that corrugated formability cannot be ensured, or that recrystallization after brazing heating becomes extremely fine and brazing property cannot be ensured. is there.

(effect)
According to this production method, as long as the heat input by individual annealing and the range of heat input by total annealing are satisfied, the corrugated formability and sacrificial anode effect are excellent regardless of the number of annealing, and high strength after brazing heating. Thus, it is possible to provide an aluminum alloy fin material for a heat exchanger that has excellent brazing properties and corrosion resistance.

Below, the effect of the present invention is explained in detail based on an example.
First, using the alloy having the composition shown in Table 2, a plate-shaped ingot was obtained by a twin-roll continuous casting and rolling method. In Table 2, (*) indicates that it is outside the range defined in the present invention.

Next, the plate-shaped ingot was subjected to annealing and cold rolling under the conditions shown in Table 3.
Table 3 shows the heat input in the annealing process and the final rolling rate in the rolling process. In this embodiment, the number of annealing times is three. Further, the final plate thickness of the fin material is 0.05 mm. Note that (*) in Table 3 indicates that it is outside the range defined in the present invention.

The obtained fin material was brazed and heated at 600 ° C. for 3 minutes with a single fin material, and the following performances (a) to (f) of the fin material were investigated. This brazing heating condition is a commonly performed condition. Table 4 shows the evaluation results. Note that (*) in Table 4 indicates that compositions and processes outside the range defined in the present invention are included.

(A) Strength before brazing heating: If the strength before brazing heating is too high, the corrugated formability is impaired. Therefore, the strength before brazing heating is preferably 230 MPa or less. For this reason, (*) was attached | subjected about what exceeds 230 Mpa.

(B) Solidus temperature: When the solidus temperature is low, there is a concern that the fin melts during brazing heating. Therefore, since it is desirable that the solidus temperature is 610 ° C. or higher, (×) is given to those below 610 ° C. The solidus temperature was determined by DSC measurement.

(C) Strength after brazing heating: The higher the strength after brazing heating, the better the durability of the heat exchanger. Therefore, it is desirable that the strength after brazing heating is 130 MPa or more. For this reason, (x) was attached | subjected to the thing below 130 MPa.

(D) Brazing diffusivity: When the amount of brazing erosion to the fin is large, there is a problem that the durability and heat exchange performance of the heat exchanger are lowered, and the size of the heat exchanger after brazing heating is not as intended. . The evaluation of wax diffusion was performed as follows. A core for evaluation was prepared using a fin material corrugated with a width of 16 mm, a height of 5 mm, and a pitch of 3 mm, and a brazing sheet with a thickness of 0.5 mm clad with JIS4045 brazing material at a ratio of 5% to the core of JIS3003. After the assembly and brazing, the cross section of the evaluation core was micro-observed with an optical microscope to confirm the presence or absence of brazing. Those with no wax erosion were marked with “○”, and those with wax erosion were marked with “x”.

(E) Natural potential: When the natural potential becomes noble, the sacrificial anode effect is small, and the corrosion resistance of the heat exchanger cannot be ensured. If the natural potential after brazing heating is −720 mV or less, it is judged that the fin material has a sufficient sacrificial anode effect, and in Table 4, “◯” indicates. When the natural potential exceeded −720 mV, it was determined that the sacrificial anode effect was not sufficient, and “x” was assigned. The measurement of the natural potential was performed in a 5% NaCl aqueous solution at 25 ° C. with the measurement solution at 25 ° C. using Ag / AgCl (s) as a reference electrode.

(F) Self-corrosion rate: When the self-corrosion rate of the fin material is fast, the time for maintaining the shape as fins in the heat exchanger is shortened, so that the durability and corrosion resistance of the heat exchanger are lowered. In accordance with JIS Z2371, a 200 hour salt spray test was performed, and then the corrosion reduction amount was measured, and the ratio of the corrosion reduction amount to the original sample mass was used as an index of the self-corrosion rate (corrosion loss). If the corrosion weight loss was less than 5%, it was judged that there was a practically sufficient self-corrosion rate. For this reason, (x) was given to 5% or more.

  According to the results of Table 4, Invention Example No. 1 to 54 have low strength and high solidus temperature before brazing heating, but high strength, low brazing diffusion, low natural potential, and low conductivity after brazing heating. It was found to be high and have little corrosion weight loss. Thereby, invention example No. In 1-54, while being excellent in corrugate moldability, it was difficult to melt during brazing heating, and it was confirmed that the strength after brazing heating was high.

On the other hand, Comparative Example No. In 55-70, any of the performance required as an aluminum alloy fin material for heat exchangers was missing or insufficient. That is, no. No. 55 had a high Si content, so the solidus temperature decreased.
No. No. 56 had a low Si content, so the strength after brazing heating was low.
No. Since No. 57 had a large Fe content, coarse crystals were generated during casting.
No. No. 58 was inferior in strength after brazing heating because the Fe content was small, and the crystal grains after brazing heating became fine and inferior in wax diffusibility.
No. No. 59 had a large Mn content, so that coarse crystals were generated during casting.
No. Since No. 60 had a low Mn content, the strength after brazing heating was inferior, the crystal grains after brazing heating became fine, and the brazing diffusivity was inferior.
No. 61 had a high Zn content and was inferior in self-corrosion resistance.
No. No. 62 had a small Zn content, and the natural potential became noble, and a sufficient sacrificial anticorrosive effect could not be secured.
No. Since 63 had too much heat input by one annealing, the intensity | strength after brazing heating fell.
No. Since No. 64 has a large amount of heat input due to the total annealing, the strength after brazing heating was lowered.
No. In 65 and 66, since the amount of heat input by one annealing was small, the material was not sufficiently softened and the strength before brazing heating was high.
No. 67 and no. Since No. 69 had a low final rolling rate, brazing diffusion occurred.
No. 68 and no. Since No. 70 had a high final rolling rate, crystal grains after brazing heating were refined and brazing diffusion occurred.

  From the above results, according to the present invention, the strength before brazing heating is low, the corrugated formability is excellent, the solidus temperature is high, it is difficult to melt during brazing heating, the strength after brazing heating is high, and the heat exchanger core. The heat exchanger core performance is less likely to be reduced due to less brazing diffusion, low natural potential, sufficient sacrificial anti-corrosion effect, high conductivity after brazing, low corrosion loss It turned out that the aluminum alloy fin material for heat exchangers excellent in self-corrosion resistance can be provided.

Claims (4)

In mass%, Si is 1.0 to 1.8%, Fe is 0.3 to 0.9%, Mn is 1.0 to 1.8%, Zn is 0.5 to 2.0%, and the balance is Al. The aluminum alloy ingot cast using an aluminum alloy composed of unavoidable impurities is subjected to at least one annealing and one or more cold rolling, and the i-th annealing calculated by the following formula 1 The heat input Ai (° C./h) per rotation is 10 or more and 40000 or less,

And the final rolling reduction rate in the said cold rolling shall be 20 to 50% of range, The manufacturing method of the aluminum alloy fin material for heat exchangers characterized by the above-mentioned. 2. The method for producing an aluminum alloy fin material for a heat exchanger according to claim 1, wherein the total heat input T calculated by the following formula 2 is 10 or more and 60000 or less.

  The said casting is performed by the twin roll type continuous casting rolling method, The manufacturing method of the aluminum alloy fin material for heat exchangers of Claim 1 or 2 characterized by the above-mentioned.   The method for producing an aluminum alloy fin material for a heat exchanger according to any one of claims 1 to 3, wherein the final plate thickness is 0.04 to 0.2 mm.

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