JP7152352B2 - Aluminum alloy fins and heat exchangers with excellent strength, formability, and corrosion resistance - Google Patents

Description

TECHNICAL FIELD The present invention relates to an aluminum alloy fin stock and a heat exchanger which are excellent in strength, formability and corrosion resistance.

As heat exchangers mounted on automobiles and the like are becoming lighter, the thickness of each aluminum member is being reduced. As for the fin material, it is necessary to increase the strength of the material in order to achieve thinning. However, when the strength of the fin material is increased, it becomes difficult to manufacture fins having the correct fin height and fin pitch during corrugation.
In addition, when a heat exchanger is mounted on a vehicle, it is necessary to maintain the rigidity of the heat exchanger. Corrosion resistance of the fin itself is also important.

For example, Patent Document 1 proposes an aluminum alloy fin material for a heat exchanger that has good corrosion resistance, low tensile strength before brazing, high tensile strength after brazing, and good thermal conductivity.
In Patent Document 2, focusing on the density of the second phase particles before brazing, it has good corrugation formability and excellent strength after brazing addition heat, and is particularly suitable for fins of heat exchangers for automobiles. An aluminum alloy fin material that can be used for fins and a method for producing the same have been proposed.
Patent Literature 3 proposes an aluminum alloy fin material having excellent brazeability and sag resistance through component design, and a method for producing the same.
Patent Literature 4 proposes a fin stock that is excellent in strength and brazeability after brazing by designing components and a reinforcing mechanism.

JP 2012-211393 A JP 2015-14034 A JP 2015-218343 A JP 2016-121393 A

However, even with conventional methods, it is difficult to achieve a good balance between formability, strength, and corrosion resistance, and it has not been possible to obtain a fin material having good properties in all of formability, strength after brazing, and corrosion resistance. .

The present invention has been made against the background of the above circumstances, and is capable of being thinned while providing a fin having excellent strength. It is an object of the present invention to provide a fin which is excellent in corrosion resistance.

According to the present invention, an aluminum alloy fin material and a heat exchanger having desired properties can be obtained by selecting an alloy composition and an appropriate manufacturing process.
That is, among the inventions of the aluminum alloy fin material excellent in strength, formability, and corrosion resistance of the present invention, the first form has, in mass%, Mn: 1.2 to 2.0%, Si: 0.5 to 1.3%, Cu: 0.05 to 0.13%, Fe: 0.1 to 0.5%, Zn: 0.5 to 3.0%, the balance being Al and inevitable impurities. on the surface of the fin material before corrugating, there are 10 to 200 grains/ ^cm2 with an equivalent circle diameter of 500 μm or more, and 90% or more of them are longer in the rolling direction than in the width direction. , a tensile strength of 200 to 250 MPa, an elongation of 1.0 to 5.0%, and a tensile strength of 140 MPa or more after a heat treatment equivalent to brazing at 600 ° C. for 3 minutes, and a neutral salt spray test Corrosion weight loss after 16 weeks is 150 mg/dm ² or less.

Another aspect of the invention of an aluminum alloy fin material for a heat exchanger that is excellent in strength, formability, and corrosion resistance is the invention of the aspect described above, wherein the aluminum alloy further comprises, in mass%, Ti: 0.01 to 0.20. %, Cr: 0.01 to 0.20%, Mg: 0.01 to 0.20%, and Zr: 0.01 to 0.20%. do.

Another aspect of the invention of an aluminum alloy fin material for a heat exchanger that is excellent in strength, formability, and corrosion resistance is the invention of the aspect described above, wherein the solidus temperature before brazing addition heat is 615 ° C. or higher, and after the heat treatment equivalent to brazing is −800 mV or more and −730 mV or less vs Ag/AgCl.

Another aspect of the invention of an aluminum alloy fin material for a heat exchanger having excellent strength, formability, and corrosion resistance is the invention of the aspect described above, wherein the recrystallization completion temperature before brazing is 450°C or less ,
The recrystallization completion temperature is obtained by cooling immediately after reaching 300 to 550 ° C. at a temperature increase rate of 100 ° C./min before brazing, and the yield strength value measured at room temperature is the yield strength value after the heat treatment equivalent to brazing. It is characterized by a temperature that begins to decrease to within +20% compared to .

A first aspect of the heat exchanger of the present invention is characterized by including the aluminum alloy fin material for a heat exchanger according to any one of the above aspects.

The reasons for limiting the components and the like defined in the present invention and their effects will be described below.

・Mn: 1.2 to 2.0% by mass
Mn precipitates an Al--Mn--Si compound and is added to obtain strength after brazing due to dispersion strengthening. If the Mn content is less than 1.2%, the effect of dispersion strengthening by the Al—Mn—Si intermetallic compound is small, and the desired strength after brazing cannot be obtained. On the other hand, if the content exceeds 2.0%, there is a concern that the Al—Mn-based giant intermetallic compound will crystallize during casting, leading to breakage during rolling. Moreover, the solid solubility in the matrix increases, the solidus temperature (melting point) decreases, and the fins may melt during brazing, which is not preferable. For these reasons, the Mn content is set within the above range. For the same reason, it is desirable that the Mn content has a lower limit of 1.4% and an upper limit of 1.8%.

・Si: 0.5 to 1.3% by mass
Si precipitates an Al--Mn--Si based intermetallic compound and is added in order to obtain strength after brazing by dispersion strengthening. If the Si content is less than 0.5%, the Al--Mn--Si based intermetallic compound has little dispersion strengthening effect, and the desired strength after brazing cannot be obtained. On the other hand, when the content exceeds 1.3%, the solid solubility in the matrix increases, the solidus temperature (melting point) decreases, and the fin may melt during brazing, which is not preferable. For these reasons, the Si content is set within the above range. For the same reason, it is desirable that the lower limit of the Si content is 0.7% and the upper limit is 1.2%.

・Cu: 0.05 to 0.13% by mass
Cu exists as a solid solution in the Al matrix or as an Al--Cu compound. If the Cu content is less than 0.05%, the contribution of solid solution strengthening to the strength after brazing is small. On the other hand, when the content exceeds 0.13%, the θ-CuAl ₂ stable phase and the θ′-CuAl ₂ metastable phase, which are nobler in potential than the matrix, are present as compounds, which become starting points for corrosion and lower the corrosion resistance, which is preferable. do not have. For these reasons, the Cu content is set within the above range. For the same reason, it is desirable that the lower limit of the Cu content is 0.07% and the upper limit is 0.12%.

・ Fe: 0.1 to 0.5% by mass
Fe crystallizes and precipitates Al--Fe-based and Al--Fe--Si-based intermetallic compounds, and is added to obtain strength after brazing due to dispersion strengthening. If the content is less than 0.1%, the effect is small and the desired strength after brazing cannot be obtained. In addition, since the use of high-purity ingots is limited, the cost increases, which is not preferable. On the other hand, when the content is 0.5% or more, the Al--Fe and Al--Fe--Si compounds act as starting points for corrosion, which lowers the corrosion resistance, which is not preferable. For these reasons, the Fe content is set within the above range. For the same reason, it is desirable that the Fe content has a lower limit of 0.15% and an upper limit of 0.45%.

・Zn: 0.5 to 3.0% by mass
Zn has the effect of forming a solid solution in the Al matrix to make the potential base, and is added to obtain the sacrificial anode effect of the fin. However, if the content is less than 0.5%, the effect of making the potential less base is small, and the desired sacrificial anode effect cannot be obtained, resulting in a large erosion depth of the combined tube. On the other hand, if the content exceeds 3.0%, the potential becomes excessively base, and the self-corrosion resistance of the fin deteriorates, which is not preferable. For these reasons, the Zn content is set within the above range. For the same reason, it is desirable that the lower limit of the Zn content is 0.8% and the upper limit is 2.5%.

・Ti, Cr, Mg, Zr: 0.01 to 0.20% by mass
Ti, Cr, Mg, and Zr form an intermetallic compound with aluminum and improve the strength by dispersion strengthening and solid solution strengthening, so one or more of them are contained if desired. However, when each content is less than the lower limit, the effect on dispersion strengthening and solid solution strengthening is small, and the effect of improving the strength is small. On the other hand, if Ti, Cr, and Zr exceed their respective upper limits, there is a concern that a giant intermetallic compound will crystallize during casting of the ingot, leading to breakage during rolling. Moreover, when Mg exceeds the upper limit, the brazeability deteriorates. Therefore, each content is defined in the above range. For the same reason, Ti, Cr, Mg, and Zr preferably have a lower limit of 0.03% and an upper limit of 0.15%.
Even when these elements are not actively added, they may be contained as impurities in an amount of less than 0.01%.

・On the surface of the fin material before corrugating, there are 10 to 200 crystal grains/cm ² with an equivalent circle diameter of 500 μm or more, and 90% or more of them have a structure that is longer in the rolling direction than in the width direction.
If the number of crystal grains with an equivalent circle diameter of 500 μm or more is 10/cm ² or less on the surface of the fin material before corrugating, the anisotropic effect of each crystal during corrugating is affected by the large size of each crystal grain in the plane. This is not preferable because the height of the crests of the fins after molding becomes uneven. On the other hand, if it exceeds 200/cm ² , there are many small crystal grains, so in high-speed corrugation molding, the increase in tension generated during unwinding may cause instantaneous breakage from the grain boundaries. . Also, small crystal grains are not preferable because they are inferior in erosion resistance during brazing. In addition, 90% or more of them have a structure that is longer in the rolling direction than in the width direction, and by matching the longitudinal direction of corrugated molding, anisotropic effects during corrugated molding can be eliminated, resulting in formability. have the effect of contributing to the improvement of
The above specification can be achieved by the continuous casting and rolling method, homogenization treatment, manufacturing process conditions such as rolling reduction, and the like.

・Tensile strength is 200-250MPa, elongation is 1.0-5.0%
If the tensile strength is less than 200 MPa before corrugating, it is not preferable because it deforms against the load during assembly of the heat exchanger. On the other hand, if the tensile strength exceeds 250 MPa, it becomes difficult to obtain the desired fin shape, fin height, and fin pitch for high-speed corrugating. It is also important to have an appropriate elongation in order to improve formability. If the elongation is less than 1.0%, breakage often occurs during unrolling or forming during corrugation. On the other hand, if the elongation exceeds 5%, it is not preferable because burrs are often generated when the fins are louvered. For these reasons, the tensile strength and elongation before corrugating are specified within the above ranges. For the same reason, it is desirable to set the lower limit to 205 MPa and the upper limit to 245 MPa for tensile strength, and the lower limit to 1.5% and the upper limit to 4.0% for elongation.
The above stipulations can be achieved by manufacturing process conditions such as rolling reduction.

・Tensile strength of 140 MPa or more after additional brazing heat As heat exchangers become lighter, thin fins with high strength are required. If the strength of the fins after brazing is low, the repeated vibrations and expansion and compression of the cooling water that are applied to the heat exchanger when mounted on a vehicle cannot be suppressed, and the tubes expand in a drum-like shape, leading to premature breakage or internal cooling. lead to water leakage. Therefore, the strength of the fin material is required, and the tensile strength after brazing addition heat is defined within the above range. For the same reason, 145 MPa or more is more desirable.
The above definition can be achieved by adjusting the homogenization treatment conditions, adjusting the number density of Al--Mn--Si compounds, and the like. The adjustment of the number density of the Al--Mn--Si compound can be carried out by adjusting the homogenization treatment conditions.
The tensile strength after the brazing heat can be measured after a brazing-equivalent heat treatment held at 600° C. for 3 minutes. This brazing-equivalent heat treatment is for making measurements by simulating standard brazing, and is not intended to limit the brazing conditions for the aluminum alloy fin material of the present invention.

・Corrosion weight loss after 16 weeks in a neutral salt spray test after brazing heat is 150 mg/dm ² or less In order to ensure the self-corrosion resistance of the fin material, a neutral salt spray test in accordance with JIS Z2371 (2015) is used. It is desirable that the corrosion weight loss of the measured fin material after 16 weeks is 150 mg/dm ² or less. If the corrosion weight loss after 16 weeks is 150 mg/dm ² or less, it is possible to suppress performance deterioration and partial dropout due to corrosion of the fins themselves even in an actual usage environment, so the characteristics as a heat exchanger can be maintained. be able to.
The above definition can be achieved by designing the composition of Fe, Cu, and the like.

・The solidus temperature is 615°C or higher The higher the solidus temperature of the fin material, the easier it is to braze. In the case of a normal brazing method, if the temperature is 615° C. or higher, brazing can be performed without melting the fins, and the solidus temperature of the fin material is defined as desired. The solidus temperature can be set by component design.

・Potential after brazing heat is -800 mV or more and -730 mV or less (vs Ag/AgCl)
If the potential of the fin material is less than −800 mV, the potential becomes excessively base (low) with respect to other members (eg, tubes and plate materials) to be joined, which accelerates corrosion of the fins due to galvanic corrosion. If the potential of the fin material exceeds −730 mV, a sufficient potential difference cannot be obtained for other members to be joined, and the sacrificial anode effect cannot be obtained. In this case, for example, tube corrosion is accelerated. For the above reason, the potential of the fin material is set within the above range as desired. More preferably, it is -735 mV or less.
The above definition can be achieved by designing the composition of Cu, Zn, and the like.

・Recrystallization is completed by 450°C during brazing heat The recrystallization temperature range during brazing heat greatly affects the brazeability of the fin. Brazing heat is generally tested in the temperature range of around 600°C, but if the recrystallization completion temperature exceeds 450°C, structural changes during recrystallization and the resulting reduction in strength at high temperatures are large, resulting in high-temperature creep. As the sag increases, the sag property decreases greatly, and the brazing properties also deteriorate accordingly. Therefore, it is desirable that the recrystallization temperature range during brazing addition heat be 450° C. or less. The recrystallization completion temperature is defined as the temperature at which the yield strength value starts to decrease to within +20% of that after brazing heat.
The above specification can be achieved by the continuous casting and rolling method, homogenization treatment, manufacturing process conditions such as rolling reduction, and the like.

As described above, according to the present invention, it is possible to obtain a fin and a heat exchanger that are excellent in formability, strength after brazing, and corrosion resistance.

It is a perspective view showing a part of heat exchanger in one embodiment of the present invention.

An embodiment of the present invention will be described below.
The aluminum alloy fin material of the present embodiment is cast using continuous casting (CC method) such as a twin roll casting machine, and the cast plate is subjected to homogenization, cold rolling, and intermediate annealing. It can be manufactured through
That is, in mass%, Mn: 1.2 to 2.0%, Si: 0.5 to 1.3%, Cu: 0.05 to 0.13%, Fe: 0.1 to less than 0.5% , Zn: 0.5 to 3.0%, optionally, further optionally, in mass%, Ti: 0.01 to 0.20%, Cr: 0.01 to 0.20%, Mg : 0.01 to 0.20%, Zr: 0.01 to 0.20%, containing one or more of 0.01 to 0.20%, with the balance being Al and inevitable impurities. Obtain an aluminum alloy cast plate by the method.

The obtained aluminum alloy ingot or cast plate must be homogenized under appropriate conditions. The homogenization treatment can be performed, for example, under the heat treatment conditions of a heating rate of 50° C./hour, a holding temperature of 400 to 500° C., a holding time of 1 to 10 hours, and a cooling rate of 10 to 100° C./hour. . As a result, the Al--Mn--Si based intermetallic compound can be uniformly dispersed in the matrix. Compounds of this type improve the strength after brazing by dispersion strengthening, and also contribute to the improvement of corrosion resistance because the potential difference with respect to the matrix is small.

After that, cold rolling is performed on the obtained aluminum alloy. During cold rolling, intermediate annealing can be performed after the rolling reduction reaches 60% or more. Intermediate annealing is performed at a temperature of 200 to 350 ° C. and a holding time of 2 to 8 hours. becomes. By setting the homogenization treatment, intermediate annealing, and cold rolling rate within the above range, the tensile strength and elongation before brazing are within the target range of the present invention, and a crystal structure state excellent in corrugation can be obtained. can. The plate thickness can be 35 to 80 μm, but the present invention is not limited to this thickness.
Through the above steps, it is possible to obtain a heat exchanger fin material having desired strength before, during, and after brazing, and a crystal structure before and after brazing.

The obtained fin material is excellent in formability, strength, corrosion resistance, and brazeability, and is suitable as a fin material for heat exchangers.

The obtained fin material is corrugated. At that time, it has a correct fin height and fin pitch due to good moldability, so it can be used for heat exchangers such as headers, tubes, and side plates. Excellent brazing jointability in combination with other materials.
In the present invention, the brazing heat treatment conditions and methods (brazing temperature, atmosphere, presence or absence of flux, type of brazing material, etc.) are not particularly limited, and brazing can be performed by a desired method. The temperature is raised from room temperature to 600 ° C. at an average temperature increase rate of 100 ° C./min, held at 600 ° C. for 3 minutes, and then cooled at a temperature decrease rate of 100 ° C./min. The fins have excellent strength and corrosion resistance, and thus contribute to high performance as a heat exchanger.
FIG. 1 shows a heat exchanger 1 manufactured by assembling tubes 3, headers 2, and side plates 5 to fins 4 of this embodiment and brazing them.

According to this embodiment, it is possible to obtain an aluminum alloy fin material for a heat exchanger and a heat exchanger that are excellent in formability, strength, corrosion resistance, and brazeability.

Examples of the present invention are described below.
A continuously cast rolled sheet was produced from a molten metal adjusted to have the components shown in Table 1 (balance Al and inevitable impurities) using the CC method. The obtained cast plate was subjected to homogenization treatment, and then subjected to cold rolling and intermediate annealing in intermediate steps. Intermediate annealing was performed at 200 to 350° C. for 2 to 8 hours to produce a fin material of 35 to 80 μm with H14 refining.
A tensile test was performed on the obtained fin material to confirm mechanical properties (tensile strength, elongation). Next, the sample surface is etched with a mixed solution of hydrochloric acid, hydrofluoric acid, and nitric acid to expose the crystal grains, and a surface photograph of a 12 mm (parallel to the rolling direction) × 9 mm (perpendicular to the rolling direction = plate width direction) field of view is taken. I took a picture. For each crystal structure, the length parallel to the rolling direction and the length perpendicular to the rolling direction are calculated by image processing, and the number of crystal grains with a circle equivalent diameter of 500 μm or more per 1 cm ² and the ratio of crystal grains that are “parallel to the rolling direction > perpendicular to the rolling direction” %” was calculated.
The solidus temperature was measured using a differential scanning calorimetry (DSC) at a heating rate of 10°C/min.
Next, corrugated fins were manufactured by carrying out corrugated molding after setting conditions by a preliminary test for fins of each plate thickness. For 20 randomly measured points, when the fin height and fin pitch were within ±10% of the target value, the difference was evaluated as ⊚, when the difference was within ±20%, and as x otherwise.

After that, in the state of a veneer that has not been corrugated, a tensile test is performed at room temperature on the plate that has been cooled immediately after reaching 300 to 550 ° C. at a heating rate of 100 ° C./min, and the recrystallization completion temperature during brazing addition heat is determined. It was measured.
Similarly, in the state of a single plate, brazing heat treatment was performed under the conditions of a heating rate of 100 ° C./min, a holding at 600 ° C. for 3 minutes, and a cooling rate of 100 ° C./min, and the mechanical properties after brazing were confirmed. .
In addition, after coating the surface with a fluoride-based flux, the veneers subjected to brazing heat treatment under the same conditions as above were subjected to potential measurement and a neutral salt spray test, and the corrosion weight loss after 16 weeks was investigated.

A sample for potential measurement is cut out from a fin material subjected to heat treatment equivalent to brazing, and the sample is immersed in a 5% NaOH solution heated to 50 ° C. for 30 seconds, and then immersed in a 30% HNO ₃ solution for 60 seconds, Furthermore, it was washed with tap water and ion-exchanged water, and the potential was measured after being immersed in a 5% NaCl solution (adjusted to pH 3 with acetic acid) at 25° C. for 60 minutes without drying. A silver-silver chloride electrode (Ag/AgCl) was used as a reference electrode.

The produced fin material was corrugated, combined with other members (header plate, tube, side plate), assembled into a mold, flux was applied and brazed to produce a heat exchanger measuring 50 cm long and 50 cm wide. After that, the joints between the fins and tubes of the heat exchanger were observed, and the number of defective joints was obtained. ) was calculated. The brazeability was evaluated with a bonding rate of 90% or more as ⊚ (good bonding state) and a bonding rate of 90% or less as x (poor bonding).

The inventive material was excellent in formability, strength and corrosion resistance. On the other hand, Comparative Examples were inferior in any of these properties. i.e.
Comparative Example 1; Low tensile strength after brazing Comparative Example 2; High tensile strength before brazing, inferior corrugate formability Comparative Example 3; Low tensile strength after brazing Comparative Example 4; Comparative Example 5 with low phase line temperature; Comparative Example 6 with low tensile strength after brazing; Low elongation before brazing, inferior corrugation formability Comparative Example 7; Example 9: Base potential, inferior corrosion resistance Comparative Example 10; High tensile strength before brazing, high elongation, inferior corrugate formability Comparative Example 11; Broken during rolling Comparative Example 12; 13; Poor corrosion resistance Comparative Example 14; Few crystal grains with an equivalent circle diameter of 500 μm or more, poor corrugation formability Comparative Example 15; Broken during rolling Comparative Example 16; Low elongation before brazing, poor corrugation formability Comparative Example 17: Broken during rolling Comparative Example 18: High tensile strength before brazing, inferior corrugation formability Comparative Example 19; Low elongation before brazing, inferior corrugation formability Comparative Example 20; Equivalent to a circle Comparative Example 21, which has many crystal grains with a diameter of 500 μm or more and is inferior in corrugation formability;

1 heat exchanger 2 header 3 tube 4 fin 5 side plate

Claims (5)

In mass %, Mn: 1.2 to 2.0%, Si: 0.5 to 1.3%, Cu: 0.05 to 0.13%, Fe: 0.1 to 0.5%, Zn: Made of an aluminum alloy having a composition containing 0.5 to 3.0% and the balance being Al and inevitable impurities,
On the surface of the fin material before corrugating, there are 10 to 200 crystal grains/cm ² with an equivalent circle diameter of 500 μm or more, and 90% or more of them have a structure that is longer in the rolling direction than in the width direction, and have a tensile strength. is 200 to 250 MPa, and the elongation is 1.0 to 5.0%,
Strength and formability characterized by having a tensile strength of 140 MPa or more after a heat treatment equivalent to brazing at 600 ° C. for 3 minutes, and a corrosion weight loss of 150 mg / dm ² or less after 16 weeks in a neutral salt spray test. , and aluminum alloy fin material with excellent corrosion resistance. The aluminum alloy further contains, in mass%, Ti: 0.01 to 0.20%, Cr: 0.01 to 0.20%, Mg: 0.01 to 0.20%, Zr: 0.01 to 2. The aluminum alloy fin material for a heat exchanger excellent in strength, formability and corrosion resistance according to claim 1, characterized by containing one or more of 0.20%. The strength according to claim 1 or 2, characterized in that the solidus temperature before brazing is 615 ° C. or higher, and the potential after the brazing equivalent heat treatment is −800 mV or more and −730 mV or less vs Ag/AgCl, Aluminum alloy fin material for heat exchangers with excellent formability and corrosion resistance. The recrystallization completion temperature before brazing is 450 ° C. or less ,
The recrystallization completion temperature is obtained by cooling immediately after reaching 300 to 550 ° C. at a temperature increase rate of 100 ° C./min before brazing, and the yield strength value measured at room temperature is the yield strength value after the heat treatment equivalent to brazing. The aluminum alloy fin material for heat exchangers excellent in strength, formability and corrosion resistance according to any one of claims 1 to 3, characterized in that the temperature starts to decrease to within +20% compared to . A heat exchanger comprising the aluminum alloy fin material for a heat exchanger according to any one of claims 1 to 4.

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