JP2005002383A - Method of producing high strength aluminum alloy fin material for heat exchanger - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of producing an aluminum alloy fin material for a heat exchanger having high strength and thermal conductivity after brazing and excellent in sagging resistance, erosion resistance, self-corrosion resistance and sacrificial anode effect. <P>SOLUTION: From molten metal having a composition comprising, by weight, 0.5 to 1.5% Si, 0.15 to 1.0% Fe, 0.8 to 3.0% Mn and 0.5 to 2.5% Zn, and in which the content of Mg as impurities is limited to ≤0.05%, and the balance Al with ordinary impurities, a thin slab with a thickness of 5 to 10 mm is continuously cast by a double belt type casting machine. The slab is rolled round a roll, is thereafter cold-rolled to a sheet thickness of 0.08 to 2.0 mm, is subjected to intermediate annealing at a holding temperature of 350 to 500°C, and is cold-rolled at a cold rolling ratio of 50 to 96% to a final sheet thickness of 40 to 200 μm. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００３３】
【表２】

【００３４】
表２の結果から、本発明の製造方法によるフィン材は従来の製造方法による比較フィン材に比べて、ろう付け後の抗張力、ろう付け後の導電率、耐サグ性、自己耐食性および耐エロージョン性のいずれも良好であることが判る。
【００３５】
〔実施例２〕
実施例１で得られた双ベルト鋳造スラブを分割し、表３に示した各中間焼鈍板厚まで冷間圧延した後、表３に示した各温度まで昇温速度５０℃／ｈｒで加熱し、２時間保持、冷却速度５０℃／ｈｒ（１００℃まで）の中間焼鈍を施して軟化させた。次いで該板を表３に示した最終冷延率で冷間圧延して厚さ８０μｍのフィン材とした。これらフィン材について、実施例１に示した方法で、ろう付け後の結晶粒径、ろう付け後の抗張力、耐サグ性、および耐エロージョン性を評価した結果を表４に示す。
【００３６】
【表３】

【００３７】
【表４】

【００３８】
表より、本発明方法で製造されたフィン材番号１、２、および４は、ろう付け後の抗張力、耐サグ性、および耐エロージョン性のいずれも良好であるのに対し、最終冷延率の少ないフィン材番号３は、ろう付け後の再結晶粒が超粗大なため抗張力が低くなり、中間焼鈍温度が高いフィン材番号５は、ろう付け後の再結晶粒が小さくなるため、耐サグ性と耐エロージョン性が劣っていることが分かる。
【００３９】
【発明の効果】
本発明によれば、ろう付け後において高い強度と熱伝導度を有し、耐サグ性、耐エロージョン性、自己耐食性、犠牲陽極効果に優れた熱交換器用アルミニウム合金フィン材の製造方法が提供される。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing an aluminum alloy fin material for heat exchangers with excellent brazing properties, and more specifically, a fin and a working fluid passage constituent material are joined by brazing such as a radiator, a car heater, and a car air conditioner. Aluminum alloy fin material used for heat exchangers, with high strength and thermal conductivity after brazing, and excellent erosion resistance, sag resistance, sacrificial anode effect, and self-corrosion resistance The present invention relates to a method for manufacturing a material.
[0002]
[Prior art]
Heat exchangers for automobile radiators, air conditioners, intercoolers, oil coolers, etc. are composed of working fluid passage materials composed of Al-Cu alloys, Al-Mn alloys, Al-Mn-Cu alloys, and Al-Mn alloys. It is assembled by brazing alloy fins. The fin material is required to have a sacrificial anode effect in order to prevent the working fluid passage constituent material from being corroded, and has excellent sag resistance and resistance to prevent deformation due to high temperature heating during brazing and penetration of the braze. Erosion is required.
[0003]
The reason why Al-Mn aluminum alloys such as JIS 3003 and JIS 3203 are used as the fin material is that Mn acts effectively to prevent deformation during brazing and erosion of the brazing. In order to impart the sacrificial anode effect to the Al—Mn alloy fin material, a method of adding Zn, Sn, In, or the like to this alloy to make it electrochemically base (Patent Document 1 (Japanese Patent Laid-Open No. 62-120455)). In order to further improve the high temperature buckling resistance (sag resistance), a method in which an Al—Mn based alloy contains Cr, Ti, Zr, etc. 50-118919)).
[0004]
Recently, however, there has been an increasing demand for weight reduction and cost reduction of heat exchangers, and it has become necessary to further reduce the thickness of heat exchanger constituent materials such as working fluid passage constituent materials and fin materials. For example, if the fins are made thinner, the heat transfer cross-sectional area becomes smaller and the heat exchange performance deteriorates, causing problems in the strength and durability of the heat exchanger as a product. Further improvements in strength, sag resistance, erosion resistance, and self-corrosion resistance are desired.
[0005]
The conventional Al-Mn alloy has a problem that the thermal conductivity is lowered because Mn is dissolved by heating during brazing. As a fin material that solves this difficulty, an aluminum alloy that limits the Mn content to 0.8 wt% or less and contains Zr 0.02 to 0.2 wt% and Si 0.1 to 0.8 wt% has been proposed (patent) Reference 3 (Japanese Patent Publication No. 63-23260)). This alloy has improved thermal conductivity, but because Mn is low, the strength after brazing is not sufficient, fins are liable to collapse and deform during use as a heat exchanger, and the potential is not sufficiently low. However, the sacrificial anode effect is small.
[0006]
On the other hand, by increasing the cooling rate when casting the slab from the molten aluminum alloy, the intermetallic compound crystallized at the stage of the slab even if the Si, Mn content, etc. is 0.05 to 1.5% by mass. It has become possible to reduce the size to a maximum value of 5 μm or less, and a proposal has been made to improve the fatigue characteristics of the fin material through a rolling process from such a slab (Patent Document 4 (Japanese Patent Laid-Open No. 2001-226730). Publication)). However, the present invention is intended to improve the fatigue life, and although there is a description of thinning the casting slab as a means for increasing the cooling rate when casting the slab, it is a twin belt casting on an actual operation scale. There is no specific disclosure of thin slab continuous casting by machine.
[Patent Document 1]
Japanese Patent Laid-Open No. 62-120455 (Claims)
[Patent Document 2]
JP 50-118919 A (Claims)
[Patent Document 3]
Japanese Patent Publication No. 63-23260 (Claims)
[Patent Document 4]
JP 2001-226730 A (Claims)
[0007]
[Problems to be solved by the invention]
An object of the present invention is to provide a method for producing an aluminum alloy fin material for a heat exchanger that has high strength and thermal conductivity after brazing and is excellent in sag resistance, erosion resistance, self-corrosion resistance, and sacrificial anode effect. That is.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the method for producing an aluminum alloy fin material for a heat exchanger according to the present invention includes Si 0.5 to 1.5 wt%, Fe 0.15 to 1.0 wt%, and Mn 0.8 to 3.0 wt%. , Containing 0.5 to 2.5 wt% of Zn, further limiting Mg as an impurity to 0.05 wt% or less, and using a double belt casting machine to melt a molten metal composed of ordinary impurities and Al with a thickness of 5 to 10 mm. After thin slabs are continuously cast and wound on a roll, they are cold-rolled to a thickness of 0.08 to 2.0 mm, subjected to intermediate annealing at a holding temperature of 350 to 500 ° C., and a cold rolling rate of 50 to 96%. Cold rolling is performed to obtain a final thickness of 40 μm to 200 μm.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
In order to develop an aluminum alloy fin material that satisfies the requirements for thinning the heat exchanger fin material, the present inventor is concerned with strength characteristics, heat transfer performance, sag resistance, erosion resistance, self-corrosion resistance, and sacrificial anode effect. As a result of studying optimization of the composition, intermediate annealing conditions, and rolling reduction while comparing the rolling material from the conventional DC slab casting and the rolling material from the twin belt type continuous casting, the present invention was completed.
The significance and reasons for limitation of the alloy components in the aluminum alloy fin material for heat exchangers of the present invention will be described below.
[0010]
[Si: 0.5 to 1.5 wt%]
Si coexists with Fe and Mn to form submicron-level Al- (Fe · Mn) -Si compounds during brazing, improving strength and reducing the solid solution amount of Mn to conduct heat. Improve the degree. If the Si content is less than 0.5 wt%, the effect is not sufficient, and if it exceeds 1.5 wt%, the fin material may melt during brazing. Therefore, the preferable content range is 0.5 to 1.5 wt%. A more preferable content of Si is in the range of 0.8 to 1.2 wt%.
[0011]
[Fe: 0.15-1.0 wt%]
Fe coexists with Mn and Si to produce submicron-level Al- (Fe · Mn) -Si compounds during brazing, improving strength and reducing Mn solid solution to conduct heat. Improve the degree. If the Fe content is less than 0.15 wt%, a high-purity bare metal is required, which is not preferable because the production cost increases. If it exceeds 1.0 wt%, coarse Al- (Fe.Mn) -Si-based crystallized matter is generated during casting of the alloy, making it difficult to produce a plate material. Therefore, the preferable content range is 0.15 to 1.0 wt%. The more preferable content of Fe is in the range of 0.2 to 0.7 wt%.
[0012]
[Mn: 0.8 to 3.0 wt%]
By coexisting with Fe and Si, Mn precipitates at a high density as a sub-micron level Al— (Fe · Mn) —Si compound at the time of brazing, and improves the strength of the alloy material after brazing. Moreover, since the submicron level Al— (Fe · Mn) —Si based precipitate has a strong recrystallization inhibiting action, the recrystallized grains become coarser to 150 μm or more, and the sag resistance and erosion resistance are improved. If Mn is less than 0.8 wt%, the effect is not sufficient, and if it exceeds 3.0 wt%, coarse Al- (Fe.Mn) -Si-based crystallized products are produced during casting of the alloy, making it difficult to produce a plate material. At the same time, the solid solution amount of Mn increases and the thermal conductivity decreases. Therefore, the preferable content range is 0.8 to 3.0 wt%. A more preferable content range of Mn is 1.0 to 2.0 wt%.
[0013]
[Zn: 0.5 to 2.5 wt%]
Zn lowers the potential of the fin material and provides a sacrificial anode effect. If the content is less than 0.5 wt%, the effect is not sufficient, and if it exceeds 2.5 wt%, the self-corrosion resistance of the material is deteriorated, and the thermal conductivity is lowered due to the solid solution of Zn. A more preferable content of Zn is in the range of 1.0 to 1.5 wt%.
[0014]
[Mg: 0.05 wt% or less]
Mg affects the brazing property, and if the content exceeds 0.05 wt%, the brazing property may be impaired. In particular, in the case of fluoride-based flux brazing, fluorine (F), which is a component of the flux, easily reacts with Mg in the alloy, and works effectively during brazing due to the formation of compounds such as MgF _2. The absolute amount of flux to be used is insufficient, and brazing defects are likely to occur. Therefore, the content of Mg as an impurity is limited to 0.05 wt% or less.
[0015]
For impurity components other than Mg, Cu is preferably limited to 0.2 wt% or less in order to make the potential of the material noble, and Cr, Zr, Ti, and V significantly reduce the thermal conductivity of the material even in a small amount. Therefore, the total content of these elements is preferably limited to 0.20 wt% or less.
[0016]
Next, the meaning of the casting conditions, the intermediate annealing conditions, the final cold rolling rate of the thin slab in the present invention, and the reasons for limitation will be described below.
[Continuous casting into a thin slab with a thickness of 5-10mm by a twin belt type casting machine]
In the double belt casting method, molten metal is poured between rotating belts facing each other up and down, and the molten metal is solidified by cooling from the belt surface to form a slab. It is a continuous casting method that is drawn out and wound into a coil.
In the present invention, the thickness of the cast slab is limited to 5 to 10 mm. With this thickness, the solidification rate in the central part of the plate thickness is fast, and with a uniform structure and with a composition within the range of the present invention, there are few coarse compounds and excellent properties with a large crystal grain size after brazing. It can be a fin material.
[0017]
That is, when the thickness of the thin slab by the twin belt type casting machine is less than 5 mm, the amount of aluminum passing through the casting machine per unit time becomes too small, and casting becomes difficult. Conversely, when the thickness exceeds 10 mm, winding with a roll becomes impossible, so the slab thickness range is limited to 5 to 10 mm.
[0018]
In addition, it is preferable that the casting speed at the time of solidification of a molten metal is 5-15 m / min, and it is desirable that solidification is completed within a belt. A casting speed of less than 5 m / min is not preferable because it takes too much time for casting and decreases productivity. When the casting speed exceeds 15 m / min, the supply of the molten aluminum cannot catch up, and it becomes difficult to obtain a thin slab having a predetermined shape.
[0019]
[Intermediate annealing is performed at a holding temperature of 350 to 500 ° C.]
The holding temperature of the intermediate annealing is limited to 350 to 500 ° C. When the holding temperature of intermediate annealing is less than 350 ° C., a sufficient softened state cannot be obtained. However, if the holding temperature of the intermediate annealing exceeds 500 ° C., most of the solid solution Mn that precipitates during brazing will precipitate as a relatively large Al— (Fe · Mn) —Si compound during intermediate annealing at a high temperature. For this reason, the recrystallization inhibiting action at the time of brazing is weakened, the recrystallized grain size becomes less than 150 μm, and the sag resistance and the erosion resistance are lowered.
[0020]
The holding time for the intermediate annealing is not particularly limited, but is preferably in the range of 1 to 5 hours. If the holding time of the intermediate annealing is less than 1 hour, the holding time may elapse while the temperature of the entire coil is not uniform, and there is a risk that a uniform recrystallized structure in the plate cannot be obtained, which is not preferable. If the holding time of the intermediate annealing exceeds 5 hours, precipitation of the solid solution Mn proceeds and not only is disadvantageous in securing a recrystallized grain size of 150 μm or more after brazing, but also the processing time is increased. This is not preferable because it is too much and the productivity is lowered.
[0021]
The temperature raising rate and the cooling rate during the intermediate annealing treatment are not particularly limited, but are preferably 30 ° C./hr or more. When the heating rate and cooling rate during the intermediate annealing process are less than 30 ° C./hr, precipitation of the solid solution Mn progresses, which is disadvantageous in securing a recrystallized grain size of 150 μm or more after brazing. Not only that, but it takes too much time for the processing and the productivity is lowered.
[0022]
[Cold rolling with a cold rate of 50 to 96%]
The final cold rolling rate is limited to 50 to 96%. When the final cold rolling rate is less than 50%, the recrystallized grains after brazing become 1000 μm or more, and the tensile strength decreases. If it exceeds 96%, the ear cracks at the time of rolling become remarkable, and the yield decreases. When the final cold rolling rate is 80% or more, depending on the composition, the product strength becomes too high, and when it is difficult to obtain a predetermined fin shape in fin molding, the final cold rolled plate is heated at 150 to 300 ° C. Even if the softening treatment is performed for about 1 to 3 hours, various characteristics are not impaired.
[0023]
The aluminum alloy fin material of the present invention is obtained by casting a thin slab having a thickness of 5 to 10 mm at a speed of 5 to 15 m / min by using a twin belt type casting machine and winding the slab on a roll. Cold-rolled, subjected to intermediate annealing at a heating rate of 30 ° C./hr or higher, a holding temperature of 350 to 450 ° C., a holding time of 1 to 5 hr, a cooling rate of 30 ° C./hr or higher, and further cold-rolled, Usually, a plate material having a thickness of 0.1 mm or less is used. This plate material is slitted to a predetermined width and then corrugated, and alternately laminated with a flat tube made of a clad plate made of a material for working fluid passage, for example, 3003 alloy coated with a brazing material, and brazed and joined. Therefore, a heat exchanger unit is obtained.
[0024]
According to the method of the present invention, at the time of thin slab casting by a twin belt type casting machine, Al- (Fe · Mn) -Si compound is crystallized uniformly and finely in the slab and supersaturated in the matrix Al. The solid solution Mn and Si are deposited at a high density as a sub-micron level Al- (Fe.Mn) -Si phase by high-temperature heating during brazing. As a result, the amount of solid solution Mn in the matrix that greatly lowers the thermal conductivity is reduced, so that the electrical conductivity after brazing is increased and excellent thermal conductivity is exhibited. For the same reason, the Al- (Fe · Mn) -Si compound finely crystallized and the submicron-level Al- (Fe · Mn) -Si phase precipitated at high density are dislocations during plastic deformation. The tensile strength of the final plate after brazing shows a high value. In addition, the sub-micron level Al- (Fe.Mn) -Si phase that precipitates during brazing has a strong recrystallization-inhibiting action, so that the recrystallized grain size after brazing is 150 μm or more, thus providing good sag resistance. Thus, for the same reason, it exhibits excellent erosion resistance even after brazing. However, if the average grain size of the recrystallized grains after brazing exceeds 1000 μm, the tensile strength decreases, which is not preferable.
[0025]
Further, the twin-belt casting machine has a high solidification rate of the molten metal, and the Al— (Fe · Mn) —Si compound crystallized in the thin slab becomes uniform and fine. Therefore, in the final fin material, second phase particles having a circle-equivalent diameter of 5 μm or more due to coarse crystals are not present, and excellent self-corrosion resistance is exhibited.
[0026]
Thus, by casting the thin slab by the twin belt type continuous casting method, the Al— (Fe · Mn) —Si compound in the slab ingot is made uniform and fine, and the submicron level Al— (Fe・ Mn) -Si phase precipitates are densified and the grain size after brazing is roughened to 150 to 1000 μm, so that strength after brazing, thermal conductivity, sag resistance, erosion resistance, By increasing the self-corrosion property and simultaneously containing Zn, the potential of the material can be reduced, the sacrificial anode effect can be improved, and the aluminum alloy fin material for heat exchanger having excellent durability can be obtained.
[0027]
【Example】
Examples of the present invention will be described below in comparison with comparative examples.
[Example 1]
As an example of the present invention, a molten alloy having the composition shown in Table 1 was melted, passed through a ceramic filter, poured into a twin belt casting mold, and a slab having a thickness of 7 mm was obtained at a casting speed of 8 m / min. The cooling rate during solidification of the molten metal was 50 ° C./sec. The slab is cold rolled to 0.8 mm to form a plate, softened by intermediate annealing at a heating rate of 50 ° C / hr and 400 ° C for 2 hours, and a cooling rate of 50 ° C / hr (up to 100 ° C). It was. Next, the plate was cold-rolled to obtain a fin material having a thickness of 80 μm.
[0028]
As a comparative example, a molten alloy having the composition shown in Table 1 was melted and subjected to conventional DC casting (thickness: 500 mm, cooling rate at solidification: about 1 ° C./sec), chamfering, soaking, hot rolling, cooling A fin material having a thickness of 80 μm was manufactured by hot rolling (thickness 0.13 mm), intermediate annealing (400 ° C. × 2 hours), and cold rolling.
The following measurements (1) to (3) were performed on the fin materials of the present invention examples and comparative examples.
[0029]
(1) A cross section parallel to the rolling direction is observed with a scanning electron microscope (reflection electron image), and the number of second phase particles having an equivalent circle diameter of 5 μm or more (pieces / mm ² ) is measured using an image analyzer. It was measured.
[0030]
(2) Heating was performed at 600 to 605 ° C. for 3.5 minutes assuming a brazing temperature, and the following items were measured after cooling.
[1] Tensile strength (MPa)
[2] After the surface is electropolished and the crystal grain structure is revealed by the Parker method, the grain size parallel to the rolling direction by the cutting method (μm)
[3] Conductivity (% IACS) according to the conductivity test method described in JIS-H0505
[4] Sag amount (mm) with a protruding length of 50 mm by the sag test method described in LWS T 8801
[5] Corrosion current density (μA / cm ² ) obtained from cathodic polarization using a silver-silver chloride electrode as a reference electrode in a 5% saline solution at a potential sweep rate of 20 mV / min.
[0031]
(3) A fin material processed into a corrugated shape is placed on a brazing material surface of a 0.25 mm thick brazing sheet (brazing material 4045 alloy clad rate 8%) coated with a non-corrosive fluoride flux (load load) 324 g), heated to 610 ° C. at a heating rate of 50 ° C./min and held for 10 minutes. After cooling, the brazed cross section was observed, and a slight erosion of the fin material crystal grain boundary was judged as good (◯ mark), and a erosion was severe and the fin material melted markedly as poor (x mark). The corrugated shape was as follows.
Corrugated shape: height 2.3 mm × width 21 mm × pitch 3.4 mm, and 10 mountain results are shown in Table 2.
[0032]
[Table 1]

[0033]
[Table 2]

[0034]
From the results of Table 2, the fin material produced by the production method of the present invention is higher in tensile strength after brazing, electrical conductivity after brazing, sag resistance, self-corrosion resistance and erosion resistance than the comparative fin material produced by the conventional production method. It turns out that all of these are good.
[0035]
[Example 2]
The twin-belt cast slab obtained in Example 1 was divided and cold-rolled to the respective intermediate annealing plate thicknesses shown in Table 3, and then heated to the respective temperatures shown in Table 3 at a heating rate of 50 ° C./hr. Softened by intermediate annealing at a cooling rate of 50 ° C./hr (up to 100 ° C.) for 2 hours. Next, the plate was cold-rolled at the final cold rolling rate shown in Table 3 to obtain a fin material having a thickness of 80 μm. Table 4 shows the results of evaluating the crystal grain size after brazing, the tensile strength after brazing, the sag resistance, and the erosion resistance of these fin materials by the method shown in Example 1.
[0036]
[Table 3]

[0037]
[Table 4]

[0038]
From the table, fin material numbers 1, 2, and 4 produced by the method of the present invention have good tensile strength, sag resistance, and erosion resistance after brazing, while the final cold rolling ratio The smaller fin material number 3 has a lower tensile strength because the recrystallized grains after brazing are super coarse, and the fin material number 5 having a higher intermediate annealing temperature has a smaller recrystallized grain after brazing, so that the sag resistance is reduced. It can be seen that the erosion resistance is poor.
[0039]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the aluminum alloy fin material for heat exchangers which has high intensity | strength and heat conductivity after brazing, and was excellent in sag resistance, erosion resistance, self-corrosion resistance, and sacrificial anode effect is provided. The

Claims (1)

Si 0.5 to 1.5 wt%, Fe 0.15 to 1.0 wt%, Mn 0.8 to 3.0 wt%, Zn 0.5 to 2.5 wt%, and Mg as impurities to 0.05 wt% or less After limiting, the remaining molten metal composed of normal impurities and Al is continuously cast by a twin-belt caster into a thin slab having a thickness of 5 to 10 mm and wound around a roll, and then the thickness is 0.08-2. Cold-rolled to 0 mm, subjected to intermediate annealing at a holding temperature of 350 to 500 ° C., and cold-rolled at a cold rolling rate of 50 to 96% to obtain a final sheet thickness of 40 μm to 200 μm. A method for producing a strength aluminum alloy fin material.