JPH059636A - Thin aluminum alloy sheet for drawless fin having excellent ironing property and production thereof - Google Patents

Abstract

PURPOSE:To provide the aluminum alloy sheet for drawless fins which is used as a fin material for room air conditioners by bulging, ironing and stretch flanging and has an excellent ironing property and the process for production of this sheet. CONSTITUTION:An alloy cast ingot consisting of 0.01 to 0.15wt.% Si, 0.10 to 0.40wt.% Fe and 0.10 to 0.40wt.% Mn and the balance Al and unavoidable impurities is heated up to 520 to 610 deg.C and is immediately subjected to hot rolling at such a draft at which the rolling at <=100mm is >=7 passes before the hot rolled sheet thickness is attained. In addition, the hot rolling is so executed that the hot rolling end temp. attains 260 deg.C and thereafter the sheet is subjected to cold rolling at >=80% draft. The alloy sheet is then subjected to temper annealing at 260 to 330 deg.C. The aluminum thin alloy sheet contg. intermetallic compds. of <=0.1mum diameter at >=5 pieces/m<3> number density in the metallic structure before molding and 33.5nOMEGAm specific resistance value is thus obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy thin plate for a drawless fin which is excellent in ironing property and is used as a fin for a room air conditioner by subjecting it to overhanging, ironing and stretch-flange processing, and a method for producing the same.

[0002]

2. Description of the Related Art Generally, an aluminum alloy fin for an air conditioner heat exchanger has a collar portion (for inserting a heat exchange tube in a plate portion (1) as shown in FIGS. 2) is formed, and is classified into a flat type (a), a louver type (b), a slit type (c), and a corrugated type (d) according to the shape of the plate portion. The molding method of the collar portion is classified into a draw method and a drawless method. Drawing method is shown in Figure 2.
As shown in (a) to (f), the process of overhanging (a), drawing (b) to (d), punching, burring (e), and flare (f) is the main process. Therefore, the fin material is required to have excellent elongation and is usually used for manufacturing a thick fin having a thickness of 0.13 mm or more. In addition, the drawless method is shown in Fig. 3 (a)-
As shown in (d), the process consists of punching, hole expansion (a), burring (b), ironing (ironing) (c), and refraining (d), and ironing is central. Therefore, the fin material is required to have excellent ironing workability and is usually used for manufacturing thin fins having a thickness of 0.13 mm or less. Recently, from the viewpoint of energy saving and resource saving, it has been desired to reduce the weight of the heat exchanger, the aluminum alloy fins have been made thinner and lighter, and the drawless method has been widely used for manufacturing the fins.

Molding defects that occur during the molding of the drawless fin include ironing cracks that occur during the ironing process and flower cracks that occur during the flare process. In particular, ironing cracks are more likely to occur as the ironing rate increases, and there has been a problem that a product dimension above a specific height cannot be obtained. In addition, all of these cracks impair the adhesion between the collar and the heat exchange tube, reduce the heat exchange characteristics and impair the appearance of the forming fins, and may reduce the value of the product. Reduction of defects is strongly desired. Further, since the corrugated type is subjected to overhanging processing, high elongation is required, but it has been difficult to simultaneously improve the strength and the elongation value in the aluminum alloy thin plate manufactured by the conventional ordinary manufacturing method.

[0004]

As a result of repeated studies to solve the above problems, the present inventors have found that when a conventional hard aluminum material for drawless fins is used, the ironing step in the drawless fin forming step is performed. In the above, the dislocation structure formed by pre-working is recovered by the work heat generated during the ironing work.Therefore, when the ironing rate is large, that is, when the work heat value is large, recovery subgrains occur unevenly, and the fracture resistance of the material As a result of falling below the ironing force, it was found that ironing cracks occur starting from that point. Therefore, based on this knowledge, as a result of diligent study on a material that is difficult to recover during ironing, that is, having high strength at high temperature, a fine intermetallic compound was uniformly dispersed in the aluminum matrix of the aluminum alloy plate before forming. It was found that the effect of hindering the growth of the recovered subgrains due to the heat generated during the ironing process can be obtained and the ironing property can be improved. Further, they have found that the elongation value of the base plate itself is improved by uniformly dispersing the fine intermetallic compound. As a result of further studies, in addition to the above, by reducing the solid solution amount of the additive element in the aluminum matrix, work hardening during ironing forming is suppressed, and the ironing force is reduced, resulting in further improvement of the ironing property. The inventors have found the above and arrived at the present invention.

That is, the invention according to claim 1 is the Si0.
01-0.15% by weight, 0.10-0.40% by weight of Fe, 0.10-0.40% by weight of Mn, and an alloy composition consisting of the balance Al and inevitable impurities, and a metallographic structure before forming. An intermetallic compound having a diameter of 0.1 μm or less was distributed in a number density of 5 / μm ³ or more, and a specific resistance value was 33.5 nΩm or less, which was excellent in ironing workability. It is an aluminum alloy thin plate for drawless fins, and the invention according to claim 2 has Si0.01 to 0.1.
5% by weight, Fe 0.10 to 0.40% by weight, Mn 0.1
An alloy ingot containing 0 to 0.40 wt% of the balance Al and unavoidable impurities was heated to a temperature of 520 to 610 ° C., immediately hot-rolled, and hot-rolled to 100 m.
Rolling with a plate thickness of m or less is performed at a reduction ratio of 7 passes or more until the plate thickness after hot rolling reaches, and after hot rolling under the condition that the end temperature is 260 ° C or more, the reduction is performed. Rate 8
The thin plate obtained by cold rolling at 0% or more is 260-330.
Heat treatment is performed at a temperature in the range of ℃, and the intermetallic compound with a diameter of 0.1 μm or less is distributed in a number density of 5 / μm ³ or more in the metal structure before forming and has a specific resistance. A method for producing an aluminum alloy thin plate for drawless fins having excellent ironing workability, characterized in that the value is 33.5 nΩm or less.

[0006]

Next, the reason why the alloy composition is limited as in the present invention will be explained. The aluminum alloy thin plate of the present invention has Si0.01
~ 0.15% by weight, Fe 0.10 to 0.40% by weight, M
It is characterized by having a composition containing 0.10 to 0.40% by weight of n and the balance being Al and unavoidable impurities. Si,
Fe and Mn components are partially solid-dissolved in aluminum, and in addition to the effect of increasing the strength of the thin plate, the alloy plate has a diameter of 1 to 10
About μm Al-Fe system, Al-Fe-Mn system, Al-
(Fe, Mn) -Si based very hard intermetallic compounds and fine intermetallic compounds that are evenly dispersed and have a diameter of about 1 to 10 μm prevent seizure with tools during ironing. However, the fine intermetallic compound has an effect of hindering recovery subgrain growth during ironing and improving the ironing property. Further, the Mn component has an effect of improving the elongation value of the alloy thin plate. Here, if the addition amount of Si is less than 0.01% by weight, the addition amount of Fe is less than 0.10% by weight, and the addition amount of Mn is less than 0.10% by weight, desired strength and elongation cannot be obtained. Since the number and size of intermetallic compounds decrease, seizures frequently occur, and
Since the amount of fine intermetallic compounds having a diameter of 0.1 μm or less is reduced, recovery subgrains are easily formed and ironing property is deteriorated. On the other hand, the addition amount of Si is more than 0.15% by weight, the addition amount of Fe is more than 0.40% by weight, and Mn is
If the amount of addition of 0.40% by weight is more than 0.40% by weight, work hardening tends to be promoted during ironing and coarsening of the intermetallic compound may occur, and the intermetallic compound may become a crack initiation point during ironing and refiring. Therefore, the moldability is deteriorated. Therefore, Si 0.01 to 0.15% by weight, F
It is necessary that the e addition amount is 0.10 to 0.40% by weight and the Mn addition amount is 0.10 to 0.40% by weight. In the present invention, the diameter of the intermetallic compound is defined to be 0.1 μm or less, because if the diameter is larger than 0.1 μm, the effect of delaying the movement of the subgrain grain boundaries becomes small and recovery subgrains are likely to occur. is there. Diameter 0.1μ
Distribution of intermetallic compounds of m or less is converted into number density of 5 / μm
^The reason why ³ or more is defined is that if the number is less than 5 pieces / μm ³ , the above effect is difficult to be obtained, and therefore the ironing property is not improved. The intermetallic compound has little effect even if it is distributed unevenly in the matrix, and it is more effective if it is dispersed uniformly. According to the present invention, in addition to the above-mentioned fine intermetallic compound distribution, the specific resistance value of the metal structure before forming is 3
It is characterized in that it is specified to be 3.5 nΩm or less. This is a numerical representation of the solid solution amount of the additional element that governs work hardening, and when the specific resistance value, which is an index of the solid solution amount, is larger than 33.5 nΩm, work hardening easily occurs. This is because cracking is likely to occur during ironing.
Therefore, it is necessary that the specific resistance value is 33.5 nΩm or less.

Next, the manufacturing method of the present invention will be described.
The present invention aims to suppress coarse precipitation during homogenization treatment, promote precipitation of fine intermetallic compounds having a diameter of 0.1 μm or less during hot rolling, and reduce the solid solution amount. Therefore, it is necessary to first raise the temperature of the ingot to a temperature of 520 to 610 ° C. and then immediately start hot rolling. Here, if the homogenization treatment temperature of the ingot is less than 520 ° C., a coarse intermetallic compound precipitates during the homogenization treatment, and a sufficient amount of solid solution for precipitation in the hot rolling step cannot be obtained.
At a temperature higher than 10 ° C., a sufficient amount of solid solution can be obtained, but the intermetallic compound is coarsely spheroidized and adversely affects the ironing property, which is not preferable. In addition, since the intermetallic compound becomes coarser and the moldability is adversely affected as the holding time becomes longer in any temperature range, the holding time should be as short as possible, preferably within 3 hours. Upon performing hot rolling immediately after the above homogenization treatment, rolling with a sheet thickness of 100 mm or less in hot rolling is performed with a reduction ratio of 7 passes or more until the thickness of the hot rolling rises, Moreover, it is necessary to set the end temperature of the hot rolling to 260 ° C. or higher. If the rolling reduction is less than 7 passes, the amount of dislocations introduced during hot rolling decreases and the nucleation sites of intermetallic compounds decrease, so precipitation of intermetallic compounds with a diameter of 0.1 μm or less during hot rolling. Is less likely to occur. Here, the plate thickness after hot rolling is about 3 to 10 mm. Also,
When the end temperature of hot rolling is set to less than 260 ° C., intermetallic compounds having a diameter of 0.1 μm or less are less likely to precipitate during hot rolling, and a predetermined intermetallic compound distribution cannot be obtained. Therefore, in the hot rolling, rolling with a plate thickness of 100 mm or less is performed with a reduction ratio of 7 passes or more until the thickness of the hot rolling rises, and the end temperature of the hot rolling is 260 ° C. or more. It is necessary. Cold rolling is performed at a rolling reduction of 80% or more because if it is less than 80%, the strength required for a drawless fin material is insufficient. In addition, the obtained thin plate has 26
By performing temper annealing at a temperature of 0 to 330 ° C., corrugation workability (overhanging property) required as a corrugated type drawless fin material can be obtained. Here, if the tempering temperature is less than 260 ° C, sufficient formability cannot be obtained, and if tempering annealing is performed at a temperature higher than 330 ° C, recrystallized grains are generated, and this becomes a starting point of cracking. The nature deteriorates. Therefore, it is necessary to carry out cold rolling at a rolling reduction of 80% or more and to subject the obtained thin plate to temper annealing at a temperature of 260 to 330 ° C. An example of a micrograph of the metal structure of the thus obtained thin plate before forming is shown in FIG. 4 (a). As can be seen from this photograph, the alloy plate of the present invention has a fine intermetallic compound of 0.1 μm or less in diameter. Are distributed in a number density of 5 pieces / μm ³ or more. On the other hand, in the conventional alloy plate,
As shown in (b), the intermetallic compound having a diameter of 0.1 μm or less is smaller than that of the alloy plate of the present invention in a number density of 5 / μm.
It is less than ³ .

[0008]

【Example】

Example 1 An ingot having an alloy composition shown in Table 1 was produced by water cooling casting, and the ingot (thickness: 400 mm) was formed on one side of 10 mm.
After both sides were machined, homogenization treatment and hot rolling were performed under the conditions shown in Table 2 to obtain a hot rolled sheet having a thickness of 6 mm. The hot rolled sheet is cold rolled into a thin sheet having a thickness of 0.115 mm, and then 270 to 270
Tensile strength of 14.0 after temper annealing in the range of 320 ℃
A thin plate for a drawless fin having a weight of ˜15.5 kg / mm ² was obtained. Table 3 shows the distribution state of the intermetallic compound of the fin material thus obtained, the specific resistance value and the formability evaluation result. Here, as for the distribution state of the intermetallic compound, the particle diameter of the intermetallic compound and the number of the particles present in a given volume were measured using a transmission electron microscope. The particle diameter was the diameter of a circle having an area equal to the projected area of the particles. Regarding the electrical resistivity, the thin plate after temper annealing was measured using a double bridge based on JIS standard. As for ironing workability, 160 fin collar parts were formed by a drawless fin actual machine using a second ironing die having a diameter of 8.29 mm and a second ironing punch having a diameter of 8.24 mm under a severe condition of an ironing rate of 78%. It was evaluated by the rate of defective ironing cracking. The corrugation processability was evaluated by the presence or absence of cracks when 100 corrugated parts were molded using a drawless fin actual machine using a corrugated plate having a molding height of 1.3 mm.

[0009]

[Table 1]

[0010]

[Table 2]

[0011]

[Table 3]

As is clear from Tables 1, 2, and 3, the alloy plate sample No. 1 to 4 are conventional alloy plate sample Nos. Excellent ironing and corrugating properties compared to 10 and 11. This is Figure 4
The alloy plate sample of the present invention as shown in the micrograph of the metal structure of
No. Conventional alloy plate sample No. 1 Compared to 11, diameter 0.1
A large number of fine intermetallic compounds with a size of μm or less are evenly present. These intermetallic compounds suppress the growth of recovery subgrains during ironing and, as a result, increase the fracture resistance of the material during ironing. In addition to that, in the alloy sheet of the present invention, the solid solution amount of the additional element in the aluminum matrix before forming is considerably reduced, the work hardening during the ironing process is suppressed, and the ironing force is also considerably reduced as compared with the conventional alloy sheet. This is because. On the other hand, the comparative alloy plate sample No. out of the range of the alloy plate of the present invention. It is understood that either the ironing property of 5 to 9 or the corrugating property is deteriorated. That is, Fe, S
i or Mn content exceeds the upper limit. No. 8 cannot reduce the amount of solid solution before processing even if a thin plate is manufactured under predetermined manufacturing conditions, and the elongation value can be improved, but significant work hardening occurs during ironing and cracks frequently occur. . On the other hand, the comparative alloy plate sample No. in which any of the Fe, Si, and Mn contents is less than the lower limit. No. 9 has few fine precipitates and is easily recovered during ironing, so that ironing breakage easily occurs under severe non-ironing conditions. Moreover, the homogenizing temperature and the hot rolling conditions were out of the range of the present invention. 5, 6, and 7 have a small number of precipitates,
Since the amount of solid solution is large, ironing property and corrugation property are not improved.

Example 2 Sample Nos. 2, 10, 11 in Table 3
The tempering annealing was performed at the temperature shown in Table 4 using the thin plate before the tempering annealing, and the tensile test and the formability test by the drawless fin actual machine were performed. The results are also shown in Table 4. The conditions of the moldability test are the same as those described in Example 1.

[0014]

[Table 4]

As is apparent from Table 4, the sample No. before temper annealing was used. No. 2 alloy sheet of the present invention obtained by subjecting the thin sheet of No. 2 to temper annealing at 260 to 320 ° C. 23 to 26 are
Conventional alloy plate sample No. It is understood that the ironing property is superior to those of 28 to 34 and the corrugation property is also good. Further, the comparative alloy plates No. 21 and 2 whose tempering temperature is out of the range of the present invention
Nos. 2 and 27 have poor ironing and corrugating properties.

[0016]

INDUSTRIAL APPLICABILITY As described above, the fin material obtained according to the present invention has excellent ironing property and corrugation property in drawless fin formation, and has a remarkable effect of significantly reducing the defect rate.

[Brief description of drawings]

1A to 1D are cross-sectional views showing the form of aluminum fins of a heat exchanger, FIG. 1A is a flat type, FIG. 1B is a louver type, and FIG. 1C is a slit type. D) is a corrugated type.

2A to 2F are explanatory views showing cross-sectional views of a fin forming method by a draw method.

3A to 3D are explanatory views showing cross-sectional views of a fin forming method by a drawless method.

FIG. 4 (a) is a micrograph showing the metal structure of the alloy plate of the present invention, and FIG. 4 (b) is a micrograph showing the metal structure of a conventional alloy plate. (Both 20,000 times)

[Explanation of symbols]

1 plate part 2 color section

Claims (2)

[Claims] 1. Si 0.01 to 0.15% by weight, Fe
It has an alloy composition containing 0.10 to 0.40 wt% and Mn 0.10 to 0.40 wt% and the balance Al and unavoidable impurities, and has a diameter of 0.1 μm in the metal structure before forming.
An aluminum alloy thin plate for a drawless fin excellent in ironing workability, wherein the following intermetallic compounds are distributed in a number density of 5 / μm ³ or more and a specific resistance value is 33.5 nΩm or less. 2. Si 0.01 to 0.15% by weight, Fe0.
10 to 0.40 wt%, Mn 0.10 to 0.40 wt%
After heating the alloy ingot containing the balance Al and inevitable impurities to a temperature of 520 to 610 ° C., hot rolling is immediately performed, and the hot rolling is performed by rolling at a plate thickness of 100 mm or less. Rolling is performed with a reduction ratio of 7 passes or more until the rolled sheet thickness is obtained, and hot rolling is performed under the condition that the end temperature is 260 ° C or more, and then cold rolling is performed with a reduction ratio of 80% or more to obtain The thin sheet thus obtained is subjected to temper annealing at a temperature in the range of 260 to 330 ° C., and the metal structure before forming has a diameter of 0.
The number density of intermetallic compounds with a diameter of 1 μm or less is 5 / μm
^A method for producing an aluminum alloy thin plate for drawless fins having excellent ironing workability, characterized by having a specific resistance value of 33.5 nΩm or less with a distribution of ³ or more.