JPH059677A - Manufacture of thin aluminum alloy sheet for drawless fin excellent in ironability - Google Patents

Abstract

PURPOSE:To provide a thin aluminum alloy sheet for a drawless fin excellent in ironability and used as a fin for a room air conditioner by executing bulging, ironing and stretch-flanging. CONSTITUTION:An alloy ingot contg., by weight 0.01 to 0.15% Si, 0.10 to 0.40% Fe, 0.10 to 0.40% Mn and the balance Al with inevitable impurities is subjected to homogenizing treatment and is thereafter immediately subjected to hot rolling. The above hot rolling is executed at a draft by which the rolling at the sheet thickness of <=100mm is executed by >=7 passes till the thickness of the sheet finished with the hot rolling as well as the finishing temp. of the hot rolling is regulated to >=200 deg.C, after that, cold rolling is executed at >=80% draft, and the obtd. thin sheet is subjected to temper annealing in the temp. range of 260 to 300 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing 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.

[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 (c), and refraining (d), and ironing is the main process. Therefore, it is required that the fin material has excellent ironing workability.
It is used for manufacturing thin fins of less than mm.

Recently, it has been desired to reduce the weight of the heat exchanger from the viewpoint of energy saving and resource saving, and 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 molding of the drawless fins include ironing cracks that occur during the ironing process and flower cracks that occur during the flare process. In particular, ironing cracks tend to occur as the ironing rate increases, and there is a problem that product dimensions above a certain height cannot be obtained. All of these cracks impair the adhesion between the collar part 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. In addition, since the corrugated type is stretched, it requires high elongation at the same time as strength.However, the aluminum alloy alloy sheet produced by the conventional ordinary production method does not provide sufficient strength and elongation, However, there was a drawback that a good product could not be obtained.

[0004]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies to solve the above-mentioned problems, and as a result, properly control the pass schedule and the reduction amount during hot rolling to recover the material during hot rolling. By suppressing the recrystallization, an aluminum alloy thin plate having a uniform fine metal structure that does not include coarse old grain boundaries, etc. can be obtained, and this alloy plate has sufficient strength and elongation value as a hard fin material for drawless fins. Based on this finding, the present invention has been completed.

That is, in the present invention, Si 0.01 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% by weight of balance Al and unavoidable impurities was homogenized, immediately hot-rolled, and hot-rolled at a plate thickness of 100 mm or less. The rolling reduction is 7 passes or more before the hot rolling finishes, and the hot rolling finish temperature is 200 ° C.
After performing as described above, cold rolling is performed at a rolling reduction of 80% or more, and the obtained thin plate is subjected to temper annealing at a temperature in the range of 260 to 300 ° C., which is excellent in ironing workability. A method for manufacturing an aluminum alloy thin plate for a drawless fin.

[0006]

First, the reason why the alloy composition is limited according to the present invention will be described. 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 an alloy composition containing 0.10 to 0.40% by weight of n and the balance Al and unavoidable impurities.
Si, Fe, and Mn components are partially solid-dissolved in aluminum, and in addition to the effect of enhancing the strength of the thin plate, Al-Fe-based alloys having a diameter of about 1 to 10 μm,
System, Al- (Fe, Mn) -Si based very hard intermetallic compound, which is uniformly dispersed and has the effect of preventing seizure with a tool 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, seizure frequently occurs and ironing property deteriorates. On the other hand, Si
Is more than 0.15% by weight, Fe is more than 0.40% by weight, and Mn is 0.40% by weight.
When it is more than wt%, work hardening is easily promoted during ironing, and the intermetallic compound becomes coarse, and the intermetallic compound becomes a starting point of cracking during ironing and flare processing, resulting in deterioration of formability. .. Therefore, the Si content is 0.01 to 0.15% by weight, and the Fe addition amount is 0.
10 to 0.40% by weight, and the Mn addition amount is 0.10 to
It is necessary to be 0.40% by weight.

Next, the manufacturing method of the present invention will be described.
The feature of the method for producing an aluminum alloy thin plate according to the present invention is that the alloy ingot is homogenized and then immediately hot-rolled until the rolling at a plate thickness of 100 mm or less reaches the thickness after hot rolling. Do more than 7 passes,
In addition, the hot rolling finish temperature is set to 200 ° C. or higher. If the number of passes is less than 7 passes, the amount of reduction in each pass becomes large, and as a result, recovery and recrystallization are repeated in each pass, resulting in the formation of many old grain boundaries in the hot-rolled sheet after the end of the final pass. Even after cold rolling, the metal structure remains and has a non-uniform metal structure, resulting in deterioration of formability. It should be noted that normal hot rolling is performed from a plate thickness of 100 mm or less to a plate thickness after hot rolling is 3
~ 5 passes. In addition, the hot rolling end temperature is set to 20
The reason why the temperature is 0 ° C. or higher is that precipitation of an intermetallic compound becomes difficult at a temperature lower than 200 ° C. The plate thickness after hot rolling is about 3 to 10 mm. Here, the homogenization treatment may be carried out based on a conventional method, but if it is held at a high temperature of about 500 to 620 ° C. for a short time, preferably within 3 hours, and if the solid solution amount of the additional element before hot rolling is increased. Since the recovery and recrystallization during hot rolling are further suppressed, the effect of the above hot rolling is high.
As a result of such a hot rolling, a micrograph of the metal structure of the hot rolled plate is shown in FIG. 4 (a), which shows a uniform work structure in which recovery recrystallization is suppressed and old grain boundaries are hardly seen. Cold rolling is performed at a rolling reduction of 80% or more because if it is less than 80%, the strength required as a drawless fin material is insufficient. Further, by subjecting the obtained thin plate to temper annealing at a temperature of 260 to 300 ° C., the formability required as a drawless fin material for corrugated type, especially the corrugated property (protruding property) is improved. 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 300 ° C, recrystallized grains are generated, and this becomes a starting point of cracking, which rather deteriorates formability. Resulting in. Therefore, it is necessary to perform 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 300 ° C. Example of macro photograph of metal structure of thin plate thus obtained is shown in FIG. 5 (a). As can be seen from this photograph, the alloy plate of the present invention has a uniform work structure in which old grain boundaries are hardly seen. ing.

[0008]

[Examples] Alloy ingots having the compositions shown in Table 1 were produced by water cooling casting, the ingots (thickness: 400 mm) were ground on both sides by 10 mm on each side, and homogenized by holding at 560 ° C for 1 hour. Immediately thereafter, hot rolling was performed under the conditions shown in Table 1 to obtain a hot rolled plate having a thickness of 6 mm. These hot-rolled sheets were cold-rolled to a thickness of 0.115 mm, and then temper-annealed in the temperature range shown in Table 2 to obtain Al alloy thin sheets for drawless fins. Table 2 shows the results of the tensile test of these thin plates and the results of the evaluation of the ironing workability and corrugation workability (overhanging property). An example of a micrograph of the metal structure of these hot rolled plates is shown in FIG. FIG. 5 shows an example of a macro photograph of the metal structure of a thin plate that has been temper-annealed through cold rolling. Here, the metallographic structure of the hot-rolled plate was observed by an optical microscope after the surface of the rolled plate and the cross section in the plate thickness direction were corroded by an electrolytic polishing method. A macrophotograph of the metal structure of the alloy plate after heat treatment was observed by etching with aqua regia (nitric acid: hydrochloric acid = 1: 1). As for ironing property, 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 property was evaluated by the presence or absence of cracks when 100 corrugated parts were molded with a drawless fin actual machine using a corrugated plate having a molding height of 1.3 mm.

[0009]

[Table 1]

[0010]

[Table 2]

As is clear from Table 2, the alloy plate sample of the present invention
No. Nos. 2 to 6 are conventional alloy plate sample Nos. That have only four passes of hot rolling with a plate thickness of 100 mm or less. Excellent ironing and corrugating properties compared to 15-20. This is Figure 4
As shown in (A) to (C), material No. with a small number of passes.
No. 3 recovered during hot rolling and recrystallization proceeded, and the hot rolled sheet exhibited a recrystallized structure containing considerably old grain boundaries (Fig. 4 (c)).
On the other hand, the material No. that has many passes. No. 1 is because recovery and recrystallization are suppressed, and a uniform processed structure in which old grain boundaries are hardly seen is exhibited (FIG. 4 (a)), which is shown in FIG.
This is because there is a significant difference in the macrostructure of the final cold-rolled sheet as shown in (c). That is, while the conventional alloy plate (C) shows a structure in which old grain boundaries are prominent, the alloy plate of the present invention (A) has a uniform processed structure in which old grain boundaries are hardly seen. It is considered that the alloy sheet of the present invention, which has fewer sources, has less uneven deformation during ironing as compared with the conventional alloy sheet, and improves the ironing workability. Further, the number of passes during hot rolling is less than the limit range of the present invention.
No. As shown in FIGS. 4 (b) and 5 (b), Nos. 8 to 14 exhibited a recrystallized structure similar to that of the conventional alloy sheet, and the ironing property was poor. Further, a comparative alloy plate sample No. having a tempering annealing temperature outside the limit range of the present invention. 1 and 7 are inferior in ironing property and corrugation property. Conventional alloy plate sample No. Nos. 15 to 17 have a small amount of intermetallic compounds, and seizure frequently occurs during ironing, so that the ironing property deteriorates.

[0012]

INDUSTRIAL APPLICABILITY As described above, the fin material obtained by the manufacturing method of the present invention has a remarkable effect of being excellent in ironing property and corrugation property in drawless type fin forming, and capable of remarkably reducing the defective rate. is there.

[Brief description of drawings]

1A to 1D are cross-sectional views showing a form of an aluminum fin 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 each showing a cross-sectional view of a fin forming method by a draw method.

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

4 (a), (b), and (c) are micrographs (20,000 times) showing the metal structure of the hot-rolled sheet.
No. 1, (b) Material No. 2, (C) Material No. It is 3.

5 (a), (b) and (c) are macro photographs showing the metallographic structure of the cold-rolled sheet after tempering. (A) is an alloy plate of the present invention, (B) a comparative alloy plate, and (C) a conventional alloy plate.

[Explanation of symbols]

 1 Plate 2 Color

Claims (1)

Claims 1. Si 0.01 to 0.15% by weight, Fe
An alloy ingot containing 0.10 to 0.40% by weight and 0.10 to 0.40% by weight of Mn and the balance of Al and unavoidable impurities was homogenized and immediately hot-rolled.
The hot rolling is performed at a rolling reduction such that rolling at a plate thickness of 100 mm or less reaches 7 passes or more before the hot rolling reaches a plate thickness, and the hot rolling end temperature is set to 200 ° C. or more. After that, it is cold-rolled at a rolling reduction of 80% or more, and the thin plate obtained is subjected to temper annealing at a temperature in the range of 260 to 300 ° C., which is excellent in ironing workability. Method for manufacturing thin alloy sheet.