JPH059678A - Manufacture of thin aluminum alloy sheet for drawless fin excellent in ironability - Google Patents

Abstract

PURPOSE:To obtain a thin Al alloy sheet for a drawless fin excellent in ironability by subjecting an Al alloy ingot having specified content of Si, Fe and Mn to homogenizing treatment, thereafter executing hot rolling, cold rolling or the like and distributing fine intermetallic compounds into the metallic structure of the thin sheet. CONSTITUTION:An alloy constituted of, by weight, 0.01 to 0.15% Si, 0.1 to 0.4% Fe, 0.1 to 0.4% Mn and the balance Al is melted. The ingot of the above ingot is subjected to homogenizing treatment and is thereafter subjected to rolling for >=7 passes to regulated its sheet thickness from 100mm to the one finished with the hot rolling as well as to regulate the finishing temp. of the rolling to >=200 deg.C. Next, the alloy is subjected to precipitation treatment at 200 to 350 deg.C for >=2hr and is subjected to cold rolling at >=80% draft, and the obtd. thin sheet is subjected to temperature annealing at 250 to 300 deg.C. Then, fine intermetallic compounds with >=0.1mum diameter are distributed into the metallic structure of the thin sheet by >=5 pieces/mum<3> as well as its specific resistance value is regulated to <=33.5nOMEGAm.

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 are more likely to occur as the ironing rate becomes higher, and there has been a problem that a product dimension larger than the specific height of the collar 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 corrugated type is subjected to overhanging processing, it requires high elongation at the same time as strength, but aluminum alloy thin plates manufactured by conventional ordinary manufacturing methods do not provide sufficient strength and elongation, as well as formability. There was a drawback that good products could not be obtained.

[0004]

Means for Solving the Problems As a result of repeated studies to solve the above problems, the present inventors appropriately controlled the pass schedule and reduction amount of hot rolling, and recovered during hot rolling, By suppressing recrystallization, it is possible to obtain an aluminum alloy thin plate that does not contain coarse old grain boundaries and has a uniform fine metal structure, and this alloy plate has sufficient strength and elongation as a hard fin material for drawless fins. However, they have found that the ironing property is excellent. In addition, as a result of further studies to solve the above problems, the following findings have been found. That is, it has been found that if the structure of the fin material is controlled by the precipitation treatment after hot rolling, the formability is improved. When a conventional hard aluminum material for drawless fins is used, in the ironing process during the drawless fin forming process, the dislocation structure formed by pre-processing recovers due to the processing heat during ironing, so if the ironing rate is large It has been found that when the amount of heat generated by processing is large, recovery subgrains are non-uniformly generated, and the fracture resistance of the material falls below the ironing force, and as a result, ironing cracks occur. Therefore, based on this knowledge, it is difficult to recover during ironing, that is, as a result of diligent examination of a material having high high temperature strength, after hot rolling,
By performing the precipitation treatment once or more, fine intermetallic compounds are uniformly dispersed in the aluminum matrix of the aluminum alloy sheet before forming, and the effect of hindering the growth of recovery subgrains due to processing heat during ironing is obtained. Therefore, it was found that the ironing property is improved. Further, they have found that evenly dispersing the fine intermetallic compound improves the elongation value of the base plate itself.
As a result of further study, it was found that, in addition to the above, by reducing the amount of solid solution in the aluminum matrix, work hardening during ironing forming is suppressed and the ironing force is reduced, resulting in further improvement of ironing property. It was.

That is, according to the present invention, Si0.01-0.
15% by weight, Fe 0.10 to 0.40% by weight, Mn0.
The alloy ingot containing 10 to 0.40% by weight, the balance of which is Al and unavoidable impurities, is homogenized, and then immediately hot-rolled. Rolling was carried out until the plate thickness reached the rolled thickness at a rolling reduction of 7 passes or more and at a hot rolling end temperature of 200 ° C. or more, and then before or after cold rolling. After that, a precipitation treatment of holding at a temperature of 200 to 350 ° C. for 2 hours or more is performed once or more, and then cold rolling is performed at a reduction rate of 80% or more, and subsequently the obtained thin plate is subjected to 250 to 3
By performing temper annealing at a temperature of 00 ° C., fine intermetallic compounds having a diameter of 0.1 μm or less are distributed in the metal structure of the obtained thin plate in an amount of 5 / μm ³ or more, and a specific resistance value of 3 is obtained.
It is a method for producing an aluminum alloy thin plate for drawless fins having excellent ironing workability, which is characterized in that it is 3.5 nΩm or less.

[0006]

Next, the reason why the alloy composition is limited as in the present invention will be explained. The aluminum alloy plate according to the present invention has a Si0.
It is characterized in that it contains 01 to 0.15% by weight, Fe 0.10 to 0.40% by weight, Mn 0.10 to 0.40% by weight, and the balance is Al and inevitable impurities. Si, F
The e and Mn components are partly solid-dissolved in aluminum and have the effect of increasing the strength of the thin plate.
It becomes an extremely hard intermetallic compound of Al-Fe-Mn type and Al- (Fe, Mn) -Si type and is dispersed uniformly, preventing seizure with a tool during ironing and improving the ironing property. is there. Further, the Mn component has an effect of improving the elongation value of the alloy thin plate. Here, the amount of Si added is 0.0
Less than 1% by weight, Fe addition amount less than 0.10% by weight, Mn
If the addition amount is less than 0.10% by weight, not only the desired strength and elongation cannot be obtained, but also the number and size of the intermetallic compounds decrease, so that seizure frequently occurs and ironing property deteriorates, which is not preferable. On the other hand, when the Si addition amount is more than 0.15% by weight, the Fe addition amount is more than 0.40% by weight, and the Mn addition amount is more than 0.40% by weight, work hardening is easily promoted during ironing. At the same time, the intermetallic compound becomes coarse, and the intermetallic compound becomes a crack starting point during the ironing process and the flare process, which deteriorates the formability. Therefore, it is necessary that the Si addition amount is 0.01 to 0.15% by weight, the Fe 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 as 0.1 μm or less because the effect of delaying the movement of the subgrain grain boundaries becomes small and the recovery subgrains are likely to occur when the diameter exceeds 0.1 μm. Is. Diameter 0.1μ
The distribution of intermetallic compounds with a diameter of m or less is set to a number density of 5 / μ
The reason for defining as m ³ or more 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 unevenly distributed in the matrix, and it is more effective if it is dispersed uniformly. The present invention is characterized in that, in addition to the above-mentioned fine intermetallic compound distribution, the specific resistance value of the metal structure before forming is 33.5 nΩm or less. This is a numerical representation of the solid solution amount of the additive element that governs the work hardenability, and the specific resistance value as an index of the solid solution amount is 33.
This is because if it exceeds 5 nΩm, work hardening is likely to occur, and cracks are 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 promote the precipitation of fine intermetallic compounds having a diameter of 0.1 μm or less and to reduce the amount of elemental solid solution. Therefore, first, after homogenization treatment, the sheet is hot-rolled. Rolling from a thickness of 100 mm to a plate thickness after hot rolling with a light reduction rate of 7 passes or more,
In addition, hot rolling is performed so that the hot rolling end temperature is 200 ° C. or higher. If the number of passes is less than 7, the precipitation of fine intermetallic compounds will not be promoted after the final pass and the amount of solid solution will not be reduced, so that problems such as easy cracking during ironing will occur. Also, with less than 7 passes,
Since the amount of reduction in each pass is large, recovery and recrystallization are repeated in each pass, resulting in many old grain boundaries in the hot-rolled sheet after the end of the final pass, which remains after cold-rolling. This is because the metal structure becomes non-uniform and the formability is deteriorated. Moreover, the reason why the hot rolling finish temperature is set to 200 ° C. or higher is that precipitation of an intermetallic compound becomes difficult at less than 200 ° C. The plate thickness after hot rolling is about 3 to 10 mm. Here, the homogenizing treatment may be carried out based on a conventional method, but if it is held at 500 to 620 ° C. for a short time, preferably within 3 hours, and if the amount of the added element solid solution before hot rolling is increased, the hot working is performed. Since the recovery and recrystallization during rolling are further suppressed, the effect of the above hot rolling is high. Further, in the present invention, the diameter is 0.
For the purpose of promoting the precipitation of fine intermetallic compounds of 1 μm or less and reducing the solid solution amount, after hot rolling, before cold rolling or after hot rolling, 200
It is necessary to carry out the precipitation treatment at a temperature of 350 ° C for 2 hours or more once or more. Here, the precipitation treatment temperature is 2
If the temperature is lower than 00 ° C, the effect is insufficient, and if the temperature is higher than 350 ° C, the intermetallic compound becomes coarse and recrystallized grains are generated depending on the temperature, which becomes a starting point of cracking, which rather deteriorates the formability. Resulting in. Therefore, the precipitation treatment temperature needs to be 200 to 350 ° C. Furthermore, if the precipitation treatment is performed more than once after hot rolling and before or after cold rolling, the precipitation of fine intermetallic compounds having a diameter of 0.1 μm or less is promoted as much. Since the amount of solid solution is further reduced, it is desirable to carry out more than once. The reason why cold rolling is performed at a rolling reduction of 80% or more is because the strength required as a fin material for drawless fins is insufficient at less than 80%. Further, by subjecting the obtained thin plate to temper annealing at a temperature of 250 to 300 ° C., corrugation workability (overhanging property) required as a corrugated type drawless fin material can be obtained. Here, when the tempering temperature is less than 250 ° C., sufficient formability cannot be obtained, and when tempering annealing is performed at a temperature higher than 300 ° C., recrystallized grains are generated, and this becomes a starting point of cracking.
On the contrary, the moldability deteriorates. Therefore, it is necessary to heat-treat the obtained thin plate at a temperature of 250 to 300 ° C.

[0008]

【Example】

[Example 1] Alloy ingots having the compositions shown in Table 1 were produced by water cooling casting, the ingots (thickness 400 mm) were machined on both sides by 10 mm on each side, and then homogenized under the conditions shown in Table 2. Immediately after that, hot rolling was performed to obtain a hot rolled plate having a thickness of 6 mm. Before or after cold rolling the hot-rolled sheet, a precipitation treatment is performed under the conditions shown in Table 2, followed by cold rolling to form a thin sheet having a thickness of 0.115 mm, and then 250 to 300. Tensile strength of 14.0 to 15.5k after temper annealing in the range of ℃
A thin plate for a drawless fin having a gf / mm ² was obtained. Table 3 shows the evaluation results of the distribution state, the specific resistance value and the formability of the fine intermetallic compound having the fin material thus obtained with the diameter of 0.1 μm or less. Here, regarding 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. The ironing workability is the same as the drawless fin actual machine with the second ironing die with a diameter of 8.29 mm and the diameter of 8.2.
Using a 4 mm second ironing punch, the ironing rate is 78
% Was evaluated by the defective rate of ironing cracks when 160 fin collar parts were molded under severe conditions. The corrugation processability 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]

[0011]

[Table 3]

As is clear from Tables 1, 2, and 3, alloy plate sample No. 1 to 7 are alloy plate samples by the conventional method
No. Excellent in ironing and corrugating properties compared to No. 13. This is because the alloy plate according to the present invention is the alloy plate sample No. according to the conventional method. Compared with No. 13, many fine intermetallic compounds of 0.1 μm or less are uniformly present, and these fine intermetallic compounds suppress the growth of recovery subgrains during ironing, and as a result, fracture of the material during ironing. In order to increase the resistance, in addition to that, in the alloy sheet according to the present invention, the solid solution amount of the additive metal in the aluminum matrix before forming is considerably reduced as compared with the alloy sheet according to the conventional method, and work hardening during ironing This is because it is suppressed and the ironing force is considerably reduced. FIG. 4 is a photomicrograph (20,000 times) of the metallographic structure of the hot-rolled sheet. (A) is according to the method of the present invention (sample No. 5), and (b) is according to the comparative method (sample No. 5). .9), and (c) is obtained by the conventional method (Sample N).
o. 13). 5 (a), (b) and (c)
It is a macro photograph of the metal structure of the final cold-rolled tempered sheet corresponding to the above-mentioned FIG. The alloy plate (Sample No. 13) prepared by the conventional method recovers during hot rolling and recrystallization progresses, whereas the hot rolled plate exhibits a recrystallized structure including old grain boundaries [Fig. 4 (c)]. The alloy plate (Sample No. 5) produced by the method of the present invention has a uniform work structure in which recovery and recrystallization are suppressed and old grain boundaries are hardly seen [FIG. 4 (a)]. This causes a significant difference in the macrostructure of the final cold-rolled tempered sheet, as shown in FIGS. That is, the alloy plate according to the conventional method in Fig. 4 (c) shows a structure in which the old grain boundaries are prominent, whereas the alloy plate in accordance with the method in the present invention in Fig. 4 (a) has a uniform work structure in which old grain boundaries are hardly seen. Therefore, it is considered that the alloy sheet according to the method of the present invention, which has a smaller number of stress concentration sources, has less uneven deformation during ironing and is improved in ironing workability than the alloy sheet according to the conventional method. On the other hand, the alloy plate sample No. according to the comparative method, which is out of the range of the alloy plate according to the method of the present invention, that is, the number of passes during hot rolling is small. 8, No.
As shown in FIGS. 4 (b) and 5 (b), Nos. 10 to 12 exhibit a recrystallized structure similar to that of the alloy plate produced by the conventional method, and the ironing property is poor. Further, the comparative alloy plate sample No. outside the range of the alloy plate according to the present invention. It can be seen that either the ironing property of 8 to 12 or the corrugating property is deteriorated.
That is, the comparative alloy plate sample No. 1 containing any of Fe, Si, and Mn exceeds the upper limit. No. 9 cannot reduce the amount of solid solution before working even if a thin plate is manufactured under predetermined manufacturing conditions, and the elongation value does not decrease, but significant work hardening occurs during ironing and cracking frequently occurs. On the other hand, comparative alloy plate sample No. 1 having Fe, Si, or Mn content less than the lower limit. 11,
No. 12 has a small amount of fine intermetallic compounds and is easily recovered during ironing, so that ironing breakage easily occurs under severe ironing conditions. Further, the comparative alloy plate sample No. whose precipitation treatment temperature deviates from the range of the present invention. In Nos. 8, 10 and 11, since the number of fine intermetallic compounds was small and the amount of solid solution was large, ironing property and corrugation property were not improved.

Example 2 As shown in Table 3, the alloy plate sample No. of the present invention method before temper annealing was used. 5 and comparative method alloy plate sample No. Using Nos. 9 and 11, temper annealing was performed at the temperatures shown in Table 4, and a tensile test and a formability test using a drawless fin actual machine were performed. The results are also shown in Table 4. The molding test conditions are the same as those described in Example 1.

[0014]

[Table 4]

As is apparent from Table 4, the alloy plate sample No. of the method of the present invention. No. 5 was subjected to temper annealing at 250 to 300 ° C., so that the comparative alloy plate sample No. The ironing property is excellent as compared with 9 and 11, and the corrugation property is also good. Further, the alloy alloy sample No. of the comparative method whose tempering annealing temperature is out of the range of the present invention.
5 ′, 5 ″ is inferior in ironing property and corrugation property.

[0016]

As described above, the aluminum alloy thin plate for fin material obtained by the method of 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. Is.

[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) to (c) are micrographs of the metallographic structure of the hot-rolled sheet. (B) Alloy sheet according to the method of the present invention (b) Alloy sheet according to the comparative method (c) Alloy sheet according to the conventional method.

5 (a) to (c) are macrophotographs of the metal structure of the final rolled heat-treated plate (a) Alloy plate according to the method of the present invention (b) Alloy plate according to the comparative method (c) Alloy plate according to the conventional method.

Claims (1)

Claims 1. Si 0.01 to 0.15% by weight, Fe
The alloy ingot containing 0.10 to 0.40% by weight and Mn 0.10 to 0.40% by weight and the balance Al and unavoidable impurities were homogenized and then immediately hot rolled.
The hot rolling is performed at a reduction ratio such that the rolling from the plate thickness of 100 mm to the plate thickness after the hot rolling becomes 7 passes or more,
And so that the hot rolling end temperature is 200 ° C. or higher, and then before or after cold rolling, 2
Precipitation treatment of holding at a temperature of 00 to 350 ° C for 2 hours or more is performed once or more, and then cold rolling is performed at a reduction rate of 80% or more, and then the obtained thin plate is temper annealed at a temperature of 250 to 300 ° C. By applying 5 micron intermetallic compounds with a diameter of 0.1 μm or less in the metal structure of the obtained thin plate.
m ³ is more distributed, and the ratio method of manufacturing an aluminum alloy sheet for Dolores fins the resistance excellent ironing properties, characterized by the following 33.5Enuomegaemu.