JPH09316615A - Production of aluminum alloy sheet for can body low in earing ratio - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a sheet material for an Al alloy having excellent characteristics as that for a beverage can body by subjecting an Al allaoy having a specified compsn. to homogenizing treatment, hot finish rolling, cold finish rolling and final finish annealing under specified temp. conditions. SOLUTION: The ingot of an Al alloy having a compsn. contg., by weight, 0.8 to 1.4% Mg, 0.8 to 1.4% Mn, 0.2 to 0.6% Fe, 0.1 to 0.4% Si, 0.1 to 0.3% Cu and 0.01 to 0.2% Zn and furthermore contg. a specified small amt. of Ti together with B according to necessary is heated at 530 to 630C for 1hr, is subjected to homogenizing treatment, is thereafter subjected to hot rough rolling and is furthermore subjected to finish rolling by tandem type hot finish rolling mill, and the hot rolled sheet is cooled by the injection of coolant oil and is subsequently subjected to cold rolling. Successively, it is rapidly heated at 360 to 560 deg.C at a heating rate of >=100 deg.C/min, is thereafter cooled to <=70 deg.C, is subjected to final cold finish rolling at >=60% rolling ratio and is furthermore subjected to final annealing treatment. The Al alloy sheet excellent in strength, ironing workability and flanging formability, low in an earing ratio and suitable for a can body can be obtd.

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 sheet which is excellent in strength, ironing workability and flange formability, has a low ear rate and is suitable for can bodies (beverage can bodies).

[0002]

2. Description of the Related Art Aluminum alloy plates for can bodies have strength (compressive strength) for maintaining a can shape, ironing workability when ironing a plate material into a cylindrical shape, flange workability after baking and flanging. A low ear rate over time is required. The ear ratio is a ratio of the height difference between the convex portion and the concave portion generated at the peripheral portion of the cup formed by squeezing the plate material into a cylindrical shape, and the difference between the heights of the convex portion and the concave portion is divided by the cup height. . Chips scatter from the tips of the ears during cup molding and ironing, resulting in defects such as pinholes and tear-offs. The dimensional accuracy of the can after flange molding is reduced. The amount of trimming after forming the can body increases, and the recesses in the peripheral portion of the can cannot be removed even after trimming. By the way, the aluminum alloy plate for the can body, for example, after the homogenization treatment of JIS-3004 alloy ingot, hot rolling,
It is then manufactured by a conventional method in which cold rolling and annealing are repeated, and it is known that the ear ratio increases as the cold rolling texture increases after the final cold rolling. As a method of lowering the ear rate, the recrystallized structure after hot rolling or annealing is made to have a cubic orientation that preferentially reduces the ear rate, and a method to resist the cold rolling texture to increase the ear rate Is taken.

[0003]

However, under the hot rolling conditions so far, it was not possible to preferentially grow the cubic orientation recrystallized structure during annealing. The present inventors have conducted diligent research on the cause, and under the conventional hot rolling conditions,
After the intermediate annealing, it was found that the texture in which the cubic orientation had priority is not sufficiently generated, and the manufacturing conditions in which the texture was sufficiently stable, particularly the hot finish rolling conditions were examined in detail. The present invention has been completed. An object of the present invention is to provide a method for producing an aluminum alloy sheet which has high strength, is excellent in ironing workability and flange formability, and has a low ear rate, which is suitable for a can body.

[0004]

According to the first aspect of the present invention,
Mg 0.8-1.4wt%, Mn 0.8-1.4wt%, Fe 0.2-0.6w
t%, Si 0.1-0.4wt%, Cu 0.1-0.3wt%, Zn 0.01-
0.2 wt% Ti 0.005-0.05 wt% Ti alone or together with B 0.0001-0.01 wt%, the balance of which is aluminum and inevitable impurities. At a heating condition of 1 hour or longer, then hot rough rolling, then hot finish rolling, using a tandem hot finishing mill with three or more stands, and a rolling start temperature of 300 to 400 ° C. , The rolling end temperature is 240
To 290 ℃, coolant oil is sprayed at a flow rate of 1000 l / min. Or more to cool the hot-rolled sheet, then cold rolling is performed, and then intermediate annealing is performed at a heating rate of 100 ℃ / min or more.
Rapid heating to a specified temperature in the temperature range of 360 to 560 ℃, immediately after reaching the specified temperature or after holding for 120 seconds,
A method for producing an aluminum alloy sheet for a can body having a low earring rate, which comprises cooling to 70 ° C or less at a cooling rate of 100 ° C / min or more, and then performing final cold rolling with a rolling rate of 60% or more. .

The invention according to claim 2 is characterized in that, after the final cold rolling, the final annealing treatment is carried out in the temperature range of 100 to 150 ° C. It is a manufacturing method of an aluminum alloy plate.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The alloy components of the aluminum alloy sheet used in the present invention will be described below. Mg contributes to strength improvement and is effective for increasing the strength of the bottom of the can. The reason for limiting the Mg content to 0.8-1.4 wt% is that if it is less than 0.8 wt%, the effect is not sufficiently obtained, and if it exceeds 1.4 wt%, work hardening tends to occur during DI molding and cracking during ironing. This is because the frequency of occurrence of is increased. The optimum Mg content considering the balance between strength and DI formability depends on the amount of other elements added and manufacturing conditions, but is 1.0 to 1.35 wt%, more preferably 1.1 to 1.
It is in the range of 3 wt%.

Mn contributes to the improvement of strength and DI moldability. Mn
Improves the DI formability because Mn forms crystallized substances such as Al-Mn-based, Al-Mn-Fe-based, and Al-Mn-Fe-Si-based which have a solid lubricating action. Emulsion type lubricants are usually used for DI molding, but this alone is insufficient for lubrication, and buildup occurs due to the adhesion between the alloy plate and the die, causing scratches called galling or scoring. Seizure may occur. By containing a predetermined amount of Mn, the occurrence of the build-up is prevented. The reason for limiting the Mn content to 0.8-1.4 wt% is that DI is less than 0.8 wt%.
Not only the effect of improving moldability is insufficient, but also the strength is insufficient.
If it exceeds 4 wt%, the DI formability and strength improving effect will be saturated, and a huge (sometimes about several mm) primary crystal compound of Al-Mn-Fe system will be generated during melt casting by combining with Fe described later. This is because it remains after rolling and causes cracks and pinholes during DI molding. The Mn content is preferably 0.9 to 1.3 wt%, more preferably 1.0 to 1.2 wt%.

[0008] Fe promotes the formation of the Mn crystallized substance and makes the distribution state uniform to further improve the DI formability. The reason for limiting the Fe content to 0.2-0.6 wt% is
This is because if it is less than 0.2 wt%, the effect cannot be sufficiently obtained, and if it exceeds 0.6 wt%, the above-mentioned giant primary crystal compound of Al-Mn-Fe system is likely to be generated. Fe content should be 0.3 ~ 0.5wt
%, And more preferably 0.3 to 0.45 wt%.

Cu, like Mg, is effective in increasing the strength of the bottom of the can. The reason for limiting the Cu content to 0.1 to 0.3 wt% is that if the content is less than 0.1 wt%, the strength is insufficient, and the rolling ratio in the final cold rolling required to secure pressure resistance becomes large.
This is because the DI formability deteriorates, and if it exceeds 0.3 wt%, the strength becomes too high and the flange formability deteriorates.

Si causes a phase transformation in an Al-Fe-Mn-based crystallized product to form an Al-Mn-Fe-Si-based precipitate to increase its hardness and contribute to the improvement of ironing workability. . 0.1% Si content
The reason for limiting the content to ˜0.5 wt% is that if it is less than 0.1 wt%, the effect cannot be sufficiently obtained, and if it exceeds 0.3 wt%, crystallized substances become enormous and conversely ironing workability deteriorates.

Zn is an Al-Mn-Fe system crystallized product [(MnFe) A
l ₆ etc.] are finely dispersed to contribute to the improvement of lubricity, and the dislocation structure after drawing and ironing is improved to improve the flange formability. The reason for limiting the Zn content to 0.01-0.2 wt% is that if it is less than 0.01 wt%, its effect is not sufficiently obtained, and if it exceeds 0.2 wt%, it has an effect on formability, but corrosion resistance decreases. Is.

Ti, or Ti and B, makes the crystal grains of the ingot uniform and fine. The reason for limiting the Ti content to 0.005 to 0.05 wt% is that if Ti is less than 0.005 wt%, the effect of uniformly refining the crystal grains of the ingot cannot be obtained, and if it exceeds 0.05 wt%, Al-Ti
This is because a giant twin compound of the system is generated during melt casting and remains after rolling to cause cracks and pinholes during DI molding. B promotes the effect of uniformly refining Ti ingot crystal grains. If the B content is less than 0.0001 wt%, the effect cannot be sufficiently obtained, and if it exceeds 0.01 wt%, a Ti-B system giant twin compound is likely to occur during melt casting, and this remains after rolling. Can cause cracks and pinholes during flange molding. Impurities are acceptable as long as the effects of the present invention are not impaired. For example, if Zn is 0.5 wt% or less, Cr is 0.3% or less, Zr is 0.1 wt% or less, and V is 0.1 wt% or less, there is no problem.

Next, the manufacturing method of the present invention will be described.
The aluminum alloy having the above composition is cast into a slab (plate-shaped ingot) by a normal DC casting method (semi-continuous casting method). The slab is first homogenized. By performing this homogenizing treatment, the strength, toughness, and deep drawability of the obtained aluminum alloy plate are improved, and the variation in the ear ratio is reduced. If the homogenization temperature is less than 530 ° C, the homogenization will not be sufficiently carried out, and if it exceeds 630 ° C, the ingot surface will swell. Further, if the holding time is less than 1 hour, it will not be sufficiently homogenized. Therefore, the homogenization treatment is performed at 530 to 630 ° C for 1 hour or more. The most desirable homogenization treatment condition in consideration of productivity and its effect is at 530 to 630 ° C for 3 to 12 hours.

After the homogenization treatment, hot rough rolling is performed by a conventional method, and then hot finish rolling is performed. In the hot finish rolling, the conditions are rigorously defined so that the structure after the intermediate annealing is a texture in which the cubic orientation is more preferentially generated. The cubic orientation-oriented texture is one kind of recrystallized texture that nucleates and grows from a portion (deformation concentration zone) where a large amount of matrix strain is accumulated. Therefore, in this hot finish rolling step, it is necessary to sufficiently accumulate strain in the matrix.

In the present invention, a tandem hot rolling mill having three or more stands is used in order to sufficiently accumulate strain in the hot finish rolling step. Here, if the number of stands is less than 3,
Strain cannot be accumulated sufficiently, and if rolling is performed with an unreasonable pass schedule such as increasing the starting plate thickness in order to sufficiently accumulate strain, the surface properties (baking, rough skin, etc.) will deteriorate. Will end up. Start temperature of hot finish rolling
The reason for limiting the temperature to 300-400 ℃ is that the starting temperature is 300 ℃.
If it is less than 400 ° C, problems such as cracking of the edges of the hot-rolled sheet will occur during rolling, and if it exceeds 400 ° C, fine α-phase (Al-Mn-Fe-Si intermetallic compound) will precipitate, and this fine α-phase will be precipitated. However, this is because the occurrence or growth of the cubic orientation that contributes to the control of the ear rate is suppressed during the annealing process in the subsequent process. It is known that a fine α phase (having an average particle size of about 1 μm or less) is likely to precipitate at a temperature of 400 ° C. or higher and lower than 500 ° C. The reason why the finish temperature of hot finish rolling is limited to 240 to 290 ℃ is that the surface condition of the plate deteriorates below 240 ℃, and the recovery of dislocations progresses above 290 ℃, and sufficient strain is generated before the intermediate annealing. Can not be accumulated. This hot finish rolling reduces the amount of coolant oil
Cool the hot-rolled sheet by jetting at a flow rate of 1000 l / min. Or more. The reason is that if the amount of coolant oil is less than 1000 l / min., The required end temperature (240 to 290 ° C) cannot be obtained, and the accumulation of strain is insufficient. If the rolling speed is slowed to lower the temperature of the hot-rolled sheet, the productivity is lowered, which is not preferable. The supply of the coolant oil is performed, for example, by arranging at least one cooling device equipped with a nozzle on each stand entry side or each stand entry side except the last stand. As described above, in the present invention, in hot rolling, sufficient strain is accumulated in the matrix, and further, rolling is performed under the condition that precipitation of fine α phase during hot rolling is avoided, so that the cubic orientation during annealing is obtained. It has become possible to obtain a texture that has occurred more preferentially.

After the hot finish rolling is completed, cold rolling is carried out by a conventional method, and then an intermediate annealing treatment is carried out. Intermediate annealing is 360
Apply in the temperature range of ~ 560 ° C. If the annealing temperature is lower than 360 ° C, the strength will be too high and the DI formability will be reduced, and if it exceeds 560 ° C, the precipitates such as Cu and Si will be re-dissolved too much, which will precipitate during the baking of the paint and flange forming. Sex decreases. In the intermediate annealing, cooling may be performed immediately after reaching the target temperature. That is, the holding time may be zero. If the holding time exceeds 120 seconds, the precipitates are too solid-resolved even if the annealing temperature is 560 ° C or less, which is not preferable. The heating and cooling rates were both set to 100 ° C / min or more in order to improve productivity. This is also because at a cooling rate of less than 100 ° C./minute, solid solution Cu and Si are precipitated and sufficient strength cannot be obtained in the subsequent final cold rolling.

After the intermediate annealing, final cold rolling is performed. The reason for limiting the rolling rate to 60% or more at this time is that the alloy sheet has insufficient pressure resistance at less than 60%.

After the final cold rolling, final annealing is applied if necessary. The final annealing restores the work structure, further improves DI formability and flange formability, and improves the can shape (roundness, etc.). If the final annealing temperature is less than 100 ° C, the effect cannot be sufficiently obtained, and if it exceeds 150 ° C or the holding time exceeds 8 hours, the solid solution element is excessively precipitated and DI formability and flange formability are deteriorated. The most desirable final annealing condition is 115 to 150 ° C for 1 to 4 hours.

[0019]

The present invention will be described below in detail with reference to examples. Example 1 An aluminum alloy having the composition shown in Table 1 was melt cast by a conventional method to obtain a plate-shaped ingot (slab) having a thickness of 500 mm. Next, this slab was faced to a thickness of 490 mm, homogenized at 600 ° C. for 6 hours, and then hot rough rolled by a conventional method. Next, hot finish rolling was performed under the conditions of a rolling start temperature of 380 ° C., a rolling end temperature of 270 ° C., and a coolant oil injection amount of 1100 l / min. Then, cold rolling was performed. Next, in a continuous annealing furnace at 440 ℃ for 0 minutes
Immediately after reaching (1), annealing was performed. The heating rate at this time was 800 ° C / min, and the cooling rate was 1050 ° C / min. Then, the final cold rolling was performed to the plate thickness of 0.3 mm by the conventional method (rolling rate 65%
%), And then subjected to final annealing at 125 ° C. for 2 hours to produce an aluminum alloy plate for a can body.

With respect to the alloy plate thus obtained,
Ear ratio, tensile strength, DI moldability, and flange moldability were investigated by the following methods. Ear ratio: A disk of 57 mmφ was cut out from the alloy plate, and this was deep-drawn with a punch having a diameter of 33 mm and a shoulder R2.5 mm at a clearance of 30%. Tensile strength: The alloy plate was heated at 200 ° C for 20 minutes (paint baking conditions), and the tensile strength (TS) before and after heating and 0.2% proof stress (Y
S) was measured. DI formability: DI can body for carbonated drinks (inner diameter 66 mmφ, side wall plate thickness)
100 μm, the thickness of the side wall tip portion was 150 μm). Flange formability: After trimming and cleaning the molded DI can body, heat it at 200 ° C for 20 minutes, then perform four steps of necking to reduce the inner diameter d of the opening to 57 mmφ, and finally Push in a conical jig with an angle of 90 ° until a flange crack occurs, and the diameter D of the opening when the crack occurs.
Is measured, and the increase rate P of the diameter of the opening is calculated by the following equation P = [(D-
It was calculated by d) / d] × 100%. The evaluation criteria are ear ratio within 2.5%, proof stress after heat treatment (200 ° C x 20 minutes) 265MPa or more, limit increase rate of diameter in flange molding
15% or more was considered good. Table 2 shows the results.

[0021]

[Table 1]

[0022]

[Table 2]

As is clear from Table 2, the products of the present invention (N
In all of o.1 to 3), the ear ratio was low, the limit increase rate of the diameter in the flange molding was large, and the flange moldability was good. The strength (proof stress) after heating at 200 ° C for 20 minutes (paint baking conditions) was 265 MPa or more, and the pressure resistance of the bottom of the can was at a high level without any problem. DI moldability was also good.
On the other hand, Comparative Examples Nos. 4 and 5 both had a low ear rate, but due to the large addition amount of Mg or Mn, respectively, ironing cracking occurred in DI molding. No. 6 is 200 because the added amount of Cu and Si is large.
Heating at 20 ℃ for 20 minutes increased the tensile strength and decreased the flange formability. No. 7 has low strength because the amount of Mg added is small,
In o.8, the amount of Mn added was small, so seizure occurred during DI molding. In No. 9, the strength decreased because the added amounts of Cu and Si were small.

Example 2 The No. A aluminum alloy shown in Table 1 was melt-cast by a conventional method to cast a slab having a thickness of 500 mm. Next, this slab is chamfered to a thickness of 490 mm, then subjected to homogenization treatment, hot rough rolling and hot finish rolling to obtain a hot rolled coil, which is cooled to room temperature and cold rolled. Then, it was subjected to intermediate annealing in a continuous annealing furnace, and subsequently cold rolled by a conventional method to produce an aluminum alloy sheet for can bodies. Some of them were subjected to final annealing after cold rolling. The conditions for homogenization, hot finish rolling, cold rolling, intermediate annealing, final cold rolling, and final annealing were variously changed as shown in Table 3. Regarding the alloy plate thus obtained, Example 1
Ear ratio, tensile strength, DI moldability, and flange moldability were investigated by the same method as described above. The ear rate was measured by using a punch with a diameter of 33 mm and a shoulder of R2.5 mm and performing deep drawing on a 57 mmφ disc with a clearance of 30%. The results are shown in Table 4. Evaluation is Example 1
Was performed in the same manner as in.

[0025]

[Table 3]

[0026]

[Table 4]

As is clear from Tables 3 and 4, the products of the present invention
(No. 10 to 15) has a low ear rate of 2.5% or less, excellent flange formability, and the strength (proof strength) after heat treatment assuming baking is 270 MPa or more, and there is no problem with the pressure resistance of the bottom of the can.
DI moldability was also good. On the other hand, in Comparative Example No. 16, the earring rate deteriorated because the finish rolling start temperature was high. Since No. 17 had a low finish rolling start temperature, edge cracking occurred at the end of rolling. No. 18 had a high finish rolling finish temperature and a small amount of coolant oil, which deteriorated the ear ratio, and also deteriorated the surface properties after finish rolling, resulting in rough skin and seizure. No. 19 had a high finish rolling temperature, resulting in poor ear coverage. In No. 20, the intermediate annealing was omitted, and in No. 21, the intermediate annealing temperature was low. Therefore, the strength was too high and draw cracking occurred in DI molding. Since No. 22 has a high intermediate annealing temperature, its strength is increased by heat treatment assuming baking (20 minutes at 200 ° C), and therefore, the coating of the tip of the can body side wall and thermal softening due to baking heating do not occur, and flange forming is performed. The sex has decreased. Since No. 23 had a low final cold rolling rate, the pressure resistance after heat treatment (200 ° C x 20 minutes) decreased. Since No. 24 had a low homogenization temperature, sufficient homogenization was not performed and the ear ratio deteriorated.

[0028]

As described above, according to the present invention,
It is possible to obtain an aluminum alloy plate having high strength, excellent ironing workability, and flange formability after paint baking, and having a low ear rate, and it has a remarkable industrial effect.

Claims (2)

[Claims] 1. A Mg content of 0.8 to 1.4 wt%, a Mn content of 0.8 to 1.4 wt%,
Fe 0.2-0.6wt%, Si 0.1-0.4wt%, Cu 0.1-0.3w
t%, Zn 0.01-0.2wt%, Ti 0.005-0.05wt
% Alone or with B 0.0001-0.01 wt%,
The aluminum alloy ingot, the balance of which is Al and unavoidable impurities, is homogenized at 530 to 630 ℃ for 1 hour or more under heating conditions, followed by hot rough rolling, then hot finish rolling, and the number of stands. Use a tandem hot finishing mill with a rolling ratio of 3 or more, with a rolling start temperature of 300 to 400 ℃, a rolling finish temperature of 240 to 290 ℃, and 1000 l / mi of coolant oil.
It is injected at a flow rate of n. or more to cool the hot-rolled sheet, then cold-rolled, and then an intermediate annealing process is performed at a heating rate of 100 deg. Immediately after reaching the specified temperature or after holding for 120 seconds or less, cool to 70 ° C or less at a cooling rate of 100 ° C / min or more, and then perform final cold rolling with a rolling rate of 60% or more. A method of manufacturing an aluminum alloy sheet for a can body having a low ear rate. 2. The method for producing an aluminum alloy sheet for a can body having a low ear rate according to claim 1, wherein a final annealing treatment is performed in a temperature range of 100 to 150 ° C. after the final cold rolling.