JP3241063B2 - Method for producing aluminum alloy hard plate for beverage can lid excellent in anisotropy and softening resistance - Google Patents

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 plate used for can lids for retort beverage cans such as coffee and oolong tea. The present invention relates to a method for producing a hard plate which does not soften, maintains high strength, and is excellent in formability.

[0002]

2. Description of the Related Art When filling coffee or oolong tea into a can, heating for sterilization, that is, retort heating is required. In addition, since the retort beverage can contains a component that easily corrodes the aluminum alloy, the inside of the can is coated with a polymer resin having a high anticorrosion effect.
Examples of the polymer resin paint include a vinyl type, a vinyl organosol type, an epoxy amino type, an epoxy phenol type, and an epoxy acrylic type. The strip (plate) -shaped hard plate is coated with a coating material by a roll coater or the like, and then dried at 250 to 300 ° C. in a continuous heat treatment furnace in view of the requirement of coating film performance.

Conventionally, a method of manufacturing an aluminum alloy sheet used for a can lid for a retort beverage can, such as coffee or oolong tea, is to homogenize an aluminum alloy ingot and then to hot-roll the aluminum ingot to a thickness of 3 to 5 mm. Cold rolling → intermediate annealing (3
00-450 ° C) → Final cold rolling method, or (2) Hot rolling to a sheet thickness of about 2 mm, intermediate annealing at the sheet thickness, or final cold rolling as hot rolling , 0.4mm
A method of using the following hard plate is generally used.

[0004]

The aluminum alloy plate for the lid of the above-mentioned retort beverage can is coated with a polymer resin paint by a roll coater or the like, heated to 250 to 300 ° C. in a continuous heating furnace, baked and dried. . At this time, in the above conventional material,
There is a disadvantage that the material is softened, the strength is reduced, and the material cannot be made thinner.

[0005] On the other hand, Japanese Patent Application No. 3-8 filed earlier.
The method of manufacturing a hard plate for suppressing softening resistance described in No. 9317 is effective. In this method, a required amount of Mn is added, and an intermediate heat treatment is performed at a low temperature, so that Al-
The Mn-based compound is finely precipitated, and further subjected to cold working to form a structure that is hardly softened. Addition of Cu promotes fine precipitation at the time of coating baking, and further hardens softening. However, in this method, since the end temperature of the hot rolling exceeds the recrystallization temperature (280 ° C.), the recrystallized grains generated in the hot-rolled plate are coarsened, and the formability of the final hard plate, especially the springback, Anisotropy tends to increase.

Here, the problem that occurs when the hard plate has a large anisotropy in the springback property will be described.

When a hard plate is drawn and formed into a shallow dish-like shape like a can lid shown in FIG. 1, the dish-shaped container tends to open its mouth due to springback of a bent portion between the bottom and the peripheral edge. At this time, since the mouth has a flange, it is not easily deformed. As a result, the deformation due to the springback appears as a “sleigh” on the bottom surface. Especially when the springback property differs in the vertical and horizontal directions in the rolling direction (when the anisotropy is large)
“Sledding” increases. A can lid having such a “sleigh” has a poor “stacking property” and is inconvenient in an automatic lid manufacturing plant. Here, poor stacking property means that when a material is subjected to drawing processing, the cup bottom is warped, and when these are stacked, the stability is deteriorated. In an actual can-making factory, shells are sometimes stacked and moved on a belt conveyor or the like. At this time, if the stacking property is poor, the shells collapse and are inconvenient.

Accordingly, an object of the present invention is to provide a method for producing an aluminum alloy hard plate having excellent anisotropy and further excellent softening resistance.

[0009]

In order to solve the above-mentioned problems, Mn, Cu, Si, Fe, Ti, and B are added and low-temperature annealing is performed. As a result of examining the relationship between the anisotropy of the final sheet and the rolling process while further improving the softening resistance during baking of the paint by precipitating Al-Mn compounds and other compounds finely, It was found that the anisotropy could be improved by regulating the temperature and the thickness at the end,
The present invention has been completed.

That is, the gist of the present invention is that Mg: 3.0.
To 6.0%, Mn: 0.4 to 0.8%, Cu: 0.05
-0.4%, Si: 0.05-0.5%, Fe: 0.1
0.5%, Ti: 0.01-0.05%, B: 0.0
It comprises 001 to 0.0010%, the aluminum alloy ingot consisting balance being Al and unavoidable <br/> impurities, rolled homogenization after thermal, the end temperature of the heat-rolling 250 ° C. or higher 28
0 ° C. or less, the thickness at the end is less than 2.5 mm, and then after an intermediate heat treatment at 200 to 250 ° C. for 1 hour or more,
This is a method for producing an aluminum alloy hard plate for a beverage can lid excellent in anisotropy and softening resistance, wherein final cold rolling of 50% or more is performed.

[0011]

The reasons for defining the components and processing conditions of the aluminum alloy of the present invention will be described.

Mg: Mg is a basic additive element in the present invention and contributes to strength. If Mg is less than 3.0%, the required strength cannot be obtained. If it exceeds 6%, cracks are likely to occur during hot rolling.

Mn: Mn is an additive element indispensable for improving softening resistance. If the amount is less than 0.4%, a sufficient effect cannot be obtained. If it exceeds 0.8%, the hot workability is reduced, and an Al-Fe-Mn-based coarse intermetallic compound is easily formed at the time of ingot making, and the formability of the hard plate is deteriorated.

Cu: Cu is an element capable of improving softening resistance similarly to Mn. In particular, it precipitates finely at the time of baking, and suppresses the movement of dislocations. If the amount exceeds 0.4%, cracks occur during hot rolling, which is not preferable. If the content is less than 0.05%, the effect cannot be obtained. Si: A compound with Mg (Mg ₂ Si) is formed at the time of coating baking, which is advantageous for increasing the material strength, but is not preferred for the formability of a hard plate.

[0015] In the present invention, it is better to keep it low, from 0.05 to 0.
A range of 5% is preferred. In order to make it less than 0.05%, it is necessary to raise the purity of the aluminum ingot, which is disadvantageous in cost. 0.
If it exceeds 5%, moldability deteriorates.

Fe: An Al—Fe—Mn coarse compound is formed at the time of agglomeration, and the formability of the hard plate is deteriorated. In the present invention, it is better to keep it low, and a range of 0.1 to 0.5% is preferable. 0.
In order to make it less than 1, it is necessary to increase the purity of the aluminum ingot,
This leads to higher costs. If it exceeds 0.5%, moldability deteriorates.

Ti: Effectively works to refine the ingot structure and improve the rollability and the formability of the hard plate. 0.01%
If it is less than 0.05%, the above effect cannot be obtained sufficiently. If it exceeds 0.05%, a coarse compound (TiB ₂ ) with B is formed, and serious defects such as pinholes are generated.

B: Like Ti, it has the effect of refining the ingot structure. If it is less than 0.0001%, the effect is not enough, and
If the content exceeds 0010%, a coarse compound (TiB ₂ ) with Ti is formed, and serious defects such as pinholes are generated.

Hot rolling: If the starting temperature is too high, the formability deteriorates due to eutectic melting and formation of coarse recrystallized grains.
0 ° C or less. If the starting temperature is lowered, the recrystallized grains become finer, which is preferable for formability. However, the efficiency during industrial production is lowered and the end temperature is too low. The hot rolling start temperature is usually 480 to 530 ° C, but it is desirable to start at 420 to 450 ° C to suppress the formation of coarse recrystallized grains.

In order to remove segregation of solute atoms in the ingot, it is desirable to perform a homogenization treatment prior to hot rolling. This homogenization treatment is usually performed at 480 to 530 ° C for 3 to 10 hours.

The hot rolling end temperature is important in the present invention. If the temperature is higher than 280 ° C., recrystallization of the hot-rolled sheet proceeds, the crystal grains become coarse, and poor stacking properties occur when a hard sheet is formed. In addition, dislocations are less likely to remain in the rolled sheet, which is disadvantageous for causing fine precipitation in the next intermediate heat treatment. On the other hand, when the temperature is lower than 250 ° C., recrystallization does not occur, so that the rolling texture is excessively developed. As a result, the 45 ° -4 direction edge of the final plate becomes too high, and the material yield deteriorates. Therefore, the hot rolling end temperature was regulated at 250 to 280 ° C.

When the thickness of the hot-rolled sheet is 2.5 mm or more, the amount of cold rolling increases to obtain a desired sheet thickness (eg, 0.4 mm or less), so that the ear ratio of the hard sheet tends to increase. The number of inter-rolling passes also increases, which is not preferable.

Intermediate heat treatment: heat treatment at a low temperature (200-250 ° C.) to finely precipitate the Al—Mn compound in the crystal grains.
For at least one hour). If the treatment temperature is lower than 200 ° C., a long holding time is required, which is industrially disadvantageous.

If the temperature is higher than 250 ° C., the dislocations remaining on the hot-rolled sheet disappear more rapidly than the precipitation of the Al—Mn compound, so that the precipitation sites of the Al—Mn compound disappear, and as a result, the uniformity is reduced. A fine precipitation state cannot be obtained, and a sufficient effect cannot be expected.

If the holding temperature is in the range of 200 to 250 ° C., the holding time is 1 hour, and uniform fine precipitation of the Al—Mn compound can be obtained. However, this effect does not change even after 24 hours or more, which is industrially disadvantageous.

Final cold rolling: has the effect of increasing the strength required as a can lid material. If the rolling reduction is less than 50%, this effect is not obtained, and if it exceeds 90%, the moldability is reduced and the ear ratio is also undesirably deteriorated. A preferred final cold rolling reduction is 75 to 90%.

Final heat treatment and coating: When the hard plate made by the above method is used for a beverage can lid, anticorrosion coating or application and printing of a polymer resin film are performed.

At this time, if the residual stress due to cold rolling is not uniform on the plate, a large warp or distortion occurs in the plate due to heat treatment for drying, thermosetting, etc. accompanying painting, pasting, printing and the like. . In order to avoid such troubles, the cold-rolled hard plate may be heated to reduce the unevenness of the residual stress. The heat treatment performed for this purpose is preferably performed at a temperature equal to or lower than that of the heat treatment accompanying painting or the like, that is, at 300 ° C. or less.

The heat treatment for relaxing the residual stress may be performed in a continuous heat treatment furnace for the strip. If a heat treatment for drying, heat curing, and the like accompanying painting is performed in a continuous heat treatment furnace that applies tension to the strip, heat treatment for relaxing residual stress can be substituted.

[0030]

【Example】

Example 1 An aluminum alloy having the composition shown in Table 1 was ingoted by a normal DC casting method, homogenized at 500 ° C for 8 hours, and then hot-rolled at 480 ° C and completed at 275 ° C. Nishi, board thickness 2.0
mm plates were obtained. Thereafter, an intermediate heat treatment was performed at 200 ° C. for 10 hours, and final cold rolling was performed to a sheet thickness of 0.25 mm (a reduction of 87.5%). The obtained cold-rolled material is kept as it is,
Heating for 0 second (the maximum temperature for baking paint) and 450 ° C
Heating for 30 seconds (heating to complete recrystallization temperature, so-called O
Material) and tested. With the value of proof stress obtained from the tensile test, the degree of softening was calculated by the following equation.

Softening degree (%) = 100 × ｛(cold rolled material−300 ° C.)
Heating material)｝ / (Cold rolled material-450 ° C heating material)｝ That is, the degree of softening is an index to determine whether or not the material softens during baking of the anticorrosion paint.
The maximum temperature of the baking temperature of the anticorrosive paint was used, and the temperature of 450 ° C. was the perfect recrystallization temperature of this alloy. Therefore, in the case of the present invention, the higher the degree of softening (100%), the worse, and the lower the degree of softening, the better the softening resistance. Table 2 shows the test results.

[0032]

[Table 1]

[0033]

[Table 2]

The material of the present invention has a proof stress after treatment at 300 ° C. of 270 MPa.
As described above, the softening degree is as small as 50% or less, and the softening resistance is excellent. Also, the ear ratio (blank diameter: 55 mm, flat bottom punch diameter: 33 mm) is small, and the stacking property is good.
As shown in Fig. 2, the method of evaluating stacking performance is to perform shallow drawing with a blank diameter of φ60mm and a flat bottom punch diameter of φ50mm (drawing ratio 1.2), and measure the cross-sectional shape parallel to the rolling direction on the bottom of the cup (contour measurement). Machine: CB-41 made by Mitoyo
The mold was drawn on a chart, and the amount of warpage (Δh) of the bottom was measured from the shape. When Δh was less than 1 mm, it was evaluated as ○.

The comparative examples were as follows.

In No. 5, since the amounts of Fe and Si are large, the elongation and Erichsen value are slightly lowered, and the proof stress and softening degree after the treatment at 300 ° C. are inferior to those of the material of the present invention. No. 6 has a large degree of softening due to insufficient Mn addition amount. In No. 7, since the amounts of Mn and Cu added were too large and cracks occurred during hot rolling, subsequent tests were stopped. No. 8 has low Mg and Mn contents, and thus has low proof stress after treatment at 300 ° C. and has the highest softening degree. No. 9 had too much added Ti and B, so Ti
Coarse compound of B ₂ are formed, a pinhole in the final cold-rolled sheet (through holes) were generated. Therefore, the subsequent tests were stopped.

Example 2 An alloy having the composition shown in Table 3 was ingot.

Table 4 shows the manufacturing conditions.

Table 5 shows the characteristic values of the obtained test materials.

The material of the invention has a proof stress of 280MP after the treatment at 300 ° C for 20 seconds.
Above a, the stacking property is improved compared to No.23, and
Ear rate is lower than No.24, and material yield is improved. No.23 has a poor stacking property due to the high hot-rolling end temperature.
Low yield strength after treatment at 0 ° C x 20s. No. 24 has a large ear ratio because the hot rolling end temperature is too low.

[0041]

[Table 3]

[0042]

[Table 4]

[0043]

[Table 5]

Example 3 A plate was prepared using the alloys shown in Table 6 under the conditions shown in Table 7.
All the homogenization treatments were performed at 500 ° C. for 8 hours.

The same test and ear ratio (evaluated with blank diameter = φ55 mm, flat bottom punch diameter = φ33 mm) as in Example 1 were performed. Table 8 shows the results.

Inventive Examples Nos. 31, 32 and 33 show that even if the condition of the intermediate heat treatment is changed in the range of 200 to 250 ° C., the effect of suppressing the softening resistance remains unchanged, and a hard plate having excellent strength formability can be obtained. It is shown that it is possible.

No. 34 and No. 35 shown as Comparative Examples have inappropriate intermediate heat treatment conditions, and thus have low softening resistance.

Comparative Example No. 36 shows the results when the sheet thickness at the end of hot rolling was increased, and the end temperature was within the range of the invention (250 to 280).
C), the final cold rolling amount has to be large, the ear ratio is large, and the formability is low. Similarly N
In the case of o.37, the stacking property is poor and the softening resistance is poor due to the high end temperature. In No. 38, the end temperature is too low, and the ear ratio and moldability are disadvantageous.

[0049]

[Table 6]

[0050]

[Table 7]

[0051]

[Table 8]

[0052]

According to the present invention, when an anticorrosive paint or the like is applied to an aluminum alloy plate used for a can lid for a retort beverage can, such as coffee or oolong tea, and then dried by heating, the strength is small. A coated plate with high strength can be obtained, and the thickness can be further reduced. In addition, a hard material having excellent moldability, a small ear ratio, and less occurrence of "warp" can be obtained. Further, the manufacturing process is short and the manufacturing cost is reduced.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a springback property.

FIG. 2 is an explanatory diagram of the amount of warpage on the bottom surface of a shallow draw cup for explaining stacking properties.

Continuation of the front page (51) Int.Cl. ⁷ Identification code FI C22F 1/00 673 C22F 1/00 673 683 683 691 691A 691B 694 694B (56) References JP-A-5-70904 (JP, A) JP JP-A-5-9680 (JP, A) JP-A-63-293144 (JP, A) JP-A-63-444 (JP, A) JP-A-3-6356 (JP, A) JP-A-2-185955 (JP) , A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C22F 1/04-1/057 C22C 21/00-21/18

Claims (2)

(57) [Claims] 1. Mg: 3.0-6.0% (mass%, the same applies hereinafter), Mn: 0.4-0.8%, Cu: 0.05-
0.4%, Si: 0.05-0.5%, Fe: 0.1-
0.5%, Ti: 0.01 to 0.05%, B: 0.00
An aluminum alloy ingot containing 0.1 to 0.0010%, the balance being Al and unavoidable impurities, is subjected to hot rolling after homogenization treatment, and the end temperature of the hot rolling is set to 250 ° C. or more to 280
℃ or less, the plate thickness at the end is less than 2.5 mm,
50% after intermediate heat treatment at 00-250 ° C for 1 hour or more
A method for producing an aluminum alloy hard plate for a beverage can lid having excellent anisotropy and softening resistance, wherein the final cold rolling is performed as described above. 2. The method for producing an aluminum alloy hard plate for a beverage can lid according to claim 1, wherein the hot rolling is started at 400 to 530 ° C.