JP2933501B2 - Method for producing aluminum alloy sheet excellent in formability of DI can bottom - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a beverage can, and more particularly, to a method for producing an aluminum alloy hard plate suitable for a DI can having excellent bottom moldability.

[0002]

2. Description of the Related Art DI (drawing with ironi)
ng) Cans are required to be thinner and lighter from the viewpoint of resource saving and cost reduction. Under such circumstances, improvements in various materials and manufacturing methods have been proposed. Conventionally, generally, hard plates made of 3004 alloy are exclusively used. There are roughly two types of manufacturing processes for this material, a rough direct passing process and a medium dulling process.

[0003] Depending on the strength (pressure resistance of the product can) required for the annealing step of annealing the hot-rolled material and then cold rolling to make the product sheet thickness, the batch method and the CAL method are used.
(See Japanese Patent Application No. 1-226746). The products obtained by any of the processes have characteristics such that the ear ratio after DI processing is low and the yield is excellent. However, in the conventional processes in these examples, since the introduction of distortion during hot rolling is not sufficient, the formation of subgrains having relatively large crystal grains with a grain size of 60 μm or more and having the effect of improving formability as fine crystal grains is performed. Is less than 5%, and the strength of the base plate is so high that the bottom of the can is not sufficiently stretched during DI processing, resulting in springback or cracking resulting in poor moldability of the can bottom. was there.

[0004] In order to improve the moldability of the bottom of the can, conventionally, finish annealing has been performed after cold rolling, or a middle dull CAL process has been employed. In the process of forming sub-grains by performing finish annealing after cold rolling, in order to actually anneal with coils,
It is very difficult to make the entire area occupied by the sub-grains uniformly, and there is variation between the inside and outside of the coil, and when the inside is 10%, the outside exceeds 30%. Further, this method has a problem that the number of steps is increased. Also, in the middle dulling CAL process, fine crystal grains having a particle size of 20 μm or less can be obtained as compared with the rough dulling process material, and the moldability at the bottom of the can can be improved. However, there is also a problem that the neck flange formability required as a characteristic of the DI can is inferior.

[0005]

In order to meet the demand for thinner and lighter weight, the present applicant has previously proposed several improved inventions such as the prior art disclosed in Japanese Patent Application Laid-Open No. 4-272151. The prior art is a process in which CAL annealing is performed on the above-described hot-rolled material and then cold-rolled to obtain a product.
However, this method does not particularly mention means for improving the moldability of the bottom of the can, and as a result, the area occupancy of the sub-grain is less than 5%, and the "back ironing" processability in DI is excellent, but the springback is low. Inability to sufficiently suppress the problem, such as a problem that the predetermined can bottom depth does not come out or the elongation at the time of forming the can bottom becomes insufficient and cracks occur at the rising portion of the can bottom, and the pressure resistance required for the can cannot be satisfied. Is still there.

In order to solve this problem, it is necessary to take measures such as improving the strength level of the base plate by adjusting the components. It does not solve the problem.

The present invention has been made to solve such problems, and an object of the present invention is to reduce the thickness and improve the productivity while maintaining high strength and good moldability. An object of the present invention is to provide a method for manufacturing an aluminum alloy sheet to be obtained.

[0008]

The present invention has the following configuration to achieve the above object. That is, in the present invention, Mn: 0.85 to 1.15 by weight%
g: 0.90 to 1.50, Fe: 0.35 to 0.55
Si: 0.15 to 0.30, Cu: 0.15 to 0.30
And Zn: 0.1 to 1.0, and 580 to 630 in an aluminum alloy ingot containing other unavoidable impurities.
C. for 2 hours or more, followed by cooling to perform hot rolling consisting of rough hot rolling and finishing hot rolling with a starting temperature of 450 to 520 ° C. The temperature immediately after finishing hot rolling to 30 to 400 to 450 ° C.
0 to 350 ° C., and the obtained hot rolled sheet is further subjected to continuous annealing at a heating / cooling rate of 100 ° C./min or more and a heating / cooling temperature of 400 to 600 ° C. for 10 minutes or less, followed by tandem When a product having a total cold rolling reduction of 83 to 87% is manufactured in one pass using a rolling mill, the exit temperature Y (° C.) and the rolling speed X (m) are set within a range of a rolling speed of 1000 to 1700 m / min. / Min) and the following relational expression: 2.1 × (3200−X) ^0.5 +63 <Y <2.1 × (3
200−X) ^0.5 + 84 and the area occupancy of the subgrain is 5% or more 25
%, Which is a method for producing an aluminum alloy sheet having excellent moldability at the bottom of a DI can, characterized in that the content is less than 0.1%.

[0009]

In describing the operation of the present invention, the reasons for limiting the chemical components will be described first. Mn: Mn is an element that is effective for improving strength and preventing seizure during ironing by generating Al-Fe-Mn-based crystals. But in this case, 0.85%
If it is less than 1%, there is no effect, and if it exceeds 1.15%, there is a possibility that a giant crystal may be formed and the formability is reduced. For the above reasons, the Mn content is 0.85% to 1.1.
5%. Mg: Mg is an element effective in improving the strength of the can.
Precipitation hardening is caused by u-Mg based precipitates, which is effective for highly strengthening the bottom of the can. However, if the content is less than 0.90%, the effect is small, and if it exceeds 1.50%, the strength becomes too high and the moldability is reduced. For the above reasons, the Mg content is in the range of 0.90% to 1.50%.

Fe: Fe is used for reducing the size of crystal grains and Mn.
Thus, the formation of Al-Fe-Mn-based crystallization is effective in improving ironing workability. But 0.3
If it is less than 5%, this effect is small, and if it exceeds 0.55%, a giant crystal is formed to lower the formability. For the above reasons, the Fe content is set to 0.35% to 0.55%. Si: Si causes a phase transformation in an Al—Fe—Mn-based crystallized substance, forms a so-called α phase, increases the hardness of the crystallized substance, and is effective in improving ironing workability (prevention of seizure). is there. However, if the content is less than 0.15%, the effect is small, and if it exceeds 0.30%, the strength becomes excessively high, and the size of the upper crystal becomes large, thereby reducing the formability. For the above reasons, the amount of Si is set to 0.15% to 0.30%.

Cu: Cu is effective in increasing strength and preventing softening due to baking during can-making based on a combination with Mg. However, if it is less than 0.15%, there is no effect, and if it exceeds 0.30%, the strength increases greatly, leading to a decrease in formability. Therefore, the amount of Cu is 0.1.
15% to 0.30%. Zn: Zn makes the dispersion of the crystallized matter appropriate, drawability,
It is effective in improving ironing workability and flange formability.
However, if the Zn content is less than 0.1%, the effect is small.
Further, even if the Zn content exceeds 1.0%, the effect is saturated and the corrosion resistance required for the beverage can may be reduced. For the above reasons, the Zn content is in the range of 0.1% to 1.0%. In addition, as other unavoidable impurities, Ti
Is 0.1% or less, and B is 0.05% or less, as long as the impurity level is not impaired.

Next, the manufacturing process will be described. Normally DC
After beveling the cast alloy base ingot, soaking is performed. This soaking affects the formation of precipitates and affects the refinement of crystal grains in the hot rolled sheet. Grain refinement is important for improving ironing workability in DI molding. Conventionally, soaking conditions are generally below 600 ° C. This is because there is a difference in the heating temperature of the ingot in the conventional pit furnace (batch furnace), and there is a risk of burning in a high temperature part. In addition, since the temperature is high conventionally (540 in case of Al-Mg alloy).
° C or less), and the effect of soaking at a higher temperature was not clear.

In the present invention, the soaking temperature is 580 to 630 ° C. When the temperature is lower than 580 ° C., nucleation of recrystallized grains by the compound is small, and the effect is not sufficient. If the temperature exceeds 630 ° C., burning may occur. More preferably, it is in the range of 600 to 620 ° C. More preferably, by using a horizontal continuous homogenizing heat treatment furnace, operation under stable homogenizing heat treatment conditions can be performed with a small difference in the heating temperature of the ingot. The horizontal continuous homogenizing heat treatment furnace is preferably one having a heating zone, a holding zone, and a cooling zone by dividing the inside of the furnace into several sections.

Subsequently, hot rolling is performed after soaking, and the introduction of strain during hot rolling further reduces the crystal grains in the hot rolled sheet. Therefore, before starting hot rolling, the ingot is cooled (cooled) to start hot rolling. At the start of hot rolling at a temperature exceeding 520 ° C., the effect of introducing strain is small, and at a temperature lower than 450 ° C., although there is an effect, productivity is particularly poor in terms of time until cooling. Therefore, the heating start temperature is in the range of 450 to 520 ° C. There are two methods for adjusting the starting temperature: a method by cooling in the furnace, and a method of cooling to room temperature and then heating to the hot rolling temperature after soaking. Excellent in each stage.

Hot rolling is performed by reverse type rough rolling and tandem finish rolling. In order to make the crystal grains of the hot rolled sheet fine, it is necessary to control the temperature at the entrance and exit during the finish rolling. The entrance temperature is preferably low, but in order to control the exit temperature to an appropriate temperature range, the entrance temperature is set to 400 to 450.
℃. The outlet temperature is also 300 ~
It needs to be 350 ° C. If the temperature is lower than 300 ° C., the entire hot rolled coil cannot be recrystallized. If the temperature exceeds 350 ° C., recrystallization is performed, but coarsening due to growth of crystal grains is caused. The reason why the entire coil is recrystallized after hot rolling is that if the remaining partially unrecrystallized grains are recrystallized by subsequent annealing, the crystal grains become coarse. The crystal grains obtained under these conditions are 20 to 40 μm. Although the thickness of the hot-rolled sheet obtained under the above conditions is not regulated in the present invention, it is 1.5 to 3.0 mm in consideration of the thickness of a general product and the required strength.

The hot-rolled sheet (coil) is thereafter subjected to so-called CAL annealing, in which case it is particularly important to control the amounts of Cu and Mg. If it is lower than 400 ° C., the amount of solid solution of Cu and Mg is small, and baking strength at the time of can making cannot be obtained. on the other hand,
When the temperature exceeds 600 ° C., the solid solution increases, and although the strength can be ensured, it leads to a decrease in formability due to an increase in work hardening. In addition, when the heating and cooling speed is low, the amount of solid solution is reduced, and the strength is also insufficient. The holding time of heating varies depending on the heating temperature, but it is sufficient that the holding time is within 10 minutes.

Next, cold rolling is performed, which is the point of the present invention. In the present invention, the characteristics of a tandem cold rolling mill have been sufficiently investigated and studied, and by utilizing the characteristics, an aluminum hard plate for DI forming with excellent can bottom formability has been developed. In order to improve the moldability of the can bottom, it was found that it is important to form sub-grains and give sufficient elongation. It is also clear that excellent properties are exhibited when the material is recovered only by cold pressure (without finish annealing) in order to improve the formability. For that purpose, it is effective to use the heat generated by the tandem cold rolling mill.However, if the reduction rate does not reach a sufficient speed even if the reduction rate is simply increased, the occupancy rate of the sub-grain is low. Thus, it was found that the contribution to the improvement of the can bottom formability was small.

As a result of investigating the relationship, it was found that a material excellent in the moldability of the can bottom can be obtained by satisfying the following requirements. That is, the total cold rolling reduction 83
A rolling speed of 1000 m / min to 1700 m is required to produce ~ 87% of the product in one pass using a tandem rolling mill.
/ Min in the outlet side temperature Y (° C) and the rolling speed X (m /
min), the following relational expression: 2.1 × (3200−X) ^0.5 +63 <Y <2.1 × (3
200−X) ^0.5 +84, and the area occupancy of subgrain is 5% or more 2
To be less than 5%.

Therefore, according to the present invention, the cold rolling reduction is 83 to 87.
% Product is manufactured in one pass using a tandem rolling mill. If the cold rolling is less than 83%, the ear of the product is 0-
The reason for this is that the ear becomes 180 ° and the DI moldability is reduced.
On the other hand, if it is 87% or more, the 45 ° ear becomes too high, and the DI formability decreases due to the increase in strength. In addition, among the currently used rolling mills other than the tandem rolling mill, one is used.
The above-mentioned cold rolling reduction cannot be obtained with a pass.

Further, regarding the rolling speed, 1000 m / mi
If it is less than n, the productivity is remarkably reduced and it is not practical. In addition, the heat generated by friction with the roll is not sufficient, and the temperature for sub-grain formation cannot be maintained. If it exceeds 1700 m / min, the distortion during rolling becomes extremely poor, which has an adverse effect on the product plate. For the above reasons, the rolling speed is 1000
m / min to 1700 m / min.

The relationship between the rolling speed and the outlet temperature does not satisfy the above equation, that is, the rolling speed is 1000 m
/ Min to 1700 m / min, and Y is 2.1 × (3
In the case of (200-X) ^0.5 +63 or less, although the amount of strain required for sub-grain formation in cold rolling can be obtained, a sufficient temperature cannot be obtained due to the cooling effect of the coolant.
The subgrain occupancy is less than 5%, and there is no effect on the improvement of can bottom formability. In addition, if the rolling coolant is squeezed, there arises a problem that the surface properties are deteriorated. On the other hand, when Y is 2.1 × (3200−X) ^0.5 +84 or more, the effect of heat generation is larger than the cooling effect of the coolant. This results in reduced workability. When the amount of coolant is increased, excessive lubrication occurs during rolling, which also deteriorates the surface properties.

Next, the sub-grain area occupancy will be described. As described above, it is important to actively form sub-grains in order to improve the moldability of the can bottom, and the effect is small when the occupancy is less than 5%. However, when 25% or more of the sub-grains are formed, the work hardening during DI processing becomes large. Normally, since ironing is performed several times in DI processing, an increase in work hardening in the first die lowers ironing workability in the next die, causing a can body crack generally called tear-off,
The properties required for a can body cannot be satisfied.

[0023]

Embodiments of the present invention will be described below. (A) Example 1: Materials were prepared by the steps and components shown in Tables 1 and 2 below, and each material was compared. The characteristics as a result of the comparison are as shown in Tables 3 and 4 below.
No. 1 and No. 2 according to the present invention are more excellent in moldability (tear-off rate) than the comparative example. In addition, the present invention example is at a level where there is no problem in the can strength, and the comparative examples having the same or higher strength than the present invention formability (tea-off rate, neck success rate, flange success rate).
Is inferior. As described above, when the moldability and the can strength are comprehensively compared, the inventive examples No. 1 and No. 2 show the comparative example No.
Results superior to No. 3 to No. 7 were obtained.

[0024]

[Table 1]

[0025]

[Table 2]

[0026]

[Table 3]

[0027]

[Table 4]

The evaluation of the moldability necessary for the DI can and the examination of the strength of the can are as follows. For the overhang property (Erichsen value), the JIS Erichsen B method was used. The ironing workability was evaluated by using a drawn cup made with a blank diameter of 140 mmφ and a punch diameter of 90 mmφ, and using a DI processing machine with a final ironing rate of 41%, performing a can-making test of about 50,000 cans. Was evaluated. The can size is 35
0 cc, and a water-soluble lubricating oil was used as the lubricating oil.

Next, the obtained DI can was baked at 205 ° C., and a four-stage neck processing was performed. Processing distribution is 2mm
/ Stage. The success rate at which a 4-stage neck was formed (neck success rate) was evaluated. Further, the hole of the flange portion was expanded (canned) with a punch having a 90 ° intersection angle on the four-stage neck can, and the success rate (flange success rate) at a flange rate of 12% (flange diameter 65 mmφ, neck diameter 58 mmφ) was evaluated. .

The pressure strength and buckling strength, which are can strengths, were determined by hydraulic load and axial compression. All of the cans subjected to the can strength test were molded under the same conditions, and the difference in pressure strength was affected by the difference in the strength of the base plate and the moldability of the can bottom (easiness of appearance and presence or absence of cracks). The sub-grains were observed by TEM to determine the area occupancy.

(B) Example 2 An alloy shown in Table 5 below was used to produce a material in the steps shown in Table 6. Step A is within the scope of the present invention, and step B is a comparative example. Tables 7 and 8 show the properties of these materials. The moldability is substantially the same in both steps A and B, but step A is superior in terms of can strength (both pressure resistance and buckling strength). This is step A
Is due to the fact that the area occupancy of the sub-grain is in an appropriate range, the springback in forming the can bottom is small, the shape is close to the target shape, and there is no crack at the rising portion of the can bottom dome.

[0032]

[Table 5]

[0033]

[Table 6]

[0034]

[Table 7]

[0035]

[Table 8]

(C) Example 3: The alloys shown in Table 9 below were used instead of the alloys shown in Table 1 below.
0, and materials were manufactured in the steps shown in Table 11. Step C
Are within the scope of the present invention, and steps D, E and F are comparative examples. Tables 12 and 13 show the properties of these materials. Regarding the formability, steps C and F are almost the same, but step C is superior in terms of can strength (both pressure resistance and buckling strength). This is because in step C, the area occupancy of the sub-grain influences, the springback in the can bottom forming is small, the shape is close to the target shape, there is no crack at the rising part of the can bottom dome, and moderate work hardening This is because the can wall strength is at an appropriate level. D,
As for E, the can strength is not particularly problematic, but the moldability is inferior to that of the present invention.

[0037]

[Table 9]

[0038]

[Table 10]

[0039]

[Table 11]

[0040]

[Table 12]

[0041]

[Table 13]

[0042]

As described above, according to the present invention, the aluminum can obtained by the method of the present invention has a high well strength required as a DI can and is excellent in formability, so that the thickness of the material can be reduced. And productivity can be improved.

Claims (1)

(57) [Claims] 1. Mn: 0.85 to 1.15 by weight%
g: 0.90 to 1.50, Fe: 0.35 to 0.55
Si: 0.15 to 0.30, Cu: 0.15 to 0.30
And Zn: 0.1 to 1.0, and 580 to 630 in an aluminum alloy ingot containing other unavoidable impurities.
C. for 2 hours or more, followed by cooling to perform hot rolling consisting of rough hot rolling and finishing hot rolling with a starting temperature of 450 to 520 ° C. The temperature immediately after finishing hot rolling to 30 to 400 to 450 ° C.
0 to 350 ° C., and the obtained hot rolled sheet is further subjected to continuous annealing at a heating / cooling rate of 100 ° C./min or more and a heating / cooling temperature of 400 to 600 ° C. for 10 minutes or less, followed by tandem When a product having a total cold rolling reduction of 83 to 87% is manufactured in one pass using a rolling mill, the exit temperature Y (° C.) and the rolling speed X (m) are set within a range of a rolling speed of 1000 to 1700 m / min. / Min) and the following relational expression: 2.1 × (3200−X) ^0.5 +63 <Y <2.1 × (3
200−X) ^0.5 + 84 and the area occupancy of the subgrain is 5% or more 25
% Of the aluminum alloy sheet having excellent DI can bottom formability.