JP2006257470A - Method for manufacturing aluminum alloy sheet for can lid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably obtain a can lid material of low earing without affecting material strength even in a manufacturing method in an SA process. <P>SOLUTION: The aluminum alloy ingot containing 0.1 to 0.3% Si, 0.2 to 0.7% Mn, 0.05 to 0.15% Cu. 0.1 to 0.5% Fe, and 2.0 to 2.5% Mg is subjected to homogenization treatment for 3 to 12 hours at (410+200xMn[mass%])°C according to the amount of the contained Mn, then to hot rolling. The coil side face temperature right after taking up to a coil form is regulated to 310 to 340°C and 5,000 to 20,000 pieces of the second phase particles of a size 0.5 to 3.5 μm at the section of the sheet are made to exist in 1 mm<SP>2</SP>and thereafter, the sheet is subjected to cold rolling of 86 to 90% in the rate of rolling without being subjected to intermediate heat treatment so that the earing rate when the sheet is made into a cylindrical deep drawn container at a deep drawing rate 48% attains ≤8%. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to an aluminum alloy plate for an aluminum can lid for a negative pressure can. That is, the beverage filled in the can is intended for coffee, tea, etc., which does not contain carbonic acid, and by tightening a can lid made of aluminum or steel and the aluminum alloy plate of the present invention, one can be Beverage can product.

There have been inventions aimed at improving the ear rate in aluminum alloy plates for can lids, but none of them has been sufficient for the following reasons.

  In Patent Document 1, only the alloy composition is specified for the reason that recyclability is excellent. However, if the manufacturing method is not specified as in the present invention, a material having a desired ear ratio cannot be obtained.

  In Patent Document 2, the area occupancy of the second phase particles having a size of 1 to 20 μm on the surface of the cold rolled sheet is specified and the opening of the can lid is improved, but the ear rate is improved. Is not sufficient to control the second phase particles of this size at this stage.

  In Patent Document 3, in order to improve the ear rate and the openability, the conditions for hot rolling and the orientation density of crystal grains in the surface layer portion of the hot rolled sheet are specified. This is effective in reducing the ear ratio, but in the production using a multi-stage tandem hot rolling mill, it is necessary to further regulate the distribution of second phase particles having a certain size as in the present invention.

JP 2000-160273 A JP 2000-273593 A JP 2001-214248 A

When the ear rate of the aluminum alloy plate is poor, the height (curl height) of the curled portion of the molded can lid body is not uniform in the circumferential direction. If the curl height becomes uneven in the circumferential direction, it will not be partly mated because the curl height will be in point contact with the can body at the part where it is partly high when mating with the can body. Will occur. For this reason, the aluminum alloy plate for can lids is required to have as low an ear rate as possible.

The manufacturing method which is the subject of the present invention is a process in which intermediate annealing is not performed after the end of hot rolling or between passes of cold rolling, so-called SA (Self-Annealing) process. Since the SA process can omit the annealing treatment, it is advantageous in terms of cost, but has the following disadvantages. That is, if the process is other than SA, the ear rate is controlled by changing the heat treatment conditions (temperature, time) of the intermediate annealing, the cold rolling reduction before the intermediate annealing, the cold rolling rate after the intermediate annealing, and the like. However, in the case of the SA process, since the heat treatment is not applied after the hot rolling, the control of the ear rate is limited.

The texture of aluminum or aluminum alloy that has been hot-rolled with a tandem hot rolling mill at a relatively high rolling ratio and recrystallized tends to have a cubic orientation. In the subsequent cold rolling, the crystal grains are elongated into fibers, and the orientation is random. In the rolled plate with the former orientation being dominant, the container formed by deep drawing has a strong ear at 0 ° and 90 ° with respect to the rolling direction, and when the latter orientation is dominant, the ear is strong at 45 °. Become. Therefore, it is necessary to produce a material with a low ear rate by balancing the two.

Control by changing the rolling reduction in cold rolling is accompanied by a change in material strength, which is a factor other than the ear rate, and is not preferable in view of the effects on the strength and formability of the can lid. Therefore, it is necessary to control the material before hot rolling, but the present inventors specify the alloy composition and the manufacturing method, so that the size of the cross section of the plate after hot finish rolling is 0.5 to 3.5 μm. The present inventors have found that an aluminum alloy plate for can lids having a good ear ratio can be manufactured by controlling the distribution state of the second phase particles.

That is, as essential elements, Si: 0.1 to 0.3% (mass%, the same applies hereinafter), Mn: 0.2 to 0.7%, Cu: 0.05 to 0.15%, Fe: 0.0. The aluminum alloy ingot containing 1 to 0.5%, Mg: 2.0 to 2.5%, and the balance Al and unavoidable impurities, depending on the amount of Mn contained, (410 + 200 × Mn [mass%] After the homogenization treatment at ± 19) ° C. for 3 to 12 hours, hot rolling is performed, and the coil side surface temperature immediately after winding into a coil shape is 310 to 340 ° C., and the cross section of the plate (the rolling direction and the thickness direction are 2). the second phase particles of the size of 0.5~3.5μm in the surface) to the side in the presence 5,000 to 20,000 pieces in 1 mm ^2, then rolling reduction 86 to 90% of the cold without intermediate heat treatment rolling The cylindrical deep-drawn container with a total drawing rate of 48% It is a manufacturing method of an aluminum alloy sheet for can lid, characterized in that to the ear rate when the is set to be 8% or less.

  According to the present invention, a low-ear can lid material can be stably obtained without affecting the material strength even in the manufacturing method in the SA process.

The reason for the action and range limitation of the alloy components in the present invention will be described.

Si: Addition amount is 0.1 to 0.3%. It affects the formation of second phase particles such as Al (Fe, Mn) Si compounds (α phase), Mg ₂ Si and the like. In order to obtain a good ear ratio as in the present invention, it is necessary to optimize the recrystallization texture formed during hot rolling or immediately after rolling as described above. The second phase particle distribution with a size of 5 to 3.5 μm is affected. If it is less than 0.1%, the particle distribution cannot be obtained no matter how the aluminum alloy sheet is produced. In the range exceeding 0.3%, coarse second-phase particles are generated, and cracks are likely to occur during rivet molding of the can lid.

Mn: Addition amount is set to 0.2 to 0.7%. While improving an intensity | strength, it influences Al-Mn-Fe type | system | group 2nd phase particle formation. Similarly to the above, if it is less than 0.2%, the distribution of the second phase particles having a certain size or more necessary for controlling the ear ratio cannot be obtained, and if it exceeds 0.7%, coarse second phase particles are not obtained. It will occur and cracks are likely to occur during rivet forming of the can lid. The homogenization temperature described later is changed according to the amount added.

Cu: Addition amount is set to 0.05 to 0.15%. Necessary for increasing strength and improving heat resistance due to Al-Mg-Cu precipitation during cold rolling and paint baking. If it is less than 0.05%, the effect is small, and if it exceeds 0.15%, the formability deteriorates due to excessive strength.
Fe: Addition amount is 0.1 to 0.5%. Like Mn, it affects the formation of Al—Mn—Fe-based second phase particles. If it is less than 0.1%, it is impossible to obtain a distribution of second phase particles of a certain size or more necessary for controlling the ear ratio, and if it exceeds 0.5%, coarse second phase particles are generated, Formability is reduced.

Mg: Addition amount is 2 to 3.5%. It contributes to strength improvement by solid solution hardening and affects the formation of second phase particles of Mg ₂ Si. If it is less than 2%, the effect is insufficient. On the other hand, if it exceeds 3.5%, work hardening during rolling or forming becomes large, and formability deteriorates.

In addition to the above elements, Al and inevitable impurities may be basically used, but one or more of Cr, Zn, and Ti may be added as necessary. These Cr,
Zn and Ti will be described in more detail.

Cr:
Cr is an element effective for improving the strength, but if it is less than 0.05%, the effect is small.
If it exceeds 5%, the formation of giant crystallized products causes a decrease in moldability, which is not preferable. Therefore, the range of Cr content when adding Cr is set to 0.05 to 0.5%. A more preferable range of the Cr content is 0.1 to 0.4%.

Zn:
The addition of Zn contributes to the strength improvement due to aging precipitation of Al—Mg—Zn-based particles.
If it is less than 5%, the effect cannot be obtained. If it exceeds 0.8%, there is no problem in terms of contribution to strength, but the corrosion resistance is deteriorated. Therefore, the range of the Zr amount when adding Zn is 0.05 to 0.
. 8%. A more preferable range of the Zn content is 0.1 to 0.5%.

Ti:
In a normal aluminum alloy, a small amount of Ti is added for refining ingot crystal grains. In this invention, a small amount of Ti may be added as necessary.
However, when the amount of Ti is less than 0.001%, the effect cannot be obtained. On the other hand, when it exceeds 0.20%, a large Al—Ti intermetallic compound crystallizes and inhibits formability. T
The amount of i was within the range of 0.001 to 0.20%. Further, it is known that the addition of a small amount of B together with Ti improves the effect of refining the ingot crystal grains. Therefore, in the present invention, addition of a small amount of B together with Ti is allowed. Thus, when adding B together with Ti, if the amount of B is less than 0.0001%, there is no effect, and if it exceeds 0.05%, Ti-B based coarse particles are mixed to impair the formability. Therefore, the amount of B when adding B together with Ti is 0.
It is desirable to be within the range of 0001 to 0.05%.

In the present invention, an aluminum ingot having the above alloy composition is produced by the following steps.

  In the homogenization treatment, the temperature is set to (410 + 200 × Mn [mass%] ± 19) ° C. for 3 to 12 hours according to the amount of Mn contained in the aluminum ingot. The homogenization treatment is an important process for controlling the distribution of the second phase particles having a size of 0.5 to 3.5 μm in the hot rolled sheet. The temperature is changed depending on the amount of Mn. Mn is not easily dissolved in Al as compared with other elements, and when adding a relatively large amount of 0.2 to 0.8% as in the present invention, the same temperature is used. Under the conditions, the second phase particles become large and densely distributed as the amount of Mn increases. Therefore, as in the present invention, in order to control the ear rate, it is necessary to obtain an optimal second phase particle distribution state, and it is necessary to change the homogenization temperature depending on the amount of Mn. The higher the temperature, the more Al-Mn-Fe-based second phase particles act in the direction of solid solution in Al, so the higher the temperature when Mn is contained, the lower the Mn content. The temperature must be set low. In particular, when the temperature is set to (410 + 200 × Mn [mass%] ± 19) ° C. as in the present invention, almost the same second phase particle distribution can be obtained even if the Mn content is different, and the final plate has an ear ratio Is stable and low. Here, ± 19 ° C. is an allowable range of temperature control, and if it exceeds ± 19 ° C., the distribution of the second phase particles is deviated. For the same reason, the allowable range of temperature control is desirably ± 10 ° C.

  After the homogenization treatment, hot rough rolling and hot finish rolling are performed. Hot finish rolling is performed using a tandem hot rolling mill at a total rolling reduction of 88 to 94% and wound into a coil. The temperature on the side surface of the coil immediately after the winding is set to 310 ° C to 340 ° C. When the coil temperature is less than 310 ° C., the material is not sufficiently recrystallized after winding the coil, resulting in an excessive increase in strength of the material and a variation in strength in the longitudinal direction. If the material temperature exceeds 340 ° C., the temperature becomes too high during hot finish rolling, resulting in surface defects such as pickup inclusion. The material temperature is controlled by adjusting the material temperature after hot rough rolling, the rolling speed of hot finish rolling, the oil temperature of the rolling oil, the flow rate, the emulsion state, and the like.

In order to obtain a good ear ratio, it is necessary to optimize the recrystallization texture formed at the time of hot rolling or immediately after rolling. In the recrystallization texture, the distribution of second phase particles having a certain size or more is present. Affect.
If second-phase particles of a certain size or larger are not present in the hot-rolled plate, the material hot-rolled by the tandem hot-rolling mill has superior cubic orientation grains, and the material is cold-rolled. The ear rate of the applied aluminum alloy plate is 0-90 ° ear height. If the second phase particles having a certain size or more are present in the hot-rolled sheet, generation and growth of crystal grains having an orientation different from the cube orientation at the interface between the particles and the parent phase are promoted. The ear rate of the aluminum alloy sheet that has been cold-rolled to a material having many crystal grains other than the cubic orientation is 45 ° high, but when the second phase particles are present in a certain amount or more in the hot-rolled sheet, During the subsequent cold rolling, the dislocations accumulate excessively with the second phase particles as nuclei, resulting in an excessively high material strength and hindering the moldability of the can lid.

Therefore, in this invention, it manufactures on said conditions and the 0.5-3.5 micrometer magnitude | size in the cross section (surface which makes a rolling direction and a thickness direction 2 sides) after hot finish rolling. There are 5000 to 20000 two-phase particles in 1 mm ² .

By setting it as such a distribution density, if it is set as the material structure of the crystal grain balance which has a cube orientation and other than that, it will become a material with a favorable ear rate and a moldability.

If the size of the second phase particles is less than 0.5 μm, it cannot be a generation site of crystal grains having an orientation different from the cubic orientation, and if it exceeds 3.5 μm, it can be a generation site. Second phase particles are not preferred because they impair can lid moldability. Further, if the distribution density is less than 5000 in 1 mm ² , the crystal grains in the cubic orientation are dominant, the ears of the product become 0-90 ° ear height, and the ear rate is increased. The strength becomes excessive and the moldability becomes worse.

After hot finish rolling, cold rolling is performed without performing intermediate annealing. However, if the cold rolling rate is less than 86%, the required strength as a can lid cannot be obtained. Excessive excess impairs moldability during can lid molding. Therefore, the cold rolling rate is 86 to 90%.

  By using the manufacturing method as described above, the ear rate when the finally obtained plate is made into a cylindrical deep-drawn container with a total drawing rate of 48% is 8% or less. If the ear rate exceeds 8%, a portion where the curl portion is partially high is formed when it is formed as a can lid, and a problem occurs when fitting with the can body portion.

  The evaluation method of characteristics in the following examples was performed as follows.

・ Second phase particle distribution of finished hot rolled sheet Photographing an arbitrary 5mm ² area of the cross section (surface with two sides in the rolling direction and thickness direction) of the buffed hot rolled sheet, and photographing The image was binarized with an image analyzer, and the size and number density of the second phase particles were measured.

-JIS No. 5 tensile test piece with the rolling direction as the longitudinal direction from the cold-rolled base plate after coating baking was processed in an oil bath equivalent to coating baking (250 ° C x 10 seconds), followed by a pulling speed of 20 mm / min. A tensile test was conducted to measure a 0.2% proof stress value. When the proof stress after painting and baking is 230 MPa or less, the required strength as a can lid is insufficient, resulting in a failure.

・ Can lid formability (rivet formability)
The final plate subjected to the paint baking process was subjected to multi-stage overmolding and visually checked for cracks. When 500 sheets were molded and even one sheet was cracked, it was judged as defective (x).

・ Ear rate (including distribution in the width direction)
A cylindrical container with a drawing ratio of 48% was prepared from a circular blank of Φ57, and the side wall height of the cylindrical container was measured at a total of 8 points at a pitch of 45 ° in the circumferential direction, and the ear ratio was obtained from the calculation of the following equation. .
Ear rate = (average height of 45 ° −0, average height of 90 °) / (average height of all measurement points)
For sampling of the circular blank, 5 points were measured at equal intervals from the width direction of the aluminum alloy plate, and an average value of 5 points was determined to be defective (x) if it exceeded 8%.

  An ingot was manufactured by melting and casting an Al alloy having an alloy composition shown in Table 1 by a conventional method. Subsequently, after homogenizing at a temperature corresponding to the amount of added Mn, hot rough rolling was performed, and the sheet was rolled to a thickness of 23 mm. Thereafter, hot finish rolling was performed with a four-stage tandem rolling mill, the reduction ratio of each stage was about 50%, the plate thickness was 1.8 mm, and the material temperature immediately after coiling was 310 to 340 ° C. Then, it cold-rolled without performing intermediate annealing and manufactured the 0.25 mm aluminum alloy plate.

  In the alloy within the composition range of the present invention, the second phase particle distribution of the hot-rolled plate satisfies the first aspect, and the ear ratio of the cylindrical container also satisfies the first aspect. Further, the yield strength after baking is ensured to be 230 MPa or more, and the can lid (rivet) moldability is also good.

  In Comparative Examples 8, 10, and 14, Si, Fe, and Mn are out of the specified lower limit of the present invention, the second phase particle distribution of the hot rolled sheet is out of the specified range, and the ear rate is poor. In Comparative Examples 12, 14, and 16, Cu, Mn, and Mg are out of the specified lower limit of the present invention, so that the proof strength after coating is not sufficiently obtained. Comparative Examples 7, 9, 11, 13, and 15 Since Si, Fe, Cu, Mn, and Mg are out of the specified upper limit of the present invention, the moldability of the can lid is inferior.

  After melting and casting the Al alloy having the alloy composition 1 shown in Table 1 by a conventional method, homogenization treatment and hot rolling were performed under the conditions shown in Table 2. Then, it cold-rolled without performing intermediate annealing and manufactured the aluminum plate. The homogenization temperature calculated from the amount of Mn of alloy composition 1 is 460 ± 19 ° C.

Table 2 shows the results of the examples.

  In the production conditions A to D of the present invention, the second phase particle distribution of the hot-rolled sheet is in the present invention, and good results are obtained in any of the ear rate, the proof strength after baking and the can lid moldability. ing.

On the other hand, in Comparative Example E, the homogenization temperature is lower than specified, the hot rolling temperature is low, the second phase particle distribution of the hot-rolled sheet is too large, the yield strength after baking is high, and the can lid (rivet) moldability bad. In Comparative Example G, the homogenization temperature is slightly lower than specified, so that the second phase particle distribution of the hot-rolled sheet is too large, the yield strength after baking is high, and the can lid (rivet) moldability is poor. In Comparative Examples F and H, the homogenization temperature is higher than specified, the distribution of the second phase particles in the hot rolled sheet is too small, and the ear rate is poor. In Comparative Example I, since the hot rolling temperature is low, the material is not recrystallized after the hot rolling is finished, the yield strength after baking is high, and the can lid (rivet) moldability is poor.

Claims (1)

As essential elements, Si: 0.1 to 0.3% (mass%, the same applies hereinafter), Mn: 0.2 to 0.7%, Cu: 0.05 to 0.15%, Fe: 0.1 to 0.1% An aluminum alloy ingot containing 0.5%, Mg: 2.0 to 2.5%, and the balance Al and unavoidable impurities is (410 + 200 × Mn [mass%] ± 19 according to the amount of Mn contained. ) After the homogenization treatment at 3 ° C for 3 to 12 hours, hot rolling is performed, the coil side surface temperature immediately after being coiled is 310 to 340 ° C, and the cross section of the plate (the rolling direction and the thickness direction are two sides) 5,000 to 20000 second phase particles having a size of 0.5 to 3.5 μm are present in 1 mm ² , and then cold rolling is performed at a rolling rate of 86 to 90% without intermediate heat treatment. By using a cylindrical deep-drawn container with a total draw ratio of 48% Method for producing an aluminum alloy sheet for can lid, wherein the ear rate is set to be 8% or less.