ALUMINUM ALLOY SHEET FOR CAN BODY, AND PROCESS FOR PRODUCING THE SAME

- UACJ CORPORATION

Provided are an Al alloy sheet having excellent characteristics for use as a can body, and a method for manufacturing the Al alloy sheet. A sheet having an Al alloy comprising a predetermined alloy composition as the material thereof, wherein an Al alloy sheet for a can body is configured so that the solid solution Mn content thereof after hot rolling is 0.25 mass % or greater, the solid solution Fe content is 0.02 mass % or greater, and the solid solution Si content is 0.07 mass % or greater, the electrical conductivity thereof is 30.0-40.0% IACS, the tensile strength in the rolling direction of a cold-rolled sheet thereof is 280-320 MPa, the tensile strength in the rolling direction after heat treatment at 205° C. for 10 minutes is 270-310 MPa, and the difference between the tensile strength in the rolling direction and the yield stress in the rolling direction after heat treatment at 205° C. for 10 minutes is 50 MPa or less.

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Description

This application is a continuation of the International Application No. PCT/JP2016/088086 filed on Dec. 21, 2016, the entireties of which are incorporated herein by reference

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates generally to an aluminum alloy sheet for a can body and a process for producing the same, and more particularly to an aluminum alloy sheet which can exhibit excellent properties in production of the can body, and a process for advantageously producing the same.

Description of Related Art

Conventionally, an aluminum (Al) alloy sheet for a can body has been produced by subjecting an Al alloy ingot to homogenization, hot rolling and cold rolling, as known well. Then, the Al alloy sheet for the can body is subjected to degreasing and washing, and oil-coating, as necessary, and further subjected to cupping, DI (Drawing and Ironing) forming, trimming, cleaning, drying, coating, baking, necking, flanging and the like, so that a can body for beverages and the like is produced.

Meanwhile, the can body for beverages and the like is required to have a practically sufficient strength, while the body strength is significantly deteriorated in the above-described baking step after the coating step (hereinafter referred to as coating and baking process). Thus, various means to prevent the deterioration of the strength of the can body, for example the following techniques, have been proposed.

JP2012-92431A1 (Patent Document 1) discloses an aluminum alloy cold-rolled sheet for a bottle can, wherein an amount of dispersed particles with a barycentric diameter of less than 1 μm represented as an a phase in a sheet structure is reduced, and a proportion of a β phase being an Al6(Fe, Mn)-based intermetallic compound and the α phase being an Al—Fe—Mn—Si-based intermetallic compound is set to be not less than 0.50 in terms of Hβ/Hα, Hα and Hβ being a largest height of an X-ray diffraction peak of the a phase and the β phase respectively, so that a hot-rolled sheet is given uniform recrystallization in the width direction, and variations in earing ratio of the sheet in the width direction can be reduced accordingly.

Furthermore, JP2011-202273A1 (Patent Document 2) discloses an aluminum alloy cold-rolled sheet for a bottle can, which has a specific alloy composition, in which amounts of solid-solubilized or dissolved Fe and Mn in a sheet structure is suitably controlled, to thereby increase a number density of relatively large dispersed particles which function as nucleation sites for recrystallization in a hot-rolled sheet, while promoting the recrystallization in a central part of the rolled sheet in the width direction, in particular in a middle part of the sheet in the thickness direction, and permitting uniform recrystallization of the hot-rolled sheet in the width direction, so that the variation of the earing ratio of the sheet in the width direction can be reduced.

Meanwhile, in recent years, it has become an important issue to recycle a reclaimed mass of used beverage cans (UBC: Used Beverage Can) in producing can bodies for beverages, in view of protection of the environment. Furthermore, to reduce an amount of use of materials, endeavors have been made to reduce the thickness and weight of can bodies. However, the reclaimed mass of UBC often contains Si, Fe and the like, so that an Al alloy ingot obtained by recycling the reclaimed mass of UBC includes a high concentration of Si and Fe. Si forms an intermetallic compound with Mn and Fe at the time of heating of the Al alloy ingot, resulting in a decrease of the amount of solid-solubilized Mn. As a result, thermal softening resistance of an obtained Al alloy sheet is reduced, thereby causing a problem that the strength of the can body is significantly deteriorated in the coating and baking process. In the case where the initial strength of the Al alloy sheet is set to be high in consideration of the reduction of the strength during the coating and baking process, there arises a problem that a risk of breakage of the can body during the DI forming increases with a decrease of the thickness and weight of a wall portion of the can body. Accordingly, in production of the can bodies for beverages by recycling the reclaimed mass of UBC, the amount of use of the reclaimed mass of UBC must be limited and a new base metal mass must be added, to thereby control a content of Si in the alloy ingot.

It is noted that Patent Document 1 discloses a technique of suppressing generation of precipitated particles (a phase) having a size of less than 1 μm, and Patent Document 2 discloses a technique of controlling only the amount of solid-solubilized Fe and Mn so as to promote recrystallization during hot rolling, thereby controlling only the earing ratio. However, these techniques can neither achieve both of the desired strength of the can body and the earing ratio at the same time, nor do they pay attention to the amounts of solid-solubilized Fe, Mn and Si, and to the fine particles (a phase) precipitated during cold rolling.

Patent Document 1: JP 2012-92431 A1

Patent Document 2: JP 2011-202273 A1

SUMMARY OF THE INVENTION

The present invention was made in view of the background art described above. Therefore, it is a technical problem of the invention to provide an Al alloy sheet having excellent properties for use as a can body, and a process for producing the same. It is another problem of the invention to provide an Al alloy sheet for use as a can body, and a process for producing the same, wherein decrease of the strength of the can body, in particular the strength of the can body after heat treatment, which influences troubles such as deterioration of the body strength and breakage of the body, is effectively suppressed by optimizing the amounts of solid-solubilized Fe, Mn and Si, and the fine particles (a phase) precipitated during cold rolling.

The above-described problems can be solved according to one mode of the invention, which provides an aluminum alloy sheet for a can body which is formed of a cold-rolled sheet obtained by cold rolling a hot-rolled sheet comprising an aluminum alloy consisting of 0.7-1.3% by mass of Mn, 0.8-1.5% by mass of Mg, 0.25-0.6% by mass of Fe, 0.25-0.50% by mass of Si, 0.10-0.30% by mass of Cu, not more than 0.25% by mass of Zn, not more than 0.10% by mass of Ti and not more than 0.05% by mass of B, and the balance being Al and inevitable impurities, wherein the hot-rolled sheet includes not less than 0.25% by mass of solid-solubilized Mn, not less than 0.02% by mass of solid-solubilized Fe and not less than 0.07% by mass of solid-solubilized Si, and has an electric conductivity of 30.0-40.0% IACS, and wherein the cold-rolled sheet has a tensile strength (TS) of 280-320 MPa in a rolling direction and a tensile strength (ABTS) of 270-310 MPa in the rolling direction after heat treatment at 205° C. for 10 minutes, and a difference between the tensile strength (TS) in the rolling direction and a yield strength (ABYS) in the rolling direction after heat treatment at 205° C. for 10 minutes is not larger than 50 MPa.

The above-described problems can also be solved according to another mode of the invention, which provides an aluminum alloy hot-rolled sheet for a can body, comprising an aluminum alloy consisting of 0.7-1.3% by mass of Mn, 0.8-1.5% by mass of Mg, 0.25-0.6% by mass of Fe, 0.25-0.50% by mass of Si, 0.10-0.30% by mass of Cu, not more than 0.25% by mass of Zn, not more than 0.10% by mass of Ti and not more than 0.05% by mass of B, and the balance being Al and inevitable impurities, wherein the hot-rolled sheet includes not less than 0.25% by mass of solid-solubilized Mn, not less than 0.02% by mass of solid-solubilized Fe and not less than 0.07% by mass of solid-solubilized Si, and has an electric conductivity of 30.0-40.0% IACS.

The above-described problems can also be solved according to a further mode of the invention, which provides an aluminum alloy sheet for a can body, comprising an aluminum alloy consisting of 0.7-1.3% by mass of Mn, 0.8-1.5% by mass of Mg, 0.25-0.6% by mass of Fe, 0.25-0.50% by mass of Si, 0.10-0.30% by mass of Cu, not more than 0.25% by mass of Zn, not more than 0.10% by mass of Ti and not more than 0.05% by mass of B, and the balance being Al and inevitable impurities, wherein the sheet has a tensile strength (TS) of 280-320 MPa in a rolling direction and a tensile strength (ABTS) of 270-310 MPa in the rolling direction after heat treatment at 205° C. for 10 minutes, and a difference between the tensile strength (TS) in the rolling direction and a yield strength (ABYS) in the rolling direction after heat treatment at 205° C. for 10 minutes is not larger than 50 MPa.

In a preferable form of the aluminum alloy sheet for a can body according to the above-described mode of the invention, the sheet has an electric conductivity of 28.4% IACS-39.8% IACS.

The above-described aluminum alloy sheet for a can body according to the invention is advantageously produced by a process comprising steps of: (a) providing an ingot of an aluminum alloy consisting of 0.7-1.3% by mass of Mn, 0.8-1.5% by mass of Mg, 0.25-0.6% by mass of Fe, 0.25-0.50% by mass of Si, 0.10-0.30% by mass of Cu, not more than 0.25% by mass of Zn, not more than 0.10% by mass of Ti and not more than 0.05% by mass of B, and the balance being Al and inevitable impurities; (b) performing hot rolling on the ingot of an aluminum alloy so as to obtain a hot-rolled sheet including not less than 0.25% by mass of solid-solubilized Mn, not less than 0.02% by mass of solid-solubilized Fe and not less than 0.07% by mass of solid-solubilized Si, and having an electric conductivity of 30.0-40.0% IACS; and (c) performing cold rolling on the hot-rolled sheet so as to form a cold-rolled sheet wherein a tensile strength (TS) in a rolling direction is 280-320 MPa and a tensile strength (ABTS) in the rolling direction after heat treatment at 205° C. for 10 minutes is 270-310 MPa, and wherein a difference between the tensile strength (TS) in the rolling direction and a yield strength (ABYS) in the rolling direction after heat treatment at 205° C. for 10 minutes is not larger than 50 MPa.

The above-described aluminum alloy sheet for a can body according to the invention is also advantageously produced by a process comprising steps of: surface-machining an ingot of an aluminum alloy consisting of 0.7-1.3% by mass of Mn, 0.8-1.5% by mass of Mg, 0.25-0.6% by mass of Fe, 0.25-0.50% by mass of Si, 0.10-0.30% by mass of Cu, not more than 0.25% by mass of Zn, not more than 0.10% by mass of Ti and not more than 0.05% by mass of B, and the balance being Al and inevitable impurities; heating the ingot to a homogenization temperature (T) within a range of 550-620° C. at a heating rate of 30-120° C. per hour; performing homogenization by keeping the ingot at the homogenization temperature (T) for a time not shorter than (145-0.24 T) hours; performing rough hot rolling on the ingot immediately or after cooling the ingot to a starting temperature of hot rolling not lower than 500° C. at a cooling rate of 10-90° C. per hour after finishing the homogenization, such that a temperature of the ingot upon termination of the rough hot rolling is within a range of 430-550° C., so as to form a sheet having a thickness of 20-40 mm; performing finish hot rolling on the sheet such that a temperature of the sheet upon termination of the finish hot rolling is within a range of 300-390° C., so that the sheet has a thickness of 1.5-4.0 mm; and performing cold rolling on the sheet such that a total working ratio of the sheet is not less than 75% and an average rolling rate in a steady part of a final pass is within a range of 700-1600 m per minute, so that the sheet has a thickness of 0.2-1.0 mm.

In a preferable form of the process for producing the aluminum alloy sheet for a can body according to the invention, the difference (S1-S2) between the electric conductivity (S1) of the sheet obtained by the finish hot rolling and the electric conductivity (S2) of the sheet obtained by the cold rolling is controlled to be 0.2-1.6% IACS.

In another preferable form of the process for producing the aluminum alloy sheet for a can body according to the invention, an area of particles having a diameter of 0.1 μm-1 μm in the ingot of an aluminum alloy subjected to the homogenization is not less than 3.5% in terms of a microphotograph taken by a scanning electron microscope.

According to the invention, there is also provided a can body for beverages, which is formed of the above-described aluminum alloy sheet.

In a preferable form of the can body for beverages according to the invention, the above-described aluminum alloy sheet for a can body is subjected to a predetermined coating and baking process.

As described above, the Al alloy sheet for the can body according to the invention is formed of the Al alloy consisting of the specific alloy composition, such that the amounts of solid-solubilized Fe, Mn and Si in the hot-rolled sheet prepared from the Al alloy and precipitation of fine particles (a phase) during cold rolling of the hot-rolled sheet are optimized. For this reason, an excellent formability and a high thermal softening resistance of the sheet are realized simultaneously, and further an excellent strength of the can body is exhibited even after the heat treatment, so that the sheet is advantageously used as a material for the can body.

Furthermore, according to the process for producing the aluminum alloy sheet for the can body according to the invention, the aluminum alloy sheet for the can body having excellent properties such as compatibility of formability and the strength of the can body after the heat treatment can be industrially advantageously produced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the amount of variation of the electric conductivity when each of two aluminum alloy materials having different alloy compositions was subjected to compression forming at a temperature of 150° C.

 DETAILED DESCRIPTION OF THE INVENTION

First of all, an aluminum alloy to provide an aluminum alloy sheet for a can body according to the invention includes 0.7-1.3% (by mass, the same for the following) of Mn, 0.8-1.5% of Mg, 0.25-0.6% of Fe, 0.25-0.50% of Si, 0.10-0.30% of Cu, not more than 0.25% of Zn, not more than 0.10% of Ti and not more than 0.05% of B, the balance being Al and inevitable impurities. The reasons for limiting the amounts of the components are as follows.

[Mn: 0.7-1.3%]

Mn (manganese), which is an essential alloy element in the Al alloy sheet according to the invention, improves the strength, and in particular contributes to an improvement of the thermal softening resistance in a solid-solubilized state. Mn forms an α-phase compound (Al—Mn—Fe—Si-base) with Fe and Si, which are also impurity elements inevitably introduced in the production process. Particles of this intermetallic compound have a quite high degree of hardness, and prevent seizure between an Al alloy material and a mold in a forming process so as to improve surface properties of a formed container. In the case where a content of Mn is less than 0.7%, the effects of Mn are not sufficiently exhibited. On the other hand, in the case where the content exceeds 1.3%, there arises a problem of an excessively high degree of the strength. The content of Mn is preferably within a range of 0.8-1.2%.

[Mg: 0.8-1.5%]

Mg (magnesium) is solid-solubilized in Al so as to contribute to an increase of the strength of the container. In the case where a content of Mg is less than 0.8%, a sufficient strength suitable for an end product is difficult to be achieved. On the other hand, in the case where the content exceeds 1.5%, there arises a problem of deterioration of formability because the strength of the can body becomes excessively high. The content of Mg is preferably within a range of 1.0-1.3%.

[Fe: 0.25-0.6%]

Fe (iron) forms, with Mn, an Al6(Fe, Mn) phase compound and an a phase (Al—Mn—Fe—Si-based) compound, and also forms an Al—Fe—Si-based compound, during casting. A solid lubricating effect of such intermetallic compounds prevents seizure between the material and the mold in the forming process. In the case where a content of Fe is less than 0.25%, the number of the intermetallic compounds becomes remarkably low, so that the material sticks to a dice in a DI forming process, thereby causing deterioration of surface properties of the container. On the other hand, in the case where the content exceeds 0.6%, there arises a problem that an excessive amount of Al—Fe—Mn-based intermetallic compound is formed, and this compound provides a starting point of cracking, thereby causing the deterioration of formability. The content of Fe is preferably within a range of 0.30-0.50%.

[Si: 0.25-0.50%]

Si (silicon) forms, with the above-described Mn and/or Fe, the a phase (Al—Mn—Fe—Si-based) compound and the Al—Fe—Si-based compound, which have the solid lubricating effect, and exhibits an effect to prevent sticking of the material to the dice in the DI forming process. The effect is not sufficiently exhibited in the case where a content of Si is less than 0.25%. On the other hand, in the case where the content of Si exceeds 0.50%, there arises a problem that an excessive amount of Al—Mn—Fe—Si-based intermetallic compound is formed, so that the compound provides a starting point of cracking, thereby causing the deterioration of formability, and an amount of solid-solubilized Mn is reduced, resulting in deterioration of the thermal softening resistance. The content of Si is preferably within a range of 0.30-0.40%.

[Cu: 0.10-0.30%]

Cu (copper) has an effect of formation and precipitation of Al—Cu—Mg-based intermetallic compound in the coating and baking process, so as to inhibit or prevent deterioration of the strength in the coating and baking process. The effect cannot be sufficiently achieved in the case where a content of Cu is less than 0.10%. On the other hand, in the case where the content exceeds 0.30%, there arises a problem that work hardenability in the forming process becomes too high, thereby causing the deterioration of formability. The content of Cu is preferably within a range of 0.15-0.25%.

[Zn: Not More than 0.25%]

Zn (zinc) is an element which improves formability. However, in the case where a content of Zn is excessive, the cost is increased, and coarse intermetallic compounds are formed, with a result of deterioration of formability. Thus, the content of Zn is controlled to be not more than 0.25%. The content of Zn is preferably within a range of 0.05-0.20%.

[Ti: Not More than 0.10% and B: Not More than 0.05%]

Ti (titanium) and B (boron) function to fine a casting structure so as to uniformize a dispersed state and a crystal grain structure of a crystallized product generated during casting. However, in the case where a content of Ti exceeds 0.10% or a content of B exceeds 0.05%, coarse intermetallic compounds are formed with a result of deterioration of formability. The content of Ti and B are preferably within ranges of not more than 0.03% and not more than 0.04% respectively.

[Al and Inevitable Impurities: the Balance]

The Al alloy to form the Al alloy sheet for the can body according to the invention consists of, in addition to the above-described alloy components, the balance of Al (aluminum) and inevitable impurities, that is, elements other than the above-described alloy components. It is preferable to minimize the amount of the inevitable impurities for reducing deterioration of properties of the sheet. The amount is generally set to be not more than the upper limit of each element in the Al alloy, which is defined by the JIS standard and the like. The total amount of elements of the inevitable impurities is generally not more than 0.15%, preferably not more than 0.10%.

The Al alloy sheet according to the invention formed of the Al alloy consisting of the above-described alloy composition includes, after the hot rolling (before the cold rolling), not less than 0.25% by mass of solid-solubilized Mn, not less than 0.02% by mass of solid-solubilized Fe and not less than 0.07% by mass of solid-solubilized Si, and has an electric conductivity of 30.0-40.0% IACS, so that the sheet exhibits a high degree of thermal softening resistance. A large amount of the solid-solubilized elements results in forming of minute particles of compounds comprising Mn, Fe and Si during cold rolling, as described later. The amount of the solid-solubilized elements in the hot-rolled sheet is restricted by the content of each element in the Al alloy. The highest electric conductivity of the sheet achieved by the amounts of the solid-solubilized elements is 40.0% IACS, and even in the case where the additive elements are solid-solubilized by a maximum degree, the electric conductivity of the sheet is not lower than 30.0% IACS. Meanwhile, in the case where the amounts of the solid-solubilized elements are less than the lower limit defined above, the strength of the sheet is significantly deteriorated in the coating and baking process.

The Al alloy sheet according to the invention initially has a tensile strength (TS) of 280-320 MPa in a rolling direction. The tensile strength (TS) less than 280 MPa results in a problem that the strength of the can body formed of the Al alloy sheet is not sufficient, while the strength more than 320 MPa causes difficulty in the DI forming. Furthermore, the Al alloy sheet according to the invention is characterized in that its tensile strength (ABTS) in the rolling direction after heat treatment at 205° C. for 10 minutes is 270-310 MPa. The tensile strength (ABTS) in the rolling direction after heat treatment less than 270 MPa results in the problem that the strength of the can body formed of the Al alloy sheet is not sufficient, while the strength more than 310 MPa causes difficulty in the DI forming. In addition, in the Al alloy sheet according to the invention, a difference (TS-ABYS) between the tensile strength (TS) in the rolling direction and a yield strength (ABYS) in the rolling direction after heat treatment at 205° C. for 10 minutes is controlled not to exceed 50 MPa, so that it is possible to simultaneously achieve both of a desired formability of the Al alloy sheet and strength after heat treatment of the can body obtained by the Al alloy sheet. strength of the can body obtained by the Al alloy sheet, even after the can body is subjected to heat treatment.

To produce the Al alloy sheet according to the invention, a material consisting of the above-described Al alloy composition is melted to make a molten metal of the Al alloy. Then, the molten metal is formed into an Al alloy ingot, such as billet and slab, by conventional casting methods such as the DC casting method. It is noted that the Al alloy ingot has a composition comprising Mn, Mg, Fe, Si, Cu, Zn, Ti and B in the amounts defined according to the invention.

Subsequently, the Al alloy ingot is subjected to the conventional surface-machining and successive specific homogenization treatment so as to obtain desired properties of the Al alloy sheet according to the invention. In such homogenization treatment, the surface-machined Al alloy ingot is heated to a homogenization temperature (T: ° C.) within a range of 550-620° C. at a heating rate of 30-120° C./h, and kept at the homogenization temperature (T) for a time not shorter than (145-0.24 T) hours (Hr). In the case where the heating rate is lower than 30° C./h, production equipment is occupied for a longer time, so that the production cost is increased. On the other hand, in the case where the heating rate is higher than 120° C./h, a large amount of fine particles is formed, thereby causing problems that the strength becomes too high and the formability is deteriorated. In the case where the homogenization temperature (T) is lower than 550° C., the effect of the homogenization is not sufficiently exhibited. On the other hand, in the case where the homogenization temperature (T) is higher than 620° C., there arises a problem that the material is partly melted so that the formability is deteriorated. The homogenization treatment has characteristics to precipitate coarse a phase compounds so that seizure in the forming process is prevented, as well as to eliminate segregation of the elements included in the Al alloy ingot so that a uniform microstructure is obtained. Furthermore, the homogenization treatment is continued for a time not shorter than (145-0.24 T) hours, whereby a cross sectional structure of the homogenized Al alloy ingot has an area of not less than 3.5% in terms of particles with a diameter of 0.1 μm-1 μm, in a microphotograph with magnification of 100-20000 times using a scanning electron microscope. In that state, an effect of preventing seizure can be obtained, and required amounts of solid-solubilized Mn, Fe and Si are secured for achieving an effective thermal softening resistance. The upper limit of the period of time of homogenization treatment is generally not longer than 30 hours, preferably not longer than 20 hours, in view of productivity and the like.

After the above-described homogenization treatment is finished, the Al alloy ingot can be directly (immediately) subjected to a hot rolling process. Alternatively, the ingot may be cooled to a starting temperature of hot rolling not lower than 500° C. at a cooling rate of 10-90° C./h, and then subjected to the hot rolling process. In the case where the Al alloy ingot is subjected to the cooling process such that the cooling rate is less (lower) than 10° C./h or the ingot is cooled to a temperature lower than 500° C., Mn, Fe and Si are precipitated in the cooling process so that the amounts of solid-solubilized elements are reduced. This causes a problem that precipitation of fine particles comprising Mn, Fe and Si is not sufficient in a subsequent cold rolling process, resulting in the deterioration of the thermal softening resistance of the Al alloy sheet. The cooling rate more (higher) than 90° C./h causes a problem that a temperature distribution within the Al alloy ingot becomes uneven so that properties of an end product are unstable.

In the invention, hot rolling of the Al alloy ingot is performed as a combination of rough hot rolling and finish hot rolling, as known, whereby a sheet whose thickness after the finish hot rolling is 1.5-4.0 mm is formed. The rough hot rolling is performed on the Al alloy ingot immediately after the above-described homogenization or after the cooling to the predetermined temperature, such that a temperature upon termination of the rough hot rolling (temperature of the ingot at the time when the rough hot rolling is terminated) is within a range of 430-550° C., so as to form a sheet having a thickness of 20-40 mm. In the case where the above-described temperature upon termination of the rough hot rolling is lower than 430° C., there arises a problem that a temperature upon termination of the finish hot rolling following the rough hot rolling tends to be lower than desired. On the other hand, in the case where the temperature upon termination of the rough hot rolling is higher than 550° C., there is a risk that coarse recrystallized grains are generated in the hot rolling process, thereby causing deterioration of the formability. Furthermore, in the case where the thickness of the sheet obtained by the rough hot rolling is smaller than 20 mm, there is a risk that a working ratio in the subsequent finish hot rolling is not sufficient so that an effective recrystallized structure cannot be obtained after the finish hot rolling. On the other hand, the thickness larger than 40 mm causes a problem that the working ratio in the finish hot rolling is too large so that anisotropy in the DI forming process is prominent.

In the finish hot rolling following the above-described rough hot rolling, the conventional rolling process is performed such that a temperature upon termination of the finish hot rolling (temperature of the ingot at the time when the finish hot rolling is terminated) is within a range of 300-390° C. so that the sheet has a thickness of 1.5-4.0 mm. In this finish hot rolling process, it is important to control the obtained sheet so as to have a recrystallized structure in the cooling process after coiling of the sheet. In the case where the above-described temperature upon termination of the finish hot rolling is lower than 300° C., there arises a problem that formation of the recrystallized structure is not sufficient so that the anisotropy is prominent and the strength of the product is excessively high. On the other hand, in the case where the temperature upon termination of the finish hot rolling is higher than 390° C., there is a risk that the recrystallized grains become coarse, so that the DI formability is deteriorated. Furthermore, in the case where the thickness of the sheet obtained by the finish hot rolling is smaller than 1.5 mm, there is a risk that a working ratio in the subsequent cold rolling process is not sufficiently high, resulting in reduction of the strength. On the other hand, the thickness larger than 4.0 mm causes a problem that the working ratio in the cold rolling process becomes excessively high, so that the strength of the sheet is too high. By the finish hot rolling, the above-described amounts of solid-solubilized Mn, Fe and Si are secured.

The thus obtained hot-rolled sheet is further subjected to cold rolling such that a total working ratio of the sheet is not less than 75% and an average rolling rate in a steady part of a final pass in the cold rolling process is within a range of 700-1600 m per minute, so that the obtained Al alloy sheet has a thickness of 0.2-1.0 mm. The cold rolling is performed in accordance with the conventional method. Here, if the total working ratio in the cold working is lower than 75% or the average rolling rate in the steady part is higher than 1600 m/m, particles of Mn-based compounds are not sufficiently precipitated, so that the thermal softening resistance may be deteriorated. On the other hand, in the case where the average rolling rate in the steady part is lower than 700 m/m, there is a problem that productivity is significantly deteriorated. Furthermore, the thickness of the obtained Al alloy sheet smaller than 0.2 mm causes a problem that a sufficient strength of the can body may not be achieved, while the thickness larger than 1.0 mm results in a problem that the weight of the sheet is too high, so that it is not suitable for use as a can for beverages.

Furthermore, according to the invention, the desired Al alloy sheet is preferably produced such that the difference (S1-S2) between the electric conductivity (S1) of the sheet (hot-rolled sheet) obtained by the above-described finish hot rolling and the electric conductivity (S2) of the sheet (cold-rolled sheet) obtained by the above-described cold rolling is 0.2-1.6% IACS, that is, the electric conductivity of the cold-rolled sheet is within a range of 28.4% IACS-39.8% IACS. A sufficient amount of solid-solubilized Mn allows particles of compounds comprising Mn, Fe and Si to be induced by the cold working and finely precipitated, so that the thermal softening resistance is improved. Meanwhile, FIG. 1 shows a result of examination of a difference of electric conductivity before and after a compression forming test at 150° C. equivalent to the cold working with respect to each of two samples formed of Al alloys comprising respective different amounts of Mn. The result indicates an increase of the electric conductivity of the sample formed of the Al alloy comprising Mn after the cold working, but substantially no change of the electric conductivity of the sample formed of the Al alloy not comprising Mn. Thus, the result proves that the Mn-based compound particles were precipitated by the cold working. Basically, in the cold working, the electric conductivity decreases due to working deformation, but the precipitation of the particles of Mn-based compound permits an increase of the electric conductivity, so that the amount of decrease of the electric conductivity generally falls within the range of 0.2-1.6% IACS. In the case where the amount of decrease of the electric conductivity is less than 0.2% IACS, the cold-working ratio is not sufficient so that the strength of the sheet is not sufficient. On the other hand, in the case where the amount of decrease is more than 1.6% IACS, the amount of precipitated Mn, Fe and Si-based particles induced by the cold rolling is not sufficient, so that the thermal softening resistance is not sufficiently improved.

The thus obtained Al alloy sheet according to the invention is subjected to the conventional working as necessary so as to be formed into the desired can body, and advantageously used as an Al-based can for beverages and the like. For example, the Al alloy sheet according to the invention is subjected to degreasing and washing, and oil-coating, as necessary, and further subjected to cupping, DI forming, trimming, cleaning, drying, coating, baking, necking, flanging and the like so as to obtain a can body (cylindrical can) for beverages. Then, a can lid (can end) is attached to the obtained can body, so that the desired Al-based can for beverages is advantageously produced.

EXAMPLES

To clarify the present invention more specifically, some examples according to the invention will be described. It is to be understood that the invention is by no means limited by the details of the illustrated examples, but may be embodied with various changes, modifications and improvements which are not described herein, and which may occur to those skilled in the art, without departing from the spirit of the invention.

Samples made from Al alloy sheets (original sheets: cold-rolled sheet) or their intermediate products, namely hot-rolled sheets, which were obtained in Examples and Comparative Examples described below, were measured or evaluated according to the following methods.

(1) Tensile Strength (TS) of an Original Sheet in a Rolling Direction

A JIS (Japanese Industrial Standard) No. 5 sample was made from each of the Al alloy sheets (original sheets) obtained in the Examples and Comparative Examples, with respect to the rolling direction. Each of the samples was subjected to a tensile test in accordance with JIS-Z-2241 so that the tensile strength (TS) of the sample in the rolling direction was measured.

(2) Tensile Strength (ABTS) and Yield Strength (ABYS) in the Rolling Direction After Heat Treatment at 205° C. for 10 Minutes

The samples formed of each of the Al alloy sheets (original sheets) were subjected to heat treatment (at 205° C. for 10 minutes) equivalent to the coating and baking process. Subsequently, the tensile test as in the above (1) was performed, and the tensile strength (ABTS) and the yield strength (ABYS) of the samples in the rolling direction after the heat treatment were measured.

(3) Measurement of the Amounts of Solid-Solubilized Si, Fe and Mn (Phenol Dissolving Method)

A small sample piece cut out from a hot-rolled sheet after finish hot rolling obtained in each of the Examples and Comparative Examples was immersed in a phenol solution of 170° C. so that matrix components in the Al alloy were dissolved, and benzylalcohol was added to the solution. The solution was kept in a liquid state and filtered through a filter having a pore diameter of 0.1 μm. Subsequently, precipitates left on the filter were dissolved by a mixed solution of hydrochloric acid and fluoric acid, and the obtained dissolved solution was diluted so as to be subjected to ICP (Inductively Coupled Plasma) optical emission spectroscopy, whereby the amounts of the precipitated Mn, Fe and Si were found. The amounts of solid-solubilized Si, Fe and Mn were calculated by subtracting the above-described amount of the precipitation from the contents in the ingot.

(4) Electric Conductivity

A sheet after the finish hot rolling (hot-rolled sheet) and a sheet after the cold rolling (original sheet: cold-rolled sheet) were subjected to measurement of the electric conductivity at a wavelength of 960 kHz by using an electric conductivity measuring device (SIGMA TEST2.069 available from FOERSTER Japan Limited), so that an average value of n=3 was calculated. In the case where the thickness of the sample was less than 1 mm, pieces of the sample (sheet) were stacked such that the total thickness was not less than 1 mm, and subjected to the measurement.

(5) Evaluation of Can Formability

Each of the Al alloy sheets (original sheets) obtained in the Examples and Comparative Examples was subjected to cupping and DI forming at an ironing ratio of 66%, trimming, and the conventional coating and baking process, according to the conventional can-making method, so that the can formability of the alloy sheet was evaluated. A state of the seizure of can walls in the can-making process was also visually examined.

Example 1

First, various Al alloys: A1-A10 having alloy component compositions indicated in the following Table 1 were smelted according to the conventional method, and Al alloy ingots were made with respect to the alloys by the semi-continuous casting method. Subsequently, each of the obtained Al alloy ingots was subjected to the conventional surface-machining, heated to a temperature of 600° C. at a heating rate of 40° C./h using an air furnace, and then subjected to homogenization at the temperature of 600° C. for 10 hours. It is noted that the value of not shorter than (145-0.24 T) hours defined according to the invention is not less than 1 hour. Thus, the above-described 10 hours of homogenization period satisfies the condition.

Subsequently, after the homogenization, each of the obtained Al alloy ingots was directly (immediately) subjected to hot rolling. First, the conventional rough hot rolling was performed by using a reversing rolling mill such that a temperature of the Al alloy ingots on the outlet side of the reversing rolling mill was within a range of 460-510° C., so as to form a sheet having a thickness of 28 mm. Then, the conventional finish hot rolling was performed by using a tandem rolling mill with four stands such that a temperature of the Al alloy ingots on the outlet side of the tandem rolling mill was within a range of 300-330° C., so that the sheet had a thickness of 2.2 mm. At last, cold rolling consisting of three passes was performed so that an Al alloy sheet having a thickness of 0.28 mm was produced. The total working ratio in the cold rolling process was 87.3%. The average rolling rate in a steady part of the final pass in the cold rolling process was set to be within a range of 900-1100 m/m. The temperature upon termination of the final pass of the cold rolling was 145-155° C.

With respect to each of the sheets formed of the Al alloys A1-A10 obtained in the above-described processes, a test material (A1-A10) was produced, and its properties were evaluated according to the above-described methods, the results of which are indicated in the following Table 2. In Table 2, the difference (S1-S2) between the electric conductivity (S1) of the hot-rolled sheet and the electric conductivity (S2) of the cold-rolled sheet is indicated as an amount of decrease of electric conductivity by cold rolling.

TABLE 1 Alloy components (mass %) Al alloy Mn Mg Fe Si Cu Zn Ti B A 1 0.7 1.1 0.45 0.33 0.24 0.12 0.05 0.00 2 1.3 1.3 0.38 0.32 0.24 0.17 0.00 0.04 3 1.2 0.8 0.50 0.43 0.19 0.19 0.05 0.04 4 0.8 1.5 0.49 0.43 0.20 0.16 0.01 0.01 5 0.8 1.1 0.26 0.39 0.18 0.01 0.08 0.04 6 0.9 1.0 0.59 0.39 0.22 0.17 0.10 0.04 7 1.2 1.1 0.33 0.27 0.21 0.10 0.04 0.03 8 1.2 1.1 0.38 0.48 0.24 0.04 0.07 0.01 9 1.0 1.3 0.32 0.41 0.13 0.25 0.04 0.00 10 0.8 0.9 0.52 0.28 0.27 0.19 0.01 0.03

TABLE 2 Sheet properties Amount of Hot-rolled sheet decrease of Solid- Solid- Solid- electric Cold-rolled sheet solubilized solubilized solubilized Electric conductivity TS- Test Mn Fe Si conductivity by cold rolling TS ABTS ABYS material (wt %) (wt %) (wt %) (% IACS) (% IACS) (MPa) (MPa) (MPa) Remarks A 1 0.29 0.09 0.23 39.3 1.3 288 272 44 Excellent can formability 2 0.46 0.06 0.18 37.5 0.8 311 295 49 Excellent can formability 3 0.42 0.11 0.24 39.1 0.9 305 288 47 Excellent can formability 4 0.36 0.12 0.16 38.9 1.0 310 294 48 Excellent can formability 5 0.34 0.11 0.15 38.3 1.0 291 274 44 Excellent can formability 6 0.39 0.12 0.19 39.2 1.1 289 273 47 Excellent can formability 7 0.37 0.10 0.13 37.3 1.3 306 290 44 Excellent can formability 8 0.41 0.14 0.22 37.4 0.8 303 287 40 Excellent can formability 9 0.33 0.08 0.18 38.0 1.2 310 295 47 Excellent can formability 10 0.28 0.13 0.10 39.5 1.3 299 283 49 Excellent can formability

As is apparent from the results shown in Tables 1 and 2, the sheets formed of the Al alloy A1-A10 had a not excessively high tensile strength (TS) in the rolling direction in a state before the coating and baking process, and were excellent in the can formability. In addition, the Al alloy sheets A1-A10 (sample sheets) had a high tensile strength in the rolling direction after heat treatment (ABTS), and were excellent also in the thermal softening resistance.

Comparative Example 1

With respect to various compositions of alloy components shown in the following Table 3, under the same conditions as in the above-described Example 1, sheets formed of each of the Al alloy B1-B13 were produced. The test material (B1-B13) obtained in the production process of the Al alloy sheets were evaluated with respect to their properties as in the above-described Example 1. The result is shown in the following Table 4.

TABLE 3 Alloy components (mass %) Al alloy Mn Mg Fe Si Cu Zn Ti B B 1 0.4 1.0 0.40 0.32 0.18 0.06 0.03 <0.01 2 1.6 0.9 0.45 0.33 0.20 0.06 0.03 <0.01 3 1.0 0.6 0.30 0.38 0.21 0.06 0.02 <0.01 4 0.9 1.7 0.31 0.30 0.18 0.08 0.03 0.01 5 1.1 1.0 0.12 0.29 0.21 0.10 0.02 <0.01 6 1.0 0.9 0.7 0.32 0.20 0.04 0.02 <0.01 7 0.9 0.9 0.44 0.19 0.21 0.06 0.02 0.01 8 1.2 1.0 0.42 0.55 0.20 0.05 0.03 <0.01 9 0.9 0.9 0.44 0.27 0.02 0.06 0.03 <0.01 10 1.1 1.0 0.32 0.38 0.50 0.06 0.02 <0.01 11 1.0 1.2 0.33 0.33 0.20 0.80 0.03 <0.01 12 1.0 1.0 0.32 0.26 0.23 0.07 0.21 <0.01 13 1.1 1.1 0.45 0.34 0.20 0.07 0.03 0.10

TABLE 4 Sheet properties Amount of Hot-rolled sheet decrease of Solid- Solid- Solid- electric Cold-rolled sheet solubilized solubilized solubilized Electric conductivity TS- Test Mn Fe Si conductivity by cold rolling TS ABTS ABYS material (wt %) (wt %) (wt %) (% IACS) (% IACS) (MPa) (MPa) (MPa) Remarks B 1 0.22 0.04 0.09 41.3 1.8 283 268 54 Strength of can body not enough 2 0.48 0.05 0.11 35.0 0.4 330 304 48 Broken during can-making 3 0.38 0.10 0.09 38.4 1.0 276 260 49 Strength of can body not enough 4 0.33 0.05 0.15 36.2 0.6 336 309 47 Broken during can-making 5 0.38 0.01 0.17 39.0 1.7 298 283 51 Roughness of can surface 6 0.34 0.09 0.18 38.5 1.1 303 287 48 Broken during can-making 7 0.40 0.18 0.05 39.1 1.7 293 268 52 Strength of can body not enough 8 0.25 0.08 0.37 38.2 1.1 311 295 45 Broken during can-making 9 0.39 0.17 0.13 38.6 1.3 291 266 53 Strength of can body not enough 10 0.40 0.06 0.11 38.3 1.4 328 296 42 Broken during can-making 11 0.35 0.07 0.23 38.8 1.1 308 292 45 Broken during can-making 12 0.34 0.11 0.11 39.0 0.8 299 283 43 Broken during can-making 13 0.37 0.16 0.23 38.8 0.9 307 290 46 Broken during can-making

As is apparent from the results shown in Tables 3 and 4, the test material B1, which was not subjected to a sufficient amount of addition of Mn, contained the solid-solubilized Mn less than required, so that the amount of precipitation of Mn in the cold rolling process was not enough and the electric conductivity of the test material greatly decreased. As a result, the amount of decrease of strength in the coating and baking process was significant and the strength of the obtained can was not sufficient. With respect to the test material B2, the amount of addition of Mn was excessive and the strength of the original sheet was too high, resulting in a problem of breakage during the can-making. Furthermore, with respect to the test material B3, the amount of addition of Mn was not enough and the strengths of the original sheet and the sheet after the coating and baking process were not enough. With respect to the test material B4, the amount of addition of Mn was excessive and the strength of the original sheet was too high, resulting in a problem of breakage during the can-making. With respect to the test material B5, the amount of addition of Fe was not enough, so that the coarse intermetallic compounds were not sufficiently formed, and the formed can had a rough surface. In addition, the amount of the solid-solubilized Fe was not enough and the amount of precipitation of Fe in the cold rolling process was not enough, so that the strength of the sheet greatly decreased in the coating and baking process.

With respect to the test material B6, the amount of addition of Fe was excessive, so that the coarse intermetallic compounds were formed, resulting in a problem of breakage during the can-making. With respect to the test material B7, the amount of addition of Si was not enough, and the amount of precipitation of Si in the cold rolling process was not enough, so that the amount of decrease of strength in the coating and baking process was significant and the strength of the obtained can was not sufficient. With respect to the test material B8, the amount of addition of Si was excessive, so that the coarse intermetallic compounds were excessively formed, resulting in a problem of breakage during the can-making. With respect to the test material B9, the amount of addition of Cu was not enough, so that the strength was not sufficiently increased by the precipitation in the coating and baking process, resulting in deterioration of the strength of the sheet due to the coating and baking process, and shortage of the strength of the can body. Furthermore, with respect to the test material B10, the amount of addition of Cu was excessive and the strength of the original sheet was too high, resulting in a problem of breakage during the can-making. In addition, with respect to the test materials B11, B12 and B13, the amounts of addition of Zi, Ti or B were excessive, so that the coarse intermetallic compounds were excessively formed, resulting in a problem of breakage during the can-making.

Example 2

According to the composition of the alloy component which provides the test material A9 (Al alloy: A9) in the Example 1, Al alloy sheets C1-C13 were produced under the various conditions of production shown in the following Table 5. The basic conditions of production not shown in Table 5 were the same as in the Example 1. The test material (C1-C13) obtained in the production process of the Al alloy sheets were evaluated with respect to their properties as in the above-described Example 1. The result is shown in the following Table 6.

TABLE 5 Conditions of production Heat history before starting hot rolling Cold rolling Homogenization Starting Total Average rolling Al Heating Temperature temperature of working rate of alloy rate T Time Cooling rate hot rolling ratio final pass sheet (° C./h) (° C.) (h) (° C./h) (° C.) (%) (m/min) C 1 35 600 5 Immediate starting of hot rolling 80 850 2 110 570 10 Immediate starting of hot rolling 82 1000 3 50 560 11 Immediate starting of hot rolling 85 1100 4 50 615 3 Immediate starting of hot rolling 85 1050 5 50 570 9 Immediate starting of hot rolling 84 1300 6 60 580 23 Immediate starting of hot rolling 86 850 7 50 570 10 Immediate starting of hot rolling 85 1100 8 60 610 3 15 580 82 850 9 50 560 11 84 518 84 900 10 50 600 5 45 510 87 1050 11 60 600 5 Immediate starting of hot rolling 77 1000 12 70 580 10 Immediate starting of hot rolling 81 800 13 40 590 10 Immediate starting of hot rolling 86 1500

TABLE 6 Sheet properties Amount of decrease of Hot-rolled sheet electric Solid- Solid- Solid- conductivity Cold-rolled sheet solubilized solubilized solubilized Electric by cold TS- Test Mn Fe Si conductivity rolling TS ABTS ABYS material (wt %) (wt %) (wt %) (% IACS) (% IACS) (MPa) (MPa) (MPa) Remarks C 1 0.36 0.06 0.14 39.0 1.1 287 271 46 Excellent can formability 2 0.39 0.07 0.13 38.0 1.0 288 272 43 Excellent can formability 3 0.44 0.10 0.19 37.3 0.9 296 280 48 Excellent can formability 4 0.31 0.05 0.08 38.7 1.1 299 283 46 Excellent can formability 5 0.27 0.10 0.15 37.1 1.5 295 279 42 Excellent can formability 6 0.36 0.11 0.12 37.9 0.8 302 286 44 Excellent can formability 7 0.40 0.11 0.20 39.1 1.2 319 302 43 Excellent can formability 8 0.41 0.08 0.29 37.8 0.7 288 272 44 Excellent can formability 9 0.46 0.04 0.11 39.0 0.7 301 286 43 Excellent can formability 10 0.41 0.04 0.28 37.8 0.7 311 294 40 Excellent can formability 11 0.38 0.07 0.26 38.6 0.9 297 282 44 Excellent can formability 12 0.38 0.07 0.19 37.6 0.6 314 299 45 Excellent can formability 13 0.33 0.08 0.09 37.9 1.0 289 273 49 Excellent can formability

As is apparent from the results shown in Tables 5 and 6, each of the Al alloy sheets (test materials) C1-C13 had an appropriate, not excessively high tensile strength in the rolling direction (TS) before it was subjected to the coating and baking process, so that the can formability of the sheet was excellent.

Comparative Example 2

According to the composition of the alloy component which provides the test material A9 (Al alloy: A9) in the Example 1, Al alloy sheets D1-D9 were produced under the various conditions of production shown in the following Table 7. The basic conditions of production not shown in Table 7 were the same as in the Example 1. The test material (D1-D9) formed of the Al alloy sheets (cold-rolled sheets) D1-D9 were evaluated with respect to their properties. The result is shown in the following Table 8.

TABLE 7 Conditions of production Heat history before starting hot rolling Cold rolling Homogenization Starting Total Average rolling Al Heating Temperature temperature of working rate of alloy rate T Time Cooling rate hot rolling ratio final pass sheet (° C./h) (° C.) (h) (° C./h) (° C.) (%) (m/min) D 1 150 600 3 Immediate starting of hot rolling 84 1200 2 40 520 21 Immediate starting of hot rolling 85 1100 3 50 635 3 Immediate starting of hot rolling 86 1050 4 60 560 3 Immediate starting of hot rolling 83 1000 5 60 560 12 5 530 85 1000 6 50 590 10 120 530 84 950 7 60 610 3 45 480 79 950 8 50 590 10 Immediate starting of hot rolling 68 1100 9 50 610 3 Immediate starting of hot rolling 86 1800

TABLE 8 Sheet properties (cold-rolled sheet) Test TS ABTS TS-ABYS material (MPa) (MPa) (MPa) Remarks D 1 325 310 47 Broken during can-making 2 300 285 51 Broken during can-making 3 293 277 52 Broken during can-making 4 311 295 51 Roughness of can surface 5 286 269 55 Strength of can body not enough 6 310 294 51 Broken during can-making 7 295 265 53 Strength of can body not enough 8 278 265 45 Strength of can body not enough 9 293 265 56 Strength of can body not enough

As is apparent from the results shown in Tables 7 and 8, the test material D1 had a high heating rate in the homogenization, so that fine Mn, Fe and Si-based particles were formed during a rise of the temperature, with a result of an increase of the strength of the sheet, thereby causing a problem of breakage during the can-making. With respect to the test material D2, the temperature kept during the homogenization was too low, so that the homogenization effect was not enough and the structure of the sheet was ununiform, resulting in a problem of breakage during the can-making. On the other hand, with respect to the test material D3 whose temperature kept during the homogenization was too high, the structure of the sheet was subjected to eutectic melting and became ununiform, resulting in a problem of breakage during the can-making. Furthermore, with respect to the test material D4, the period of time of homogenization was shorter than (145-0.24 T), so that Mn—Fe—Si-based compound particles having an equivalent circle diameter of 0.1-1.0 μm, which shows a solid lubricating effect, were not sufficiently formed, resulting in the seizure on the surface of the formed can.

With respect to the test material D5, the rate of cooling to the starting temperature of hot rolling was low, so that the precipitation was promoted during the cooling, the amounts of solid-solubilized Mn, Fe and Si were decreased, and the precipitation of Mn—Fe—Si-based fine particles during the cold rolling was not enough, resulting in deterioration of the thermal softening resistance of the sheet. On the other hand, with respect to the test material D6, whose rate of cooling to the starting temperature of hot rolling was high, the temperature inside the ingot became ununiform and its material structure had a variation, resulting in a problem of breakage during the can-making. In addition, with respect to the test material D7, the rate of cooling to the starting temperature of hot rolling was low, so that the precipitation was promoted during the cooling to the starting temperature, the amounts of solid-solubilized Mn, Fe and Si were decreased, and the precipitation of Mn—Fe—Si-based fine particles during the cold rolling was not enough, resulting in deterioration of the thermal softening resistance of the sheet. As a result, the strength of the formed can after the coating and baking process was not sufficient.

Furthermore, the test material D8 did not have a sufficiently high total working ratio in the cold rolling process, so that it had an inherent problem of insufficient strength of the can body. In addition, with respect to the test material D9, the rolling rate in the final pass of the cold rolling process was too fast, so that the precipitation of Mn—Fe—Si-based fine particles during the cold rolling was not enough, resulting in a problem that the thermal softening resistance of the sheet was deteriorated.

Claims

1. An aluminum alloy sheet for a can body, which is formed of a cold-rolled sheet obtained by cold rolling a hot-rolled sheet comprising an aluminum alloy consisting of 0.7-1.3% by mass of Mn, 0.8-1.5% by mass of Mg, 0.25-0.6% by mass of Fe, 0.25-0.50% by mass of Si, 0.10-0.30% by mass of Cu, not more than 0.25% by mass of Zn, not more than 0.10% by mass of Ti and not more than 0.05% by mass of B, and the balance being Al and inevitable impurities,

wherein the hot-rolled sheet includes not less than 0.25% by mass of solid-solubilized Mn, not less than 0.02% by mass of solid-solubilized Fe and not less than 0.07% by mass of solid-solubilized Si, and has an electric conductivity of 30.0-40.0% IACS,
and wherein the cold-rolled sheet has a tensile strength (TS) of 280-320 MPa in a rolling direction and a tensile strength (ABTS) of 270-310 MPa in the rolling direction after heat treatment at 205° C. for 10 minutes, and a difference between the tensile strength (TS) in the rolling direction and a yield strength (ABYS) in the rolling direction after heat treatment at 205° C. for 10 minutes is not larger than 50 MPa.

2. An aluminum alloy hot-rolled sheet for a can body, comprising an aluminum alloy consisting of 0.7-1.3% by mass of Mn, 0.8-1.5% by mass of Mg, 0.25-0.6% by mass of Fe, 0.25-0.50% by mass of Si, 0.10-0.30% by mass of Cu, not more than 0.25% by mass of Zn, not more than 0.10% by mass of Ti and not more than 0.05% by mass of B, and the balance being Al and inevitable impurities,

wherein the hot-rolled sheet includes not less than 0.25% by mass of solid-solubilized Mn, not less than 0.02% by mass of solid-solubilized Fe and not less than 0.07% by mass of solid-solubilized Si, and has an electric conductivity of 30.0-40.0% IACS.

3. An aluminum alloy sheet for a can body, comprising an aluminum alloy consisting of 0.7-1.3% by mass of Mn, 0.8-1.5% by mass of Mg, 0.25-0.6% by mass of Fe, 0.25-0.50% by mass of Si, 0.10-0.30% by mass of Cu, not more than 0.25% by mass of Zn, not more than 0.10% by mass of Ti and not more than 0.05% by mass of B, and the balance being Al and inevitable impurities,

wherein the sheet has a tensile strength (TS) of 280-320 MPa in a rolling direction and a tensile strength (ABTS) of 270-310 MPa in the rolling direction after heat treatment at 205° C. for 10 minutes, and a difference between the tensile strength (TS) in the rolling direction and a yield strength (ABYS) in the rolling direction after heat treatment at 205° C. for 10 minutes is not larger than 50 MPa.

4. The aluminum alloy sheet for a can body according to claim 3, which has an electric conductivity of 28.4% IACS-39.8% IACS.

5. A process for producing an aluminum alloy sheet for a can body, comprising steps of:

providing an ingot of an aluminum alloy consisting of 0.7-1.3% by mass of Mn, 0.8-1.5% by mass of Mg, 0.25-0.6% by mass of Fe, 0.25-0.50% by mass of Si, 0.10-0.30% by mass of Cu, not more than 0.25% by mass of Zn, not more than 0.10% by mass of Ti and not more than 0.05% by mass of B, and the balance being Al and inevitable impurities;
performing hot rolling on the ingot of the aluminum alloy so as to obtain a hot-rolled sheet including not less than 0.25% by mass of solid-solubilized Mn, not less than 0.02% by mass of solid-solubilized Fe and not less than 0.07% by mass of solid-solubilized Si, and having an electric conductivity of 30.0-40.0% IACS; and
performing cold rolling on the hot-rolled sheet so as to form a cold-rolled sheet wherein a tensile strength (TS) in a rolling direction is 280-320 MPa and a tensile strength (ABTS) in the rolling direction after heat treatment at 205° C. for 10 minutes is 270-310 MPa, and wherein a difference between the tensile strength (TS) in the rolling direction and a yield strength (ABYS) in the rolling direction after heat treatment at 205° C. for 10 minutes is not larger than 50 MPa.

6. A process for producing an aluminum alloy sheet for a can body, comprising steps of:

surface-machining an ingot of an aluminum alloy consisting of 0.7-1.3% by mass of Mn, 0.8-1.5% by mass of Mg, 0.25-0.6% by mass of Fe, 0.25-0.50% by mass of Si, 0.10-0.30% by mass of Cu, not more than 0.25% by mass of Zn, not more than 0.10% by mass of Ti and not more than 0.05% by mass of B, and the balance being Al and inevitable impurities;
heating the ingot to a homogenization temperature (T) within a range of 550-620° C. at a heating rate of 30-120° C. per hour;
performing homogenization by keeping the ingot at the homogenization temperature (T) for a time not shorter than (145-0.24 T) hours;
performing rough hot rolling on the ingot immediately or after cooling the ingot to a starting temperature of hot rolling not lower than 500° C. at a cooling rate of 10-90° C. per hour after finishing the homogenization, such that a temperature of the ingot upon termination of the rough hot rolling is within a range of 430-550° C., so as to form a sheet having a thickness of 20-40 mm;
performing finish hot rolling on the sheet such that a temperature of the sheet upon termination of the finish hot rolling is within a range of 300-390° C., so that the sheet has a thickness of 1.5-4.0 mm, and
performing cold rolling on the sheet such that a total working ratio of the sheet is not less than 75% and an average rolling rate in a steady part of a final pass is within a range of 700-1600 m per minute, so that the sheet has a thickness of 0.2-1.0 mm.

7. The process for producing an aluminum alloy sheet for a can body according to claim 6, wherein the difference (S1-S2) between the electric conductivity (S1) of the sheet obtained by the finish hot rolling and the electric conductivity (S2) of the sheet obtained by the cold rolling is 0.2-1.6% IACS.

8. The process for producing an aluminum alloy sheet for a can body according to claim 6, wherein an area of particles having a diameter of 0.1 μm-1 μm in the ingot of the aluminum alloy subjected to the homogenization is not less than 3.5% in terms of a microphotograph taken by scanning electron microscope.

9. A can body for beverages, which is formed of the aluminum alloy sheet according to claim 1.

10. The can body for beverages according to claim 9, which is subjected to a predetermined coating and baking process.

11. A can body for beverages, which is formed of the aluminum alloy sheet according to claim 3.

12. The can body for beverages according to claim 11, which is subjected to a predetermined coating and baking process.

Patent History
Publication number: 20180282848
Type: Application
Filed: May 30, 2018
Publication Date: Oct 4, 2018
Applicant: UACJ CORPORATION (Tokyo)
Inventor: Shingo IWAMURA (Chiyoda-Ku)
Application Number: 15/992,662
Classifications
International Classification: C22F 1/047 (20060101); C22C 21/06 (20060101);