JP2005076041A - Method for manufacturing hard aluminum alloy sheet for can body - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for inexpensively manufacturing a material for a DI can body, which is superior in the balance of strength, a low earing rate, ironing properties and flange formability. <P>SOLUTION: The manufacturing method comprises homogenizing an ingot of an Al-Mg-Mn alloy; hot-rolling it while controlling a starting temperature to 350 to 590°C, the distribution of surface temperatures in a width direction of a rolling roll contacting with a plate to be rolled to 100°C or lower, temperatures of the material during rolling it from the plate thickness of 50 mm to the final rolled sheet thickness to 280 to 450°C, the fluctuation widths of the material temperatures in a rolling direction and a transverse direction to 100°C or lower, the material temperature at the end of the hot rolling to 280 to 350°C, the final sheet thickness to 1.5 to 2.8 mm, and a cooling rate to room temperature to 100°C/h or lower; and subsequently cold-rolling it with a reduction of 65% or higher while skipping an intermediate annealing step. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method of manufacturing a hard plate of an Al-Mg-Mn aluminum alloy used in a can body for a two-piece aluminum can by DI molding (drawing-ironing process), and in particular, a deep drawing ear is stably low and Produces a hard aluminum alloy plate for DI cans that has high strength after paint baking and has excellent moldability during DI processing, such as ironing, and excellent moldability after baking, such as flange formability. It is about how to do.

  In general, the manufacturing process for two-piece aluminum cans (DI cans) is to form can bodies by deep-drawing and ironing the can body material, and then trimming to the specified dimensions and shape. Apply and degrease, wash, paint, print, bake (baking), then neck and flange the can body edge, seaming with a separately formed can lid It is normal to perform.

  As a material for a DI can body produced in this manner, a hard plate of JIS3004 alloy made of an Al—Mg—Mn alloy has been widely used. This 3004 alloy is excellent in ironing workability and exhibits relatively good formability even when cold-rolled at a high rolling rate in order to increase strength, and is therefore suitable as a DI can body. Has been.

  In addition, as a method of manufacturing such a hard plate for a DI can body made of 3004 alloy, in general, after casting by a DC casting method or the like, the ingot is subjected to homogenization treatment and further subjected to predetermined rolling by hot rolling and cold rolling. In general, a method is used in which intermediate thickness annealing is performed for recrystallization in the plate thickness and before cold rolling after hot rolling in the process or in the middle of cold rolling.

  By the way, it is strongly desired to reduce the thickness of the two-piece aluminum can body (DI can) mainly from the viewpoint of reducing the material cost. When reducing the wall thickness in this way, it is indispensable to increase the strength of the material in order to avoid problems such as a reduction in the buckling strength of the can associated with the reduction in wall thickness.

  Furthermore, it is desired that the DI can body material has a stable and low ear rate during DI molding. That is, the stable and low ear rate at the time of DI molding is important from the viewpoint of improving the yield at the time of DI molding and preventing can barrel breakage due to cutting off of the can barrel.

  In addition, it is also important that the flange formability (mouth spreadability) at the time of DI can manufacture is excellent and the ironing property (can tear resistance) is excellent.

  Here, these strengths, ear ratios, flange formability (mouth spreadability), and ironing properties (canning resistance) are not necessarily excellent, but they are well balanced and comprehensive. In addition to the requirements from the material characteristics as described above, it is also important that the manufacturing cost is low.

By the way, in the general manufacturing method of the conventional hard plate for 3004 alloy can body, as described above, intermediate annealing is performed for recrystallization before cold rolling after hot rolling or in the middle of cold rolling. It is normal. If the conventional main manufacturing processes are classified from the viewpoint of such intermediate annealing, they can be divided into the following processes (a) to (c).
(A) Hot rolling-batch annealing process This is a method of annealing using a box annealing furnace (batch annealing furnace; BAF) having a slow heating rate after normal hot rolling.
(B) Hot rolling-continuous annealing process This is a method of annealing using a continuous annealing furnace (CAL) having a high heating rate after normal hot rolling.
(C) Cold rolling intermediate continuous annealing process This is a method of annealing using a continuous annealing furnace having a high heating rate in the middle of cold rolling after normal hot rolling.

Further, in addition to the processes (a) to (c), there is a method (d) as follows.
(D) Self-recrystallization process This is a method in which the material is self-recrystallized (self-annealed) in the state after hot rolling by controlling the temperature at which hot rolling rises above the recrystallization temperature of the material.

  Among the processes (a) to (d) as described above, when the processes (a), (b), and (d) are applied, all of the obtained can bodies have poor ironing properties. There is a common problem. The process (d) has been put to practical use in the case of using a tandem hot rolling mill, but the hot finish rolling is performed in a reverse rolling mill (reversing mill, reversing warming mill). In the case where the rolling mill for both hot rough rolling and hot finish rolling is a reverse type rolling mill, the present situation is that the practical use of the process has not been achieved, and the process (d) is performed by tandem heat. If it is applied with a rolling mill to improve the ironing ability of the can body, there is a problem that the material strength is insufficient. Furthermore, when the process (c) is applied, the iron formability is excellent as a can body material, but there is a problem that the flange formability is inferior. In addition, in the processes (a), (b), and (c) that require annealing for recrystallization after hot rolling, there is a problem that the manufacturing cost is high.

  Here, as a prior art method already proposed as a method for manufacturing a DI can body made of an Al-Mg-Mn alloy, there are methods as shown in Patent Documents 1 to 8, for example. Among them, the methods of Patent Literature 1 to Patent Literature 5 and Patent Literature 8 all require annealing after hot rolling or in the middle of cold rolling, and there are problems in terms of cost as described above. was there.

  Patent Document 6 also discloses a method of performing final cold rolling without annealing after hot rolling. However, Patent Document 6 uses a tandem rolling mill as a hot rolling mill. This method is not disclosed in the case of using a reverse rolling mill. The optimum hot rolling process conditions are usually different between a tandem rolling mill and a reverse rolling mill. Therefore, even if the method shown in Patent Document 6 is used when a reverse rolling mill is used, However, it is not always possible to obtain a can body material excellent in the above characteristics.

  Furthermore, even in the method of Patent Document 7, it is said that annealing after hot rolling may be omitted, but the method of Patent Document 7 also uses a tandem rolling mill as a hot rolling mill, Also, the hot rolling conditions are not strictly defined, so that even if the method of Patent Document 7 is diverted when a reverse rolling mill is used, a DI can body having an excellent balance of the above characteristics can be obtained. There was no.

JP-A-11-256290 JP 11-256291 A Japanese Patent Laid-Open No. 11-256292 JP 2000-234158 A JP 2002-212691 A Japanese Patent Laid-Open No. 10-310837 JP-A-11-140576 JP 2001-40461 A

  The present invention has been made against the background described above, and is a material that can satisfy various properties desired as a DI can body in a well-balanced manner, that is, has a high strength and at the same time has a stable and low ear ratio, and has a flange formability. The purpose of the present invention is to provide a method for obtaining an aluminum alloy plate for a DI can body that has excellent ironing properties and a comprehensive balance of these characteristics at a low cost. An object of the present invention is to provide a method suitable for obtaining a high-quality DI can body as described above at a low cost by using a reverse rolling mill instead of a tandem rolling mill.

  As a result of repeated various experiments and examinations by the present inventors to solve the above-mentioned problems, the hot rolling conditions are appropriately controlled, and in particular, the surface temperature variation of the rolling roll and the plate temperature variation during hot rolling. Using a process that can obtain high-quality DI can body materials, especially by using a reversing mill type hot rolling mill, by appropriately regulating, omitting annealing for recrystallization after hot rolling. The present inventors have found that a process capable of obtaining a high-quality DI can body can be realized, and have reached the present invention.

Specifically, the manufacturing method of the aluminum alloy hard plate for a can body of the invention of claim 1 is Mg 0.5-2.0%, Mn 0.5-2.0%, Fe 0.1-0.7%, An aluminum alloy containing 0.05 to 0.5% of Si, the balance being Al and inevitable impurities is used as a raw material, and after casting the raw material aluminum alloy, it is kept at a temperature within a range of 520 to 630 ° C. for 1 hour or more. When performing the homogenization process and then hot rolling,
(1) The hot rolling start temperature is in the range of 350 to 590 ° C,
(2) About the surface temperature of the rolling roll at the contact portion with the rolled sheet during hot rolling, the temperature difference between the center in the sheet width direction and the end is maintained at 100 ° C. or less,
(3) The temperature fluctuation width of the material in the direction orthogonal to the rolling direction and the rolling direction in each pass during hot rolling is controlled to 100 ° C. or less,
(4) The temperature of the rolled sheet material at the stage from the sheet thickness of 50 mm to the increased sheet thickness during hot rolling is controlled within the range of 450 to 280 ° C.
(5) The material temperature after hot rolling is in the range of 280 to 350 ° C.,
(6) The hot-rolled finished sheet thickness is in the range of 1.5 to 2.8 mm,
(7) The average cooling rate from the temperature within the range of 280 to 350 ° C. after the hot rolling to 100 ° C. is controlled to 100 ° C./hour or less,
Hot rolling is performed according to the above (1) to (7) to cool to room temperature, a hot rolled sheet having a proof stress of 120 MPa or less is obtained, and cold rolling is performed at a rolling rate of 65% or more without performing intermediate annealing. It is characterized by rolling.

  According to a second aspect of the present invention, there is provided a method for producing an aluminum alloy hard plate for a can body according to the first aspect of the present invention. 0.05% to 0.5%, Cr 0.05% to 0.3%, Zn 0.05% to 0.5%, Ti containing 0.005% to 0.20% or one containing two or more types It is characterized by.

  According to the method for producing an aluminum alloy hard plate for a can body of the present invention, a plate having an excellent balance as a hard plate for a DI can body, that is, having a high strength as a strength after painting and baking, and an ear rate is stably low. Moreover, it is possible to obtain a plate excellent in both ironing property and flange formability, and to obtain an excellent material as described above in a process in which intermediate annealing is omitted after hot rolling or in the middle of cold rolling. Since it is possible, a high-quality material can be obtained at a low cost.

  First, the reasons for limiting the component composition of the aluminum alloy used in the aluminum alloy hard plate for a can body of the present invention will be described.

Mg:
The addition of Mg is effective in improving the strength by solid solution of Mg itself, and can be expected to improve the strength by increasing the work hardening amount accompanying the solid solution of Mg, and further, Mg ₂ Si by coexistence with Si. Therefore, Mg is an indispensable element for obtaining the strength required as a can body material. Further, Mg has an effect of multiplying dislocations at the time of processing, and is therefore effective for making recrystallized grains finer. However, if the amount of Mg is less than 0.5%, the above-mentioned effect is small. On the other hand, if it exceeds 2.0%, high strength can be easily obtained, but the deformation resistance during DI processing increases and the drawability and squeezing property are improved. Make it worse. Therefore, the Mg content is set in the range of 0.5 to 2.0%.

Mn:
Mn is an effective element that contributes to improvement in strength and formability. In particular, Mn is particularly important for the can body material, which is the intended application of the present invention, because ironing is applied during DI molding. Emulsion-type lubricants are usually used in ironing of aluminum plates, but if there are few Mn-based crystallized products, even if they have the same level of strength, the emulsion-type lubricants alone are not sufficient for lubrication. In addition, appearance defects such as scuffing and seizure called goling may occur. Goling is known to be affected by the size, amount, and type of crystallized matter, and Mn is an indispensable element for forming the crystallized product. If the amount of Mn is less than 0.5%, the effect of solid lubrication by the Mn-based compound cannot be obtained. On the other hand, if the amount of Mn exceeds 2.0%, an Al ₆ Mn primary intermetallic compound is generated. Formability will be impaired. Therefore, the amount of Mn is set in the range of 0.5 to 2.0%. Here, the solid solution Mn in the product plate has an effect of suppressing recovery during processing and an effect of reducing softening during coating baking.

Fe:
Fe is an element necessary for accelerating crystallization and precipitation of Mn to control the amount of Mn solid solution in the aluminum matrix and the dispersion state of the Mn-based intermetallic compound. In order to obtain an appropriate compound dispersion state, it is necessary to add Fe according to the amount of Mn added. If the Fe content is less than 0.1%, it is difficult to obtain an appropriate compound dispersion state. On the other hand, if the Fe content exceeds 0.7%, a primary giant intermetallic compound is likely to be generated with the addition of Mn. Thus, the moldability is remarkably impaired. Therefore, the range of Fe content is set to 0.1 to 0.7%.

Si:
The addition of Si contributes to improvement of the strength of the can body material through age hardening by precipitation of Mg ₂ Si-based compounds. Si is an element necessary for generating an Al—Mn—Fe—Si intermetallic compound and controlling the dispersion state of the Mn intermetallic compound. If the amount of Si is less than 0.05%, the above effect cannot be obtained. On the other hand, if it exceeds 0.5%, the material becomes too hard due to age hardening, thereby impairing the moldability. Therefore, the range of Si content is set to 0.05 to 0.5%.

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

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, if the amount of Ti is less than 0.005%, the effect cannot be obtained. On the other hand, if it exceeds 0.20%, a large Al—Ti intermetallic compound crystallizes and inhibits formability. The amount of Ti was in the range of 0.005 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 preferably within the range of 0.0001 to 0.05%.

Cu:
Cu is made into a solution in the aluminum base, and contributes to the strength improvement utilizing precipitation hardening by depositing as an Al—Cu—Mg based precipitate during the coating baking process. If the amount of Cu is less than 0.05%, the effect cannot be obtained. On the other hand, if Cu is added in excess of 0.5%, age hardening can be easily obtained, but it becomes too hard and inhibits formability. Moreover, corrosion resistance also deteriorates. Therefore, the range of the amount of Cu when adding Cu is set to 0.05 to 0.5%.

Cr:
Cr is an element effective for improving the strength. However, if it is less than 0.05%, the effect is small, and if it exceeds 0.3%, formability is reduced due to the formation of giant crystals, which is not preferable. Therefore, the range of the Cr amount when adding Cr is set to 0.05 to 0.3%.

Zn:
Addition of Zn contributes to strength improvement by aging precipitation of Al—Mg—Zn-based particles. However, if it is less than 0.05%, the effect cannot be obtained, and if it exceeds 0.5%, there is a problem regarding contribution to strength. There is no, but deteriorates the corrosion resistance. Therefore, the range of the Zr amount when adding Zn is set to 0.05 to 0.5%.

  Next, the manufacturing process of the aluminum alloy hard plate for can bodies of this invention is demonstrated.

  First, an aluminum alloy ingot having the above alloy composition is cast by a DC casting method (semi-continuous casting method) according to a conventional method. The ingot is then homogenized to homogenize the ingot segregation and optimize the size and distribution of Mn, Fe, and Si-based second phase particles. Also, the size and distribution of such second phase particles may affect the texture of the final plate. If the homogenization temperature is less than 520 ° C., not only the homogenization effect is insufficient, but there is a possibility that an optimal texture cannot be obtained, while if it exceeds 630 ° C., eutectic melting may occur. If the homogenization treatment time is less than 1 hour, not only the homogenization effect is insufficient, but there is a possibility that an optimum texture cannot be obtained. Accordingly, the homogenization treatment condition was defined as 1 hour or more at a temperature in the range of 520 to 630 ° C. The upper limit of the homogenization treatment time is not particularly defined, but it is preferably 48 hours or less in consideration of economy.

Hot rolling is performed on the ingot subjected to the homogenization treatment. In the case of the method of the present invention, since a method in which annealing is not performed after hot rolling is applied, it is necessary to sufficiently recrystallize in the state of the hot rolled up plate, and recrystallization during hot rolling The behavior greatly affects the reduction of ear rate and the improvement of ironing ability through the control of texture. Therefore, in the present invention, not only the hot rolling start temperature and hot rolling end temperature (hot rolling temperature), but also the temperature variation at the contact portion of the rolling roll with the rolled plate during hot rolling, Conditions from the stage to the heat rise (material temperature, variation in material temperature in the plate width direction), conditions after the heat rise and until it is cooled to a temperature close to room temperature (temperature of 100 ° C or less) Is strictly prescribed. Specifically, the following conditions (1) to (7) are necessary.
(1) The hot rolling start temperature is controlled within a range of 350 to 590 ° C.
(2) About the surface temperature of the rolling roll in the contact portion with the rolled sheet during hot rolling, the temperature difference between the center in the sheet width direction and the end is maintained at 100 ° C. or less.
(3) The temperature fluctuation width of the material in the direction orthogonal to the rolling direction and the rolling direction is controlled to 100 ° C. or less in each pass during hot rolling.
(4) The rolled sheet material temperature at the stage from the sheet thickness of 50 mm to the increased sheet thickness during hot rolling is controlled within a range of 450 to 280 ° C.
(5) The material temperature after hot rolling is set within a range of 280 to 350 ° C.
(6) The hot rolled sheet thickness is set in the range of 1.5 to 2.8 mm.
(7) The average cooling rate from the temperature within the range of 280 to 350 ° C. after the hot rolling to 100 ° C. is controlled to 100 ° C./hour or less.

  In the method of the present invention, a reversing mill and a reversing worm mill are used as a hot rolling finish rolling mill, or a reversing mill is used as a hot rolling rough rolling and finishing rolling combined mill. The above conditions (1) to (7) are also stipulated as effective conditions at least when a reverse rolling mill is used for finish rolling. In each of the above conditions, “during hot rolling from a plate thickness of 50 mm to a raised plate thickness” is included in the finish rolling by the reverse method.

  Next, the hot rolling conditions (1) to (7) will be described in detail.

(1) The hot rolling start temperature is controlled within the range of 350 to 590 ° C:
The hot rolling start temperature strongly affects the recovery and recrystallization behavior of the material during hot rolling. When the hot rolling start temperature is less than 350 ° C., recrystallization hardly occurs during rolling, the ductility of the material is lowered, and the edge cracking phenomenon of the plate is likely to occur during rolling. On the other hand, if hot rolling is started at a temperature exceeding 590 ° C., coarse crystal grains are easily formed, and the surface quality of the plate is lowered. Therefore, the hot rolling start temperature is set in the range of 350 to 590 ° C.

(2) With respect to the surface temperature of the rolling roll during hot rolling, particularly the roll surface temperature at the contact portion with the rolled sheet, the temperature fluctuation width between the center in the sheet width direction and the end is maintained at 100 ° C. or less:
In order to keep the ear ratio in the coil width direction uniform, it is necessary to keep the surface temperature distribution of the rolling roll uniform. In general, the temperature in the center portion in the width direction of the roll increases, while the end portion in the roll width direction tends to decrease in temperature. Such a temperature distribution tendency affects the temperature distribution in the width direction of the plate, which in turn causes fluctuations in the ear rate, so that it is indispensable to control appropriately. If the temperature fluctuation width in the rolling roll width direction exceeds 100 ° C, it becomes extremely difficult to uniformly control the temperature in the sheet width direction, so it is necessary to keep the temperature fluctuation width in the rolling roll width direction at 100 ° C or less. Preferably, the fluctuation range is kept within 20 ° C. One specific method for controlling the rolling roll temperature fluctuation range to 100 ° C. or lower, preferably 20 ° C. or lower as described above is the same as described in detail in the section (4) later. There is a method in which the coolant is directly sprayed on the surface of the rolling roll in accordance with the temperature distribution and the spray amount and temperature are appropriately adjusted. Moreover, the surface quality of a board can be improved by reducing the surface temperature of a rolling roll by direct injection of a coolant in this way.

(3) In each pass during hot rolling, the temperature fluctuation width in the rolling direction (coil longitudinal direction) and the direction orthogonal to the rolling direction (coil width direction) is controlled to 100 ° C. or less:
Since the material temperature drop in each pass gradually increases as hot rolling progresses, high-speed rolling is generally performed to ensure a predetermined hot rolling temperature. This is also advantageous. Here, by performing multi-pass high-speed rolling using a reversing mill, the temperature drop in the central portion in the longitudinal direction of the rolled sheet and the central portion in the width direction is alleviated by the processing heat generated by the material. Heat is relatively easy to escape from both ends and both ends of the width, and the temperature drop in these portions is greater than that in the central portion, so that the material temperature fluctuates in the coil during hot rolling. If this temperature fluctuation range exceeds 100 ° C., the recrystallization behavior in all the coils greatly fluctuates, and it becomes difficult to keep the mechanical properties of the material, particularly the ear ratio, uniform. It was decided to control as follows. Even within this range, it is particularly preferable to control the temperature within 20 ° C. As one of the control methods, it is important to inject coolant directly onto the plate surface and change the amount of the direct injection coolant according to the temperature distribution, not constant. That is, the material temperature fluctuation range can be appropriately regulated by injecting a large amount of coolant to the high temperature part and injecting a small amount of coolant to the low temperature part. Thus, the coolant can be used not only for lubrication during rolling but also for controlling the material temperature.

(4) Control the temperature of the rolled sheet material from the sheet thickness of 50 mm to the increased sheet thickness during hot rolling within a range of 450 to 280 ° C .:
Among the stages in hot rolling, the material temperature particularly in the stage from the thickness of 50 mm to the finished thickness depends on the recrystallization behavior during hot rolling, the formation of the texture of the final plate, and consequently the ear rate of the final plate. Influence. And controlling the material temperature at this stage within the range of 450 to 280 ° C. adjusts the recrystallization behavior of the hot-rolled sheet appropriately, and controls the texture / ear ratio of the final sheet to an appropriate range. Is necessary for. If the material temperature at this stage is less than 280 ° C., the surface quality may be deteriorated and serious edge cracking may occur. On the other hand, if it exceeds 450 ° C., the recrystallization progresses quickly, and the required texture / Since the ear ratio cannot be obtained, it is necessary to be within the range of 450 to 280 ° C. Even within this temperature range, it is particularly preferable to control the temperature within the range of 290 to 390 ° C.

(5) The material temperature after hot rolling is in the range of 280 to 350 ° C .:
If the end temperature of hot rolling is less than 280 ° C., it is difficult to obtain sufficient recrystallization, and when this is cold-rolled to the final thickness without being annealed as it is, the ears of the DI can become high and formability deteriorates. Invite. On the other hand, when the hot rolling finish temperature exceeds 350 ° C., the material is completely recrystallized, but the surface quality may be deteriorated. Therefore, the end temperature of hot rolling is set within a range of 280 to 350 ° C. Even within this range, 290 to 340 ° C. is particularly preferable.

(6) The hot-rolled finished sheet thickness is set in the range of 1.5 to 2.8 mm:
If the thickness after hot rolling is less than 1.5 mm, it is difficult to control the thickness accuracy with a hot rolling mill. On the other hand, if the plate thickness after hot rolling exceeds 2.8 mm, the subsequent cold rolling rate becomes too high, and high strength can be easily obtained, but the ear rate becomes large. Therefore, the hot rolled plate thickness is set in the range of 1.5 to 2.8 mm.

(7) The average cooling rate from the temperature in the range of 280 to 350 ° C. after the hot rolling to the temperature of 100 ° C. or less is controlled to 100 ° C./hour or less:
The process of cooling the hot rolled material (coil) from a temperature in the range of 280 to 350 ° C. to a temperature of 100 ° C. or less is a process of recrystallization and a process of growing cubic (Cube) oriented grains. But there is. If the cooling rate in this process exceeds 100 ° C./hour, recrystallization cannot proceed sufficiently and the formation of Cube-oriented crystal grains becomes insufficient. As a result, the ear rate of the final plate cannot be sufficiently lowered, and the moldability may be lowered. Therefore, the average cooling rate in the cooling process from the temperature in the range of 280 to 350 ° C. after the hot rolling to the temperature of 100 ° C. or less was set to 100 ° C./hour or less.

  The hot-rolled sheet that has been hot-rolled in accordance with the above conditions (1) to (7), wound on a coil, and further cooled to a temperature of 100 ° C. or lower becomes a substantially complete recrystallized structure by self-annealing. Such a hot-rolled sheet having a substantially completely recrystallized structure can be finished into a high-quality final sheet at a low cost without subsequent intermediate annealing for recrystallization.

  Furthermore, as a characteristic of the hot-rolled sheet obtained by the means (1) to (7), the proof stress needs to be 120 MPa or less. When the proof stress in the hot-rolled sheet exceeds 120 MPa, the strength is excessively increased in the final sheet, and there is a possibility that the ironing performance is lowered. Here, since the proof stress is lower in the material of the almost complete recrystallized structure than the material of the non-recrystallized structure, it is possible to evaluate whether or not the almost complete recrystallized structure is obtained from the proof stress value.

  The hot-rolled sheet is then cold-rolled to the final sheet thickness without any subsequent intermediate annealing for recrystallization. Here, the cold rolling rate needs to be 65% or more. That is, in order to make the final cold rolling reduction less than 65% without performing the intermediate annealing, if considering the thickness of the final product (usually 0.35 to 0.25 mm), the hot rolled sheet is less than 1 mm. However, this is not only extremely difficult in actual operation, but there is a risk that the material will not be strengthened by cold work hardening, and sufficient material strength may not be obtained. It is also disadvantageous for rate control. Therefore, the cold rolling rate is set to 65% or more.

  Each alloy of alloy symbols A to E shown in Table 1 was cast by a DC casting method according to a conventional method. The resulting ingot is homogenized, hot-rolled and wound into a coil, cooled to 100 ° C. or lower, further cold-rolled to the final thickness, and the final plate (product plate) It was. Specific conditions of these processes are shown in production numbers 1 to 5 in Tables 2 and 3.

  In hot rolling, a reversing mill was used as a finishing mill, and all rolling at the stage where the plate thickness was 50 mm or less was performed by the reversing mill.

  The roll temperature during hot rolling and the temperature tracking of the plate (longitudinal direction and width direction) during hot rolling were measured using a non-contact radiation thermometer. The temperature after hot rolling was measured with a contact thermometer on the wound coil side surface.

  Further, the amount of coolant sprayed for temperature adjustment during hot rolling was in the range of 1000 liters / minute to 10000 liters / minute, and the coolant temperature was controlled within the range of 55 to 65 ° C.

  Here, the strength (tensile strength and proof stress in the rolling direction) of the hot-rolled sheet was examined at the stage where it was cooled to a temperature of 100 ° C. or less after the hot rolling was completed, and the results are shown in Table 3. .

  In addition, with respect to the final plate (thin plate for can body; base plate) obtained as described above, the tensile strength (TS), proof stress (YS) of the base plate using tensile test pieces taken in parallel with the rolling direction, The elongation (EL) was measured, and the tensile strength (TS), proof stress (YS), and elongation (EL) after heat treatment at 200 ° C. for 20 minutes assuming coating baking (baking) were measured.

  Further, the ear rate of the base plate was examined, and the DI can moldability using the base plate was examined. As DI can moldability, “successful success rate” was examined as an index of ironability, “mouth spread rate” was examined as an index of flange formability (mouth spreadability), and DI can pressure resistance was further investigated. These results are shown in Table 4.

Here, with respect to the final plate, the final plate was subjected to a drawing test on a total of 35 points, 7 points at equal intervals in the longitudinal direction of the coil and 5 points at equal intervals in the width direction, and the maximum and minimum values of the ear rate were obtained. . The ear value in the 45 ° direction relative to the rolling direction was defined as “+”, and the ear value generated in the 90 ° direction relative to the rolling direction was defined as “−”. The drawing test conditions were a punch diameter of 32 mm and a blank diameter of 56 mm. In addition, the “successful ironing rate” as an index of ironing performance is 100 consecutive cans when the second die is removed in the DI can molding and the ironing rate of the first and third dies is set to 55%. The ratio of cans that could not be cut out was examined. Furthermore, the “opening ratio” as an index of flange formability (spreading ability) is a 15 ° gradient at the upper opening of the DI can after trimming, washing, and baking the DI can after four-stage necking. A test was conducted in which a punch having a crack was pushed in until the material was cracked, and the spread rate until the crack was generated was determined by the following equation.
Spreading rate = [R1-R0] x 100%
However, R0: Radius of DI can opening after 4 steps necking (29mm)
R1: Radius of the opening when the mouth is expanded to the limit where cracking occurs

  Further, the DI can pressure resistance was tested by increasing the internal pressure of the can until the bottom deformed, and the maximum pressure until deformation was determined.

  In Tables 2 to 4, production numbers 1 to 3 are all examples produced according to the production method defined in the present invention using alloys within the component composition range defined in the present invention. Then, as shown in Table 4, the maximum ear rate is 4% or less, the fluctuation range is 2.6% or less, the ear rate is uniformly low, the strength after baking is sufficiently high, and the DI moldability It is clear that the ironing property is particularly excellent.

On the other hand, although the production number 4 used the alloy within the component range prescribed | regulated by this invention, it is a comparative example from which the manufacturing method removed from the range of this invention. That is,
(1) The maximum material temperature from 50 mm to hot rolling was as high as 466 ° C., which was outside the range of 280 to 450 ° C. defined in the present invention.
(2) The maximum temperature difference in the longitudinal direction of the material was as high as 105 ° C., which was out of the scope of the present invention.
(3) The maximum temperature difference in the width direction of the rolling roll was as high as 118 ° C., which was outside the scope of the present invention.

  In the comparative example with such production number 4, the fluctuation of the ear rate was large and the ironing property was also inferior.

  Furthermore, although production number 5 followed the manufacturing method of this invention, it is a comparative example from which the range of the alloy component (Fe) deviated from the range of this invention. In this comparative example, the maximum value of the ear rate was high, and the ironing property and the mouth spreading property were inferior.

  According to the present invention, as a hard plate for a DI can body, a plate having an excellent balance, that is, having a high strength as a strength after being baked on a coating, and at the same time, having a stable and low ear ratio, and having both ironing and flange formability. An excellent plate can be obtained by a low-cost process that eliminates intermediate annealing after hot rolling or during cold rolling.

Claims (2)

Mg 0.5-2.0% (mass%, the same shall apply hereinafter), Mn 0.5-2.0%, Fe 0.1-0.7%, Si 0.05-0.5%, the balance being Al and An aluminum alloy composed of unavoidable impurities is used as a raw material, and after casting the raw material aluminum alloy, a homogenization treatment is performed for 1 hour or more at a temperature within a range of 520 to 630 ° C., and then hot rolling is performed.
(1) The hot rolling start temperature is in the range of 350 to 590 ° C,
(2) About the surface temperature of the rolling roll at the contact portion with the rolled sheet during hot rolling, the temperature difference between the center in the sheet width direction and the end is maintained at 100 ° C. or less,
(3) The temperature fluctuation width of the material in the direction orthogonal to the rolling direction and the rolling direction in each pass during hot rolling is controlled to 100 ° C. or less,
(4) The temperature of the rolled sheet material at the stage from the sheet thickness of 50 mm to the increased sheet thickness during hot rolling is controlled within the range of 450 to 280 ° C.
(5) The material temperature after hot rolling is in the range of 280 to 350 ° C.,
(6) The hot-rolled finished sheet thickness is in the range of 1.5 to 2.8 mm,
(7) The average cooling rate from the temperature within the range of 280 to 350 ° C. after the hot rolling to 100 ° C. is controlled to 100 ° C./hour or less,
Performing hot rolling according to the above (1) to (7) and cooling to room temperature, obtaining a hot rolled sheet having a proof stress of 120 MPa or less,
Furthermore, cold rolling is performed at a rolling rate of 65% or more without performing intermediate annealing, a method for producing an aluminum alloy hard plate for a can body. In the manufacturing method of the aluminum alloy hard plate for can bodies according to claim 1,
As a raw material aluminum alloy, in addition to the above components, Cu 0.05 to 0.5%, Cr 0.05 to 0.3%, Zn 0.05 to 0.5%, Ti 0.005 to 0.20% The manufacturing method of the aluminum alloy hard board for can bodies using what contains 1 type, or 2 or more types.