JPH06136491A - Production of aluminum alloy sheet for forming with low ear rate - Google Patents

Abstract

PURPOSE:To obtain an aluminum alloy sheet for forming, suitable for two-piece can body material, excellent in strength and formability, and reduced in ear rate, by using a hot rolled plate prepared by means of continuous casting and rolling as a stock. CONSTITUTION:An aluminum alloy having a composition containing 0.5-2.0% Mg, 0.5-1.8% Mn, 0.1-0.7% Fe, 0.05-0.5% Si, 0.005-0.20& Ti, and 0.0001-0.05% B, and one or more kinds among 0.05-0.5% Cu, 0.05-0.3% Cr, and 0.1-0.5% Zn is cast to 10-50mm plate thickness at (1 to 20)m/min solidification boundary moving velocity, heated and held at 560-620 deg.C for >=1min, hot-rolled at 230-600 deg.C, and cold-rolled. Then the resulting cold rolled sheet is subjected to annealing under the conditions of 400-600 deg.C ultimate temp., >=1 deg.C/s average temp. rise rate, <=10min holding time, and cooling down to <=150 deg.C at >=1 deg.C/s cooling rate, and then to cold rolling at >=40% rolling rate, by which, in the surface microstructure, the maximum crystalline grain size in a direction perpendicular to rolling direction is regulated to <=60mum and intermetallic compounds of >=5mum is allowed to exist by >=500 pieces/mm<2>.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an aluminum plate having excellent ear ratio, strength and moldability. More specifically, it is Al-Mn for a two-piece aluminum can body (DI can). And a method for manufacturing a Mg-based aluminum alloy plate.

[0002]

2. Description of the Related Art Conventionally, a JIS 3004 alloy hard plate is often used as a body of a can because it has a relatively good formability even when it is cold-rolled to a high degree in order to increase its strength. This hard plate is often manufactured by homogenizing, then hot rolling according to a conventional method, and then performing intermediate annealing with or without cold rolling.
However, in recent years, Al alloy plates used as can materials have been made thinner and have higher strength. This expects an economic effect by using a thin plate having higher strength. For this reason, with the widespread use of continuous annealing furnaces (CAL) in recent years, it has become possible to reach a high temperature and perform rapid cooling by intermediate annealing, and the solutionizing effect of this makes it possible to obtain high strength even if the final cold rolling reduction is relatively small. A manufacturing process is also proposed.

[0003]

The conventional method for manufacturing a can material employs a method in which a DC ingot having a thickness of 500 mm is heated at 500 ° C. or higher and then hot-rolled. A method of using a hot rolled coil that has been cast and rolled has also been proposed. This method is excellent in energy saving and cost saving since it performs in-line casting and hot rolling using the residual heat of casting. However, as can be seen in the patent application publication No. Hei 4-503534, the can material produced by this method is more difficult to control the ear rate than the conventional DC cast material. Moreover, it has been found that a large amount of the cast structure remains due to a low rolling ratio after casting, which causes a problem in the uniformity of the structure, resulting in poor flange formability during DI can forming. The present invention solves such a problem and is based on a hot-rolled coil which is continuously cast and rolled, and has a rather excellent characteristic rather than a DC material in terms of ear ratio, strength and formability. It is intended to produce materials.

[0004]

In order to ensure the homogeneity of continuously cast and rolled material, the inventor has found that 560 to 620
It has been found that the above object can be achieved by adding a step of carrying out a homogenizing treatment at ℃, and by adopting CAL intermediate annealing in which the ear ratio can be easily controlled and the strength reduction after baking by the solutionizing effect is small. Came to do. That is, Mg: 0.5 to 2.0%, Mn: 0.5 to 1.8.
%, Fe: 0.1 to 0.7%, Si: 0.05 to 0.5
%, Ti: 0.005 to 0.
20% alone or B: 0.0001 to 0.05%
And Cu: 0.05-0.5%,
An aluminum alloy containing one or more of Cr: 0.05 to 0.3% and Zn: 0.1 to 0.5%, the balance of which is Al and impurities, has a moving speed of 1 to 1 at the solidification interface.
At 20 m / min, casting is performed with a finished plate thickness of 10 to 50 mm, after casting, heating and holding is performed at a temperature range of 560 to 620 ° C for 1 minute or more, and then hot rolling is performed at a temperature range of 230 to 600 ° C. After performing cold rolling as necessary, the reached temperature is 400 to 600 ° C., the average temperature rising rate from the temperature at the start of annealing to the reached temperature is 1 ° C./s or more, and the holding time after reaching the reached temperature is 10 minutes. 15 at a cooling rate of 1 ° C / s or more
Annealing is performed after cooling to 0 ° C. or lower, and then the rolling rate is 40
% Or more, and the surface microstructure after cold rolling has a maximum crystal grain size (minor diameter) of 60 μm or less in the direction perpendicular to the rolling direction and 500 / mm of intermetallic compounds of 5 μm or more It is a method for producing an aluminum alloy sheet for forming which has excellent strength and formability and has a low earring rate, which is characterized by the presence of ^two or more.

[0005]

First, the reasons for limiting the chemical components in the present invention will be explained. The following alloy components are added for the purpose of enhancing the strength of aluminum and controlling the ear ratio and formability. Mg; Mg can be aged precipitation hardening by Mg ₂ Si or Al-Cu-Mg due to coexistence with Si / Cu, and when performing intermediate annealing having a solutionizing effect as in the present invention, especially after coating baking. It is effective in suppressing the decrease in strength. Furthermore, Mg alone is an element that has the effect of strengthening the solid solution. Although it is an element that is indispensable for improving strength, M
If g is less than 0.5%, the effect is small and the strength that can be used is not reached, and if added in excess of 2%, there is no problem in draw forming, but it is easy to work harden, so redrawing And ironing property are deteriorated, which is not preferable. Therefore M
The g amount is in the range of 0.5 to 2%. Mn; Mn is an element that contributes to the improvement of strength and is effective in improving the formability. In particular, in the can body material, which is an application aimed at by the present invention, Mn is particularly important for ironing. Emulsion type lubricants are usually used in ironing of aluminum sheets, but if Mn-based crystallized substances are small, even if they have similar strength, the emulsion type lubricants alone lack sufficient lubricating ability. However, appearance defects such as scratches and seizure called "goring" occur. It is known that this phenomenon is affected by the size, amount, and type of crystallized substances, and Mn is an essential element for forming the crystallized substances. If the Mn content is less than 0.5%, M
The solid lubrication effect of the n compound cannot be obtained. On the other hand, if it exceeds 1.8%, primary crystal giant intermetallic compounds of MnAl ₆ are generated, and formability is significantly impaired. Therefore, the amount of Mn is set in the range of 0.5 to 1.8%. Fe; Fe is an element necessary for promoting crystallization and precipitation of Mn and controlling the amount of Mn solid solution in the aluminum matrix and the dispersed state of the Mn-based insoluble compound. Fe content is 0.
If it is less than 1%, it is difficult to obtain a proper compound dispersion state, and if it exceeds 0.7%, a primary crystal giant compound is likely to be formed together with the added Mn, and formability is significantly impaired. Therefore, the amount of Fe is set to the range of 0.1 to 0.7%. Si; Si contributes to the strength improvement by age hardening due to the formation of the Mg ₂ Si-based compound. Further, in the present invention, it is an important element that works together with Fe to obtain a proper dispersed state of crystallized substances necessary for DI molding. If the amount of Si is less than 0.05%, the effect cannot be obtained, and if it exceeds 0.5%, the dispersion of crystallized substances is saturated and age hardening is easily obtained, but it becomes too hard and hinders moldability. Therefore, the Si content is 0.
The range is from 05% to 0.5%. Ti, B; In ordinary aluminum alloys, a small amount of Ti and B is added for refining and stabilizing ingot crystal grains, and in the present invention, Ti: 0.00
5 to 0.20% alone or B: 0.0001 to
It is essential to contain it together with 0.05%. If the amount of Ti is less than 0.005%, the effect cannot be obtained and 0.2%
If it exceeds, primary TiAl ₃ crystallizes and hinders formability. Therefore, the Ti amount is set in the range of 0.005 to 0.20%. Further, when B is added together with Ti, this effect is improved. However, when B is added, if it is less than 0.0001%, it has no effect, and if it exceeds 0.05%, coarse particles of TiB ₂ are mixed and impair the formability, so that B is 0.0
The range is 001 to 0.05%.

Cu, Cr, and Zn are elements that contribute to the improvement of strength, and in the present invention, one or more of them are contained. Cu: Cu is an element that contributes to the strength improvement by utilizing the age hardening that occurs in the precipitation process of Al-Cu-Mg-based precipitates during the baking treatment. If the Cu content is less than 0.05%, the effect cannot be obtained. On the other hand, if the Cu content is more than 0.5%, age hardening is easily obtained, but it becomes too hard and hinders moldability. Therefore, the amount of Cu is set to the range of 0.05 to 0.5%. Cr; Cr is an element effective in improving strength, but if the addition amount is less than 0.05%, its effect is small, and 0.3%
If it exceeds, the formation of a huge crystallized product causes deterioration of moldability, which is not preferable. Therefore, the amount of Cr is set to 0.05 to 0.3%. Zn; Zn addition contributes to the strength improvement by aging precipitation of Mg ₂ Zn ₃ Al ₂ , but if it is less than 0.1%, it has no effect, and if it exceeds 0.5%, the corrosion resistance deteriorates, so the content is controlled below this. There is a need to. Therefore, the Zn content is 0.1
The range is 0.5%. The balance of each of the above components is Al and inevitable impurities.

Next, the manufacturing process in the present invention will be described. Casting: First, a cast plate is manufactured by casting an aluminum alloy having the above-mentioned alloy composition under the conditions that the moving speed at the solidification interface is 1 to 20 m / min and the finished plate thickness is 10 to 50 mm. If the finished plate thickness is less than 10 mm, or if the solidification interface moving speed is faster than 20 m / min, the appropriate crystallized product distribution necessary for ironing during DI processing cannot be obtained, and the intermetallic compound becomes fine and 5 μm. The above intermetallic compounds are less than 500 / mm ^2, and galling occurs at DI. When the finished plate thickness is thicker than 50 mm, it is difficult to obtain a hot-rolled plate by in-line rolling thereafter, and even when it is not in-line, it is difficult to handle in a length usually used as a can material. The moving speed of the solidification interface is higher than 1 m / min in terms of productivity.
As another desirable condition, the cooling rate of the surface portion is 10 which is the cooling rate calculated by the measurement between dendrite dendrites.
It is better to be slower than 0 ° C./sec, and if it is faster than this value, the crystallized substance becomes finer, leading to the occurrence of galling. Therefore, it is preferable to avoid using a material having a high thermal conductivity, such as copper, at a place where the molten metal is first contacted and cooled. Further, in the material obtained by the main casting, streak-like defects called coating occur in the state of subsequent hot rolling. This is not a problem in terms of mechanical properties or the like in terms of material properties, but since the appearance quality becomes a problem in the can material that is used in the present invention, it is desirable to mechanically or chemically remove the plate surface layer. Soaking: Next, the ingot is heated as a homogenizing treatment. This point is one of the features of the present invention, and the one having a temperature lower than 550 ° C. in the ascending casting is 560 to 6
Heat to 20 ° C. and hold for 1 minute or more to homogenize. If the temperature exceeds 600 ° C, it may take a short time, but 5
It is desirable to hold for 5 minutes or more at a low temperature of about 60 ° C. At a temperature of 560 ° C. or lower, the in-line homogenizing effect is small, and conversely, at a temperature of 620 ° C. or higher, local melting or the like occurs to impair the appearance, and softening causes inconvenience in handling and the like. Hot Rolling After the soaking treatment, hot rolling is continued. The conditions for hot rolling up are not particularly limited, but in view of hot ductility, an up temperature of 230 ° C. or higher is preferable. 60 on the entry side
From the viewpoint of coating, a temperature lower than 0 ° C is preferable. When the target plate thickness is thin, it is desirable to reduce the thickness by hot rolling and cold rolling to the required plate thickness as necessary. Intermediate annealing Next, heat treatment is performed at a high temperature of at least 400 ° C or higher. If it is not higher than 400 ° C., solid solution of metal elements such as Cu, Mg and Si does not proceed, and strength improvement due to solution effect cannot be expected. The upper limit of the ultimate temperature is 600 ° C. The higher the temperature, the more the strength can be expected to be improved by the solution treatment effect. However, if the temperature is higher than this temperature, there is a risk of inconvenience in production due to softening due to eutectic melting and deterioration of the appearance of the product. Also, the time when the material is in the temperature range over 400 ° C is 10
Hold it for less than a minute. If the time is longer than this, the formation of an oxide film on the surface impairs the cold rolling property after the annealing and the appearance of the product. The average heating rate is preferably 1 ° C./s or more, and if it is slower than this, precipitation of alloying elements such as Cu, Mg, Si, etc. proceeds and the precipitates become coarse, and the alloys in the precipitates are also retained by heating at high temperature. It takes time to form a solid solution with an element. Compared with the DC cast material, the present cast material usually has a large amount of solid solution of Mn and the like. Therefore, if the heating rate of the intermediate annealing is slow, the precipitation rate and the recrystallization rate compete with each other, so that Mn or the like precipitates during recrystallization. Zene, which hinders the growth of crystal grains
The r-drag effect causes coarsening of recrystallized grains, and the maximum crystal grain size (minor diameter) in the direction perpendicular to the rolling direction is 60.
Many crystal grains with a size of μm or more are generated. As a result, deep drawability and necking formability deteriorate. Therefore, it is better that the temperature rising rate is faster. The cooling rate from the ultimate temperature is 1 ℃
/ s or more. If it is slower than this, solid-dissolved alloy elements will precipitate during the cooling process, and the contribution to the strength improvement due to the solution treatment effect will decrease. The upper-air annealing step is intended to reduce the strength reduction after coating baking by annealing at a high cooling rate with a remarkable solution treatment effect, and can be achieved by ordinary CAL annealing, but is not particularly limited thereto. Not a thing. As described above, since the alloying elements are solid-dissolved by the intermediate annealing described above and the strength reduction can be less than the age precipitation hardening during coating baking, the rolling rate is low in the cold rolling after annealing and the work hardening amount is at least the desired strength. It is possible to control the ear rate sufficiently. In order to further control the ear rate, Japanese Patent Application No. 4-14671 filed by the present inventors has already filed.
Adoption of a process in which a partial recrystallization treatment by batch annealing described in No. 7 is followed by a 5-30% light reduction and a further CAL intermediate annealing is performed. Partial recrystallization by CAL annealing described in Japanese Patent Application No. 4-166974. This can be achieved by adopting a process in which a CAL intermediate annealing is further carried out after the treatment by lightly reducing the pressure by 5 to 30%, and further, a method by the CAL two-step annealing described in Japanese Patent Application No. 4-263065. The maximum recrystallized grain after annealing is 40 μm due to main annealing
The following is obtained, and in particular, the formation of wrinkles during drawing such as deep drawing and necking is reduced. Cold rolling After that, cold rolling is performed, but the required strength cannot be obtained unless the cold rolling rate is 40% or more. Final Annealing After the cold rolling, it is possible to improve the deep drawability by performing final annealing at about 100 to 200 ° C., if necessary.

[0008]

EXAMPLES Examples of the present invention will be described below. An aluminum alloy having the chemical composition shown in Table 1 was rolled and heat treated by the manufacturing method shown in Table 2 to prepare a sample. Table 1
Alloy A shown in 1) satisfies the range of the alloy composition of the present invention, and Alloy B is a comparative alloy in which the amounts of Mg and Mn are deviated. In the column of "Method" of casting in Table 2, "DC" means DC casting, "CC" means that by continuous casting and rolling, and "Speed" column means the moving speed (m / m) of the solidification interface. mi
n). The unit of each "plate thickness" of casting, hot rolling, cold rolling, and final annealing is mm, and the column of soaking and the column of conditions of intermediate annealing / final annealing show temperature × holding time. However, the holding time of "0" indicates that the cooling was started immediately (without holding) after the temperature reached, and the unit of "temperature" in the hot rolling column is ° C. The cold rolling rate after the intermediate annealing is 60%. The underlined portions in Tables 1 and 2 are conditions outside the present invention.

[0009]

[Table 1]

[0010]

[Table 2]

With respect to the obtained sample, the tensile strength (TS: N / mm ² ) and proof stress (YS: N / mm ² ) of each of the base plate and the heat treatment of 200 ° C. × 20 min corresponding to coating baking,
Elongation (EL:%) is checked and the original plate is 38mmφ shoulder R
The ear ratio (%) was also measured by deep-drawing a 66 mmφ circle with a clearance of 30% using a 2.5 mm punch. The results are shown in Table 3. In addition, DI molding was actually performed to check the continuous formability, and those with cans that were broken due to goring (longitudinal defects) were marked with an X in the "Continuous" column of Table 3, and those that were not broken were ○. Was written. Furthermore, after painting and baking the DI cans actually obtained, four stages of necking were performed and the degree of wrinkling at this time was observed. Marked with an X.
After that, 100 cans of flange formation were carried out. When one or more cracks were generated, the "flange" column was marked with X, and when no cracks were generated, it was marked with ◯. Regarding the maximum crystal grain size, the polarization microstructure was observed on the plate surface, and the maximum value (μm) of the minor axis of the ellipse was observed. Observation of the intermetallic compound was performed by binarizing the surface portion with an image analyzer after polishing, and measuring the number of compounds of 5 μm or more (pieces / m 2
m ² ) was counted. The results are shown in Table 3.

[0012]

[Table 3]

Each of these will be described below. No. No. 3 is an example of the invention, and the alloy composition and the manufacturing method are within the scope of the present invention. By carrying out this soaking treatment, excellent performances over the conventional material in ear ratio and strength are obtained, The other performances were similar to those of the conventional material. No. 1, the alloy composition is included in the scope of the present invention,
This is a conventional example in which DC casting is performed and CAL intermediate annealing is performed, and the yield strength after baking is low and the earring rate is high as compared with the invention examples. No. No. 2 is a material obtained by continuous casting and rolling using the invention alloy, but is a comparative example which is different in that it is not heated and held after casting. Compared with the material (No. 3) heated and held, the strength and DI property are the same, but the ear ratio and the necking / flanging formability are inferior. No. No. 4 is No. This is a comparative example in which the intermediate annealing of No. 3 is performed by a batch furnace, and the strength and earring rate are poor, and further, the crystal grains become coarse and the necking formability is slightly poor. No. No. 5 is due to continuous casting and rolling, but the finished plate thickness is as thin as 7 mm, and as a result, the crystallized substance becomes fine, resulting in a problem of can-out due to galling in DI continuous molding. No.
No. 6 is a case where the alloy component is out of the present invention (5052), and the production method is also out of the present invention (the production method itself is a normal CAL).
No. (Same as the conventional example of No. 1), Mn, F
Since the amount of e is small, there is a problem that continuous DI molding cannot be performed due to can breakage due to galling during DI molding.

[0014]

[Effect] As described in detail above, according to the present invention, the strength reduction after baking is small even though the strength of the can body material before DI molding is low due to the solutionizing effect of the CAL annealed material and the decrease in strength during baking. Is obtained and the DI moldability is improved. Further, since it is possible to maintain a state in which the amount of solid solution of the alloy component is larger than that of the conventional DC material, it is possible to increase the strength, thereby reducing the cold rolling rate after the intermediate annealing, which results in It also has the advantage of low ear coverage. As described above, according to the method of the present invention, it is possible to obtain a good aluminum alloy sheet which is excellent in strength and has a low ear rate and excellent in overall formability, particularly DI formability. Therefore, it is possible to provide a material that is particularly suitable for applications such as can materials that are subjected to paint baking.

Claims (1)

[Claims] 1. Mg: 0.5 to 2.0% (weight%, the same applies hereinafter), Mn: 0.5 to 1.8%, Fe: 0.1 to 0.
7%, Si: 0.05 to 0.5%, Ti: 0.005 to 0.20% alone or together with B: 0.0001 to 0.05% for microstructuring / stabilization, Furthermore, Cu: 0.05-0.5%, Cr: 0.05-0.
Aluminum alloy containing 3%, Zn: 0.1 to 0.5% of 1 type or 2 types or more, and the balance Al and impurities, the moving speed of the solidification interface is 1 to 20 m / min, and the finished plate thickness. Is cast to 10 to 50 mm, and after casting 5
After heating and holding in the temperature range of 60 to 620 ° C. for 1 minute or more, hot rolling is then performed in the temperature range of 230 to 600 ° C., and cold rolling is performed as necessary, and then the ultimate temperature is 400 to 600.
C., annealing at which the average temperature rising rate from the temperature at the start of annealing to the reached temperature is 1 ° C./s or more, the holding time is 10 minutes after reaching the reached temperature, and the cooling rate is 150 ° C. or less at a cooling rate of 1 ° C./s or more. After that, cold rolling with a rolling rate of 40% or more is performed, and the surface microstructure after cold rolling has a maximum crystal grain size (minor axis) in the direction perpendicular to the rolling direction of 60 μm or less and 5 μm or less.
strength and manufacturing method of the low excellent ear index moldability molding aluminum alloy sheet for intermetallic compounds or m is characterized by the presence 500 / mm ² or more.