TW201512416A - Aluminum alloy sheet for battery cases, and method for producing same - Google Patents

Abstract

Disclosed is an aluminum alloy sheet for battery cases that is made of an aluminum alloy including 0.8-2.0 mass% (referred to hereinafter as %) Fe, 0.03-0.20% Si, 0-1.00% Cu, and 0.004-0.050% Ti, with Mg being restricted to 0.02% or less, Mn being restricted to 0.02% or less, and the remainder comprising Al and inevitable impurities, wherein, in a metallographic structure up to a depth of at least 5 [mu]m in the sheet-thickness direction from the surface of the aluminum alloy sheet having a final sheet thickness, the average circle-equivalent diameter of Al-Fe-based intermetallic compounds having circle-equivalent diameters of 1.0-16.0 [mu]m is 1.3-1.9 [mu]m, the coefficient of variation of said circle-equivalent diameters is 0.55 or less, the average number density of said Al-Fe-based intermetallic compounds is 20-150 pieces/2500 [mu]m2, and the coefficient of variation of said number density is 0.30 or less. Also disclosed is a method for producing said aluminum alloy sheet. Accordingly, the present invention provides: an aluminum alloy sheet for battery cases that has excellent laser weldability, formability, and corrosion resistance after long-term storage; and a method for producing said aluminum alloy sheet.

Description

Aluminum alloy plate for battery case and manufacturing method thereof Technical field

The present invention relates to an aluminum alloy which is suitable for use as a battery case for a lithium battery such as an automobile, a mobile phone, a digital camera, a notebook personal computer, etc., and which has excellent laser fusion properties, formability, and corrosion resistance after long-term storage. The board and the method of producing the excellent aluminum alloy in good yield. Moreover, the aluminum alloy plate obtained by the invention can also be used as a battery cover.

Background technique

Many lithium secondary batteries use aluminum in both the shell material composed of the can body and the lid. In general, a can system is manufactured by deep drawing and shrink forming an aluminum or aluminum alloy sheet by molding. The cover is formed by punching or machining to form an aluminum plate or an aluminum alloy plate into a predetermined shape joined to the can body, and is provided with a hole for mounting a terminal, a recess, a liquid inlet, and the like. The can body has a deep cylindrical shape, and the cover has a shape close to a flat plate. The can body and the lid are sealed by laser welding after sealing the internal structure of the electrode or the like.

Thus, the battery case material requires excellent formability and good laser fusion properties. In particular, in batteries for automobiles and the like, the situation in which the laser joint portion requires long-term durability is increased. In recent years, in order to make battery production efficient, Therefore, the laser welding speed is increased, and the difficulty of laser welding is increased. It is sought to obtain an aluminum alloy plate for a battery case of a stable joint even if the penetration depth or the weld bead width is small under high-speed laser welding.

Al-Mn JIS3003 aluminum alloy plate due to solidification shrinkage The force is applied to the remaining portion of the liquid phase, and it is easy to cause weld cracks (solidified cracks, hot-rolled cracks), and there is a problem that the strength of the welded portion is lowered. As for the pure aluminum JIS1050, although the welding crack is not easily generated, the stability of the laser welding is insufficient. As an aluminum alloy sheet having excellent laser fusion properties, an Al-Fe-based aluminum alloy sheet represented by JIS8079 or JIS8021 has been proposed (Patent Documents 1 to 3).

In order to obtain laser fusion properties, Patent Documents 1 and 2 specify Fe and the like. The content, Patent Document 3 specifies the content of Fe or the like and the dispersion density of the intermetallic compound of 2 to 5 μm. The content of Fe has a great influence on the laser weldability, and in particular, since the presence of an intermetallic compound increases the laser absorptivity, it is known that a deep penetration is easily obtained.

However, in these technologies, laser welding is not properly grasped. The cause of the stability is not impeded, and the solution is not suggested. In these conventional techniques, stable laser welding properties cannot be obtained under the welding conditions in which the welding is accelerated due to the high speed of welding or the like. Specifically, in the case where the intermetallic compound is partially dispersed or in the presence of a coarse intermetallic compound, the penetration depth or the bead may become non-uniform and may become slag or metal particles scattered in the fusion. (Splash) causes the so-called weld defect of the bead defect. The durability of the welded portion is lowered by such unevenness or welding defects, thereby causing a shortened life of the battery. Techniques in Patent Documents 1 to 2 Among them, the dispersion state of the intermetallic compound is not closely controlled, and in the technique of Document 3, the effect of uniformly dispersing the intermetallic compound is insufficient, and there is a fear that the unevenness of the welded portion and the weld defect may occur.

The battery case combination is composed of deep drawing processing and shrinking processing. In recent years, it has been molded in a few steps, but in recent years, battery production efficiency has been sought, and the deep drawing and shrink forming of the shell, the punching of the battery cover, and the speed of machining have been speeded up. High-speed forming or high-speed machining causes sticking of aluminum to the surface of the mold during forming or processing, or sticking due to oxidation of condensed aluminum, so that the lubricity between the mold and the aluminum alloy sheet is lowered. As a result, streaks or defects are liable to occur on the surface after forming, or problems that cannot be formed or processed into a predetermined shape are liable to occur. Therefore, it is desirable to have an aluminum alloy sheet which is excellent in moldability, particularly in surface quality and shape stability after molding.

Further, due to the productivity of the battery, the formed or processed materials may be stored for a long period of time, and the materials may be collected for laser welding. At this time, if it reacts with moisture in the atmosphere to cause corrosion and forms an oxide during long-term storage, fusion cracks or pores may occur due to the oxide during laser welding. Although the formation of oxides can be prevented by controlling the environmental gas in the storage place of the formed or processed material, since the cost is high, it is desirable to have excellent corrosion resistance after long-term storage without controlling the ambient gas. Aluminum alloy plate.

Prior technical literature Patent literature

Patent Document 1: Japanese Laid-Open Patent Publication No. 2011-140708

Patent Document 2: Japanese Laid-Open Patent Publication No. 2007-262559

Patent Document 3: Japanese Laid-Open Patent Publication No. 2009-52126

Summary of invention

The present invention has been made in view of the above circumstances, and an object thereof is to provide an excellent laser welding, which is capable of accurately and appropriately controlling the composition of an aluminum alloy and the equivalent diameter and number density of an Al-Fe-based intermetallic compound. Aluminum alloy sheet for battery cans with moldability and corrosion resistance after long-term storage. The aluminum alloy plate obtained by the invention can also be used as a battery cover.

The present inventors have repeatedly studied intensively to solve the problems as described above, and as a result, it has been found that the contents of Fe, Si, Cu, Ti, Mg, and Mn of the aluminum alloy are closely adjusted, and the manufacturing procedure is particularly strictly limited. The present invention is accomplished by solving the above problems by the cooling rate at the time of casting.

Specifically, in the item 1, the present invention is an aluminum alloy plate for a battery can, which is characterized in that it is composed of an aluminum alloy containing: Fe: 0.8 to 2.0% by mass, Si: 0.03 to 0.20% by mass Cu: 0 to 1.00% by mass, Ti: 0.004 to 0.050% by mass, and Mg: 0.02% by mass or less and Mn: 0.02% by mass or less, and the remainder is composed of Al and unavoidable impurities. The average circular equivalent diameter of the Al-Fe-based intermetallic compound having a circular equivalent diameter of 1.0 to 16.0 μm in the metal structure from the surface of the aluminum alloy sheet having the final thickness to a depth of at least 5 μm in the thickness direction is 1.3 to 1.9 μm, and the coefficient of variation of the equivalent diameter of the circle is 0.55 or less. The average number density of the Al-Fe-based intermetallic compound is 20 to 150/2500 μm ² , and the coefficient of variation of the number density is 0.30 or less.

The present invention provides a method for producing an aluminum alloy sheet for a battery can, the method for producing an aluminum alloy sheet for a battery can according to claim 1, comprising: a casting step of casting the aluminum alloy plate; a cutting step; a homogenization treatment step of homogenizing the ingot before or after the planar cutting step; the hot rolling step consisting of a hot rough rolling stage and a hot finishing rolling stage; a cold rolling step; an annealing step; and a surface The treatment step is carried out before or after at least one of the aforementioned homogenization treatment step, hot rolling step, cold rolling step and annealing step. The annealing step has at least one of an intermediate annealing stage in the middle of the cold rolling step and a final annealing stage after the cold rolling step. In the above casting step, the cooling rate at the time of solidification of the ingot position of the surface of the aluminum alloy plate corresponding to the final thickness is 2 to 20 ° C / sec.

In Item 3, the present invention does not have any one or both of the aforementioned planar cutting step and surface treatment step in Item 2.

In the item 4, the invention is the item 2 or 3, wherein the hot rolling step has a heating holding stage in which the ingot is heated and maintained before the hot rough rolling stage, and the homogenization after the plane cutting step is replaced by the aforementioned heating and holding stage The homogenization treatment step after the treatment step or the casting step.

In the item 5, in the item 2 to 4, in the aforementioned homogenization treatment step, the ingot is maintained at a temperature of 450 to 620 ° C for 1 to 20 hours.

In the item 6, the invention is any one of the items 2 to 5, wherein the start temperature in the hot rough rolling stage is 380 to 550 ° C, and the end temperature is 330. Up to 480 ° C, and the starting temperature in the aforementioned hot finish rolling stage is within a range of 20 ° C of the end temperature of the hot rough rolling stage, and the end temperature is 250 to 370 ° C.

In item 7, the invention is in any one of items 2 to 6, currently In the case where the intermediate annealing step is provided in the middle of the cold rolling step, the rolling reduction ratio in the cold rolling step from the hot rolling step to the intermediate annealing step is 50 to 85%, and when the intermediate rolling step is not provided in the middle In the case of the annealing stage, the rolling reduction ratio in the cold rolling step from the hot rolling step to the final annealing step is 50 to 85%.

In item 8, the invention is in any one of items 2 to 7, the aforesaid In the final annealing stage and the intermediate annealing stage of the annealing step, the rolled product is maintained at a temperature of 350 to 450 ° C for 1 to 8 hours in a batch annealing furnace, or 400 to 550 ° C in a continuous annealing furnace. Hold at temperature for 0 to 30 seconds.

According to the present invention, it is possible to provide an aluminum alloy sheet excellent in laser weldability, moldability, and corrosion resistance after storage for a long period of time, and a method for producing the excellent aluminum alloy in a good yield. Moreover, the aluminum alloy plate obtained by the invention can also be used as a battery cover.

1‧‧‧ battery case

Simple description of the schema

Figure 1 is a conceptual diagram of a DC casting process and a graph showing changes in solidification speed in a cross section of a DC ingot.

Fig. 2 is an explanatory view showing the position of the thickness of the ingot corresponding to the surface of the aluminum alloy plate of the final thickness.

Figure 3 is a cross-sectional view of a square shell in which a plurality of stages of compression molding are carried out.

Form for implementing the invention

Hereinafter, the present invention will be described in detail.

1. Composition of aluminum alloy

First, the component composition and the reason for limitation of the aluminum alloy sheet for a battery can of the present invention will be described.

1-1. Fe: 0.8 to 2.0% by mass

Fe is an important component element that has a considerable influence on laser weldability, formability, and corrosion resistance after long-term storage. Most of the Fe in the parent phase exists as an Al-Fe-based intermetallic compound. By the presence of the Al-Fe-based intermetallic compound, the laser absorptivity is increased, and the effect of penetration at the time of laser welding can be enhanced. Further, depending on the state of dispersion of the Al-Fe-based intermetallic compound, the post-drawing step, for example, the recrystallization behavior during annealing or after the hot rolling, is changed, so that the amount of Fe is rough after forming due to coarse grains. The production has a great impact. Further, the Al-Fe-based intermetallic compound, particularly the coarse Al-Fe-based intermetallic compound, also serves as a starting point for corrosion after long-term storage.

When the Fe content is less than 0.8% by mass (hereinafter, simply referred to as "%"), the surface roughness due to coarsening of crystal grains may occur. Further, since the number density of the Al-Fe-based intermetallic compound having a circular equivalent diameter of 1.0 to 16.0 μm becomes loose, the average value of the number density is small and the coefficient of variation is large, and the stable laser fusion property cannot be obtained. Further, the cleaning effect described later could not be obtained, and the surface quality and the molding stability after molding could not be obtained.

On the other hand, when it is more than 2.0%, it will be generated more than In the case of a coarse Al-Fe-based intermetallic compound having a circular equivalent diameter of 16.0 μm, the laser absorptivity is locally increased, the penetration depth or the bead width becomes uneven, and the stability of the laser fusion is deteriorated. Further, since the starting point of cracking occurs during the forming process, the formability is remarkably deteriorated. Further, since corrosion occurs from a coarse Al-Fe-based intermetallic compound as a starting point, it is a cause of welding cracks or pores during laser welding.

According to the above, the Fe content is set to 0.8 to 2.0%. Further, a preferred Fe content is from 1.0 to 1.6%.

1-2. Si: 0.03 to 0.20%

The Si system has an important influence on the laser weldability and formability. When the Si content is less than 0.03%, it is necessary to use a high-purity aluminum ingot to increase the cost. On the other hand, when it exceeds 0.20%, the temperature difference between the liquidus and the solidus line becomes large. Since the temperature difference becomes large, the amount of the liquid phase remaining at the time of solidification after the laser welding is increased, and the stress of the solidification shrinkage is added to the remaining portion of the liquid phase to easily cause the weld crack. Further, a coarse Al-Fe-Si-based compound having a circular equivalent diameter of more than 16.0 μm crystallizes, and not only the penetration depth or the bead width becomes uneven, but also becomes a starting point for cracking during the forming process. According to the above, the Si content is set to 0.03 to 0.20%. Further, a preferred Si content is from 0.04 to 0.15%.

1-3. Cu: 0 to 1.00%

The Cu system has an influence on the laser weldability, formability, and corrosion resistance after long-term storage. Therefore, in order to obtain such effects, Cu may be selectively added. Most of the added Cu will be dissolved in the matrix, which will reduce the thermal conductivity of the aluminum alloy. By reducing the thermal conductivity, the laser absorption rate can be increased, so even a low output can deepen the penetration of the laser fusion. As a result, with a small amount of energy The amount of input can be completed, so that the manufacturing cost can be reduced. On the other hand, since the temperature difference between the liquidus and the solidus line is increased by the addition of Cu, the fusion crack is likely to occur once the Cu content exceeds 1.00%. Further, when the Cu content exceeds 1.00%, the corrosion resistance is lowered after long-term storage. Further, when the Cu content is less than 0.05%, the above effect may be insufficient, and therefore the Cu content is preferably from 0.05 to 1.00%, and more preferably from 0.20 to 0.80%.

Also, in the case of lithium batteries that are repeatedly charged and discharged, there will be batteries The problem of bulging resistance caused by the latent deformation of the battery due to an increase in internal pressure during the reaction. By adding Cu, the strength and the bulging resistance of the shell can be improved, so that the strength and the bulging resistance can be improved. The Cu content is preferably set to 0.05 to 1.00%, and more preferably 0.20 to 0.80% from the viewpoint of improving strength and bulging resistance.

1-4. Ti: 0.004 to 0.050%

The Ti system has a considerable influence on the solidification structure of the aluminum alloy. When the Ti content is less than 0.004%, the crystal grains of the ingot are not fined to form a coarse crystal structure, which causes not only the occurrence of streaky defects on the aluminum alloy sheet, but also causes the surface to be rough after molding. Further, since the effect of miniaturization of the solidified structure of the laser welded portion is small, it is a cause of welding cracks. On the other hand, when the Ti content exceeds 0.050%, the effect of refining the solidification structure of the laser welded portion is saturated, so that excessive addition causes a cost increase. Further, when the Ti content is more than 0.050%, the Ti-based intermetallic compound is easily formed, and the intermetallic compound is distributed in a stripe shape on the rolled sheet to cause surface defects. According to the above, the Ti content is set to 0.004 to 0.050%. Further, a preferred Ti content is from 0.007 to 0.030%.

1-5.Mg: 0.02% or less

The Mg-based element can greatly improve the strength and the bulging resistance, but the laser welding property is remarkably deteriorated. Specifically, since Mg has a low vapor pressure, it is not only a cause of pores in the welded portion at the time of laser welding, but also causes a temperature difference between the liquidus and the solidus to increase, thereby causing a weld crack to occur. After long-term storage, it is easy to form an oxide on the surface of the aluminum alloy plate, and pores or weld cracks may occur due to the oxide. By limiting the amount of Mg to 0.02% or less, the characteristics of the aluminum alloy sheet for battery cans are not impaired. When the amount of Mg exceeds 0.02%, the laser fusion property and the corrosion resistance after long-term storage deteriorate. According to the above, the Mg content is limited to 0.02% or less, and more preferably 0.01% or less. Further, the lower limit of the Mg content is not particularly specified and may be 0%, but less than 0.001% does not particularly improve the effect, and the raw material cost is increased by using a high-purity aluminum material. Therefore, the lower limit of Mg is preferably 0.001%.

1-6. Mn: 0.02% or less

The Mn system and the Mg are elements which can greatly improve the strength and the bulging resistance, but are also elements which affect the circular equivalent diameter or the number density of the Al-Fe-based intermetallic compound. By adding Mn, the equivalent diameter of the Al-Fe-based intermetallic compound dispersed in the aluminum alloy sheet becomes large, and the number density becomes small. Further, a coarse Al-Mn-based intermetallic compound is formed. By limiting the amount of Mn to 0.02% or less, the characteristics of the aluminum alloy sheet for a battery can be not impaired. However, when the amount of Mn exceeds 0.02%, the laser welding property is deteriorated or the cleaning effect described later is impaired, so that damage is caused. The reason for the surface quality after forming. According to the above, the Mn content is limited to 0.02% or less, and more preferably 0.01% or less. Further, the lower limit of the Mn content is not particularly specified and may be 0% but less than 0.001% also does not particularly improve the effect, but also increases the cost of raw materials due to the use of high-purity aluminum. Therefore, the lower limit of Mn is preferably 0.001%.

1-7. Other ingredients

In order to refine the grain structure, at least one of B and C may be added in a trace amount in combination with Ti. In the case where both of B and C are added, the total amount of addition of the two is preferably 0.0001 to 0.0020%, or the addition amount thereof is added instead, and it is also preferably 0.0001 to 0.0020%. Further, the amount of addition is more preferably 0.0005 to 0.0015%. When the amount of addition is less than 0.0001%, the effect of sufficiently refining the crystal grains cannot be obtained. On the other hand, when the amount of addition is more than 0.0020%, not only the effect of refining the crystal grains is saturated, but also surface defects due to coarse aggregates of the Ti—B-based compound or the Ti—C-based compound are likely to occur.

1-8. Unavoidable impurities

In the case of the unavoidable impurities, one or two or more kinds of these may be contained in the case of Cr: 0.02% or less, Zn: 0.02% or less, Zr: 0.02% or less, and a total of 0.05% or less. If it is so content, it does not impair the characteristics of the aluminum alloy sheet used as the battery can.

2. The equivalent diameter and number density of Al-Fe intermetallic compounds in the metal structure of aluminum alloy

In the aluminum alloy sheet for a battery can according to the present invention, it is necessary to specify not only the composition of the aluminum alloy as described above but also the equivalent diameter and number density of the Al-Fe-based intermetallic compound in the metal structure in the finally prepared state.

The circular equivalent diameter and number density of the Al-Fe intermetallic compound have a considerable influence on the laser weldability, formability, and corrosion resistance after long-term storage. In the aluminum alloy, an Al-Fe-based intermetallic compound is dispersed. In the present invention, the average of Al-Fe-based intermetallic compounds having a circular equivalent diameter of 1.0 to 16.0 μm in the metal structure from the surface of the aluminum alloy sheet having the final thickness to the depth of at least 5 μm in the thickness direction. The equivalent diameter of the circle is 1.3 to 1.9 μm, and the coefficient of variation of the equivalent diameter of the circle is 0.55 or less. Further, the average density between the Al-Fe-based intermetallic compounds is 20 to 150/2500 μm ² , and the variation of the number density The coefficient is 0.30 or less.

By specifying the circle of the Al-Fe-based intermetallic compound as described above The equivalent diameter and the number density can obtain a stable welded joint with uniform penetration depth or bead width, and a perfect welded portion without weld defects can be obtained. Such an effect is obtained by using an Al-Fe-based intermetallic compound to increase the laser absorptivity, and also to reduce the variation of the circle equivalent diameter and the number density of the Al-Fe-based intermetallic compound. It is roughly uniform. Then, since the coarse Al-Fe-based intermetallic compound which is a starting point of corrosion is small, the corrosion resistance after long-term storage can be improved. Further, by dispersing the Al-Fe-based intermetallic compound having the circular equivalent diameter as described above at a density as described above, the condensed aluminum or alumina which has been condensed on the mold during the molding can be removed. That is, since the cleaning effect is obtained, deterioration of the surface quality and the formation stability after the forming process can be prevented.

2-1. Round equivalent diameter of Al-Fe intermetallic compounds

The fine Al-Fe-based intermetallic compound having a circular equivalent diameter of less than 1.0 μm has almost no influence on the laser fusion property and a cleaning effect. Therefore, in the present invention, those having the equivalent diameter of the circle are not regarded as objects. Further, when a coarse Al-Fe-based intermetallic compound having a circular equivalent diameter of more than 16.0 μm is present, an increase in the laser absorptivity occurs locally. Therefore, not only is the penetration in this partial part particularly deep, Moreover, weld cracks and the like occur due to uneven weld beads or splashes. Further, a coarse Al-Fe-based intermetallic compound having a circular equivalent diameter of more than 16.0 μm becomes a starting point of corrosion, and causes damage to the origin of cracking during molding. In the present invention, a coarse Al-Fe-based intermetallic compound having a circle equivalent diameter exceeding 16.0 μm which is a cause of the above-mentioned damage is prevented from being formed. Therefore, in the present invention, a coarse Al-Fe-based intermetallic compound having a circle equivalent diameter of more than 16.0 μm is not considered as an object. As described above, in the present invention, an Al-Fe-based intermetallic compound having a circle equivalent diameter of 1.0 to 16.0 μm is used as a target, and the Al-Fe-based intermetallic compound is adjusted by a circle or the like. The effective diameter and the number density are used to obtain an aluminum alloy material having excellent laser fusion properties, formability, and corrosion resistance after long-term storage.

When the average circular equivalent diameter of the Al-Fe-based intermetallic compound having a circular equivalent diameter of 1.0 to 16.0 μm is less than 1.3 μm, each Al—Fe-based intermetallic compound is small, so that the cleaning effect and the surface after molding are not obtained. Quality and form stability deteriorated. Moreover, in this case, the effect of increasing the absorption rate of the laser light is small, and the effect of deepening the penetration of the laser welding is lowered, and the penetration depth of the stability cannot be obtained. On the other hand, when the average circular equivalent diameter exceeds 1.9 μm, the number density of the Al-Fe-based intermetallic compound becomes small, and the distribution of the Al-Fe-based intermetallic compound becomes loose, so that the bead width or the penetration depth cannot be obtained. Laser fusion. Further, in this case, the cleaning effect is not obtained, and the surface quality and the formation stability after molding are deteriorated. Further, in this case, since a relatively large number of coarse Al-Fe-based intermetallic compounds are used as a starting point of corrosion, corrosion resistance is lowered after long-term storage. According to the above, an Al-Fe system having a circle equivalent diameter of 1.0 to 16.0 μm is used. The average circular equivalent diameter of the intermetallic compound is set to 1.3 to 1.9 μm. Further, a preferred average circular equivalent diameter is 1.4 to 1.8 μm. Here, the average circle equivalent diameter is the arithmetic mean of the circle equivalent diameters.

Next, the coefficient of variation of the equivalent diameter of the circle will be described. Round equivalent The coefficient of variation of the diameter is a parameter showing the relative variation of the circle equivalent diameter of the Al-Fe-based intermetallic compound having a circle equivalent diameter of 1.0 to 16.0 μm. When the coefficient of variation exceeds 0.55, the difference in the circle equivalent diameter of the Al-Fe-based intermetallic compound is large, and the relative variation in the equivalent diameter of each circle is also large, and the laser fusion property in which the bead width or the penetration depth is stable cannot be obtained. When the coefficient of variation of the equivalent diameter of the circle is 0.55 or less, the size of the Al-Fe-based intermetallic compound is small and the uniformity is excellent, so that the problem of exceeding 0.55 does not occur. Therefore, the coefficient of variation of the circle equivalent diameter is set to 0.55 or less. Further, the coefficient of variation of the preferred circle equivalent diameter is 0.50 or less. Further, the lower limit of the coefficient of variation is not particularly limited, but can be naturally determined according to the method for producing an aluminum alloy used in the present invention and the method for producing an aluminum alloy material. In the present invention, 0.30 is a lower limit.

2-2. Number density of Al-Fe intermetallic compounds

Al-Fe-based metal when the average number density of the Al-Fe-based intermetallic compound having a circular equivalent diameter of 1.0 to 16.0 μm is less than 20/2500 μm ² (the intermetallic compound is present in an average number per 2500 μm ² ) The distribution of the intermetallic compound becomes loose, so that the laser fusion property of the bead width or the penetration depth stability cannot be obtained. Moreover, in this case, the cleaning effect is not obtained, and the surface quality and the formation stability after molding are deteriorated. Further, since the coarse Al-Fe-based intermetallic compound is increased, the corrosion resistance is lowered after long-term storage. On the other hand, when the average number density exceeds 150 / 2500 μm ² , the equivalent diameter of the Al-Fe-based intermetallic compound is small, so that the cleaning effect is not obtained, and the surface quality and the formation stability after molding are deteriorated. Further, in this case, the effect of increasing the increase in the laser absorptivity is small, and the effect of deepening the penetration at the time of laser welding is lowered, and the penetration depth of the stability cannot be obtained. According to the above, the average number density of the Al-Fe-based intermetallic compound having a circle equivalent diameter of 1.0 to 16.0 μm is set to 20 to 150/2500 μm ² . Further, it is preferable that the above average density is 30 to 130 / 2500 μm ² .

Next, the coefficient of variation of the number density will be described. Change in number density When the number exceeds 0.30, the relative variation of the distribution of the Al-Fe-based intermetallic compound is large and the distribution becomes uneven, and the laser fusion property of the bead width or the penetration depth stability cannot be obtained. When the coefficient of variation of the number density is 0.30 or less, the relative variation in the distribution of the Al-Fe-based intermetallic compound is small and the uniformity is excellent, so that the problem of exceeding 0.30 does not occur. Thus, the coefficient of variation of the number density is set to 0.30 or less. Further, the preferred coefficient of variation is 0.25 or less. Further, the lower limit of the coefficient of variation is not particularly limited, and can be naturally determined according to the method for producing an aluminum alloy used in the present invention and the method for producing an aluminum alloy material. In the present invention, 0.10 is a lower limit.

Moreover, the variation coefficient of the equivalent diameter and the number density of the circle is also called For relative standard deviation, in the statistics, the standard deviation/arithmetic mean is defined, which is a parameter showing the degree of relative deviation. The coefficient of variation is not affected by the arithmetic mean and can be uniform. For example, when the arithmetic mean value is 100 and the standard deviation (degree of the difference) is 1, the coefficient of variation is (1/100) × 100 = 1 (%). On the other hand, the average is 10,000 and the standard deviation The coefficient of variation when the degree of the difference is 100 is also (100/10000) × 100 = 1 (%). It can be seen from the standard deviation that the latter has a large difference, but if it is based on the coefficient of variation, it is a 1% difference. If you want to rely on the arithmetic mean and you can grasp the degree of variation shown, it is advisable to use the standardized coefficient of variation. The smaller the value of the coefficient of variation, the more excellent the uniformity.

It is assumed that each Al-Fe-based intermetallic compound dispersed in an aluminum alloy When there is the same circle equivalent diameter, then the variation coefficient of the circle equivalent diameter is 0. Further, when the intermetallic compounds are dispersed at equal intervals, the number density of all the places is also the same and the coefficient of variation of the number density is zero. Thus, the lower limit of the coefficient of variation is theoretically zero, but in the case of an industrially produced aluminum alloy sheet, it is practically impossible to disperse (uniformly) the intermetallic compounds having the same circle equivalent diameter at intervals. The lower limit of the coefficient of variation of the circle equivalent diameter and the number density of the invention is 0.30 and 0.10 as described above.

As described above, the average circular equivalent diameter of the Al-Fe-based intermetallic compound having a circular equivalent diameter of 1.0 to 16.0 μm is 1.3 to 1.9 μm, and the coefficient of variation of the circular equivalent diameter is 0.55 or less. An Al-Fe-based intermetallic compound having an average number density of 20 to 150/2500 μm ² and a coefficient of variation of a number density of 0.30 or less is suitable for an Al-Fe-based intermetallic compound dispersed in a metal structure. The equivalent diameter and the number density of the circle of the range are small, and the relative defects in the equivalent diameter and the number density are small and the uniformity is excellent. Therefore, good laser welding properties, moldability, and corrosion resistance after long-term storage can be achieved. Further, it is necessary to satisfy the circular equivalent diameter or the number density of the intermetallic compound in the metal structure from the surface of the aluminum alloy sheet having the final thickness to a depth of at least 5 μm in the thickness direction. In addition, in the region from the surface of the final plate to the depth of the plate thickness exceeding 5 μm, the effect on the weldability, cleaning effect or corrosion resistance due to the equivalent diameter or number density of the intermetallic compound may be greater than that from the surface. The region up to a depth of 5 μm in the thickness direction is small, and therefore, in the region of such a depth exceeding 5 μm, the above-described circle equivalent diameter or number density is not particularly limited.

Further, the Al-Fe-based intermetallic compound means an intermetallic compound such as Al ₃ Fe, Al ₆ Fe, Al _m Fe, α-AlFeSi, or β-AlFeSi. In addition, the circular equivalent diameter and the number density of the Al-Fe-based intermetallic compound in the metal structure are obtained by scanning electron microscopy using a scanning electron microscope to form a reflected electron composition image (COMP image) at a depth of 5 μm in the thickness direction of the aluminum alloy material. And obtain the microscope image obtained by image analysis.

3. Method for manufacturing aluminum alloy plate

Next, a method of producing the aluminum alloy sheet for a battery can of the present invention will be described in detail. The method for producing an aluminum alloy sheet for a battery can according to claim 1 is characterized in that it comprises: a casting step of casting an aluminum alloy sheet; a plane cutting step; and a homogenization The processing step is to homogenize the ingot before or after the planar cutting step; a hot rolling step consists of a hot rough rolling stage and a hot finishing rolling stage; a cold rolling step; an annealing step; and a surface treatment The step is before or after at least any of the homogenization treatment step, the hot rolling step, the cold rolling step, and the annealing step. The annealing step has at least any one of an intermediate annealing stage in the middle of the cold rolling step and a final annealing stage after the cold rolling step. Casting In the production step, the cooling rate at the time of solidification of the ingot thickness of the surface of the aluminum alloy plate corresponding to the final thickness is 2 to 20 ° C / sec.

Here, when the surface of the ingot is very smooth or there is no oxide, etc. When the object is observed, either or both of the planar cutting step and the surface treatment step may be omitted. Moreover, it is also possible to have a heating and holding stage for heating and holding the ingot before the hot rough rolling stage of the hot rolling step, and to replace the homogenization treatment step after the plane cutting step or the homogenization treatment after the casting step by the heating and holding stage step.

3-1. Casting step

First, the aluminum alloy melt which has been adjusted to the above-described composition range is appropriately subjected to a melt treatment such as a degassing treatment or a filtration treatment, and then cast according to a usual method such as a DC casting method.

Figure 1 shows a conceptual diagram of the DC casting method and shows the solidification A graph of the change in cooling rate. The molten metal injected into the mold is rapidly cooled by contact with the water-cooled mold wall. The surface layer of the ingot formed by solidification shrinks to create a gap between the surface of the ingot and the mold. Compared with the mold or the sprayed water, the heat transfer resistance of the void is very large, so that the heat which is diffused from the ingot to the outside is reduced, and the cooling rate at the time of solidification is also lowered. When the ingot is lowered and the surface of the ingot is in contact with the spray water, the cooling rate at the time of solidification is rapidly increased. In the area where it is exposed to the water-cooled mold wall and is rapidly cooled, a finely solidified structure called a chill layer is formed. Further, in a region where the cooling rate at the time of solidification is reduced due to a gap between the surface of the ingot and the mold, a coarse micro-solidified structure called a coarse cell layer is formed. Next, when the ingot is lowered and the surface of the ingot is in contact with the spray water, the cooling rate is rapidly increased during solidification. A micro-coagulated tissue called a micro-cell layer is formed in the region.

In a region where the cooling rate at the time of solidification is reduced, for example, in a coarse cell layer, it is easy to form a coarse Al-Fe-based intermetallic compound exceeding 16.0 μm , and an Al-Fe-based intermetallic compound having a circular equivalent diameter of 1.0 to 16.0 μm . The circular equivalent diameter or the number density tends to be non-uniform, and thus the laser fusion property, the moldability, and the corrosion resistance after long-term storage are lowered. On the other hand, in a region where the cooling rate at the time of solidification increases, for example, in the micro cell layer, since the Al-Fe-based intermetallic compound is finely dispersed, the average circular equivalent diameter of the Al-Fe-based intermetallic compound becomes small and average The number density becomes larger. As a result, the cleaning effect is not obtained, and the surface quality and the formation stability after molding are deteriorated.

The inventors found that by controlling the aluminum equivalent to the final thickness The cooling rate at the time of solidification of the ingot position of the surface of the alloy sheet can obtain an aluminum alloy sheet having an equivalent diameter or a number density of the Al-Fe-based intermetallic compound and having such a small difference and uniformity. Specifically, when the cooling rate at the time of solidification is reduced to less than 2 ° C / sec, the average circular equivalent diameter and the circle equivalent diameter of the Al-Fe-based intermetallic compound having a circular equivalent diameter of 1.0 to 16.0 μm The coefficient of variation becomes large, and the average number density of the Al-Fe-based intermetallic compound is small, and the coefficient of variation of the number density becomes large. As a result, the laser weldability, the formability, and the corrosion resistance after long-term storage are deteriorated. On the other hand, when the cooling rate at the time of solidification increases and exceeds 20 ° C / sec, the Al-Fe-based intermetallic compound is finely dispersed, so that the average circular equivalent diameter of the Al-Fe-based intermetallic compound becomes small and the average The density becomes larger. As a result, the cleaning effect is not obtained, and the surface quality and the formation stability after molding are deteriorated.

According to the above, the surface of the aluminum alloy plate corresponding to the final thickness The cooling rate at the time of solidification of the ingot thickness position is set to 2 to 20 ° C / sec. Further, it is preferred that the cooling rate during solidification is 3 to 10 ° C / sec. The cooling rate at the time of solidification can be adjusted by controlling the casting speed, the material of the mold, the cooling conditions, or the temperature of the melt. Specifically, since there is a region where the cooling rate at the time of solidification is reduced by creating a gap between the surface of the ingot and the mold, the above-described control is used to narrow the aforementioned region or to alleviate the cooling rate during solidification in the region. The amount of reduction is further changed to further change the cooling rate at the time of solidification of the entire casting region including the region.

Here, the cooling rate at the time of solidification can be calculated by observing the dendritic structure of the ingot and measuring the secondary dendritic spacing (DAS). Specifically, the sheet having a predetermined thickness is cut along a plane at right angles to the casting direction. Next, the section of the chip was ground and the polished observation surface was subjected to electrolytic treatment with Barker's solution. Then, the DAS measurement of the observation surface was performed by an optical microscope. Thus, the DAS of the entire cut surface can be known. In addition, the DAS (μm) and the cooling rate C (°C/sec) at the time of solidification are constants of b and n, and the relational expression of DAS=bC ⁿ (hereinafter referred to as relational expression 1) is established. Here, b is 33.4 and n is -0.33.

3-2. Plane cutting step

The ingot after the casting step can also perform planar cutting in accordance with the state or shape of the surface of the ingot and the distribution of the cooling rate during solidification in the ingot. If the surface of the ingot is rich in undulating shape, or if the surface of the ingot has oxides or dirt formed or adhered in the casting step, once the hot rolling or cold rolling is performed, the stripe pattern on the final plate will be obtained. Or why, so Plane cutting must be performed. The plane cutting amount is determined as described above so that the cooling rate at the time of solidification at the ingot position of the surface of the aluminum alloy plate corresponding to the final thickness is 2 to 20 ° C / sec. Moreover, even if the surface of the ingot is smooth and there is little oxide or dirt on the surface, if the cooling rate of the surface of the ingot is less than 2 ° C / sec or more than 20 ° C / sec, the plane cutting is performed to make the final equivalent. The cooling rate at the time of solidification of the ingot thickness of the surface of the aluminum alloy plate having a plate thickness may be 2 to 20 ° C / sec. Further, when combined with the surface treatment step described later, the amount of surface removal may be considered and the amount of planar cutting may be determined.

3-3. Surface treatment steps

After at least one of the homogenization treatment step, the hot rolling step, the cold rolling step and the annealing step after the casting step, the purpose of removing the dirt or oxide film on the surface of the ingot may be to set chemical, electrochemical or A surface treatment step that mechanically removes the surface of the material. In the surface treatment step, since one part of the surface of the aluminum alloy plate is removed, it is necessary to determine the amount of surface removal so that the cooling rate at the position of the ingot of the surface of the aluminum alloy plate corresponding to the final thickness is 2 to 20 ° C. /second. Also, the surface treatment step may be provided before or after any of the homogenization treatment step, the hot rolling step, the cold rolling step, and the annealing step. Also, the surface treatment step can be set once or more times.

The position of the ingot thickness corresponding to the surface of the aluminum alloy sheet having the final thickness can be estimated from the thickness of the ingot after casting, the amount of planar cutting in the plane cutting step, the amount of surface removal in the surface treatment step, and the thickness of the surface treatment step. For example, as shown in FIG. 2, a planar cutting step is applied to the cast ingot after the casting, and in the homogenization treatment step, the hot rolling step, the cold rolling step, and the retreat In the case where the surface treatment is provided once in the middle of the fire step, the position of the ingot thickness of the surface of the aluminum alloy plate corresponding to the final thickness can be expressed by the following formula.

X=(t-Δt)×(T-Δs)/t where X: the thickness of the ingot corresponding to the center of the ingot plate thickness of the final plate thickness (mm), T: casting The distance from the central position of the ingot to the surface (mm), △s: the plane cutting amount (mm) of one surface in plane cutting, Δt: the surface removal amount (mm) of one surface in the surface treatment step, t: the distance (mm) from the center position of the ingot to the surface of the sheet in the surface treatment step.

Further, in the case where a plurality of surface treatment steps are provided, in the above formula, the same can be calculated by using each of the surface treatment steps Δt and t.

The manufacturing steps other than the casting step, the planar cutting step, and the surface treatment step are not particularly limited, but from the viewpoints of formability, swell resistance, and surface quality of the final sheet, it is preferred to use a manufacturing step as described below.

3-4. Homogenization process steps

A homogenization treatment step of homogenizing the ingot at a temperature of 450 to 620 ° C for a period of 1 to 20 hours may be provided. If the temperature of the homogenization treatment is lower than 450 ° C or the retention time of the homogenization treatment is less than 1 hour, the homogenization effect is small, and the hot rough rolling stage and the hot finish rolling stage, and the intermediate annealing stage and the final annealing stage are described later. The crystal grains will be coarsened. Such coarse recrystallized grains constitute a cause and surface roughness is likely to occur after forming. When the temperature of the homogenization treatment exceeds 620 ° C, one part of the ingot is melted and the aluminum alloy sheet cannot be stably produced. Moreover, even if the holding time of the homogenization treatment exceeds 20 hours, the homogenization effect cannot be improved, and it becomes uneconomical from the viewpoint of cost. According to the above, the homogenization treatment conditions should be set to a temperature of 450 to 620 ° C And the holding time is 1 to 20 hours, and more preferably set to a temperature of 480 to 600 ° C and a holding time of 3 to 15 hours.

3-5. Hot rolling step

The hot rolling step is composed of a hot rough rolling stage and a hot finishing rolling stage, but may also have a heating holding stage before the hot rough rolling stage.

3-5-1. Heating retention phase

If a heat holding phase is provided before the hot rough rolling stage of the hot rolling step, in this stage, the ingot before rolling is heated at a predetermined temperature for a predetermined time. Here, before the hot rolling step, the heating and holding step of the hot rolling step is set to an appropriate condition (holding temperature and holding time), and the hot holding step is used to impart hot rolling together. Pre-heating effect and homogenization treatment effect. By replacing the homogenization treatment step with the heating and holding step, not only the effect similar to the homogenization treatment but also the number of manufacturing steps or the reduction can be obtained as compared with the case where the homogenization treatment step is provided before and after the plane cutting step. It is advantageous in terms of cost. On the other hand, if the heating and holding step is carried out without homogenization treatment and the effect of not obtaining the homogenization treatment effect, the recrystallization grains in the subsequent hot rough rolling stage and hot finish rolling stage, and the intermediate annealing stage and the final annealing stage are performed. It will be coarsened and it is prone to surface roughness after forming.

In order not to provide a homogenization treatment step but to obtain a homogenization treatment effect by the heat retention stage, it is preferable to set the temperature to 450 to 620 ° C and the retention time of 1 to 20 hours. When the temperature is kept below 450 ° C or the holding time is less than 1 hour, the homogenization effect is small, and the recrystallized grains in the hot rough rolling stage and the hot finishing rolling stage as well as the intermediate annealing stage and the final annealing stage will be It will be coarsened, and it is easy to produce surface roughness after forming. If the temperature is maintained above 620 ° C, one part of the ingot will melt and the aluminum alloy sheet cannot be stably produced. Moreover, even if the holding time exceeds 20 hours, the homogenization effect cannot be improved, and it is not economical from the viewpoint of cost. Moreover, the manufacturing efficiency of the subsequent hot rough rolling stage and hot finish rolling stage is lowered.

Also, if the heat retention phase is not used instead of the homogenization treatment In the case where a homogenization treatment step is provided, the ingot can be sufficiently homogenized in the homogenization treatment step. Therefore, in this case, the holding time and the holding temperature in the heat retention phase may not be limited as described above, and the ingot may be held for 1 to 10 hours under normal conditions, for example, a temperature of 380 to 560 °C.

3-5-2. Hot rough rolling stage

When the hot rough rolling start temperature is lower than 380 ° C, there is a possibility that a uniform recrystallized structure after the end of hot rough rolling may not be obtained, which may cause a rough surface after forming. On the other hand, when the hot rough rolling start temperature exceeds 550 ° C, the recrystallized grains after the hot rough rolling is coarsened may cause coarsening of the surface after molding. Further, there is a possibility that the oxide (roll coating) formed on the surface of the roll is transferred to the surface of the aluminum alloy plate to cause streaky defects. According to the above, the hot rough rolling start temperature is preferably set to 380 to 550 °C.

When the hot rough rolling end temperature is less than 330 ° C, there is a possibility that a uniform recrystallized structure after completion of hot rough rolling may be obtained, which may cause a rough surface after forming. On the other hand, when the hot rough rolling start temperature exceeds 480 ° C, the recrystallized grains after the hot rough rolling is coarsened may be a cause of surface roughness after molding. According to the above, the hot rough rolling end temperature is preferably set to 330 to 480 °C.

3-5-3. Hot finishing stage

The hot finish rolling method is exemplified by a combination of a plurality of rolling mills and a reverse rolling method in which a separate rolling mill is used for hot rolling. The term "hot finish rolling" refers to the rolling of a plurality of rolling mills in a tandem manner, and in the case of the reverse rolling method, the rolling of the coils is carried out immediately before rolling to the final rolling. The thickness of the hot finish rolling is about 15 to 40 mm. Further, since the hot finish rolling is performed immediately after the completion of the hot rough rolling, the temperature difference between the hot rough rolling end temperature and the hot finish rolling start temperature is set to be within 20 °C. If the temperature difference is within 20 ° C, there is no loss in formability. Also, usually, the hot finish rolling start temperature is lower than the hot rough rolling end temperature.

If the hot finish rolling temperature is less than 250 ° C, the components contained therein The amount of solid solution is reduced and it becomes difficult to work harden. As a result, there may be a case where the strength after molding is lowered and the bulging resistance is poor. On the other hand, when the hot finish rolling end temperature exceeds 370 ° C, the solid solution amount of the component contained therein increases, and the work hardening becomes easy. As a result, there is a possibility that cracks are generated at the time of forming. Furthermore, since the rolled and rolled material is in a high temperature state after the hot finish rolling step, not only the recrystallization in the hot finish rolling state is continued, but the recrystallized grains are coarsened, which may cause the surface roughness after forming. . According to the above, the hot finish rolling end temperature is preferably set to 250 to 370 °C.

3-6. Cold rolling step after hot rolling

The rolled product subjected to the hot finish rolling step is delivered to the cold rolling step. The rolling reduction in this cold rolling step has a considerable influence on the recrystallization behavior in the subsequent annealing step (intermediate annealing stage or final annealing stage). When the rolling reduction ratio is less than 50%, there may be recrystallization grains coarsened due to the small amount of accumulated strain. condition. As a result, it becomes a cause of rough surface after forming. On the other hand, once the rolling reduction ratio exceeds 85%, the number of cold rolling increases, which is not preferable from the viewpoint of cost. Therefore, the rolling reduction ratio of the cold rolling step after the hot rolling step is preferably set to 50 to 85%. Here, the rolling reduction ratio in the cold rolling step after the hot rolling step is the rolling in the cold rolling step from the hot rolling step to the intermediate annealing step in the case where the intermediate annealing step is provided in the middle of the cold rolling step. The shrinkage rate, in the case where the intermediate annealing stage is not provided, refers to the rolling reduction rate of the cold rolling step from the hot rolling step to the final annealing stage.

3-7. Annealing step and further cold rolling step (final cold rolling step)

In combination with the thermal conditioning of the final aluminum alloy sheet, the final annealing stage may be applied after the cold rolling step without the intermediate annealing stage, or may be performed after the intermediate annealing stage is applied on the middle of the cold rolling step. The cold rolling step serves as a further cold rolling step. The conditions of the final annealing stage and the intermediate annealing stage are not particularly limited and may be carried out according to a usual method. In terms of preferred annealing conditions, in the case of using a batch annealing furnace, the temperature is 350 to 450 ° C and the holding time is 1 to 8 hours, and in the case of using the continuous annealing furnace, the temperature is 400 to 550 ° C and 0. The hold time to 30 seconds (wherein the hold time of 0 seconds means cooling immediately after reaching the predetermined temperature). Further, in the case where the intermediate annealing stage is provided, the rolling reduction ratio in the final cold rolling step after the intermediate annealing stage is preferably set to 20 to 60%. Moreover, after the final cold rolling step or the final annealing stage, the leveling step of the leveling machine, the surface treatment step, the degreasing step using an organic solvent or warm water, and the oiling to prevent the occurrence of scratches when the aluminum alloy sheets are overlapped may also be provided. Oil step, etc.

Again, the homogenization process step is not provided but is maintained by heating In the case where the stage is replaced by the homogenization treatment step, if the difference between the temperature in the heating and holding stage and the hot rough rolling start temperature is large, it is preferable to cool the mixture to a hot portion after the ingot is delivered to the heating and holding stage and heated to a predetermined temperature. The hot rough rolling stage is performed after the rolling start temperature. In this case, the heating and holding of the ingot is controlled by cooling, and the starting temperature and the ending temperature of the hot rough rolling stage or the hot finishing rolling stage are adjusted to an appropriate temperature. On the other hand, when the above temperature difference is small, the ingot can be hot-roughed immediately after the heating and holding stage without passing through the cooling stage. In this case, since it has not passed through the cooling stage, it can be quickly moved to the hot rough rolling stage, but the start temperature and the end temperature of the hot rough rolling stage or the hot finish rolling stage tend to become high, and there may be coarse recrystallized grains. The amount of solid solution of the component, which may or may be contained, increases and becomes easy to work harden.

[Examples]

Hereinafter, the present invention will be described in more detail based on examples of the invention and comparative examples. Further, the conditions described in the claims are the conditional range of the usual methods. The inventive examples and comparative examples do not limit the technical scope of the present invention.

Inventive Examples 1 to 16 and Comparative Examples 17 to 27

An ingot having a thickness of 550 mm was cast by a semi-continuous casting method using an aluminum alloy having the composition shown in Table 1. Further, a component of less than 0.01% is regarded as 0.00%. The obtained ingot was subjected to a planar cutting step as shown in Table 2, and then subjected to a homogenization treatment step at a temperature of 540 ° C for 4 hours. Next, the ingot was temporarily cooled to room temperature. Further, after the cooled ingot was subjected to a heating and holding phase which was heated and maintained at a temperature of 460 ° C for 4 hours (not in place of the homogenization treatment step), the starting temperature was 430 ° C and the end temperature was 360 ° C. In the rolling stage, next, a hot-rolling stage in which the end temperature was 270 ° C was applied to the rolled sheet to obtain a hot-rolled sheet having a thickness of 3 mm. The obtained hot rolled sheet was subjected to a cold rolling step, and the surface treatment shown in Table 2 was carried out. Then, the cold-rolled sheet was subjected to final annealing at a temperature of 390 ° C for a period of 3 hours using a batch annealing furnace to obtain an aluminum alloy sheet having a final thickness of 0.8 mm.

Further, the ingots of Examples 12 and 27 of the present invention have a smooth surface and an oxide Or the dirt is slight, so the ingot obtained is subjected to a homogenization treatment step, a hot rolling step (hot rough rolling stage and hot finish rolling stage), a cold rolling step and a final annealing stage without planar cutting. In the first example of the present invention, the hot finish rolling stage The subsequent hot rolled sheet was subjected to a surface treatment step, and in the inventive examples 9 and 13, the cold-rolled sheets obtained in the middle of the cold rolling step were subjected to surface treatment steps, respectively. Further, in Inventive Examples 3 and 10 and Comparative Example 21, the hot-rolled sheet was subjected to a cold rolling step to a thickness of 0.81 mm, and then the cold-rolled sheet was subjected to a final annealing step, and then it was subjected to a surface treatment step.

(DAS measurement)

For the ingot after the casting step, the solidification cooling rate at the position of the ingot of the surface of the aluminum alloy plate corresponding to the final thickness was determined. First, from the ingot after the casting step, the sheet having a thickness of 20 mm was cut at a right angle to the casting direction. Next, all the sections of the sliced plate were ground, and the ground observation surface was subjected to electrolytic treatment by pasteurized liquid. Then, the DAS of the observation surface was measured using an optical microscope. The X shown in Table 2 corresponds to the ingot thickness position of the surface of the aluminum alloy plate of the final thickness. Then, the cooling rate at the time of solidification shown in Table 2 was calculated using the DAS of the position X and calculated by the above relational expression 1.

The aluminum alloy sheet sample prepared as described above was evaluated by the following method.

(Dispersion state of Al-Fe-based intermetallic compound)

The surface of the obtained aluminum alloy plate is ground according to a usual method, and the degree of grinding is from about 2 to 3 μm from the final surface to the thickness direction. The circular equivalent diameter and the number density of the Al-Fe-based intermetallic compound dispersed on the surface of the polished aluminum alloy plate were measured. Specifically, it is measured whether or not an Al-Fe-based intermetallic compound having a circle equivalent diameter of more than 16 μm exists, and a circle equivalent diameter of an Al—Fe-based intermetallic compound having a circle equivalent diameter of 1.0 to 16.0 μm and number density. In addition, it is necessary to observe the magnification of an Al-Fe-based intermetallic compound having an equivalent circle diameter of 1.0 μm or more, for example, at a magnification of 500 times or more.

The average circular equivalent diameter of the Al-Fe-based intermetallic compound was obtained by photographing a reflected electron composition image (COMP image) at a scanning voltage electron microscope at an acceleration voltage of 15 kV and an observation field area of 250,000 μm ² , and imaging the obtained microscope photograph. Analyze and find. Further, at an acceleration voltage of 15 kV, the electron beam intrusion depth of aluminum is about 2 to 3 μm, and the COMP image obtained by observation contains information of a depth of 2 to 3 μm in the thickness direction. The equivalent circle equivalent diameter (arithmetic mean) and standard deviation were determined from the circle equivalent diameters of all Al-Fe-based intermetallic compounds having a circle equivalent diameter of 1.0 to 16.0 μm observed in the measurement field of view. Further, the coefficient of variation of the circle equivalent diameter is calculated by dividing the standard deviation of the circle equivalent diameter by the average circle equivalent diameter. The results are shown in Table 3.

Further, the number density of the Al-Fe-based intermetallic compound having a circular equivalent diameter of 1.0 to 16.0 μm is obtained by dividing the observation field of 250,000 μm ² into 100 narrow fields of view of 50 μm × 50 μm, and the measurement exists in each narrow field of view ( The total number of the above intermetallic compounds in 2500 μm ² ). Next, the arithmetic mean of the number of measurements of each narrow field of view was obtained as the average number density (number / 250,000 μm ² ). Further, the standard deviation of the number density is obtained from the number density of each narrow field of view, and the coefficient of variation of the number density is calculated by dividing the average density by the average number density. The results are shown in Table 3.

Further, in the pre-experimental aspect, the same sample was used, and the unpolished surface, the surface which had been polished from the surface by 2 to 3 μm, and the surface which had been polished from the surface by 4 to 5 μm were used, and the equivalent diameter of the intermetallic compound was measured as described above. For the number density, the confirmation is to obtain roughly the same data.

(laser welding)

Two rolls of the above-mentioned aluminum alloy plate sample (short side: 60 mm, long side: 100 mm, thickness: 0.8 mm) were butted to each other with a long side, covering a full length of 100 mm for a laser welding test. Moreover, planar processing is performed using a slicing disk on the mating surface. The welding was performed at a welding speed of 5 m/min and 15 m/min. The condensing diameter is 0.1 mm Φ, and the output of the laser welding is adjusted so that the average penetration depth of the final plate is 0.8 mm, and the average penetration depth is 70%, and the laser is welded under the condition of continuous wave (CW). Terminal processing that reduces the output phase in the terminal unit is not performed.

<The soundness of laser welding>

For the above-mentioned laser welded sample, the full length (100 mm) of the welded portion was visually observed. Further, visually observe the cross section of the welded portion (phase For the welding direction, it has an orthogonal cross section) 10 fields of view. Moreover, the interval of each field of view of the cross section of the welded portion is set to 5 mm or more.

In the appearance observation and cross-section observation, no weld cracks were generated, The bead defect and the pores were judged to be good (○ mark), and at least one of the weld crack, the bead defect, and the pore was judged to be defective (× mark). The results are shown in Table 3.

<The stability of laser welding>

In the same manner as the soundness evaluation, the sample after laser welding was observed for observation and cross-sectional observation. Regarding the width of the bead, the bead width at 10 arbitrary positions was measured in the total length of the welded portion of 100 mm, and the average bead width wave was calculated. Further, the penetration depth of the cross section of the welded portion (straight cross section with respect to the welding direction) was measured in 10 fields of view, and dave was calculated from the average penetration depth. Further, the interval between the respective fields of view on the surface of the welded portion and the cross section is set to 5 mm or more.

Measure the maximum bead width wmax, the minimum bead width wmin, The maximum penetration depth dmax and the minimum penetration depth dmin, and wmax/wave, wmin/wave, dmax/dave, and dmin/dave are all judged to be the most excellent (◎ mark) in the range of 0.90 to 1.10, and are 0.85 or more and less than 0.90 or The range of more than 1.10 and 1.15 or less is excellent (○ mark), and the range of 0.80 or more and less than 0.85 or more than 1.15 and 1.20 or less is good (Δ mark), and it is bad in the range of less than 0.8 or more than 1.2 (× mark). The results are shown in Table 3.

(corrosion resistance after long-term storage)

The aluminum alloy plate sample (short side: 60 mm, long side: 100 mm, thickness: 0.8 mm) was kept for 100 hours in a humid gas atmosphere at 50 ° C and a humidity of 95%. Next, the long sides of the samples were brought into contact with each other to cover a full length of 100 mm for the laser welding test. Prior to holding in the humid gas environment, planar processing is performed using the butt joint of the dicing disc. The welding was performed at a welding speed of 5 m/min. The condensing diameter was 0.1 mm Φ, and the output system was adjusted so that the average penetration depth of the sheet thickness of the rolled material was 0.6 mm, and the laser was welded under the condition of continuous wave (CW). Terminal processing that reduces the output phase in the terminal unit is not performed. The appearance of the bead and the cross-sectional observation were performed in the same manner as the evaluation of the soundness of the laser welded portion described above. In the observation of the appearance and the observation of the cross section, the weld crack, the weld bead defect, and the pores were judged to be good (○ mark), and at least one of the weld crack, the bead defect, and the pore was judged to be defective (× mark). The results are shown in Table 3.

<formability>

The above-mentioned aluminum alloy sheet was subjected to multi-stage forming, specifically, a deep drawing test of 3 stages and a drawing forming of 10 stages. The rectangular battery can 1 shown in Fig. 3 was formed. The battery can 1 has a rectangular cross section of 30 mm in width, 8 mm in height, and 45 mm in depth (not shown), and has an average thickness of 0.62 mm on the side surface, an average thickness of 0.51 mm on the upper surface and the bottom surface, and an angle R of 1.5 mm.

Further, in the high-speed forming test, the battery case 1 of the above rectangular shape was formed by performing the 7-stage drawing forming step without performing the 10-stage drawing forming step.

The appearance evaluation of the shell 1 was carried out. Surface defects such as cracks generated during molding, rough surface, and streaks that are not caused by accumulation and burning are judged to be the most excellent (◎ mark), no surface defects, and although rough or striped patterns are generated Slightly judged as excellent (○ remember No.), no surface defects and rough surface or striped pattern can not be said to be slight, but no practical problem is judged as good (△ mark), resulting in any practical surface defects, surface roughness and streaks The person judged to be defective (× mark). The results are shown in Table 3.

<tensile strength>

Using the above-mentioned aluminum alloy plate sample, a JIS No. 5 test piece specified in JIS Z 2201 was produced, and a tensile test was carried out in accordance with JIS 2241 at room temperature. The results of tensile strength are shown in Table 3.

In the inventive examples 1 to 16, the average circular equivalent diameter of the Al-Fe-based intermetallic compound having a circular equivalent diameter of 1.0 to 16.0 μm is 1.3 to 1.9 μm, and the coefficient of variation of the circular equivalent diameter is 0.55 or less. Further, the average number density of the Al-Fe-based intermetallic compound is 20 to 150/2500 μm ² , and the coefficient of variation of the number density is 0.30 or less, and the laser fusion property, corrosion resistance after long-term storage, formability, and stretching The characteristics are qualified. In particular, the tensile strength of Examples 3, 5 to 12 of the present invention was particularly high.

In Comparative Example 17, since the Fe content is large, formation of a circle or the like is formed. A coarse Al-Fe-based intermetallic compound having a diameter of 16.0 μm. Therefore, the laser absorption rate locally increases, the penetration depth or the bead width becomes uneven, and the stability of the laser fusion deteriorates. Moreover, it becomes a starting point of the crack generate|occur|produce at the time of shaping|molding, and a crack generate|occur| In addition, after long-term storage, corrosion occurs starting from a coarse Al-Fe-based intermetallic compound, which causes welding cracks or pores during laser welding, and corrosion resistance deteriorates after long-term storage.

In Comparative Example 18, since the Si content is large, the temperature difference between the liquidus and the solidus line becomes large, and fusion cracks are generated and the laser fusion property is deteriorated. Chemical. Further, a coarse Al-Fe-Si-based compound having a circular equivalent diameter of more than 16.0 μm is crystallized, the penetration depth or the bead width becomes uneven, and the stability of the laser fusion property is deteriorated, and further, cracking occurs in the forming process. The starting point is that cracks are formed during molding and the formability is deteriorated. Further, after long-term storage, corrosion occurs starting from a coarse Al-Fe-based intermetallic compound, which causes welding cracks or pores during laser welding, and the corrosion resistance is deteriorated after long-term storage. On the other hand, since the amount of Ti is small, the crystal grains of the ingot are not fined to form a coarse crystal grain structure, and not only a stripe-like defect is generated on the aluminum alloy sheet, but also the surface is rough after molding, and the formability is deteriorated.

In Comparative Example 19, liquidus and solid phase were present due to the large amount of Cu. The temperature difference between the wires is large, and weld cracks are generated and the soundness of the laser weldability is deteriorated. Moreover, corrosion resistance is lowered after long-term storage, and it is a cause of welding cracks or pores during laser welding after long-term storage, and the corrosion resistance is deteriorated after long-term storage.

In Comparative Example 20, Ti-based metal was formed due to a large amount of Ti. The intermetallic compound is distributed in a stripe shape on the rolled sheet to cause surface defects, and is a starting point of cracking during molding, and cracks are formed during molding to deteriorate the moldability.

In Comparative Example 21, since the amount of Mg was large, it was produced in the welded portion. Stomatal or welded cracks and the deterioration of the weldability of the laser deteriorates. Moreover, after long-term storage, an oxide is formed on the surface of the aluminum alloy plate, and pores or weld cracks are generated by the oxide, and the corrosion resistance after long-term storage is deteriorated.

In Comparative Example 22, since the amount of Fe was small, crystal grains were produced. The rough surface causes the surface to be rough after forming, and the average value of the number density is small and variable. The dynamic coefficient becomes large, and the stability of the laser fusion is deteriorated. Further, the cleaning effect is not obtained, and the surface quality and the formation stability after molding are not good, and the formability is deteriorated.

In Comparative Example 23, since the amount of Fe was small, and the amount of Si and the amount of Mn were large, Therefore, the average value and the coefficient of variation of the circle-equivalent diameter of the Al-Fe-based intermetallic compound are large, and the average value of the number density is small, and the coefficient of variation of the number density becomes large, and the weld crack is generated and the soundness of the laser fusion property is deteriorated. Further, the coarse Al-Fe-Si-based compound and the Al-Mn-based compound having a circle equivalent diameter of more than 16.0 μm are crystallized, the penetration depth or the bead width becomes uneven, and the stability of the laser fusion property deteriorates, and the formation becomes more complicated. The starting point of cracking occurs during processing, and cracks are formed during molding, and the formability is deteriorated. Further, after long-term storage, corrosion occurs starting from a coarse Al-Fe-based intermetallic compound, which causes welding cracks or pores during laser welding, and the corrosion resistance after long-term storage is deteriorated.

In Comparative Example 24, due to the aluminum alloy corresponding to the final sheet thickness The cooling rate of the ingot at the thickness of the surface of the gold plate is small, so the average value and the coefficient of variation of the equivalent diameter of the Al-Fe intermetallic compound are large, and the average value of the number density is small, and the coefficient of variation of the number density Become bigger. As a result, the stability of the laser weldability, the formability, and the corrosion resistance after long-term storage are deteriorated.

In Comparative Example 25, due to the aluminum alloy corresponding to the final sheet thickness Since the cooling rate of the ingot at the thickness of the surface of the gold plate is large, the average circular equivalent diameter of the Al-Fe-based intermetallic compound is small, and the average number density becomes large. As a result, the stability of the laser weldability is deteriorated, the cleaning effect is not obtained, and the surface quality and the formation stability after molding are poor and the formability is deteriorated.

In Comparative Example 26, due to the aluminum alloy corresponding to the final sheet thickness The cooling rate of the ingot at the thickness of the surface of the gold plate is small, so the average value and the coefficient of variation of the equivalent diameter of the Al-Fe intermetallic compound are large, and the average value of the number density is small, and the coefficient of variation of the number density Become bigger. As a result, the stability of the laser weldability, the formability, and the corrosion resistance after long-term storage are deteriorated.

In Comparative Example 27, since the cooling rate was large at the position of the ingot thickness at the surface of the aluminum alloy sheet corresponding to the final sheet thickness, the average circular equivalent diameter of the Al-Fe-based intermetallic compound was small, and the average number density was Big. As a result, the stability of the laser fusion property is deteriorated, and the cleaning effect is not obtained, and the surface quality and the formation stability after molding are poor and the formability is deteriorated.

According to the present invention, it is possible to provide an aluminum alloy sheet for a battery can which is excellent in laser fusion properties, moldability, and corrosion resistance after long-term storage. Moreover, according to the method for producing an aluminum alloy sheet for a battery can of the present invention, the aluminum alloy sheet for a battery can can be obtained with good and stable yield in a good yield. The aforementioned aluminum alloy plate for a battery can also exhibits excellent characteristics as a battery cover.

Claims (8)

An aluminum alloy plate for a battery can, which is characterized in that it is composed of an aluminum alloy containing Fe: 0.8 to 2.0% by mass, Si: 0.03 to 0.20% by mass, Cu: 0 to 1.00% by mass, Ti: 0.004 to 0.050% by mass, and Mg: 0.02% by mass or less and Mn: 0.02% by mass or less, and the remainder is composed of Al and unavoidable impurities, and the surface of the aluminum alloy sheet having a final thickness is at least 5 μm in the thickness direction. In the metal structure, an Al-Fe-based intermetallic compound having a circular equivalent diameter of 1.0 to 16.0 μm has an average circular equivalent diameter of 1.3 to 1.9 μm, and a coefficient of variation of a circular equivalent diameter of 0.55 or less, the aforementioned Al- The Fe-based intermetallic compound has an average number density of 20 to 150/2500 μm ² and a coefficient of variation of the number density of 0.30 or less. A method for producing an aluminum alloy sheet for a battery can, the method for producing an aluminum alloy sheet for a battery can of claim 1, comprising: a casting step of casting the aluminum alloy sheet; a planar cutting step; and a homogenization treatment step, The ingot is homogenized before or after the planar cutting step; the hot rolling step is composed of a hot rough rolling stage and a hot finishing rolling stage; a cold rolling step; an annealing step; and a surface treatment step are performed in the foregoing homogenization Performing at least one of a processing step, a hot rolling step, a cold rolling step, and an annealing step, the annealing step having at least one of an intermediate annealing stage in the middle of the cold rolling step and a final annealing stage after the cold rolling step, In the foregoing casting step, the solidification of the surface of the ingot corresponding to the final thickness of the aluminum alloy plate is cold at the time of solidification. However, the speed is 2 to 20 ° C / sec. The method for producing an aluminum alloy sheet for a battery can according to claim 2, which does not have any one or both of the above-described planar cutting step and surface treatment step. The method for producing an aluminum alloy sheet for a battery can according to claim 2 or 3, wherein the hot rolling step has a heating maintaining stage in which the ingot is heated and maintained before the hot rough rolling stage, and the planar cutting step is replaced by the aforementioned heating and holding stage. The subsequent homogenization treatment step or the homogenization treatment step after the casting step. The method for producing an aluminum alloy sheet for a battery can according to any one of claims 2 to 4, wherein, in the aforementioned homogenization treatment step, the ingot is maintained at a temperature of 450 to 620 ° C for 1 to 20 hours. The method for producing an aluminum alloy sheet for a battery can according to any one of claims 2 to 5, wherein a starting temperature in the hot rough rolling stage is 380 to 550 ° C, an end temperature is 330 to 480 ° C, and the hot rolling is performed. The starting temperature in the stage is within a range of 20 ° C at the end of the hot rough rolling stage, and the end temperature is 250 to 370 ° C. The method for producing an aluminum alloy sheet for a battery can according to any one of claims 2 to 6, wherein the cold annealing step to the intermediate annealing step is performed when an intermediate annealing step is provided in the middle of the cold rolling step. The rolling reduction ratio in the rolling step is 50 to 85%, and the rolling reduction ratio in the cold rolling step from the hot rolling step to the final annealing step in the case where the intermediate annealing step is not provided in the middle of the aforementioned cold rolling step It is 50 to 85%. The method for producing an aluminum alloy sheet for a battery can according to any one of claims 2 to 7, wherein the intermediate annealing step and the final annealing step of the annealing step are the same In the section, the rolled web is maintained at a temperature of 350 to 450 ° C for 1 to 8 hours in a batch annealing furnace or 0 to 30 seconds at a temperature of 400 to 550 ° C in a continuous annealing furnace.