KR20140004797A - Aluminum alloy plate with excellent formability and weldability for cell case - Google Patents

Abstract

The present invention provides a 1000-based aluminum alloy plate which has high strength applicable to a large lithium ion battery container, is excellent in moldability and also excellent in laser weldability. Si: 0.01 to 0.4% by mass, Fe: 0.01 to 0.5% by mass, Co: 0.003 to 0.5% by mass, which is composed of the remainder part Al and unavoidable impurities, and the number of second phase particles having a circular equivalent diameter of 3 µm or more is 100 An aluminum alloy plate having a metal structure of less than pieces / mm 2. The cold rolled annealing plate shows a value of elongation of 30% or more.

Description

Aluminum alloy plate for battery case with excellent moldability and weldability {ALUMINUM ALLOY PLATE WITH EXCELLENT FORMABILITY AND WELDABILITY FOR CELL CASE}

TECHNICAL FIELD This invention relates to the high strength aluminum alloy plate excellent in moldability and laser weldability used for containers for secondary batteries, such as a lithium ion battery.

Since the Al-Mn-based 3000-based alloy is relatively excellent in strength, formability and laser weldability, the Al-Mn-based 3000 alloy is intended to be used as a raw material when producing a container for a secondary battery such as a lithium ion battery. After shaping | molding to a desired shape, it seals by laser welding and uses as a container for secondary batteries. In addition to the 3000-based alloy, the development of an aluminum alloy plate for a secondary battery container based on an existing 3000-based alloy and having high strength and formability has been made.

For example, in patent document 1, as a composition of an aluminum alloy plate, Si: 0.10-0.60 mass%, Fe: 0.20-0.60 mass%, Cu: 0.10-0.70 mass%, Mn: 0.60-1.50 mass%, Mg: 0.20 to 1.20% by mass, Zr: more than 0.12 but less than 0.20% by mass, Ti: 0.05 to 0.25% by mass, B: 0.0010 to 0.02% by mass, consisting of the remainder part Al and unavoidable impurities, cylindrical container dip An aluminum alloy sheet for rectangular cross-sectional battery containers is described, wherein a 45 ° earing rate with respect to the rolling direction is 4 to 7% by the drawing molding method.

On the other hand, in recent years, aluminum alloy plates for rectangular lithium ion battery cases, which have sufficient strength, axial-ironing processability, and creep characteristics, have excellent laser weldability, and can suppress an increase in case thickness during charge and discharge cycles, have also been developed as battery cases. have. In patent document 2, Mn: 0.8 mass% or more, 1.8 mass% or less, Mg: exceeding 0.6 mass%, 1.2 mass% or less, Cu: 0.5 mass%, 1.5 mass% or less are contained, Fe as an impurity is contained 0.5 mass% or less, Si is regulated to 0.3 mass% or less, has the composition which consists of remainder part Al and an unavoidable impurity, and has the orientation density C of the {001} <100> orientation, and the orientation density S of the {123} <634> orientation The aluminum alloy plate for rectangular battery containers whose ratio (C / S) is 0.65 or more and 1.5 or less, tensile strength after final cold rolling is 250 Mpa or more and 330 Mpa or less, and elongation is 1% or more is described.

However, in an aluminum alloy plate whose composition is improved using a 3000-series alloy as a base, abnormal beads may be generated, and it is known that there is a problem in laser weldability.

Therefore, the aluminum alloy plate for secondary battery containers excellent in the laser welding property based on 1000 type | system | group is also developed. Patent Document 3 discloses an aluminum alloy material and a battery case for pulsed laser welding, in which the occurrence of abnormal portions is prevented by pulsed laser welding of an A1000-based aluminum material and a uniform and good welded portion can be formed. According to this, conventionally, Ti, which has been added to suppress coarsening of crystal grains in the casting process, adversely affects the welded portion, and in order to prevent the formation of an abnormal portion when welding A1000 aluminum by pulse laser welding, What is necessary is just to regulate Ti contained in pure aluminum to less than 0.01 mass%.

Japanese Patent No. 4001007 Japanese Patent Application Laid-Open No. 2010-126804 Japanese Patent Application Laid-Open No. 2009-127075

Certainly, in the 1000 system, the elongation value is high, the moldability is excellent, and the number of abnormal beads in laser welding decreases, so that the weldability is stable. Therefore, it is anticipated that high-strength characteristics will also be required in the midst of the enlargement of a lithium ion battery, and it is also considered to apply the comparatively thick 1000-type aluminum plate material as it is.

By the way, in recent years, the container for lithium ion batteries made from aluminum alloys, and its cover are generally joined by pulse laser welding. As described above, in a relatively thick 1000-based sheet, the moldability is excellent, and the number of abnormal beads decreases, but the thermal conductivity may be good. In order to perform pulse laser welding, for example, to increase the energy per pulse, etc. It is necessary to perform the bonding under more severe conditions. However, even if it is a 1000 type board | plate material, when laser welding is performed under such severe conditions, it becomes a problem that a welding defect called an undercut and a blow hole generate | occur | produces in a weld bead.

Disclosure of Invention The present invention has been made to solve such a problem, and an object of the present invention is to provide a 1000-based aluminum alloy plate having a thickness applicable to a large-sized lithium ion battery container, excellent moldability, and excellent laser weldability. will be.

In order to achieve the object, the aluminum alloy sheet for battery cases excellent in moldability and weldability of the present invention contains Si: 0.01 to 0.4% by mass, Fe: 0.01 to 0.5% by mass, and Co: 0.003 to 0.5% by mass, and the remaining amount It is characterized by having the component composition which consists of a part Al and an unavoidable impurity, and metal structure whose number of 2nd phase particle | grains of 3 micrometers or more is less than 100 piece / mm <2>.

It is preferable to have a value of 30% or more of elongation.

Since the aluminum alloy plate of this invention has high thermal conductivity, is also excellent in moldability, and has the outstanding laser weldability, the container for secondary batteries excellent in the sealing performance can be manufactured at low cost.

1 is an Al-Co-Fe reaction diagram.
FIG. 2 is a state diagram of the Al-Co-Fe ternary system (liquid phase shaving).
3 is a conceptual diagram for explaining a method of measuring / evaluating the number of weld defects.

A secondary battery is manufactured by attaching and sealing a cover by welding or the like after placing the electrode body in a container. When such a secondary battery is used in a cellular phone or the like, when charging, the temperature inside the container may increase, and the pressure inside the container may increase. For this reason, when the intensity | strength of the material which comprises a container is low, there exists a problem that big expansion arises in the manufactured container. Therefore, when a 1000-series aluminum alloy plate is selected as a material to be used, it is necessary to design a container of a relatively thick container.

Moreover, since the press method is generally used as a method of constructing a container, it is required to have excellent press formability in the material itself.

In addition, since a welding method is used as a method of sealing and attaching the lid, excellent weldability is also demanded. In many cases, a laser welding method is used as a welding method for manufacturing a secondary battery container or the like.

By the way, regarding laser weldability, (1) stability of welding bead width, stability of penetration depth, and (2) suppression of welding defect generation, such as an undercut in a weld bead, a blow hole, are mentioned as a subject.

In general, when a 1000-based aluminum alloy sheet is used as the material of the container, it is found that the welding bead width is stabilized, and fewer welding defects such as undercuts and blow holes in the welding bead are reduced.

In addition, since the 1000-based aluminum alloy plate has good thermal conductivity, in order to perform pulse laser welding of a thick material, it is necessary to increase the energy per pulse or the like to perform bonding under more severe conditions.

By irradiation of such a pulsed laser, it is inferred that the surface temperature of the welding bead being joined reaches the high temperature of 2000 degreeC or more locally. Aluminum is a highly reflective material and reflects about 70% of the laser beam. Therefore, intermetallic compounds, such as Al ₃ Fe and Al-Fe-Si, which were originally present in the vicinity of the surface of the aluminum alloy plate, exhibit a color close to black, and thus are easier to absorb laser light than α-Al. It is reasonable to think that it melts by heating first. The irradiation time of one pulse of the pulse laser is a very short time of nanoseconds and femtoseconds. Therefore, when α-Al in the matrix is dissolved and phase transitions into the liquid phase, intermetallic compounds such as Al ₃ Fe and Al-Fe-Si exposed on the surface of the weld bead rapidly expand in volume by evaporation.

As the intermetallic compound evaporates locally in this manner, welding defects called undercuts and blow holes are generated in the weld bead, resulting in a decrease in the airtightness of the container. Therefore, the inventors of the present application found that the intermetallic compound produced when casting the one-slab of the 1000-based aluminum alloy sheet was the cause, based on the above-described undercut and blowhole generating mechanism, and found to be 0.003 as a composition. By containing 0.5 mass%-0.5 mass, it succeeded in remarkably reducing the number of welding defects of a welding bead, and arrived at this invention.

MEANS TO SOLVE THE PROBLEM The present inventors earnestly examined and obtained this invention in order to obtain the aluminum alloy plate which is excellent in press formability, and also excellent in laser weldability through irradiation of the number of undercuts and blowholes which generate | occur | produced in the weld part.

The contents will be described below.

First, the effect | action of each element contained in the aluminum alloy plate for secondary battery containers of this invention, appropriate content, etc. are demonstrated.

Fe : 0.01 to 0. 5 mass %

Since Fe is an element constituting Al ₃ Fe which is an intermetallic compound, in order to reduce welding defect, it is preferable to reduce the content as much as possible. However, when Fe content is less than 0.01 mass%, since high purity aluminum foil is used and a cost increase cannot be avoided, it is not preferable.

When the Fe content exceeds 0.5% by mass, the coarse intermetallic compound of Al ₃ Fe is crystallized at the time of ingot casting, the formability in the final plate is lowered, and these intermetallic compounds are added to the Al matrix at the time of laser welding. Since it is easy to evaporate compared with the number of welding defects, such as an undercut and a blowhole, and weldability falls, it is unpreferable.

Therefore, Fe content is taken as the range of 0.01-0.5 mass%. More preferable Fe content is the range of 0.01-0.4 mass%. More preferable Fe content is the range of 0.02-0.4 mass%.

Si : 0.01 to 0. 4 mass %

Si is an element that lowers the formability, and is an elemental Si that is easy to crystallize at grain boundaries and is an element that promotes crystallization of Al ₆ Fe, which becomes metastable. Therefore, in order to reduce welding defects, reducing the content as much as possible desirable. However, when Si content is less than 0.01 mass%, since high purity aluminum foil is used and a cost increase cannot be avoided, it is unpreferable.

When Si content exceeds 0.4 mass%, coarse intermetallic compound of Al ₆ Fe will crystallize at the time of ingot casting, single-crystal Si will crystallize easily at a grain boundary, and the moldability in a final board will fall, and these metals The liver compound is not preferable because it is easier to evaporate compared to the Al matrix during laser welding, and the weld defects such as undercuts and blow holes increase and the weldability decreases.

Therefore, Si content is taken as the range of 0.01-0.4 mass%. More preferable Si content is the range of 0.01-0.3 mass%. More preferable Si content is the range of 0.02-0.2 mass%.

Co : 0.003 to 0. 5 mass %

Co is an extremely important element in the liquid phase of the solidifying slab, because it produces very fine clusters of step Al ₉ Co ₂ . Within the scope of suitable initial concentration ratio of Co / Fe, the process of the Al ₉ Co ₂ cluster are all step Al ₃ Fe, first generation, it is considered to act as nuclei of step Al ₃ Fe. In addition, when the initial concentration ratio of Co / Fe is relatively large, in the liquid phase of the solidifying slab, step Al ₉ Co ₂ is crystallized using this cluster as a nucleus, and crystallization of step Al ₃ Fe is thermodynamically suppressed. As a result, Co has effects and (2) a step of refining the step Al ₃ Fe to increase the density of the crystallized site in the Co / of Fe but depending also the cooling rate at the time of the initial concentration ratio, and solidified, (1) a step Al ₃ Fe Al the crystallization of Fe ₃ there are two effects of the effects of thermodynamic suppressed. When Co content is less than 0.003 mass%, the above effects are not expressed. When Co content exceeds 0.5 mass%, since manufacturing cost simply increases, it is unpreferable. Therefore, Co content is taken as 0.003 to 0.5 mass%. More preferable Co content is 0.004 to 0.3 mass% of range. More preferable Co content is 0.005 to 0.1 mass%.

Initially, the inventors of the present invention found that Co, which is a transition element, has a higher boiling point than Al, and by containing Co in a 1000-based aluminum alloy, Fe, for example, a transition element in an intermetallic compound such as Al ₃ Fe, Al-Fe-Si, It was assumed that a new intermetallic compound substituted with Co was generated as metastable at the time of casting solidification. And it was inferred that the boiling point of this new intermetallic compound which remained to the last board was high, and it was hard to vaporize at the time of laser welding. However, the result of the intermetallic compound identification by X-ray diffraction in the final plate completely denied the above speculation.

Next, the mechanism which the present inventors think most likely at the present time is described.

First, consider the Al-Co-Fe reaction degree shown in FIG. In this scheme, the crystals which may be present in the liquid Al-Co-Fe alloy molten metal are shown to be Al ₃ Fe and Al ₉ Co ₂ , depending on the Co concentration and the Fe concentration. Of course, since the Al alloy composition of the present invention is a subprocess composition for both Co and Fe, α-Al is crystallized as an initial crystal in the initial stage of casting solidification.

The process temperature in the Al-Co based binary alloy system is 657 占 폚, and the process temperature in the Al-Fe based binary alloy system is 655 占 폚. Here, in order to simplify the description, the phase transformation of the Al-Co-Fe ternary alloy is considered without considering the influence of other elements such as Si.

The liquid surface of Al-Co-Fe ternary system is shown in FIG. Although accurate prediction is difficult, that is, if it is quasi-equilibrium, when the Al-Co-Fe alloy molten metal of composition Q cools and becomes lower than Al liquid surface, (alpha) -Al of the corresponding composition in Al solid-state surface will be crystallized, The composition of the side is changed so as to follow the arrow, for example, on the Al liquid phase with temperature drop, and intersects with the Al-Co process line.

That is, a process reaction such as Al (L) → Step Al + Al ₉ Co ₂ occurs to generate a process structure consisting of Step Al and Al ₉ Co ₂ . Due to this process reaction, latent heat of solidification is generated, but according to the phase rate, since the degree of freedom (F = C-P + 1) is C = 3 and P = 3 under atmospheric pressure (when the pressure is constant), F = 1. The temperature of the region is not constant but is variable in temperature. Until this process reaction is complete | finished, the composition of this area | region changes along a process line, and temperature falls gradually. Of course, in the actual solidification process, since it is non-equilibrium, it becomes supercooled, and the trace of liquid (composition and temperature) passes below the Al liquid surface (low temperature side) in the equilibrium diagram, and is lower than the process line (low temperature). Side), and a process reaction such as Al (L)-> Al + Al ₉ Co ₂ occurs.

It should be noted that, especially under the crystallization temperature of primary α-Al, the solubility of Co in the α-Al phase is smaller than that of Fe in the α-Al phase. That is, since the equilibrium distribution coefficient (k = Cs / C _L ) at the solid-liquid interface of the Al-Co-Fe alloy molten metal is smaller than the equilibrium distribution coefficient of Fe, the Co concentration in the liquid phase is uneven. It is estimated to proceed faster than Fe concentration. As a result, compared with the initial concentration ratio of Co / Fe in the liquid phase, it is considered that the Co / Fe concentration ratio in the liquid phase after primary α-Al is crystallized is increased.

Therefore, although the composition Q in FIG. 2 shows the case where the initial concentration ratio of Co / Fe is 1, even if the initial concentration ratio of Co / Fe is smaller than 1, for example, it is equal to 0.05, The Co / Fe concentration ratio in the liquid phase after α-Al is crystallized gradually increases, and the liquid phase (composition and temperature) reaches the lower side (low temperature side) of the process line [Al (L)-> Al + Al ₉ Co ₂ ]. . That is, even in the same supercooled state, the process Al ₉ Co ₂ is crystallized before the process Al ₃ Fe.

By the way, the process Al ₉ Co ₂ is considered to be a very fine cluster at the initial generation. When such fine process Al ₉ Co ₂ clusters are present in the cooling liquid phase, these clusters may become nuclei of the process Al ₃ Fe depending on the Co / Fe concentration ratio in the liquid phase. Therefore, the formation of a fine process Al ₉ Co ₂ cluster first in the supercooled state means the generation of homogeneous nuclei for the process Al ₉ Co ₂ and, in some cases, the generation of heterogeneous nuclei for the process Al ₃ Fe. . Of course, when the initial concentration ratio of Co / Fe is 1 as shown in Fig. 2, the concentration ratio of Co / Fe in the liquid phase is higher than 1, so that the crystallization of the step Al ₃ Fe is thermodynamically suppressed and the step Al generated in the liquid phase. _It is thought that a cluster of ₉ Co ₂ acts as a homogeneous nucleus. As a result, since the fine process Al ₉ Co ₂ cluster in the liquid phase is produced uniformly and with high density, the process Al ₃ Fe is crystallized using the cluster as a nucleus within the range of the initial concentration ratio of Co / Fe that is appropriate. The process Al ₃ Fe is refined. In other words, Co can be made into a fine Al ₃ Fe process.

This is a mechanism for inhibiting crystallization and refinement of the process Al ₃ Fe in the presence of Co. Further, the inventors of the present invention estimate that the process Al ₉ Co ₂ is much finer than the process Al ₃ Fe, is difficult to evaporate at the time of laser welding, and is difficult to cause welding defects. In the alloy composition range of the present invention, by containing 0.003 to 0.5% by mass of Co, it is possible to achieve crystallization suppression and miniaturization of step Al ₃ Fe, such as undercuts and blow holes in the welding beads of laser welding. Weld defects can be reduced.

In the metal structure Circle equivalent diameter  2 μm or more second phase Number of particles  Less than 100 / mm2

In order to reduce welding defects such as undercuts and blow holes in the welding beads of laser welding, it is necessary to set the number of second phase particles having a diameter of 3 µm or more in a circle structure in the metal structure to less than 100 / mm 2. If such a metal structure is present, the density of the presence of intermetallic compounds, such as Al ₃ Fe, which are relatively rough, will be reduced, and the welding defects such as undercuts and blow holes in the welding beads of laser welding can be reduced. .

In the alloy composition range of the present invention, by containing 0.003 to 0.5% by mass of Co, crystallization suppression and miniaturization of step Al ₃ Fe can be achieved, and the second phase having a circular equivalent diameter of 3 µm or more in the metal structure. The number of particles can be made less than 100 / mm 2.

Other Inevitable  impurities

Unavoidable impurities are inevitably mixed from the raw materials, recovery scrap, and the like, and their permissible contents are, for example, less than 0.50% by mass of Ni, Mo, and Zr, Cu, Mn, Mg, Zn, Ti, Less than 0.01% by mass of each of B, Ga, V, and Nb, Pb, Bi, Sn, Na, Ca, and Sr, respectively, is less than 0.005% by mass, and other than 0.02% by mass, respectively. Even if it contains, it does not interfere with the effect of this invention.

Cold rolling Annealing material : The value of elongation is 30% or more

However, when applying a 1000-series aluminum alloy plate to a large lithium ion battery container or the like, it is necessary that not only excellent laser weldability but also excellent moldability are required. The formability of the material can be seen by the value of the elongation at the time of tensile test.

The details are postponed by the description of the later examples, and as the 1000-based aluminum alloy plate of the present invention applied to a large-size lithium ion battery container or the like, it is suitable to have a characteristic that the value of the elongation is 30% or more.

Next, the method of manufacturing the above-mentioned aluminum alloy plate for secondary battery containers is briefly introduced.

Solvent, Solvent

When the raw material is added to the melting furnace and reaches a predetermined dissolution temperature, the flux is appropriately added and stirred, and if necessary, degassing in the furnace using a lance or the like is carried out, and then it is truly held and held from the surface of the molten metal. Remove the debris.

In this dissolving and solvent, since it is a predetermined alloy component, it is also important to add raw materials such as a master alloy again, but it is extremely important to take a sufficient time to cool down until the flux and the residue are separated from the aluminum alloy molten metal to the hot water surface. . It is preferable to take calm time 30 minutes or more normally.

In some cases, the aluminum alloy molten metal melted in the melting furnace may be cast after being once molten in the holding furnace, but may be cast directly from the melting furnace and cast. More preferred soothing time is 45 minutes or more.

As needed, you may let in-line degassing and a filter pass.

In-line degassing is a mainstream type of blowing inert gas or the like into a molten aluminum from a rotary rotor to diffuse hydrogen gas in the molten metal into bubbles of the inert gas to remove it.

When using nitrogen gas as an inert gas, it is important to manage dew point to -60 degrees C or less, for example. It is preferable to reduce the amount of hydrogen gas in the ingot to 0.20 cc / 100 g or less.

When the amount of hydrogen gas in the ingot is large, a procedure occurs in the final solidification part of the ingot. Therefore, the reduction ratio per pass in the hot rolling step is regulated to 7% or more, for example, to crush the procedure. There is.

In addition, although the hydrogen gas solid-dissolved in the ingot is dependent on the homogenization treatment condition before the hot rolling process, it may be precipitated during laser welding after forming the final plate, and a large number of blow holes may be generated in the beads. For this reason, the amount of hydrogen gas of the ingot is more preferably 0.15 cc / 100 g or less.

casting

Ingots are produced by semi-continuous casting (DC casting). In the case of normal semi-continuous casting, since the thickness of the ingot is generally about 400 to 600 mm, the solidification cooling rate at the center of the ingot is about 1 ° C / sec. For this reason, especially when semi-continuous casting of the aluminum alloy molten metal with high Fe and Mn content exists in the ingot center part, there exists a tendency for relatively coarse intermetallic compounds, such as Al-Fe-Si, to crystallize out from aluminum alloy molten metal.

The casting speed in semi-continuous casting depends on the width and thickness of the ingot, but is usually 50 to 70 mm / min in consideration of productivity. However, in the case of performing inline degassing, considering the actual residence time of the molten metal in the degassing tank, the flow rate of the aluminum molten metal (melt supply amount per unit time) is small depending on the degassing conditions such as the flow rate of the inert gas. The degassing efficiency in a collection tank improves, and it is possible to reduce the amount of hydrogen gas of an ingot. Although it depends also on the number of swelling of casting, etc., in order to reduce the amount of hydrogen gas of an ingot, it is preferable to restrict a casting speed to 30-50 mm / min. More preferred casting speed is 30 to 40 mm / min. Of course, if a casting speed is less than 30 mm / min, since productivity falls, it is unpreferable. Moreover, it is a matter of course that the slower the casting speed, the inclination of the sump (solid / liquid interface) in the ingot is gentle and the casting crack can be prevented.

Homogenization  Treatment: 420 to 620 ° C x 1 hour or more

The ingot obtained by casting by the semi-continuous casting method is homogenized.

A homogenization process is a process which hold | maintains an ingot at high temperature in order to make rolling easy, and eliminates the segregation of a casting and the residual stress in an ingot. In this invention, it is necessary to hold | maintain for 1 hour or more at holding temperature of 420-620 degreeC. In this case, it is also a process for making the matrix to solidify the transition element etc. which comprise the intermetallic compound determined at the time of casting to some extent. If the holding temperature is too low or the holding temperature is short, the solid solution of the transition element or the like does not proceed, the recrystallized grains become rough, and there is a fear that the external appearance surface after DI molding may not be finished cleanly. In addition, when the holding temperature is too high, it is caused by the amount of hydrogen in the ingot, but may cause expansion. More preferable homogenization treatment temperature is 420-600 degreeC.

Hot rolling process

The ingot held at a high temperature for a predetermined time is suspended by a crane as it is after the homogenization treatment, transported to a hot rolling mill, and is also hot rolled by a few rolling passes, although it is also based on a model of a hot rolling mill, and has a predetermined thickness, for example, 4 It is wound up to a roll as a hot rolled sheet of about 8 mm.

Cold rolling process

The roll wound up the hot rolled sheet is passed through a cold rolling machine, usually cold rolling of several passes. At this time, since work hardening occurs by plastic deformation introduced by cold rolling, an intermediate annealing treatment is performed as necessary. Since intermediate | middle annealing is also a softening process normally, you may insert a cold rolling roll into a batch furnace although it is a material, and you may hold | maintain for 1 hour or more at the temperature of 300-450 degreeC. If the holding temperature is lower than 300 ° C., softening is not promoted. If the holding temperature is higher than 450 ° C., the treatment cost is increased. In addition, intermediate | middle annealing is hold | maintained within 15 second by the continuous annealing furnace at the temperature of 400 degreeC-550 degreeC, for example, and can also serve as a solution treatment if it cools rapidly after that. If the holding temperature is lower than 400 ° C, softening is not promoted. If the holding temperature is higher than 550 ° C, there is a fear that expansion occurs.

final Annealing

In the present invention, the final annealing performed after the final cold rolling may be, for example, a batch treatment held at a temperature of 300 to 500 ° C. for 1 hour or more by an annealing furnace, but is 400, for example, by a continuous annealing furnace. If it is hold | maintained within 15 second at the temperature of C-550 degreeC, and rapidly cools after that, it can also serve as a solution treatment.

In the end, in the present invention, the final annealing is not necessarily required, but considering the moldability in ordinary DI molding, it is preferable that the final plate has a certain degree of stretching. In consideration of the moldability in the mold forming step, it is preferable to use an annealing material or a solution treatment material.

When the mechanical strength is higher than the formability, the material is provided in a cold rolled state.

final Cold Rolling Rate

It is preferable that the final cold rolling rate in the case of performing final annealing is 50 to 90% of range. When the final cold rolling rate is within this range, the average recrystallized grain in the final plate after annealing can be set to 20 to 100 µm, the value of the elongation can be made 30% or more, and the appearance surface after molding can be finished cleanly. More preferred final cold rolling rate is in the range of 60 to 90%.

On the other hand, it is preferable to make the final cold rolling rate into the range of 5 to 40% when making into a material of a cold rolling state, without performing final annealing. When the ironing process is increased during DI molding, it is necessary to provide a final plate slightly harder than the annealing material. More preferred final cold rolling rate is in the range of 10 to 30%.

By passing through the usual steps as described above, an aluminum alloy plate for a secondary battery container can be obtained.

Example

Making of the final edition

Predetermined various ingots were weighed and blended, and 6 kg (8 total test materials) ingots were inserted and loaded into the # 20 crucible to which the release material was applied. These crucibles were inserted into an electric furnace, melted at 780 ° C. to remove debris, and then the molten metal was held at 760 ° C., and then each 6 g of the degreasing flux was surrounded by aluminum foil and pressed into a phosphorizer. Added.

Subsequently, a lance was inserted into the molten metal, and N ₂ gas was blown at a flow rate of 1.0 L / min for 10 minutes to perform degassing treatment. Subsequently, the sample was cooled for 30 minutes, the residues floating on the surface of the molten metal were removed by a stirring rod, and a disk sample was collected in a component analysis mold with a spoon.

Subsequently, the crucible was taken out from the inside of an electric furnace sequentially using the jig, and the aluminum molten metal was cast into the preheated metal mold (250 mm x 200 mm x 30 mm). The disk sample of each test material was analyzed for composition by emission spectroscopy. The results are shown in Table 1.

After cutting the hot water, the ingot was faced on both sides by 2 mm to have a thickness of 26 mm.

The ingot was inserted into an electric furnace, heated to 430 ° C at a temperature increase rate of 100 ° C / hr, subjected to a homogenization treatment of 430 ° C for 1 hour, and then hot rolling until it became 6 mm thick with a hot rolling mill. Was carried out.

A cold rolled annealing plate cold-rolled without performing intermediate annealing to the said hot rolled sheet, and obtained the cold rolled sheet of 1 mm. The final cold rolling rate in this case was 83%. In the final annealing, the cold rolled sheet was inserted into the annealer, and after the annealing treatment at 390 ° C for 1 hour, the cold rolled sheet was taken out from the annealer and air cooled.

Next, the formability and laser weldability were evaluated about the final board (each test material) obtained in this way.

Evaluation of formability

The moldability evaluation of the obtained final board was performed by the elongation (%) of a tensile test.

Specifically, the JIS No. 5 test piece was sampled so that the tensile direction was parallel to the rolling direction, and a tensile test was performed in accordance with JIS Z2241 to obtain a tensile strength, 0.2% yield strength, and elongation at break (break elongation).

In the final plate annealed after cold rolling, the test material whose elongation value was 30% or more was made into good moldability ((circle)), and the test material which was less than 30% was made into moldability defect (x). The evaluation results are shown in Table 2.

Laser welding condition

About the obtained final board, pulse laser irradiation was performed and laser weldability was evaluated. Using the YAG laser welding machine JK701 made by LUMONICS Corporation, the above disclosure was made under the conditions of frequency 37.5 kHz, welding speed 400 mm / min, energy 9.0J per pulse, pulse width 1.5 msec, and shield gas (nitrogen) flow rate 1.5 (L / min). Two sheets of ash were faced to each other without gaps, and pulse laser welding having a total length of 100 mm was performed along the portion.

Evaluation of Laser Weldability

Measuring / evaluating the number of welding defects

Next, as an evaluation of laser weldability, the number of welding defects generated in the weld portion was measured. First, the area | region of 80 mm length except the 20 mm length welding line of a welding start part was defined as the measurement area | region among the said 100 mm length welding wire. The part near the welding start is unstable and therefore excluded.

And as shown in FIG. 3, the X-ray CT image in the plate thickness cross section parallel to a weld line was obtained by X-ray CT inspection of the weld bead cross section formed along the 80 mm-long weld line. Moreover, based on this X-ray CT image, black defect part was detected by image editing software, and the area of black part defect was computed by image analysis software. The particle number corresponding to each circular equivalent diameter was computed from this black part defect area.

In this specification, the test material whose number of black part defects with a circular equivalent diameter 0.4mm or more was less than 10 was made into the welding defect number evaluation good ((circle)), and the number of the black part defects with a circular equivalent diameter 0.4mm or more was 10 or more. The ash was made into defects of weld defect evaluation (x). The evaluation results are shown in Table 2.

Evaluation of each disclosure

The specimens of Examples 1 to 7 are within the range of the alloy composition of the present invention, and satisfactorily satisfies less than ten of the weld defect number criteria, and thus, excellent laser weldability. Moreover, since the value of the elongation in a tensile test is also 30% or more, it is also excellent in moldability. The test material of the comparative example 1 has extremely low Co content of 0.0001 mass%, the number of welding defects is 12, and laser weldability is inferior. The test material of Comparative Example 2 had a low Co content of 0.0005% by mass, a number of welding defects of 12, and inferior laser weldability. The test material of the comparative example 3 has a low Co content of 0.0008 mass%, has 11 welding defects, and is inferior to laser weldability. The test material of Comparative Example 4 had a high Fe content of 0.70 mass%, a number of welding defects of 24, and inferior laser weldability. The test material of Comparative Example 5 had a high Si content of 0.42% by mass, 17 defects in welding, and inferior laser weldability. The test material of Comparative Example 6 has a high Si content of 0.65 mass%, has 10 weld defects, and is inferior in laser weldability.

The longitudinal section (cross section perpendicular to the LT direction) parallel to the rolling direction of the obtained final plate was cut out, embedded in a thermoplastic resin, mirror polished, and etched with an aqueous hydrofluoric acid solution to observe the metal structure. Photomicrograph of a micro metal structure was carried out by an optical microscope (area per field of view; 0.0334 mm <2>, 15 field of view of each sample), the image analysis of a photograph is carried out, and the 2nd phase particle of 3 micrometers or more of circular equivalent diameter per unit area (1 mm <2>) The number was measured. In the present specification, in the case of less than the number of the second phase particles having a diameter of 3 µm or more in a circle equivalent shape less than 100 / mm 2, the evaluation is satisfactory (○), and in the case of the number of the second phase particles having a diameter of 3 µm or more in a shape of 100 µm or more / mm 2 or more. And evaluation were made into defect (x).

Table 3 shows the image analysis results.

As a result of image analysis

As a result of image analysis of the second phase particles in the metal structure of each specimen, the number of the second phase particles having a diameter of 3 µm or more in a circle equivalent to 3 µm or more in Examples 1 to 7 was less than 100 particles / mm 2, and relatively rough Al ₃ Fe and the like. It was thought that the presence density of an intermetallic compound was low, and evaluation was favorable ((circle)). On the other hand, with respect to Comparative Examples 1 to 6, it is thought that the number of second phase particles having a diameter of 3 µm or more in a circular equivalent is 100 particles / mm 2 or more, and that the abundance density of intermetallic compounds such as relatively rough Al ₃ Fe is high. (×). The evaluation result of the image analysis of the 2nd phase particle in these metal structures is consistent with the evaluation result of the laser weldability mentioned above.

According to the present invention, there is provided a 1000-based aluminum alloy plate having a thickness applicable to a large-sized lithium ion battery container, excellent moldability and excellent laser weldability.

Claims (2)

Si: 0.01 to 0.4% by mass, Fe: 0.01 to 0.5% by mass, Co: 0.003 to 0.5% by mass, which is composed of the remainder part Al and unavoidable impurities, and the number of second phase particles having a circular equivalent diameter of 3 µm or more is 100 The aluminum alloy plate for battery cases excellent in moldability and weldability which has a metal structure of less than piece / mm <2>. The value of the elongation is 30% or more, The aluminum alloy plate for battery cases excellent in moldability and weldability of Claim 1 characterized by the above-mentioned.

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