TW201303036A - Aluminum alloy plate with excellent formability and weldability for cell case - Google Patents

Abstract

There is provided a 1000-series aluminum alloy plate having high strength suitable for use in a large lithium-ion cell container and demonstrating excellent formability and laser weldability. The aluminum alloy plate contains 0.01-0.4 mass% of Si, 0.01-0.5 mass% of Fe, and 0.003-0.5 mass% of Co, the remainder consisting of Al and unavoidable impurities, and has a metal structure in which the number of second phase particles having a circular equivalent diameter of 3 [mu]m or greater is less than 100 particles per mm2. A cold-rolled annealed plate of the aluminum alloy exhibits an elongation value of 30% or greater.

Description

Aluminum alloy plate for battery casing with excellent formability and weldability Technical field

The present invention relates to a high-strength aluminum alloy sheet having excellent formability and laser fusion properties for use in a container for a lithium ion battery.

Background technique

Since the Al-Mn series 3000 series alloy is excellent in strength, moldability, and laser welding property, it is used as a material for manufacturing a secondary battery container such as a lithium ion battery. After forming a desired shape, it is sealed by a laser fusion package and used as a container for a secondary battery. At present, an aluminum alloy sheet for a secondary battery container in which the 3000 series and the existing 3000 series alloy are formed together to further improve strength and formability has been developed.

For example, the patent document describes an aluminum alloy plate for a rectangular cross-section battery container, which is characterized by containing Si: 0.10 to 0.60% by mass, Fe: 0.20 to 0.60% by mass, Cu: 0.10 to 0.70% by mass, and Mn: 0.60 to 1.50. Mass %, Mg: 0.20 to 1.20% by mass, Zr: more than 0.12 and less than 0.20% by mass, Ti: 0.05 to 0.25 mass%, and B: 0.0010 to 0.02 mass%, and the residual portion is composed of Al and unavoidable impurities And in the cylindrical container deep drawing method, the 45° ear formation rate in the relative rolling direction is 4 to 7%.

On the other hand, in the recent development of an angular lithium ion battery case which has sufficient strength, tensile-traction workability, creep characteristics, excellent laser fusion properties, and an increase in the thickness of the outer casing during charge and discharge cycles. Aluminum alloy plate as a battery case. Patent Document 2 describes an aluminum for a prismatic battery container The alloy sheet has a composition containing Mn: 0.8% by mass or more and 1.8% by mass or less, Mg: more than 0.6% by mass and 1.2% by mass or less, and Cu: more than 0.5% by mass and 1.5% by mass or less, as impurities. Fe is limited to 0.5% by mass or less, Si is limited to 0.3% by mass or less, and the residual portion is composed of Al and unavoidable impurities, and the orientation density C of {001}<100> orientation and {123}<634> The ratio (C/S) of the azimuth density S of the orientation is 0.65 or more and 1.5 or less, and the tensile strength after the final cold rolling is 250 MPa or more and 330 MPa or less, and the elongation is 1% or more.

However, in an aluminum alloy sheet in which the composition of the 3000 series alloy is improved, it is known that abnormal solder beads are sometimes generated and there is a problem of laser fusion.

Therefore, an aluminum alloy plate for a secondary battery container in which the 1000 series is excellent in laser fusion properties has been developed. Patent Document 3 describes an aluminum alloy plate for pulsed laser welding and a battery container which can be welded to an A1000-based aluminum material to prevent occurrence of an abnormal portion and uniformly form a good welded portion. Therefore, conventionally, Ti added to the coarsening of the crystal grains during the casting process has an adverse effect on the welded portion, and in order to prevent the formation of an abnormal portion when the A1000-based aluminum is welded by pulsed laser welding, it is necessary to use pure aluminum. The Ti content contained may be limited to less than 0.01% by mass.

Prior technical literature Patent literature

Patent Document 1: Japanese Patent No. 4001007

Patent Document 2: Japanese Laid-Open Patent Publication No. 2010-126804

Patent Document 3: Japanese Laid-Open Patent Publication No. 2009-127075

Summary of invention

Since the 1000 series has a high elongation value and excellent formability, and the number of abnormal beads at the time of laser welding is small, the weldability is surely stabilized. Therefore, it is expected that in the progress of the enlargement of the lithium ion battery, high strength characteristics are also required, and it is also considered to use the relatively thick 1000 series aluminum plate as it is.

Further, in recent years, containers for lithium ion batteries made of aluminum alloy and their covers are generally joined by pulsed laser welding. As mentioned above, the thicker 1000 series of sheets have excellent formability, and the number of abnormal beads is small, but they have good thermal conductivity, and for pulsed laser welding, it is necessary to increase the energy of each pulse, etc. Bonding under severe conditions. However, even in the 1000 series of sheets, when laser welding is performed under such severe conditions, there is a problem that the welded beads are so-called over-melting and low-hole welding defects.

The present invention has been made in order to solve such problems, and an object of the invention is to provide a 1000 series aluminum alloy sheet having a thickness suitable for a large-sized lithium ion battery container and having excellent formability and excellent laser welding properties.

In order to achieve the object, the aluminum alloy sheet for a battery can having excellent formability and weldability of the present invention is characterized in that it contains Si: 0.01 to 0.4% by mass, Fe: 0.01 to 0.5% by mass, and Co: 0.003~. 0.5% by mass, and the residual portion is composed of a component composed of Al and an unavoidable impurity; and a metal structure having a second phase particle number of 3 μm or more and less than 100 particles/mm ² .

It is preferred to have an elongation value of 30% or more.

The aluminum alloy sheet of the present invention has high thermal conductivity and excellent formability, and has excellent laser fusion properties, so that a container for a secondary battery having excellent sealing performance can be manufactured at low cost.

Simple illustration

Figure 1 is an Al-Co-Fe reaction diagram.

Figure 2 is a state diagram of the Al-Co-Fe ternary system (liquid phase diagram).

Fig. 3 is a conceptual diagram illustrating a method of measuring/evaluating the number of weld defects.

The best form for implementing the invention

The secondary battery is manufactured by capping the electrode body after it is placed in a container, and sealing by welding or the like. When such a secondary battery is used in a mobile phone or the like, the temperature inside the container rises during charging, and the pressure inside the container increases. Therefore, when the strength of the material constituting the container is low, there is a problem that large expansion occurs in the container to be produced. Therefore, when selecting the 1000 series aluminum alloy plate as the material to be used, it is necessary to design a relatively thick container.

Moreover, since the press method is generally used as a method of constituting a container, the material itself used needs to have excellent press formability.

Further, since the welding method is used as a method of capping the sealing, it is also required to have excellent welding properties. Further, there are many cases in which the laser welding method is used as a welding method for manufacturing a container for a secondary battery.

Further, regarding the laser welding property, (1) stability of the width of the welded bead and stability of the penetration depth, and (2) suppression of fusion defects such as occurrence of over-melting, pores, and the like in the welded bead are Question.

It is generally understood that the 1000 series aluminum alloy plate is used as the material of the container. When the material is mixed, the width of the welded bead is stable, and the welding defects in the welded bead are too low, and the welding holes and the like have few welding defects.

Further, since the aluminum alloy sheets of the 1000 series have good thermal conductivity, they are thick materials for pulsed laser welding, and it is necessary to increase the energy of each pulse and the like, and to perform bonding under more severe conditions.

By irradiating such a pulsed laser, it is presumed that the surface temperature of the welded bead in the joint locally reaches a high temperature of 2000 ° C or higher. Aluminum is a highly reflective material and reflects about 70% of the laser beam. Therefore, the intermetallic compound such as Al ₃ Fe, Al-Fe-Si, etc., which is present near the surface of the aluminum alloy plate, exhibits a color close to black, so that it is easy to absorb the laser light than α-Al, and it is appropriate to heat and melt first. of. The irradiation time of the pulse of the pulsed laser is a very short time of so-called nanoseconds and femtoseconds. Therefore, when the α-Al of the matrix is melted and the phase is transferred to the liquid phase, the intermetallic compound such as Al ₃ Fe or Al-Fe-Si which exposes the surface of the welded bead is rapidly expanded by evaporation.

Since the intermetallic compound evaporates in such a manner, a fusion defect of the so-called over-melting and sag is generated in the welded bead, and the airtightness of the container is lowered. Therefore, the inventors of the present application have conducted a keen review based on the above-described over-melting and sag formation mechanism, and as a result, ascertained that the reason is the intermetallic compound formed when casting the raw material of the 1000 series aluminum alloy sheet. The composition of 0.00 to 0.5% by mass of Co is used as a composition, and the number of weld defects of the welded bead is remarkably reduced, and the invention of the present application is completed.

The inventors of the present invention have repeatedly reviewed the aluminum alloy sheet which has excellent press formability and which has excellent laser fusion properties through the investigation of the over-melting and the number of pores generated in the welded portion, and has completed the present invention.

The contents are explained below.

First, the action of each element contained in the aluminum alloy plate for a container for a secondary battery of the present invention, an appropriate content, and the like will be described.

Fe: 0.01 to 0.5% by mass

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

When the Fe content is more than 0.5% by mass, the coarse intermetallic compound of Al ₃ Fe crystallizes at the time of casting the ingot, and the formability in the final sheet is lowered, and the intermetallic compounds are easily evaporated than the Al matrix at the time of laser welding, and The number of fusion defects such as over-melting, stomata, and the like is increased to lower the weldability, which is not preferable.

Therefore, the Fe content is in the range of 0.01 to 0.5% by mass. A preferred Fe content is in the range of 0.01 to 0.4% by mass. A more desirable Fe content is in the range of 0.02 to 0.4% by mass.

Si: 0.01 to 0.4% by mass

The Si-based element which lowers the moldability, and the monomer Si are easily crystallized at the grain boundary, and is also an element which promotes the crystal of Al ₆ Fe in the quasi-stationary phase. Therefore, in order to reduce the fusion defect, it is preferable to reduce the content as much as possible. However, when the Si content is less than 0.01% by mass, a high-purity aluminum substrate is used, and an increase in cost cannot be avoided, which is not preferable.

When the Si content is more than 0.4% by mass, the coarse intermetallic compound of Al ₆ Fe crystallizes at the time of casting the ingot, the monomer Si easily precipitates at the grain boundary, and the formability in the final sheet is lowered, and the intermetallic compounds are in the thunder. When the shot is welded, it is more likely to evaporate than the Al matrix, and the number of fusion defects such as over-melting and stomping increases, and the weldability is lowered, which is not preferable.

Therefore, the Si content is in the range of 0.01 to 0.4% by mass. A preferred Si content is in the range of 0.01 to 0.3% by mass. A more desirable Si content is in the range of 0.02 to 0.2% by mass.

Co: 0.003 to 0.5% by mass

Co is a very important element in the formation of very fine eutectic Al ₉ Co ₂ clusters in the solidified liquid phase of solidification. The eutectic Al ₉ Co ₂ cluster is formed earlier than the eutectic Al ₃ Fe in a range of an appropriate initial concentration ratio of Co/Fe, and is considered to have a function as a nucleus of eutectic Al ₃ Fe. Further, when the initial concentration of Co/Fe is relatively large, the eutectic Al ₉ Co ₂ crystallizes in the cluster phase in the solidified liquid phase, and thermodynamically suppresses the crystallization of the eutectic Al ₃ Fe. Thus, Co is also based on Co / Fe initial concentration ratio and cooling rate during the solidification, and having (1) to increase the density of the eutectic Al ₃ Fe fine crystal side of the Al ₃ Fe of the eutectic effect, and (2) Two effects of thermodynamically suppressing the effect of crystallization of eutectic Al ₃ Fe.

When the Co content is less than 0.003 mass%, the effects as described above are not found. When the Co content is more than 0.5% by mass, only the manufacturing cost is increased, which is not preferable. The Co content is in the range of 0.003 to 0.5% by mass. A preferred Co content is in the range of 0.004 to 0.3% by mass. More preferably, the Co content is in the range of 0.005 to 0.1% by mass.

Originally, the inventors of the present invention assumed that the boiling point of the transition element Co is not higher than Al, and that the 1000 series aluminum alloy plate contains Co. For example, the transition element Fe in the intermetallic compound such as Al ₃ Fe or Al-Fe-Si is replaced with The new intermetallic compound of Co forms a quasi-stable phase during casting solidification. Further, it is presumed that the new intermetallic compound which may not remain in the final plate has a high boiling point and is not easily vaporized when the laser is welded. However, the result of identifying the intermetallic compound by X-ray diffraction in the final plate completely negates the above speculation.

Next, the inventor of the present invention explained the consideration of the institution with the highest possibility. First, consider the Al-Co-Fe reaction diagram shown in Fig. 1. In the reaction diagram, the crystals in the Al-Co-Fe alloy melt which can be present in the liquid phase are also Al ₃ Fe and Al ₉ Co ₂ depending on the Co concentration and the Fe concentration. Of course, in the case of both Co and Fe, the Al alloy composition of the invention of the present application is a hypoeutectic composition, and therefore, α-Al crystallizes as a primary crystal at the initial stage of casting solidification.

Further, the eutectic temperature in the Al-Co binary alloy system was 657 ° C, and the eutectic temperature in the Al-Fe binary alloy system was 655 ° C. Here, in order to simplify the description, the phase change of the Al-Co-Fe ternary alloy was investigated without considering the influence of other elements such as Si. The liquid phase of the Al-Co-Fe ternary system is shown in Fig. 2. Correct prediction is difficult, but in short, if it is quasi-equilibrium, when the Al-Co-Fe alloy melt composed of Q is cooled to a temperature lower than the liquid surface of Al, the corresponding composition α in the solid surface of Al - Al crystallizes, and the composition on the liquid phase side changes with temperature in the manner of, for example, an arrow on the liquid surface of Al, and intersects the Al-Co eutectic line.

That is, a eutectic reaction such as Al(L)→eutectic Al+Al ₉ Co ₂ occurs to form a eutectic structure composed of eutectic Al and Al ₉ Co ₂ . By the eutectic reaction, latent heat of solidification is generated, but according to the phase law at atmospheric pressure (when the pressure is constant), the degree of freedom (F=C-P+1) is C=3, P=3, so F=1, The composition of the region changes along the eutectic line and the temperature slowly decreases. Of course, in the actual solidification process, it is too cold because it is non-equilibrium, and the trajectory of the liquid phase (composition, temperature) passes through the lower side (low temperature side) of the Al liquid phase in the equilibrium state diagram, and further reaches the lower side of the eutectic line. (low temperature side), and a eutectic reaction such as Al(L)→eutectic Al+Al ₉ Co ₂ occurs.

It should be noted that, particularly below the crystallization temperature value of the primary crystal α-Al, the Co-solidification limit ratio to the α-Al phase is smaller than the Fe solid-solution limit to the α-Al phase. That is, the equilibrium distribution coefficient of Co in the solid-liquid interface of the Al-Co-Fe alloy melt (k=Cs/C _L ) is smaller than the equilibrium distribution coefficient of Fe, and therefore it is estimated that Co is concentrated in the liquid phase even in the case of non-equilibrium. It proceeds faster than Fe concentration. As a result, it is considered that the Co/Fe concentration ratio in the liquid phase after the primary crystal α-Al crystallizes becomes higher than the initial concentration ratio of Co/Fe in the liquid phase.

Therefore, in the composition diagram of Fig. 2, the initial concentration ratio of Co/Fe is 1, but the initial concentration ratio of Co/Fe is smaller than 1, for example, 0.05, primary crystal α-Al. The Co/Fe concentration ratio in the liquid phase after crystallization is also gradually increased, and the liquid phase (composition, temperature) reaches the eutectic line (Al(L)→eutectic Al+Al ₉ Co ₂ ) Side (low temperature side). That is, even in the same supercooled state, the eutectic Al+Al ₉ Co ₂ crystallizes earlier than the eutectic Al ₃ Fe.

Further, it is considered that the eutectic Al+Al ₉ Co ₂ is a very fine cluster at the initial stage of its formation. When such a cluster of fine eutectic Al+Al ₉ Co ₂ is present in the liquid phase in cooling, the clusters can form a nucleus of eutectic Al ₃ Fe depending on the Co/Fe concentration ratio in the liquid phase. Therefore, the cluster of fine eutectic Al+Al ₉ Co ₂ in the supercooled state indicates that a homogeneous nucleus is formed with respect to the eutectic Al+Al ₉ Co ₂ , and sometimes it also indicates that no eutectic Al ₃ Fe is generated. Homogeneous core. Of course, as shown in Fig. 2, when the initial concentration ratio of Co/Fe is 1, the Co/Fe concentration ratio in the liquid phase is higher than 1, considering that the crystallization of the eutectic Al ₃ Fe is thermodynamically suppressed, and in the liquid The cluster of eutectic Al+Al ₉ Co ₂ generated in the phase functions as a homogeneous nucleus. In short, the clusters of fine eutectic Al+Al ₉ Co _{2 in} the liquid phase are uniformly and densely formed. Therefore, the eutectic Al ₃ Fe is crystallized by the cluster in the range of the appropriate Co/Fe initial concentration ratio. As a result, the eutectic Al ₃ Fe is refined. In other words, Co can be a fine agent for Fe.

The above is a mechanism for suppressing and miniaturizing the crystallization of the eutectic Al ₃ Fe in the presence of Co. Further, the inventors of the present application presume that the eutectic Al+Al ₉ Co ₂ is much finer than the eutectic Al ₃ Fe, and is less likely to evaporate when the laser is welded, and is less likely to be a cause of fusion defects. In the alloy composition range of the present application, by containing 0.003 to 0.5% by mass of Co, crystallization inhibition and miniaturization of the eutectic Al ₃ Fe can be achieved, and the over-melting in the fusion-welded bead of the laser welding can be reduced. Welding defects such as traps, pores, etc.

The number of the second phase particles having a circle diameter of 3 μm or more in the metal structure is less than 100/mm ²

In order to reduce welding defects such as over-melting and sag in the welded bead of the laser welding, it is necessary that the number of the second phase particles having a circle diameter of 3 μm or more in the metal structure is less than 100/mm ² . If such a metal structure is present, the presence density of the relatively coarse intermetallic compound such as Al ₃ Fe becomes low, and the fusion defects of the over-melting, the stomata, etc. in the welded bead of the laser fusion can be reduced. .

In the alloy composition range of the invention of the present application, by containing 0.003 to 0.5% by mass of Co, crystallization of the eutectic Al ₃ Fe can be suppressed and refined, and the equivalent diameter of the metal structure can be 3 μm or more. The number of 2-phase particles is less than 100/mm ² .

Other inevitable impurities

Inevitable impure matter is inevitable from raw material substrate, recycled waste, etc. In addition, it is allowed to be mixed, and for example, Ni, Mo, and Zr are each less than 0.50% by mass, and Cu, Mn, Mg, Zn, Ti, B, Ga, V, and Nb are each less than 0.01% by mass, and as far as Pb In addition, Bi, Sn, Na, Ca, and Sr are each less than 0.005% by mass, and each of them is less than 0.02% by mass, and even if the external element is contained within the range, the effect of the present invention is not impaired.

Cold rolled annealed material: elongation value is 30% or more

Moreover, when a 1000 series aluminum alloy plate is used for a large-sized lithium ion battery or the like, it is required to have not only excellent laser fusion properties but also excellent moldability. The formability of the material can be known from the elongation value at the time of the tensile test.

In the description of the examples to be described later, the 1000 series aluminum alloy sheets of the present invention used for a large-sized lithium ion battery or the like have characteristics in which the elongation value is 30% or more.

Next, a method of manufacturing the aluminum alloy sheet for a secondary battery container as described above will be briefly described.

Melting, melting

After the raw material is put into the melting furnace and the predetermined melting temperature is reached, the flux is appropriately supplied and stirred, and if necessary, the inside of the furnace is degassed using a spray gun or the like, and then the mixture is kept calm and the dross is separated from the surface of the melt.

In the melting and melting, it is important to re-inject a raw material such as a master alloy in order to form a predetermined alloy component, but the sedation time is sufficiently maintained until the flux and the dross are floated and separated from the aluminum alloy melt. Very important. Usually the sedation time is best kept for more than 30 minutes.

The melted aluminum alloy melt in the melting furnace is sometimes cast from one end of the melt to the holding furnace. Sometimes moved directly from the melting furnace The melt is taken out and cast. More preferably, the sedation time is 45 minutes or more.

It can also be passed through a series of degassing and filters as needed.

In the mainstream form of the tandem deaeration, an inert gas or the like is blown into the aluminum melt by the rotary rotor, and the hydrogen in the melt is diffused into the bubble of the inert gas to be removed. When nitrogen is used as the inert gas, it is important to manage the dew point to, for example, -60 ° C or lower. The amount of hydrogen in the ingot should be reduced to less than 0.20 cc / 100 g.

When the amount of hydrogen in the ingot is large, pores are generated in the final solidified portion of the ingot. Therefore, it is necessary to limit the reduction ratio to, for example, 7% or more in the hot rolling program to crush the pores.

Moreover, the hydrogen which is supersaturated and solid-dissolved in the ingot sometimes precipitates in the laser welding after the formation of the final sheet according to the homogenization treatment conditions before the hot rolling process, and a large number of pores are generated in the bead. Therefore, the amount of hydrogen of the better ingot is 0.15 cc/100 g or less.

Casting

The ingot is manufactured by semi-continuous casting (DC casting). In the case of usual semi-continuous casting, the thickness of the ingot is generally about 400 to 600 mm, so the solidification cooling rate in the central portion of the ingot is about 1 ° C / sec. Therefore, in particular, in the semi-continuous casting of an aluminum alloy melt having a high Mn content, there is a tendency that a relatively coarse intermetallic compound such as Al-Fe-Si is crystallized from the aluminum alloy melt at the center portion of the ingot.

The casting speed in consideration of semi-continuous casting is also determined according to the width and thickness of the ingot, but it is usually 50 to 70 mm/min in consideration of productivity. However, in the case of tandem degassing, considering the residence time of the substantial melt in the degassing tank, it is also determined by the degassing conditions such as the flow rate of the inert gas. The smaller the flow rate of the melt (the amount of molten liquid supplied per unit time), the higher the degassing efficiency in the tank, and the smaller the amount of hydrogen in the ingot. Although depending on the number of castings cast, in order to reduce the amount of hydrogen in the ingot, the casting speed should be limited to 30 to 50 mm/min. A better casting speed is 30 to 40 mm/min. Of course, when the casting speed is less than 30 mm/min, it is not preferable because the productivity is lowered. Further, in terms of a slow casting speed, the inclination of the pool of the ingot (the interface of the solid phase/liquid phase) becomes gentle, and of course, the casting crack can be prevented.

Homogenization treatment: 420~620°×1 hour or more

The ingot obtained by the semi-continuous casting method was subjected to homogenization treatment.

The homogenization treatment is a process in which the ingot is kept at a high temperature by easy rolling, and the residual stress inside the ingot is eliminated by casting segregation. In the present invention, it is necessary to maintain the temperature at 420 to 620 ° C for 1 hour or longer. In this case, it is also a treatment for solidifying a transition element such as an intermetallic compound which crystallizes during casting to a certain extent in the matrix. When the holding temperature is too low or the temperature is kept short, the solid solution of the above-mentioned transition element or the like does not proceed, and the recrystallized grain becomes thick, and the surface of the appearance after DI molding cannot be beautifully finished. Further, when the temperature is kept too high, depending on the amount of hydrogen in the ingot, there is a possibility of swelling. A better homogenization treatment temperature is 420 to 600 °C.

Hot rolling procedure

The ingot which is kept at a high temperature for a predetermined period of time is hoisted by a hanger after the homogenization treatment, and is taken to a hot rolling mill, and depending on the type of the hot rolling mill, it is usually hot rolled by rolling several times. A predetermined thickness, for example, a hot rolled sheet of about 4 to 8 mm is taken up and wound into a roll.

Cold rolling procedure

The coil of the coiled hot rolled sheet is passed to a cold rolling mill, and usually subjected to cold rolling several times. At this time, since the work hardening is caused by the plastic strain introduced by the cold rolling, the intermediate annealing treatment is performed as needed. Usually, the intermediate annealing is also a softening treatment, so that the cold rolled coil can also be inserted into the batch furnace according to the material, and maintained at a temperature of 300 to 450 ° C for more than 1 hour. When the temperature is kept lower than 300 ° C, softening cannot be promoted, and when the temperature is maintained above 450 ° C, the temperature cost is increased. Further, if the intermediate annealing is maintained in a continuous annealing furnace at a temperature of, for example, 400 to 550 ° C for 15 seconds or less, and then rapidly cooled, it can also serve as a melt treatment. When the temperature is kept lower than 400 ° C, the softening cannot be promoted, and when the temperature is maintained above 550 ° C, there is a possibility of swelling.

Final annealing

In the present invention, the final annealing after the final cold rolling may be, for example, a batch treatment in which the annealing furnace is maintained at a temperature of 300 to 500 ° C for 1 hour or more, but if it is subjected to a continuous annealing furnace, for example, at a temperature of 400 to 550 ° C. Keep it within 15 seconds, then cool it quickly, or double it as a melt treatment.

In summary, the final annealing is not necessarily required in the present invention, but in consideration of the moldability in the usual DI forming, the final sheet preferably has a certain degree of elongation. When the moldability in the mold forming process is also considered, it is preferable to form an annealed material or a melted processed material.

When the mechanical strength is prioritized over the formability, it is supplied as a cold-rolled original material.

Final cold rolling rate

The final cold rolling rate at the time of final annealing is preferably in the range of 50 to 90%. If the final cold rolling rate is within this range, the final plate after annealing can be obtained. The average recrystallized grain is 20 to 100 μm, and the elongation value is 30% or more, and the formed surface after molding can be beautifully finished. Better, the final cold rolling rate is in the range of 60 to 90%.

On the other hand, the final cold rolling ratio when the cold-rolled original material is not subjected to final annealing is preferably in the range of 5 to 40%. When the shrinking process is increased during DI forming, it is necessary to provide a final plate which is slightly harder than the annealed material. Better, the final cold rolling rate is in the range of 10 to 30%.

An aluminum alloy plate for a secondary battery container can be obtained by the usual procedure as described above.

Example Make the final board

Each of the predetermined ingots was measured and mixed with an instrument, and 6 kg of ingots (total of 8 test materials) were inserted one by one into the #20坩埚 of the coated release profile. The crucibles were inserted into an electric furnace, and the dross was melted and removed at 780 ° C. Then, the temperature of the melt was maintained at 760 ° C, and then 6 g of each flux for deodorization was wrapped in an aluminum foil and pressed in with a bell jar.

Next, the spray gun was inserted into the melt, and N ₂ gas was blown at a flow rate of 1.0 L/min to carry out a degassing treatment. Then, the mixture was sedated for 30 minutes, and the dander which was floated to the surface of the melt was removed by a stir bar, and the disc sample was taken in a mold for component analysis.

Next, the crucible was sequentially taken out from the electric furnace using a jig, and the aluminum melt was injected into the preheated mold (250 mm × 200 mm × 30 mm). The disc samples of each of the test materials were subjected to composition analysis by luminescence spectrometry. The results are shown in Table 1.

After the ingot was cut and pushed out of the melt, the both sides were cut by 2 mm each to have a thickness of 26 mm.

The ingot was inserted into an electric heating furnace, heated to 430 ° C at a temperature elevation rate of 100 ° C / hour, and subjected to homogenization treatment at 430 ° C for 1 hour, followed by hot rolling to a thickness of 6 mm by a hot rolling mill.

The cold-rolled annealed sheet was subjected to cold rolling without performing intermediate annealing on the hot-rolled sheet to obtain a cold-rolled sheet of 1 mm. The final cold rolling rate at this time was 83%. In the final annealing, the cold-rolled sheet was inserted into an annealing furnace, and after annealing at 390 ° C for 1 hour, the cold-rolled sheet was taken out from the annealing furnace and then cooled in the air.

Next, the final plate (each test material) thus obtained was evaluated for formability and laser weldability.

Evaluation of formability

The formability evaluation of the obtained final sheet was carried out by the elongation (%) of the tensile test.

Specifically, a JIS No. 5 test piece was taken in such a manner that the stretching direction was parallel to the rolling direction, and a tensile test was performed in accordance with JIS Z 2241, and tensile strength, 0.2% fall strength, and elongation (elongation at break) were determined.

In the final sheet which was annealed after cold rolling, the test piece having an elongation of 30% or more was excellent in moldability (○), and the test piece having less than 30% was poor in formability (×). The evaluation results are shown in Table 2.

Laser welding condition

For the final plate obtained, laser welding was performed, and the evaluation of the laser welding properties was performed. The YAG laser welding machine JK701 manufactured by LUMONICS was used, and the frequency was 37.5 Hz, the welding speed was 400 mm/min, the energy per pulse was 9.0 J, the pulse width was 1.5 msec, and the shielding gas (nitrogen) flow rate was 1.5 (L/min). The ends of the two plates of the same test piece are not separated from each other, and the grounding is performed along the portion to perform pulsed laser welding of a length of 100 mm.

Evaluation of laser fusion Welding defect day measurement/evaluation

Next, the number of weld defects generated in the welded portion was measured as an evaluation of the laser weldability. First, in the above-described 100 mm-length weld line, the area of the remaining 80 mm length is defined as the measurement area except for the 20 mm-length weld line of the fusion start portion. The vicinity of the beginning of the fusion is unstable and is therefore excluded.

Further, as shown in Fig. 3, the cross section of the welded bead formed along the 80 mm length of the weld line was examined by X-ray CT to obtain an X-ray CT image parallel to the plate thickness section of the weld line. Then, the black defect portion is detected by the image editing software based on the X-ray CT image, and the area of the black defect portion is calculated by the image analysis software. The number of particles corresponding to the respective diameters of the respective circles was calculated from the area of the black defect portion.

In the present specification, a test material having a number of black defects having a diameter of 0.4 mm or more and a number of black defects of less than 10 is a test material having a good number of weld defects (○), and a number of black defects having a diameter of 0.4 mm or more and a number of black defects of 10 or more. The evaluation of the number of weld defects was poor (×). The evaluation results are shown in Table 2.

Evaluation of each test material

The test materials of Examples 1 to 7 were within the range of the alloy composition of the present invention, and the number of weld defects was sufficiently satisfied to be less than 10 of the standard, so that the laser welding property was excellent. Further, since the elongation in the tensile test is also 30% or more, it also has excellent formability. The Co content of the test piece of Comparative Example 1 was extremely as low as 0.0001% by mass, and the number of weld defects was 12, and the laser fusion property was poor. The Co content of the test piece of Comparative Example 2 was as low as 0.0005 mass%, and the number of weld defects was 12, and the laser fusion property was poor. The Co content of the test piece of Comparative Example 3 was as low as 0.0008 mass%, and the number of weld defects was 11, and the laser fusion property was poor. The Fe content of the test material of Comparative Example 4 was as high as 0.70% by mass, and the melting The number of defects is 24, and the laser fusion is not good. The Si content of the test piece of Comparative Example 5 was as high as 0.42% by mass, and the number of weld defects was 17, and the laser fusion property was poor. The Si content of the test piece of Comparative Example 6 was as high as 0.65 mass%, and the number of weld defects was 10, and the laser fusion property was poor.

A longitudinal section (a section perpendicular to the LT direction) parallel to the rolling direction of the obtained final sheet was cut out, and the thermoplastic resin was embedded and mirror-polished, followed by etching with a hydrofluoric acid aqueous solution, and metal structure observation was performed. The micro-metal structure was photographed by an optical microscope (area per field of view: 0.0334 mm ² , and each sample 15 was photographed), and image analysis of the photograph was performed, and the circle equivalent diameter per unit area (1 mm ² ) was measured to be 3 μm. The number of the second phase particles above. In the present specification, when the number of the second phase particles having a circular equivalent diameter of 3 μm or more is less than 100/mm ² , the evaluation is good (○), and the number of second phase particles having a circle equivalent diameter of 3 μm or more is 100/mm. ^{When it is 2} or more, it is evaluated as bad (x).

The image analysis results are shown in Table 3.

Image analysis result

As a result of image analysis of the second phase particles in the metal structure of each of the test materials, in the first to seventh embodiments, the number of second phase particles having a circle equivalent diameter of 3 μm or more is less than 100/mm ² and is relatively coarse. The intermetallic compound such as Al ₃ Fe has a low density and is evaluated as good (○). On the other hand, in Comparative Examples 1 to 6, it is considered that the number of second phase particles having a circle-equivalent diameter of 3 μm or more is 100/mm ² or more, and the presence of a relatively coarse intermetallic compound such as Al ₃ Fe is high. The evaluation was bad (×). The results of image analysis of the second phase particles in the metal structures were consistent with the results of the evaluation of the above-described laser fusion properties.

Industrial availability

According to the present invention, it is possible to provide a 1000 series aluminum alloy sheet having a thickness which is applicable to a large-sized lithium ion battery container and which has excellent formability and also excellent laser fusion properties.

Figure 1 is an Al-Co-Fe reaction diagram.

Figure 2 is a state diagram of the Al-Co-Fe ternary system (liquid phase diagram).

Fig. 3 is a conceptual diagram illustrating a method of measuring/evaluating the number of weld defects.

Claims (2)

An aluminum alloy plate for a battery case having excellent formability and weldability, characterized in that it 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 residual portion It is composed of Al and an unavoidable impurity, and has a metal structure having a circular equivalent diameter of 3 μm or more and a second phase particle number of less than 100 particles/mm ² . The aluminum alloy sheet for a battery case having excellent formability and weldability as in the first aspect of the patent application has a coefficient of elongation of 30% or more.