Aluminum alloy plate for lithium-ion battery lid and its manufacturing method

Abstract

The purpose of the present invention is to provide an aluminum alloy sheet for a lithium-ion battery lid, the aluminum alloy sheet having suitable strength and making it possible to realize excellent moldability, etc. This invention has: a component composition containing, by mass, 1.05 to 1.50% of Fe, 0.10 to 0.40% of Mn, 0.002 to 0.150% of Ti, and less than 0.05% of B, with the remainder made up by Al and impurities, the impurities comprising Si restricted to less than 0.40%, Cu restricted to less than 0.03%, Mg restricted to less than 0.05%, and V restricted to less than 0.03%; a total Fe and Mn content of 1.80% or below; and　a tensile strength of 115-140 MPa or below.

Description

[Technical Field]

[0001] The present invention relates to an aluminum alloy plate having high strength and excellent formability, etc., and being used as a lid material for lithium ion batteries, and a method for producing the same. [Background technology]

[0002] Lithium-ion secondary batteries are widely used as power sources for electric vehicles, electric motorcycles, mobile phones, and personal computers. In particular, demand for electric vehicles as environmentally friendly vehicles has been increasing in recent years. Aluminum alloy sheets are used as lid and case materials for lithium-ion batteries, and are required to have excellent formability, adequate strength, work-softening properties, etc.

[0003] Known as such an aluminum alloy sheet is an aluminum alloy sheet for battery lids used in forming one-piece explosion-proof valves, which contains 1.05 to 1.50 mass% Fe, 0.30 to 0.70 mass% Mn, 0.002 to 0.15 mass% Ti, and less than 0.04 mass% B, with the balance being Al and impurities, and which has a component composition in which the Fe / Mn ratio is regulated to 1.8 to 3.5, and the impurities are regulated to less than 0.20 mass% Si, less than 0.03 mass% Cu, less than 0.05 mass% Mg, and less than 0.03 mass% V, and which has an electrical conductivity of 53.0% IACS or more, a 0.2% proof stress of 40 MPa or more, an elongation of 40% or more, has a recrystallized structure, and has an elongation of 5.0% or more after cold rolling at a reduction of 80% and an elongation of 5.0% or more after cold rolling at a reduction of 90% (see Patent Document 1). Patent Document 1 describes that this aluminum alloy plate has excellent heat dissipation properties, deformation resistance, and formability, has little variation in operating pressure, and is excellent in repeated fatigue resistance properties.

[0004] Another known aluminum alloy sheet for battery lids is one that has a composition consisting of 1.15 to 1.35 mass% Fe, 0.40 to 0.60 mass% Mn, the balance being Al and impurities, with the impurities being regulated to 0.15 mass% or less of Si, 0.05 mass% or less of Cu, and 0.05 mass% or less of Mg, and has a structure in which, on the rolled surface, the maximum grain width in the direction perpendicular to the rolling direction is 100 μm or less and the average grain width is 25 μm or less (see Patent Document 2). Patent Document 2 describes that when manufacturing a lid for a battery case using this aluminum alloy sheet as a material, even a thin explosion-proof part can be obtained integrally by press working without employing an annealing process. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2019 / 111970 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-261008 Summary of the Invention [Problem to be solved by the invention]

[0006] Aluminum alloy sheets used for the cases and lids of lithium-ion batteries require basic performance such as formability, but for next-generation batteries, higher strength and thinner walls are increasingly required. Patent Document 1 discloses the addition of Mn to an Al-Fe base. The addition of Fe improves formability by increasing local elongation and also provides work softening properties, while the addition of Mn contributes to improved pressure strength, softening resistance, and high-temperature creep properties. However, the base metal tensile strength of Patent Document 1 is approximately 110 MPa, which leaves room for improvement in light of the recent demand for higher strength.

[0007] In Patent Document 2, like Patent Document 1, Mn and Fe are contained as essential elements, but the Fe content is higher than the Mn content, with the Mn content being relatively high at 0.4 to 0.6 mass%. Therefore, there is room for improvement in terms of formability, etc., by making the Al(Fe-Mn)-based compounds finer and less, and reducing the amount of Mn in solid solution in the ingot, thereby reducing the tensile strength of the base material. Furthermore, as a material for battery lids, etc., it is important that the base material has an appropriate strength, but Patent Document 2 does not specifically consider controlling the tensile strength of the base material within an appropriate range.

[0008] Therefore, an object of the present invention is to provide an aluminum alloy sheet for use as a lid for a lithium ion battery, which has a novel structure, has adequate strength, and can achieve excellent formability and the like. [Means for solving the problem]

[0009] To achieve the above object, the present inventors have investigated the composition of aluminum alloy sheets (particularly the Mn content). As a result, the present inventors have found that, on the premise that the aluminum alloy sheet is given an appropriate strength by utilizing solid solution strengthening due to the Mn content and work hardening due to rolling, by appropriately controlling the Mn content (i.e., not including an excessive amount), it is possible to avoid coarsening or an increase in the number of Fe-based intermetallic compounds, thereby avoiding an excessive increase in the tensile strength of the aluminum alloy sheet, thereby improving the formability when manufacturing an explosion-proof valve for a battery lid, and also improving the stability of the operating pressure of the explosion-proof valve. Furthermore, the present inventors have found that by performing batch annealing in the intermediate annealing step, the maximum attainable strength can be further reduced, and the formability when manufacturing an explosion-proof valve for a battery lid can be further improved, and also the stability of the operating pressure of the explosion-proof valve can be further improved.

[0010] The present invention, which has achieved the above object, is as follows. (1) An aluminum alloy sheet for a lithium-ion battery lid, characterized in that it contains, by mass%, 1.05 to 1.50% Fe, 0.10 to 0.40% Mn, 0.002 to 0.150% Ti, and less than 0.05% B, with the balance being Al and impurities, with the impurities being regulated to less than 0.40% Si, less than 0.03% Cu, less than 0.05% Mg, and less than 0.03% V, the total content of Fe and Mn being 1.80% or less, and the tensile strength being 115 to 140 MPa or less. (2) The aluminum alloy plate for a lithium-ion battery lid according to (1), characterized in that the tensile strength is 120 to 135 MPa. (3) The aluminum alloy sheet for a lithium-ion battery lid according to (1) or (2), characterized in that the maximum strength reached is 190 MPa or less. (4) A method for producing an aluminum alloy plate for a lithium-ion battery lid according to any one of (1) to (3), (1) A slab casting process for obtaining an ingot from a molten aluminum alloy having the composition described above by a semi-continuous casting method; a homogenization treatment step including homogenizing the ingot at a holding temperature of 520 to 620 ° C for a holding time of 1 hour or more; After the homogenization treatment step, a hot rolling step is performed in which the ingot is hot-rolled at a starting temperature of 420 to less than 520 ° C. to obtain a hot-rolled plate. A cold rolling step before intermediate annealing, in which the hot-rolled sheet is cold-rolled to obtain a cold-rolled sheet; The cold rolled sheet is subjected to a holding temperature of 300 to 450 ℃ an intermediate annealing process in which batch annealing is performed under conditions of 1 hour or more to obtain a batch annealed sheet; a rolling process after intermediate annealing in which the batch annealed sheet is cold rolled at a rolling reduction of 10 to 25%; A method for producing an aluminum alloy plate for a lithium-ion battery lid, comprising: [Effects of the Invention]

[0011] According to the present invention, it is possible to obtain an aluminum alloy sheet for use as a lid for a lithium ion battery, which has an appropriate strength and can realize excellent formability and the like. ) DETAILED DESCRIPTION OF THE INVENTION

[0012] <Aluminum alloy plate for lithium-ion battery lids> The aluminum alloy plate for a lithium-ion battery lid according to an embodiment of the present invention is The alloy contains, by mass%, 1.05 to 1.50% Fe, 0.10 to 0.40% Mn, 0.002 to 0.150% Ti, and less than 0.05% B, with the remainder being Al and impurities. The impurities are regulated to less than 0.40% Si, less than 0.03% Cu, less than 0.05% Mg, and less than 0.03% V, the total content of Fe and Mn being 1.80% or less, and the tensile strength is 115 to 140 MPa or less.

[0013] Generally, increasing the strength of aluminum alloy sheets leads to a problem of reduced formability. Specifically, when Mn is added to aluminum alloy sheets, the Mn dissolves in the matrix, promoting solid-solution strengthening, and high strength (assessed by tensile strength) is achieved. However, the Al-Fe-Mn intermetallic compounds become coarse and increase in number, resulting in a decrease in formability if excessive strength is achieved through solid-solution strengthening. Furthermore, when cold-rolling aluminum alloy sheets, increasing the reduction rate to promote work hardening to achieve high strength results in a decrease in formability if excessive strength is achieved through work hardening. Therefore, the present inventors have found that, on the premise of maintaining a moderate strength (115 MPa or more) in the aluminum alloy plate by setting the Mn content to 0.10 mass% or more, the Mn content can be set to 0.40 mass% or less to prevent excessive Mn inclusion, and the reduction rate in cold rolling after intermediate annealing can be set to 25% or less, thereby suppressing the tensile strength and imparting excellent formability to the aluminum alloy plate, and that an explosion-proof valve made of the aluminum alloy can be imparted with excellent stability of operating pressure.

[0014] Furthermore, the present inventors have found that, in order to further improve the formability and the like of the aluminum alloy sheet, the intermediate annealing is batch annealing so as not to excessively increase the tensile strength, and that the total content of Fe and Mn is set to 1.80% or less so as to suppress the formation of coarse crystals in the alloy sheet, thereby making it possible to set the maximum attainable strength described below to 190 MPa or less, thereby imparting even better formability to the aluminum alloy sheet, and also imparting even better stability of the operating pressure to an explosion-proof valve manufactured from this aluminum alloy.

[0015] In summary, the present inventors have achieved an aluminum alloy sheet for use as a lid material for lithium ion batteries, which has high strength and excellent formability, etc., and is usable as a lid material for lithium ion batteries, by combining mainly the following four findings (i) to (iv). The combination of these findings and the fact that an Al-Fe-Mn-based aluminum alloy sheet having high strength and excellent formability, etc., can be obtained thereby have not been known in the past, and have now been revealed for the first time by the present inventors. (i) By setting the Mn content to 0.10% by mass or more and sufficiently containing Mn, Mn is dissolved in the matrix to promote solid solution strengthening, thereby achieving high strength, and thereby realizing an appropriate strength (tensile strength of 115 MPa or more) in the aluminum alloy sheet; (ii) By limiting the Mn content to 0.40 mass% or less and not including an excessive amount of Mn, it is possible to avoid the coarsening and increase in the amount of Al-Fe-Mn intermetallic compounds, suppress excessive increases in tensile strength, and achieve excellent formability (tensile strength of 140 MPa or less). (iii) By setting the reduction rate to 25% or less in the cold rolling process after intermediate annealing and not increasing the reduction rate excessively, the alloy sheet is prevented from being excessively work-hardened, thereby realizing excellent formability (tensile strength of 140 MPa or less); (v) By carrying out batch annealing in which the intermediate annealing is carried out at a temperature of 300 to 450°C for 1 hour or more, the batch annealed sheet has a recrystallized structure, and by setting the total content of Fe and Mn to 1.80% or less, the generation of coarse crystals in the alloy sheet is suppressed, thereby making it possible to set the maximum attainable strength to 190 MPa or less, and imparting even better formability to the aluminum alloy sheet, and also imparting even better stability of operating pressure to explosion-proof valves made of this aluminum alloy.

[0016] Hereinafter, the aluminum alloy sheet for lithium-ion battery lids according to the embodiment of the present invention will be described in more detail. In the following description, the unit of content of each element, "%", means "mass%" unless otherwise specified. In addition, in this specification, "to" indicating a numerical range is used to mean that the numerical values ​​before and after it are included as the lower limit and upper limit unless otherwise specified.

[0017] [Fe: 1.05-1.50%] Fe is an essential element because Fe-based intermetallic compounds, such as Al-(Fe·Mn)-Si, crystallized in the ingot during casting absorb the Mn dissolved in the matrix during homogenization. To fully achieve this effect, the Fe content must be 1.05% or more. If the Fe content is less than 1.05%, the size and number of Fe-based intermetallic compounds in the ingot decrease, making it impossible to sufficiently reduce the amount of Mn dissolved in the ingot during homogenization. This may result in significant work hardening at high working ratios in the base metal (final aluminum alloy sheet). The Fe content may be 1.10% or more, 1.15% or more, 1.20% or more, or 1.25% or more. On the other hand, if the Fe content exceeds 1.50%, the size and number of Fe-based intermetallic compounds increase, resulting in an excessive increase in the tensile strength of the base metal and a decrease in formability. Therefore, the Fe content must be 1.50% or less. The Fe content may be 1.45% or less, 1.40% or less, or 1.35% or less.

[0018] [Mn: 0.10~0.40%] Mn is an essential element because it increases the yield strength and improves high-temperature creep properties of aluminum alloy sheets. A portion of Mn dissolves in the matrix to promote solution strengthening, making it an essential element. To achieve these effects, the Mn content must be 0.10% or more. If the Mn content is less than 0.10%, the Fe-based intermetallic compounds in the ingot may become needle-like, potentially reducing the elongation of the base material. Furthermore, if Mn is not present, the diffusion rate of solute Mn in the aluminum matrix increases, resulting in an increased dislocation velocity and poor high-temperature creep properties. The Mn content may be 0.10% or more, 0.15% or more, 0.20% or more, or 0.23% or more. On the other hand, if the Mn content exceeds 0.40%, the Fe-based intermetallic compounds become coarse and numerous, resulting in an excessive increase in tensile strength and reduced formability. Furthermore, if the Mn content exceeds 0.40%, the amount of solute Mn in the ingot may become too high, potentially increasing the tensile strength of the base material. Therefore, the Mn content is set to 0.40% or less. The Mn content may be 0.39% or less, 0.36% or less, 0.33% or less, or 0.30% or less.

[0019] [Ti: 0.002~0.150%] Ti is an essential element because it acts as a grain refiner during casting and can prevent casting cracks. While Ti may be added alone, its coexistence with B is expected to produce a more powerful grain refinement effect, so the molten alloy may be prepared using a rod hardener such as Al-5%Ti-1%B. To achieve this effect, the Ti content must be 0.002% or more. If the Ti content is less than 0.002% by mass, the grain refinement effect during casting is insufficient, which may lead to casting cracks. The Ti content may be 0.005% or more, 0.008% or more, 0.011% or more, or 0.014% or more. On the other hand, if the Ti content exceeds 0.150%, coarse intermetallic compounds such as TiAl3 may crystallize during casting, potentially resulting in an excessive increase in tensile strength and a decrease in formability. Therefore, the Ti content must be 0.150% or less. The Ti content may be 0.125% or less, 0.100% or less, 0.070% or less, or 0.050% or less.

[0020] [B: Less than 0.05%] B is an optional element, and its coexistence with Ti can be expected to provide a more powerful grain refinement effect than when Ti is added alone. Of course, B may be added alone, but as mentioned above, the molten alloy may be adjusted using a rod hardener such as Al-5%Ti-1%B. If the B content is 0.05% or more, depending on the Ti content, the Ti-B compound is likely to stabilize and become TiB2, reducing the grain refinement effect and causing TiB2 to settle in the furnace and accumulate on the hearth. Therefore, the B content is set to less than 0.05%. The B content may be 0.04% or less, 0.03% or less, 0.02% or less, or 0.01% or less.

[0021] [V: Less than 0.03%] In the present invention, V is an impurity. If the V content is 0.03% or more, relatively large Fe-based intermetallic compounds are crystallized during casting, and the elongation after cold rolling at a rolling reduction of 90% becomes less than 5.0%, which may result in poor formability. Therefore, the V content is set to less than 0.03%. The V content may be 0.02% or less, or 0.01% or less.

[0022] [Si: less than 0.40%] In the present invention, Si is an impurity. Si crystallizes Fe-based intermetallic compounds such as Al-(Fe·Mn)-Si during casting, and some of them dissolve in the matrix, thereby increasing the strength of the aluminum alloy sheet. If the Si content is 0.40% or more, the amount of Si dissolved in the base material increases, which may result in an excessive increase in tensile strength and poor formability. Therefore, the Si content is set to less than 0.40%. The Si content may be 0.35% or less, 0.30% or less, 0.25% or less, 0.20% or less, 0.15% or less, or 0.10% or less.

[0023] [Cu: less than 0.03%] In the present invention, Cu is an impurity. If the Cu content is 0.03% or more, elongation may decrease, resulting in poor formability. Therefore, the Cu content is set to less than 0.03%. The Cu content may be 0.02% or less, or 0.01% or less.

[0024] [Mg: Less than 0.05%] In the present invention, Mg is an impurity. If the Mg content is 0.05% or more, the formability of the base metal may be reduced and work hardening may be significantly promoted at high working ratios. Therefore, the Mg content is set to less than 0.05%. The Mg content may be 0.04% or less, 0.03% or less, 0.02% or less, or 0.01% or less.

[0025] [Other unavoidable impurities] Inevitable impurities are uncontrolled elements that are inevitably mixed in from raw metals, returned materials, etc., and their allowable contents are, for example, Cr: less than 0.20%, Zn: less than 0.20%, Ni: less than 0.10%, Ga: less than 0.05%, (each of Pb, Bi, Sn, Na, Ca, Sr): less than 0.02%, and (each of other elements, for example, Co, Nb, Mo, W): less than 0.05%. Even if uncontrolled elements are contained within these ranges, the effects of the present invention are not hindered.

[0026] [Total content of Fe and Mn: 1.80% or less] In the present invention, Fe is added to increase the local elongation of the aluminum alloy sheet for lithium-ion battery lids while maintaining work softening properties, and Mn is further added to improve pressure resistance, high-temperature creep properties, and softening resistance. However, if the total content of Fe and Mn exceeds 1.80%, coarse crystals are formed in the alloy sheet, which may result in an excessively high maximum strength (described later), and ultimately, when an explosion-proof valve is manufactured using the alloy, an excellent operating pressure may not be achieved. Therefore, the total content of Fe and Mn is set to 1.80% or less. The total content of Fe and Mn may also be 1.75% or less, 1.70% or less, 1.65% or less, 1.60% or less, 1.55% or less, or 1.50% or less.

[0027] [Tensile strength: 115-140MPa] When thinning is required for an aluminum alloy used as a material for a battery lid, appropriate strength and excellent formability are required. In the present invention, the tensile strength (MPa) of the base material is used as an index for evaluating strength and formability. A tensile strength of less than 115 MPa may result in insufficient strength, so the tensile strength is set to 115 MPa or more. The tensile strength may be 120 MPa or more, 125 MPa or more, 130 MPa or more, or 134 MPa or more. On the other hand, a tensile strength of more than 140 MPa may result in reduced formability, so the tensile strength is set to 140 MPa or less. The tensile strength may be 139 MPa or less, 138 MPa or less, 137 MPa or less, 136 MPa or less, or 135 MPa or less.

[0028] [Maximum strength achieved: 190MPa or less] The maximum ultimate strength refers to the maximum tensile strength when work-hardening curves are created for multiple test pieces obtained by cold-rolling with different reduction ratios on an intermediate-annealed sheet obtained by cold-rolling followed by batch annealing or continuous annealing after hot rolling. When using an aluminum alloy sheet for a lithium-ion battery lid for an explosion-proof valve, particularly heavy working is required. In an aluminum alloy sheet having the composition specified in the present invention, the Mn content is relatively low, so the maximum ultimate strength during heavy working is relatively low. Therefore, when an explosion-proof valve is manufactured using the aluminum alloy sheet for a lithium-ion battery lid of the present invention, excellent formability is achieved, and the explosion-proof valve manufactured using the alloy sheet can be imparted with excellent operating pressure stability. In the present invention, the maximum ultimate strength required to achieve these effects is 190 MPa or less. The maximum ultimate strength may be 188 MPa or less, 187 MPa or less, 186 MPa or less, 185 MPa or less, or 185 MPa or less.

[0029] <Method of manufacturing aluminum alloy sheets for lithium-ion battery lids> Next, a method for manufacturing an aluminum alloy plate for a lithium-ion battery lid according to an embodiment of the present invention will be described. The following description is intended to exemplify a characteristic method for manufacturing an aluminum alloy plate for a lithium-ion battery lid according to an embodiment of the present invention, and is not intended to limit the aluminum alloy plate for a lithium-ion battery lid to one manufactured by the manufacturing method described below.

[0030] A method for producing an aluminum alloy plate for a lithium-ion battery lid according to an embodiment of the present invention comprises: The method for producing the aluminum alloy plate for lithium-ion battery lids described above, a slab casting step of obtaining an ingot from a molten aluminum alloy having the above-mentioned component composition by a semi-continuous casting method; a homogenization treatment step including homogenizing the ingot at a holding temperature of 520 to 620 ° C for a holding time of 1 hour or more; After the homogenization treatment step, a hot rolling step is performed in which the ingot is hot-rolled at a starting temperature of 420 to less than 520 ° C. to obtain a hot-rolled plate. a cold rolling step before intermediate annealing in which the hot-rolled sheet is subjected to cold rolling to obtain a cold-rolled sheet; The cold rolled sheet is subjected to a holding temperature of 300 to 450 ℃ an intermediate annealing process in which batch annealing is performed under conditions of 1 hour or more to obtain a batch annealed sheet; a cold rolling step after intermediate annealing in which the batch annealed sheet is cold rolled at a rolling reduction of 10 to 25%; Each step will be described in detail below.

[0031] [Melting / refining process] First, raw materials are charged into a melting furnace. Once the predetermined melting temperature is reached, flux is added and stirred as needed. Further, if necessary, the furnace is degassed using a lance or other device. The melt is then allowed to settle and the slag is separated from the surface of the molten aluminum alloy. While additional raw materials, such as master alloys, are important in this melting and refining process to achieve the desired alloy composition, it is also crucial to allow sufficient settling time for the flux and slag to float to the surface of the molten aluminum alloy. A settling time of 30 minutes or more is usually desirable. From this perspective, the settling time may be 33 minutes or more, 36 minutes or more, 39 minutes or more, or 42 minutes or more. Furthermore, although the molten aluminum alloy produced in the melting furnace may be transferred to a holding furnace before casting, a more desirable settling time is 45 minutes or more, since the molten aluminum alloy may also be directly tapped from the melting furnace for casting. From this perspective, the settling time may be 48 minutes or more, 51 minutes or more, 54 minutes or more, or 57 minutes or more.

[0032] Furthermore, during the melting process, in-line degassing treatment or filtration of the molten metal using a specific filter may be performed as necessary. The most common type of in-line degassing treatment involves blowing an inert gas or the like into the molten aluminum from a rotating rotor, thereby removing the hydrogen gas in the molten metal by diffusing it into the inert gas bubbles. When using nitrogen gas as the inert gas, it is important to control the dew point to, for example, −60°C or below (also available as −65°C or below, or −70°C or below). It is preferable to reduce the amount of hydrogen gas in the ingot to 0.20 cc / 100 g or below (also available as 0.18 cc / 100 g or below, or 0.16 cc / 100 g or below).

[0033] If the ingot contains a large amount of hydrogen gas, porosity may occur in the final solidification portion of the ingot. Therefore, it is preferable to eliminate porosity by restricting the reduction rate per pass in the hot rolling process to, for example, 7% or more (8% or more, or even 9% or more). Furthermore, depending on the heat treatment conditions of the cold-rolled coil, the supersaturated hydrogen gas dissolved in the ingot may crystallize even after press-forming of the base material, for example, during laser welding of the battery lid and battery container, causing numerous blowholes in the weld bead. For this reason, a more preferable amount of hydrogen gas in the ingot is 0.15 cc / 100 g or less (or 0.12 cc / 100 g or less, or even 0.10 cc / 100 g or less).

[0034] [Slab casting process] Ingots are produced by semi-continuous casting (DC casting). In typical semi-continuous casting, the thickness of the ingot is generally around 400 to 600 mm, so the solidification cooling rate at the center of the ingot is around 1°C / sec. For this reason, when semi-continuous casting molten aluminum alloys with particularly high Fe and Mn contents, relatively coarse intermetallic compounds such as Al6(Fe·Mn) and α-Al-(Fe·Mn)-Si tend to crystallize out of the molten aluminum alloy at the center of the ingot.

[0035] The casting speed in semi-continuous casting is typically 50 to 70 mm / sec, taking productivity into consideration, although it depends on the width and thickness of the ingot. This casting speed can also be set to 52 to 68 mm / sec, 55 to 65 mm / sec, or 58 to 62 mm / sec. However, when performing in-line degassing, considering the actual residence time of the molten aluminum in the degassing treatment tank, the lower the flow rate of the molten aluminum (the amount of molten aluminum supplied per unit time), the more efficient the degassing in the tank, and the more likely it is to reduce the amount of hydrogen gas in the ingot. Depending on factors such as the number of pours, it is desirable to limit the casting speed to 50 mm / sec or less to reduce the amount of hydrogen gas in the ingot. This casting speed may be set to 45 mm / sec or less, 40 mm / sec or less, or 40 mm / sec or less. On the other hand, a casting speed of less than 30 mm / sec is undesirable due to reduced productivity, so the casting speed is set to 30 mm / sec or more. In addition, when the casting speed is slow, the slope of the sump (interface between the solid phase and the liquid phase) in the ingot becomes particularly gentle, making it possible to prevent casting cracks.

[0036] [Homogenization process] The ingot obtained by semi-continuous casting is subjected to homogenization treatment. Homogenization treatment is a process in which the ingot is maintained at a high temperature to facilitate rolling and eliminate casting segregation and residual stress within the ingot. In the present invention, it is necessary to include a homogenization treatment at a holding temperature of 520 to 620°C for at least one hour. This treatment also aims to dissolve transition elements and other elements constituting the intermetallic compounds crystallized during casting into the matrix to some extent. If the holding temperature is too low or too short, the dissolution process may not proceed, resulting in an unsatisfactory appearance after molding. Therefore, it is essential to hold the ingot at a holding temperature of 520°C or higher for at least one hour. The holding temperature may be 530°C or higher, 540°C or higher, or 550°C or higher. The holding time may be 2 hours or higher, 3 hours or higher, 4 hours or higher, or 5 hours or higher. On the other hand, if the holding temperature is too high, the eutectic portion, which is the microscopic final solidification portion of the ingot, may melt, resulting in so-called burning. Therefore, the holding temperature may be 610°C or less, 600°C or less, or 590°C or less. In this step, if the process includes treatment at a holding temperature of 520 to 620°C for 1 hour or more, the temperature may be subsequently lowered and the treatment may be performed to hold the temperature for a certain period of time (for example, treatment at 480°C for 1 hour).

[0037] [Hot rolling process] In this way, by subjecting the ingot to homogenization treatment at a holding temperature of at least 520 to 620°C for a holding time of at least one hour, and by setting the start temperature of hot rolling to less than 520°C, it becomes possible to reduce the Mn and Si dissolved in the matrix. If the start temperature of hot rolling is 520°C or higher, it becomes difficult to reduce the Mn and Si dissolved in the matrix. Therefore, the start temperature of hot rolling is less than 520°C. The start temperature of hot rolling may be 510°C or lower, 500°C or lower, or 490°C or lower. On the other hand, if the start temperature of hot rolling is less than 420°C, the roll pressure required for plastic deformation during hot rolling becomes high, the reduction rate per pass becomes too low, and productivity decreases. Therefore, the start temperature of hot rolling is 420°C or higher. The start temperature of hot rolling may be 430°C or higher, 440°C or higher, or 450°C or higher. The ingot removed from the soaking furnace is then lifted by a crane and brought to the hot rolling mill, where it is hot rolled, usually through multiple passes, to a desired thickness, for example, about 4 to 8 mm, and wound into a coil.

[0038] [Cold rolling process before intermediate annealing] Next, the hot-rolled sheet is cold-rolled as follows to obtain a cold-rolled sheet. The coil wound in the hot rolling mill is passed through a cold rolling mill, and typically multiple passes of cold rolling are performed. Since work hardening occurs due to plastic strain introduced by cold rolling, annealing is performed as necessary. Typically, this annealing also serves as a softening treatment, and depending on the material, the cold-rolled coil may be inserted into a batch furnace and held at a temperature of 300 to 400°C for at least one hour. Holding temperatures below 300°C do not promote softening. Holding temperatures may be 310°C or higher, 320°C or higher, or 330°C or higher. On the other hand, holding temperatures above 400°C may result in reduced productivity. Holding temperatures may be 390°C or lower, 380°C or lower, or 370°C or lower.

[0039] [Intermediate annealing process] The cold-rolled sheet obtained as described above is subjected to intermediate annealing. The intermediate annealing process performed after the cold rolling process described above may be continuous annealing or batch annealing. However, for example, batch annealing in an annealing furnace at a temperature of 300 to 450°C for 1 hour or more is preferred because it can achieve a maximum strength of 190 MPa or less. By performing batch annealing in this manner, a recrystallized structure is generated in the resulting annealed sheet. Temperatures exceeding 450°C result in over-annealing, resulting in coarsening of crystal grains, which leads to reduced strength, reduced formability, and reduced stability of the explosion-proof valve operating pressure. From this perspective, the holding temperature in batch annealing may be 425°C or less, 400°C or less, or 375°C or less. Note that holding temperatures below 300°C may result in insufficient recrystallization, which may lead to improved strength, reduced formability, and reduced stability of the explosion-proof valve operating pressure.

[0040] [Cold rolling process after intermediate annealing] In the present invention, a cold rolling process is further performed after the intermediate annealing process to adjust the strength of the base material (specifically, to improve the tensile strength). In the cold rolling process after the intermediate annealing, the annealed sheet is cold rolled at a rolling reduction of 10 to 25% to produce a base material with a tensile strength of 115 to 140 MPa. If the rolling reduction exceeds 25%, the base material will be excessively work-hardened, resulting in a tensile strength exceeding 140 MPa. This will excessively increase the press load during high-pressure processing, such as when processing the base material into an explosion-proof valve, and may result in a decrease in workability, making it difficult to achieve excellent formability. The rolling reduction may be 23% or less, 21% or less, 19% or less, or 17% or less. Note that the lower limit of the rolling reduction is set to 10%, as a realistic cold rolling ratio, considering the difficulty of manufacturing at a lower rolling reduction. The rolling reduction may be 12% or more, 14% or more, or 15% or more.

[0041] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples in any way. [Example]

[0042] In the following examples, aluminum alloy plates for lithium ion battery lids according to the embodiments of the present invention were produced under various conditions, and the tensile strength and maximum strength of the obtained aluminum alloy plates for lithium ion battery lids were investigated.

[0043] <Comparison of reference examples from lab experiments> Below, laboratory tests were carried out to identify the composition and other properties of the aluminum alloy plate for use as a lid for a lithium-ion battery according to the present invention. Five kg of each ingot with four compositions A to D was placed in a #20 crucible, which was then heated in a small electric furnace to melt the ingot. A lance was then inserted into the molten metal, and N2 gas was blown in at a flow rate of 1.0 L / s for 5 minutes to degas the metal. The mixture was then allowed to settle for 30 minutes, after which slag that had risen to the surface was removed with a stirrer. The crucible was then removed from the small electric furnace, and the molten metal was poured into a mold with internal dimensions of 250 x 200 x 30 mm to produce ingots. Test materials with compositions A to D were obtained from the molten metal in each crucible. Disk samples of these test materials were subjected to compositional analysis by optical emission spectroscopy. The results are shown in Table 1.

[0044] [Table 1]

[0045] Both sides of these ingots were chamfered by 5 mm to a thickness of 20 mm, and then homogenized at 590°C for 1 hour and 480°C for 1 hour. They were then hot-rolled to obtain 6.0 mm thick hot-rolled sheets A to D. These hot-rolled sheets were then cold-rolled to obtain 1.0 mm thick cold-rolled sheets A to D. Furthermore, these cold-rolled sheets were inserted into an annealer and annealed at 340°C for 1 hour to simulate batch annealing, obtaining annealed sheets A to D.

[0046] Next, the annealed sheet A was not cold-rolled, and was designated as the as-annealed sheet A0, which was used as the base material. In contrast, the annealed sheet A was cold-rolled at a reduction of 50 to 95%, and was designated as the cold-rolled material A1 (five levels of reduction: 50%, 70%, 80%, 90%, and 95%), which was used as the base material.

[0047] Annealed sheet B was not cold-rolled, but was designated as as-annealed sheet B0 and used as the base material. In contrast, annealed sheet B was cold-rolled at a reduction of 50 to 95%, and cold-rolled material B1 (five levels of reduction: 50%, 70%, 80%, 90%, and 95%) was used as the base material.

[0048] Annealed sheet C was not cold-rolled, but was designated as as-annealed sheet C0 and used as the base material. In contrast, annealed sheet C was cold-rolled at a reduction of 50 to 95%, and cold-rolled material C1 (five levels of reduction: 50%, 70%, 80%, 90%, and 95%) was used as the base material.

[0049] Annealed sheet D was not cold-rolled, and was designated as as-annealed sheet D0, which was used as the base material. In contrast, annealed sheet D was cold-rolled at a reduction of 50 to 95%, and was designated as cold-rolled material D1 (five levels of reduction: 50%, 70%, 80%, 90%, and 95%), which was used as the base material.

[0050] [Measurement of tensile strength and maximum strength] Of these base materials, the tensile strength was measured for the as-annealed material A0, the as-annealed material B0, the as-annealed material C0, and the as-annealed material D0. For the tensile strength, JIS No. 5 test pieces were prepared from each test material and tested in accordance with JIS Z22241, with the tension direction parallel to the rolling direction.

[0051] Furthermore, among these base materials, the maximum strength was measured for cold-rolled material A1 (five levels of rolling reduction), cold-rolled material B1 (five levels of rolling reduction), cold-rolled material C1 (five levels of rolling reduction), and cold-rolled material D1 (five levels of rolling reduction). Regarding the maximum strength, for example, for the five cold-rolled materials A1 resulting from composition A, work-hardening curves were created for each of these cold-rolled materials, and the tensile strength immediately before work softening was compared to measure the value at which the tensile strength reached its maximum (maximum strength). These results are shown in Table 2.

[0052] [Table 2]

[0053] Referring to Table 2, the cold-rolled material using Annealed Sheet A (Reference Example 2) had a lower maximum temperature (196 MPa) than the cold-rolled material using Annealed Sheet B (Reference Example 4), the cold-rolled material using Annealed Sheet C (Reference Example 6), and the cold-rolled material using Annealed Sheet D (Reference Example 8). This is because the Mn content (0.20%) of Annealed Sheet A was lower than that of Annealed Sheets B to D, preventing the formation of coarse and abundant Fe-based intermetallic compounds. Note that in laboratory experiments, the slabs used were smaller than those used in tests using actual equipment. Therefore, the solidification rate and heat conduction during hot rolling differed, resulting in higher solid solubility, which tended to result in higher overall strength. Therefore, the maximum strength values ​​in the laboratory experiments were thought to be approximately 10 MPa higher than those in tests using actual equipment. Based on these findings, it is appropriate to define a preferred range for the maximum temperature in the present invention as 190 MPa or less.

[0054] In addition, in the cold-rolled materials (Reference Examples 4 and 6) using annealed sheets B and D, the total content of Fe and Mn exceeds 1.80%, which causes coarse crystals to form in the alloy sheet, resulting in an excessively high maximum strength. For this reason, it is appropriate to set the total content of Fe and Mn to a preferred range of 1.80% or less.

[0055] Furthermore, in the cold-rolled material (Reference Example 6) using annealed sheet C, the Fe content (0.97%) was too low, resulting in the crystallization of Al-Mn alone, resulting in an excessively high maximum strength. However, as mentioned above, if the Fe content exceeds 1.50%, the size and number of Fe-based intermetallic compounds increase, resulting in an excessive improvement in tensile strength and a decrease in formability. For these reasons, it is appropriate to set the Fe content in the preferred range of 1.05 to 1.50%.

[0056] <Comparison of Examples, Comparative Examples, and Reference Examples Using Actual Equipment> Next, tests were carried out using actual equipment on the aluminum alloy sheet for lithium ion battery lids according to the present invention. Molten metals with four compositions E to H shown in Table 3 were each produced in a melting furnace, and semi-continuous casting (DC casting) was used to produce ingots measuring 1190 mm wide x 560 mm thick x 3800 mm long. Both sides of these ingots were chamfered, inserted into a soaking furnace, and heated. They were then homogenized at 590°C for 1 hour and 480°C for 1 hour. They were then hot-rolled and coiled into 7.0 mm thick hot-rolled sheets. These hot-rolled sheets were then cold-rolled to 0.98 mm thick cold-rolled sheets (the cold-rolling step before intermediate annealing). Cut sheets E to H of appropriate dimensions were then obtained from these cold-rolled sheets.

[0057] [Table 3]

[0058] Next, the cut sheet E was inserted into an annealer and annealed at 340 °C for 1 hour to simulate batch annealing, resulting in batch annealed sheet E1. Another cut sheet E was heated in a salt bath at 425 °C for 15 seconds, then water-cooled to produce continuously annealed sheet E2, simulating continuous annealing at 425 °C for 10 seconds. Furthermore, the batch annealed sheet E1 and the continuously annealed sheet E2 were each subjected to cold rolling after intermediate annealing at an 18% reduction to obtain cold-rolled material E118 and cold-rolled material E218 with thicknesses of 0.8 mm, which were used as base materials. Also used as base materials were batch annealed material E100, which was not subjected to cold rolling after intermediate annealing, and cold-rolled material E130, which was subjected to cold rolling after intermediate annealing at a 30% reduction.

[0059] Similarly, for cut sheets F, G, and H, batch annealing was simulated by inserting them into an annealer and annealing them at 340°C for 1 hour to produce batch annealed sheets F1, G1, and H1. Furthermore, each of the batch annealed sheets F1, G1, and H1 was subjected to intermediate annealing at a rolling reduction of 18%, followed by cold rolling to obtain cold-rolled material F118, cold-rolled material G118, and cold-rolled material H118, all with a thickness of 0.8 mm, which were used as the base materials.

[0060] The tensile strength and maximum strength were measured for each of the cold-rolled materials E118, E218, F118, G118, and H118 prepared as described above. For the batch-annealed E100 and E130 cold-rolled materials, only the tensile strength was measured. The tensile strength and maximum strength were measured by cold-rolling the materials at different reduction ratios to create work-hardening curves, and then using the maximum strengths obtained. The results are shown in Table 4.

[0061] [Table 4]

[0062] Referring to Table 4, the cold-rolled sheet E118, the cold-rolled sheet E218, and the cold-rolled sheet F118 all had a Mn content of 0.10% by mass or more, so Mn was dissolved in the matrix to promote solid-solution strengthening and achieve high strength, thereby achieving appropriate strength (tensile strength of 115 MPa or more) in the aluminum alloy sheet. Furthermore, the cold-rolled sheet E118, the cold-rolled sheet E218, and the cold-rolled sheet F118 all had a Mn content of 0.40% by mass or less, so coarsening or an increase in the amount of Al-Fe-Mn-based intermetallic compounds was avoided, and an excessive increase in tensile strength was suppressed, thereby achieving excellent formability (tensile strength of 140 MPa or less).

[0063] In the case of cold-rolled sheet G118, the Mn content (0.49%) is too high, which causes the Al-Fe-Mn intermetallic compounds to become coarse and increase in number, making it impossible to suppress excessive improvement in tensile strength (tensile strength 141 MPa), and it can be said that excellent formability cannot be achieved.In addition, in the case of cold-rolled sheet H118, the Mn content is 0.00%, so solid solution strengthening by adding Mn cannot be achieved, and the level of high strength is relatively low.

[0064] For the batch-annealed E100 material, it was not subjected to cold rolling after intermediate annealing, which meant that work hardening was not achieved sufficiently and excellent tensile strength (115 MPa or more) was not achieved.For the cold-rolled E130 material, the reduction rate (30%) was too high, so the tensile strength was too high (151 MPa), and it is thought that excellent formability was not achieved.

[0065] <Comparison of Examples and Reference Examples for Evaluation of High-Temperature Creep Properties> Next, the cold-rolled material E118 (Example 1) and the cold-rolled material H118 (Reference Example 9) shown in Table 4 above were subjected to a load of 1.5 MPa in a 130°C environment for 300 hours, and the strain values ​​(%) were measured to evaluate the high-temperature creep properties. These results are shown in Table 5. The strain values ​​are preferably 0.070% or less. The strain values ​​may also be 0.060% or less, 0.050% or less, or 0.040% or less.

[0066] [Table 5]

[0067] Referring to Table 5, the cold-rolled material E118 showed little change in strain after 300 hours from the initial strain, with the strain value being 0.05% or less, and was therefore evaluated as having good high-temperature creep properties. This is due to the addition of Mn to the cold-rolled material E118. That is, the addition of an appropriate amount of Mn to the cold-rolled material E118 reduces the diffusion rate of solute Mn in the aluminum matrix, thereby slowing the dislocation motion velocity, presumably resulting in good high-temperature creep properties. For the above reasons, it is presumed that adding approximately 0.10 to 0.40% Mn will result in good high-temperature creep properties, similar to those of the cold-rolled material E118. Furthermore, based on the results for the cold-rolled material E118, it is believed that solute Mn significantly contributes to high-temperature creep properties. Therefore, the cold-rolled material E218 (Example 2) and the cold-rolled material F118 (Example 3) are also expected to have good high-temperature creep properties due to the inclusion of Mn.

[0068] In contrast, the cold-rolled material H118 was evaluated as having poor high-temperature creep properties because the strain value was greater than 0.05%. This is because no Mn was added to the cold-rolled material H118. In other words, the lack of Mn in the cold-rolled material H118 increases the dislocation velocity, which is thought to be why the high-temperature creep properties were poor.

Claims

1. An aluminum alloy plate for use as a lid for lithium-ion batteries, characterized in that it has a component composition containing, by mass%, 1.05 to 1.50% Fe, 0.10 to 0.40% Mn, 0.002 to 0.150% Ti, and less than 0.05% B, with the balance being Al and impurities, the impurities being regulated to less than 0.40% Si, less than 0.03% Cu, less than 0.05% Mg, and less than 0.03% V, the total content of Fe and Mn being 1.80% or less, and the tensile strength being 115 to 140 MPa or less.

2. The aluminum alloy plate for lithium ion battery lids according to claim 1, characterized in that the tensile strength is 120 to 135 MPa or less.

3. 3. The aluminum alloy sheet for a lithium ion battery lid according to claim 1, wherein the aluminum alloy sheet has a maximum strength of 190 MPa or less.

4. A method for manufacturing an aluminum alloy plate for a lithium-ion battery lid according to claim 1 or 2, comprising: a slab casting step of obtaining an ingot from a molten aluminum alloy having the component composition according to claim 1 by a semi-continuous casting method; a homogenization treatment step including homogenizing the ingot at a holding temperature of 520 to 620°C for a holding time of 1 hour or more; After the homogenization treatment step, a hot rolling step is performed in which the ingot is hot-rolled at a starting temperature of 420 to less than 520 ° C. to obtain a hot-rolled plate. A cold rolling step before intermediate annealing, in which the hot-rolled sheet is cold-rolled to obtain a cold-rolled sheet; An intermediate annealing step in which the cold-rolled sheet is subjected to batch annealing at a holding temperature of 300 to 450 ° C. for 1 hour or more to obtain a batch annealed sheet; a cold rolling step after intermediate annealing in which the batch annealed sheet is cold rolled at a rolling reduction of 10 to 25%; A method for producing an aluminum alloy plate for a lithium-ion battery lid, comprising:

Images