Aluminum alloy sheet for deep drawing and method for manufacturing the same

Abstract

To provide an Al-Fe-Mn-based aluminum alloy sheet that has excellent hardness and formability, and a predetermined earing ratio.SOLUTION: An aluminum alloy sheet for drawing process contains Fe by 1.05 to 1.50%, Mn by 0.40% or less, Ti by 0.002 to 0.150%, and B by less than 0.05% in mass%, and the remainder consists of Al and impurities. The alloy sheet has a component composition regulated to Si: less than 0.40%, Cu: less than 0.03%, Mg: less than 0.05%, and V: less than 0.03% as impurities, and has the tensile strength of 170 MPa or less, the earing ratio of -2% or more and 2% or less.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an Al-Fe-Mn-based aluminum alloy sheet (including the case where Mn is not contained; the same shall apply hereinafter) having high strength, excellent formability, and a predetermined ear ratio, which is used as a material for drawn products such as battery cases, and a method for manufacturing the same.

Background Art

[0002] Aluminum alloy sheets are used as materials for lid materials and case materials of lithium-ion batteries, and also as materials for other drawn products such as utensils. It is desired to have appropriate strength, excellent formability, and further processing softening characteristics. When an aluminum alloy sheet is used particularly as a case material for a lithium-ion battery, so-called ears are easily formed by drawing, and there is an inherent problem of yield. Therefore, from the viewpoint of improving the yield, it is necessary to obtain an aluminum alloy sheet having a predetermined ear ratio. So far, in order to suppress the ear ratio low, the composition and manufacturing conditions of the aluminum alloy sheet have been adjusted.

[0003] As such an aluminum alloy sheet, Si: 0.10 to 0.60 wt%, Fe: 0.20 to 0.60 wt%, Cu: 0.10 to 0.70 wt%, Mn: 0.60 to 1.50 wt%, Mg: 0.20 to 1.20 wt%, Zr: exceeding 0.12 wt% and less than 0.20 wt%, Ti: 0.05 to 0.25 wt%, B: 0.0010 to 0.02 wt% are contained, and the balance is Al and inevitable impurities. An aluminum alloy sheet for a rectangular cross-section battery container having a 45° ear ratio of 4 to 7% with respect to the rolling direction by a cylindrical container deep drawing forming method is known (see Patent Document 1). Patent Document 1 describes that this aluminum alloy sheet has a high product yield, good rectangular DI formability of thin plates (DI forming containers with a thickness of 4 to 7 mm × width of 20 to 30 × height of 40 to 60 mm), and excellent weldability of a pulsed laser.

[0004] Another aluminum alloy sheet has a composition containing Fe: 0.3-1.5 mass%, Mn: 0.3-1.0 mass%, and Ti: 0.002-0.20 mass%, with a Mn / Fe mass ratio of 0.2-1.0, and the remainder being Al and impurities, with impurities of less than 0.30 mass% Si, less than 0.20 mass% Cu, and less than 0.20 mass% Mg, and a second-phase particle count of 500 particles / mm² with an equivalent circle diameter of 5 μm or more. 2 An aluminum alloy sheet for battery cases is known that has a metallic structure of less than 5%, exhibits an elongation of 5% or more, and a tensile strength of 90 MPa or more, and is a cold-rolled material with excellent formability and weldability (see Patent Document 2). Patent Document 2 states that this aluminum alloy sheet has high strength (90 MPa or more) applicable to large lithium-ion battery containers, and also has excellent formability and laser weldability. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2004-197172 [Patent Document 2] Japanese Patent Publication No. 2012-177186 [Overview of the project] [Problems that the invention aims to solve]

[0006] Aluminum alloy sheets used as case materials for lithium-ion batteries require basic performance characteristics such as formability, which are necessary for deep drawing processes. However, for next-generation batteries, there is an increasing demand for higher strength and thinner walls. Patent Document 1 describes a 45° ear ratio of 4-7% in deep drawing of cylindrical containers relative to the rolling direction, but with the recent demand for thinner walls, there is a need to further reduce the ear ratio. Also, Patent Document 1 has a relatively high Mn content (0.60-1.50 wt%). Therefore, there is room for improvement in reducing the amount of Mn solid solution in the matrix to reduce work hardening due to cold working, suppressing the tensile strength of the base material, and making Al-Fe-Mn intermetallic compounds finer and less abundant.

[0007] In Patent Document 2, the final cold rolling ratio when final annealing is performed is relatively high, at 50-90%. Therefore, there is room for improvement in further reducing work hardening due to cold working and thereby reducing the tensile strength of the base material. In addition, while it is important for materials for deep-drawn products such as battery cases to have a predetermined edge ratio, Patent Document 2 does not specifically consider how to bring the edge ratio close to 0%.

[0008] Therefore, the present invention aims to provide an Al-Fe-Mn aluminum alloy sheet that, based on a novel structure, possesses moderate strength, excellent formability, and a predetermined edge ratio. [Means for solving the problem]

[0009] To achieve the above objective, the inventors investigated the composition of the aluminum alloy sheet (especially the Mn content), the annealing method in the continuous annealing process after the cold rolling process, and the presence or absence of a cold rolling process after the continuous annealing process, as well as the reduction ratio when such a cold rolling process is adopted. As a result, the inventors found that, based on the premise of providing the aluminum alloy sheet with appropriate strength by utilizing solid solution strengthening due to Mn content and work hardening by rolling, by appropriately controlling the Mn content (i.e., not including excessive Mn) and appropriately controlling the reduction ratio when a rolling process after the continuous annealing process is adopted (i.e., not increasing the reduction ratio excessively), it is possible to avoid the Fe-based intermetallic compounds becoming coarse or numerous, thereby preventing the tensile strength of the aluminum alloy sheet from becoming excessively large and ultimately improving its formability. Furthermore, the inventors have found that by avoiding excessive Mn content, limiting the annealing type to continuous annealing, and appropriately controlling the reduction ratio when a cold rolling process is used after the continuous annealing process, it is possible to suppress the precipitation of intermetallic compounds and achieve a predetermined ear ratio (bringing the ear ratio close to 0%). The inventors then completed the present invention by combining these findings.

[0010] The present invention, which has achieved the above objectives, is as follows. (1) An aluminum alloy sheet for deep drawing, characterized by having a composition of components such as Fe: 1.05 to 1.50% by mass, Mn: 0.40% or less, Ti: 0.002 to 0.150%, and B: less than 0.05%, with the remainder being Al and impurities, and having impurities restricted to less than 0.40% Si, less than 0.03%, less than 0.05%, and less than 0.03%, a tensile strength of 170 MPa or less, and an ear ratio of -2% to 2% or less. (2) The aluminum alloy sheet for deep drawing described in (1), characterized in that Mn is 0.10% or more by mass. (3) An aluminum alloy sheet for deep drawing according to (1) or (2), characterized in that its tensile strength is 100 to 160 MPa or less. (4) A method for manufacturing an aluminum alloy sheet for deep drawing according to any one of (1) to (3), (1) A slab casting process to obtain an ingot from molten aluminum alloy having the component composition described above by a semi-continuous casting method, The ingot is subjected to a homogenization process that includes a homogenization treatment with a holding temperature of 520 to 620°C and a holding time of 1 hour or more. After the homogenization process, a hot rolling process is performed to obtain a hot-rolled plate by hot-rolling the ingot with the starting temperature set to less than 420-520°C. The aforementioned hot-rolled sheet is subjected to cold rolling to obtain a cold-rolled sheet, a cold rolling process before the continuous annealing process, A continuous annealing process is performed on the cold-rolled sheet, in which the sheet is heated to a temperature in the range of 350 to 550°C at an average heating rate of 1°C / second or more, and then continuously annealed at an average cooling rate of 1°C / second or more without holding or with holding for 10 minutes or less, in order to obtain an annealed sheet. If the annealed sheet is cold-rolled after the continuous annealing process, the cold-rolling process after the continuous annealing process is performed with a reduction ratio of 10 to 40%. A method for manufacturing aluminum alloy sheets for deep drawing, characterized by including the following: [Effects of the Invention]

[0011] According to the present invention, it is possible to obtain an Al-Fe-Mn aluminum alloy sheet that has high strength, excellent formability, and a predetermined edge ratio, which can be used as a material for deep-drawn products such as battery cases. [Modes for carrying out the invention]

[0012] <Aluminum alloy sheet for deep drawing> An aluminum alloy sheet for deep drawing according to an embodiment of the present invention is It is characterized by a composition containing, by mass%, Fe: 1.05-1.50%, Mn: 0.40% or less, Ti: 0.002-0.150%, and B: less than 0.05%, with the remainder being Al and impurities, and having a restricted composition of impurities of less than 0.40%, less than 0.03%, less than 0.05%, and less than 0.03%, a tensile strength of 170 MPa or less, and an ear ratio of -2% to 2%.

[0013] Generally, increasing the strength of an aluminum alloy sheet results in a decrease in formability. Specifically, by incorporating manganese (Mn) into the aluminum alloy sheet, solid solution strengthening is promoted by solid solution strengthening, achieving high strength (evaluated by tensile strength). However, this can lead to coarsening or an increase in the amount of Al-Fe-Mn intermetallic compounds, and if the strength increase through solid solution strengthening is excessive, formability will decrease. Furthermore, when cold rolling an aluminum alloy sheet, increasing the reduction ratio to promote work hardening can achieve high strength, but if the strength increase through work hardening is excessive, formability will decrease. Therefore, the inventors have found that by limiting the Mn content to 0.40 mass% or less to avoid excessive Mn content, and by limiting the reduction ratio during cold rolling to 40% or less when cold rolling is performed after a continuous annealing process, tensile strength can be suppressed, thereby providing excellent formability to the aluminum alloy sheet.

[0014] Furthermore, the inventors have also conducted extensive research to improve the yield of processed products when aluminum alloy sheets are drawn, specifically by reducing the edge ratio (specifically, the edge ratio shown by the formula described later) of the processed products to approximately 0%. One reason for the formation of edges in drawn products is that when Mn is included in excess, a large number of Al-Fe-Mn intermetallic compounds precipitate during annealing, inhibiting recrystallization and leaving a rolled texture. In addition, when annealing is performed in batches, the heating is slow, and Al-Fe and Al-(Fe·Mn) intermetallic compounds precipitate before softening due to recrystallization begins, inhibiting recrystallization and making it easier for a rolled texture to remain, which is one of the causes of edge formation. Furthermore, if the reduction ratio in the cold rolling process after the continuous annealing process is too high, excessive work hardening occurs, which is also one of the causes of edge formation.

[0015] Based on these findings, the inventors of this invention, By limiting the Mn content to 0.40% by mass or less, excessive Mn content can be avoided, thus preventing the precipitation of numerous Al-Fe-Mn intermetallic compounds during annealing and reducing the likelihood of retaining the rolled texture. · By making annealing continuous annealing, the temperature rise can be made relatively fast, avoiding the precipitation of a large number of Fe-based intermetallic compounds during annealing, promoting the growth of crystal grains of recrystallized textures such as Cube orientation, and · When cold rolling is performed after the continuous annealing process, by setting the rolling reduction rate to 40% or less, the alloy sheet is not overly work-hardened can be achieved. By combining these effects, it has been found that when the aluminum alloy sheet is drawn, the ear rate of the processed product (including both the 0° ear rate and the 45° ear rate described later) can be made -2% or more and 2% or less.

[0016] Summarizing the above, the inventors have achieved an Al-Fe-Mn-based aluminum alloy sheet with high strength, excellent formability, and an ear rate of -2% or more and 2% or less by mainly combining the following five findings (i) to (v). This combination of findings and the fact that an Al-Fe-Mn-based aluminum alloy sheet with high strength, excellent formability, and a predetermined ear rate can be obtained have not been known conventionally and have been first revealed by the inventors this time. (i) By setting the Mn content to 0.40 mass% or less and not excessively containing Mn, it is possible to avoid the coarsening or increase of Al-Fe-Mn-based intermetallic compounds, suppress the excessive improvement of tensile strength, and achieve excellent formability (tensile strength of 170 MPa or less). (ii) When cold rolling is performed on the aluminum alloy sheet after continuous annealing, by setting the rolling reduction rate to 40% or less and suppressing the increase in strength due to work hardening, excellent formability (tensile strength of 170 MPa or less) can be achieved. (iii) By setting the Mn content to 0.40 mass% or less and not excessively containing Mn, it is possible to avoid the precipitation of a large number of Al-Fe-Mn-based intermetallic compounds during annealing, make it difficult for the rolling texture to remain, and achieve a predetermined ear rate (ear rate of -2% or more and 2% or less). (iv) By making the annealing after the cold rolling process a continuous annealing, the temperature rise can be made relatively fast, avoiding the precipitation of a large number of Fe-based intermetallic compounds during annealing, and promoting the growth of crystal grains of the recrystallized texture such as Cube orientation, thereby enabling the realization of a predetermined earing rate (the earing rate is -2% or more and 2% or less), and (v) When a cold rolling process is employed after continuous annealing, by setting the rolling reduction rate to 40% or less, the alloy sheet is not overly work-hardened, thereby enabling the realization of a predetermined earing rate (the earing rate is -2% or more and 2% or less).

[0017] Hereinafter, the aluminum alloy sheet for drawing according to the embodiment of the present invention will be described in more detail. In the following description, the unit “%” of the content of each element means “mass %” unless otherwise specified. Also, in this specification, “~” indicating a numerical range is used to mean including the numerical values described before and after it as the lower limit value and the upper limit value, unless otherwise specified.

[0018] [Fe: 1.05 to 1.50%] Fe is an essential element because it can absorb Mn dissolved in the matrix during the homogenization treatment by Fe-based intermetallic compounds such as Al-(Fe·Mn)-Si crystallized in the ingot during casting. In order to sufficiently obtain such an effect, the Fe content should 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 Mn solid solution amount in the ingot during the homogenization treatment. Therefore, when drawing is performed on the base material (the final aluminum alloy sheet), there is a risk of significant work hardening. 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 a decrease in formability due to an excessive increase in the tensile strength of the base material. Therefore, the Fe content should be 1.50% or less. The Fe content may be 1.45% or less, 1.40% or less, or 1.35% or less.

[0019] [Mn:0.40% or less] Mn is an element that increases the yield strength of aluminum alloy sheets and improves thermal creep properties. Since some of it can dissolve in the matrix and promote solid solution strengthening, it is a desirable element to add. To obtain these effects, the Mn content should be 0.10% or higher. If the Mn content is less than 0.10%, the shape of the Fe-based intermetallic compounds in the ingot may become needle-like, potentially reducing the elongation of the base material. The Mn content may be 0.10% or higher, 0.15% or higher, 0.20% or higher, or 0.23% or higher. On the other hand, if the Mn content exceeds 0.40%, the Fe-based intermetallic compounds become coarse and abundant, leading to a decrease in formability due to an excessive increase in tensile strength. Furthermore, if the Mn content exceeds 0.40%, the amount of Mn dissolved in the ingot may become too high, potentially increasing the tensile strength of the base material too much. Therefore, the Mn content should be 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.

[0020] [Ti: 0.002~0.150%] Ti is an essential element because it acts as a grain refiner during casting, preventing casting cracks. While Ti can be added alone, coexisting with B (carbon) can provide an even stronger grain refinement effect, so alloy molten metal may be prepared using a rod hardener such as Al-5%Ti-1%B. To achieve this effect, the Ti content should be 0.002% or higher. If the Ti content is less than 0.002% by mass, the grain refinement effect during casting will be insufficient, potentially leading to casting cracks. The Ti content may also be 0.005% or higher, 0.008% or higher, 0.011% or higher, or 0.014% or higher. On the other hand, if the Ti content exceeds 0.150%, coarse intermetallic compounds such as TiAl3 may crystallize during casting, potentially leading to excessive tensile strength and reduced formability. Therefore, the Ti content should be 0.150% or less. The Ti content may be 0.125% or less, 0.100% or less, 0.075% or less, or 0.050% or less.

[0021] [B: Less than 0.05%] B is an optional additive element, and by coexisting with Ti, a stronger grain refinement effect can be expected compared to adding Ti alone. Of course, B may be added alone, but as mentioned above, the molten alloy may also be prepared 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 tends to stabilize into TiB2, reducing the grain refinement effect, and there is a risk that TiB2 will settle in the furnace and accumulate at the bottom. Therefore, the B content should be less than 0.05%. The B content may also be 0.04% or less, 0.03% or less, 0.02% or less, or 0.01% or less.

[0022] [V: Less than 0.03%] In this invention, V is an impurity. If the V content is 0.03% or more, relatively large Fe-based intermetallic compounds may crystallize during casting, and the elongation after cold rolling at a reduction ratio of 90% may be less than 5.0%, potentially resulting in poor formability. Therefore, the V content should be less than 0.03%. The V content may also be 0.02% or less, or 0.01% or less.

[0023] [Si: Less than 0.40%] In this invention, Si is an impurity. During casting, Si causes Fe-based intermetallic compounds such as Al-(Fe·Mn)-Si to crystallize, and some of it dissolves in the matrix, 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 becomes high, which may excessively increase the tensile strength and impair the formability. Therefore, the Si content should be less than 0.40%. The Si content may also 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.

[0024] [Cu: Less than 0.03%] In this invention, Cu is an impurity. If the Cu content is 0.03% or more, the elongation may decrease, resulting in poor moldability. Therefore, the Cu content should be less than 0.03%. The Cu content may also be 0.02% or less, or 0.01% or less.

[0025] [Mg: Less than 0.05%] In this invention, Mg is an impurity. If the Mg content is 0.05% or more, the formability of the base material will decrease, and work hardening may be significantly accelerated at high processing rates. Therefore, the Mg content should be 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.

[0026] [Other unavoidable impurities] Inevitable impurities are uncontrolled elements that inevitably mix in from the raw metal, return material, etc., and their acceptable content is, for example, less than 0.20% for Cr, less than 0.20% for Zn, less than 0.10% for Ni, less than 0.05% for Ga, less than 0.02% for each of Pb, Bi, Sn, Na, Ca, and Sr, and less than 0.05% for each of other elements, such as Co, Nb, Mo, and W. The effects of the present invention are not hindered even if uncontrolled elements are present within these ranges.

[0027] [Tensile strength: 100~170MPa] When thinning is required for aluminum alloys used as materials for deep-drawn products, appropriate strength and excellent formability are required. In this invention, the tensile strength (MPa) of the base material is used as an index to evaluate strength and formability. Since a tensile strength of less than 100 MPa may result in insufficient strength, it is preferable that the tensile strength be 100 MPa or higher. The tensile strength may also be 105 MPa or higher, 110 MPa or higher, 115 MPa or higher, or 120 MPa or higher. On the other hand, if the tensile strength exceeds 170 MPa, formability may decrease, so the tensile strength should be 170 MPa or lower. The tensile strength may also be 165 MPa or lower, 160 MPa or lower, 155 MPa or lower, 150 MPa or lower, 145 MPa or lower, or 140 MPa or lower.

[0028] [Ear rate: A value calculated using a predetermined formula, ranging from -2% to 2%] The edge ratio is an index that represents the anisotropy of the drawing that occurs when an aluminum alloy sheet is drawn. When a circular cut-out aluminum alloy sheet (blank) is used as a cup for drawing, the height from the bottom to the edge of the cup is not constant, and a protruding portion may occur at the edge. This protruding portion is what is known as the edge, and the edge ratio is an index that quantifies this edge. The edge is correlated with the texture of the aluminum alloy sheet, and is generally caused by the Cube orientation which is preferentially formed by recrystallization and the rolled texture which develops by rolling.

[0029] In this specification, one line drawn in the rolling direction of the aluminum alloy sheet, passing through the center of the circular blank in a plan view, is defined as the 0° line (the other line as the 180° line). Then, considering the lines forming a 45° angle (line 2), a 90° angle (line 3), a 135° angle (line 4), a 180° angle (line 5), a 225° angle (line 6), a 270° angle (line 7), and a 315° angle (line 8) in a counterclockwise direction with respect to the 0° line (line 1) passing through the center of the circular blank. Under these premises, for the cup after drawing, the distance from the bottom to the edge in the directions of lines 1, 3, 5, and 7 was compared with the distance from the bottom to the edge in the directions of lines 2, 4, 6, and 8. If the distance from the bottom to the edge in the directions of lines 1, 3, 5, and 7 was long, it was designated as a positive ear, and if the distance from the bottom to the edge in the directions of lines 2, 4, 6, and 8 was long, it was designated as a negative ear. That is, in the case of a positive ear, peaks appear in the directions of lines 1, 3, 5, and 7, and valleys appear in the directions of lines 2, 4, 6, and 8. On the other hand, in the case of a negative ear, valleys appear in the directions of lines 1, 3, 5, and 7, and peaks appear in the directions of lines 2, 4, 6, and 8. Under the above premises, for both positive and negative ears, the average distance from the bottom to the edge of the peak is defined as H1, and the average distance from the bottom to the edge of the valley is defined as H2. Then, for positive ears, the ear rate (%) is defined as the value shown by (H1-H2) / H2×100, and for negative ears, the ear rate (%) is defined as the value shown by -(H1-H2) / H2×100.

[0030] Under these premises, in this invention, a good yield is defined as a 0° ear rate (%) where the value calculated from (H1-H2) / H2×100 is 2% or less, and a good yield is defined as a 45° ear rate (%) where the value calculated from -(H1-H2) / H2×100 is -2% or more.

[0031] <Method for manufacturing aluminum alloy sheets for deep drawing> Next, a method for manufacturing an aluminum alloy sheet for deep drawing according to an embodiment of the present invention will be described. The following description is intended to illustrate a characteristic method for manufacturing an aluminum alloy sheet for deep drawing according to an embodiment of the present invention, and is not intended to limit the aluminum alloy sheet for deep drawing to one manufactured by the manufacturing method described below.

[0032] A method for manufacturing an aluminum alloy sheet for deep drawing according to an embodiment of the present invention is as follows: The above-mentioned method for manufacturing aluminum alloy sheets for deep drawing, A slab casting process to obtain an ingot from molten aluminum alloy having the above-mentioned component composition by a semi-continuous casting method, The ingot is subjected to a homogenization process that includes a homogenization treatment with a holding temperature of 520 to 620°C and a holding time of 1 hour or more. After the homogenization process, a hot rolling process is performed to obtain a hot-rolled plate by hot-rolling the ingot with the starting temperature set to less than 420-520°C. The aforementioned hot-rolled sheet is subjected to cold rolling to obtain a cold-rolled sheet, a cold rolling process before the continuous annealing process, A continuous annealing process is performed on the cold-rolled sheet, in which the sheet is heated to a temperature in the range of 350 to 550°C at an average heating rate of 1°C / second or more, and then continuously annealed at an average cooling rate of 1°C / second or more without holding or with holding for 10 minutes or less, in order to obtain an annealed sheet. If the annealed sheet is cold-rolled after the continuous annealing process, the cold-rolling process after the continuous annealing process is performed with a reduction ratio of 10 to 40%. It is characterized by including the following. Each process will be explained in detail below.

[0033] [Melting / refining process] First, the raw materials are placed in the melting furnace, and once the predetermined melting temperature is reached, flux is added as needed and stirred. Further degassing of the furnace is performed using a lance or the like if necessary, and then the mixture is allowed to settle and hold to separate the slag from the surface of the molten metal. In this melting and production process, it is important to add raw materials such as the master alloy again in order to obtain the predetermined alloy composition, but it is extremely important to allow sufficient settling time for the flux and slag to float and separate from the molten aluminum alloy to the surface. The settling time is usually preferably 30 minutes or more. 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, it may also be drawn directly from the melting furnace and cast, so a more desirable settling time is 45 minutes or more. 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.

[0034] Furthermore, during the melting process, in-line degassing or molten metal filtration using a specific filter may be performed as needed. The most common type of in-line degassing involves blowing an inert gas or the like into the molten aluminum from a rotating rotor, and diffusing and removing the hydrogen gas in the molten metal into bubbles of the inert gas. When nitrogen gas is used as the inert gas, it is important to control the dew point to, for example, -60°C or below (it may also be -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 / 100g or less (it may also be 0.18 cc / 100g or below, or 0.16 cc / 100g or below).

[0035] If the amount of hydrogen gas in the ingot is high, porosity may occur in the final solidification area of ​​the ingot. Therefore, it is preferable to suppress porosity by restricting the reduction ratio per pass in the hot rolling process to, for example, 7% or more (8% or more, or 9% or more). In addition, hydrogen gas supersaturated and dissolved in the ingot may crystallize even after the press forming of the base material, for example, during laser welding of the battery cover and battery container, depending on the heat treatment conditions of the cold-rolled coil, and may cause 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 (0.12 cc / 100 g or less, or 0.10 cc / 100 g or less).

[0036] [Slab casting process] The ingots are manufactured by semi-continuous casting (DC casting). In typical semi-continuous casting, the thickness of the ingot is generally around 400-600 mm, so the solidification and cooling rate in the center of the ingot is about 1°C / second. For this reason, especially when semi-continuous casting molten aluminum alloy with high Fe and Mn content, relatively coarse intermetallic compounds such as Al6(Fe·Mn) and α-Al-(Fe·Mn)-Si tend to crystallize from the molten aluminum alloy in the center of the ingot.

[0037] In semi-continuous casting, the casting speed is usually 50-70 mm / second, taking productivity into consideration, although this depends on the width and thickness of the ingot. This casting speed can also be 52-68 mm / second, 55-65 mm / second, or 58-62 mm / second. However, when performing in-line degassing, considering the actual residence time of the molten metal in the degassing tank, the degassing efficiency in the tank improves as the flow rate of molten aluminum (molten metal supply per unit time) decreases, depending on the degassing conditions such as the flow rate of the inert gas, and it is possible to reduce the amount of hydrogen gas in the ingot. Depending on the number of pours in the casting, it is desirable to restrict the casting speed to 50 mm / second or less in order to reduce the amount of hydrogen gas in the ingot. This casting speed may also be 45 mm / second or less, 40 mm / second or less, or 40 mm / second or less. On the other hand, a casting speed of less than 30 mm / second is undesirable because it reduces productivity, so the casting speed should be 30 mm / second or higher. Furthermore, when the casting speed is slow, the slope of the sump (solid / liquid phase interface) in the ingot becomes gentler, which helps prevent casting cracks. This casting speed may be 32 mm / second or higher, 34 mm / second or higher, or 36 mm / second or higher.

[0038] [Homogenization process] The ingots obtained by casting using a semi-continuous casting method are subjected to a homogenization treatment. The homogenization treatment is a process that involves holding the ingots at a high temperature to facilitate rolling, thereby eliminating casting segregation and residual stress within the ingots. In this invention, it is necessary to include a homogenization treatment in which the ingots are held at a holding temperature of 520 to 620°C for one hour or more. In this case, it is also a treatment to solidify to some extent the transition elements and other components that constitute the intermetallic compounds that crystallized during casting into the matrix. If the holding temperature is too low or too short, the solid solution may not proceed, and the surface finish after molding may not be smooth. Therefore, it is important to hold the ingots at a holding temperature of 520°C or higher for one hour or more. 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 more, 3 hours or more, 4 hours or more, or 5 hours or more. On the other hand, if the holding temperature is too high, there is a risk of so-called burning occurring, where the eutectic portion, which is the microscopic final solidification part of the ingot, melts. Therefore, the holding temperature may be 610°C or lower, 600°C or lower, or 590°C or lower. Furthermore, if this process includes treatment at a holding temperature of 520-620°C for one hour or more, it is also permissible to perform a subsequent treatment where the temperature is lowered and held for a certain period of time (for example, treatment at 480°C for one hour).

[0039] [Hot rolling process] Thus, by performing a homogenization treatment on the ingot with a holding temperature of at least 520-620°C and a holding time of at least 1 hour, and by setting the starting temperature for hot rolling to below 520°C, it is possible to reduce the amount of Mn and Si dissolved in the matrix. If the starting temperature for hot rolling is 520°C or higher, it becomes difficult to reduce the amount of Mn and Si dissolved in the matrix. Therefore, the starting temperature for hot rolling is below 520°C. The starting temperature for hot rolling may be 510°C or lower, 500°C or lower, or 490°C or lower. On the other hand, if the starting temperature for hot rolling is below 420°C, the roll pressure required for plastic deformation during hot rolling becomes high, and the reduction ratio per pass becomes too low, reducing productivity. Therefore, the starting temperature for hot rolling is 420°C or higher. The starting temperature for hot rolling may be 430°C or higher, 440°C or higher, or 450°C or higher. The ingots removed from the soaking furnace are then lifted by a crane and brought to a hot rolling mill. Depending on the model of the hot rolling mill, they are typically hot-rolled through multiple rolling passes to a predetermined thickness, such as 4-8 mm, and then wound into coils.

[0040] [Cold rolling process before continuous annealing process] Next, the hot-rolled sheet is subjected to cold rolling as follows to obtain a cold-rolled sheet. The coil wound in the hot-rolling mill is passed through the cold-rolling mill, and cold rolling is usually performed in multiple passes. At this time, work hardening occurs due to the plastic strain introduced by cold rolling, so annealing is performed as needed. This annealing is usually also a softening treatment, so depending on the material, the cold-rolled coil may be inserted into a batch furnace and held at a temperature of 300-400°C for more than one hour. If the holding temperature is below 300°C, softening will not be promoted. The holding temperature may be 310°C or higher, 320°C or higher, or 330°C or higher. On the other hand, if the holding temperature exceeds 400°C, productivity may decrease. The holding temperature may be 390°C or lower, 380°C or lower, or 370°C or lower.

[0041] [Continuous annealing process] The cold-rolled sheet obtained as described above is subjected to continuous annealing. In this invention, the annealing performed after the cold-rolling process described above is continuous annealing. Continuous annealing involves heating to a temperature range of 350 to 550°C at an average heating rate of 1°C / second or more, holding without holding or for 10 minutes or less, and cooling at an average cooling rate of 1°C / second or more to obtain an annealed sheet. The case of "without holding" refers to the use of annealing equipment with a rapid temperature rise, such as an electromagnetic induction furnace. For example, this includes simulating continuous annealing of a cold-rolled material at 425°C for 10 seconds by heating in a salt bath at 425°C for 15 seconds and then water-cooling. In contrast, the case of "holding for 10 minutes or less" refers to the use of a furnace with a relatively slow temperature rise, such as a hot air furnace. By performing continuous annealing under these conditions, crystal grains with recrystallized textures, such as Cube orientation, are more likely to grow during annealing, and as a result, a base material with an ear ratio of -2% to 2% can be obtained. In batch annealing, the heating process is relatively slow, causing intermetallic compounds to precipitate before softening occurs during annealing, thus inhibiting recrystallization. As a result, the rolled texture tends to remain, and the anisotropy in the base material increases, potentially leading to an ear ratio of less than -2% or greater than 2%. Therefore, batch annealing is not used in this annealing process.

[0042] If a cold rolling process is not performed after the continuous annealing process, for example, when there is no need to improve the tensile strength of the base material, the continuous annealing process becomes the final process, and the annealed material obtained in the continuous annealing process is used as the base material. On the other hand, if a cold rolling process is adopted after the continuous annealing process, for the purpose of improving the tensile strength of the base material, as described later, then another final annealing process may be performed after the cold rolling process.

[0043] [Cold rolling process after continuous annealing process] In this invention, a cold rolling process may be performed after the continuous annealing process to adjust the strength of the base material. In the cold rolling process after continuous annealing, the annealed sheet is cold-rolled to a reduction ratio of 40% or less to obtain the base material. By cold-rolling the annealed sheet, the tensile strength of the base material can be improved. If the reduction ratio exceeds 40%, not only will the base material become excessively work-hardened, but the rolled texture will increase, leading to higher anisotropy and potentially resulting in an ear ratio of less than -2% or greater than 2%. The reduction ratio may be 35% or less, 30% or less, 25% or less, or 20% or less. The lower limit of the reduction ratio is set at 10% as a realistic cold rolling ratio, considering that manufacturing at a lower reduction ratio is difficult. The reduction ratio may be 12% or more, 14% or more, or 15% or more.

[0044] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way to these examples. [Examples]

[0045] In the following embodiments, aluminum alloy sheets for deep drawing according to the present invention were manufactured under various conditions, and the tensile strength and edge ratio of the obtained aluminum alloy sheets for deep drawing were investigated.

[0046] [Preparation of the base material] Three levels of molten metal with compositions A to D, as shown in Table 1, were melted in a melting furnace, and ingots A to D with dimensions of 1190 mm wide x 560 mm thick x 3800 mm long were obtained using a semi-continuous casting machine (DC casting machine). Both sides of each ingot were milled, and they were placed in a soaking furnace and heated, followed by homogenization treatments at 590°C for 1 hour and 480°C for 1 hour in succession. Subsequently, they were hot-rolled to obtain 7.0 mm thick hot-rolled plates A to D, which were then wound into coils. After that, these hot-rolled plates A to D were cold-rolled to obtain 0.98 mm thick cold-rolled plates A to D, which were also wound into coils. Finally, cut plates of appropriate dimensions A to D were taken from these cold-rolled plates A to D.

[0047] [Table 1]

[0048] Next, for cut plates A to D, continuous annealing at 425°C for 10 seconds was simulated by heating them in a salt bath at 425°C for 15 seconds, followed by water cooling to obtain annealed plates A1, B1, C1, and D1, respectively. Separately, for cut plates A and C, batch annealing was simulated by inserting them into an annealer and subjecting them to annealing at 340°C for 1 hour to obtain annealed plates A2 and C2, respectively.

[0049] Annealed plate A1 that was not cold-rolled was used as the base material, as annealed plate A100. In contrast, annealed plate A1 was cold-rolled at reduction ratios of 18%, 30%, 40%, and 52%, respectively, and these were used as base materials, as cold-rolled material A118, cold-rolled material A130, cold-rolled material 140, and cold-rolled material A152.

[0050] Annealed sheet A2 that was not cold-rolled was used as the base material, designated as as-annealed sheet A200. In contrast, annealed sheet A2 was cold-rolled at reduction ratios of 18% and 30%, respectively, designated as cold-rolled material A218 and cold-rolled material A230, respectively, and used as the base material.

[0051] Annealed plates B1, C1, C2, and D1 were not subjected to cold rolling and were used as base materials, designated as as-annealed plates B100, C100, C200, and D100. In contrast, annealed plate C2 was cold-rolled at reduction ratios of 18% and 30%, respectively, and these were used as base materials, designated as cold-rolled materials C218 and C230.

[0052] [Measurement of tensile strength and earloop ratio] For these base materials A100 to D100, tensile strength was measured to evaluate appropriate strength and excellent formability, and the edge ratio was also measured to evaluate yield. For tensile strength, JIS No. 5 test specimens were prepared from each base material and tested in accordance with JIS Z22241, with the tensile direction parallel to the rolling direction. For edge ratio, circular blanks prepared from each base material were subjected to deep drawing to form cups, and the 45° edge ratio (%) as defined herein was measured. These results are shown in Table 2.

[0053] [Table 2]

[0054] Referring to Table 2, in Comparative Example 1, the reduction ratio during cold rolling exceeded 40%, resulting in excessive work hardening and preventing the tensile strength from being reduced to 160 MPa or less (poor formability). Furthermore, due to the excessive work hardening, the ear ratio could not be reduced to between -2% and 2%. In Comparative Examples 2 to 4, batch annealing was employed, resulting in a relatively slow heating rate. During annealing, Fe-based intermetallic compounds precipitated, inhibiting recrystallization, and a rolled texture remained, making it impossible to achieve an ear ratio between -2% and 2%. In Comparative Example 5, the Mn content exceeded 0.40%, causing a large number of Al-Fe-Mn intermetallic compounds to precipitate during annealing, inhibiting recrystallization, and resulting in a rolled texture remaining, making it impossible to achieve an ear ratio between -2% and 2%. In Comparative Examples 6-8, the Mn content exceeded 0.40%, which made it easier for the rolled texture to remain. Furthermore, the use of batch annealing caused Fe-based intermetallic compounds to precipitate, inhibiting recrystallization and resulting in the remaining rolled texture. As a result, it was not possible to achieve an ear ratio of -2% to 2%.

[0055] In contrast to these, Examples 1 to 6 satisfy all the requirements: a predetermined composition (especially Mn content: 0.4% or less), a predetermined cold rolling rate in the cold rolling process after the continuous annealing process (40% or less), and a predetermined annealing type (continuous annealing). As a result, we were able to obtain an Al-Fe-Mn aluminum alloy sheet with a tensile strength of 170 MPa or less (good formability) and an ear ratio of -2% to 2%, which is suitable for use as a material for deep-drawn products such as battery cases, possessing high strength, excellent formability, and a predetermined ear ratio. In addition, since Examples 1 to 5 all had a tensile strength of 100 MPa or more, they can be said to have strength that is more suitable as a material for deep-drawn products such as battery cases.

Claims

1. An aluminum alloy sheet for deep drawing, characterized by having a composition of less than 0.40% by mass of Fe, 0.10 to 0.40%, Ti, 0.002 to 0.150%, and B, with the remainder being Al and impurities, and having a restricted composition of less than 0.40% Si, less than 0.03% Cu, less than 0.05%, and less than 0.03% V as impurities, having a tensile strength of 170 MPa or less, and an ear ratio of -2% to 2% or less.

2. The aluminum alloy sheet for deep drawing according to claim 1, characterized in that it has a tensile strength of 100 to 160 MPa.

3. A method for manufacturing an aluminum alloy sheet for deep drawing according to claim 1 or 2, A slab casting step to obtain an ingot from molten aluminum alloy having the component composition described in claim 1 by a semi-continuous casting method, The ingot is subjected to a homogenization process that includes a homogenization treatment with a holding temperature of 520 to 620°C and a holding time of 1 hour or more. After the homogenization process, a hot rolling process is performed to obtain a hot-rolled plate by hot-rolling the ingot with the starting temperature set to less than 420 to 520°C. The aforementioned hot-rolled sheet is subjected to cold rolling to obtain a cold-rolled sheet, a cold rolling process before the continuous annealing process, A continuous annealing step is performed on the cold-rolled sheet, heating it to a temperature in the range of 350 to 550°C at an average heating rate of 1°C / second or more, holding it without holding time or for 10 minutes or less, and then performing continuous annealing at an average cooling rate of 1°C / second or more to obtain an annealed sheet. If the annealed sheet is cold-rolled after the continuous annealing process, the cold-rolling process after the continuous annealing process is performed with a reduction ratio of 10 to 40%. A method for manufacturing aluminum alloy sheets for deep drawing, characterized by including the following:

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