Aluminum alloy foil, and method for producing aluminum alloy foil

Abstract

An aluminum alloy foil has a composition containing 1.0% to 1.8% by mass of Fe, 0.01% to 0.10% by mass of Si, 0.005% to 0.05% by mass of Cu, and Mn regulated to be 0.01% by mass or less, with the balance Al and incidental impurities, wherein with regard to crystal grains surrounded by high inclination angle grain boundaries which are grain boundaries having a misorientation of 150 or more in analysis of crystal orientation per unit area using electron backscatter diffraction, an average grain size of the crystal grains is 5 m or less, and a maximum grain size of the crystal grains/the average grain size of the crystal grains <3.0, and when a thickness of the foil is 30 m, elongations in directions making 15, 450 and 90 with respect to a rolling direction are 25% or more respectively.

Claims

1. An aluminum alloy foil having a composition containing 1.0% by mass or more and 1.8% by mass or less of Fe, 0.01% by mass or more and 0.10% by mass or less of Si, 0.005% by mass or more and 0.05% by mass or less of Cu, Mn regulated to be 0.01% by mass or less, and the balance Al and incidental impurities, wherein: with regard to crystal grains surrounded by high inclination angle grain boundaries which are grain boundaries having a misorientation of 15° or more in analysis of crystal orientation per unit area using electron backscatter diffraction, an average grain size of the crystal grains is 5 μm or less, and a maximum grain size of the crystal grains/the average grain size of the crystal grains is ≤3.0; when a thickness of the foil is 30 μm, elongations in directions making 0°, 45° and 90° with respect to a rolling direction are 25% or more respectively; and in analysis of crystal orientation per unit area using electron backscatter diffraction, when grain boundaries having a crystal misorientation of 15° or more are defined as high inclination angle grain boundaries, grain boundaries having a crystal misorientation of 2° or more and less than 15° are defined as low inclination angle grain boundaries, an average length of the high inclination angle grain boundaries is defined as L1, and an average length of the low inclination angle grain boundaries is defined as L2, L1/L2 >2.0.

2. A method for producing the aluminum alloy foil according to claim 1, comprising: subjecting an ingot of an aluminum alloy having said composition to homogenization treatment comprising holding the ingot at 420° C. to 480° C. for 6 hours or more, and after the homogenization treatment, subjecting the ingot to hot rolling such that a rolling finishing temperature becomes 230° C. or more and less than 300° C., and then during subsequent cold rolling, performing intermediate annealing at 300° C. to 400° C. to achieve a final cold-rolling rate after the intermediate annealing of 92% or more.

Description

BRIEF DESCRIPTION OF DRAWING

(1) FIG. 1 shows the plane shape of a square type punch for use in an ultimate forming height test in Examples according to the present invention.

DESCRIPTION OF EMBODIMENTS

(2) A method for producing an aluminum alloy foil according to one embodiment of the present invention will be described.

(3) As an aluminum alloy, an aluminum alloy ingot was produced in such a way that the aluminum alloy ingot is produced to have a composition containing 1.0% by mass or more and 1.8% by mass or less of Fe, 0.01% by mass or more and 0.10% by mass or less of Si, 0.005% by mass or more and 0.05% by mass or less of Cu, and containing Mn regulated to be 0.01% by mass or less, with the balance consisting of Al and other incidental impurities. The method for producing an ingot is not limited in particular, and can be performed by a conventional method such as semi-continuous casting. The resulting ingot is subjected to homogenization treatment involving holding the ingot at 400 to 480° C. for 6 hours or more.

(4) After homogenization treatment, hot rolling is performed, and a rolling finishing temperature is set to 230° C. or more and less than 300° C. Subsequently, cold rolling is performed, and intermediate annealing is performed in the course of the cold rolling. In the intermediate annealing, the temperature is set to 300° C. to 400° C. The time for intermediate annealing is preferably 3 hours or more and less than 10 hours. In the case where the time for intermediate annealing is less than 3 hours, when the annealing temperature is low temperature, softening of the material is likely to be insufficient, and annealing for a prolonged time of 10 hours or more is not preferable in an economical viewpoint.

(5) Cold rolling after intermediate annealing corresponds to the final cold rolling, and final cold-rolling rate in this cold rolling is 92% or more. The thickness of the foil is not limited in particular, and can be, for example, 10 μm to 40 μm.

(6) The resulting aluminum alloy foil has excellent elongation properties, and when the thickness of this aluminum alloy foil is, for example, 30 μm, the elongation in each of directions making 0°, 45° and 90° with respect to a rolling direction is 25% or more.

(7) Also, in analysis of crystal orientation per unit area using electron backscatter diffraction (EBSD), an average size of crystal grains surrounded by high inclination angle grain boundaries which are grain boundaries having a misorientation of 15° or more is 5 μm or less, and a maximum grain size of the crystal grains/the average grain size of the crystal grains ≤3.0, and as a result of this, the crystal grains become fine. As a result, surface deteriorations on the deformed surface can be suppressed.

(8) In addition, in analysis of crystal orientation per unit area using electron backscatter diffraction (EBSD), when grain boundaries having a misorientation of 15° or more are defined as high inclination angle grain boundaries, grain boundaries having a misorientation of 2° or more and less than 15° are defined as low inclination angle grain boundaries, a length of the high inclination angle grain boundaries is defined as L1, and a length of the low inclination angle grain boundaries is defined as L2, L1/L2>2.0. As a result of this, higher high elongation has been achieved.

(9) In the aluminum alloy foil, the density of the intermetallic compound is desirably satisfies the following definition.

(10) The Density of an Al—Fe Based Intermetallic Compound Having a Grain Size of 1 μm or More and Less than 3 μm: 1×10.sup.4/Mm.sup.2 or More

(11) The grain size of 1 μm or more is generally said to be a grain size which will be a nucleation site in recrystallization, and as a result of the distribution of such intermetallic compounds in a highly dense manner, it tends to obtain recrystallized fine grains in the annealing. When the grain size is less than 1 μm, or the density is less than 1×10.sup.4/mm.sup.2, the intermetallic compound tends not to serve as a nucleation site in recrystallization, and a grain size of more than 3 μm tends to result in pin holes in the rolling and decrease in the elongation. Therefore, the density of an Al—Fe based intermetallic compound having a grain size of 1 μm or more and less than 3 μm is desirably in the above range.

(12) The Density of an Al—Fe Based Intermetallic Compound Having a Grain Size of 0.1 μm or More and Less than 1 μm: 2×10.sup.5/Mm.sup.2 or More

(13) In general, it is said that the above-described size tends not to result in a nucleation site in recrystallization; however, the results are obtained, in which it is believed that grain refining and recrystallization behavior is highly influenced by the above-described size. An overall picture of this mechanism has not become apparent; however, as a result of the coarse intermetallic compounds having a grain size of 1 to 3 μm, and in addition, as a result of the fact that the fine compounds less than 1 μm are present in a highly dense manner, it has been confirmed that the recrystallized grains after the final annealing are refined, and decrease in the length of HAGBs/the length of LAGBs is suppressed. This is likely to promote grain division (Grain subdivision mechanism) in cold rolling.

(14) Therefore, it is desirable that the density of the Al—Fe based intermetallic compound having a grain size of 0.1 μm or more and less than 1 μm is in the above range.

(15) The resulting aluminum alloy foil can be deformed by press forming and the like, and can be conveniently used as, for example, a packaging material for food and lithium ion batteries. Applications of the aluminum alloy foil of the present invention are not limited to those described above, and the aluminum alloy foil of the present invention can be used for suitable applications.

EXAMPLES

(16) Ingots of an aluminum alloy having a composition shown in Table 1 were produced by semi-continuous casting method. Subsequently, under production conditions shown in Table 1 (the conditions of homogenization treatment, the finishing temperatures of hot rolling, the sheet thickness in intermediate annealing, the condition of intermediate annealing and the final cold-rolling rates), the resulting ingots were subjected to homogenization treatment, hot-rolled, cold-rolled, subjected to intermediate annealing, and again cold rolled, to produce aluminum alloy foils.

(17) The thickness of the foils was 30 μm.

(18) The resulting aluminum alloy foil was subjected to the measurement and evaluation described below.

(19) Tensile Strength and Elongation

(20) Both of the tensile strength and the elongation were determined by a tensile test. The tensile test was in accordance with JIS Z 2241, and a test piece of JIS No. 5 was obtained from the sample in such a way that elongation in each of directions making 0°, 45° and 90° with respect to a rolling direction can be measured, and the test piece was tested at a stretching speed of 2 mm/min by using a universal tensile testing machine (AGS-X 10 kN manufactured by Shimadzu Corporation). The calculation of the elongation rate is as follows. First of all, before the test, two lines are made as markings at the center of the test piece in a longitudinal direction in a direction perpendicular to the test piece with an interval of 50 mm, which is a gauge distance. After the test, the fracture surfaces of the aluminum alloy foil were opposed against one another to determine a distance between the markings, and the amount of elongation (mm) obtained by subtracting the gauge distance (50 mm) from the distance between the markings was divided by the distance between gauge marks (50 mm) to determine the elongation rate (%).

(21) The measurement results of elongation (%) and tensile strength (MPa) at each of the directions are shown in Table 2.

(22) Grain Size

(23) After subjecting a surface of the foil to electrolytic polishing, crystal orientation analysis was performed by SEM (Scanning Electron Microscope)-EBSD, and grain boundaries having a misorientation between the crystal grains of 15° or more was defined as HAGBs (high inclination angle grain boundary) to determine the size of the crystal grains surrounded by HAGBs. Three fields of view were measured at a magnification factor of ×1000 by using the size of field of view of 45×90 μm to calculate the average grain size, and the maximum grain size/the average grain size. The individual grain size was calculated by using the equivalent circle diameter, and an Area method (Average by Area Fraction Method) of EBSD was used to calculate the average grain size. OIM Analysis manufactured by TSL Solutions company was used for this analysis.

(24) Length of HAGBs/Length of LAGBs

(25) After subjecting a surface of the foil to electrolytic polishing, crystal orientation analysis was performed by SEM-EBSD to observe high inclination angle grain boundaries (HAGBs) having a misorientation between the crystal grains of 15° or more, and low angle grain boundaries (LAGBs) having a misorientation of 2° or more and less than 15°. Three fields of view were measured at a magnification factor ×1000 by using the size of field of view of 45×90 μm to determine the length of HAGBs and the length of LAGBs within these fields of view, and the ratio of the length of HAGBs and the length of LAGBs was calculated. The calculated ratios are shown as HAGBs/LAGBs in Table 2.

(26) Ultimate Forming Height

(27) The forming height was evaluated by a square-tube forming test. The test was performed by using a universal thin sheet forming testing machine (model 142/20 manufactured by ERICHSEN company), and an aluminum foil having a thickness of 30 μm was employed for this test by using a square type punch (the length L of one side=37 mm, and the chamfering diameter R of a corner=4.5 mm) having a shape shown in FIG. 1. With regard to the test conditions, wrinkle restraining force was set to 10 kN, and the scale of the moving-up speed of punch (forming rate) was set to 1, and subsequently, a mineral oil was applied onto one face of the foil (a face to be in contact with the punch) as a lubricant. The foil was formed by contacting a punch moving up from the lower part of the apparatus to the foil, and at this time, the maximum height to which the punch has moved up in the case where the forming could be accomplished without cracking and pin holes in continuous forming of three times was defined as the ultimate forming height (mm) of the material of interest. The height of the punch was changed with intervals of 0.5 mm.

(28) The Density of the Intermetallic Compound

(29) With regard to the intermetallic compound, a parallel section (RD-ND plane) of the foil was cut by using a CP (Cross section polisher) and was observed by using a field-emission scanning electron microscope (FE-SEM: NVision40 manufactured by Carl Zeiss company). With regard to the “Al—Fe based intermetallic compounds having a grain size of 1 μm or more and less than 3 μm”, five fields of view observed at a magnification factor ×2000 were subjected to image analysis to calculate the density of the intermetallic compounds having such a grain size. With regard to the “Al—Fe based intermetallic compounds having a grain size of 0.1 μm or more and less than 1 μm”, 10 fields of view observed at a magnification factor ×10000 were subjected to image analysis to calculate the density of the intermetallic compounds having such a grain size. The calculation results are shown in Table 2.

(30) TABLE-US-00001 TABLE 1 Production conditions Homogenization Hot rolling Intermediate annealing Final cold- Chemical component treatment finishing Sheet rolling (mass %) Temperature Time temperature thickness Temperature Time reduction rate No. Si Fe Cu Mn (° C.) (h) (° C.) (mm) (° C.) (h) (%) Examples 1 0.05 1.5 0.01 0.004 460 8 247 1.2 360 4 97.5 2 0.02 1.4 0.008 0.005 460 8 239 1.2 400 4 97.5 3 0.08 1.6 0.01 0.003 460 8 260 1.2 330 4 97.5 4 0.03 1.1 0.012 0.003 420 10 252 1.2 360 4 97.5 5 0.06 1.7 0.009 0.005 470 6 281 1 360 4 97.0 6 0.03 1.5 0.006 0.009 460 10 255 1.2 360 3 97.5 7 0.05 1.4 0.03 0.001 460 8 267 0.8 330 4 96.3 Comparative 8 0.13 1.3 0.01 0.004 460 8 249 1.2 360 4 97.5 Examples 9 0.05 0.8 0.008 0.005 420 10 238 1.2 360 4 97.5 10 0.08 2.0 0.01 0.005 460 8 280 1.2 330 4 97.5 11 0.06 1.5 0.001 0.003 460 10 257 1.2 330 4 97.5 12 0.04 1.4 0.07 0.005 450 8 247 1.2 360 4 97.5 13 0.02 1.5 0.01 0.03 460 8 271 1.2 360 4 97.5 14 0.05 1.5 0.01 0.004 350 3 220 1.2 400 4 97.5 15 0.05 1.5 0.01 0.004 530 8 294 1.2 360 4 97.5 16 0.03 1.5 0.006 0.009 480 8 330 1.2 330 4 97.5 17 0.08 1.6 0.01 0.003 460 8 245 1.2 250 3 97.5 18 0.08 1.6 0.01 0.003 460 8 270 1.2 450 3 97.5 19 0.05 1.5 0.01 0.004 420 10 248 0.23 330 3 87.0 20 0.05 1.5 0.01 0.004 470 6 289 None — — 99.3

(31) TABLE-US-00002 TABLE 2 Crystallized grain structure Average Intermetallic compound Mechanical properties Ultimate grain size Grain size HAGBs/ 1.0~3.0 μm 0.1~1.0 μm Elongation (%) Tensile strength (MPa) bulging height No. (μm) ratio LAGBs (×10.sup.4/mm.sup.2) (×10.sup.5/mm.sup.2) 0° 45° 90° 0° 45° 90° (mm) Examples 1 4.0 2.3 3.5 1.7 2.2 27.5 31.2 26.8 108 99 103 9.5 2 3.4 2.0 3.3 1.8 2.5 28.4 31.8 27.9 110 101 106 10.0 3 4.6 2.6 3.0 1.5 2.2 26.5 30.4 26.0 106 96 100 9.5 4 4.8 2.8 3.8 1.1 2.0 25.8 29.1 25.4 103 98 100 9.5 5 3.9 2.4 2.9 1.9 2.3 27.2 30.6 26.5 108 98 103 9.5 6 4.8 2.7 3.9 1.7 2.3 26.1 28.8 26.3 102 94 101 9.5 7 3.6 2.2 3.5 1.7 2.2 27.4 32.3 26.8 112 103 106 9.5 Comparative 8 6.4 2.8 3.6 1.5 1.1 21.6 27.0 21.2 96 91 94 8.0 Examples 9 6.9 3.3 3.0 0.8 1.2 20.4 26.2 19.9 88 80 86 8.0 10 4.7 2.6 2.6 2.2 1.6 22.7 28.3 21.5 110 99 104 8.5 11 12.2 6.4 1.8 1.7 2.2 17.5 24.1 16.9 92 89 91 7.5 12 4.3 2.5 2.3 1.8 2.2 24.7 30.6 23.9 120 111 116 8.5 13 3.2 2.9 1.6 1.5 2.0 23.5 31.4 23.0 114 105 110 8.5 14 4.4 5.4 2.2 1.3 0.5 23.9 29.1 23.0 114 103 109 8.5 15 5.3 3.4 2.3 1.5 1.8 24.8 30.1 24.2 106 99 103 9.0 16 6.2 4.2 2.9 1.7 2.5 22.3 27.2 21.7 96 90 94 8.0 17 5.0 3.8 1.3 1.6 1.9 23.5 30.2 22.8 107 98 101 8.5 18 5.8 2.5 2.8 1.6 1.8 24.3 29.0 23.9 100 92 96 8.5 19 7.2 2.6 2.7 1.7 2.3 22.2 24.6 22.4 94 89 93 8.0 20 3.2 2.5 1.1 1.7 1.5 22.4 34.6 21.6 124 106 114 8.0

(32) As shown in Table 2, in Examples 1 to 7 that satisfy the definitions according to the present invention, good results has been achieved with regard to the elongation, the tensile strength and ultimate bulging height, and by contrast to this, good results have not been achieved in Comparative Examples 8 to 20 that do not satisfy one or more of the definitions according to the present invention.