KR101536772B1 - Aluminum alloy plate for battery case with excellent laser welding property - Google Patents

Abstract

The present invention provides an aluminum alloy sheet material for a battery case lid having excellent laser welding performance and excellent laser weldability capable of achieving a good melting state even at low output. The aluminum alloy sheet material has a composition of Fe: 1.4% to 2.0% Cu: 0.2% or less, Mg: and contains more than 0.2%, the balance is composed of a composition of aluminum alloys having made of Al and unavoidable impurities, 40 a is an intermetallic compound of less than 2 ㎛ than 5 ㎛ in the matrix 10000 ㎛ ² gae Or more.

Description

TECHNICAL FIELD [0001] The present invention relates to an aluminum alloy sheet for a battery case cover,

The present invention relates to an aluminum alloy plate excellent in workability and laser weldability for a lithium ion battery case cover used for a portable telephone, a notebook type personal computer and the like.

Aluminum-Mn-based A3003 aluminum alloy plates have begun to be used for lithium ion battery case materials in place of steel plates and stainless steel plates, because parts that are incorporated in portable telephones or notebook personal computers are strongly required to be lightweight.

In a prismatic battery case formed by combining drawing and ironing of a plurality of processes, the Al-Mn-based A3003 aluminum alloy is used as a material capable of reducing the thickness of the casing while maintaining a glossy and beautiful surface state. to be. Thinning is an important factor in increasing the capacity of the battery, which is directly related to an increase in internal volume, and the rectangular cell case is sealed with a pure aluminum alloy A1050 alloy covering material by laser welding.

However, in the lithium ion battery which repeats charging and discharging, the internal pressure rises and the temperature rises during the reaction, so that the aluminum alloy sheet under this condition is creep deformed, resulting in an increase in the thickness of the battery case If the amount of deformation of the thickness is large, the influence (failure, breakage, etc.) on the apparatus may be caused.

In addition, the pure aluminum alloy used for the covering material is not preferable because it has a high thermal conductivity as compared with the A3003 alloy system, and the penetration tends to be shallow from the viewpoint of laser weldability. Although it is possible to increase the laser welding output to obtain a predetermined penetration depth, there is a possibility that the internal structure of the battery case may be damaged by the increase of the heat input energy. The battery case lid member is provided with an explosion-proof function for locally thinning the plate thickness (about 20 mu m) for the purpose of mitigating the pressure rise inside the battery.

In recent years, lithium ion batteries are required to have higher capacity, and it has become a challenge to increase the inner volume without increasing the outer dimensions of the battery case. For this reason, the material has to be made thinner, but when it becomes thinner, creep deformation tends to occur, and therefore an aluminum alloy sheet for a battery case which is not easily deformed by creep is required.

The prismatic battery case material is required to have more rigorous formability than the drawing-ironing process used in the beverage can forming, and it is also important that there is practically no problem with the laser welding property. As a material satisfying such characteristics, for example, a material containing 1% to 1.5% of Mn, 0.3% to 0.8% of Mg, 0.3% to 0.6% of Cu, 0.05% to 0.25% of Si and 0.2% Al) and inevitable impurities (Japanese Patent Laid-Open No. 2004-156138). In consideration of moldability, an aluminum alloy sheet containing 0.3% to 1.5% of Mn and 1.0% to 1.8% of Fe and consisting of the remaining Al and inevitable impurities has also been proposed (JP-A-2003-7260) .

Use of the above material for the battery case lid material is considered to be advantageous from the viewpoint of laser weldability, but since the material strength is higher than that of the pure aluminum-based alloy, it is difficult to form an explosion proofing function. Further, in the alloy system containing a large amount of Fe and Mn, a coarse intermetallic compound is easily formed at the time of casting, and if such a coarse intermetallic compound exists in the forming processing section imparting explosion-proofing function, It is undesirable as a starting point.

(Japanese Unexamined Patent Publication (Kokai) No. 2007-107048) discloses an aluminum alloy plate for a battery case containing as main components 0.4% to 0.6% of Mn and 1.15% to 1.35% of Fe and exhibits excellent explosion-proofing properties. The specific characteristics are unclear, and all of the aluminum alloy sheets proposed above do not have the characteristics that must be satisfied as a material for the lithium ion battery case cover.

The inventors have found that the presence of an intermetallic compound containing Fe functions to improve the depth of penetration during laser welding as a result of repeated testing and examination of the structure of an aluminum material for improving laser weldability . The present inventors have clarified the reason for this, and as a result, it has been found that a large number of these intermetallic compounds are dispersed, the absorption rate of YAG laser light used in the laser welder is increased, and the absorbed light becomes heat energy to melt the material.

The object of the present invention is to provide a laser welding method and a laser welding method capable of achieving good welding performance even with low output power, And an aluminum alloy sheet for a case cover.

In order to achieve the above-mentioned object, an aluminum alloy sheet material for a battery case cover having an excellent laser weldability according to claim 1 has a composition of Fe: 1.4 to 2.0%, Si: 0.3% or less, Cu: 0.2% And an aluminum alloy having a composition consisting of Al and inevitable impurities, wherein the matrix contains at least 40 intermetallic compounds of 2 占 퐉 or more and 5 占 퐉 or less per 10000 占 퐉 ² . With this configuration, there is provided an aluminum alloy plate for a battery case lid having good laser weldability without compromising processability.

The aluminum alloy sheet for a battery case cover according to claim 2 is characterized in that the aluminum alloy further contains Mn: not less than 0.05% and not more than 0.3%. By the inclusion of Mn, the laser weldability can be further improved.

The aluminum alloy sheet for a battery case cover according to claim 3, wherein the aluminum alloy comprises 0.01 to 0.2% Zr, 0.01 to 0.2% Cr, Or two kinds thereof. With this constitution, the recrystallized structure can be made finer, the molding processability can be enhanced, and weld cracking can be suppressed.

According to the present invention, it is possible to obtain a deeper penetration than the pure aluminum-based alloy plate material of the conventional material with the same heat input during laser welding, and particularly, to provide an aluminum An alloy sheet is provided.

The significance of the alloy component in the aluminum alloy sheet for the battery case cover according to the present invention and the reason for its limitation will be described.

Fe: Fe functions to improve the depth of penetration during laser welding in a state in which Fe exists as an intermetallic compound, as described above. If the Fe content is less than 1.4% (mass%, the same is true hereinafter), the penetration depth is not sufficient and the bonding strength is lowered. If it is contained in an amount of more than 2.0%, a crystallized product (intermetallic compound) of 100 m or more is formed at the time of casting, and is present as a compound of 15 m or more in the state of the product plate. The existence of these coarse intermetallic compounds in the part becomes a starting point of cracking. A more preferable content of Fe is 1.5% to 1.7%.

Mn: Mn also bonds with Al or Fe to form an intermetallic compound, thereby improving the penetration depth during laser welding. If the content is less than 0.05%, the effect is not sufficient. If the content is 0.3% or more, a large Al-Fe-Mn-based intermetallic compound of 100 탆 or more tends to be formed at the time of casting.

Si: Si is mixed as an impurity. However, if the content exceeds 0.3%, the strength is increased and the formability tends to be lowered. Therefore, it is preferable to regulate Si to 0.3% or less. In order to reduce the amount of Si, a base metal of high purity is used, and the production cost is increased. Therefore, the Si content is preferably in the range of 0.05% to 0.15%.

Cu, Mg: Cu, and Mg are easily evaporated during laser welding, causing fumes, which may cause welding failure. Therefore, it is preferable to control Cu to 0.2% or less and Mg to 0.2% or less.

Zr, Cr: Zr, and Cr are effective elements because they make the recrystallized structure finer and improve the moldability. In addition, there is an action of suppressing weld cracking. The preferred content is in the range of 0.01 to 0.2% of Zr and 0.01 to 0.2% of Cr, respectively. When the lower limit is less than the upper limit, the above effect is not sufficient. If the upper limit is exceeded, Gender deteriorates.

Ti and B: Minimize the texture of the ingot and function so that the formability of the product plate is stabilized at a high level. Therefore, Ti is preferably not less than 0.01% and not more than 0.2%, B is not less than 5 ppm and not more than 100 ppm One or two of them may be contained.

Intermetallic compound dispersion state: As described above, when the dispersion state of the intermetallic compound containing Fe greatly affects the laser weldability and the intermetallic compound is observed with an optical microscope, the size is 2 μm to 5 μm In the case where there are 40 or more intermetallic compounds per 10000 μm ² , penetration during laser welding is significantly deepened. This is because the laser absorption rate is increased by the intermetallic compound as described above. Further, the additive element and the impurity are easily segregated at the interface between the intermetallic compound and the matrix and the melting point is lowered.

It is difficult to accurately grasp the dispersed state by an optical microscope and the superiority of the laser weldability is judged by accurately distinguishing the dispersion state in the range of 2 탆 to 5 탆 . Intermetallic compounds exceeding 5 탆 have little influence on laser weldability. In addition, since the coarse intermetallic compound having a particle size exceeding 15 mu m becomes a starting point of cracking in the processing of a molded part (about 20 mu m in thickness) for imparting an explosion-proof function and cracks tend to occur near the intermetallic compound, It is necessary to inhibit the formation of an intermetallic compound. When the intermetallic compound having 2 to 5 占 퐉 is less than 40 per 10000 占 퐉 ² , it is difficult to obtain a sufficient effect. The upper limit of the number is not specifically defined, but the upper limit is naturally determined by the composition and the manufacturing process, and the upper limit is about 70 to 100 in practice.

In the aluminum alloy sheet material for a battery case cover of the present invention, the ingot mass is homogenized and hot rolled in accordance with a conventional method, subjected to intermediate heat treatment if necessary, cold rolled to a final sheet thickness, Heat treatment is used. As the battery case lid member, it is preferable to use the battery case lid member as a soft fire (O material) in consideration of moldability and explosion-proof function. In order to have 40 or more intermetallic compounds having a diameter of 2 to 5 占 퐉 per 10000 占 퐉 ² , the homogenization treatment is carried out in a temperature range of 550 占 폚 to 620 占 폚 for 2 hours or more, Or more, and the rolling degree of the cold rolling is preferably 50% or more.

<Examples>

Hereinafter, the embodiment of the present invention will be described in comparison with the comparative example, and the effect thereof will be demonstrated. These embodiments show one embodiment of the present invention, and the present invention is not limited thereto.

<Examples and Comparative Examples>

The aluminum alloy having the composition shown in Table 1 was subjected to semi-continuous casting. Further, 0.01% of Ti and 50 ppm of B were added to the aluminum alloy. The obtained ingot was homogenized, hot rolled, and cold rolled according to a conventional method to prepare a plate having a thickness of 0.8 mm. Thereafter, final heat treatment was performed at a temperature of 380 DEG C, and the obtained plate material was evaluated as the test material in the following manner. The evaluation results are shown in Table 2. Also, in Tables 1 to 2, those that are outside the conditions of the present invention are underlined.

alloy
Composition (mass%) Fe Mn Si Cu Mg Zr Cr A
B
C
D
E
F
G
H 1.45
1.56
1.60
1.82
1.60
1.74
1.65
1.52 0.07
-
-
-
0.12
-
-
- 0.12
0.09
0.14
0.17
0.08
0.11
0.13
0.09 0.02
0.02
0.01
0.01
0.01
0.01
0.01
0.02 0.02
0.02
0.02
0.01
0.02
0.02
0.01
0.01 -
-
-
-
-
-
0.08
- -
-
-
-
-
-
-
0.13 I
J
K
L
M
N
O
P
Q 1.15
0.95
1.21
2.10
1.75
1.45
1.64
1.57
0.33 -
-
0.45
0.58
1.05
-
0.48
-
- 0.09
0.09
0.09
0.08
0.08
0.09
0.51
0.09
0.09 0.02
0.01
0.02
0.02
0.01
0.01
0.02
0.45
0.02 0.01
0.02
0.02
0.01
0.01
0.02
0.02
0.67
0.01 -
-
-
-
-
0.37
-
-
- -
-
-
-
-
-
0.35
-
-

Tensile properties: A JIS No. 5 test piece specified by JIS Z 2201 was prepared and subjected to a tensile test according to JIS 2241 at room temperature. When the tensile strength is less than 130 MPa as an index of moldability, it is acceptable. When the tensile strength is 130 MPa or more, the processability is inferior.

Microstructure: The microstructure of the test material was observed with an optical microscope, and an intermetallic compound having a size in the range of 2 탆 to 5 탆 was measured using an image analyzer to find the number per 10000 탆 ² . Also, the coarse intermetallic compound exceeding 15 탆 was also measured, and even one coarse intermetallic compound having an average particle size exceeding 15 탆 was observed as an index of moldability.

Laser weldability: The laser output was set to 210 W using a semiconductor excitation pulse oscillation type YAG laser (HP300? Manufactured by Kataoka Seisakusho Co., Ltd.), and the test piece was moved at 900 mm / minute to measure the maximum penetration depth Respectively. Five sections were observed at intervals of 2 ㎝ in the measurement, and the average value of the maximum penetration depth was calculated. It was judged that the penetration depth was not less than 200 占 퐉 and less than 200 占 퐉 was not welded.

Test material
synthesis
gold Seal
burglar
MPa History
(Proof load)
MPa kidney
(%)
Number of intermetallic compounds
/ 10000 탆 ² laser
Weldability 2 탆 to 5 탆 15 ㎛ or more Penetration depth ㎛ One
2
3
4
5
6
7
8 A
B
C
D
E
F
G
H 108
104
107
112
115
110
112
110 44
43
52
55
56
51
48
44 40
39
41
40
38
40
41
40 45
47
48
52
49
45
44
43 0
0
0
0
0
0
0
0 216
220
222
240
236
235
230
215 9
10
11
12
13
14
15
16
17 I
J
K
L
M
N
O
P
Q 105
65
108
132
133
107
131
143
87 42
36
58
60
62
43
62
80
26 40
42
40
37
37
38
35
33
42 35
30
38
53
54
45
50
46
7 0
0
0
One
3
One
One
0
0 190
185
195
245
250
206
238
195
177

, It had an elongation of 38% or more and had good tensile properties without any problems in the molding of the cover material. There were more than 40 intermetallic compounds of 2 탆 to 5 탆 in size per 10000 탆 ² , and no intermetallic compound of 15 탆 or larger was present. Also, after laser welding, a penetration depth of 200 μm or more was obtained.

On the other hand, in the test materials 9, 10 and 11, the number of intermetallic compounds decreases because the amount of Fe added is small, and sufficient penetration depth is not obtained. The test material 12 contains an intermetallic compound exceeding 15 탆 due to a large amount of addition of Fe and Mn, and there is a problem in formability as a battery case lid material. The test material 13 contains a large amount of Mn and has an intermetallic compound of more than 15 탆, which is problematic in terms of formability as a battery case lid.

The test material 14 contains an intermetallic compound exceeding 15 탆 due to a large amount of Zr added, which poses a problem of moldability as a battery case lid material. The test material 15 contains an intermetallic compound exceeding 15 탆 due to a large amount of Cr added, which poses a problem of moldability as a battery case lid material. The amount of Mg and Cu added to the test material 16 is so large that the laser weldability is impaired and a sufficient penetration depth is not obtained. The test piece 17 is a conventional 1050 material, and the intermetallic compound number is small and sufficient penetration depth is not obtained.

Claims (4)

At most 0.3% of Si, at most 0.2% of Cu, at most 0.2% of Mg, at least 0.05% of Mn and less than 0.3% of Fe, and the balance Al and inevitability Wherein the aluminum alloy sheet has an average of at least 40 intermetallic compounds of 2 占 퐉 or more and 5 占 퐉 or less per 10000 占 퐉 ^{2 in the} matrix. delete The battery case according to claim 1, wherein the aluminum alloy further contains one or two of Zr: 0.01% to 0.2% and Cr: 0.01% to 0.2% Aluminum alloy sheet. delete