JP6033141B2 - Aluminum alloy plate for large rectangular battery case - Google Patents

Description

  The present invention relates to an aluminum alloy plate for a large rectangular battery case used for a lithium ion secondary battery case or the like.

  Lithium ion secondary batteries are widely used as power sources for mobile phones, notebook computers, etc., but due to their excellent characteristics, they have recently begun to be used as power sources for electric vehicles and hybrid vehicles. Conventionally, the material of the case (hereinafter referred to as the battery case) that is the exterior of the secondary battery satisfies the miniaturization and weight reduction of the battery and the formability for forming the battery case (mainly the battery case main body). Aluminum alloy plates are used.

The battery case is manufactured by applying press processing (deep drawing-ironing processing) to an aluminum alloy plate, and after putting an electrode agent (electrode and electrolyte), it is laser welded to the lid member. For this reason, the aluminum alloy plate for battery cases requires excellent formability. In addition, in the case of lithium ion secondary batteries for mobile phones and notebook computers, the battery case must be strong enough to resist battery swelling, and in the case of in-vehicle lithium ion secondary batteries, such as car collisions. The strength to protect the electrode agent from external impact is necessary. For this reason, the aluminum alloy plate for battery cases requires high strength as a material and excellent laser weldability.
As an aluminum alloy plate having such formability, material strength, and laser weldability, many Al-Mn aluminum alloy plates based on JIS3003 have been developed (see Patent Documents 1 to 9).

JP 2000-129384 A JP 2002-140669 A JP 2002-339049 A JP 2004-2985 A JP 2005-336540 A JP 2006-188744 A JP 2011-38122 A JP2012-177186A JP 2012-197489 A

  The battery case for in-vehicle use is larger than the battery case for a mobile phone or a notebook computer. For example, as described in Patent Document 9, the bottom width is 10 mm or more, the width is 70 mm or more, and the height is 60 mm. The above-mentioned bottomed square tube is used. Such a battery case is formed by applying a progressive press process (multi-stage drawing-ironing process) to the aluminum alloy sheet as a raw material using a large progressive press machine. There is a problem that it is easy to do.

  In addition, in-vehicle battery cases have a large outer shape and a large material thickness, and in order to obtain a predetermined welding strength, it is necessary to increase the penetration depth in laser welding. In a battery case for a mobile phone or a notebook personal computer, the penetration depth is 0.2 to 0.3 mm, but for an in-vehicle battery case, about 0.5 to 1.0 mm is desired. In laser welding of an on-vehicle battery case, continuous oscillation laser welding is mainly used because it is necessary to obtain a deep penetration depth. However, there is a problem that welding defects such as weld cracks, irregular beads, undercuts, and adhesion of weld spatter are more likely to occur as the penetration depth increases.

  The present invention has been made in order to solve the above-mentioned problems associated with the production of large-sized rectangular battery cases for automobiles, etc., and is excellent in press workability, laser weldability, and high strength. It aims at providing the Al-Mn type aluminum alloy plate which can manufacture a case.

The aluminum alloy plate for a large square battery case according to the present invention has Mn: 0.5 to 1.5 mass%, Cu: 0.4 to 1.2 mass%, Mg: less than 0.2 mass%, Si: It contains less than 0.6% by mass, Fe: less than 0.8% by mass, has a Si / Fe mass ratio of less than 3.0, and consists of the balance Al and inevitable impurities. This aluminum alloy plate further includes Ti: less than 0.02 mass%, B: less than 20 mass ppm, Zr: 0.15 mass% or less, Cr: 0.40 mass% or less, and Zn: 0.3 mass% or less. Any one or two or more of these may be contained as additive elements or as inevitable impurities.
The aluminum alloy plate according to the present invention is formed into a large rectangular battery case according to the quality of O or H. In the above composition, the proof stress value of the O material is 50 to 110 MPa. In the case of H material, it is desirable to adjust the proof stress value in the range of 160 to 260 MPa.

The aluminum alloy plate according to the present invention is excellent in formability, is free from cracks and seizures in press work, and is excellent in the production of a large rectangular battery case. Since the aluminum alloy plate is work-hardened during the forming process, a large-strength large rectangular battery case can be manufactured.
Further, this aluminum alloy plate is excellent in laser weldability with no generation of welding defects even when the penetration depth is increased in laser welding. Therefore, the welding depth can be increased and the welding strength can be increased in the laser welding with the lid member, which is suitable for a large rectangular battery case such as an in-vehicle lithium ion secondary battery.

Hereinafter, the aluminum alloy plate for a large rectangular battery case according to the present invention will be described more specifically.
(Composition of aluminum alloy plate)
Mn: 0.5 to 1.5% by mass
Mn has the effect of being dissolved in the matrix and increasing the strength of the aluminum alloy plate and improving the pressure strength. However, when the Mn content is less than 0.5% by mass, this effect is small. On the other hand, if the content of Mn exceeds 1.5% by mass, coarse intermetallic compounds (Al-Fe-Mn, Al-Fe-Mn-Si intermetallic compounds) are generated, which becomes the starting point of cracking during molding. This is easy and the formability of the aluminum alloy plate is lowered. Therefore, the Mn content is in the range of 0.5 to 1.5 mass%, preferably 0.7 to 1.2 mass%.

Mg: Less than 0.2% by mass Mg has the effect of increasing the strength of the aluminum alloy plate by solid solution strengthening and improving the pressure strength. However, when the Mg content is 0.2% by mass or more, when the H material is formed into a large rectangular battery case by press working, the strength becomes too high due to work hardening, and cracking occurs. Also, when the Mg content is 0.2 mass% or more, the weld bead shape is disturbed due to weld cracking or irregular bead generation in CW (continuous oscillation) laser welding, or inside the weld bead. Prone to defects. Therefore, the Mg content is less than 0.2% by mass (excluding 0%), preferably 0.03 to 0.15% by mass.

Cu: 0.4 to 1.2% by mass
Cu has the effect of increasing the strength of the aluminum alloy plate by solid solution strengthening and improving the pressure strength. However, when the Cu content is less than 0.4% by mass, this effect is small. On the other hand, if the Cu content exceeds 1.2% by mass, the work curability becomes too high, and cracking occurs during press working. On the other hand, if the Cu content exceeds 1.2% by mass, weld cracking occurs in CW (continuous oscillation) laser welding. Therefore, the Cu content is 0.4 to 1.2% by mass, preferably more than 0.6 to 1.2% by mass, and more preferably 0.7 to 1.0% by mass.

Si: Less than 0.6% by mass Si is present in the aluminum alloy as an inevitable impurity. Moreover, Si has the effect of increasing the strength of the aluminum alloy plate by solid solution strengthening, improving the pressure strength, and further improving the formability of the aluminum alloy plate, and is added to the aluminum alloy as necessary. . However, when the Si content is 0.6% by mass or more, the Al—Fe—Mn—Si intermetallic compound is coarsened, which tends to be a starting point of cracking during forming, and the formability of the aluminum alloy plate is lowered. Moreover, when Si content exceeds 0.6 mass%, it will become easy to produce a weld crack. Therefore, the content of Si present in the aluminum alloy as an inevitable impurity or added to the aluminum alloy as necessary is less than 0.6% by mass. Desirably, the Si content is 0.05 to 0.5 mass%.

Fe: Less than 0.8 mass% Fe exists in an aluminum alloy as an unavoidable impurity. Fe has an effect of increasing the strength of the aluminum alloy plate, and is added to the aluminum alloy as necessary. However, when the Fe content exceeds 0.8% by mass, the Al—Fe—Mn and Al—Fe—Mn—Si intermetallic compounds are coarsened, and this tends to be the starting point of cracking during the formation of the aluminum alloy plate. The moldability of the is reduced. Therefore, the content of Fe present in the aluminum alloy as an inevitable impurity or added to the aluminum alloy as necessary is less than 0.8% by mass. Desirably, the Fe content is 0.1 to 0.6 mass%.

Si / Fe mass ratio <3
When the Si / Fe mass ratio is 3 or more, a large amount of Al—Fe—Si and Al—Fe—Mn—Si intermetallic compounds are formed, and constriction and cracking are likely to occur during press forming of an aluminum alloy sheet. Therefore, it is desirable that the Si / Fe mass ratio is less than 3.

Ti: Less than 0.02% by mass Ti has the effect of refining and homogenizing (stabilizing) the cast structure of an aluminum alloy, and is usually used in an aluminum alloy for the purpose of preventing casting cracks during ingot formation of a rolling slab. 0.02 mass% or more is added. On the other hand, when Ti is added excessively, a coarse intermetallic compound is crystallized and tends to be a starting point of cracking during molding. Therefore, Ti is added within a range of 0.15% by mass or less.
However, when CW (continuous oscillation) laser welding is performed on an aluminum alloy plate containing Ti, porosity defects remain in the solidified beads during melting (660 to 750 ° C.), and the penetration is deeply formed, which solidifies. Abnormal parts (disorder of the shape of the weld bead due to irregular beads) are likely to occur.
Ti is included as an inevitable impurity in the metal (including scrap) and can be added to the aluminum alloy if necessary, but in any case, the aluminum alloy plate according to the present invention has a Ti content. It is necessary to regulate to less than 0.02% by mass (including 0%). The smaller the Ti content, the better the weldability, preferably 0.01% by mass or less, more preferably 0.006% by mass or less.

B: 20 mass ppm or less B is usually positively added together with Ti as a Ti-B master alloy for the purpose of preventing casting cracks during slab ingot formation of an aluminum alloy.
However, when the B content of the aluminum alloy plate exceeds 20 ppm by mass, porosity defects remain in the solidified beads in CW (continuous oscillation) laser welding as in the case of Ti, and the penetration is deeply formed. An abnormal part occurs.
B is contained as an inevitable impurity in the metal (including scrap) and can be added if necessary, but in any case, the aluminum alloy plate according to the present invention has a B content of less than 20 ppm by mass ( (Including 0%). The smaller the B content, the better the weldability, preferably 10 ppm by mass or less, more preferably 8 ppm by mass or less.

Zr: 0.15 mass% or less Cr: 0.40 mass% or less Zr and Cr have the effect of refining and homogenizing (stabilizing) the aluminum alloy structure. However, if the Zr content exceeds 0.15% by mass or the Cr content exceeds 0.40% by mass, a coarse intermetallic compound is crystallized, which tends to be a starting point of cracking during forming. The moldability of the is reduced. In addition, since Zr and Cr can refine | miniaturize the recrystallized grain when it resolidifies at the time of welding and a weld crack can be avoided, it is preferable that Zr and Cr contain 0.05 mass% or more, respectively.
Zr and Cr are also included as inevitable impurities in the aluminum alloy and can be added if necessary. In any case, in the aluminum alloy sheet according to the present invention, the Zr content is 0.15% by mass. Below (including 0%), the Cr content is limited to 0.40 mass% or less (including 0%).

Zn: 0.3% by mass or less Since Zn has a low vapor pressure, it is scattered during laser welding, easily contaminates the surroundings, and deteriorates the laser weldability of the aluminum alloy plate. Therefore, the Zn content is restricted to 0.3% by mass or less (including 0%).

(Manufacture of aluminum alloy sheets)
The aluminum alloy plate according to the present invention can be manufactured, for example, by the following process.
An aluminum alloy having a predetermined component is melted and cast to produce an ingot, and the ingot is chamfered and then subjected to a homogenization heat treatment at a temperature of 480 ° C. or higher and lower than the melting point of the aluminum alloy. Next, the homogenized heat-treated ingot is hot-rolled and cold-rolled to produce a rolled plate. And when manufacturing O material of an aluminum alloy plate, this rolled plate is heated to the temperature range of 300-450 degreeC, and the annealing which hold | maintains for 0.5 hour or more is given. When the H material is manufactured, the O material is further cold-rolled at a rolling rate of about 20 to 50%.

(Strength of aluminum alloy sheet)
The aluminum alloy plate according to the present invention is formed into a large rectangular battery case according to the quality of O or H. In the above composition, the proof stress value of the O material is approximately 50 to 110 MPa. Since the O material is soft, it is easy to process and can be easily formed into a large rectangular battery case by drawing and ironing. Moreover, although the proof stress of O material is low, the intensity | strength of the battery case after shaping | molding can fully be improved by the work hardening accompanying shaping | molding process.
In order to increase the strength of the battery case as much as possible, it is effective to set the quality of the aluminum alloy plate to H. On the other hand, the H material is inevitably deteriorated in formability as compared with the O material, and is likely to crack during molding. By adjusting the proof stress value of the H material within the range of 160 to 260 MPa, the strength of the battery case can be improved and cracking during molding can be prevented.

(Laser welding)
A large rectangular tube battery case suitable for a lithium ion secondary battery for in-vehicle use has a bottomed rectangular tube having a bottom width of 10 mm or more, a width of 70 mm or more, and a height of 60 mm or more. The large rectangular battery case targeted by the present invention also has this size. This large rectangular battery case has a welded portion thickness of about 0.5 to 2.0 mm, and a laser welding depth of about 0.5 to 1.0 mm is desired. In order to obtain this depth of penetration, continuous wave (CW) laser welding is preferably used, and the large rectangular battery case formed of the aluminum alloy plate according to the present invention is a continuous wave (CW) laser. Excellent weldability in welding. There are a keyhole type and a heat conduction type in continuous wave (CW) type laser welding, and a keyhole type capable of obtaining a deep penetration depth is preferable.
For laser welding of the aluminum alloy plate according to the present invention, a pulse laser or a combination method of a pulse laser and a continuous wave (CW) type laser can be applied.

  An aluminum alloy having the composition shown in Table 1 was melted and cast into an ingot, and the ingot was chamfered and then subjected to homogenization heat treatment at 550 ° C. for 4 hours. This homogenized ingot was subjected to hot rolling and further cold rolling to obtain an aluminum alloy plate having a plate thickness of 1.0 mm. The cold-rolled rolled plate was heated to 370 ° C. and subjected to batch-type annealing that was maintained at this temperature for 4 hours to obtain a plate material (O material) for property evaluation. In addition, for the H material, hot rolling and further cold rolling are performed to obtain a sheet thickness of 1.4 mm. After performing the intermediate annealing under the same conditions as the batch annealing of the O material, the sheet thickness is further reduced by cold rolling. A plate material for characteristic evaluation was prepared as an aluminum alloy plate of 0.0 mm.

  Using the manufactured aluminum alloy plates (O material, H material), a tensile test, a formability evaluation test, and a weldability evaluation test were performed in the following manner. The results are shown in Tables 1 and 2.

(Tensile test)
A JIS No. 5 tensile test piece was cut out from each evaluation plate so that the rolling direction was the longitudinal direction, and tensioned with a floor-mounted universal tensile testing machine AG-I manufactured by Shimadzu Corporation in accordance with the provisions of JISZ2241. A test was conducted to determine the yield strength. The crosshead speed was 5 mm / min, and the test piece was run at a constant speed until the test piece broke.

(Formability evaluation test)
An elliptical blank plate is cut out from each evaluation plate material so that the long axis is parallel to the rolling direction, and a progressive press machine is used for drawing and ironing in a total of 11 steps, and the side wall ironing rate is 30. %, A box-shaped rectangular battery case (case body) having a bottom width of 20 mm, a bottom width of 200 mm, and a height of 150 mm was formed.
At this time, it can be molded without cracking, and after molding, it is evaluated as a pass `` ◎ '' as having excellent moldability if it has no surface discoloration or vertical stripe pattern due to seizure, and it can be molded without cracking Slight surface discoloration and vertical streak patterns were evaluated as “Good” as good moldability, and cracks occurred during molding, or those with significant discoloration and vertical streaks were formed. It was evaluated as a failure “x” as being defective.

(Weldability evaluation test)
A test piece having a size of 30 mm × 100 mm was cut out from each evaluation plate, and a bead with a 90 mm weld length using a welding machine using a continuous wave fiber laser (IPG Photonics Japan Co., Ltd., model: YLR-10000) as a heat source. Welded on plate. The welding conditions were a laser output of 1.5 to 2.0 kW, a welding speed of 10.0 m / min, and a forward angle of 5 deg. Then, the laser output was adjusted so that the penetration depth of the welded portion was 0.7 to 0.8 mm.
About the weld bead part of each test piece, the welding external appearance evaluation and the radiation transmission test were done in the following way.

<Evaluation of welding appearance>
About the weld bead part, the presence or absence of a weld crack, the uniformity of the weld bead width, the presence or absence of an undercut, and the presence or absence of welding spatter adhesion were observed. As a result, the weld bead portion has no cracks, the weld bead width is uniform, the weld bead portion has no undercut, bumped portion, and spatter adhesion with a diameter of 1 mm or more, and the weld appearance is good. ◎ ”, spatter adhesion with a diameter of 1 mm or more was observed only at one spot per 90 mm weld length, but there was no cracking, the weld bead width was uniform, and undercuts and bumping parts were seen in the bead part. Those not present were evaluated as an acceptable range “◯”, “◎” and “◯” were evaluated as acceptable, and all other cases were evaluated as rejected “X” because the weld appearance was poor.

<Radiation transmission test>
This test inspects scratches (porosity, etc.) in the weld bead and was performed in accordance with JISZ3105. A weld bead classified as Class 1 or 2 of the four-level evaluation specified in the JISZ3105 appendix is evaluated as a pass “○” as good, and it is difficult to classify as a Class 3 or 4 As a failure, it was evaluated as “x”.

As shown in Tables 1 and 2, in Examples 1 to 21, the alloy compositions satisfy the requirements of the present invention, the proof stress values of the O material and the H material are within the specified range of the present invention, and the formability and laser weldability are Both O and H materials are excellent. Examples 2, 5, 8, 11, 17, 18, and 20 in which either one or both of the Ti and B contents are smaller than the others are particularly excellent in laser weldability.
On the other hand, in Comparative Example 1, since the Mn content is too small, the proof stress values are low for both the O material and the H material. For this reason, the strength of the product battery case is insufficient.
In Comparative Example 2, since the Mn content was excessive, cracking occurred in press processing for both the O material and the H material. This is probably because a coarse intermetallic compound containing Mn was generated.
In Comparative Example 3, since the Mg content was excessive, the H material was cracked by press working. This is presumably because the strength became too high due to work hardening. In addition, cracks occurred in the weld bead portion in both the O material and the H material, irregular beads were generated, and the bead width became non-uniform, and many scratches such as porosity were detected in the weld bead.

In Comparative Example 4, since the Cu content was excessive, the O material and the H material both cracked during press working. This is presumably because the strength became too high due to work hardening. In addition, cracks occurred in the weld bead portion of both the O material and the H material, irregular beads were generated, the bead width was nonuniform, and many scratches such as porosity were detected in the bead.
In Comparative Example 5, since the Si content was excessive, the O material and the H material both cracked during press working. This is probably because a coarse intermetallic compound containing Si was generated. In addition, both the O material and the H material were cracked in the weld bead portion, and many scratches such as porosity were detected in the bead.

Since Comparative Example 6 has an excessive Ti and B content, Comparative Examples 7 and 8 have an excessive B content. Therefore, irregular beads are generated in both the O and H materials, and the bead width is uneven. Many scratches such as porosity were detected in the bead.
Since Comparative Example 9 has an excessive Zr content, Comparative Examples 10 and 11 have an excessive Cr content, and Comparative Example 12 has an excessive Fe content. There has occurred. This is probably because a coarse intermetallic compound was formed.

In Comparative Example 13, since the Zn content was excessive, weld spatter adhered, and many scratches such as porosity were detected in the beads.
In Comparative Examples 14 and 15, since the Si / Fe content ratio was excessive, both the O material and the H material were cracked during press working. This is considered to be because many intermetallic compounds containing Si were formed.

Claims (8)

Mn: 0.5 to 1.5 mass% (except Mn: 0.9 mass% or less) , Cu: 0.4 to 1.2 mass%, Mg: less than 0.2 mass%, Si: 0 Less than .6% by mass, Fe: less than 0.8% by mass, Si / Fe mass ratio is less than 3.0, and excellent press formability and laser weldability consisting of the balance Al and inevitable impurities Aluminum alloy plate for large rectangular battery case. Mn: 0.5 to 1.5 mass%, Cu: more than 0.6 mass% to 1.2 mass%, Mg: less than 0.2 mass%, Si: less than 0.6 mass%, Fe: 0.8 An aluminum alloy plate for a large rectangular battery case that contains less than mass%, has a Si / Fe mass ratio of less than 3.0, and is excellent in press formability and laser weldability , which comprises the balance Al and inevitable impurities . The aluminum alloy plate for a large rectangular battery case according to claim 1 or 2, characterized by containing Ti: less than 0.02 mass% and B: less than 20 mass ppm. The aluminum alloy plate for a large rectangular battery case according to any one of claims 1 to 3, comprising at least one of Zr: 0.15 mass% or less and Cr: 0.40 mass% or less. . Zn: 0.3 mass% or less is contained, The aluminum alloy plate for large sized rectangular tube battery cases described in any one of Claims 1-4 characterized by the above-mentioned. The aluminum alloy plate for a large rectangular battery case according to any one of claims 1 to 5, wherein the aluminum alloy plate is excellent in weldability by continuous wave laser welding. The aluminum alloy plate for a large rectangular battery case according to any one of claims 1 to 6, which is an O material having a proof stress of 50 to 110 MPa. The aluminum alloy plate for a large rectangular battery case according to any one of claims 1 to 6, which is an H material having a proof stress of 160 to 260 MPa.