JP5725345B2 - Aluminum alloy sheet for battery cases with excellent formability and weldability - Google Patents

Description

  The present invention relates to a high-strength aluminum alloy plate excellent in formability and laser weldability, which is used for a secondary battery container such as a lithium ion battery.

  Al-Mn-based 3000 series alloys are relatively excellent in strength, formability and laser weldability, and have come to be used as raw materials when manufacturing secondary battery containers such as lithium ion batteries. Yes. After forming into a desired shape, it is hermetically sealed by laser welding and used with a secondary battery container. Development has been made on an aluminum alloy plate for a secondary battery container, which is based on an existing 3000 series alloy as well as the 3000 series alloy and has further improved strength and formability.

  For example, in Patent Document 1, as the composition of the aluminum alloy plate, Si: 0.10 to 0.60 mass%, Fe: 0.20 to 0.60 mass%, Cu: 0.10 to 0.70 mass%, Mn : 0.60 to 1.50 mass%, Mg: 0.20 to 1.20 mass%, Zr: more than 0.12 and less than 0.20 mass%, Ti: 0.05 to 0.25 mass%, B : 0.0010 to 0.02% by mass, comprising the balance Al and inevitable impurities, and having a 45 ° ear ratio in the rolling direction of 4 to 7% in the cylindrical container deep drawing method. An aluminum alloy plate for rectangular cross-section battery containers is described.

  On the other hand, recently, aluminum for prismatic lithium-ion battery cases has sufficient strength as a battery case, draw-ironing workability, creep characteristics, excellent laser weldability, and can suppress increase in case thickness during charge / discharge cycles. Alloy plates have also been developed. In Patent Document 2, Mn: 0.8% by mass or more, 1.8% by mass or less, Mg: more than 0.6% by mass and 1.2% by mass or less, Cu: more than 0.5% by mass, and 1.5% by mass % And below, Fe as an impurity is regulated to 0.5 mass% or less, Si is regulated to 0.3 mass% or less, and the composition consists of the balance Al and inevitable impurities, and the {001} <100> orientation The ratio (C / S) of the orientation density C of {123} <634> orientation is 0.65 or more and 1.5 or less, and the tensile strength after the final cold rolling is 250 MPa or more and 330 MPa. Hereinafter, an aluminum alloy plate for a rectangular battery container having an elongation of 1% or more is described.

However, it is known that an aluminum alloy plate based on a 3000 series alloy and improved in its composition may have insufficient weld penetration depth, which may cause abnormal beading and a problem in laser weldability. Yes.
Therefore, an aluminum alloy plate for a secondary battery container that is excellent in laser weldability based on 1000 series has also been developed. Patent Document 3 describes an aluminum alloy material for pulse laser welding and a battery case capable of preventing the occurrence of abnormal parts by pulse laser welding of an A1000 series aluminum material and forming a uniform good weld part. . According to this, Ti, which has been added to suppress the coarsening of crystal grains in the casting process, has an adverse effect on the welded portion, and an abnormal portion is formed when A1000 series aluminum is welded by pulse laser welding. In order to prevent this, Ti contained in pure aluminum should be regulated to less than 0.01% by mass.

Japanese Patent No. 4001007 JP 2010-126804 A JP 2009-127075

Certainly, the 1000 series has problems that the weldability is stable (the number of abnormal beads is small) and the formability is excellent, but the strength is low. Therefore, as the size of the lithium ion battery is increased, it is expected that high strength characteristics are required, and there is a problem in applying the 1000 series aluminum material as it is.
As described above, although a 3000 series alloy plate can provide strength and deep penetration depth, it has a tendency to have inferior formability and a large number of abnormal beads compared to a 1000 series alloy plate. In addition, a 1000 series alloy plate is excellent in formability and the number of abnormal beads decreases, but there is a concern that the strength is insufficient.
The present invention has been devised to solve such problems, has high strength applicable to large-sized lithium ion battery containers, is excellent in moldability, and further has laser weldability. Is intended to provide an excellent Al—Fe-based aluminum alloy sheet.

In order to achieve the object, the aluminum alloy plate for battery case excellent in formability and weldability of the present invention is Fe: 0.3-1.5 mass%, Mn: 0.3-1.0 mass%. Cu: 0.2 to 1.0% by mass, Mg: 0.2 to 1.0% by mass, Ti: 0.002 to 0.20% by mass, Zr: 0.05 to 0.20% by mass And a component composition in which the mass ratio of Mn / Fe is 0.2 to 1.0, the balance is Al and impurities, and Si as an impurity is less than 0.20 % by mass, and an equivalent circle diameter of 5 μm or more. It is characterized by being a cold-rolled material having a metal structure in which the number of second phase particles is less than 500 particles / mm ² and exhibiting an elongation value of 2% or more and a tensile strength of 160 MPa or more.
Fe: 0.3-1.5% by mass, Mn: 0.3-1.0% by mass, Cu: 0.2-1.0% by mass, Mg: 0.2-1.0% by mass, Ti: 0.002 to 0.20% by mass, Zr: 0.05 to 0.20% by mass, the mass ratio of Mn / Fe is 0.2 to 1.0, and the balance is Al and impurities. And a component composition in which Si as an impurity is less than 0.20 mass% and a metal structure in which the number of second phase particles having an equivalent circle diameter of 5 μm or more is less than 500 particles / mm ² , and an elongation of 20% or more. It may be characterized by being a cold-rolled annealing material exhibiting a value and a tensile strength of 130 MPa or more.

Since the aluminum alloy plate of the present invention has high strength, excellent formability, and excellent laser weldability, it is possible to reduce the cost of a secondary battery container that has excellent sealing performance and can suppress swelling. Can be manufactured.
In particular, in the case of a cold-rolled material, it has an elongation value of 2% or more and a tensile strength of 160 MPa or more. When a cold-rolled annealing material is used, not only the tensile strength of 130 MPa or more but also the elongation value is 20% or more. And exhibits excellent moldability.

Conceptual diagram explaining how to measure / evaluate abnormal bead count Conceptual diagram explaining the measurement / evaluation method of penetration depth

Secondary batteries are manufactured by putting an electrode body in a container and then sealing it with a lid by welding or the like. When such a secondary battery is used for a mobile phone or the like, when charging, the temperature inside the container may rise and the pressure inside the container may increase. For this reason, if the strength of the material forming the container is low, there is a problem that the produced container is greatly swollen. Therefore, a material having high strength is required as a material to be used.
Further, since a press method is generally used as a method for forming a container, the material itself is required to have excellent press formability.

In addition, since a welding method is used as a method of sealing with a lid, it is also required to have excellent weldability. In many cases, a laser welding method is used as a welding method for manufacturing a secondary battery container or the like.
By the way, regarding laser weldability, (1) stability of the weld bead width and stability of the penetration depth and (2) obtaining a deeper penetration depth with respect to the weld bead width can be cited as problems.
In general, as the weld bead width increases, the penetration depth tends to increase. For this reason, the weld bead width is locally wide at the abnormal bead portion and the penetration depth is deep, and if it is severe, penetration of the melted portion or the like occurs, leading to deterioration in battery performance and reliability.

On the other hand, in order to investigate the penetration depth, it is necessary to observe many cross sections, which is labor intensive. However, as described above, there is a correlation between the weld bead width and the penetration depth within the same alloy, so by measuring the weld bead width and detecting an abnormal (coarse) bead, the abnormal penetration depth in question is detected. The bead ratio can be easily investigated.
The present inventors have intensively studied to obtain an aluminum alloy plate having high strength and excellent press formability, as well as excellent laser weldability through investigation of the number of abnormal beads generated in the weld and the penetration depth in the weld. Again, the present invention has been reached.
The contents will be described below.

First, the effect | action of each element contained in the aluminum alloy plate for secondary battery containers of this invention, appropriate content, etc. are demonstrated.
Fe: 0.3-1.5 mass%
Fe is an essential element for increasing the strength of the aluminum alloy plate and ensuring the penetration depth in laser welding. If the Fe content is less than 0.3% by mass, the strength of the aluminum alloy plate is lowered, and the penetration depth during laser welding is reduced, which is not preferable. When the Fe content exceeds 1.5% by mass, coarse intermetallic compounds such as Al— (Fe · Mn) —Si and Al ₆ Fe crystallize during ingot casting, and the formability in the final plate is reduced. These intermetallic compounds tend to evaporate during laser welding as compared to the Al matrix, and the number of abnormal beads increases and weldability decreases, which is not preferable.
Therefore, the Fe content is in the range of 0.3 to 1.5 mass%. A more preferable Fe content is in the range of 0.5 to 1.5 mass%. A more preferable Fe content is in the range of 0.7 to 1.5 mass%.

Mn: 0.3 to 1.0% by mass
Mn is an essential element for increasing the strength of the aluminum alloy plate and ensuring the penetration depth in laser welding. If the Mn content is less than 0.3% by mass, the strength of the aluminum alloy plate is lowered, and the penetration depth during laser welding is reduced, which is not preferable. When the content of Mn exceeds 1.0% by mass, coarse intermetallic compounds such as Al- (Fe · Mn) -Si, Al ₆ Mn crystallize during ingot casting, and the formability in the final plate is reduced. These intermetallic compounds tend to evaporate during laser welding as compared to the Al matrix, and the number of abnormal beads increases and weldability decreases, which is not preferable.
Therefore, the Mn content is in the range of 0.3 to 1.0 mass%. A more preferable Mn content is in the range of 0.3 to 0.8% by mass. A more preferable Mn content is in the range of 0.4 to 0.7% by mass.

Ti: 0.002 to 0.20 mass%
Ti acts as a crystal grain refining agent during ingot casting and can prevent casting cracks. Of course, Ti may be added alone, but by coexisting with B, a more powerful grain refinement effect can be expected, so addition with a rod hardener such as Al-5% Ti-1% B There may be.
If the Ti content is less than 0.002% by mass, the effect of refining at the time of ingot casting is insufficient, which may cause casting cracks, which is not preferable. When the Ti content exceeds 0.20% by mass, a coarse intermetallic compound such as TiAl ₃ is crystallized during ingot casting, which is not preferable.
Accordingly, the Ti content is in the range of 0.002 to 0.20 mass%. A more preferable Ti content is in the range of 0.002 to 0.15 mass%. A more preferable Ti content is in the range of 0.005 to 0.10% by mass.

Zr: 0.05-0.20 mass%
Zr, like Ti, acts as a grain refiner during ingot casting and can prevent casting cracks. Further, when Ti and Zr coexist, cracking at the time of solidification of the weld bead portion accompanied by rapid solidification is prevented, and the speed of pulse laser welding can be increased. When Ti, Zr, and B coexist, the effect of preventing the occurrence of cracks during solidification of the weld bead portion accompanied by rapid solidification becomes more remarkable.
When the Zr content exceeds 0.20% by mass, a coarse intermetallic compound such as ZrAl ₃ is crystallized at the time of ingot casting, which is not preferable. If the Zr content is less than 0.05% by mass, sufficient effects cannot be obtained. Therefore, the preferable Zr content is 0.05 to 0.20 mass%. A more preferable Zr content is in the range of 0.07 to 0.20 mass%. A more preferable Zr content is in the range of 0.07 to 0.18% by mass.

B: 0.0005 to 0.10% by mass
B, like Ti and Zr, acts as a crystal grain refining agent during ingot casting and can prevent casting cracks. For this reason, it contains as needed.
When the B content exceeds 0.10% by mass, TiB ₂ becomes a stabilized intermetallic compound, and the effect of grain refinement is attenuated and the appearance of the skin after DI molding may be roughened. Absent. If the B content is less than 0.0005 mass%, a sufficient crystal grain refining effect cannot be obtained. Therefore, the preferable B content is 0.0005 to 0.10% by mass. A more preferable B content is in the range of 0.001 to 0.05 mass%. A more preferable B content is in the range of 0.001 to 0.01% by mass.

Cu content: 0.2-1.0 mass%
Cu precipitates in the Al matrix together with Mg as a CuMgAl ₂ phase, thereby increasing the strength of the aluminum alloy plate. If the Cu content is less than 0.2% by mass, the increase in strength is insufficient, which is not preferable. On the other hand, when the Cu content exceeds 1.0% by mass, the formability of the final plate is lowered, which is not preferable.
Therefore, the Cu content is in the range of 0.2 to 1.0 mass%. A more preferable Cu content is in the range of 0.2 to 0.9 mass%. A more preferable Cu content is in the range of 0.2 to 0.8% by mass.

Mg content: 0.2-1.0 mass%
Mg precipitates in the Al matrix together with Cu as a CuMgAl ₂ phase, thereby increasing the strength of the aluminum alloy plate. If the Mg content is less than 0.2% by mass, the increase in strength is insufficient, which is not preferable. On the other hand, if the Mg content exceeds 1.0% by mass, an oxide film is generated during laser welding and weldability is lowered, which is not preferable.
Therefore, the Mg content is in the range of 0.2 to 1.0 mass%. A more preferable Mg content is in the range of 0.2 to 0.9 mass%. A more preferable Mg content is in the range of 0.2 to 0.8 mass%.

Si content as impurity: less than 0.30% by mass The content of Si as an inevitable impurity is preferably limited to less than 0.30% by mass. When the Si content is 0.30% by mass or more, coarse intermetallic compounds such as Al— (Fe · Mn) —Si are crystallized at the time of ingot casting, and formability is deteriorated. A more preferable Si content is less than 0.25% by mass. Further preferable Si content is less than 0.20 mass%.
In this invention, if Si content is less than 0.20 mass%, it will not fall about characteristics, such as a moldability and weldability.

Other inevitable impurities are inevitable mixed from raw metal, return material, etc., and their allowable contents are, for example, less than 0.25 mass% of Zn and 0.20 mass of Ni. %, Ga and V are less than 0.05% by mass, Pb, Bi, Sn, Na, Ca, Sr are each less than 0.02% by mass, and each other is less than 0.05% by mass. However, the inclusion of an element outside the control does not impede the effects of the present invention.

Mn / Fe mass ratio: 0.2 to 1.0
If the Mn / Fe ratio is less than 0.2 within the range of the Fe and Mn contents within the scope of the present invention, the penetration depth during laser welding decreases, which is not preferable. If the Mn / Fe ratio exceeds 1.0 within the range of Fe and Mn contents within the scope of the present invention, the number of abnormal beads increases, which is not preferable.
By the way, the mass ratio of Mn / Fe affects the type and amount of intermetallic compounds that crystallize during ingot casting. For example, it is also well known that when the Mn / Fe mass ratio increases, the number of Al ₆ Mn intermetallic compounds increases.

On the other hand, these intermetallic compounds such as Al ₆ Mn are easily evaporated and unstable compared with intermetallic compounds such as Al—Fe—Si, Al ₆ Fe, and Al ₃ Fe during laser welding. For this reason, when Mn / Fe ratio exceeds 1.0, it is thought that the number of abnormal beads at the time of laser welding increases and weldability deteriorates.
Further, since Mn increases the thermal resistance of the material by being dissolved in an Al matrix, Mn is an element more important than Fe in securing the penetration depth during laser welding. For this reason, it is thought that the penetration depth at the time of laser welding is insufficient when the Mn / Fe ratio is less than 0.2.

Tensile strength and elongation value
Cold-rolled material: elongation value of 2% or more and tensile strength of 160 MPa or more
Cold-rolled annealed material: When the elongation value is 20% or more and the tensile strength is 130 MPa or more, when applying an Al—Fe-based aluminum alloy plate to a large-sized lithium ion battery container, etc., it has high strength and excellent laser weldability. In addition to having it, it is necessary to have excellent moldability. The strength of the material can be known from the tensile strength when the tensile test is conducted, and the formability can be known from the elongation value at the tensile test.
The details will be given in the description of the examples below. As the Al-Fe-based aluminum alloy plate of the present invention applied to a large-sized lithium ion battery container or the like, the elongation value is 2% or more in the cold-rolled material, In addition, a material having a tensile strength of 160 MPa or more is suitable for a cold-rolled annealed material, and an elongation value of 20% or more and a tensile strength of 130 MPa or more are suitable.

The number of second phase particles having an equivalent circle diameter of 5 μm or more in the metal structure is less than 500 / mm ^{2 The} above-mentioned characteristics are that the metal structure of the Al—Fe-based aluminum alloy plate having the specific component composition is finely adjusted. Expressed by
Specifically, the number of second phase particles having an equivalent circle diameter of 5 μm or more in the metal structure may be less than 500 / mm ² .
There is no difference in the metal structure between the cold rolled material and the cold rolled annealed material. If it has the metal structure as described above, it exhibits an elongation value of 2% or more and a tensile strength of 160 MPa or more in the cold-rolled material, and 20% or more in the cold-rolled annealed material. It exhibits an elongation value and a tensile strength of 130 MPa or more.

Next, a method for producing the above-described aluminum alloy plate for a secondary battery container will be briefly introduced.
When the raw material is charged into the melting / melting melting furnace and the predetermined melting temperature is reached, the flux is appropriately charged and stirred, and further, if necessary, degassing in the furnace using a lance or the like, Hold the sedation to separate the soot from the surface of the melt.
In this melting / melting process, it is important to add raw materials such as a master alloy again because it is a predetermined alloy component, but a sufficient sedation time is allowed until the flux and soot float and separate from the molten aluminum alloy to the molten metal surface. It is extremely important to take The sedation time is usually preferably 30 minutes or longer.

In some cases, the molten aluminum alloy melted in the melting furnace may be cast after it is once transferred to the holding furnace, but may be cast directly from the melting furnace. A more desirable sedation time is 45 minutes or more.
If necessary, in-line degassing or filtering may be performed.
In-line degassing is mainly of a type in which an inert gas or the like is blown into a molten aluminum from a rotating rotor, and hydrogen gas in the molten metal is diffused and removed in 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 lower. The amount of hydrogen gas in the ingot is preferably reduced to 0.20 cc / 100 g or less.

When the amount of hydrogen gas in the ingot is large, porosity is generated in the final solidified portion of the ingot. Therefore, the reduction rate per pass in the hot rolling process is restricted to, for example, 7% or more, and the porosity is crushed. There is a need.
In addition, hydrogen gas that is supersaturated in the ingot is deposited during laser welding after forming the final plate, depending on the conditions of the homogenization treatment before the hot rolling process, and a large number of blown gases are blown into the beads. In some cases, holes are generated. For this reason, the more preferable amount of hydrogen gas in the ingot is 0.15 cc / 100 g or less.

The cast ingot is manufactured by semi-continuous casting (DC casting). In the case of normal semi-continuous casting, since the thickness of the ingot is generally about 400 to 600 mm, the solidification cooling rate at the center portion of the ingot is about 1 ° C./sec. For this reason, particularly when a molten aluminum alloy with a high content of Fe and Mn is semi-continuously cast, a relatively coarse intermetallic compound such as Al- (Fe.Mn) -Si is formed in the center of the ingot. There is a tendency to crystallize from the molten metal.

  The casting speed in the semi-continuous casting depends on the width and thickness of the ingot, but is usually 50 to 70 mm / min in consideration of productivity. However, when performing in-line degassing, considering the substantial molten metal residence time in the degassing treatment tank, the flow rate of molten aluminum (melt per unit time) depends on the degassing conditions such as the flow rate of the inert gas. The smaller the (supply amount), the better the degassing efficiency in the tank, and it is possible to reduce the amount of hydrogen gas in the ingot. Although depending on the number of castings and the like, it is desirable to limit the casting speed to 30 to 50 mm / min in order to reduce the amount of hydrogen gas in the ingot. A more desirable casting speed is 30 to 40 mm / min. Of course, when the casting speed is less than 30 mm / min, productivity is lowered, which is not desirable. Needless to say, when the casting speed is slower, the slope of the sump (solid phase / liquid phase interface) in the ingot becomes gentler, and casting cracks can be prevented.

Homogenization treatment: Homogenization treatment is performed on an ingot obtained by casting by a semi-continuous casting method at 420 to 600 ° C. for 1 hour or longer .
The homogenization process is a process in which the ingot is kept at a high temperature to facilitate rolling, and casting segregation and elimination of residual stress inside the ingot are performed. In the present invention, it is necessary to hold at a holding temperature of 420 to 600 ° C. for 1 hour or longer. In this case, it is also a process for dissolving the transition elements constituting the intermetallic compound crystallized during casting to some extent in the matrix. When the holding temperature is too low or the holding temperature is short, the solid solution of the transition element or the like does not progress, the recrystallized grains become rough, and the appearance skin after DI molding may not be finished cleanly. If the holding temperature is too high, eutectic parts such as CuMgAl ₂ which is the microscopic final solidified part of the ingot may melt, so-called burning may occur. A more preferable homogenization temperature is 420 to 590 ° C.

The ingot held at a high temperature for a predetermined time in the hot rolling process is suspended by a crane after homogenization and brought to the hot rolling mill. Depending on the type of hot rolling mill, it is usually how many times. It is hot-rolled by such a rolling pass and wound on a roll as a hot-rolled sheet having a predetermined thickness, for example, about 4 to 8 mm.

Cold Rolling Process The roll on which the hot rolled sheet is wound is passed through a cold rolling machine and usually subjected to several passes of cold rolling. At this time, since work hardening occurs due to plastic strain introduced by cold rolling, an intermediate annealing treatment is performed as necessary. Usually, since the intermediate annealing is also a softening treatment, although depending on the material, a cold rolling roll may be inserted into the batch furnace and held at a temperature of 300 to 450 ° C. for 1 hour or longer. When the holding temperature is lower than 300 ° C., softening is not promoted, and when the holding temperature exceeds 450 ° C., the processing cost increases. Moreover, intermediate annealing can also serve as a solution treatment if it is kept within a temperature of, for example, 450 ° C. to 550 ° C. for 15 seconds in a continuous annealing furnace and then cooled rapidly. When the holding temperature is lower than 450 ° C., softening is not promoted, and when the holding temperature exceeds 550 ° C., burning may occur.

Final annealing In the present invention, the final annealing performed after the final cold rolling may be, for example, a batch process of holding at a temperature of 400 to 500 ° C. for 1 hour or more by an annealing furnace, but by a continuous annealing furnace, for example, 500 ° C. to If it is kept at a temperature of 550 ° C. within 15 seconds and then cooled rapidly, it can also serve as a solution treatment.
In any case, final annealing is not necessarily essential in the present invention, but it is desirable to make the final plate as soft as possible in view of formability in normal DI molding. Considering the moldability in the mold forming process, it is desirable to use an annealed material or a solution treated material.
When the mechanical strength is prioritized over the moldability, it is provided as a cold rolled material.

Final cold rolling rate When the final annealing is performed, the final cold rolling rate is preferably in the range of 50 to 90%. If the final cold rolling rate is within this range, the average recrystallized grains in the final plate after annealing can be set to 20 to 100 μm, the elongation value can be set to 20% or more, and the appearance skin after molding is finished beautifully. be able to. A more preferable final cold rolling rate is in the range of 60 to 90%.
On the other hand, the final cold rolling rate when the material is cold rolled without being subjected to final annealing is preferably in the range of 5 to 40%. If the ironing process increases during DI molding, it is necessary to provide a final plate that is slightly harder than the annealed material. If the final cold rolling rate is less than 5%, depending on the composition, it becomes difficult to make the tensile strength of the final plate 160 MPa or more. If the final cold rolling rate exceeds 40%, the final plate depends on the composition. It is difficult to make the elongation value at 2% or more.
If the final cold rolling rate is within this range, the elongation value in the final plate can be 2% or more and the tensile strength can be 160 MPa or more with cold rolling. A more preferable final cold rolling rate is in the range of 10 to 30%.
An aluminum alloy plate for a secondary battery container can be obtained through the normal steps as described above.

Preparation of Final Plate Various predetermined ingots were weighed and blended, and 6 kg each (total 8 test materials) of ingots were inserted and loaded into a # 20 crucible coated with a release material. These crucibles are inserted into an electric furnace and melted at 780 ° C. to remove the soot, and then the molten metal temperature is maintained at 760 ° C. Then, each 6 g of degassing flux is wrapped in aluminum foil and becomes a phosphorizer. And added.
Subsequently, a lance was inserted into the molten metal, and N ₂ gas was blown at a flow rate of 1.0 L / min for 10 minutes to perform degassing treatment. Thereafter, the sedation was performed for 30 minutes, and the cocoon floating on the surface of the molten metal was removed with a stirring rod, and a disk sample was collected with a spoon as a mold for component analysis.
Next, the crucible was sequentially taken out from the electric furnace using a jig, and molten aluminum was cast into a preheated mold (250 mm × 200 mm × 30 mm). The disk sample of each sample material was subjected to composition analysis by emission spectroscopic analysis. The results are shown in Table 1.

The ingot was chamfered by 2 mm on each side after cutting the hot water to a thickness of 26 mm.
This ingot is inserted into an electric heating furnace, heated to 430 ° C. at a temperature rising rate of 100 ° C./hr, homogenized at 430 ° C. × 1 hour, and subsequently heated to a thickness of 6 mm with a hot rolling mill. It hot-rolled until it became.
This hot-rolled sheet was cold-rolled to obtain a cold-rolled sheet having a thickness of 1.25 mm. The cold-rolled sheet was inserted into an annealer, and after annealing at 390 ° C. for 1 hour, the annealed sheet was taken out from the annealer and air-cooled. Next, this annealed plate was cold-rolled to obtain a cold-rolled plate having a thickness of 1.0 mm. The final cold rolling rate in this case was 20%.
The cold-rolled annealed plate was cold-rolled without subjecting the hot-rolled plate to intermediate annealing to obtain a 1 mm cold-rolled plate. The final cold rolling rate in this case was 83.3%. In the final annealing, the cold-rolled sheet was inserted into the annealer, and after annealing at 390 ° C. for 1 hour, the cold-rolled sheet was taken out from the annealer and air-cooled.

Next, the final plate (each sample material) thus obtained was evaluated for formability and laser weldability.
Evaluation of formability Evaluation of formability of the obtained final plate was performed by elongation (%) of a tensile test.
Specifically, a JIS No. 5 test piece was sampled so that the tensile direction was parallel to the rolling direction, and a tensile test was performed according to JISZ2241, to determine tensile strength (UTS), 0.2% proof stress (YS), and elongation. (Elongation at break) was determined.
In the final plate as cold-rolled, the test material having an elongation value of 2% or more was defined as good moldability (◯), and the test material that was less than 2% was defined as poor moldability (x). The evaluation results are shown in Table 2.
In the final plate that was annealed after cold rolling, the test material having an elongation value of 20% or more was considered as good moldability (◯), and the test material that was less than 20% was considered as poor moldability (×). did. The evaluation results are shown in Table 3.
In Table 3, the test material No. Shows each specimen No. shown in Table 1. No. with 10's. Is shown.

Laser welding conditions The final plate obtained was subjected to pulsed laser irradiation to evaluate laser weldability. Using LUMONICS YAG laser welder JK701, under conditions of frequency 37.5 Hz, welding speed 450 mm / min, energy per pulse 6.0 J, shield gas (nitrogen) flow rate 1.5 (L / min), Two plates of the test material were butted without gaps between the end portions, and pulse laser welding having a total length of 120 mm was performed along the portion.

Evaluation of laser weldability
Measurement / Evaluation of Abnormal Bead Number Next, as an evaluation of laser weldability, the number of abnormal beads generated in the weld was measured. First, among the 120 mm long weld lines, a 60 mm long weld line at the center was determined as a measurement region. Next, as shown in FIG. 1, the width of the round molten bead formed by each pulse formed along the weld line having a length of 60 mm was continuously measured at intervals of 0.05 mm in the welding direction, and a length of 10 mm (1 The “average weld bead width” for each section) was calculated, and the number of locations showing bead widths that deviated by 1.1 or more from the “average weld bead width” in each section was counted. This count was totaled for 60 mm (6 sections) to obtain the number of abnormal beads of the specimen.
In the present specification, the test material having an abnormal bead number of less than 10 was evaluated as being good (O), and the test material having an abnormal bead number of 10 or more was being evaluated as having an abnormal bead number evaluation (x). did. The evaluation results are shown in Table 2 for the cold-rolled materials and in Table 3 for the cold-rolled annealed plates.

Measurement / Evaluation of Penetration Depth Next, as an evaluation of laser weldability, the penetration depth in the weld was measured. As shown in FIG. 2, a plate cross section in a direction perpendicular to the welding direction was cut out, embedded in a thermoplastic resin and mirror-polished, and the metal structure of the weld cross section was observed.
The intermetallic compound crystallized at the time of casting is heated to a high temperature by heating by pulse laser irradiation, dissolved in aluminum, and immediately after that, the molten bead is quenched, and elements such as Fe, Mn, and Si constituting the intermetallic compound Becomes a supersaturated solid solution in the Al matrix.

Therefore, by observation of the metal structure of the vertical cross section of the weld zone, the area of only the Al matrix in which no intermetallic compound is observed in the cross section is a molten part, and by measuring the maximum depth from the surface of the final plate of the area, The penetration depth can be measured.
The penetration depth of 5 cross sections was measured for one specimen, and the average value was defined as the penetration depth (μm) in the specimen. In this case, the cross section of the above-described abnormal bead is not subject to measurement.
In the present specification, a specimen having a penetration depth of 220 μm or more was regarded as good penetration evaluation (◯), and a specimen having a penetration depth of less than 220 μm was regarded as poor penetration depth evaluation (×). The evaluation results are shown in Table 2 for the cold-rolled materials and in Table 3 for the cold-rolled annealed plates.

Evaluation of each test material Examples 1 to 5 in Table 2 showing the evaluation results of the cold-rolled materials are cold-rolled materials within the composition range of the present invention, and laser weldability (abnormal bead number evaluation, penetration depth). Evaluation) and moldability were all good (◯).
In Comparative Example 1, the Mn content is as high as 1.27% by mass, the Mn / Fe ratio is 2.59, which is outside the range of the present invention, the penetration depth evaluation is good (◯), and the moldability is good (◯). The abnormal bead number was poorly evaluated (x).
In Comparative Example 2, the Fe content was as high as 1.6% by mass, outside the range of the present invention, and the penetration depth evaluation was good (◯), but the formability was poor (x) and the abnormal bead number was poor. (X).
In Comparative Examples 3 to 5, both Fe and Mn were low and out of the scope of the present invention, and the moldability was good (◯) and the abnormal bead number evaluation was good (◯), but the penetration depth evaluation was poor (x). there were.
In Comparative Example 6, the Si content was as high as 0.5% by mass, which was outside the scope of the present invention, and the penetration depth evaluation was good (◯) and the abnormal bead number evaluation was good (◯). (X).

Examples 11 to 15 in Table 3 showing the evaluation results for the cold-rolled annealed materials are annealed materials within the composition range of the present invention, both of laser weldability (evaluation of abnormal bead number and penetration depth evaluation) and formability. All were good (◯).
In Comparative Example 11, the Mn content is as high as 1.27% by mass, the Mn / Fe ratio is 2.59, which is out of the range of the present invention, the penetration depth evaluation is good (◯), and the moldability is good (◯). The abnormal bead number was poorly evaluated (x).
In Comparative Example 12, the Fe content was as high as 1.6% by mass, which was outside the scope of the present invention, and the penetration depth evaluation was good (O), but the formability was poor (x) and the abnormal bead number was poor. (X).
In Comparative Examples 13 to 15, both Fe and Mn were low and out of the scope of the present invention, and the moldability was good (◯) and the abnormal bead number evaluation was good (◯), but the penetration depth evaluation was poor (x). there were.
Comparative Example 16 had a high Si content of 0.5% by mass and was outside the scope of the present invention. The penetration depth evaluation was good (◯) and the abnormal bead number evaluation was good (◯). (X).

Measurement of the number of second phase particles in the metal structure A longitudinal section parallel to the rolling direction of the obtained final plate (section perpendicular to the LT direction) is cut out, embedded in a thermoplastic resin and mirror-polished, and the metal structure is observed. went. The micro metallographic structure is photographed with an optical microscope (area per field of view; 0.0334 mm ² , 10 fields of view of each sample), image analysis of the photograph is performed, and the second phase with a circle equivalent diameter of 5 μm or more per unit area The number of particles was measured.
The measurement results by image analysis are shown in Table 4 for the as-cold rolled materials and in Table 5 for the cold-rolled annealed plates.

From Table 4 showing the evaluation results for the cold-rolled material, when the number of second phase particles having a circle-equivalent diameter of 5 μm or more in the metal structure is 500 particles / mm ² or more (Comparative Examples 2 and 6), the tensile test is compared. It can be seen that the value of elongation is as low as less than 2% because peeling tends to occur at the interface between the coarsely-grown second phase particles and the matrix.
Therefore, it can be seen that in order to set the elongation value to 2% or more, the number of second phase particles having a circle-equivalent diameter of 5 μm or more in the metal structure needs to be less than 500 particles / mm ² .

From Table 5 showing the evaluation results for the cold-rolled annealed material, when the number of second phase particles having a circle-equivalent diameter of 5 μm or more in the metal structure is 500 particles / mm ² or more (Comparative Examples 12 and 16), comparison is made in the tensile test. It can be seen that the value of elongation is as low as less than 20% because peeling tends to occur at the interface between the coarsely-grown second phase particles and the matrix.
Therefore, it can be seen that in order to set the elongation value to 20% or more, the number of second phase particles having an equivalent circle diameter of 5 μm or more in the metal structure needs to be less than 500 particles / mm ² .

Claims (2)

Fe: 0.3-1.5 mass%, Mn: 0.3-1.0 mass%, Cu: 0.2-1.0 mass%, Mg: 0.2-1.0 mass%, Ti: 0.002 to 0.20% by mass, Zr: 0.05 to 0.20% by mass, the mass ratio of Mn / Fe is 0.2 to 1.0, and the balance is Al and impurities. A component composition in which Si as an impurity is less than 0.20 % by mass and a metal structure in which the number of second phase particles having an equivalent circle diameter of 5 μm or more is less than 500 particles / mm ² , and an elongation value of 2% or more And an aluminum alloy plate for battery cases having excellent formability and weldability, characterized by being a cold-rolled material exhibiting a tensile strength of 160 MPa or more. Fe: 0.3-1.5 mass%, Mn: 0.3-1.0 mass%, Cu: 0.2-1.0 mass%, Mg: 0.2-1.0 mass%, Ti: 0.002 to 0.20% by mass, Zr: 0.05 to 0.20% by mass, the mass ratio of Mn / Fe is 0.2 to 1.0, and the balance is Al and impurities. Having a component structure in which Si is less than 0.20 % by mass and a metal structure in which the number of second phase particles having an equivalent circle diameter of 5 μm or more is less than 500 particles / mm ² , and an elongation value of 20% or more, An aluminum alloy sheet for battery cases having excellent formability and weldability, characterized by being a cold-rolled annealed material exhibiting a tensile strength of 130 MPa or more.

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