JP2007277588A - Aluminum alloy rolled sheet for battery case having excellent multistage workability, and its production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aluminum alloy sheet for a battery case having excellent multistage workability and blistering resistance. <P>SOLUTION: An alloy having a composition comprising 0.8 to 2.0% Mn, 0.5 to 1.5% Mg, 0.1 to 0.5% Fe, 0.1 to 0.3% Si and 0.3 to 0.8% Cu is cast by the conventional method, is subjected to soaking treatment at 480 to 620°C for 1 to 20 hr, is thereafter hot-rolled, is subsequently cold-rolled at a draft of ≥15%, is subjected to process annealing so as to be heated at 380 to 580°C at a heating rate of ≥5°C/s, to be held for 0 to 200 s, and to be immediately cooled at a cooling rate of ≥5°C/s, and is thereafter subjected to final cold rolling at a draft of 40 to 70%, thus its tensile strength TS is controlled to ≥210 N/mm<SP>2</SP>, yield strength YS to ≥200 N/mm<SP>2</SP>, TS-YS to ≤25 N/mm<SP>2</SP>, and earing ratio to ≤6%. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an aluminum alloy rolled sheet for forming, and more particularly to an aluminum alloy rolled sheet for multi-stage working used in a battery case used for a personal computer or a mobile phone.

  Conventionally, for example, a case of a small prismatic Li-ion battery mounted on a mobile phone has been formed by multi-stage pressing combining a plurality of processes of drawing and ironing. It is common to use a board as a material. As a case material for this rectangular battery or the like, an Al—Mn 3003 alloy having excellent workability and corrosion resistance is suitable. In the Li-ion battery, a battery member is incorporated in the case, and the lid member is laser welded to be in a sealed state.

In recent years, from the viewpoint of increasing strength, a material in which Mg or Cu is added based on this 3003 alloy has been used. Some aluminum materials have been proposed so far. For example, Patent Document 1 proposes an aluminum alloy excellent in swelling resistance and a method for producing the same by regulating the amount of Mn, Fe and Si added and the production conditions, and adjusting the amount of dissolved Mn, the proof stress, and the crystal grains. Has been. Patent Document 2 proposes an aluminum alloy excellent in press formability and blistering resistance by adding an appropriate amount of Mg, Cu, Cr, Zr, Ti or the like in addition to Mn, Fe, and Si. Further, in Patent Document 3, in addition to the additive element, by controlling the processing rate, the crystal grain size, and the area occupation ratio of the intermetallic compound during cold rolling, the case and the lid are excellent in laser weldability and pressure strength. Alloys have been proposed.
JP 2000-017364 A JP 2000-336448 A JP 2001-181766 A

  A Li ion battery is mounted on a mobile phone or the like, and may generate heat when it is repeatedly charged and discharged. In addition, when left in an automobile under conditions of high outside temperature such as in summer, there is a possibility of being exposed to high temperatures. In such a case, the reaction proceeds in the battery, the internal pressure increases, and the case may be deformed. In order to suppress this deformation, it is necessary to increase the strength of the case material. In order to increase the strength of non-heat-treatable aluminum alloys, it is common practice to add elements such as Mn, Mg, and Cu. However, by adding these elements, even if strength improvement is achieved, molding processability may be reduced, and breakage is likely to occur during drawing and ironing. Even if processing is possible, it is often a problem that the shape of the case and the thickness distribution are not uniform. As described above, in the rolled aluminum alloy sheet, strength improvement is relatively easy, but improvement of workability is a major issue.

  As a result of intensive studies aimed at improving the multi-stage workability of these high-strength battery case materials, the present inventors can develop materials that maintain high strength and are excellent in multi-stage workability. It was.

That is, the invention according to claim 1 is made of Mn 0.8 to 2.0%, Mg 0.5 to 1.5%, Fe 0.1 to 0.5%, Si 0.05 to 0.3%, Cu 0.3 0.8%, the more the content and the balance inevitable impurities and Al, and tensile strength TS is 210N / mm ² or more, yield strength YS is 200 N / mm ² or more, TS-YS is 25 N / mm ² or less, the ear rate Is an aluminum alloy rolled sheet for battery cases excellent in multi-stage workability, characterized by being 6% or less.

  The invention according to claim 2 is that the aluminum alloy ingot having the composition according to claim 1 is soaked at 480 to 620 ° C. for 1 to 20 hours, and then hot-rolled, and thereafter the rolling rate is 15%. Cold-rolled, further heated to 380 ° C. to 580 ° C. at a heating rate of 5 ° C./s or more, held for 0 to 200 seconds and immediately cooled at a cooling rate of 5 ° C./s or more, and then reduced. It is a method for producing an aluminum alloy rolled sheet for a battery case excellent in multi-stage workability, characterized in that final cold rolling at a rate of 40 to 70% is performed.

  Furthermore, the invention according to claim 3 is excellent in multi-stage workability according to claim 2, characterized in that after cold rolling, final annealing is further performed at 100 to 150 ° C. for 0.5 to 3 hours. A method for producing a rolled aluminum alloy sheet for a battery case.

  In the present invention, by selecting the additive element of the aluminum alloy, its addition amount, and appropriate production conditions, and controlling the tensile strength TS, proof stress YS and TS-YS, and the ear ratio of the rolled sheet to appropriate values. Thus, it is possible to provide a battery case material that is excellent in multi-stage processability and resistance to blistering. The rolled sheet of the present invention can be applied not only to battery cases but also to various uses in which multistage processing is performed.

  First, the alloy components will be described.

Mn is an additive element that contributes to improvement in mechanical strength mainly in a solid solution state and contributes to improvement in swelling resistance. This is because the dissolved Mn acts as a resistance to dislocation movement related to creep deformation during heating and internal pressure loading.
Further, Mn forms an intermetallic compound with Fe or Si added simultaneously. This intermetallic compound plays an important role in improving ironing processability.
If the amount of Mn added is less than 0.8%, these effects are insufficient, and the mechanical strength is also lowered. If the amount of Mn added exceeds 2%, coarse crystallized substances increase and workability becomes a problem, so that it is not suitable as a case processing material.

  Mg is an additive element that contributes to the improvement of mechanical strength by solid solution strengthening and has the effect of improving the swelling resistance together with solid solution Mn. However, it exhibits the effect of reducing laser weldability due to excessive addition. If the added amount of Mg is less than 0.5%, the effect on the mechanical strength and the resistance to swelling is insufficient. If the amount of Mg exceeds 1.5%, laser weldability is lowered, specifically, cracks are likely to occur in the welded portion, which is inappropriate.

   Fe has an effect of slightly increasing the strength. Moreover, it forms an intermetallic compound with Mn and Si, and contributes to the improvement of ironing workability. However, if Fe is added in excess of 0.5%, coarse crystallized products are likely to be produced, which is unsuitable because it adversely affects the case moldability. The amount of Fe added is more preferably 0.4% or less. It is not appropriate to reduce Fe to less than 0.1% because it requires high-purity bullion and increases costs, although it does not lead to further improvement in characteristics.

Si has the effect of promoting the precipitation of Mn as the content increases. Therefore, if it exceeds 0.3% and Si is contained, the effect of preventing dandruff due to solute Mn is hindered and the anti-swelling resistance is lowered, which is inappropriate. Also,
Si is an important additive element because it forms an intermetallic compound with Mn and Fe and contributes to the improvement of ironing workability. It is not appropriate to reduce Si to less than 0.05% because a high-purity metal is required and the cost is high although it does not lead to further improvement in characteristics.

Cu is an additive element effective in improving mechanical strength and swelling resistance by solid solution and precipitation. By adding 0.3 to 0.8% of Cu, the mechanical strength is improved and the resistance to swelling is improved.
If it is less than 0.3%, this effect is small, and if it exceeds 0.8%, cracks are likely to occur during laser welding, so care must be taken.

  Other than the above, it consists of inevitable impurities and Al. In addition, for example, by adding 0.02 to 0.1% of Cr and Zr, the resistance to heating swelling is improved and the crystal grains are stabilized, so that variations in characteristics are reduced. good. Further, Ti caused by a Ti-based or Ti-B-based refining agent generally added for refining the ingot structure during the casting of an aluminum alloy is 0.1% or less, and B is 0.03. % Or less may be included.

  Next, the manufacturing method of this invention is demonstrated.

  A soaking treatment is applied to the ingot cast by a conventional method. The soaking is performed at 480 to 620 ° C. for 1 to 20 hours. Heating at a lower temperature or shorter time than the specified temperature is inadequate because the effect of the homogenization treatment is insufficient, and eventually the material becomes coarse crystal grains, and the ear becomes larger due to non-uniform deformation during molding. It is. In addition, treatment at a higher temperature is inappropriate because local melting may occur. If the time is longer than this range, the precipitation of Mn occurs excessively and the case swelling at the time of heating and internal pressure load becomes large, which is inappropriate.

  Next, hot rolling is performed. Although it does not specifically limit about hot rolling, It is desirable for the material temperature during rolling not to exceed 410 degreeC. If the temperature is higher than this, precipitation of Mn excessively occurs and the resistance to swelling of the molded case is lowered, which is inappropriate. In hot rolling, it is desirable to apply a reduction of at least 50%.

  After hot rolling, cold rolling at a reduction rate of 15% or more is performed, intermediate annealing by rapid heating and cooling is performed, and then cold rolling at a reduction rate of 40 to 70% is performed.

  If the rolling reduction ratio of the cold rolling before the intermediate annealing is lower than 15%, the recrystallization in the intermediate annealing becomes unstable and there is a fear that the structure becomes uneven.

  The intermediate annealing is desirably performed by a continuous annealing line (CAL), heated to 380 to 580 ° C. at a heating rate of 5 ° C./s or more, held for 0 to 200 s and immediately cooled at a cooling rate of 5 ° C./s or more. Perform under conditions. Here, holding for 0 s is a condition for cooling immediately after reaching a predetermined temperature. If annealing is not performed by such rapid heating and cooling, Mn precipitates and the amount of Mn solid solution decreases, which is inappropriate.

  The rolling reduction in the final cold rolling after the intermediate annealing is set to 40 to 70%. If it is lower than this, the mechanical strength is insufficient, and large blisters occur due to initial plastic deformation, which is inappropriate. When the rolling reduction exceeds 70%, the ear rate exceeds 5%, and mechanical strength such as proof stress increases, but press molding becomes difficult. In addition, the movable dislocations increase even in the case after the molding is finally formed including many movable dislocations in the organization, so that creep deformation is likely to occur, which is inappropriate.

  Although the final annealing is performed as necessary, the temperature in that case must be 100 ° C. or higher and 150 ° C. or lower. If the temperature is high, the recovery of the material proceeds, and generally the workability is improved. However, when the value of TS-YS becomes large and multistage processing is performed like a battery case, work hardening becomes too large, and workability may deteriorate, which is not preferable. When the temperature exceeds 150 ° C., this tendency becomes strong. Below 100 ° C, there is almost no recovery and the workability is not improved. If it is less than 0.5 hours, the effect of recovery is insufficient, and if it exceeds 3 hours, the work curability is increased, which is not preferable.

Tensile strength TS of the rolled plate 210N / mm ² or more, proof stress YS must be 200 N / mm ² or more. If the value is less than these values, the strength is low. Therefore, creep deformation occurs when the case is heated to 70 to 90 ° C., and sufficient swelling resistance cannot be obtained. The upper limit is not particularly specified, but if it is too high, the workability will be lowered, so that it may be within the processable range.

TS-YS must be 25 N / mm ² or less. TS-YS is an index indicating whether the deep drawing workability is good or bad. YS is the stress at which plastic deformation starts, and TS is the rupture stress. In general, it is determined that the deeper the drawability, the better the difference TS-YS. On the other hand, a material having a large TS-YS has a higher work curability than a small material. For this reason, in a process in which drawing and ironing are performed many times as in a battery case, the strength becomes too high due to work hardening, which may make the process difficult. If TS-YS exceeds 25 N / mm ² , the probability of occurrence of processing defects increases, which is not preferable.

  Ear rate must be less than 6%. When the ear rate is high, the shape of the drawn case end becomes non-uniform, and problems such as breakage of the high ear part due to multistage processing occur. In addition, a material with a high ear rate has a large processing anisotropy, and causes problems such as non-uniform thickness distribution of the processed case. A nonuniform thickness distribution is not preferable because it causes a deterioration in swelling resistance. This tendency becomes a serious problem as the wall thickness of the case side wall becomes thinner.

  As described above, the main point of the present invention is that the tensile strength TS, proof stress YS and TS-YS, and the ear rate of the rolled sheet are specified to appropriate values. In order to achieve the object of the present invention, it is important to appropriately select an additive element, its addition amount, and production conditions. Examples will be described in detail below.

  An aluminum alloy having the alloy composition shown in Table 1 was cast by a conventional method, and the ingot was homogenized under the soaking conditions shown in Table 2. Subsequently, after hot rolling by a conventional method, under the conditions shown in Table 2, cold rolling before intermediate annealing, intermediate annealing, cold rolling after intermediate annealing, and final annealing were performed, and an aluminum alloy having a thickness of 0.6 mm A rolled plate was used.

Each rolled plate was subjected to a tensile test and measured for tensile strength TS and yield strength YS. Regarding the ear ratio, a deep drawing cup was molded under the conditions of a blank diameter of 57 mmΦ, a punch diameter of 32 mmΦ−shoulder R of 2.0 mm, and a die diameter of 33.82 mmΦ−shoulder of 6.5 mm, and the ear ratio was measured. Ear rate was calculated by the following equation.
Ear rate (%) = (average of mountain height−average of valley height) / average of valley height × 100

  Each rolled plate was formed into a square case having a thickness of 5 mm, a width of 30 mm, a height of 50 mm, and a thickness of 0.3 mm by multistage drawing and ironing. The ones that could be molded without problems were marked with ◯, the ones with constriction or perforation in part were marked with Δ, and the ones that were broken during processing were marked with ×.

  Further, an internal pressure of 0.2 MPa was applied to the case, and the case was held at 85 ° C. for 24 hours to measure the amount of swelling. The amount of blistering means the amount of increase in thickness in the outer shape of the case where the blister is at its maximum. The difference in case thickness before and after the test was measured and used as the amount of blistering. The conditions of this blister test are quite severe, and blisters are generated in any sample. However, if it is 1.6 mm or less, it may be disadvantageous if it exceeds 1.6 mm. The results are shown in Table 3.

  Sample numbers 1 to 7 are examples of the present invention, and all exhibited good processability and anti-swelling resistance.

In Sample No. 8, the amount of Mn added was less than the specified value, so that the amount of the crystallization compound effective in improving the ironing workability was small, and some galling occurred during ironing. The initial strength met the conditions, but the amount of swelling was large. In Sample No. 9, since the amount of Mn added was too large, the strength and work curability were high, and molding was not successful. Sample No. 10 had no problem in workability, but the amount of Mg added was low, the initial strength was too low, and the amount of swelling increased. In Sample No. 11, the amount of Mg added was over, the strength was too high, and the processing was not successful. In Sample No. 12, the amount of Fe added was too large, so that a coarse crystallized compound was the cause, and some cases were constricted or perforated. In Sample No. 13, the amount of Si added exceeded the specified range, the Mn compound was easily precipitated, and the solid solution amount of Mn decreased, resulting in an increase in the amount of swelling. Sample No. 14 had a low initial strength due to a small amount of Cu added, and also had a low heat resistance. Sample No. 15 had a Cu addition amount exceeding the specified range, and cracking occurred during processing. Samples Nos. 16 and 17 had a high ear rate because the soaking temperature was low, and an ear-cutting trouble occurred during processing. Since Sample No. 18 was not subjected to soaking, the ear rate was high, and many ears were cut off during processing, and processing was impossible. Sample Nos. 19 and 20 had a low intermediate annealing temperature and insufficient recrystallization during annealing, resulting in a very high ear rate after the final cold rolling. For this reason, ear cutting frequently occurred and could not be processed. Since sample No. 21 was not subjected to intermediate annealing, the ear rate was high and could not be processed. Sample Nos. 22, 23, 24, and 25 had a high final annealing temperature, and TS-YS was larger than specified. Therefore, work hardening was large, and molding cracks occurred during the processing. Samples Nos. 26 and 27 were too cold and could not be processed well because the rolling ratio of the final cold rolling was too high.

Claims (3)

Mn 0.8-2.0 mass% (hereinafter abbreviated as%), Mg 0.5-1.5%, Fe 0.1-0.5%, Si 0.05-0.3%, Cu 0.3-0.8 %, more will balance inevitable impurities and Al contained, the tensile strength TS is 210N / mm ² or more, yield strength YS is 200 N / mm ² or more, TS-YS is 25 N / mm ² or less, the ear of not more than 6% A rolled aluminum alloy sheet for battery cases having excellent multi-stage processability. The aluminum alloy ingot having the composition according to claim 1 is soaked at 480 to 620 ° C. for 1 to 20 hours, then hot rolled, then cold rolled at a rolling rate of 15%, and further heated at 5 ° C. Heating at 380 ° C. to 580 ° C. at / s or more, holding for 0 to 200 seconds, immediately performing intermediate annealing under the condition of cooling at a cooling rate of 5 ° C./s or more, and then performing final cold rolling at a reduction rate of 40 to 70%. A method for producing a rolled aluminum alloy sheet for battery cases having excellent multi-stage processability. 3. The production of an aluminum alloy rolled sheet for a battery case excellent in multi-stage workability according to claim 2, characterized in that after the cold rolling, final annealing is further performed at 100 to 150 [deg.] C. for 0.5 to 3 hours. Method.