JP2006152371A - Aluminum alloy for food can having excellent casting-crack resistance - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the casting-crack resistance of an Al-Mn-Mg-Cu-based alloy used as a material for food cans. <P>SOLUTION: The aluminum alloys for food cans having the excellent casting-crack resistance is characterized by containing 0.1 to 2.8% Mg and 0.1 to 0.5 Cu and containing the amounts of Mn, Fe and Si excluding a region simultaneously satisfying Fe<0.2% and Mn>2Fe+0.8 within a range of 0.8 to 1.5% Mn, 0.1 to 0.3 Fe, and 0.1 to 0.25% Si, respectively and a region simultaneously satisfying Si<0.12% and Si<Fe<Si+0.2 and the balance Al with unavoidable impurities. Further preferably, Ti alone is incorporated into the aluminum alloy or Ti in combination with 0.0001 to 0.2% B or 0.0001 to 0.2% C is incorporated therein at 0.015 to 0.20% in the concentration of Ti. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an aluminum alloy for food cans that has a good production yield because it is less prone to casting cracks during production, and has excellent corrosion resistance and mechanical properties.

  As aluminum alloy for food cans, JIS3003 alloy (Al-Mn-Cu alloy) or JIS3004 alloy (Al-Mn-Mg alloy), and their improvements, due to the good balance between formability, corrosion resistance and mechanical properties An alloy (Al-Mn-Mg-Cu alloy) is used.

  For example, Patent Document 1 describes as “an improved container including an aluminum panel having a lead portion”, essentially one or two of up to 3% copper, up to 4% magnesium, or up to 1.5% manganese. A total of 1 to 7% of the above is described, and an alloy excellent in corrosion resistance and mechanical properties is described, characterized in that the balance is essentially composed of aluminum, an accompanying element and impurities, and the balance is inevitable impurities.

Further, Patent Document 2 discloses an “easy open lid made of a composite aluminum plate” in which the core material is Cu 0 to 0.8%, Mg 0 to 2.8%, Mn 0 to 1.5%, Fe 0 to 0.5%, and Si 0 to 0.5. An easy-open lid made of an aluminum alloy containing% is described.
Japanese Patent Laid-Open No. 52-8388 Japanese Patent Publication No.05-7263

  When an aluminum alloy sheet is used as a food can material, it is desired that it has excellent corrosion resistance in addition to material strength and formability. For this reason, the plurality of characteristics are optimized by adjusting the amounts of various component elements within an appropriate range. For example, Mg improves the strength as a can, but 0 to 2.8% is desirable in terms of corrosion resistance. Mn is effective in improving strength and corrosion resistance, and is preferably less than 2.0%, preferably in the range of 0.8 to 1.5% from the viewpoint of workability. Cu not only has the effect of improving the strength, but also exhibits the effect of bringing the aluminum material into an electrochemically noble state, so that corrosion is more effectively prevented.

In such an Al-Mn-Mg-Cu alloy, as the amount of added Cu increases, the probability of occurrence of casting cracks during ingot production increases, and the production yield is degraded and productivity is inferior. there were.

In order to improve the cast cracking property of an alloy, a method of adding an Al—Ti—B-based crystal grain refining agent has been conventionally known. For 1000 series alloys and Al-Mn-Cu series alloys, methods for limiting the Fe content, Si content and Fe / Si content ratio are also known. For example, Patent Document 3 discloses that “aluminum alloy plate for secondary battery case and secondary battery case using the same” has Si of 0.3 to 0.7%, Fe of 0.2% or less, and Fe / Si ratio of 3 or more. Further, a battery case comprising 0.4 to 0.9% of Cu and 0.8 to 1.5% of Mn and the balance being Al and impurities, and Mg in the impurities is 0.01% or less, Zn is 0.01% or less, Cr is 0.01% or less, and Ti is contained. As a battery case of 0.03% or less, an aluminum alloy plate for a secondary battery case that is excellent in moldability and pressure resistance, does not cause weld cracking, and has excellent weldability is described. Here, weld cracks are cracks generated by solidification shrinkage stress in the coexistence of solid-liquid phases, and are generated by the same mechanism as cast cracks. It is. The effect on the cracking improvement is described as the effect of Al-Fe-Si based crystals and Al-Mn-Fe-Si based crystals, but the crack generation mechanism is not clear.
Japanese Patent Laid-Open No. 2004-2985

  Therefore, the present inventors examined various effects of the alloying elements on the cast cracking properties of Al-Mn-Mg-Cu based alloys, which are materials for food cans with excellent corrosion resistance, in addition to material strength and formability, It has been found that the cast cracking property is greatly improved by optimizing the addition amount of Mn, the addition amount of Fe, the addition amount of Si, and the addition amount of Ti.

That is, the invention described in claim 1
Mg content 0.1-2.8% (mass%, the same shall apply hereinafter), Cu content 0.1-0.5%,
And in the range of Mn amount 0.8-1.5%, Fe amount 0.1-0.3%, Si amount 0.1-0.25%
Containing Mn, Fe, and Si content excluding a region that simultaneously satisfies Fe <0.2% and Mn> 2Fe + 0.8, and a region that simultaneously satisfies Si <0.12% and Si <Fe <Si + 0.2;
The balance is made of aluminum and inevitable impurities, and is an aluminum alloy for food cans having excellent cast cracking characteristics.

The invention of claim 2 further improves the cast cracking property by combining the grain refining effect by the commonly known Al-Ti-B master alloy. The aluminum alloy of claim 1 further includes Ti Alone or in combination with 0.0001 to 0.2% of B or 0.0001 to 0.2% of C, and containing 0.015% to 0.20% of Ti concentration.

  According to the present invention, the occurrence rate of casting cracks in aluminum alloys for cans found in the conventional method is greatly reduced, stable production is possible, and processing costs can be reduced. It is done.

  As a result of investigating and conducting tests on various casting cracks, the inventors of the present invention have a Mn of 0.8 to 1.5%, more preferably Mn of 1.0 to 1.2, in the Al-Mn alloy in which cracking is unlikely to occur. %. When Mg is added to this alloy, the rate of casting cracks is reduced as the amount of Mg added increases, so Mg is preferably as much as possible, but corrosion resistance deteriorates as the amount of Mg increases, so the amount of Mg is 0.4 to 2.8%, More preferably, the content is 0.8 to 1.3%.

The casting crack occurrence rate in the Al-Mn-Mg alloy described above is better as the Si content and Fe content increase, but it is necessary to satisfy Mn ≦ 2Fe + 0.8 between the Mn content and the Fe content. is there. On the other hand, if the amount of Fe and Si are increased, the corrosion resistance due to the Al-Fe-Si-based crystallized product is reduced, so the Fe amount is 0.1 to 0.3% and the Si amount is 0.1 to 0.25%. Increasing the amount of Ti further reduces the rate of casting cracking. However, if the amount of Ti is excessively large, TiB ₂ intermetallic compound particles formed during melting of the alloy are likely to enter the material and cause foreign object defects. Therefore, the Ti content is 0.015 to 0.05% or less, more preferably 0.015 to 0.02%.

FIG. 1 shows the composition range of the present invention.
(a) shows the range of the contents of Mn and Fe.
(b) is the figure which each showed the range of content of Fe and Si.

Cu increases the rate of occurrence of casting cracks as the amount added increases, so 0.5% or less, more preferably 0.4% or less, and still more preferably 0.2% or less. The aforementioned effects of optimizing the Mn content, Fe content, and Si content are more remarkable in alloys containing 0.1 to 0.5% Cu.

  Mn, Fe and Si are crystallized as (Al-Mg)-(Mn, Fe) -Si-based crystallized grains at the grain boundaries, and it is considered that casting cracks are likely to occur when the amount is large. The cracking property is lowered by setting the optimum addition amount of Mn, Fe and Si. Addition of Mg suppresses the growth of dendrite that grows during solidification and also improves the strength and elongation in the solid-liquid coexistence zone of the grain boundary by solid solution in the aluminum matrix, thereby suppressing casting cracks. . In the present invention, the casting cracking property is lowered by setting the Mg amount optimally in consideration of the corrosion resistance.

On the other hand, Cu promotes dendrite growth and crystallizes as an Al-Mg-Cu-based crystallized product at grain boundaries. For this reason, if the amount of added Cu exceeds 0.1%, it becomes extremely easy to crack.

In addition, the alloy of the present invention is subjected to casting, hot rolling, cold rolling, and intermediate annealing in accordance with a conventional method, and then rolled into a plate material having a thickness of about 0.25 mm to form a food can. Receive.

Next, the present invention will be further described with reference to examples. In addition, this invention is not limited to this Example.

  Cast crackability was evaluated by I-beam type cast crack test. The I-beam casting crack test is a known casting crack evaluation test method described in, for example, light metal vol.33, No.12, p705-711 (1983). This is an index of cast cracking property. In this experiment, an I-beam casting cracking test was performed on each alloy having the chemical composition shown in Table 1 at a melt temperature of 720 ° C. and a mold temperature of 250 ° C. in a mold length of 20 mm to 190 mm. The evaluation of crackability is based on the mold length that does not cause cracking. Cracks do not occur even when the mold length is 190 mm, cracks occur when the mold length is 140 mm or more, and cracks occur when the mold length is 70 mm or more. The evaluation was made in four stages: Δ, and cracking occurred when the mold length was 20 mm or more. It should be noted that the longer the crack generation mold length is, the more difficult it is to crack, and in the case of an alloy that cracks with a length of 140 mm or more, the frequency of crack generation in actual DC casting is significantly reduced.

In addition, the characteristics as a food can material were evaluated by producing plates in the laboratory.
An alloy with the chemical composition shown in Table 1 is cast into an ingot of 150 mm x 400 mm x 1500 mm, the surface is chamfered by 12 mm, heated immediately at 450 ° C for 12 hours, and then hot rolled immediately (at 420 ° C). Finished with a thickness of 3 mm and finished to 0.25 mm by cold rolling.

In order to evaluate the corrosion resistance, the aluminum alloy plate prepared by the above method was immersed in tap water added with 10 ppm of Cu ²⁺ for 4 weeks, the pitting depth was measured, 30 μm or less ○, those exceeding 30 μm ×, It was evaluated in two stages.

As for the evaluation of the formability, the evaluation was made in two stages of ○ / × from the good / bad formability of the plate material such as deep drawing and overhanging.

Table 1 shows the alloy composition and performance evaluation results of the test materials.
In Comparative Examples 1 and 3, the amount of Fe added is outside the lower limit of the numerical range regulated by the present invention, and the occurrence of cracks becomes significant.
In Comparative Examples 9 and 10, the Mn content and the Fe content do not satisfy the relationship of Mn ≦ 2Fe + 0.8 defined in the present invention, and the occurrence of cracks is remarkable.
In Comparative Example 6, the amount of Mn and the amount of Fe do not satisfy the relationship of Mn ≦ 2Fe + 0.8 defined in the present invention, and the Si amount excluded in the present invention is Si <Fe <Si + 0.2 ( Since it is in the numerical range of Si <0.12), cracking is remarkable.
In Comparative Example 7, the amount of Mn and the amount of Fe do not satisfy the relationship of Mn ≦ 2Fe + 0.8 defined in the present invention, and the amount of Cu deviates from the upper limit of the numerical range regulated in the present invention. And cracking is remarkable.
In Comparative Example 8, the amount of Mn and the amount of Fe do not satisfy the relationship of Mn ≦ 2Fe + 0.8 defined in the present invention, and the amount of Mg deviates from the lower limit of the numerical range regulated in the present invention. And cracking is remarkable.
In Comparative Examples 2 and 4, the amount of Mn added deviates from the upper and lower limits of the numerical range regulated by the present invention, and the casting crackability is good, but the moldability is significantly impaired.
In Comparative Example 5, the addition amount of Fe is outside the upper limit of the numerical range regulated by the present invention, and addition of Cu is outside the lower limit of the numerical range regulated by the present invention, although the cast cracking property is good. Corrosion resistance is impaired.
As described above, if the upper and lower limits of the numerical range of the additive element amount regulated by the present invention and the optimum additive amount of Mn, Fe, Si defined by the present invention are deviated, the occurrence of cracks becomes significant or Performance deterioration required as an aluminum plate for cans occurs.

On the other hand, in the inventive example, the occurrence of casting cracks is remarkably suppressed as compared with the comparative example, and the workability and corrosion resistance required as an aluminum plate material for food cans are sufficiently satisfied. When actually carried out on the production line, in the conventional case, casting cracks occur at a frequency of 15%, but with the alloy components according to claim 1, the frequency of occurrence of cracks can be suppressed to 4% or less. When the described alloy components are used, the crack generation rate can be suppressed to less than 1%. In any case, the characteristics required as a food can are maintained, and the production yield can be remarkably improved by the present invention.

FIG. 5 is a diagram showing the composition range of the present invention, wherein (a) shows the range of Mn and Fe contents, and (b) shows the range of Fe and Si contents.

Explanation of symbols

The alphabets in the figure are symbols corresponding to the examples in Table 1 of the examples.

Claims (2)

Mg content 0.1-2.8% (mass%, the same shall apply hereinafter), Cu content 0.1-0.5%,
And in the range of Mn amount 0.8-1.5%, Fe amount 0.1-0.3%, Si amount 0.1-0.25%,
Containing Mn, Fe, and Si content excluding a region that simultaneously satisfies Fe <0.2% and Mn> 2Fe + 0.8, and a region that simultaneously satisfies Si <0.12% and Si <Fe <Si + 0.2;
An aluminum alloy for food cans having excellent cast cracking characteristics, wherein the balance is made of Al and inevitable impurities. The cast cracking property according to claim 1, characterized by containing Ti alone or in combination with 0.0001 to 0.2% of B or 0.0001 to 0.2% of C and containing 0.015% to 0.20% of Ti. Excellent aluminum alloy for food cans.

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