JPH0320458B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for producing an aluminum alloy for packaging, and more specifically, to produce an aluminum alloy that has excellent formability, pressure resistance, can openability, and pitting resistance, and has a fine average grain size. It has excellent formability such as stretchability, riveting formability, and drawability, and can be hardened by baking coating to improve pressure resistance and rigidity. The present invention relates to a method for producing an aluminum alloy for packaging that has excellent pitting resistance. [Prior art] In general, aluminum alloy plates for can ends are produced by: (1) Shell processing after coating and printing are applied to the aluminum alloy plate. (2) Multi-stage overhang processing. (3) Score processing. (4) Rivet processing. Among these processes, the most important process is multi-stage stretching, which is influenced by mechanical properties, distribution of intermetallic compounds, crystal grain size, etc. Additionally, the molded can end has (1) pressure resistance. (2) Openability. (3) Tab removability. (4) Corrosion resistance. In particular, thinner materials require improved pressure resistance (higher strength). In recent years, materials have become thinner and have higher strength from the perspective of cost reduction, but thinner materials and higher strength have resulted in lower formability. High strength is required. On the other hand, molding speeds have been increasing in order to improve productivity, which has further led to a decline in workability. However, the conventionally used 5052,
With materials such as 5058 and 5182, the strength significantly decreases during baking after coating and printing, so in order to achieve high strength, it is necessary to contain solid solution elements and increase the final cold rolling rate. In this case, elongation is reduced and crystal grains are increased in length, resulting in a reduction in formability such as stretchability. In addition, various studies have been conducted on the shape of the score that is press-fitted into the lid for opening cans with the aim of improving can opening efficiency. Although the effect is recognized, if the residual pressure is reduced too much, cracks will occur in the score section, causing the contents to leak, and there is a limit to the reduction of the residual pressure. In addition, the conventionally used 5052,
For aluminum alloys such as 5082 and 5182, when the content is highly corrosive, such as when the C1 ions in the contents are high (several hundred ppm or more), the protective oxide film of the aluminum alloy is easily destroyed, causing local dissolution. This naturally leads to pitting, which can lead to fatal accidents as a container, so there are limits to its use. In particular, when a material more electrically noble than aluminum or aluminum alloy, such as tinplate, chin-free steel (TFS), or steel, is used for the can body, the galvanic effect is added in addition to the corrosive effect of the contents themselves. Alternatively, the rate of progress of pitting occurring in aluminum alloy materials will increase, and restrictions on the use of aluminum or aluminum alloy materials depending on the contents will become even more severe. [Problems to be Solved by the Invention] In view of the various problems of the conventional aluminum alloys for packaging explained above, the present inventor has conducted extensive research and repeated examinations. There is almost no loss in strength during baking, and
It is a bake-hard type that improves strength, makes it possible to reduce the final cold rolling reduction, and
Because the crystal grains before the final cold rolling are fine, this aluminum alloy for packaging has excellent formability, and can also improve can openability and pitting resistance due to high strength. They developed a manufacturing method. [Means for solving the problems] The method for producing an aluminum alloy for packaging according to the present invention is characterized by: Cu0.05-1wt%, Mn0.3-1.5wt%, Mg0.3-2.8wt% After melting and casting an aluminum alloy containing 0.03 to 0.3 wt% of Cr and the remainder A1 and unavoidable impurities, the aluminum alloy is heated to 500 to 600 degrees Celsius.
After soaking and hot rolling at a temperature of
Heating to a temperature of 400 to 600℃ at a heating rate of 100℃/min or more, immediately after heating, or after holding for less than 10 minutes, cooling to a temperature of 200℃ at a cooling rate of 100℃/hour or more, average The goal is to keep the crystal grain size to 25μ or less, keep components that contribute to bake hardening in a solid solution state, and perform cold rolling of 30% or more to improve formability, pressure resistance, can openability, and pitting resistance. This is a method for producing a bake-hardening aluminum alloy for packaging with excellent properties. The method for producing an aluminum alloy for packaging according to the present invention will be described in detail below. First, the components and content ratios of the aluminum alloy used in the method for producing an aluminum alloy for packaging according to the present invention will be explained. Cu is an element that coexists with Mg and has the effect of increasing strength, and also makes aluminum alloys noble.If the content is less than 0.05wt%, the bake-hard effect cannot be obtained, and if the content is less than 1wt%, If it is contained in excess, the bake-hardening effect cannot be expected to be as great as when it is contained, and susceptibility to intergranular corrosion increases. Therefore, the Cu content is set to 0.05 to 1 wt%. Although Mn does not directly affect the bake-hard effect, it is effective in improving strength and refining crystal grains. Like Cu, this Mn enriches aluminum alloys electrochemically, and also improves corrosion resistance. improve,
In addition, it is an element that improves can opening properties through the action of intermetallic compounds [Al ₆ (Mn, Fe)], etc., and its content is
If the content is less than 0.3 wt%, these effects will not be sufficient, and if the content exceeds 1.5 wt%, coarse intermetallic compounds will be formed, which will become a starting point for cracking, especially in multi-step overhang processing such as can-end. Therefore, the Mn content is set to 0.3 to 1.5 wt%. Mg is an effective element for improving strength, and is especially essential to obtain a bake-hard effect. If the content is less than 0.3wt%, high strength for thinning the wall cannot be obtained, and if the content is less than 0.3wt%, If the content exceeds this amount, the corrosion loss will increase and the corrosion resistance will decrease. Therefore, the Mg content is set to 0.3 to 2.8 wt%. Like Mn, Cr is electrochemically noble, and is also a very important element for improving corrosion resistance and can opening properties through the action of intermetallic compounds.The content is 0.03wt. If the content is less than 0.3 wt%, this effect will not be observed, and if the content exceeds 0.3 wt%, the size of the intermetallic compound will grow and the formability will deteriorate. Therefore, the Cr content is 0.03~0.3wt%
shall be. There are no particular restrictions on the elements other than those listed above, as long as they are impurities normally contained in commercially available pure aluminum, but Si and
The smaller the amount of Fe, the more desirable it is, and it is desirable that each of Zn and Ti be 0.05 wt% or less. Next, a method for producing an aluminum alloy for packaging according to the present invention will be explained. An aluminum alloy with the above-mentioned components and content ratios is melted and cast using a normal method to form an ingot, and this ingot is soaked at a temperature of 500 to 600°C. This is to obtain good rolling and stretchability (particularly small-diameter multistage stretchability), and if the soaking temperature is less than 500°C, edge cracks are likely to occur during hot rolling, and many fine precipitates are generated. Stretchability decreases, and burning and blistering occur at soaking temperatures exceeding 600°C, leading to deterioration of product properties such as workability and surface quality. Therefore, the soaking temperature is set at 500 to 600°C. Although there are no particular conditions for the subsequent hot rolling, it is preferable to finish the hot rolling at a temperature of 250°C or higher. Cold rolling may or may not be performed after this hot rolling. The next step is intermediate annealing, which is an important step in order to obtain a bake-hard effect and excellent formability (fine crystal grains).
The temperature is set at 600°C to form a solid solution of Mg and Cu, which are necessary for bake-hardening.If the heating temperature is lower than 400°C, solid solution will not be achieved sufficiently, and the subsequent bake-hardening effect cannot be expected. At a heating temperature exceeding .degree. C., this effect is saturated and cannot be expected much, and instead causes burning and the like, leading to deterioration of characteristics. Therefore, the heating temperature is 400 to 600°C.
The heating rate at this time must be 100/min or more, and the heating rate must be 100/min or more immediately after heating or after holding for less than 10 minutes.
It is necessary to cool to a temperature of 200℃ or less at a cooling rate of ℃/hour or more, and this is to create fine crystal grains (25μm or less) that are effective for formability, and to force Mg and Cu into solid solution. Outside these ranges, bake hard effects and high formability due to fine crystal grains cannot be obtained. Note that holding the holding time within 10 minutes does not improve the bake-hard effect even if the holding time exceeds 10 minutes, instead causing crystal grain growth and wasting energy. The reason for cooling is to harden by baking. [Example] An example of the method for producing an aluminum alloy for packaging according to the present invention will be described. Experiment 1 An aluminum alloy ingot with the ingredients and content ratios shown in Table 1 was soaked at 590°C for 4 hours and hot rolled to form a 4 mm hot rolled plate, and then cold rolled to a thickness of 1 mm. Intermediate annealing was performed at 500°C for 0 seconds (temperature increase/decrease at 800°C/min). Next, it was cold rolled to a thickness of 0.33 mm. In addition, in the case of the composition of the comparative example in Table 1,
Since burning occurred under the above soaking conditions (590°C x 4 hours), soaking was performed at 510°C x 4 hours. Table 2 shows the mechanical properties (as rolled, after baking), grain size after intermediate annealing, multistage stretch formability, open can test results, and corrosion resistance evaluation results. From this Table 2, aluminum alloy (No.
1, No. 2, and No. 3) showed bake-hardening phenomenon due to Al-Cu-Mg-based fine precipitates, the tensile strength was improved by baking, and the crystal grain size was the same as that of the present invention. All aluminum alloys for packaging
It can be seen that the aluminum alloy for packaging according to the present invention has an excellent multi-stage elongation property with a diameter of 25 μm or less, and also has excellent can opening properties due to the coexistence of Mn and Cr, and also has excellent corrosion resistance. Comparative Example No. 6 shows a baking phenomenon and has small crystal grains and good moldability, but it does not contain Cr and therefore has problems in can openability and corrosion resistance.

【table】

【table】

【table】

[Table] Experiment 2 Intermediate annealing in Example 1 at 370°C for 2 hours.
When carried out at a heating and cooling rate of 40℃/hour,
Mechanical properties of 0.3mm thickness, grain size after intermediate annealing,
Table 3 shows the multi-stage stretch formability, can opening test results, and corrosion resistance evaluation results. As can be seen from Table 3, when intermediate annealing is carried out under the conventional conditions of 370°C x 2 hours and a heating and cooling rate of 40°C/hour, the aluminum alloy used in the method for producing an aluminum alloy for packaging according to the present invention Regarding the components and content ratios, the softening due to baking is large and high strength cannot be obtained, and the crystal grains after intermediate annealing are 25 μm or more. Although there is no problem in forming with the current plate thickness, it is difficult to obtain high strength. There is a problem in some cases.

【table】

【table】

[Table] Experiment 3 For the No. 1 alloy shown in Table 1, intermediate annealing was performed under the conditions shown in Table 4, and the mechanical properties and crystal grains after intermediate annealing at a thickness of 0.3 mm are shown in Table 4. show. Note that the holding time at the reached temperature (heating temperature) is 0.
Seconds. From this table 4, the reached temperature (heating temperature) is 400
The heating temperature must be 400 to 600 degrees Celsius, considering burning, etc.
Furthermore, if the heating rate is less than 100℃/min, fine crystal grains cannot be obtained, and if the cooling rate is 100℃/hour (1.7℃/min), fine grains cannot be obtained.
minutes), Cu and Mg, which are effective for baking hard, precipitate during cooling and hardening during baking cannot be achieved.

[Table] [Effects of the Invention] As explained above, since the method for producing an aluminum alloy for packaging according to the present invention has the above configuration, the produced aluminum alloy has no bake-hard effect during the baking process during coating printing. It maintains high strength by utilizing this, and has excellent formability such as stretchability, rivetability, and drawability due to the refinement of crystal grains, and also has excellent can openability and pitting resistance.
(1) Due to the bake-hard effect and grain refinement, it has high strength and excellent formability in various forms, as well as excellent openability and corrosion resistance, making it ideal for the lids and bodies of regular beverage cans (DRD cans). It is. (2) Due to its excellent pitting resistance, the lids of all-steel cans for beverages and other foods containing salt can be changed to aluminum, which is ideal for easy-open lids. (3) The aluminum alloy plate for packaging according to the present invention has good properties as a lid material for all-aluminum cans as well. (4) Can also be used for food can bodies (DRD cans). It has this effect.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between load and elongation, FIG. 2 is a diagram showing a corrosion resistance test method for a single product, and FIG. 3 is a diagram showing a corrosion resistance test method in combination with tinplate.

Claims (1)

[Claims] 1. An aluminum alloy containing 0.05 to 1 wt% of Cu, 0.3 to 1.5 wt% of Mn, 0.3 to 2.8 wt% of Mg, and 0.03 to 0.3 wt% of Cr, with the balance consisting of A1 and inevitable impurities. After melting and casting, 500℃~600℃
After soaking and hot rolling at a temperature of
Heating to a temperature of 400 to 600°C at a heating rate of 100°C/min or more, immediately after heating, or after holding for within 10 minutes, cooling to a temperature of 200°C or less at a cooling rate of 100°C/hour or more, Formability, pressure resistance, can openability, and pitting resistance are characterized by having an average grain size of 25 μ or less, keeping components that contribute to bake hardening in a solid solution state, and performing cold rolling of 30% or more. A method for manufacturing a bake-hardening aluminum alloy for packaging with excellent properties.