JPH04107237A - Al alloy sheet for can end excellent in corrosion resistance and its manufacture - Google Patents

Abstract

PURPOSE:To obtain an Al alloy sheet material for a can end excellent in corrosion resistance and stress corrosion cracking resistance by executing soaking treatment to an Al allay ingot obtd. by adding specified ratios of Mg, Mn or the like to Al and thereafter subjecting it to hot rolling and cold rolling under specified conditions. CONSTITUTION:As an Al alloy as a can-top material for beer and carbonated drinks, the one having a compsn. contg., by weight, 2.0 to 4.O% Mg and 0.5 to 1.2% Mn in such a manner that 3.0%<=Mg+Mn<=5.0% and Fe+Mn<=1.5% are satisfied or furthermore contg. at least one kind among <=0.6% Cu, <=0.3% Cr and <=0.5% Zn is melted. The ingot of this Al alloy is subjected to soaking treatment, is thereafter hot-rolled into a steel sheet, is successively cold-rolled at >=50% rolling ratio, is thereafter subjected to annealing treatment and is moreover cold-rolled at 50 to 80% rolling ratio into the shape of a thin sheet. The Al allay sheet material for a can end in which the areal occupancy ratio of crystallized products in the surface is regulated to <=1.5% and excellent in stress corrosion cracking resistance can be manufactured.

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to an AnQ metal plate for can lids for beer and carbonated beverages, and more specifically, it is suitable for this type of use and has excellent corrosion resistance, especially positive pressure corrosion cracking resistance. (Internal pressure) An for cans
The present invention relates to a method for manufacturing composite plywood. (Prior Art) Conventionally, AA5182 or AA5082 has been used as a lid material for positive pressure cans for beer, carbonated drinks, etc. These An composite plywood materials are painted, then waxed and processed into lids. By the way, there are two methods of painting An plywood: a method of painting in sheet form and a method of continuously painting coils. In the former case, if the rolled board is painted as is, processing distortion (board warpage) will be relaxed due to the thermal effect during painting, and the holding part of the board will come into contact with the material, which may cause coating defects. For this reason, in the case of sheet coating, strain relief annealing is performed in advance at a temperature of 100 to 200° C. for the purpose of removing processing strain. (Problems to be Solved by the Invention) By the way, as mentioned above, sheet coating materials manufactured by conventional manufacturing processes have problems in corrosion resistance. In other words, 100 to 200
When heat treated (strain relief annealing) at a temperature of ℃, the conventional 5
Since 182 and 5082 materials contain a large amount of Mg, Mg atoms gather at grain boundaries with many lattice defects during the heat treatment,
The β phase (MgzAn) preferentially precipitates at that site. Since this β phase has a base potential compared to the base material An, it preferentially dissolves when exposed to a corrosive environment, causing intergranular corrosion or stress corrosion cracking when stress is applied. When such a material is used as a lid material for a beverage can, if the tensile stress caused by the internal pressure of the can and the corrosive environment overlap, leakage of contents occurs due to stress corrosion cracking. In recent years, the cost of beverage can lids has been reduced by making them thinner and stronger, and the above problem will become even more important in the future. Therefore, as a method for removing machining strain, heat treatment that removes machining strain without precipitating the β phase, that is, heat treatment in a continuous annealing furnace at high temperature and for a short time, can be considered, but in this case, since the product plate is thin, In addition to being subject to restrictions on equipment capacity, this also causes problems such as easy variation in product strength, and also leads to increased product costs. On the other hand, according to the method of heat treatment at a temperature exceeding 200℃, the β phase also precipitates inside the crystal grains, and the potential difference between the inside of the crystal grains and the grain boundaries becomes smaller, and although a slight improvement effect is recognized, it is still insufficient. It is. In addition, in the case of heat treatment exceeding 200° C., a material cleaning step is required to prevent rolling oil from seizing, which increases costs. As mentioned above, the reality is that there is a demand for materials that do not undergo intergranular corrosion or stress corrosion cracking in their raw state. The present invention has been made in response to these demands, and provides an Al alloy plate with excellent corrosion resistance, particularly stress corrosion cracking resistance, for use in can lids for beer and carbonated beverages. The object of the present invention is to provide a method for producing the same. (Means for Solving the Problems) In order to achieve the above object, the present inventors have conducted extensive research to develop a canned material that has strength equivalent to that of current materials and has high corrosion resistance. As a result, it was found that intergranular corrosion or stress corrosion cracking is greatly affected by the amount of Mg added, and practically there is no problem if it is 4.0% or less. However, as the amount of Mg added decreases, the strength of the material also decreases, and we have found that Mn is the most excellent element for increasing strength without decreasing corrosion resistance. In this case, it has been found that when the amount of Mn added increases, a large number of intermetallic compounds are formed, and the strength is too high, leading to processing cracks, so it is necessary to appropriately control it. Based on these findings, we have conducted further experimental research and have hereby accomplished the present invention. That is, the present invention provides Mg:2. O~4.0% and Mn
: Contains 0.5-1.2%, and satisfies 3.0%≦Mg +Mn≦5.0% Fe+Mn≦1.5%, and if necessary, further Cu≦0.6% ,Cr
Contains at least one of ≦0.3% and Zn≦0.5%, the remainder consists of An and impurities, and the area occupation rate of crystallized substances on the plate surface of the cold-rolled plate is 1°5% or less The object of the present invention is to provide an An alloy plate for can ends which is characterized by excellent corrosion resistance. In addition, the manufacturing method includes soaking an An alloy ingot having the above chemical components, hot rolling it, and then rolling it at a rolling rate of 5.
After cold rolling at 0% or more and further intermediate annealing, 50 to 8
It is characterized by cold rolling at 0% to obtain a cold-rolled sheet with an area occupation rate of crystallized substances on the plate surface of 1.5% or less. The present invention will be explained in more detail below. (Function) First, the reason for limiting the chemical composition of the An-gold alloy in the present invention will be explained. Mg is an important element that imparts strength, and at least 2
．． If 0% or more is not added, the strength is low and it cannot be used as an end material. On the other hand, if it exceeds 4.0%, although a high-strength material can be obtained, the corrosion resistance will be significantly reduced, so the amount of Mg added should be in the range of 2.0 to 4.0%. Mn is also an important element that imparts strength, and at least 0
．． Unless 5% or more is added, strength as an end material cannot be obtained. On the other hand, if it exceeds 1.2%, processing cracks are likely to occur due to increased formation of intermetallic compounds. Therefore, M
The amount of n added is in the range of 0.5 to 1.2%. However, the total amount of Mg and Mn (Mg+Mn) has a large effect on strength and formability, and when the amount of Mg + Mn is 3
If it is less than 0%, the strength required for the end material cannot be obtained. On the other hand, if the amount of M g + M n exceeds 5.0%, although it is effective for increasing the strength, the moldability is significantly reduced. Therefore, it is necessary to satisfy the relationship 3.0%≦Mg+Mn≦5.0%. Furthermore, the total amount of Fe and Mn (Fe+Mn) also has a large effect on the moldability, and when the Fe+Mn amount exceeds 1.5%, the moldability is significantly reduced due to the formation of giant crystallized substances. Therefore, it is necessary to satisfy the relationship Fe+Mn≦1.5%. Note that, if necessary, at least one of Cu, Cr, and Zn can be added in an appropriate amount. Although Cu is an effective element for improving strength, 0.6%
If the amount exceeds 0.6%, the corrosion resistance will decrease (general corrosion), so the amount added should be 0.6% or less. Like Cu, Cr is effective in improving strength and stabilizing the structure, but if it exceeds 0.3%, giant crystallized substances will be generated and cause processing cracks, so its addition is not recommended. The amount shall be 0.3% or less. Zn is an effective element for making crystallized substances finer, but at 0.5
%, the corrosion resistance decreases (general corrosion), so the amount added should be 0.5% or less. Next, the manufacturing method of the present invention will be explained. The An gold alloy ingot having the above chemical composition is subjected to a soaking treatment by a conventional method, then hot rolled, and then cold rolled including intermediate annealing. However, the cold rolling ratio before intermediate annealing affects the crystal grains and formability, and if it is less than 50%, the crystal grains during subsequent intermediate annealing will become larger, resulting in a decrease in formability. The cold rolling rate needs to be 50% or more. Although the intermediate annealing method is not particularly specified, it is essential to obtain completely recrystallized grains, and from the viewpoint of crystal grains, continuous annealing (CAL) is preferably used. Further, the cold rolling rate after intermediate annealing affects the strength and formability, and if it is less than 50%, the strength required as an end material cannot be obtained. On the other hand, if it exceeds 80%, although it is effective for increasing the strength, it is not preferable because the strength is too high, leading to processing cracks, and the anisotropy of the material increases. Therefore, the cold working rate after intermediate annealing is 50~8
The range is 0%. In addition, the distribution of crystallized substances on the plate surface in the final product thickness affects the formability and tearability when opening the can, and when the area occupation rate of crystallized substances exceeds 1.5%, the tearing load decreases. Although the can-openability is excellent, the moldability is significantly reduced, so the area occupancy of the crystallized matter needs to be 1.5% or less. The material of the present invention can be applied to either sheet coating or continuous coil coating, and sheet coating does not require strain relief annealing. (Example) Examples of the present invention are shown below. An alloy ingot having the chemical composition shown in Table 1 was subjected to soaking treatment at a temperature of 500° C. for 3 hours, and then hot rolled to a plate thickness of 4 mm. Then, by cold rolling 1. It was set to O+am. after that,
CAL annealing (heating/cooling rate 700° C./win, final temperature 450° C., holding time 2 seconds) was performed, and the product was further cold rolled to a product thickness of 0.3 noodle shoulders. In addition, the end material is molded after painting, so the length of 20"
Cx was subjected to baking treatment for 20 minutes under the same conditions as when painting. Table 2 shows the evaluation results of mechanical properties, formability (riveting workability), and corrosion resistance after baking for a product with a thickness of 0.3 mm. In addition, the area occupancy rate of crystallized substances is also listed. Note that the riveting processability is determined using the processability shown in Figure 1.
Evaluation was made based on the limit overhang height. Corrosion resistance was evaluated by the cracking life of stress corrosion cracking using the U-bend energization method shown in FIG. The area occupancy rate of crystallized substances is determined by SEMIt after surface polishing.
It was determined through image processing by the inspector. In Table 2, the comparison material NQI has a small amount of Mg, so it cannot have the strength as an end material, and also has a low rivet workability because of the small amount of Mg. Nα2 and &3 of the present invention materials have good strength, riveting workability, and corrosion resistance. Comparative material Na 4 has a small amount of Mn, so it does not have enough strength as an end material, and has a practical problem. The material Nc5 of the present invention is excellent in strength, riveting workability, and corrosion resistance. Comparative material &6 had a crystallized substance area occupation rate greater than the range of the present invention, resulting in a significant decrease in riveting workability. Inventive material N1117 is excellent in strength, riveting workability, and corrosion resistance.6 Conventional materials Nα8 and Nα9 have problems in corrosion resistance.

[Left below] A hot-rolled sheet having chemical components (within the scope of the present invention) of (11) and 15 in Table 1 of Example 1 was cold-rolled under the rolling rate conditions shown in Table 3. Ta. Note that the intermediate annealing was performed under the same conditions as in Example 1, and the final plate thickness was also the same as in Example 1. Furthermore, since the end material is molded after painting, the 200'
CX was subjected to baking treatment for 20 minutes under the same conditions as when painting. Table 3 shows the evaluation results of mechanical properties, formability (rivet workability), and corrosion resistance after baking treatment for a product with a thickness of 0.3 mm. In addition, anisotropy and area occupancy of crystallized substances are also listed. The evaluation procedures for riveting workability and corrosion resistance and the method for measuring the area occupancy of crystallized substances were the same as in Example 1.
The anisotropy is the reduction rate (%) obtained using the following formula using a 40% reduction cup.
) was evaluated. Since the rolling rate before inter-annealing is low, the rivet workability deteriorates due to coarsening of crystal grains, and it cannot be used as an end material. Comparative material Ma 3 has a low rolling rate after intermediate annealing, so it cannot be used as an end material because it does not have the strength. Nα4 and Nα5 of the present invention material are strength, riveting workability,
It has good corrosion resistance and also good anisotropy. Comparative material 6 has a large rolling reduction after intermediate annealing and has high strength, but has practical problems due to decreased riveting workability and increased anisotropy. Comparative material Na 7, like comparative material Nα3, has a low rolling reduction after intermediate annealing and has the best riveting workability, but does not have the strength as an end material. The N118 and Na9 materials of the present invention have good strength, riveting workability, corrosion resistance, and anisotropy. [Blank below] In Table 3, Nc 1 and &2 of the comparative materials are medium (effects of the invention). Since it greatly contributes to improving corrosion cracking resistance and provides appropriate strength, the use of the material of the present invention is sufficient to meet the requirements for thin walls and high strength. It is also superior in terms of manufacturing (stability, cost).

[Brief explanation of drawings]

Figures 1 (a), (b), and (C) are diagrams explaining the processing method for evaluating rivet workability, where (a) is the first stage, (b)
) shows the second stage, (c) shows the third stage, and Fig. 2 shows the U-
It is a figure explaining the point of the Bend energization method. (Q)? st Patent applicant: Kobe Steel, Ltd. Patent attorney Hisashi Nakamura (b) 2nd draw d (C) rd

Claims (3)

[Claims] (1) In weight% (the same applies hereinafter), Mg: 2.0 to 4.0
% and Mn: 0.5 to 1.2%, and 3.0%≦
It satisfies Mg+Mn≦5.0% Fe+Mn≦1.5%, the remainder consists of An and impurities, and the area occupation rate of crystallized substances on the plate surface of the cold-rolled plate is 1.5% or less. Al alloy plate for can ends with excellent corrosion resistance. (2) Furthermore, Cu≦0.6%, Cr≦0.3% and Zn
The Al alloy plate according to claim 1, containing at least one of ≦0.5%. (3) After soaking an Al alloy ingot having the chemical composition according to claim 1 or 2, hot rolling is performed, and then cold rolling is performed at a rolling rate of 50% or more, and further after intermediate annealing, 50～
A method for producing an Al alloy plate for can ends having excellent corrosion resistance, characterized by cold rolling at a rolling rate of 80% and obtaining a cold rolled plate having an area occupancy of crystallized matter of 1.5% or less on the plate surface.