Metal treatment – Stock – Aluminum base
Reexamination Certificate
2001-12-21
2004-05-18
Wyszomierski, George (Department: 1742)
Metal treatment
Stock
Aluminum base
C148S692000, C420S550000, C420S551000, C420S553000
Reexamination Certificate
active
06736911
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an aluminum alloy, an aluminum alloy foil and a container excellent in corrosion resistance and a method of preparing an aluminum alloy foil, and more particularly, it relates to an aluminum alloy and an aluminum alloy foil for a container for a beverage or food, a building material, a food wrapping material, a domestic article and a decorative article having high strength and sufficient elongation improving formability and exhibiting excellent rollability and a method of preparing the same.
BACKGROUND ART
Among aluminum alloys, particularly those for containers for weak-acidic food containing soy sauce or sodium chloride must have sufficient corrosion resistance, strength and elongation for increasing its formability, and hence aluminum alloys such as JIS (Japanese Industrial Standard) nominal 3003, 3004 and 5052 of about 50 to 200 &mgr;m in thickness are employed in general. Table 1 shows typical compositions of these alloys.
TABLE 1
Alloy Name
Additional Element for Aluminum Alloy (mass %)
(JIS Nominal)
Fe
Si
Cu
Mn
Mg
Cr
Zn
Ti
3003
0.7
0.6
0.1
1.2
—
—
0.10
—
3004
0.7
0.30
0.25
1.2
1.0
—
0.25
—
5052
0.40
0.25
0.10
0.10
2.5
0.20
0.10
—
1030
0.6
0.35
0.10
0.10
0.05
—
0.10
0.03
8021
1.2
0.07
0.01
—
—
—
0.10
—
8079
0.9
0.07
0.01
—
—
—
0.10
—
In these alloys, a corrosive phenomenon referred to as “pitting corrosion” readily takes place in general. It is known that a surface of aluminum or an aluminum alloy is generally covered with a strong natural oxide film and hence excellent in corrosion resistance. When this oxide film is partially broken for some cause, however, corrosion takes place only in this portion and progresses in the depth direction. This phenomenon is referred to as pitting corrosion.
In order to prevent this pitting corrosion, Japanese Patent Laying-Open No. 3-261549, for example, discloses a cladding material having an aluminum film of high purity formed on its surface as a covering material. Japanese Patent Laying-Open No. 60-221546 discloses a technique of preventing pitting corrosion by adding zinc to an aluminum alloy. Further, Japanese Patent Laying-Open No. 10-183283 discloses an aluminum alloy cladding material excellent in corrosion resistance employing an aluminum alloy containing tin as a covering material.
When high-purity aluminum is employed as the covering material, however, dust is readily caused in forming due to excessive softness of the high-purity aluminum, to result in a problem of contamination.
When zinc or tin is added, the material is generally corroded although pitting corrosion can be prevented. Therefore, the quantity of corrosion is so large that the aluminum alloy is unsuitable for a container for food or the like.
Further, employment of a cladding material for a food container is generally unprofitable in consideration of the cost.
While high strength and formability are required to an aluminum alloy applied to a container for a beverage or food, those described in the aforementioned gazettes cannot sufficiently satisfy these characteristics.
High corrosion resistance and high strength are required also to an aluminum alloy foil for a building material employed as a heat insulating material, a wrapping material directed to prevention of deterioration of food or chemicals, a domestic article and a decorative article, for example, other than the container, i.e., in the field where the aluminum alloy foil is used with a thickness of not more than 50 &mgr;m. However, the aluminum alloys of the aforementioned JIS nominal 3003, 3004 are 5052 are so remarkably work-hardened in rolling that it is difficult to roll the aluminum alloys into foils of not more than 50 &mgr;m in thickness. In particular, it is practically impossible to obtain an aluminum alloy foil of not more than 20 &mgr;m.
Aluminum-iron alloys such as JIS nominal 8021 and 8079 shown in Table 1 are generally employed for these thin foils. In these alloys, however, presence of aluminum-iron intermetallic compounds reduces corrosion resistance and suppresses refinement of grains for attaining sufficient strength. Therefore, these aluminum alloys are insufficient in strength and never satisfactory.
Accordingly, the present invention has been proposed in order to solve the aforementioned problems, and an object of the present invention is to provide an aluminum alloy capable of preventing pitting corrosion and general corrosion without being worked into the form of a cladding material and excellent in strength, formability and workability, an aluminum alloy foil consisting of this aluminum alloy and a method of preparing the same, and a container employing this aluminum alloy foil.
DISCLOSURE OF THE INVENTION
In order to solve the aforementioned problems, the inventors have made various studies, to prove that copper and silicon are elements extremely reducing pitting corrosion resistance of an aluminum alloy while zinc and tin are elements causing general corrosion of the aluminum alloy under weak-acidic environment. Therefore, corrosion resistance of the aluminum alloy is reduced if any of these elements is added to the aluminum alloy.
It has also been proved that manganese, iron, chromium, titanium and zirconium are elements capable of increasing the strength without damaging the corrosion resistance of the aluminum alloy and providing sufficient elongation for improving the formability and high rollability for obtaining a thin foil by selecting proper contents and manufacturing conditions.
According to these recognitions, the inventors have succeeded in developing an aluminum alloy excellent in corrosion resistance, strength, formability and rollability.
An aluminum alloy according to an aspect of the present invention, proposed according to these recognitions, contains at least 0.0001 mass % and not more than 0.03 mass % of copper, at least 0.0005 mass % and not more than 0.2 mass % of silicon, at least 0.5 mass % and not more than 4 mass % of manganese and at least 0.5 mass % and not more than 3 mass % of iron, with the rest containing aluminum and unavoidable impurities.
Preferably, the aluminum alloy contains at least 0.0001 mass % and not more than 0.03 mass % of copper, at least 0.0005 mass % and not more than 0.2 mass % of silicon, at least 1.0 mass % and not more than 3.0 % of manganese and at least 0.7 mass % and not more than 1.2 mass % of iron, with the rest containing aluminum and unavoidable impurities.
An aluminum alloy according to another aspect of the present invention further contains at least one of at least 0.01 mass % and not more than 0.5 mass % of chromium, at least 0.01 mass % and not more than 0.5 mass % of titanium and at least 0.01 mass % and not more than 0.5 mass % of zirconium in either one of the aforementioned aluminum alloys.
An aluminum alloy foil according to the present invention consists of an aluminum alloy having any of the aforementioned compositions, and has a thickness, yield strength and elongation so selected that the relation between the yield strength YS (N/mm
2
) and the thickness X (&mgr;m) satisfies an inequality YS>28.7 1n(X)−30 and the relation between the elongation El (%) and the thickness X (&mgr;m) satisfies an inequality El>0. 15X+3.5.
A method of preparing the aluminum alloy foil according to the present invention having the aforementioned mechanical characteristics comprises the following steps:
(a) A step of heating up an ingot of an aluminum alloy to a temperature of at least 350° C. and not more than 580° C.
(b) A step of hot-rolling the ingot of the aluminum alloy at a starting temperature of at least 350° C. and not more than 530° C. after the heating up thereby obtaining a plate material.
(c) A step of cold-rolling the plate material after the hot rolling.
(d) A step of softening the plate material after the cold rolling.
Preferably, the aforementioned preparation method further comprises a step of holding the ingot of the aluminum alloy at a temperature of at least 350° C. and not more than 580° C. for not more than 15 hours after the step of heati
Abe Masaaki
Hashizume Yoshiki
Ro Akinori
Combs Morillo Janelle
Fasse W. F.
Fasse W. G.
Toyo Aluminium Kabushiki Kaisha
Wyszomierski George
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