Metal treatment – Stock – Aluminum base
Reexamination Certificate
1999-08-06
2003-08-19
Ip, Sikyin (Department: 1742)
Metal treatment
Stock
Aluminum base
C148S689000, C420S532000
Reexamination Certificate
active
06607615
ABSTRACT:
TECHNICAL FIELD
The present invention relates to aluminum alloy extruded materials for structural members of automotive bodies having excellent mechanical strength, impact absorbability, spot weldability, and surface treatment property, and that can be produced at low cost using, as a raw material, recycling aluminum materials, such as recycled aluminum cast scraps of automobiles and aluminum can scraps. The present invention also relates to a method for producing the aluminum alloy extruded materials.
Further, the present invention relates to aluminum alloy extruded materials for structural members of automotive bodies having excellent mechanical strength, bendability, spot weldability, and surface treatment property, and that can be produced at low cost using, as a raw material, recycling aluminum materials, such as recycled aluminum cast scraps of automobiles, recycled aluminum scraps of aluminum cans, and recycled aluminum scraps of aluminum sashes. The present invention also relates to a method for producing the aluminum alloy extruded materials.
BACKGROUND ART
Many structural members of automobiles are complicated in shape and are hollow, and since aluminum alloy materials are light in weight and more suitable for extrusion than other materials, use of extruded materials of aluminum alloys as structural members of automotive bodies is now studied. The extruded materials of aluminum alloys are especially suitable since they are not only light but also highly rigid, and then they can absorb energy at the time of a collision through crushing themselves increasing safety.
However, the materials conventionally used in such aluminum alloy extruded materials are mainly 6000-series aluminum alloys, such as 6063 aluminum alloy, and since 6000-series aluminum alloys have relatively low mechanical strength and impact-absorption energy, in comparison with other materials, they have the problem that it is required to increase the thickness of the material shaped. Further, they have the problem that they have poor bendability; that is, when these alloys are subjected to severe bending, cracks occur. Furthermore, there are other problems; for example, the spot weldability is low, requiring a very large electric current for spot welding in the assembling process for automobiles, thereby lowering productivity; and the degreasing property and the chemical conversion property, for example, in the case for surface coating, are poor, thereby making it difficult to secure a coating with good durability. Among structural members of automobiles, particularly those called structural members for bodies, such as side frames, rear frames, center pillars, side sills, and floor frames, are fixed, for example, by spot welding, and they are also exposed to the outside environment, as well as to a corrosive environment, including muddy water. Therefore, the structural members for the bodies are materials that essentially require the chemical conversion susceptivity, since, for example, they are covered by coating for improving the corrosion resistance.
However, hitherto, materials that have various performance properties required for structural members of automotive bodies, such as workability, spot weldability, and surface treatment property, and extrudability and mechanical strength, required for aluminum alloys, and that are also excellent in recycling ability, have not yet been developed.
(i) Although, for example, JP-A-58-31055 (“JP-A” means unexamined published Japanese patent application) discloses an aluminum alloy for structure improved in mechanical strength, weldability, and cutting ability/machinability, which comprises 2.3 to 6% by weight of Si, 0.4 to 1.0% by weight of Mg, 0.4 to 1.0% by weight of Mn, small amounts of Zn and Sn, and the balance being made of Al, it is not satisfactory in bendability and spot weldability, and it is greatly different from the present invention, in that it is not one wherein both elements of Cu and Zn are contained, whereby the melting temperature of the aluminum alloy is lowered and the spot weldability and the chemical conversion property (zinc phosphatability (the property of being attached with zinc phosphate)) at the time of pretreatment for coating or the like are improved.
(ii) Further, although JP-A-61-190051 discloses a process for the production of an Al-series hollow extruded material, wherein use is made of an aluminum alloy containing 5 to 15% by weight of Si, and up to 1.0% by weight of Mg, and having an Fe content of 0.5% by weight or less, with Cu, Mn, etc., amounting to 0.25% by weight or less, this aluminum alloy is larger in the amount of added Si than the present invention, and it is an alloy improved in heat resistance and wear resistance properties, such that it is used for high-temperature exposure members of automobiles, rod materials for slide members, and thick extrusion-shape materials, but it is low in spot weldability and surface treatment property, such as zinc phosphatability, and it lacks extrudability. Accordingly, this material is not one that can be used as an extruded material for body structures, as the present invention can.
(iii) Further, JP-A-5-271834 discloses an aluminum alloy fine in crystal grains and stable in artificial aging, which contains 0.2 to 1.2% by weight of Mg, and 1.2 to 2.6% by weight of Si, with the value of {Si (% by weight)—Mg (% by weight)/1.73} being over 0.85 but less than 2.0, and the balance being made of Al. This is an alloy whose composition ratio of Mg to Si is such that Si is in excess in terms of stoichiometric composition, thereby allowing Mg
2
Si to be formed readily. This is an alloy whose component ranges of Mg and Si in the compositions of conventional JIS 6N01 alloys and AA6005 alloys are simply increased, and the extrudability is excellent, but other properties, i.e. the spot weldability and the surface treatment property, are not satisfactory.
(iv) Furthermore, JP-A-8-225874 describes an aluminum alloy extruded material for automotive structural members that contains 0.5 to 2.5% by weight of Si, 0.2 to 1.0% by weight of Fe, 0.45 to 1.5% by weight of Zn, 0.05 to 1.0% by weight of Cu, and 0.4 to 1.5% by weight of Mn. Although this extruded material is excellent in extrudability, mechanical strength, and surface treatment property, the electrical resistance of the material is low, and the spot weldability is still problematic. That is, in the spot welding in the mass production line of structural members of automotive bodies, the wearing of the welding electrode tip is a problem, and, as the wearing of the electrode tip progresses, the texture of the welded part becomes unstable and the nugget size changes, thereby lowering the strength of the welded part. Therefore, the electrode tip must be replaced frequently, which is a prime cause to adversely affect productivity in the mass production line, and hence the wearing of the welding electrode tip is a prime problem involved in spot welding.
Furthermore, in recent years, in view of environmental problems, effective exploitation of resources, and the like, the importance of recycling of used products is on the increase, leading to activities for legislation to make the recycling of automotive parts obligatory. Hence and the reuse of metal scrap is also being studied in various ways. In particular, there is a need for an established technique for regenerating high-quality materials from recycled aluminum cans, from recycled scraps of aluminum sashes, and from scraps of abandoned automobiles.
Accordingly, an object of the present invention is to provide an aluminum alloy extruded material for structural members of automotive bodies that is excellent in spot weldability and surface treatment property, such as the chemical conversion property and degreasing property, that has high mechanical strength and ductility, and that has excellent impact absorbability.
Further, another object of the present invention provides a method for the production of an aluminum alloy extruded material for structural members of automotive bodies that
Bekki Yoichiro
Hayashi Noboru
Kashiwazaki Kazuhisa
Ohara Nobuaki
Birch & Stewart Kolasch & Birch, LLP
Ip Sikyin
LandOfFree
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