Alloys or metallic compositions – Aluminum base – Copper containing
Reexamination Certificate
2000-12-15
2004-04-06
King, Roy (Department: 1742)
Alloys or metallic compositions
Aluminum base
Copper containing
C420S545000, C420S549000, C420S535000
Reexamination Certificate
active
06716390
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an aluminum alloy extruded material for automotive structural members, such as a frame or a beam, which is excellent in mechanical strength, fatigue strength, toughness, weldability, and extrusion property. The present invention also relates to a production method of the aluminum alloy extruded material.
BACKGROUND OF THE INVENTION
Hitherto, 6000-series alloys, such as JIS 6061 alloy, 6N01 alloy, or 6063 alloy, have been generally used as an aluminum alloy extruded material for automotive structural members, such as a shape (product) for a space frame. However, these alloys require an extremely large electric current in performing spot welding, raising a problem that the welding electrode tip life decreases. Further, since these alloys have a low degreasing property and a low chemical conversion property, it has been difficult to apply a coat having good durability onto these alloys.
As characteristics desired in extruded materials for automotive structural members, there are, for example, ease in extrusion of a hollow cross section, high mechanical strength, high elongation, high bending processability, and excellent fatigue property, in addition to the aforesaid spot weldability, and surface treatment properties, such as degreasing property and chemical conversion property.
Further, in recent years, from the view-point of environmental problems and effective utilization of resources, the importance of recycling used products is increasing, and also there is movement to legislate the obligation to recollect automobile parts, and various studies are carried out on the reutilization of metal scrap. Particularly among these, the establishment of a technique for reproducing high-quality materials from scrap of discarded automobiles and others, is eagerly desired. For this reason, an excellent recycling property is a characteristic that will become more important in aluminum alloy materials.
Also, toughness of a certain degree is required, to sustain a load as an automotive structural member.
However, as described below, the conventional materials do not have these characteristics at the same time.
(i) For example, JP-A-58-31055 (“JP-A” means unexamined published Japanese patent application) discloses an aluminum alloy for a structure with improved mechanical strength, weldability, and cutting ability, which contains 2.3 to 6 wt % of Si, 0.4 to 1.0 wt % of Mg, 0.4 to 1.0 wt % of Mn, and small amounts of Zn and Sn, with the balance being made of Al. However, the bending processability and spot weldability of the alloy are insufficient, and the alloy is greatly different from one for use in the present invention, in that the alloy is not one containing both elements of Cu and Zn, to lower the melting point of the aluminum alloy, with improved spot weldability and chemical conversion property at the time of pre-treatment, such as coating (adhesion property of zinc phosphate).
(ii) Further, JP-A-61-190051 discloses a method of producing an Al-series hollow extruded shape material, in which use is made of an Al alloy containing 5 to 15 wt % of Si, and up to 1.0 wt % of Mg, having an Fe content of not more than 0.5 wt %, and containing not more than 0.25 wt % of Cu, Mn, and other elements. However, this Al alloy has a larger amount of added Si than the present invention, with improved heat resistance and abrasion resistance properties, and it is used as a high-temperature exposure member, or as a thick extruded material or rod material for sliding members of an automobile. Further, it has low spot weldability and a low surface treatment property, such as the adhesion property of zinc phosphate, and it has an insufficient extrusion property. Therefore, this material cannot be used as an automotive structural member, like the present invention can.
(iii) Further, JP-A-5-271834 discloses an aluminum alloy containing 0.2 to 1.2 wt % of Mg and 1.2 to 2.6 wt % of Si, having a value of {Si (wt %)−Mg (wt %)/1.73} exceeding 0.85 and being less than 2.0, with the balance being made of Al, and having fine recrystallized grains and a stable artificial aging property. This alloy enables easier generation of Mg
2
Si, by allowing the compositional ratio of Mg and Si to be on the Si-excessive side than the stoichiometric composition, and this alloy merely has increased component ranges of Mg and Si with respect to the compositions of conventional JIS 6N01 alloy or AA6005 alloy.
(iv) Furthermore, JP-A-8-25874 discloses an aluminum alloy extruded material for automotive structural members, which contains 0.5 to 2.5 wt % of Si, 0.2 to 1.0 wt % of Fe, 0.45 to 1.5 wt % of Zn, 0.05 to 1.0 wt % of Cu, and 0.4 to 1.5 wt % of Mn. Although this extruded material is excellent in extrusion property, mechanical strength, and surface treatment property, it has low electric resistance of the material, and it has a problem in spot weldability. In other words, in the spot welding of car body structural members of an automobile on a mass production line, the wear and loss of the electrode tip for welding are problems. If the wear and loss of the electrode tip get larger and larger, the structure of the welded part becomes unstable, and the nugget dimension changes, to lower the strength of the welded part, so that exchange of electrode tips must be frequently carried out. This is the greatest factor in disturbing productivity on a mass production line, and the life of the electrode tip for welding is the greatest problem involved in spot weldability.
SUMMARY OF THE INVENTION
In one aspect of the present invention, an aluminum alloy extruded material for automotive structural members is provided. Advantageously, the aluminum alloy extruded material includes 2.6 to 5 wt % of Si, 0.15 to 0.3 wt % of Mg, 0.3 to 2 wt % of Cu, 0.05 to 1 wt % of Mn, 0.2 to 1.5 wt % of Fe, 0.2 to 2.5 wt % of Zn, 0.005 to 0.1 wt % of Cr, and 0.005 to 0.05 wt % of Ti, and satisfies the relationship of the following expression (I): expression (I) (Content of Mn (wt %))+0.32×(content of Fe (wt %))+0.097×(content of Si (wt %))+3.5×(content of Cr (wt %))+2.9×(content of Ti (wt %))≦1.36.
In one aspect of the invention, this aluminum alloy extruded material for automotive structural members is made with automotive part scrap with at least a portion comprising about 1.5 to 14 wt % of Si.
DETAILED DESCRIPTION OF THE INVENTION
In view of the aforesaid problems, the present inventors have made eager studies by having an eye to a phenomenon that appears by composite action of plural elements, in addition to the effect that each element of an aluminum alloy material exhibits individually and singly. One of such phenomena is crystallization of an intermetallic compound composed of plural kinds of constituent elements, which decreases the bending property and toughness. Conventionally, studies are made on a relationship of the content of each element constituting a giant intermetallic compound, in an alloy composition in which the generation of giant intermetallic compound is small. As a result of studies, the present inventors have found that, unlike the conventional reports, the content of Si which is not a constituent element of the intermetallic compound gives an influence on this phenomenon in the generation of an intermetallic compound containing Mn, Fe, Cr, and Ti, and that an aluminum alloy extruded material preferable as an automotive structural member can be obtained, which material has each of the aforesaid physical properties if these elements satisfy a specific relationship such as described below. The present invention has been made based on these findings.
That is, according to the present invention there is provided:
(1) An aluminum alloy extruded material for automotive structural members, containing 2.6 to 5 wt % of Si, 0.15 to 0.3 wt % of Mg, 0.3 to 2 wt % of Cu, 0.05 to 1 wt % of Mn, 0.2 to 1.5 wt % of Fe, 0.2 to 2.5 wt % of Zn, 0.005 to 0.1 wt % of Cr, and 0.005 to 0.05 wt % of Ti, and satisfying relationship of the follo
Bekki Yoichiro
Hayashi Noboru
Combs Morillo Janelle
King Roy
Knobbe Martens Olson & Bear LLP
The Furukawa Electric Co. Ltd.
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