Alloys or metallic compositions – Aluminum base – Copper containing
Reexamination Certificate
1999-08-17
2001-05-15
King, Roy (Department: 1742)
Alloys or metallic compositions
Aluminum base
Copper containing
C148S438000, C148S439000, C148S440000
Reexamination Certificate
active
06231809
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an Al—Mg—Si aluminum alloy sheet (hereinafter referred to as “Al—Mg—Si sheet”) having good press-formability and, in particular, good surface properties. More specifically, the present invention relates to an Al—Mg—Si sheet for forming which is desirable to be used, for example, as a building material for roofs, interior members, curtain walls and the like, and as a material for utensils, electrical parts, optical instruments, vehicles such as automobiles, railcars, and aircraft, general mechanical parts and the like.
2. Related Art
Conventionally, an Al—Mg alloy has been mainly used as an aluminum alloy sheet having good formability. The Al—Mg alloy has, however, drawbacks such that baking hardenability is low, and that stretcher strain marks are liable to be produced when it is subjected to press forming. Therefore, an Al—Mg—Si alloy is attracting notice as an alloy to replace the Al—Mg alloy. The Al—Mg—Si alloy has advantages such that it has good cold formability and high corrosion resistance, and obtains high strength by aging treatment.
However, as described in Japanese Patent Preliminary Publication No. Hei 7-228956 and Japanese Patent Preliminary Publication No. Hei 8-232052, there is a problem that when an Al—Mg—Si alloy sheet is subjected to forming, surface roughness called “ridging marks” is produced on the sheet surface. The ridging marks are stripe-like irregularities which are produced in the direction parallel to the direction of rolling when the sheet is subjected to forming. They are produced conspicuously especially when forming such as stretch forming, ironing, deep drawing or bulging is applied to the sheet in the direction perpendicular to the direction of rolling. A sheet with ridging marks cannot be used for products which particularly require a fine surface such as an interior member, a camera case, an exterior sheet for an automobile and the like, because of its defective appearance.
Japanese Patent Preliminary Publication No. Hei 7-228956 and Japanese Patent Preliminary Publication No. Hei 8-232052 mentioned above intend to prevent production of ridging marks by strictly controlling conditions in each process such as conditions in hot rolling to thereby produce crystal grains which are fine and random in crystal orientation.
However, those prior art documents do not find out the composition of a sheet in which ridging marks are not produced, and cannot sufficiently meet a recent strict demand for quality of a surface.
The Al—Mg—Si aluminum alloy disclosed in Japanese Patent Preliminary Publication No. hei 8-325663 was developed with attention focused on stretchability, while no consideration was paid to the surface properties. Therefore, the alloy cannot sufficiently meet a recent strict demand for quality of a surface.
SUMMARY OF THE INVENTION
The object of the present invention is to provide an Al—Mg—Si aluminum alloy sheet for forming in which ridging marks are prevented from being produced and quality of a surface is superior.
The inventors of the present invention has found out that in order to restrain the production of ridging marks in an Al—Mg—Si alloy sheet, it is effective to perform texture control precisely to thereby reduce textures of Goss orientation, PP orientation and Brass orientation in a final product.
Specifically, an Al—Mg—Si alloy sheet having good surface properties as a material for forming according to the present invention has textures in which orientation distribution density of Goss orientation is 3 or lower, orientation distribution density of PP orientation is 3 or lower and orientation distribution density of Brass orientation is 3 or lower.
As long as an Al—Mg—Si alloy has textures as described above, production of ridging marks are restrained. An especially desirable Al—Mg—Si alloy according to the present invention contains 0.2 to 1.5% of Mg and 0.2 to 1.5% of Si. The Al—Mg—Si type alloy may contain one or more elements selected from the group consisting of Mn, Cr, Fe, Zr, V and Ti in a total amount of 0.01 to 1.5 wt % on the condition that Mn is in a quantity of 1.0 wt % or less, Cr is in a quantity of 0.3 wt % or less, Fe is in a quantity of 1.0 wt % or less, Zr is in a quantity of 0.3 wt % or less, V is in a quantity of 0.3 wt % or less and Ti is in a quantity of 0.1 wt % or less. Also, the Al—Mg—Si type alloy may contain one or more elements selected from the group consisting of Cu, Ag, Zn and Sn in a total amount of 0.01 to 1.5 wt % on the condition that Cu is in a quantity of 1.0 wt % or less, Ag is in a quantity of 0.2 wt % or less, Zn is in a quantity of 1.0 wt % or less and Sn is in a quantity of 0.2 wt % or less.
The present invention can provide an Al—Mg—Si type alloy sheet as a material for forming in which production of ridging marks is restrained.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
After various research on the cause of ridging marks which are produced when a conventional aluminum alloy is subjected to press forming, the inventors have found out that production of ridging marks is due to insufficient texture control.
Here, textures of an aluminum alloy will be described. In an aluminum alloy, there exist orientation components of Cube orientation, RW orientation, CR orientation, Brass orientation, Goss orientation, PP orientation, C orientation and S orientation, which are as follows:
Cube orientation . . . {001}<100>
RW orientation . . . {001}<110>
CR orientation . . . {001}<520>
Brass orientation . . . {011}<211>
Goss orientation . . . {011}<100>
PP orientation . . . {011}<122>
C orientation . . . {112}<111>
S orientation . . . {123}<634>.
In the present invention, an orientation component deviating from one of the above exact orientation by ±10 degrees or less is basically considered to belong to that orientation component. Only regarding Brass orientation and PP orientation component, an orientation deviating from exact Brass or PP orientation by ±8 degrees or less is considered to belong to Brass or PP orientation component.
An ordinary aluminum alloy is composed of textures of the above orientation components. If the composition ratio changes, plastic anisotropy (described later) of a sheet changes and press formability becomes better or worse.
Quantitative evaluation of orientations is performed by orientation distribution density. Orientation distribution density is represented by ratio of magnitude of an orientation to magnitude of a random orientation, and obtained by measuring at least three conventional pole figures by an ordinary X-ray diffraction method and using crystallite orientation distribution function [see Reference 1: Shin-ichi Nagashima, “Texture” (published by Maruzen Kabushiki Kaisha) 1984, pp. 8-44; Reference 2: Metallurgical Society Seminar, “Texture” (edited by Metallurgical Society of Japan) 1981, pp. 3-7]. Alternatively, orientation distribution density can be obtained based on data obtained by electron beam diffraction method, SEM(Scanning-Electron-Microscopy)-ECP(Electron-Channeling-Pattern) method, SEM-EBSP(Electron-Back-Scattered-Pattern) method or the like measuring crystallite orientation distribution. Since the orientation distribution varies in the direction of thickness of a sheet, the average of orientation distribution densities at some points arbitrarily chosen in the direction of thickness is calculated.
The inventors researched on the mechanism of producing ridging marks, varying textures of Al—Mg—Si alloy sheets and examining whether ridging marks were produced in those sheets, and found out that Goss orientation, PP orientation and Brass orientation which show strong in-plane plastic anisotropy cause ridging marks.
Specifically, in Goss orientation, PP orientation and Brass orientation, r-value (Lankford value) shows in-plane plastic anisotropy far larger than in other orientations. More specifically, in Go
Matsumoto Katsushi
Takaki Yasuo
Yanagawa Masahiro
Coy Nicole
Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel Ltd).
King Roy
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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