Alloys or metallic compositions – Aluminum base – Copper containing
Reexamination Certificate
1998-05-28
2001-07-31
King, Roy (Department: 1742)
Alloys or metallic compositions
Aluminum base
Copper containing
C420S535000
Reexamination Certificate
active
06267922
ABSTRACT:
TECHNICAL FIELD
This invention relates to precipitation-hardened aluminum alloys intended primarily for automotive structural applications. More particularly, the invention relates to such alloys within the 6000 series (aluminum alloys wherein the major alloying elements are magnesium and silicon).
BACKGROUND ART
The use of aluminum sheet material is increasing steadily in the manufacture of light-weight automobiles and similar vehicles. For skin applications, such as hoods, trunk lids and fenders, alloy AA6111 is becoming the preferred choice of the North American automakers. This alloy, developed by Alcan, the assignee of the present application, has good forming properties prior to a paint/bake cycle and good dent resistance after forming and painting. For body structure construction, however, the alloy is too strong and the medium strength AA5754 alloy has been recommended for this application (so-called 5000 series aluminum alloys have magnesium as the major alloying element and are generally softer than the 6000 series aluminum alloys). For the most part, 5000 series alloys are well suited for manufacturing all-aluminum body structures, but somewhat higher strength would be advantageous and there is a concern about the recycling of vehicles containing both 5000 and 6000 series alloys since they are chemically incompatible.
Aluminum alloys suggested for use in the automotive industry include those disclosed in the following U.S. Pat. Nos.: 4,082,578 to Evancho et al.; 4,589,932 to Park; 4,784,921 to Hyland et al.; and 4,840,852 also to Hyland et al.
Unfortunately, no known aluminum alloys that are chemically compatible with skin alloy AA6111 satisfy the demands of structural applications in vehicles, including adequate (but not too high) strength and an ability to collapse uniformly upon impact.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide an aluminum alloy that can be recycled with aluminum alloys used for skin applications in vehicles, particularly alloy AA6111.
Another object of the invention is to provide an aluminum alloy of the 6000 series that is suitable for structural applications in vehicles.
The inventors of the present invention have found that the yield strength in the T4 temper (solution treated and naturally aged) of the aluminum alloys considered here, change linearly with total amounts of Cu, Mg and Si in the alloy matrix when this is expressed in atomic weight percent. Further, the desired combination of mechanical properties is obtained when the total amount of Cu, Mg and Si in atomic weight percent is more than 1.2 and less than 1.8%, and preferably, the total amount is between 1.2 and 1.4 atomic weight percent.
Therefore, according to one aspect of the invention, there is provided a rolled aluminum alloy material in which the alloy contains in weight percent:
0.60 ≦ Mg ≦ 0.9
0.25 ≦ Si ≦ 0.6
0.25 ≦ Cu ≦ 0.9
where, additionally, the total amount of (Cu+Mg+Si) in atomic weight percent is less than 1.8% and more than 1.2%.
The alloy may also contain one or more additional elements, including (in weight percent): Fe up to 0.4%, Mn up to 0.4%, Cr up to 0.1%, V up to 0.1%, Zn up to 0.25%, Ti up to 0.10%, Be up to 0.05% and Zr up to 0.1%. In the presence of Fe, or Fe and Mn together, the Si in the matrix is reduced by ⅓ of the amount of Fe or (Fe+Mn) in weight percent as a result of the formation of insoluble Fe-bearing intermetallic compounds. When the overall Si content is in the low part of the stated range (i.e. 0.25-0.3 wt.%), compensation may be made for this loss by the addition of an excess of Si equal to ⅓ of the amount of Fe or Fe+Mn. The maximum total Si level that can result from such additions would be 0.57% by wt., i.e.:
0.4
%
Fe
+
0.4
%
Mn
3
+
0.3
%
Si
which is still within the stated range for the Si content, namely 0.25 to 0.6% by wt. Hence, such compensations (when employed) do not affect the ranges required by the present invention for the amounts of the Si.
Alloys in the above composition ranges and processed according to conventional conditions, including homogenization between 470 and 580° C., hot rolling between 450 to 580° C. to an intermediate thickness, cold rolling to final thickness in one or more passes, solutionizing between 470 and 580° C., rapidly cooling and natural ageing at room temperature, are suitable for structural applications in aluminum intensive vehicles.
Alloys of the invention are of medium strength and have good long-term stability and resistance to over-ageing. As such, the alloys offer good crash-worthiness properties in that structural members constructed from these alloys convolute smoothly and resist cracking when subject to an impact collapse force, even after prolonged exposure to above-ambient temperatures, which would cause loss of ductility and cracking with conventional 6000 series alloys. The alloys also have good recycling compatibility with other aluminum alloys used in vehicle construction.
While the alloys of the invention are intended primarily for vehicle structural purposes, they are also suitable for body panel applications and other applications, here e.g. as extrusions for automotive structural members, again because of their good combination of a modest T4 strength level and good long term thermal stability.
For ease of understanding, some of the terms used in the present application will be explained immediately below before progressing to a more detailed description of the invention.
The term “T8 temper” designates an alloy that has been solution heat-treated, cold worked and then artificially aged. Artificial aging involves holding the alloy at elevated temperature(s) over a period of time. An alloy that has only been solution heat-treated and artificially aged is said to be in the “T6 temper”, whereas if the aging has taken place naturally under room temperature conditions, the alloy is said to be in the “T4 temper.”
The term “body-structure” is an expression used in the automotive trade to describe the structural frame of an automobile to which the main closure sheet components (fenders, doors, hood and trunk lid), and all the engine, transmission and suspension units, are subsequently attached.
REFERENCES:
patent: 3594133 (1971-07-01), Cole et al.
patent: 4082578 (1978-04-01), Evancho et al.
patent: 4589932 (1986-05-01), Park
patent: 4784921 (1988-11-01), Hyland et al.
patent: 4840852 (1989-06-01), Hyland et al.
patent: 5571347 (1996-11-01), Bergsma
patent: 1183703 (1985-03-01), None
patent: 2096366 (1993-12-01), None
patent: 2152402 (1995-05-01), None
patent: 0 679 199 B1 (1994-11-01), None
patent: 2407049 (1979-05-01), None
patent: 2601040 (1988-01-01), None
patent: 1129676 (1968-10-01), None
patent: 9514113 (1995-05-01), None
Translation of WO 95/14113 May 1995 Rhenalu, P.
Patent Abstracts of Japan vol. 94, No. 0010,Japanese Patent Abstract06 287671 (Kyushu Mitsui Alum. Kogyo K.K.) Oct. 11, 1994.
Patent Abstracts of Japan vol. 18, No. 068, Feb. 4, 1994,Japanese Abstract 05 279780(Furukawa Alum. Co. Ltd.) Oct. 26, 1993.
International Preliminary Examination Report PCT Written Opinion Nov. 28, 1996.
“Aluminium Automobil und Recyclying”;Bericht Nr.:515; Auftraggeber:Aluminium-Zentrale e.V.; Verfasser: Dipl.-Ing.C.Rink (no translation available) Apr. 1994.
Bull Michael Jackson
Gupta Alok Kumar
Wheeler Michael John
Alcan International Limited
Cooper & Dunham LLP
King Roy
McGuthry-Banks Tima
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