Metal treatment – Process of modifying or maintaining internal physical... – With casting or solidifying from melt
Reexamination Certificate
1999-12-22
2001-08-21
Wyszomierski, George (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
With casting or solidifying from melt
C148S693000, C148S697000
Reexamination Certificate
active
06277219
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an improved aluminum alloy product suitable for use in aircraft applications and more particularly, it relates to an improved aluminum alloy and method of manufacturing therefor having improved resistance to fatigue crack growth and fracture toughness and is suitable for use as aircraft skin.
BACKGROUND OF THE INVENTION
For the purpose of this invention sheet material is to be understood as a rolled product having a thickness of not less than 1.3 mm (0.05 inch) and not more than 6.3 mm (0.25 inch), and plate material is to be understood as a rolled product having a thickness of more than 6.3 mm. See also Aluminum Standards and Data, Aluminum Association, Chapter 5 Terminology, 1997.
A cast ingot or slab is a three dimensional object having by definition a length (normally the casting direction in case in (semi)-continuous casting), a width and a thickness, where the width is equal to or greater than the thickness.
The design of commercial aircraft requires different sets of properties for different types of structures of the aircraft. In many parts, resistance to crack propagation either in the form of high fracture toughness or low fatigue crack growth is essential. Therefore, many significant benefits can be realized by improving fracture toughness and fatigue crack growth propagation.
A new material with improved toughness, for example, will have a higher level of damage tolerance. Cyclic loading occurs on a commercial aircraft during the take off/landing when the interior of the aircraft is pressurised. Typically, aircraft may see over 100,000 pressurisation cycles during their normal service lifetime. Thus, it will be noted that great benefit is derived from improved fracture toughness and resistance to fatigue crack growth, both of which are related to cyclic loading.
In the aerospace industry the Aluminum Association alloy AA2024 and modifications thereof have been widely used as a high damage tolerant aluminum alloy, mostly in a T3 temper condition or modifications thereof. As known in the art, alloy of a T3 temper condition has been solution heat treated, cold worked, and naturally aged to a substantially stable condition. Products of these alloys have a relatively high strength to weight ratio and exhibit good fracture toughness, good fatigue properties, and adequate corrosion resistance.
From the European patent no. EP-B-0 473 122 (Alcoa) a method of producing a damage tolerant aluminum alloy sheet product is known, comprising:
(a)
providing a body of an aluminum base alloy containing (in wt. %):
Cu
3.8-4.5
Mg
1.2-1.85
Mn
0.3-0.78
Fe
0.5 max., preferably 0.12 max.
Si
0.5 max., preferably 0.10 max. remainder aluminum, optionally 0.2 max. Zn, 0.2
max. Zr, 0.5 max. Cr, and impurities;
(b)
hot rolling the body to a slab;
(c)
heating said slab to above 488° C. to dissolve soluble constituents;
(d)
hot rolling the slab in a temperature range of 315 to 482° C. to a sheet product;
(e)
solution heat treating;
(f)
cooling; and
(g)
ageing to produce a sheet product having high strength and improved levels of
fracture toughness and resistance to fatigue crack growth.
The damage tolerant sheet product obtained by the known method is provided in the T3-condition and is commercially available.
SUMMARY OF THE INVENTION
An object of the invention is to provide an aluminum alloy product with improved damage tolerance properties in comparison with the aluminum sheet product in a T3-condition obtained from the method in accordance with EP-B-0 473 122.
Another object of the present invention is to further improve the mechanical properties of the aluminum sheet product.
Yet another object of the invention is to provide a method for manufacturing the improved aluminum alloy product.
According to the invention in one aspect there is provided in a product comprising an aluminum base alloy consisting of (in weight %): 3.8-4.9% Cu, 1.2-1.8% Mg, 0.1-0.9% Mn, max. 0.12% Fe, max. 0.10%Si, max. 0.15%Ti, max. 0.20% Zn, max. 0.10% Cr, impurities each max. 0.05%, total impurities max. 0.15%, balance aluminum, and the product having a minimum L-0.2%yield strength of 300 MPa or more, a minimum LT-0.2%yield strength of 270 MPa or more, a minimum T-L fracture toughness K
C(ao)
of 100 MPa m more for a 700 mm wide center cracked fracture toughness test panel (CCT-panel), and having in both L/ST- and LT/ST-sections an average grain size of at least 6 according to ASTM E-112.
REFERENCES:
patent: 5213639 (1993-05-01), Colvin et al.
patent: 0473122 (1992-03-01), None
patent: 473122 (1992-04-01), None
patent: 0489408 (1992-06-01), None
patent: 0723033 (1996-07-01), None
patent: 60-251260 (1985-12-01), None
Patent Abstracts of Japan, vol. 010, No. 128, May 13, 1996 & JP 60 251260 published Dec. 11, 1985.
Haszler Alfred Johann Peter
Heinz Alfred Ludwig
Combs-Morillo Janelle
Corus Aluminium Walzprodukte GmbH
Stevens Davis Miller & Mosher LLP
Wyszomierski George
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