Metal treatment – Process of modifying or maintaining internal physical... – With casting or solidifying from melt
Reexamination Certificate
2001-08-21
2003-04-22
Wyszomierski, George (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
With casting or solidifying from melt
C148S693000, C148S697000, C148S702000
Reexamination Certificate
active
06551424
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method for the manufacturing of an aluminium-magnesium-lithium product with less anisotropy of mechanical properties, and further the invention relates to the use of the obtained product for structural components of aircraft.
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). See also Aluminium Standards and Data, Aluminium Association, Chapter 5 Terminology, 1997. Thin plate material is to be understood as a rolled product having a thickness of not less than 6.3 mm and not more than 12 mm.
A cast ingot or slab is a three dimensional object having by definition a length (normally the casting direction in case of (semi)-continuous casting), a width and a thickness, whereby the width is equal to or larger than the thickness.
DESCRIPTION OF THE RELATED ART
It is well known that adding lithium as an alloying element to aluminium alloys results in beneficial mechanical properties. Aluminium-lithium alloys exhibit improvements in stiffness and strength while reducing density to a significant extent. Consequently, these types of alloys have utility as structural materials in aircraft and aerospace applications. Examples of known aluminium-lithium alloys include the British alloy AA8090, the American alloys AA2090 and AA2091, and the Russian alloy 01420.
Problems exist both with aluminium-lithium alloys and the aluminium-magnesium-lithium alloys, particularly in the anisotropy of mechanical properties and fracture toughness. Fracture toughness values in the T-L direction tend to be significantly lower than fracture toughness values in the main direction, viz. the L-T direction.
Some other disclosures of Al—Li alloys found in the prior art literature will be mentioned below.
WO-92/03583 proposes an alloy useful in aircraft and airframe structures which has low density. The composition is, in wt. %:
Mg 0.5-10.0, preferably 7.0-10.0
Li 0.5-3.0, preferably 1.0-1.5
Zn 0.1-5.0, preferably 0.3-1.0
Ag 0.1-2.0, preferably 0.3-1.0
balance aluminium,
and with the proviso that the total amount of alloying elements does not exceed 12.0, and with the further proviso that when Mg ranges from 7.0 to 10.0, Li cannot exceed 2.5% and Zn cannot exceed 2.0%.
Said alloy includes a mandatory amount of silver. In order the manufacture rolled product of this aluminium alloy standard processing parameters have been applied.
GB-A-2146353 proposes an alloy having a high electrical resistance and an excellent formability, useful in structures suffering the action of high magnetic field, nuclear fusion reactors or the like. The composition is, in wt. %:
Mg 1.0-8.0, preferably 2.0-7.0
Li 0.05-1.0
at least one element selected from the group consisting of:
Ti 0.05-0.20
Cr 0.05-0.40
Zr 0.05-0.30
V 0.05-0.35
W 0.05-0.30
Mn 0.05-2.0
balance aluminium and incidental impurities.
Further, Bi in the range of 0.05 to 0.50 wt. % may be contained in this alloy. In order the manufacture rolled product of this aluminium alloy standard processing parameters have been applied.
DE-A-1558491 discloses the Russian alloy development for their 1420 alloy referenced above, the alloy contains, in wt. %:
Mg 4-7
Li 1.5-2.6
Zr 0.05-0.3 or alternatively Ti 0.05-0.15
Mn 0.2-1.0
balance aluminium and impurities.
JP-A-61227157 discloses an Al—Li and a method of its manufacture, the disclosed alloy consists of, in wt. %:
Li 1.0-5.0
one or more selected from the group consisting of:
Zr 0.05-0.3
Cr 0.05-0.3
Mn 0.05-1.5
V 0.05-0.3
Ti 0.005-0.1
balance aluminium
In order the manufacture rolled product of this aluminium alloy standard processing parameters have been applied.
SUMMARY OF THE INVENTION
In view of the drawbacks in aluminium-lithium alloys and in aluminium-magnesium-lithium alloys with respect to fracture toughness, a need has developed to provide a method of improving the T-L fracture toughness for these types of alloys. In response to this need, the present invention provides a method therefor which significantly increases the fracture toughness of aluminium-magnesium-lithium alloys in the T-L direction, thereby improving their suitability for more commercial applications, in particular for use as structural components in aircraft.
In accordance with the invention there is provided in a method for the manufacturing of an aluminium-magnesium-lithium product with less anisotropy of mechanical properties, comprising the steps of subsequently:
(a) providing an aluminium alloy consisting of (in weight %):
Mg 3.0-6.0
Li 0.4-3.0
Zn up to 2.0
Mn up to 1.0
Ag up to 0.5
Fe up to 0.3
Si up to 0.3
Cu up to 0.3
0.02-0.5 selected from the group consisting of (Sc 0.010-0.40, Hf 0.010-0.25, Ti 0.010-0.25, V 0.010-0.30, Nd 0.010-0.20, Zr 0.020-0.25, Cr 0.020-0.25, Y 0.005-0.20, and Be 0.0002-0.10), and balance consisting essentially of aluminium and incidental elements and impurities;
(b) casting the aluminium alloy into an ingot;
(c) preheating the ingot;
(d) hot rolling the preheated ingot to a hot worked intermediate product;
(e) cold rolling the hot worked intermediate product to a rolled product in both the length and in the width direction with a total cold rolling reduction of at least 15%;
(f) solution heat treating the cold rolled product in the temperature range of 465 to 565° C. for a soaking time in the range of 0.15 to 8 hours;
(g) cooling the solution heat treated product from the solution heat treating temperature to below 150° C. with a cooling rate of at least 0.2° C./sec;
(h) ageing the cooled product to provide a sheet or thin plate product having a minimum yield strength of 260 MPa or more and a minimum tensile strength of 400 MPa or more in at least the L- and LT-direction, a minimum yield strength of 230 MPa or more and a minimum tensile strength of 380 MPa or more in the 45° to the L-direction, and further having a minimum T-L fracture toughness K
CO
of 80 MPa.m or more for 400 mm wide Centre Cracked Fracture Toughness testpanels (CCT-panels).
With the method in accordance with the invention it is now possible to provide a sheet product or a thin plate product of the indicated type having the mechanical properties as set out, which properties are much more isotropic than manufactured in a coil production route. In particular this method allows for an improvement of the relevant properties in the T-L direction of the obtained product. And a further advantage of this method is that it allows for the production of much wider sheet products, for example up to 2.5 meter wide, in comparison with conventional coil production routes.
In an embodiment of the method in accordance with the invention the obtained product may be provided with a cladding. Such clad products utilise a core of the aluminium-magnesium-lithium base alloy as set out in more detail below and a cladding on at least one side of the core, which cladding is usually of higher purity (higher percentage aluminium than in the core) and which, in particular, enhance appearance and corrosion protects the core. The cladding includes, but is not limited to, essentially unalloyed aluminium or aluminium containing not more than 0.1 or 1% of all other elements. Aluminium alloys herein designated 1xxx-type series include all Aluminium Association (AA) alloys, including the sub-classes of the 1000-type, 1100-type, 1200-type and 1300-type. In addition, AA alloy 7072 containing zinc (0.8 to 1.3%) can serve as the cladding and alloys of the AA6000-series alloys, such as 6003 or 6253, which contain typically more than 1% of alloying additions, can serve as cladding. Other alloys could also be useful as cladding as long as they provide in particular sufficient overall corrosion protection to the core alloy. The clad layer or layers are usually much thinner than the core, each constituting 0.5 to 15 or 20 or possibly 25% of the total composite thickness. A cladding layer more typically constitutes around 0.5 to 12% of the total composite thickness.
The preheating of the cast ingot prior to hot rolling is usua
Haszler Alfred Johann Peter
Keidel Christian Joachim
Combs-Morillo Janelle
Corus Aluminium Walzprodukte GmbH
Stevens Davis Miller & Mosher LLP
Wyszomierski George
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