Method for the manufacturing of an aluminium-magnesium-lithium alloy product

Abstract

Method for manufacturing of an aluminium-magnesium-lithium product, 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 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, Be 0.0002-0.10), 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 treatment 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 Kco of 80 MPa.{square root}m or more for 400 mm wide CCT-panels.

Description

[0001] 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.[0002] 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.[0003] A cast ingot or slab is a three dimensional object having by definition a length is (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[0004] It is well known that adding lithium as an alloy...

AI Technical Summary

Benefits of technology

[0028] 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.

[0060] The expensive alloying element silver, which is frequently used in this type of alloys, may be added. Although it can be added in the usual range of up to about 0.5%, and preferably in the range of up to 0.3%, it may not result in a significant increase in properties, but may enhance the ageing response, which is extremely useful for welding.

Problems solved by technology

Problems exist both with aluminium-lithium alloys and the aluminium-magnesium-lithium alloys, particularly in the anisotropy of mechanical properties and fracture toughness.

If the treatment is carried out below 360.degree. C., the resultant homogenisation effect is inadequate.

Furthermore, due to substantial increase in deformation resistance of the ingot, industrial hot rolling is difficult for temperatures below 360.degree. C.

Mg levels below 3.0% do not provide the required strength and when the addition exceeds 6.0% severe cracking may occur during the casting and hot rolling of the product.

Zinc levels above 1.5% do not provide good welding performance, and further increases density.

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