High damage tolerant aa6xxx-series alloy for aerospace application

Abstract

A weldable aluminum alloy wrought product having high strength and improved resistance to intergranular corrosion, the alloy consisting essentially of, in weight percent: Si 0.2-1.3, Mg 0.4-1.5, Cu 0.1-1.1, Mn up to 0.7, Fe 0.02-0.3, Zn up to 0.9, Cr up to 0.25, Ti 0.06-0.19, Zr up to 0.2, Ag up to 0.5, and wherein 0.1<Ti+Cr<0.35, other elements and unavoidable impurities each <0.05, total <0.20, and the balance aluminum.

Description

CROSS-REFERENCE TO RELATED APPLICATION[0001]This claims the benefit of United States provisional patent application No. 60 / 814,068 filed Jun. 16, 2006, and claims priority of European patent application number 06012379 filed Jun. 16, 2006, both incorporated herein by reference.FIELD OF THE INVENTION[0002]This invention pertains to aluminum aerospace alloys. More particularly, this invention pertains to aluminum alloys of the AA6xxx-series (or AA6000-series) that are suitable for welding, yet have improved performance properties, particularly corrosion resistance and damage tolerance properties.BACKGROUND TO THE INVENTION[0003]As will be appreciated herein below, except as otherwise indicated, alloy designations and temper designations refer to the Aluminum Association designations in Aluminum Standards and Data and the Registration Records, as published by the Aluminum Association.[0004]For any description of alloy composition or preferred alloy compositions, all references to perce...

AI Technical Summary

Benefits of technology

[0014]A principal objective of the present invention is to provide an improved AA6xxx series alloy that is weldable, yet exhibits improved corrosion resistance properties.

[0015]An object of the present invention is to provide a weldable AA6xxx-type series alloy product having improved resistance to intergranular corrosion compared to its AA6013 counterpart.

[0016]A further object is to provide a weldable AA6xxx-type series alloy product having improved damage tolerance properties compared to its AA6013 counterpart.

[0017]Another object is to provide a weldable AA6xxx-type series alloy product having an improved balance of intergranular corrosion resistance and damage tolerance properties compared to its AA6013 counterpart.

[0019]In the peak aged condition (i.e. T6 type condition), the aluminum alloy of this invention offers greater resistance to intergranular corrosion resistance compared to its AA6013 aluminum alloy counterpart. Furthermore, in the peak aged condition, the aluminum alloy of this invention offers an improved ratio of UPE (Unit Propagation Energy) versus tensile strength.

Problems solved by technology

These known alloys lack, however, sufficient strength for most structural aerospace applications.

Several other Aluminum Association (“AA”) 6000 series alloys are generally unsuitable for the design of commercial aircraft which require different sets of properties for different types of structures.

However, there are at least two factors limiting the application of this AA6013 alloy.

The first one is that the AA6013 alloy is susceptible to intergranular corrosion (IGC) attack, which can increase local stress concentrations when an alloy product is subjected to stress conditions such as repeated pressurization and depressurization of an aircraft fuselage in use, see for example the paper of T. D. Burleigh, “Microscopic Investigation of the Intergranular Corrosion of Alloy 6013-T6”, ICAA3, Trondheim, 1992, p.

And the second drawback is that the AA6013 alloy has significant lower damage tolerant properties compared to its AA2x24 counterpart.

However, it has been reported that also this AA6056 alloy is susceptible to intergranular corrosion.

This specific overaging practice has been disclosed in U.S. Pat. No. 5,858,134, but has amongst others the drawback of a significant decrease in strength compared to peak aged tempers.

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