Aluminum-silicon alloy sheet for use in mechanical, aircraft and

Details Aluminum-silicon alloy sheet for use in mechanical, aircraft and Aluminum-silicon alloy sheet for use in mechanical, aircraft and

1996-01-22

1998-11-17

Ryan, Patrick

Metal treatment

Process of modifying or maintaining internal physical...

With casting or solidifying from melt

148697, 148698, 420549, 420548, 420546, 420544, C22C 2104

Patent

active

058370706

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The invention relates to the field of medium- and high-strength aluminum alloy sheets used in mechanical, aircraft and spacecraft construction, and in armaments.


PRIOR ART

High-strength aluminum alloys have been used in aircraft and spacecraft construction for many years, particularly Al--Cu alloys from the 2000 series (according to the designation of the Aluminum Association in the USA), for example the alloys 2014, 2019 and 2024, and the Al--Zn--Mg and Al--Zn--Mg--Cu alloys from the 7000 series, for example the alloys 7020 and 7075.
The selection of an alloy and a transformation range, particularly a heat treatment range, is the product of an often delicate compromise between various working properties such as the static mechanical properties (tensile strength, yield strength, modulus of elasticity, elongation); fatigue strength, which is important for aircraft subjected to repeated takeoff-and-landing cycles; toughness, that is, resistance to crack propagation; and stress corrosion. It is also necessary to take into account the alloy's ability to be cast, rolled, and heat-treated under proper conditions, its density, and possibly its weldability.
For over thirty years, continued progress has been made in improving the properties of the 2000 and 7000 alloys used in thin metal sheets for aircraft fuselages and in medium and thick metal sheets for wings or for cryogenic vessels for rockets or missiles, for the specific purpose of lightening the structures in weight without compromising the other properties.
Major progress in lightening weight was made with the development of aluminum-lithium alloys. Thus, an 8090 alloy with 2.6% lithium results in a specific modulus (the ratio of the modulus of elasticity to the density) which is about 20% higher than that of 2024 and 24% higher than that of 7075. Alloys with a higher copper content and lower lithium content, such as 2095, were also developed because of their effective compromise between density, modulus of elasticity, and weldability. In this case the gain in the specific modulus is about 12% relative to 2219. However, these alloys are still not very widely used, essentially because of their high production cost.


OBJECT OF THE INVENTION

In the process of researching alloys for lightening the weight of aircraft structures, Applicant has discovered that another category of alloys, Al--Si alloys of the 4000 series, which are usually used in cast form, would not only make it possible to substantially improve the specific modulus by 3 to 10% relative to the 2000 and 7000 alloys, but would also have a collection of properties related to toughness, fatigue strength and stress corrosion which meet the strict requirements of aircraft construction, without posing any difficult problems during casting, rolling or heat-treatment. Moreover, these alloys have a degree of weldability which is far greater than that in most of the 2000 and 7000 alloys, and which is at least equivalent to that in the alloys in these series which were specially developed for welding, such as the alloys 2219 and 7020. Finally, they have a temperature resistance which is far greater than that of most of the 2000 and 7000 alloys, and which is at least equivalent to that of the alloys in these series which were specially developed for their temperature resistance, such as the alloys 2019 and 2618.
Al--Si alloys are quite widely used in the production of molded castings. However, in this form, their mechanical strength, fatigue strength and toughness properties are substantially lower than those of the transformed 2000 and 7000 wrought alloys used in structural parts. In rare cases, they can be used in rolled form, particularly for coating plated metal sheet intended for the production of brazed heat exchangers. Hence, the alloys 4343, 4104, 4045 and 4047 are used, since the desired properties in this case are essentially a low melting temperature and good wettability.
Al--Si alloys can also be drawn in the form of bars or sections which, because of their good tempe

REFERENCES:
patent: 3466170 (1969-09-01), Dunkel et al.
patent: 5571347 (1996-11-01), Bergsma

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