High strength aluminum based alloy and the article made thereof

Details High strength aluminum based alloy and the article made thereof High strength aluminum based alloy and the article made thereof

2002-05-22

2004-04-27

Wyszomierski, George (Department: 1742)

Alloys or metallic compositions

Aluminum base

Copper containing

C420S535000, C148S417000

Reexamination Certificate

active

06726878

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to non-ferrous metallurgy, and in particular it relates to high strength aluminium based alloys of Al—Zn—Mg—Cu system. The invented alloy is suitable for producing extruded, rolled and forged semiproducts (mainly articles having large sections) used for manufacture loaded members of aircraft, lorries and cars, seagoing and river vessels, agricultural machinery.
BACKGROUND OF THE INVENTION
Al—Zn—Mg—Cu alloys are widely used in the aircraft and aerospace industries. Well-known is the Russian alloy of said system comprising (mass. %):
Zn 6.5-7.3
Fe 0.2-0.4
Mg 1.6-2.2
Si < 0.2
Cu 0.8-1.2
Al-balance
Said alloy doesn't provide high (UTS,YTS) properties and fracture toughness (K
1c
). The articles made from said alloy have limited efficiency in weight and unsatisfactory service life (Handbook, Aluminium alloys, 1984, Moscow, publ. “Metallurgy”.
The American alloys of Al—Zn—Mg—Cu system (7000 series) developed by ALCOA are also well-known. For instance, the alloy described in U.S. Pat. No. 4,828,631 comprises (in mass. %):
Zn 5.9-8.2
Ti < 0.06
Mg 1.5-4.0
Si < 0.12
Cu 1.5-3.0
Fe < 0.15
Zr 0.08-0.15
impurities < 0.05 each and < 0.15 in total
B < 0.01
Al-balance
Cr < 0.4
This alloy has been developed for particular use in aircraft and aerospace articles. It has superior exfoliation corrosion resistance, but its hardenability is sacrificed. In case the semiproduct has the thickness of more than 100 mm, the service characteristics (fracture toughness, strength, plasticity, corrosion resistance and uniformity of properties in semiproducts' volume) become worse. All these shortcomings do not allow to produce large—sized articles from said alloy.
The alloy described in U.S. Pat. No. 4,832,758 comprises (in mass. %):
Zn 4.0-8.0
Mg 1.5-3.0
Cu 1.0-2.5
at least one element from the group:
Cr 0.05-0.3
Mn 0.1-0.5
Zr 0.05-0.3
Al-balance
This alloy is intended to be used for producing semiproducts (plates) of the limited thickness (not more than 64 mm) because when increasing the thickness of a semiproduct, its mechanical properties, fracture toughness and corrosion resistance are essentially reduced.
The alloy desclosed in EP 0829552 comprises (in mass. %):
Zn 5.2-6.8
Si ≦ 0.06
Mg 1.6-2.1
Fe ≦ 0.06
Cu 1.75-2.4
Fe + Si ≦ 0.11
Zr 0.08-0.15
Al-balance
This alloy may be used for manufacture of wing members of jet aircraft, mainly spars, lower skins, etc. The disadvantage of this alloy is its' high sensibility to quenching rate which leads to sharp reducing the strength and fracture toughness in case the semiproduct has the thickness more than 60 mm. Therefore when irregular-shaped members (fittings, landing gear elements, etc) are to be manufactured from said alloy, the great difficulties arise in the process of mechanical working.
Pechiney of France also has claimed several alloys of Al—Zn—Mg—Cu system. The alloy described in EP 0391815 comprises (in mass. %):
Zn 5.5-8.45
Si ≦ 0.5
Mg 2.0-3.5
Fe ≦ 0.5
Cu 0.5-2.5
other elements 0.05 each but not more
Cr 0.3-0.6
than 0.15 in total amount
Mn 0.3-1.1
Al-balance
This alloy is intended to be used for producing small-sized semiproducts (sheets, plates, extruded articles) prepared by powder metallurgy method.
The disadvantage of such products is the low level of fracture toughness (K
1c
) and low technological properties.
The high strength Al alloy described in PCT/FR 97/00144 comprises (in mass. %):
Zn 5.9-8.7
Si < 0.11
Mg 1.7-2.5
Fe < 0.14
Cu 1.4-2.2
Zr 0.05-0.15
Cr < 0.02
Mg + Cu < 4.1
Mn < 0.02
Al-balance
The technological properties (flowability, technological plasticity) of this alloy are insufficient, and besides it has a reduced level of fracture toughness (K
1c
).
The articles made from this alloy (i.e. fittings, frames) have non-uniform strength properties and fracture toughness upon thickness particularly in case of large sections.
DESCRIPTION OF THE INVENTION
The object of the present invention is to provide aluminium-based alloy of Al—Zn—Mg—Cu system having the improved combination of properties such as flowability, technological plasticity, increased fracture toughness, and also ensuring the uniformity of mechanical properties and fracture toughness upon product's thickness while preserving high levels of strength properties, and to provide the articles made from said alloy with said properties.
Accordingly, there is provided Al—Zn—Mg—Cu alloy comprising (in mass. %):
Zn
6.35-8.0
Si
0.01-0.2
Mg
0.5-2.5
Fe
0.06-0.25
Cu
0.8-1.3
Zr
0.07-0.2
Cr
0.001-0.05
Ti
0.03-0.1
Mn
0.001-0.1
Be
0.0001-0.05
at least one element from the group consisting of alkali-earth metals:
K
0.0001-0.01
Na
0.0001-0.01
Ca
0.0001-0.01
Al-balance
Zr+2Ti≦0.3 andSi:Be≦2
and the article made thereof.
Alloying of the claimed alloy with additional elements—Be and at least one element from the group consisting of alkali-earth metals—K, Na, Ca, leads to increase in melt flowability upon casting due to their interaction with blisters and hydrogen being present in the metal, which in turn allows to perform melt filtration and degassing more effectively, that means to increase its purity and, as a result, to improve the technological plasticity of ingots.
The optimum ratio of Zr and Ti combined with lower amount of Cu and in presence of at least one of the alkali-earth metals—K, Na, Ca, provide improved level of fracture toughness while preserving high level of strength properties due to the reduction of volume content of primary phases and their refining, and also provide great uniformity of mechanical properties and fracture toughness upon product's thickness owing to more uniform distribution of secondary phases' particles in micrograin's volume, which ensures better hardenability of the present alloy.


REFERENCES:
patent: 4711762 (1987-12-01), Vernam et al.
patent: 4828631 (1989-05-01), Ponchel et al.
patent: 4832758 (1989-05-01), Brown
patent: 5047092 (1991-09-01), Faure
patent: 6027582 (2000-02-01), Shahani et al.
patent: 0391815 (1990-10-01), None
patent: 0829552 (1998-03-01), None
patent: 2744136 (1997-08-01), None
patent: 604813 (1948-07-01), None
patent: 436876 (1974-07-01), None
patent: 9727343 (1997-07-01), None
English translation of the Abstract of EP 0391815 Dated Oct. 10, 1990.
English translation of the abstract of FR 2744136 dated Aug. 1, 1997.
Industrial Aluminum Alloys, Ed. F.I. Kvasov, et al. “Metallurgia”, (1984).

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