U.S. patent application number 10/639776 was filed with the patent office on 2008-03-13 for al-cu alloy with high toughness.
This patent application is currently assigned to Aleris Aluminum Koblenz GmbH. Invention is credited to Rinze BENEDICTUS, Hinrich HARGARTER, Alfred HASZLER, Alfred HEINZ, Christian KEIDEL.
Application Number | 20080060724 10/639776 |
Document ID | / |
Family ID | 31896920 |
Filed Date | 2008-03-13 |
United States Patent
Application |
20080060724 |
Kind Code |
A2 |
BENEDICTUS; Rinze ; et
al. |
March 13, 2008 |
Al-Cu ALLOY WITH HIGH TOUGHNESS
Abstract
Disclosed is an Al--Cu alloy of the AA2000-series alloys with
high toughness and an improved strength, including the following
composition (in weight percent) Cu 4.5-5.5, Mg 0.5-1.6,
Mn.ltoreq.0.80, Zr.ltoreq.0.18, Cr.ltoreq.0.18, Si.ltoreq.0.15,
Fe.ltoreq.0.15, the balance essentially aluminum and incidental
elements and impurities, and wherein the amount (in weight %) of
magnesium is either: (a) in a range of 1.0 to 1.6%, or
alternatively (b) in a range of 0.50 to 1.2% when the amount of
dispersoid forming elements such as Cr, Zr or Mn is controlled and
(in weight %) in a range of 0.10 to 0.70%.
Inventors: |
BENEDICTUS; Rinze; (DELFT,
NL) ; KEIDEL; Christian; (MONTABAUR, DE) ;
HEINZ; Alfred; (NIEDERAHR, DE) ; HASZLER; Alfred;
(VALLENDAR, DE) ; HARGARTER; Hinrich; (ALKMAAR,
NL) |
Correspondence
Address: |
STEVENS DAVIS MILLER & MOSHER, LLP
1615 L STREET, NW
SUITE 850
WASHINGTON
DC
20036
UNITED STATES
202-785-0100
202-408-5200
|
Assignee: |
Aleris Aluminum Koblenz
GmbH
Carl-Spaeter-Strasse 10
KOBLENZ
DE
56070
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20040060618 A1 |
April 1, 2004 |
|
|
Family ID: |
31896920 |
Appl. No.: |
10/639776 |
Filed: |
August 13, 2003 |
Current U.S.
Class: |
148/552; 148/417;
420/533 |
Current CPC
Class: |
C22F 1/057 20130101;
C22C 21/16 20130101 |
Class at
Publication: |
148/552; 148/417;
420/533 |
International
Class: |
C22F 1/04 20060101
C22F001/04; C22C 21/12 20060101 C22C021/12 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 20, 2002 |
EP |
02078445.0 |
Claims
1. Al--Cu alloy rolled product with a high toughness and an
improved strength, comprising the following composition in weight
percent: TABLE-US-00017 Cu 4.5-5.5 Mg 0.5-1.6 Mn .ltoreq.0.80 Zr
.ltoreq.0.18 Cr .ltoreq.0.18 Si .ltoreq.0.15 Fe .ltoreq.0.15,
the balance aluminum and incidental elements and impurities, the
alloy is substantially Ag-free, and wherein a proviso is selected
from the group consisting of: a) the content in weight % of Mg is
in a range of 1.0 to 1.6%, or b) the content in weight % of Mg is
in a range of 0.50 to 1.2% and the sum of dispersoid forming
elements is controlled and in weight % is in a range of 0.10 to
0.70%.
2. Alloy product according to claim 1, wherein the content in
weight % of Mg is in a range of 1.0 to 1.6 and the sum of
dispersoid forming elements, such as Cr, Zr and Mn, is controlled
and in weight % in a range of 0.10 to 0.70%.
3. Alloy product according to claim 1, wherein in proviso a) the
content in weight % of Mg is in a range of 1.0 to 1.5%.
4. Alloy product according to claim 1, wherein in proviso a) the
content in weight % of Mg is in a range of 1.0 to 1.2%.
5. Alloy product according to claim 1, wherein the Mn content in
weight % is in a range of 0.30 to 0.60%.
6. Alloy product according to claim 1, wherein the Mn content in
weight % is in a range of 0.45 to 0.55%.
7. Alloy product according to claim 1, wherein in proviso b) the
content in weight % of Mg is in a range of 0.9 to 1.2% and the sum
of dispersoid forming elements, such as Cr, Zr and Mn, is
controlled and in weight % is in a range of 0.10 to 0.70%.
8. Alloy product according to claim 1, wherein in proviso b) the
content in weight % of Mg is in a range of 1.0 to 1.2%, and the sum
of dispersoid forming elements, such as Cr, Zr and Mn, is
controlled and in weight % is in a range of 0.10 to 0.70%.
9. Alloy product according to claim 1, wherein the sum in weight %
of dispersoids forming elements consists of [Cr]+[Zr]+[Mn] in a
range of 0.20 to 0.70%.
10. Alloy product according to claim 9, wherein the sum in weight %
of [Cr]+[Zr]+[Mn] is in a range of 0.35 to 0.55%, and preferably in
a range of 0.35 to 0.45%.
11. Alloy product according to claim 9, wherein the sum in weight %
of [Cr]+[Zr]+[Mn] is in a range of 0.35 to 0.45%.
12. Alloy product according to claim 1, wherein the amount in
weight % of Zr is in a range of 0.08 to 0.15%.
13. Alloy product according to claim 1, wherein the amount in
weight % of Cr is in a range of 0.08 to 0.15%.
14. Alloy product according to claim 1, wherein Zr is at least
partially replaced by Cr, and wherein [Zr]+[Cr]<0.30%.
15. Alloy product according to claim 1, wherein the Cu-content in
weight % is in a range of 4.6 to 5.5%.
16. Alloy product according to claim 1, wherein the Cu-content in
weight % is in a range of 4.6 to 5.1%.
17. Alloy product according to claim 1, wherein the Fe-content in
weight % is in a range of <0.10%.
18. Alloy product according to claim 1, wherein the Si-content in
weight % is in a range of <0.10%.
19. Alloy product according to claim 1, wherein said alloy further
comprises one or more of the elements Zn, Hf, V, Sc, Ti or Li, the
total amount less than 1.00 weight %.
20. Alloy product according to claim 1, wherein the alloy product
is in a T3 temper condition.
21. Alloy product according to claim 20, wherein the alloy product
is in a T3 temper condition selected from the group consisting of a
T39 or T351 temper.
22. Alloy product according to claim 1, wherein said alloy product
is recrystallized to at least 75%.
23. Alloy product according to claim 1, wherein said alloy product
is recrystallized to at least 80%.
24. Alloy product according to claim 1, having a microstructure
wherein the grains have an average length to width aspect ratio of
smaller than about 4 to 1.
25. Alloy product according to claim 1, having a microstructure
wherein the grains have an average length to width aspect ratio of
smaller than about 3 to 1.
26. Alloy product according to claim 1, wherein the alloy product
has a fatigue crack growth rate of less than 0.001 mm/cycles at
.DELTA.K=20 MPa m when tested according to ASTM-E647 on 80 mm wide
M(T) panels at R=0.1 at constant load and at a frequency of 8
Hz.
27. Alloy product according to claim 26, wherein the alloy product
has a fatigue crack growth rate of less than 0.01 mm/cycles at
.DELTA.K=40 MPa m when tested according to ASTM-E647 on 80 mm wide
M(T) panels at R=0.1 at constant load and at a frequency of 8
Hz.
28. Alloy product according to claim 1, wherein the alloy product
has a thickness of in a range of 2.0 to 12 mm.
29. Alloy product according to claim 1, wherein the alloy product
has a thickness of in a range of 25 to 50 mm.
30. Alloy product according to claim 1, wherein the alloy product
is processed into a fuselage sheet of an aircraft.
31. Alloy product according to claim 1, wherein the alloy product
is processed into a lower-wing member of an aircraft.
32. Alloy product according to claim 1, wherein the dispersoid
forming elements are selected from the group consisting of Cr, Zr
and Mn.
33. Al--Cu alloy rolled product according to claim 1, with a high
toughness and an improved strength, consisting of the following
composition in weight percent: TABLE-US-00018 Cu 4.5-5.5 Mg 1.0-1.6
Mn .ltoreq.0.80 Zr .ltoreq.0.18 Cr .ltoreq.0.18 Si .ltoreq.0.15 Fe
.ltoreq.0.15,
the balance essentially aluminum and incidental elements and
impurities, the alloy is Ag-free.
34. Al--Cu alloy rolled product according to claim 1, with a high
toughness and an improved strength, consisting of the following
composition in weight percent: TABLE-US-00019 Cu 4.5-5.5 Mg 0.5-1.2
Mn .ltoreq.0.80 Zr .ltoreq.0.18 Cr .ltoreq.0.18 Si .ltoreq.0.15 Fe
.ltoreq.0.15,
the balance essentially aluminum and incidental elements and
impurities, the alloy is substantially Ag-free, and wherein and the
sum of dispersoid forming elements is controlled and in weight % is
in a range of 0.10 to 0.70%.
35. Alloy rolled product according to claim 34, wherein the
dispersoid forming elements are selected from the group consisting
of Cr, Zr and Mn.
36. A method for producing an Al--Cu alloy according to claim 1,
with high toughness and an improved strength, comprising the steps
of a) casting an ingot with the following composition in weight
percent: TABLE-US-00020 Cu 4.5-5.5 Mg 0.5-1.6 Mn .ltoreq.0.80 Zr
.ltoreq.0.18 Cr .ltoreq.0.18 Si .ltoreq.0.15 Fe .ltoreq.0.15,
the balance essentially aluminum and incidental elements and
impurities, wherein a proviso is selected from the group consisting
of: a1) the amount in weight % of magnesium is in a range of 1.0 to
1.6%, or a2) the amount in weight % of magnesium is in a range of
0.50 to 1.2% and the amount of dispersoid forming elements, such as
Cr, Zr or Mn, is controlled and in weight % in a range of 0.10 to
0.70%; b) homogenizing and/or pre-heating the ingot after casting;
c) hot rolling or hot deforming the ingot and optionally cold
rolling into a rolled product; d) solution heat treating; e)
optionally quenching the heat treated product; f) stretching the
quenched product; and g) naturally ageing the rolled and
heat-treated product.
37. Method according to claim 36, wherein after hot rolling the
ingot, annealing and/or reheating the hot rolled ingot and again
hot rolling the rolled ingot.
38. Method according to claim 36, wherein said hot rolled ingot is
inter-annealed before and/or during cold rolling.
39. Method according to claim 36, wherein said rolled and
heat-treated product is stretched in a range of up to 10% and
naturally aged for more than 5 days.
40. Method according to claim 36, wherein in step f) the naturally
ageing the rolled and heat-treated product is to provide a T3
temper condition.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to an aluminum-copper alloy
having improved combinations of toughness and strength while
maintaining good resistance to fatigue crack growth, a method for
producing an aluminum-copper alloy with high toughness and an
improved strength and to a rolled, forged or extruded
aluminum-copper alloy sheet or plate product with high toughness
and an improved strength for aeronautical applications. More
specifically, the present invention relates to a high damage
tolerant ("HDT") aluminum-copper alloy designated by the Aluminum
Association ("AA")2xxx-series for structural aeronautical
applications with improved properties such as fatigue crack growth
resistance, strength and fracture toughness. The alloy according to
the invention is preferably useful for aeronautical plate
applications. More specifically, the invention relates to a rolled,
forged or extruded alloy product suitable to be used as fuselage
skin or lower wing skin of an aircraft.
BACKGROUND OF THE INVENTION
[0002] It is known in the art to use heat treatable aluminum alloys
in a number of applications involving relatively high strength such
as aircraft fuselages, vehicular members and other applications.
Aluminum alloys AA2024, AA2324 and AA2524 are well known heat
treatable aluminum alloys which have useful strength and toughness
properties in T3, T39 and T351 tempers. Heat treatment is an
important means for enhancing the strength of aluminum alloys. It
is known in the art to vary the extent of enhancement by altering
the type and amount of alloying constituents present. Copper and
magnesium are two important alloying constituents.
[0003] The design of a commercial aircraft requires various
properties for different types of structures on the aircraft.
Especially for fuselage skin or lower wing skin it is necessary to
have properties such as good resistance to crack propagation either
in the form of fracture toughness or fatigue crack growth. At the
same time the strength of the alloy should not be reduced. A rolled
alloy product either used as a sheet or as a plate with an improved
damage tolerance will improve the safety of the passengers, will
reduce the weight of the aircraft and thereby improve the fuel
economy which translates to a longer flight range, lower costs and
less frequent maintenance intervals.
[0004] It is known in the art to have AA2x24 alloy compositions
with the following broad chemistry, in weight percent:
TABLE-US-00001 Cu 3.7-4.4 Mg 1.2-1.8 Mn 0.15-0.9 Cr 0.05-0.10 Si
.ltoreq.0.50 Fe .ltoreq.0.50 Zn .ltoreq.0.25 Ti .ltoreq.0.15
[0005] the balance aluminum and incidental impurities.
[0006] U.S. Pat. No. 5,593,516 discloses a high damage tolerant
Al--Cu alloy with a balanced chemistry comprising essentially the
following composition (in weight %): TABLE-US-00002 Cu 2.5-5.5 Mg
0.1-2.3 Cu.sub.max -0.91 Mg + 5.59 Cu.sub.min -0.91 Mg + 4.59 Zr up
to 0.2, or Mn up to 0.8
[0007] balance aluminum and unavoidable impurities. It also
discloses T6 and T8 tempers of such alloys which gives high
strength to a rolled product made of such alloy.
[0008] U.S. Pat. No. 5,897,720 and U.S. Pat. No. 5,938,867 disclose
a high damage tolerant Al--Cu alloy with an "AA2024"-chemistry
comprising essentially the following composition (in weight %):
TABLE-US-00003 Cu: 3.8-4.9 Mg: 1.2-1.8 Mn: 0.3-0.9
[0009] the balance aluminum and unavoidable impurities wherein the
alloy is annealed after hot rolling at a temperature at which the
intermetallics do not substantially dissolve. The annealing
temperature is between 398.degree. C. and 455.degree. C. U.S. Pat.
No. 5,938,867 also discloses an alloy where the ingot is
inter-annealed after hot rolling with an anneal temperature of
between 385.degree. C. and 468.degree. C.
[0010] EP-0473122, as well as U.S. Pat. No. 5,213,639, disclose an
aluminum base alloy comprising essentially the following
composition (in weight %): TABLE-US-00004 Cu 3.8-4.5 Mg 1.2-1.8 Mn
0.3-0.9 Fe .ltoreq.0.12 Si .ltoreq.0.10
[0011] the remainder aluminum, incidental elements and impurities,
wherein such aluminum base is hot rolled, heated and again hot
rolled, thereby obtaining good combinations of strength together
with high fracture toughness and a low fatigue crack growth rate.
More specifically, U.S. Pat. No. 5,213,639 discloses an
inter-anneal treatment after hot rolling the cast ingot with a
temperature between 479.degree. C. and 524.degree. C. and again hot
rolling the inter-annealed alloy. Such alloy appear to show a 5%
improvement over the above mentioned conventional 2024-alloy in T-L
fracture toughness and an improved fatigue crack growth resistance
at certain .DELTA.K-levels.
[0012] EP-1045043 describes an aluminum-copper alloy of the general
2024-type which is highly deformable and which comprises
essentially the following composition (in weight %): TABLE-US-00005
Cu 3.8-4.5 Mg 1.2-1.5 Mn 0.3-0.5
[0013] the remainder aluminum, incidental elements and impurities,
wherein such aluminum alloy is preferably used for sheet
applications with gauges in a range of 1.6-5.9 mm. Most examples
given are directed to a reduced amount of copper, namely an amount
(in weight %) of 3.9-4.2, thereby keeping the amount of magnesium
above 1.2.
[0014] EP-1026270 discloses another 2024-type aluminum-copper alloy
for aeronautical lower wing applications. Such alloy comprises
essentially the following composition (in weight %): TABLE-US-00006
Cu 3.8-4.4 Mg 1.0-1.5 Mn 0.5-0.8 Zr 0.08-0.15,
[0015] the remainder aluminum, incidental elements and impurities.
Such alloy shows an enhanced combination of strength, fatigue crack
growth resistance, toughness and corrosion resistance. The alloy
may be used for rolled, extruded or forged products wherein the
addition of zirconium adds strength to the alloy composition
(R.sub.m/R.sub.p (L)>1.25).
[0016] EP-A-1114877 discloses another aluminum alloy composition of
the AA2xxx-type alloys for fuselage skin and lower wing
applications having essentially the following composition (in
weight %): TABLE-US-00007 Cu 4.6-5.3 Mg 0.1-0.5 Mn 0.15-0.45
[0017] the remainder aluminum, incidental elements and impurities.
The method includes a solution heat treatment, stretching and
annealing. Such alloy has been mentioned as being useful for thick
plate applications such as wing structures of airplanes. The levels
of magnesium are below 0.5 weight % wherein it is disclosed that
such low magnesium level is advantageous for age formability.
However, it is believed that such low magnesium levels have a
negative influence with regard to the alloy's resistance to
corrosion, its response to natural aging and its strength
level.
[0018] U.S. Pat. No. 5,879,475 discloses an age-hardenable
magnesium-copper-magnesium alloy suitable for aerospace
applications. Such alloy comprises essentially the following
composition (in weight %): TABLE-US-00008 Cu 4.85-5.3 Mg 0.5-1.0 Mn
0.4-0.8 Ag 0.2-0.8 Zr 0.05-0.25 Fe .ltoreq.0.10 Si
.ltoreq.0.10,
[0019] the balance aluminum, incidental elements and impurities.
The alloy is substantially vanadium-free and lithium-free wherein
the non-presence of vanadium has been reported as being
advantageous for the observed typical strength values. At the same
time the addition of silver has been reported as to enhance the
achievable strength levels of T6-type tempers. However, such alloy
has the disadvantage that it is quite expensive for applications
such as structural members of an aircraft even though it is
reported to be suitable for higher temperature applications such as
aircraft disc rotors, calipers, brake drums or other high
temperature vehicular applications.
SUMMARY OF THE INVENTION
[0020] It is a preferred object of the present invention to provide
a high damage tolerant AA2xxx-type alloy rolled product having
improved combinations of toughness and strength while maintaining
good resistance to fatigue crack growth and corrosion.
[0021] It is another preferred object of the present invention to
provide aluminum alloy sheet products as well as plate products
having an improved fracture toughness and resistance to fatigue
crack growth for aircraft applications such as fuselage skin or
lower-wing skin.
[0022] It is another preferred object of the present invention to
provide rolled aluminum alloy sheet or plate products and a method
for producing those products so as to provide structural members
for aircrafts which have an increased toughness and resistance to
fatigue crack growth while still maintaining high levels of
strength.
[0023] More specifically, there is a general requirement for rolled
AA2000-series aluminum alloys within the range of 2024 and 2524
alloys when used for aeronautical applications that the fatigue
crack growth rate ("FCGR") should not be greater than a defined
maximum. A FCGR which meets the requirements of high damage
tolerance 2024-series alloy products is, e.g., FCGR below 0.001
mm/cycles at .DELTA.K=20 MPa m and 0.01 mm/cycles at .DELTA.K=40
MPa m.
[0024] The present invention preferably solves one or more of the
above-mentioned objects.
[0025] In accordance with the invention there is disclosed an
aluminum-copper alloy rolled product with high toughness and an
improved strength, comprising the following composition (in weight
%): TABLE-US-00009 Cu 4.5-5.5 Mg 0.5-1.6 Mn .ltoreq.0.80, and
preferably .ltoreq.0.60 Zr .ltoreq.0.18 Cr .ltoreq.0.18 Si
.ltoreq.0.15, and preferably <0.10 Fe .ltoreq.0.15, and
preferably <0.10,
[0026] a) the balance essentially aluminum and incidental elements
and impurities, the alloy is substantially Ag-free, and wherein
[0027] b) the amount (in weight %) of magnesium is in a range of
1.0 to 1.6, or alternatively
[0028] the amount (in weight %) of magnesium is in a range of 0.50
to 1.2 and the amount of dispersoid forming elements, such as Cr,
Zr or Mn, is controlled and (in weight %) is in a range of 0.10 to
0.70.
[0029] The alloy product of the present invention has preferably
one or more dispersoid forming elements wherein the amount of these
dispersoid forming elements, and which are preferably selected from
the group consisting of Cr, Zr and Mn, is controlled and are
present in a range of (in weight %) 0.10 to 0.70. By controlling
the amount of dispersoid forming elements and/or by selecting a
specific amount of magnesium it is possible to obtain a very high
toughness by using high levels of copper thereby maintaining good
strength levels, a good fatigue crack growth resistance and
maintaining the corrosion resistance of the alloy product. Hence,
the present invention either uses (i) an amount of magnesium which
is above 1.0 (in weight %) but below 1.6 with or without dispersoid
forming elements such as Cr, Zr and Mn, or alternatively (ii) the
amount of magnesium is selected in range of below 1.2 while adding
one or more dispersoid forming elements which are controlled in a
specific range as described in more detail below.
[0030] The sum of added dispersoid forming elements (in weight %)
of [Cr]+[Zr]+[Mn] is preferably in a range of 0.20 to 0.70, more
preferably in a range of 0.35 to 0.55, and most preferably in a
range of 0.35 to 0.45. The alloy of the present invention
preferably comprises Mn-containing dispersoids wherein said
Mn-containing dispersoids are in a more preferred embodiment at
least partially replaced by Zr-containing dispersoids and/or by
Cr-containing dispersoids. It has surprisingly been found that
lower levels of manganese result in a higher toughness and an
improved fatigue crack growth resistance. More specifically, the
alloy product of the present invention has a significantly improved
toughness while using low amounts of manganese and controlled
amounts of magnesium. Hence, it is important to carefully control
the chemistry of the alloy.
[0031] The amount (in weight %) of manganese is preferably in a
range of 0.30 to 0.60, most preferably in a range of 0.45 to 0.55.
The higher ranges are in particular preferred when no other
dispersoid forming elements are present. Manganese contributes to
or aids in grain size control during operations that can cause the
alloy microstructure to recrystallize. The preferred levels of
manganese are lower than those conventionally used in
AA2.times.24-type alloys while still resulting in sufficient
strength and improved toughness. Here, it is important to control
the amount of manganese also in relation to other dispersoid
forming elements such as zirconium or chromium.
[0032] The amount (in weight %) of copper is preferably in a range
of 4.6 to 5.1. Copper is an important element for adding strength
to the alloy. It has been found that a copper content of above 4.5
adds strength and toughness to the alloy while the formability and
corrosion performance may still be balanced with the level of
magnesium and the dispersoid forming elements.
[0033] The preferred amount (in weight %) of magnesium is either
(i) in a range of 1.0 to 1.5, more preferably in a range of 1.0 to
1.2, or alternatively (ii) in a preferred range of 0.9 to 1.2, most
preferably in a range of 1.0 to 1.2 when the amount of dispersoid
forming elements such as Cr, Zr or Mn is controlled and (in weight
%) in a range of 0.10 to 0.70. Magnesium provides also strength to
the alloy product.
[0034] The preferred amount (in weight %) of zirconium is in a
range of 0.08 to 0.15, most preferably in a range of about 0.10.
The preferred amount (in weight %) of chromium is also in a range
of 0.08 to 0.15, most preferably in a range of about 0.10.
Zirconium may at least partially be replaced by chromium with the
preferred proviso that [Zr]+[Cr]<0.30, and more preferably
<0.25. Throughout the addition of zirconium more elongated
grains may be obtained which also results in an improved fatigue
crack growth resistance. The balance of zirconium and chromium as
well as the partial replacement of Mn-containing dispersoids and
Zr-containing dispersoids result in an improved recrystallization
behavior.
[0035] Furthermore, throughout carefully controlling the dispersoid
forming elements such as manganese, chromium and/or zirconium it is
possible to balance strength versus toughness. By controlling these
dispersoid forming elements the copper and magnesium window can be
further extended to lower levels. While U.S. Pat. No. 5,593,516 is
teaching to maintain the copper and magnesium level below the
solubility limit it has surprisingly been found that it is possible
to choose copper and magnesium levels above the solubility limit
with controlling the dispersoid forming elements and hence
obtaining very high values of toughness and maintaining good
strength levels.
[0036] A preferred alloy composition of the present invention
comprises the following composition (in weight %): TABLE-US-00010
Cu 4.6-4.9 Mn 0.48-0.52 Mg 1.0-1.2 Fe <0.10 Si <0.10.
[0037] Another preferred alloy according to the present invention
comprises the following composition (in weight %): TABLE-US-00011
Cu about 4.2 Mn 0.45-0.65 Mg 1.14-1.17 Fe <0.10 Si <0.10.
[0038] Even more preferred an alloy according to the present
invention comprises the following composition (in weight %):
TABLE-US-00012 Cu: 4.0-4.2 Mn: 0.30-0.32 Mg: 1.12-1.16 Zr: about
0.10 Cr: about 0.10 Fe: <0.10 Si: <0.10.
[0039] The balance in the alloy product according to the invention
is made by aluminum and inevitable impurities and incidental
elements. Typically, each impurity element is present at 0.05%
max., and the total of impurities should be below 0.20% max.
[0040] The alloy according to the present invention may further
comprise one or more of the elements Zn, Hf, V, Sc, Ti or Li, the
total amount less than 1.00 (in weight %), and preferably less than
0.50%. These additional elements may be added to further improve
the balance of the chemistry and/or to enhance the forming of
dispersoids.
[0041] The best results are achieved when the alloy rolled products
have a recrystallized microstructure meaning that 75% or more, and
preferably more than 80% of the grains in a T3 temper, e.g. T39 or
T351, are recrystallized. In another aspect of the microstructure
it has the grains have an average length to width aspect ratio of
smaller than about 4 to 1, and typically smaller than about 3 to 1,
and more preferably smaller than about 2 to 1. Observations of
these grains may be done, for example, by optical microscopy at
50.times. to 100.times. in properly polished and etched samples
observed through the thickness in the longitudinal orientation.
[0042] A method for producing an aluminum-copper alloy as set out
above with high toughness and an improved strength according to the
invention comprises the steps of:
[0043] a) casting an ingot with the following composition (in
weight percent): TABLE-US-00013 Cu: 4.5-5.5 Mg: 0.5-1.6 Mn:
.ltoreq.0.80, and preferably .ltoreq.0.60 Zr: .ltoreq.0.18 Cr:
.ltoreq.0.18 Si: .ltoreq.0.15, and preferably <0.10 Fe:
.ltoreq.0.15, and preferably <0.10,
[0044] the balance essentially aluminum and incidental elements and
impurities, wherein
[0045] a1) the amount (in weight %) of magnesium is in a range of
1.0 to 1.6, or
[0046] a2) the amount (in weight %) of magnesium is in a range of
0.50 to 1.2 and the amount of dispersoid forming elements such as
Cr, Zr or Mn is controlled and (in weight %) in a range of 0.10 to
0.70,
[0047] b) homogenizing and/or pre-heating the ingot after
casting,
[0048] c) hot rolling or hot deforming the ingot and optionally
cold rolling into a rolled product,
[0049] d) solution heat treating,
[0050] e) optionally quenching the heat treated product,
[0051] f) stretching the quenched product, and
[0052] g) naturally ageing the rolled and heat-treated product.
[0053] After hot rolling the ingot it is possible to anneal and/or
reheat the hot rolled ingot and again hot rolling the rolled ingot.
It is believed that such re-heating or annealing enhances the
fatigue crack growth resistance by producing elongated grains
which--when recrystallized--maintain a high level of toughness and
good strength. It is furthermore possible to conduct a solution
heat treatment between hot rolling and cold rolling at the same
temperatures and times as during homogenization, e.g. 1 to 5 hours
at 460.degree. C. and about 24 hours at 490.degree. C. The hot
rolled ingot is preferably inter-annealed before and/or during cold
rolling to further enhance the ordering of the grains. Such
inter-annealing is preferably done at a gauge of app. 4.0 mm for 1
hour at 350.degree. C. Furthermore, it is advisable to stretch the
rolled and heat-treated product in a range of up to 10%, and
preferably in a range of up to 4%, and more preferably in a range
of 1 to 2%, and then naturally aging the stretched product for more
than 5 days, preferably for about 10 to 15 days.
[0054] The present invention provides also a rolled, forged or
extruded aluminum-copper alloy sheet or plate product with a high
toughness and an improved strength with an alloy composition as
described above or which is produced in accordance with the method
as described above. The rolled alloy sheet product has preferably a
gauge of around 2.0 mm to 12 mm for applications such as fuselage
skin and about 25 mm to 50 mm for applications such as lower wing
skin. For other structural members of the aircraft it is possible
to use a rolled plate product according to the present invention
from which aerospace structural parts may be machined. Hence, the
present invention also supplies an improved aircraft structural
member produced from a rolled, forged or extruded aluminum-copper
alloy plate or sheet with an alloy composition as described above
and/or produced in accordance with a method as described above.
[0055] The foregoing and other features and advantages of the alloy
according to the present invention will become readily apparent
from the following detailed description of some preferred
embodiments.
EXAMPLE
[0056] On an industrial scale 7 different aluminum alloys have been
cast into ingots having the following chemical composition as set
out in TABLE 1. TABLE-US-00014 TABLE 1 Chemical composition of the
DC-cast aluminum alloys, in weight %, Si about 0.05%, Fe about
0.06%, balance aluminum and inevitable impurities. Alloy Cu Mn Mg
Zr Cr AA2024 4.4 0.59 1.51 0 0 AA2524 4.3 0.51 1.39 0 0 1 4.7 0.51
1.05 0 0 2 4.6 0.44 1.20 0.09 0 3 4.8 0.51 1.02 0 0 4 4.9 0.50 1.20
0 0 5* 4.2 0.46 1.15 0 0 6* 4.2 0.31 1.15 0 0.10 7 4.0 0.30 1.13
0.10 0 *hot deformation at different temperatures
[0057] The alloys have been processed to a 2.0 mm sheet in the T351
temper. The cast ingots were homogenized at about 490.degree. C.,
and then hot rolled at 410.degree. C. Alloys No. 5 and 6 hot
deformed at about 460.degree. C.
[0058] Thereafter, the plates were further cold rolled, solution
heat treated and stretched by about 1%. All alloys have been tested
at least after 10 days of natural aging. All alloys were tested in
comparison with two reference alloys. As shown in Table 1 AA2024
and AA2524 alloys were used as reference alloys. Both reference
alloys were processed in accordance with the above-mentioned
method.
[0059] Thereafter, strength and toughness was tested. As shown in
TABLES 2 and 3 the tensile yield strength in both L-direction and
LT-direction as well as the ultimate tensile strength in
L-direction and LT-direction have been tested. Furthermore, the
unit propagation energy (UPE) in LT-direction and the notch
toughness (TS/R.sub.p) were tested in the LT-direction and
TL-direction.
[0060] The testing was done in accordance with ASTM-B871 for the
Kahn tear tests, and EN-10.002 for the tensile tests.
TABLE-US-00015 TABLE 2 Tensile properties (tensile yield strength
R.sub.p; ultimate tensile strength R.sub.m) of Alloys 1 to 7 of
Table 1 and reference alloys in the L and LT-direction. L LT Alloy
Rp (MPa) Rm (MPa) Rp (MPa) Rm (MPa) AA2024 344 465 304 465 AA2524
338 447 301 439 1 337 458 296 444 2 336 461 303 449 3 322 444 285
432 4 434 457 309 453 5 296 463 -- -- 6 301 459 -- -- 7 324 438 301
433
[0061] From the examples of Table 2 it can be seen that for the
inventive alloys approx. the same strength levels can be obtained
as for the reference alloys AA2024 and AA2524. TABLE-US-00016 TABLE
3 Toughness properties (unit propagation energy, UPE; notch
toughness TS/R.sub.p) of Alloys 1 to 7 and reference alloys of
Table 1 in the LT-direction and TL-direction L-T T-L Alloy UPE
(kJ/m.sup.2) TS/Rp TS/Rp AA2024 219 1.70 1.74 AA2524 320 1.86 1.99
1 416 2.03 2.09 2 375 2.09 2.21 3 322 1.99 2.18 4 332 1.96 2.08 5
329 2.20 -- 6 355 2.19 -- 7 448 2.05 2.11
[0062] Table 3 shows that the Alloys 1 to 7 exhibit significantly
higher toughness properties than the reference alloys M2024 or
M2524. From alloys 6 and 7 it can be seen that lower levels of
manganese and the replacement of Mn-forming dispersoids by
Cr-forming dispersoids and/or Zr-forming dispersoids exhibit better
properties than alloys with higher levels of manganese. At the same
time it is possible to still maintain levels of manganese in a
range of 0.50 to 0.55 when the levels of copper are above 4.5. In
that case the toughness is as good as adding dispersoid forming
elements and using lower levels of copper and manganese.
[0063] By balancing the levels of copper, magnesium and manganese
it is possible to obtain a new group of alloys from the
AA2000-series having a significantly higher toughness than prior
art alloys. These alloys are specifically advantageous for
aeronautical fuselage applications and lower wing skin
applications.
[0064] Having now fully described the invention, it will be
apparent to one of ordinary skill in the art that many changes and
modifications can be made without departing from the scope or
spirit of the invention as hereon described.
* * * * *