U.S. patent application number 09/845181 was filed with the patent office on 2001-09-27 for damage tolerant aluminum alloy product and method of its manufacture.
Invention is credited to Haszler, Alfred Johann Peter, Heinz, Alfred Ludwig.
Application Number | 20010023721 09/845181 |
Document ID | / |
Family ID | 27443704 |
Filed Date | 2001-09-27 |
United States Patent
Application |
20010023721 |
Kind Code |
A1 |
Heinz, Alfred Ludwig ; et
al. |
September 27, 2001 |
Damage tolerant aluminum alloy product and method of its
manufacture
Abstract
The invention relates to a product comprising an aluminum base
alloy consisting of (in weight %): Cu 3.8 - 4.9, Mg 1.2 - 1.8, Mn
0.1 - 0.9, Fe max. 0.12, Si max. 0.10, Ti max. 0.15, Zn max. 0.20,
Cr max. 0.10, impurities each max. 0.05, total max. 0.15, balance
aluminum. The product having a minimum L-0.2% yield strength of 300
MPa or more, a minimum LT-0.2% yield strength of 270 MPa, a minimum
T-L fracture toughness K.sub.C(ao) of 100 MPa.{square root}m or
more for a 700 mm wide CCT-panel, and has in both L/ST- and
LT/ST-sections an average grain size of at least 6 according to
ASTM E-112. Further the invention relates to a method for the
manufacturing of such a product.
Inventors: |
Heinz, Alfred Ludwig;
(Niederahr, DE) ; Haszler, Alfred Johann Peter;
(Vallendar, DE) |
Correspondence
Address: |
STEVENS, DAVIS, MILLER & MOSHER, LLP
1615 L Street, N.W., Suite 850
Washington
DC
20036
US
|
Family ID: |
27443704 |
Appl. No.: |
09/845181 |
Filed: |
May 1, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09845181 |
May 1, 2001 |
|
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|
09468812 |
Dec 22, 1999 |
|
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60130709 |
Apr 22, 1999 |
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Current U.S.
Class: |
148/439 ;
148/552 |
Current CPC
Class: |
B32B 15/016 20130101;
Y10T 428/12764 20150115; C22C 21/16 20130101; C22F 1/057
20130101 |
Class at
Publication: |
148/439 ;
148/552 |
International
Class: |
C22C 021/16; C22F
001/04 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 22, 1998 |
EP |
98204372.1 |
Jun 9, 1999 |
EP |
99201822.6 |
Claims
1. A damage tolerant alloy product comprising an aluminum base
alloy consisting essentially of (in weight %):
10 Cu 3.8-4.9 Mg 1.2-1.8 Mn 0.1-0.9 Fe max. 0.12 Si max. 0.10 Ti
max. 0.15 Zn max. 0.20 Cr max. 0.10 impurities each max. 0.05 total
max. 0.15
balance aluminum, said product having a minimum L-0.2% yield
strength of 300 MPa or more, a minimum LT-0.2% yield strength of
270 MPa, a minimum T-L fracture toughness K.sub.C(ao) of 100
MPa.{square root}m or more for a 700 mm wide CCT-panel, and having
in both L/ST- and LT/ST-sections an average grain size of at least
6 according to ASTM E-112.
2. The product in accordance with claim 1, wherein the Cu content
is in a range of 3.8 to 4.7%.
3. The product in accordance with claim 1, wherein the Cu content
is in a range of 3.9 to 4.6%.
4. The product in accordance with claim 1, wherein the Mg content
is in a range of 1.2 to 1.7%.
5. The product in accordance with claim 1, wherein the Mn content
is in a range of 0.1 to 0.8%.
6. The product in accordance with claim 1, wherein the product has
minimum longitudinal (L)-0.2% yield strength of 360 MPa or more,
the minimum 0.2% yield strength in the TL-direction (transverse
direction) is 300 MPa.
7. The product in accordance with claim 1, wherein the product has
minimum transverse (TL)-tensile strength of 440 MPa or more and a
minimum longitudinal (L)-tensile strength of 475 MPa or more.
8. The product in accordance with claim 1, wherein the product has
minimum L-T fracture toughness K.sub.C(ao) of 105 MPa.{square
root}m for 700 mm wide CCT-panels.
9. The product in accordance with claim 1, wherein the minimum T-L
fracture toughness K.sub.C(ao) is 170 MPa.{square root}m or more
for 2000 mm wide CCT-panels.
10. The product in accordance with claim 1, wherein the minimum T-L
fracture toughness K.sub.C(ao) is 175 MPa.{square root}m or more
for 2000 mm wide CCT-panels.
11. The product in accordance with claim 1, wherein the grain
aspect ratio in both L/ST- and LT/ST-sections is 1:4 or less.
12. The product in accordance with claim 1, wherein the grain
aspect ratio in both L/ST- and LT/ST-sections is 1:3 or less.
13. The product in accordance with claim 1, wherein the grain
aspect ratio in both L/ST- and LT/ST-sections is 1:2 or less.
14. The product in accordance with claim 1, wherein the product is
a sheet product.
15. The product in accordance with any one of claim 1, wherein the
product is a plate product.
16. A composite comprising the product in accordance with claim 1,
and a cladding on the product, the cladding comprising a higher
purity aluminum alloy than said product.
17. A composite comprising the product in accordance with claim 1,
and a cladding on the product, the cladding comprising a member of
the group consisting of: (i) an alloy of the Aluminum Association
AA1000 series; (ii) an alloy of the Aluminum Association AA6000
series; and (iii) an alloy of the Aluminum Association AA7000
series.
18. A method for manufacturing a damage tolerant alloy product,
comprising the steps of: (a) casting an ingot or a slab comprising
an aluminum alloy consisting of (in wt. %):
11 Cu 3.8-4.9 Mg 1.2-1.8 Mn 0.1-0.9 Fe max. 0.12 Si max. 0.10 Ti
max. 0.15 Zn max. 0.20 Cr max. 0.10 impurities each max. 0.05 total
max. 0.15
balance aluminum; (b) hot rolling the ingot to form an intermediate
product; (c) cold rolling the intermediate product to form a rolled
product in both the length and in the width direction with a total
cold deformation of more than 60%; (d) solution heat treating the
intermediate product after cold rolling in at least one direction;
(e) cooling the solution heat treated intermediate product; and (f)
ageing the cooled intermediate product; said damage tolerant
product having a minimum L-0.2% yield strength of 300 MPa or more,
a minimum LT-0.2% yield strength of 270 MPa, a minimum T-L fracture
toughness K.sub.C(ao) of 100 MPa.{square root}m or more for a 700
mm wide CCT-panel, and having in both L/ST- and LT/ST-sections an
average grain size of at least 6 according to ASTM E-112.
19. The method in accordance with claim 18, wherein during step (b)
the ingot is hot rolled in both the length and in the width
direction.
20. The method in accordance with claim 18, wherein during step (c)
the intermediate product is first cold rolled in the one direction
with a total cold deformation in the range of 20 to 55% and then
further cold rolled in the other direction to a rolled product with
a total cold deformation of 60% or more.
21. The method in accordance with claim 20, wherein the process
step (c) comprises the sequential steps of: (c-i) first cold
rolling the intermediate product in one direction with a total cold
deformation in the range of 20 to 55%; (c-ii) solution heat
treating the intermediate product after cold rolling; (c-iii)
tempering the solution heat treated intermediate product to a T3 or
a T351-temper; (c-iv) soft annealing the tempered intermediate
product; and (c-v) cold rolling of the soft annealed intermediate
product in at least another direction to a final gauge thickness
with a total cold deformation of more than 60%.
22. The method in accordance with claim 21, wherein during process
step (c-v) the soft annealed intermediate product is being cold
rolled in both the length and in the width direction.
23. The method in accordance with claim 21, wherein the hot rolling
of the ingot to the intermediate product occurs after
homogenization at a temperature of 400 to 505.degree. C.
24. The method in accordance with claim 21, wherein solution heat
treating of the intermediate product after cold rolling in at least
one direction occurs at a temperature of 460 to 505.degree. C. for
5 to 120 minutes.
24. The method in accordance with claim 21, wherein the solution
heat treated intermediate product is cooled to a temperature of
175.degree. C. or lower.
25. The method in accordance with claim 21, wherein soft annealing
of the cooled intermediate product occurs at a temperature of 300
to 430.degree. C. for 0.5 to 12 hours.
26. The method in accordance with claim 21, wherein between cold
rolling passes, the intermediate product is inter-annealed at a
temperature of 300 to 430.degree. C. for 0.5 to 12 hours.
27. An aircraft skin comprising a sheet or plate of the damage
tolerant alloy product of claim 1.
28. An aircraft skin comprising a sheet or plate of the damage
tolerant alloy product made by the method of claim 18.
29. A damage tolerant alloy product comprising an aluminum base
alloy consisting of (in weight %):
12 Cu 3.8-4.9 Mg 1.2-1.8 Mn 0.1-0.9 Fe max. 0.12 Si max. 0.10 Ti
max. 0.15 Zn max. 0.20 Cr max. 0.10 impurities each max. 0.05 total
max. 0.15
balance aluminum, said product having a minimum L-0.2% yield
strength of 300 MPa or more, a minimum LT-0.2% yield strength of
270 MPa, a minimum T-L fracture toughness K.sub.C(ao) of 100
MPa.{square root}m or more for a 700 mm wide CCT-panel, and having
in both L/ST- and LT/ST-sections an average grain size of at least
6 according to ASTM E-112.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority from U.S. Provisional
Application No. 60/130,709 filed Apr. 22, 1999, incorporated herein
by reference.
FIELD OF THE INVENTION
[0002] The invention relates to an improved aluminum alloy product
suitable for use in aircraft applications and more particularly, it
relates to an improved aluminum alloy and method of manufacturing
therefor having improved resistance to fatigue crack growth and
fracture toughness and is suitable for use as aircraft skin.
BACKGROUND OF THE INVENTION
[0003] 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), and plate
material is to be understood as a rolled product having a thickness
of more than 6.3 mm. See also Aluminum Standards and Data, Aluminum
Association, Chapter 5 Terminology, 1997.
[0004] A cast ingot or slab is a three dimensional object having by
definition a length (normally the casting direction in case in
(semi)-continuous casting), a width and a thickness, where the
width is equal to or greater than the thickness.
[0005] The design of commercial aircraft requires different sets of
properties for different types of structures of the aircraft. In
many parts., resistance to crack propagation either in the form of
high fracture toughness or low fatigue crack growth is essential.
Therefore, many significant benefits can be realized by improving
fracture toughness and fatigue crack growth propagation.
[0006] A new material with improved toughness, for example, will
have a higher level of damage tolerance. Cyclic loading occurs on a
commercial aircraft during the take off/landing when the interior
of the aircraft is pressurised. Typically, aircraft may see over
100,000 pressurisation cycles during their normal service lifetime.
Thus, it will be noted that great benefit is derived from improved
fracture toughness and resistance to fatigue crack growth, both of
which are related to cyclic loading.
[0007] In the aerospace industry the Aluminum Association alloy
AA2024 and modifications thereof have been widely used as a high
damage tolerant aluminum alloy, mostly in a T3 temper condition or
modifications thereof. As known in the art, alloy of a T3 temper
condition has been solution heat treated, cold worked, and
naturally aged to a substantially stable condition. Products of
these alloys have a relatively high strength to weight ratio and
exhibit good fracture toughness, good fatigue properties, and
adequate corrosion resistance.
[0008] From the European patent no. EP-B-0 473 122 (Alcoa) a method
of producing a damage tolerant aluminum alloy sheet product is
known, comprising:
[0009] (a) providing a body of an aluminum base alloy containing
(in wt. %):
[0010] Cu 3.8-4.5
[0011] Mg 1.2-1.85
[0012] Mn 0.3-0.78
[0013] Fe 0.5 max., preferably 0.12 max.
[0014] Si 0.5 max., preferably 0.10 max. remainder aluminum,
optionally 0.2 max. Zn, 0.2 max. Zr, 0.5 max. Cr, and
impurities;
[0015] (b) hot rolling the body to a slab;
[0016] (c) heating said slab to above 488.degree. C. to dissolve
soluble constituents;
[0017] (d) hot rolling the slab in a temperature range of 315 to
482.degree. C. to a sheet product;
[0018] (e) solution heat treating;
[0019] (f) cooling; and
[0020] (g) ageing to produce a sheet product having high strength
and improved levels of fracture toughness and resistance to fatigue
crack growth.
[0021] The damage tolerant sheet product obtained by the known
method is provided in the T3-condition and is commercially
available.
SUMMARY OF THE INVENTION
[0022] An object of the invention is to provide an aluminum alloy
product with improved damage tolerance properties in comparison
with the aluminum sheet product in a T3-condition obtained from the
method in accordance with EP-B-0 473 122.
[0023] Another object of the present invention is to further
improve the mechanical properties of the aluminum sheet
product.
[0024] Yet another object of the invention is to provide a method
for manufacturing the improved aluminum alloy product.
[0025] According to the invention in one aspect there is provided
in a product comprising an aluminum base alloy consisting of (in
weight %): 3.8-4.9% Cu, 1.2-1.8% Mg, 0.1-0.9% Mn, max. 0.12% Fe,
max. 0.10% Si, max. 0.15% Ti, max. 0.20% Zn, max. 0.10% Cr,
impurities each max. 0.05%, total impurities max. 0.15%, balance
aluminum, and the product having a minimum L-0.2% yield strength of
300 MPa or more, a minimum LT-0.2% yield strength of 270 MPa or
more, a minimum T-L fracture toughness K(ao) of 100 MPa {square
root}m more for a 700 mm wide center cracked fracture toughness
test panel (CCT-panel), and having in both L/ST- and LT/ST-sections
an average grain size of at least 6 according to ASTM E-112.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 shows a plot of data of crack propagation
characteristics in the T-L direction.
[0027] FIG. 2 shows a plot of data of crack propagation
characteristics in the L-T direction.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0028] This product in accordance with the invention has improved
strength levels and fatigue properties compared with the aluminum
sheet obtained from the known method. This product can be provided
both as sheet and plate material. It is believed that the excellent
properties are the result of the specific chemistry window in
combination with the fine grain structure (ASTM E-112 grain size of
6 or higher) of the product and a relatively small aspect ratio of
the grain structure in at least the L/ST- and LT/ST-direction. A
further advantage of the product in accordance with the invention
is that the properties are more isotropic, in particular the
fatigue properties. A more isotropic structure results in
particular in improved mechanical properties in the T-L direction
of the product, in particular the fatigue properties, which
improvement enhances the application of the product.
[0029] The product in accordance with the present invention
comprises an aluminum base alloy consisting essentially (in weight
%) of (typically consisting of) 3.8 to 4.9% Cu, 1.2 to 1.8% Mg, 0.1
to 0.9% Mn, the balance being aluminum and trace and impurity
elements. For the trace and impurity elements zinc, titanium and
chromium present in the product, the maximum allowable amount of
zinc is 0.20%, of titanium is 0.15%, and of chromium is 0.10%. For
the impurity elements iron and silicon, the maximum allowable
amount of iron is 0.12% and of silicon is 0.10%. For any other
remaining trace elements, each has a maximum limit of 0.05%, with a
maximum total for the remaining trace elements being 0.15%. Unless
otherwise indicated, all % compositions of the present
specification are in weight percent.
[0030] In a more preferred embodiment of the product in accordance
with this invention the Cu content is limited to a range of 3.8 to
4.7%, and more preferably to a range of 3.8 to 4.6%, and most
preferably in the range of 3.9 to 4.6% to maintain good strength in
combination with the improved fatigue properties.
[0031] In a more preferred embodiment of the product in accordance
with the invention the Mg content is limited to a range of 1.2 to
1.7%, and more preferably to a range of 1.2 to 1.6% to maintain
good strength in combination with the improved fatigue
properties.
[0032] The Cu and Mg levels must be controlled in the indicated
ranges to maintain good strength while providing the benefits in
toughness and fatigue.
[0033] In a more preferred embodiment of the product in accordance
with the invention the Mn content is limited to a range of 0.1 to
0.8%, and more preferably to a range of 0.2 to 0.8%.
[0034] The Fe and Si contents are restricted to very low contents
in order to prevent formation of substantial amounts of iron and
silicon containing particles, which are detrimental for the
fracture toughness and fatigue crack growth resistance.
[0035] In another preferred embodiment of the product in accordance
with this invention the product has minimum longitudinal
(L)-0.2%yield strength of 320 MPa or more, and more preferably of
340 MPa or more, and more preferably of 360 MPa or more, and most
preferably of 370 MPa or more. The preferred minimum 0.2%yield
strength in the TL-direction (transverse direction) is 270 MPa or
more, preferably 280 MPa or more, and more preferably 300 MPa or
more, and more preferable 310 MPa or more, and most preferably a
minimum of 320 MPa or more.
[0036] In another preferred embodiment of the product in accordance
with this invention the product is a sheet product and has minimum
transverse (TL)-tensile strength of 440 MPa or more, preferably 450
MPa or more, and more preferably 460 MPa or more. Further the sheet
product has a minimum longitudinal (L)-tensile strength of 475 NPa
or more, preferably of 485 MPa or more, and more most preferably of
490 MPa or more, and most preferably of 495 MPa or more.
[0037] In yet another preferred embodiment of the product in
accordance with the invention the product has a minimum T-L
fracture toughness K.sub.C(ao) of 170 MPa.{square root}m or more
for 2000 mm wide CCT-panels, and preferably of 175 MPa.{square
root}m or more, and more preferably of 180 MPa.{square root}m or
more, and more preferably a minimum of 185 MPa.{square root}m or
more. The preferred minimum L-T fracture toughness K.sub.C(ao) for
2000 mm wide CCT-panels is 170 MPa.{square root}m or more,
preferably 180 MPa.{square root}m or more, and more preferably 190
MPa.{square root}m or more, and most preferably 200 MPa.{square
root}m or more. The preferred minimum L-T fracture toughness
K.sub.C(ao) for 700mm wide CCT-panels is 105 MPa.{square root}m,
preferably 110 MPa.{square root}m or more, and more preferably 115
MPa.{square root}m or more, and more preferably 120 MPa.{square
root}m or more, and most preferably 125 MPa.{square root}m or
more.
[0038] LT-0.2% stands for the 0.2% Proof Strength in the
LT-direction. Measurement of tensile properties is well known in
the art. K.sub.C(ao) is also a known expression in the art. The
dimensions follow the width of the panel.
[0039] The product in accordance with the invention can be used
both as sheet or as plate material. However the product is ideally
a sheet product for use in structural components of aircraft. The
sheet product has preferably an average grain size according to
ASTM E-112 of 6 or higher, more preferably ASTM E-112 of 7 to 8 in
at least both the L/ST- and LT/ST-section. An L/ST section is to be
understood as having a surface with edges in the following two
directions: L-direction (longitudinal, normally the rolling
direction) and ST-direction (short transverse, normally the
thickness of the product). An LT/ST section is to understood as
having a surface with edges in the following two directions:
LT-direction (long-transverse, normally the width of the product)
and ST-direction (short transverse). The aspect ratio of the grain
structure of the sheet product is preferably in the range of
1:.ltoreq.4, and preferably in the range 1:.ltoreq.3, and more
preferably in the range 1:.ltoreq.2 in both at least the L/ST- and
LT/ST-sections. The more equi-axed the grain structure is, the more
isotropic are the mechanical properties obtained, in particular the
fatigue properties.
[0040] The invention also comprises that the product of this
invention may be provided with a cladding. Such clad products
utilize a core of the aluminum base alloy of the invention and a
cladding of usually higher purity (higher percentage aluminum than
the core) which, in particular, corrosion protects the core. The
cladding includes, but is not limited to, essentially unalloyed
aluminum or aluminum containing not more than 0.1 or 1% of all
other elements. Aluminum alloys herein designated 1xxx-type series
include all Aluminum Association (AA) alloys, including the
sub-classes of the 1000-type, 1100-type, 1200-type and 1300-type.
Thus, the cladding on the core maybe selected from various Aluminum
Association alloys such as 1060, 1045, 1100, 1200, 1230, 1135,
1235, 1435, 1145, 1345, 1250, 1350, 1170, 1175, 1180, 1185, 1285,
1188, 1199, or 7072. In addition, alloys of the AA7000-series
alloys, such as 7072 containing zinc (0.8 to 1.3%), can serve as
the cladding and alloys of the AA6000-series alloys, such as 6003
or 6253, which contain typically more than 1% of alloying
additions, can serve as cladding. Other alloys could also be useful
as cladding as long as they provide in particular sufficient
overall corrosion protection to the core alloy. The clad layer or
layers are usually much thinner than the core, each constituting 1
to 15 or 20 or possibly 25% of the total composite thickness. A
cladding layer more typically constitutes around 1 to 12% of the
total composite thickness.
[0041] According to the Aluminum Association: 1xxx is 99.00 percent
aluminum minimum and greater, AA6xxx are aluminum alloys with
magnesium and silicon as their major alloying elements, AA7xxx are
aluminum alloys with zinc as their major alloying elements.
[0042] In another aspect, the invention provides a method of
manufacture of a damage tolerant rolled product having strength and
improved levels of fracture toughness and resistance to fatigue
crack growth, comprising the steps:
[0043] (a) casting an ingot or a slab comprising an aluminum alloy
consisting of (in wt. %): 3.8-4.9 Cu, 1.2-1.8 Mg, 0.1-0.9 Mn, max.
0.12 Fe, max. 0.10 Si, max. 0.15 Ti, max. 0.20 Zn, max. 0.10 Cr,
impurities each max. 0.05 and total max. 0.15, balance
aluminum;
[0044] (b) hot rolling the ingot to form an intermediate
product;
[0045] (c) cold rolling the intermediate product to form- a rolled
product in both the length and width direction with a total cold
deformation of more than 60%;
[0046] (d) solution heat treating the intermediate product after
cold rolling in at least one direction;
[0047] (e) cooling the solution heat treated intermediate product;
and
[0048] (f) ageing the cooled intermediate product to produce the
rolled product having strength and improved levels of fracture
toughness and resistance to fatigue crack growth.
[0049] The method in accordance with the invention achieves
manufacture of a rolled product having a minimum L-0.2%yield
strength of 300 MPa or more, a minimum LT-0.2%yield strength of 270
MPa or more, a minimum T-L fracture of toughness K.sub.C(ao) of 100
MPa.{square root}m or more for a 700 mm wide CCT-panel, and having
in both L/ST- and LT/ST-direction an average grain size of at least
6 according to ASTM E-112. A further advantage of this method is
that it results in a rolled product having more isotropic
properties, in particular in isotropic fatigue properties, and a
grain structure with a relatively small aspect ratio. Another
advantage of this method is that it allows for the production of
much wider plate or sheet products in comparison with conventional
coil production routes. A further advantage of this method is that
it allows for the production of much wider plate or sheet products
in comparison with coil production routes such as set out in
EP-B-0473 122. Yet a further advantage of the-method in accordance
with the invention is that the intermediate heating of the slab to
above 488.degree. C. to dissolve soluble constituents during the
hot rolling process as described in EP-B-0 473 122 is no longer
essential to achieve the desired mechanical properties, however
optionally it may be applied.
[0050] The aluminum alloy as described herein can be provided in
process step (a) as an ingot or slab for fabrication into a
suitable wrought product by casting techniques currently employed
in the art for cast products, e.g. DC-casting, EMC-casting,
EMS-casting. Slabs resulting from continuous casting, e.g. belt
casters or roll casters, also may be used.
[0051] The cast ingot or slab may be homogenized prior to hot
rolling and/or it may be preheated followed directly by hot
rolling. The homogenization and/or preheating of AA2024 series
alloys and modifications thereof prior to hot rolling are usually
carried out at a temperature in the range 400 to 505.degree. C. in
single or in multiple steps. In either case, the segregation of
alloying elements in the material as cast is reduced and soluble
elements are dissolved. If the treatment is carried out below
400.degree. C., the resultant homogenization effect is inadequate.
If the temperature is above 505.degree. C., eutectic melting might
occur resulting in undesirable pore formation. The preferred time
of the above heat treatment is between 2 and 30 hours. Longer times
are not normally detrimental. Homogenization is usually performed
at a temperature above 485.degree. C., and a typical homogenization
temperature is 493.degree. C. A typical preheat temperature is in
the range of 440 to 460.degree. C. with a soaking time in a range
of 5 to 15 hours.
[0052] Typically, prior to hot rolling, the rolling faces of both
the cladded and the non-cladded products are scalped in order to
remove segregation zones near the cast surface of the ingot.
[0053] The hot rolling procedure of the method in accordance with
the invention during process step (b) involves preferably hot
rolling in both the length and width directions, for which there is
no preference, from a metallurgical point of view, with which
direction is started. During the hot rolling process rolling
directions can be changed alternatively more than once. In a
preferred embodiment of the hot rolling procedure of the method in
accordance with the invention to obtain the desired grain
structure, the product receives a hot rolling deformation in the
length direction in the range of 20 and 98% and a hot rolling
deformation in the width direction is in the range of 20 to 98%.
Hot rolling deformation is defined here as
(h.sub.0-h.sub.1)/h.sub.0, where h.sub.0 is the starting thickness,
and h, is the end thickness for each relevant rolling practice
(length or width wise). More preferably the hot rolling deformation
in length direction is in the range of 25 to 95%, more preferably
in the range of 30 to 95% and even more preferably in the range of
35 to 95%. The hot rolling deformation in the width direction is
preferably in the range of 25 to 95%, preferably in the range of 30
to 95%, more l.5 preferably in the range of 35 to 95%, and most
preferably in the range of 40 to 90%.
[0054] By hot rolling the product in both the length and in the
width direction, a much finer grain structure in the final cold
rolled product (ASTM E-112 grain size of 6 or higher in at least
both the L/ST- and LT/ST-sections) is obtained as is a much more
equi-axed grain structure.
[0055] When necessary during the hot rolling process in accordance
with the invention the intermediate plate product can be cut into
sub-products as to allow for hot rolling in both the length and
width directions.
[0056] The final gauge of the intermediate product is kept
preferably significantly larger than is usually practiced for the
production of this type of products, this to allow a larger total
cold roll deformation during the cold rolling process for the
required final cold rolled gauge. After hot rolling and prior to
cold rolling the obtained intermediate plate product might be
stretched in a range of typically 0.5 to 1.0% of its original
length to make the intermediate plate product flat enough to allow
subsequent ultrasonic testing for quality control reasons.
[0057] The cold rolling procedure of the method in accordance with
the present invention during process step (c) is preferably
accomplished in as few passes as possible and involves a total cold
deformation of more than 60%, preferably more than 80%, and
preferably not more than 95%. The higher range of total cold
deformation is in particular preferred for sheet material. The
total cold deformation is understood as being the total reduction
in thickness of the product during cold rolling. A total cold
deformation of less than 60% will result in lower strength levels
than desired for applications in aircraft structures and total cold
deformation levels of more than 95% will result in increased
susceptibility of the product to breaking during a final stretching
operation.
[0058] By cold rolling the product in both the length and in the
width direction a much finer grain structure (ASTM E-112 grain size
of 6 or higher in at least both the L/ST- and LT-ST-sections) is
obtained, as is a much more equi-axed grain structure. A more
equi-axed grain structure results in favorable and more isotropic
mechanical properties, in particular for the desired more isotropic
fatigue properties.
[0059] In a preferred embodiment of the cold rolling procedure of
the method in accordance with this invention as to obtain the
desired grain structures, the intermediate product is first cold
rolled in one direction, which can be either the length or the
width direction, with a total cold deformation in the range of 20
to 55%, preferably in the range of 30 to 55% and more preferably in
the range of 40 to 55%, and then 90.degree. turned and then further
cold rolled in the other direction to a rolled product with a total
cold deformation of more than 60%, preferably more than 70%,
preferably more than 80%, preferably more than 85%, and preferably
not more than 95%. From a metallurgical point of view there is no
real preference to start first with cold rolling the intermediate
product in the length direction and subsequently in the width
direction, and vice versa. In particular a high total cold
deformation is preferred to obtain high mechanical properties and a
very fine grain structure (ASTM E-112 grain size of 7 or higher in
at least both the L/ST- and LT/ST-sections). Further a higher total
cold deformation enhances recrystallization is subsequent
heat-treatments. A total cold deformation of less than 60% will not
give the desired grain structure, while a cold deformation of more
than 95% will require many interanneals with the risk of Cu
diffusion into the clad layer, and increased cost, and lower
processing yield due to an increased handling and surface
damage.
[0060] In a further preferred embodiment of the cold rolling
procedure of the method in accordance with the invention, the
intermediate product, which may be a plate or a sheet product, is
first, by process step (c-i), cold rolled in at least one
direction, which can be either the length or the width direction,
or a combination thereof, with a total cold deformation in the
range of 20 to 55%, preferably in the range of 30 to 55%. Following
this first cold rolling step, the intermediate product is solution
heat treated, process step (c-ii), and then quenched to below
175.degree. C., and preferably to room temperature. Following the
cooling the quenched intermediate product is brought, by process
step (c-iii), to a T3, and more preferably to a T351-temper by
means of stretching in the range of 0.5 to 8% of its original
length, preferably in the range of 0.5 to 4%, and most preferably
in the range of 0.5 to 3%. Subsequently, the intermediate product
is aged, preferably by means of natural ageing in the range of at
least 2 days, preferably for at least 5 days, and more preferably
for at least 7 days. Following ageing the intermediate product is
soft annealed, process step (c-iv), and then cold rolled, process
step (c-v), to a final gauge thickness by cold rolling in the other
direction, such that the total cold deformation is at least 60% or
more, preferably by cold rolling in both the length and in the
width direction. During the cold rolling to final gauge the product
may be inter-annealed as set out above. With this improved
embodiment it is possible to achieve the higher levels of strength
and fracture toughness in the product and further to achieve more
isotropic properties in the final product.
[0061] After the alloy product is initially cold rolled the
intermediate product is during process step (c-ii) typically
solution heat treated at a temperature in the range of 460 to
505.degree. C. for a time sufficient for solution effects to
approach equilibrium, with typical soaking times in the range of 5
to 120 minutes. The solution heat treatment is typically carried
out in a batch furnace. Typical soaking times at the indicated
temperature is in the range of 5 to 40 minutes. However, with clad
products, care should be taken against too long soaking times since
in particular copper may diffuse into the cladding which can
detrimentally affect the corrosion protection afforded by the
cladding. After solution heat treatment, it is important that the
aluminum alloy be-cooled to a temperature of 175.degree. C. or
lower, preferably to room temperature, to prevent or-minimize the
uncontrolled precipitation of secondary phases, e.g. Al.sub.2CuMg
and Al.sub.2Cu. On the other hand cooling rates should not be too
high in order to allow for a sufficient flatness and low level of
residual stresses in the product. Suitable cooling rates can be
achieved with the use of water, e.g. water immersion or water
jets.
[0062] The soft annealing during process step (c-iv) can be carried
out by holding the product at a temperature in the range of 300 to
430.degree. C. for a soaking time, wherein the product is at
temperature, in the range of 0.5 to 12 hours. A more preferred soft
annealing treatment involves a temperature in the range of 350 to
410.degree. C. for a soak time in the range of 1 to 8 hours.
[0063] Between the various cold rolling passes of the various
embodiments of the cold rolling practice as set out above, an
inter-anneal treatment or intermediate anneal can be applied to
improve workability by recrystallization of the non-cladded cold
rolled product. Typically the inter-anneal involves a soft-anneal
treatment at a temperature in the range of 300 to 430.degree. C.
and a soak-time in the range of 0.5 to 12 hours. A more preferred
soft-anneal treatment involves a temperature in the range of 350 to
410.degree. C. for a soak time in the range of 0.5 to 8 hours.
After soft-annealing the product is preferably cooled slowly in
order to control properties of the final product. The
soft-annealing results in a very soft product which can bear cold
rolling reductions of 60% or more. In addition the relatively high
temperature in combination with the slow cooling rate are thought
to result in a coarse particle distribution which results in high
localized strain around the particles and thus increases the
tendency for recrystallization in the following heat treatment
step. For the cladded cold rolled product a lower temperature range
may be required, but not by way of limitation, in order to avoid in
particular excessive diffusion of, in particular, copper from the
core alloy to the cladding. This diffusion can detrimentally affect
the corrosion protection afforded by the cladding. In this case the
inter-anneal treatment or intermediate anneal can de done typically
in the temperature range of 220 to 350.degree. C. and a soak-time
in the range of 10 min. to 12 hours. At such relatively low
temperatures full recrystallization does not occur until the final
solution heat treatment step (d). However such heat-treatment
results in sufficient recovery as to improve workability of the
product.
[0064] Preferably, but not by way of limitation, after cold rolling
in one direction, which can be either the length or the width
direction, and prior to rolling in the other direction the product
is solution heat treated at a temperature in the range of 460 to
505.degree. C. for a time sufficient for solution effects to
approach equilibrium. Typical soaking times are in the range of 5
to 120 minutes, and preferably in a range of 5 to 45 min.
[0065] After the alloy product is cold rolled the product is during
process step (d) typically solution heat treated at a temperature
in the range of 460 to 505.degree. C. for a time sufficient for
solution effects to approach equilibrium, with typical soaking
times in the range of 5 to 120 minutes. The solution heat treatment
is typically carried out in a batch furnace. Typical soaking times
at the indicated temperature is in the range of 5 to 30 minutes.
However, with clad products, care should be taken against too long
soaking times since in particular copper may diffuse into the
cladding which can detrimentally affect the corrosion protection
afforded by said cladding. After solution heat treatment, it is
important that the aluminum alloy during process step (e) be cooled
to a temperature of 175.degree. C. or lower, preferably to room
temperature, to prevent or minimize the uncontrolled precipitation
of secondary phases, e.g. Al.sub.2CuMg and Al.sub.2Cu. On the other
hand cooling rates should not be too high in order to allow for a
sufficient flatness and low level of residual stresses in the
product. Suitable cooling rates can be achieved with the use of
water, e.g. water immersion or water jets.
[0066] The product may be further cold worked, for example, by
stretching up in the range of 0.5 to 8% of its original length in
order to relieve residual stresses therein and to improve the
flatness of the product. Preferably the stretching up is in the
range of 0.5 to 6%, more preferably of 0.5 to 4% and most
preferably of 0.5 to 3%.
[0067] After cooling the product is during process step (f)
naturally aged, typically at ambient temperatures, and
alternatively the product can be artificially aged. Artificial
ageing during process step (f) can be of particular use for higher
gauge products.
[0068] The product in accordance with the invention could be
provided to a user in a non-solution heat treated condition, such
as an "F" temper or an annealed "O" temper, and then formed and
solution heat treated and aged by the user.
[0069] The invention further includes the use of the aluminum alloy
of this invention or the product obtained in accordance with the
method of this invention as aircraft skin. More preferably the
aircraft skin is a wing skin or an aircraft fuselage panel.
[0070] The invention will now be illustrated by several
non-limiting examples.
EXAMPLE 1
[0071] Non-cladded sheet material of 3.17 mm alloy product in the
T3-condition was manufactured on an industrial scale in accordance
with the method of this invention. The processing route included:
DC-casting an industrial scale ingot with dimensions
440.times.1470.times.2700 mm (thickness.times.width.times.length)
and having the following composition (in weight percent): 4.52% Cu,
1.45% Mg, 0.69% Mn, 0.087% Si, 0.091% Fe, 0.023% Zn, 0.020% Ti,
0.001% Zr, balance aluminum and inevitable impurities. The ingot
has been homogenized for 25 hours at 493.degree. C., cooled to room
temperature, scalped by milling 15 mm per side, preheated to
450.degree. C. for 10 hours, hot rolled in a width direction to an
intermediate gauge of 312 mm, turned 90.degree. and hot rolled
about 20 mm in a length direction, subsequently cut into sub-plates
and cooled to room temperature to form an intermediate product.
Then the intermediate product was cold rolled in its length
direction to a gauge of 10 mm and then solution heat treated for 35
minutes soak at 495.degree. C., cooled to room temperature by means
of a spray quench with cold water and stretched for about 1.5% of
its original length. Subsequently the product was cold rolled in
its width direction to a gauge of 5.0 mm and soft annealed for 2
hours at 400.degree. C. and cooled to room temperature with a
cooling rate of not more than 15.degree. C./hour. Then cold rolled
in width direction to a final gauge of 3.17 mm. At final gauge the
sheet product has been solution heat treated for 15 min. at
495.degree. C. and spray quenched with cold water to room
temperature. The solution heat treated sheet product was then
stretched for about 2% of its original length and subsequently
artificially aged.
[0072] The average grain size (both in micron and in ASTM E-112
classification) and the aspect-ratio of the grain structure has
been measured and compared with 4.14 mm sheet material manufactured
in accordance with the method known from EP-B-0 473 122. The
results are given in Table 1.
[0073] From the results in Table 1 it can be seen that the sheet
material manufactured in accordance with the invention has a much
finer grain size and further has a much more equi-axed grain
structure compared with the product obtained by the known
method.
1 TABLE 1 L/ST-section LT/ST-section Average Average grain size
Aspect grain size Aspect Micron ASTM ratio Micron ASTM ratio This
invention 26 7-8 1:1.9 26 7-8 1:1.8 EP-0 473 122 122 3 1:8.3 80 4-5
1:4.7
EXAMPLE 2
[0074] Sheet material of 1.6 mm of non-cladded alloy product having
the same composition as with Example 1 and in the T3-condition has
been manufactured on an industrial scale in accordance with the
method of this invention. The processing route and the chemical
composition was identical to Example 1, with the exception that the
sheet material is cold rolled to a final gauge of 1.6 mm instead of
3.17 mm. The non-cladded sheets were supplied as four panels
nominally 1200 mm.times.2000 mm. These panels had been prepared
such that two had an L-T orientation and two had a T-L
orientation.
[0075] Tensile test pieces with a 6 mm gauge width and 30 mm gauge
length were machined from the sheets in the longitudinal and
transverse directions and with their tensile axis between 0.degree.
to 90.degree., at 30.degree. intervals, to the final rolling
direction. The tensile tests were carried out according to BS 18,
Category 2 1987. BS 18, Category 2 1987 is a British Standard of
testing.
[0076] Fatigue crack growth tests were carried out at stress ratios
(R)=0.1 and 0.385 under sinusoidal loading at a frequency of 20 Hz
using 420=nm.times.160 mm wide center cracked test panels. Crack
length measurements were taken every 0.3 mm of crack growth using a
pulsed double probe DC potential drop method.
[0077] Fracture resistance curves were determined using center
cracked fracture toughness (CCT) test panels for panel widths of
700 mm and 2000 mm. For panel widths up to 700 mm an l/W ratio of
1.5 was used as recommended in ASTM E561-86 (incorporated herein by
reference), whereas for the 2000 mm wide panels a l/W ratio =0.5
had to be used; "l" is the distance between the grips and "W" is
the test panel width. In both cases the initial starter slot length
(2a) was 0.3 W. The final 5 mm of the slot used for the 2000 mm
wide panel was made using a 0.3 mm thick jig saw blade whereas the
final 10 mm of the slot for the smaller panels was made using a
0.25 mm thick jewellers saw blade. Anti-buckling plates were used
during the tests which completely covered the test panel; the inner
faces were greased to prevent load transfer from the test panel.
The fracture toughness data and the fracture resistance curve (R
curve) were determined according to ASTM E561-86 and to the GARTEur
recommendations. The Koiter finite width correction was used for
panels with l/W ratio 1.5 and 2.0 and the R.A.E. developed
correction for panels with l/W ratio 0.5, see also the article by
G. R. Sutton et al., in Fatigue & Fracture of Engineering
Materials and Structures, 14, 823(1991). R.A.E. stands for Royal
Aircraft Establishment, it is a department of DRA (Defense Research
Agency), Aerospace Division, RAE, Farnborough, Hampshire, UK. The
net section stress was calculated using the compliance crack length
minus the Irwin plastic zone correction. The fracture toughness
values K.sub.C(ao) and K.sub.C were calculated using the maximum
load with the original starter slot length and compliance crack
length respectively. In American based literature K.sub.C(ao) of a
material is often referred to as K.sub.app or as apparent fracture
toughness.
[0078] The tensile data for the different sheets are presented in
Table 2. The effects of test orientation are presented in Table 3.
From these data it can be seen that the material in accordance with
the invention provides very high tensile properties, and further
that the properties are much more isotropic than conventional
2024-T3 material or what might be expected from material obtained
by the known method.
[0079] The fracture toughness in the T-L and L-T directions are
presented in Table 4 (1 ksi.{square root}inch=1.1 MPa.{square
root}m) from these results it can be seen that the material in
accordance with the invention provides very high fracture toughness
and high fracture resistance, and further that these properties are
much more isotropic than AA2024-T3 material reported so far.
[0080] The fatigue crack growth rates (in mm/cycle) in the T-L and
L-T directions are listed in Table 5. No macro-crack deviation
occurred over the stress intensity factor range investigated for
either stress ratio. The fatigue crack growth rates under
sinusoidal loading for stress ratios R=0.1 and R=0.385 were
independent of test orientation. The presence of a clad layer would
not change this independency. From these results it can be seen
that the sheet material manufactured in accordance with the
invention exhibits a good resistance to fatigue crack growth for
both testing directions.
2 TABLE 2 Sheet 0.2% PS (MPa) TS (MPa) Elong (%) Longitudinal 1 389
504 19.1 405 506 19.7 2 388 502 18.8 389 505 20.4 3 389 507 17.5
388 507 20.5 4 384 496 18.6 371 498 18.8 Transverse 1 323 485 21.4
325 487 21.6 2 325 486 22.2 327 488 22.6 3 330 412 21.5 333 488
21.1 4 326 479 24.8 320 476 23.9
[0081] In the Tables of this specification, 0.2% PS stands for 0.2%
Proof Strength, TS stands for Tensile Strength; Elong. stands for
Elongation at fracture. These are measured according to BS 18
etc.
3TABLE 3 Test angle 0.2% PS TS Elong. Sheet to RD (MPa) (MPa) (%) 1
0 413 501 15.7 30 363 482 15.8 60 354 484 22.2 90 325 478 21.4 2 0
378 490 19.0 30 329 477 21.8 60 317 471 21.9 90 316 470 19.7 3 0
378 490 20.6 30 333 473 21.3 60 324 468 21.8 90 318 469 22.2
[0082] In Table 3, RD stands for Rolling Direction.
4TABLE 4 Panel width 0.2% PS Net section K.sub.c(ao) K.sub.c (mm)
l/W (MPa) stress (MPa) (MPa.check mark.m) L-T orientation 700 1.5
397 375 148 212 2000 0.5 389 348 219 283 2000 0.5 376 354 219 281
T-L orientation 700 1.5 325 325 128 194 2000 0.5 326 325 196
261
[0083]
5TABLE 5 Delta K R = 0.1 R = 0.385 (MPa..check mark.m) T-L L-T T-L
L-T 5.0 6.0 E-6 4.0 E-6 1.4 E-5 1.5 E-5 6.0 1.5 E-5 1.0 E-5 2.3 E-5
1.3 E-5 7.0 3.8 E-5 3.0 E-5 4.8 E-5 4.8 E-5 8.0 5.2 E-5 4.0 E-5 7.5
E-5 7.5 E-5 9.0 7.0 E-5 6.0 E-5 1.0 E-4 1.0 E-4 10.0 9.0 E-5 8.0
E-5 1.5 E-4 1.5 E-4 15.0 2.0 E-4 1.8 E-4 3.5 E-4 3.5 E-4 20.0 5.0
E-4 4.5 E-4 9.0 E-4 8.5 E-4 30.0 2.0 E-3 2.0 E-3 7.0 E-3 7.0
E-3
EXAMPLE 3
[0084] On an industrial scale three ingots (A, B, and C) have been
DC-cast and processed in various ways, summarized in Table 6. The
cast ingots had dimensions of 440.times.1470.times.2700 mm. The
chemical compositions of all three ingots were identical, and were
(in weight %): 4.36% Cu, 1.45% Mg, 0.56% Mn, 0.045% Si, 0.043% Fe,
0.019% Ti, balance aluminum and inevitable impurities. The cast
ingots have been homogenized in a two-step homogenization cycle in
which they were first soaked for 2 hours at 460.degree. C. and then
25 hours at 495.degree. C. Then the cast and homogenized ingots
were cooled to room temperature by air cooling, and scalped by
milling 20 mm per side, preheated prior to hot rolling for 10 hours
at 410C. All three homogenized ingots have been cladded with
AA1xxx-series material via 20 mm plates per side. With ingot A
material the cladded ingot has been hot rolled in its length
direction to 100 mm intermediate gauge, while with ingot B and C
material the cladded ingots were first hot rolled in their length
direction to an intermediate of 380 mm in order to establish a
bonding with the cladding and the core, and subsequently hot rolled
in their width direction to an intermediate gauge of 233 mm. Then
depending on the ingot material they have been hot rolled to a
final intermediate hot rolled product. Following the intermediate
products have been cold rolled in length direction (ingot A and C
material) or in width direction (ingot B material), with an
intermediate gauge of 9, 9 and 18 mm respectively for ingot A, B
and C material. Following the first cold rolling step the product
was solution heat treated (SHT) at 495.degree. C. form soak time
depending on the intermediate gauge thickness. Following solution
heat treatment the products have been cooled to room temperature by
means of a spray quench with cold water and stretched for about
1.5% of its original length. The intermediate products were then
brought to an T351-temper by holding them for 10 days at room
temperature to allow for natural ageing. Following ageing and prior
to further cold rolling the products have been soft annealed by
holding the products for about 30 to 60 min at 350.degree. C. (this
intermediate ageing treatment has been indicated in Table 6 as
BG4). Depending on the ingot material cold rolled products of three
different gauges have been produced, namely, 4.5, 3.6 and 3.2 mm,
by rolling in the length or width direction. With ingot C material
also an intermediate soft anneal has been applied. Following cold
rolling to final gauge thickness the products have been solution
heat treated by holding for about 15 to 20 minutes at 495.degree.
C., quenching with cold water to room temperature and stretching
for about 1.5% of its original length. Subsequently the products
were brought to an T351 -temper by holding them at least for 10
days at room temperature to allow for natural ageing.
[0085] Following natural ageing the products have been tested for
their mechanical properties in both the L- and LT-direction as a
function of the final gauge thickness. The results of the tensile
tests are listed in Table 7.
[0086] Further the products have been tested in the L-T and T-L
directions in the Kahn-tear-test in accordance with ASTM-B871
(1996-edition). For this the test specimens have been milled on
both sides prior to testing to a final thickness of 2.0 mm. The
results are listed in Table 8, were TS stands for tear strength and
UPE stands for unit propagation energy.
[0087] Further the products have been tested at two gauges in the
L-T and T-L directions for their K.sub.C and K.sub.C(ao) in
accordance with ASTM E561-86 for 760 mm wide CCT-panels. The
results are listed in Table 9.
[0088] Further 3.2 mm sheet material from ingot C has been tested
for its crack propagation characteristics in the T-L and L-T
direction, of which the results are shown in FIG. 1 for the T-L
direction and in FIG. 2 for the L-T direction. The testing samples
had a width of 400 mm, and a thickness of 3.2 mm. The testing
conditions were a laboratory environment, a test frequency of 8 Hz,
and the R-ratio was 0.1. Usually 2024 material is tested to
.DELTA.K-values of about 35 MPa.{square root}m. The range of
standard 2024 material is plotted in these figures and extrapolated
to higher values (dashed lines, 2024 max th., and 2024 min th.).
The term "th" stands for "theory", it is a theoretical
extrapolation. In FIGS. 1 and 2 the measured results for the higher
.DELTA.K-values are given for the sheet material in accordance with
the invention.
[0089] From the results of Table 7 it can be seen that the yield
strength and the tensile strength increase with increasing cold
rolling degree. Further it can be seen that the best results for
the yield strength and the tensile strength for both the L- and
LT-direction are obtained by the material processed of ingot C,
which includes cold rolling in both the length and the width
direction after the T351 -temper followed by soft annealing.
Further in the ingot C material a better balance is obtained in the
two testing directions.
[0090] From the results of Table 8 it can be seen that for the TS,
which is an indication for the crack initiation properties of a
material, the best results are obtained with ingot C material. The
best results for the UPE, which is an indication for the crack
propagation, are obtained also with ingot C material.
[0091] From these results it can be seen that in order to achieve
the highest levels of mechanical properties and the best isotropic
properties, a high cold rolling degree is preferred in combination
with cold rolling in both the length and the width direction, which
cold rolling in both directions is preferably applied after cold
rolling and a T351-temper of an intermediate cold rolled
product.
[0092] From the results of Table 9 it can be seen that the best
results of fracture toughness values are obtained with ingot C
material.
[0093] From the results of FIGS. 1 and 2 it can be seen that the
material in accordance with the invention has da/dN values which
fall within the range of standard 2024 sheet material for the
.DELTA.K-values up to about 35 MPa.{square root}m. For the higher
.DELTA.K-values the material in accordance with the invention has
significantly lower crack growth rates than what would be expected
from standard 2024 material in both testing directions, which is an
unexpected improvement.
6TABLE 6 Processing step Ingot A Ingot B Ingot C Homogenization
460.degree. C. for 2 hours/495.degree. C. for 25 hours 1.sup.st hot
rolling length 100 mm length 380 mm 2.sup.nd hot rolling width 18
mm width 233 mm 3.sup.rd hot rolling -- length 18 mm length 30 mm
1.sup.st cold rolling length 9 mm width 9 mm length 18 mm SHT
495.degree. C. for 30 min. 495.degree. C. for 60 min. BG4 10 days
natural ageing/350.degree. C. for 1 hour 2.sup.nd cold rolling
width to length to width 9 mm 4.5/3.6/3.2 mm 4.5/3.6/3.2 mm
Interanneal -- -- 350.degree. C. for 30 min. 3.sup.rd cold rolling
-- -- length to 4.5/3.6/3.2 mm SHT 495.degree. C. for 15 min. +
quench Stretching 1.5% of original length Ageing 10 days natural
ageing
[0094]
7 TABLE 7 0.2% PS UTS Elong. Ingot Final (MPa) (MPa) (%) material
gauge L LT L LT L LT A 4.5 318 298 448 440 20.5 19.8 3.6 328 307
451 444 21.7 19.4 3.2 344 317 457 445 20.1 18.3 B 4.5 321 304 453
445 21.8 20.2 3.6 321 304 451 442 21.0 19.5 3.2 335 312 453 455
20.1 21.0 C 4.5 328 306 465 452 20.0 20.8 3.6 367 332 471 452 17.7
17.7 3.2 373 339 465 452 16.6 16.7
[0095]
8 TABLE 8 TS UPE Ingot Final (MPa) (kJ/m.sup.2) material gauge L-T
T-L L-T T-L A 4.5 544 555 226 246 3.6 545 579 215 224 3.2 551 572
207 214 B 4.5 515 557 212 248 3.6 551 568 220 285 3.2 551 594 249
262 C 4.5 558 527 308 227 3.6 587 558 291 245 3.2 561 586 246
257
[0096]
9 TABLE 9 K.sub.c K.sub.c(ao) Ingot Final (MPa.check mark.m)
(MPa.check mark.m) material gauge L-T T-L L-T T-L A 3.2 206 196 144
132 4.5 216 198 145 128 B 3.2 234 218 150 134 4.5 215 203 144 129 C
3.2 241 212 155 134 4.5 222 189 149 132
[0097] 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 spirit or
scope of the invention as set forth by the claims appended
hereto.
* * * * *