U.S. patent application number 16/112218 was filed with the patent office on 2018-12-20 for recrystallized aluminum alloys with brass texture and methods of making the same.
The applicant listed for this patent is ARCONIC INC.. Invention is credited to Soonwuk Cheong, Edward Llewellyn, Paul E. Magnusen, Dirk C. Mooy, Roberto J. Rioja, Gregory B. Venema, Cagatay Yanar.
Application Number | 20180363103 16/112218 |
Document ID | / |
Family ID | 39811756 |
Filed Date | 2018-12-20 |
United States Patent
Application |
20180363103 |
Kind Code |
A1 |
Cheong; Soonwuk ; et
al. |
December 20, 2018 |
RECRYSTALLIZED ALUMINUM ALLOYS WITH BRASS TEXTURE AND METHODS OF
MAKING THE SAME
Abstract
A recrystallized aluminum alloy having brass texture and Goss
texture, wherein the amount of brass texture exceeds the amount of
Goss texture, and wherein the recrystallized aluminum alloy
exhibits at least about the same tensile yield strength and
fracture toughness as a compositionally equivalent unrecrystallized
alloy of the same product form and of similar thickness and
temper.
Inventors: |
Cheong; Soonwuk;
(Pittsburgh, PA) ; Rioja; Roberto J.;
(Murrysville, PA) ; Magnusen; Paul E.;
(Pittsburgh, PA) ; Yanar; Cagatay; (Pittsburgh,
PA) ; Mooy; Dirk C.; (Bettendorf, IA) ;
Venema; Gregory B.; (Le Claire, IA) ; Llewellyn;
Edward; (Murrysville, PA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ARCONIC INC. |
Pittsburgh |
PA |
US |
|
|
Family ID: |
39811756 |
Appl. No.: |
16/112218 |
Filed: |
August 24, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11865526 |
Oct 1, 2007 |
|
|
|
16112218 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C22F 1/04 20130101; C22C
21/00 20130101; C22C 21/12 20130101 |
International
Class: |
C22C 21/00 20060101
C22C021/00; C22C 21/12 20060101 C22C021/12; C22F 1/04 20060101
C22F001/04 |
Claims
1. A method for making a recrystallized aluminum alloy sheet
product, the method comprising: (a) completing a hot rolling and a
cold work step on an aluminum alloy sheet; (b) subjecting the
aluminum alloy sheet to a first recrystallization anneal; (c)
completing at least one of (i) another cold work step; and (ii) a
recovery anneal step on the aluminum alloy sheet; (d) subjecting
the aluminum alloy sheet to a second recrystallization anneal; and
(e) aging the aluminum alloy sheet, thereby producing a
recrystallized aluminum sheet product; wherein the recrystallized
aluminum sheet product has brass texture and Goss texture, wherein
the amount of brass texture exceeds the amount of Goss texture, and
wherein the recrystallized aluminum alloy exhibits at least about
the same tensile yield strength and fracture toughness as a
compositionally equivalent unrecrystallized alloy of the same
product form and of similar thickness and temper.
2. The method of claim 1, wherein the ratio of brass texture
intensity to Goss texture intensity in the recrystallized aluminum
sheet product is at least about 2 to 1.
3. The method of claim 1, wherein the ratio of the area fraction of
brass oriented grains to the area fraction of Goss oriented grains
in the recrystallized aluminum alloy product is at least about
2
4. The method of claim 1, wherein the recrystallized aluminum sheet
product has a peak R-value in the range of from about 40.degree. to
about 60.degree..
5. The method of claim 1, wherein the aluminum alloy is a 2XXX
series alloy.
6. The method of claim 5, wherein the aluminum alloy comprises up
to about 7.0 wt. % copper and up to about 4.0 wt. % lithium.
7. The method of claim 5, wherein the aluminum alloy is a 2199
series alloy.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a divisional of U.S. patent application
Ser. No. 11/865,526, filed Oct. 1, 2007, entitled "RECRYSTALLIZED
ALUMINUM ALLOYS WITH BRASS TEXTURE AND METHODS OF MAKING THE SAME",
which is incorporated herein by reference in its entirety.
BACKGROUND
[0002] Aluminum alloy pieces may be produced via rolling, extrusion
or forging processes. As a result of manipulating the shape of the
aluminum alloy pieces, or through the cooling of molten aluminum,
undesirable mechanical properties and stresses may be induced in
the alloy. Heat treating encompasses a variety of processes by
which changes in temperature of the metal are used to improve the
mechanical properties and stress conditions of the alloy. Solution
heat treatment, quenching, precipitation heat treatment, and
annealing are all different methods used to heat treat aluminum
products.
SUMMARY OF THE INVENTION
[0003] Broadly, the present invention relates to aluminum alloy
products having a recrystallized microstructure containing
relatively high amounts of brass texture relative to Goss texture,
and methods for producing the same. The aluminum alloy products may
exhibit an improved strength to toughness relationship compared to
conventional products produced with conventional methods.
[0004] In one aspect, recrystallized aluminum alloys are provided.
In one approach, a recrystallized aluminum alloy has brass texture
and Goss texture, and the amount of brass texture exceeds the
amount of Goss texture. In one embodiment, the amount of brass
texture is at least 2 times greater than the amount of Goss
texture. In one embodiment, the amount of brass texture relative to
Goss texture is determined by comparing the measured brass texture
intensity to the measured Goss texture intensity for a given
polycrystalline sample, as determined using x-ray diffraction
techniques. In another embodiment, the amount of brass texture
relative to Goss texture is determined by comparing the area
fraction of brass oriented grains to the area fraction of Goss
oriented grains for a given polycrystalline sample using
orientation imaging microscopy. In one embodiment, the area
fraction of brass oriented grains for a given polycrystalline
sample is at least about 10%. In one embodiment, the area fraction
of Goss oriented grains for a given polycrystalline sample is not
greater than about 5%. In one embodiment, a recrystallized sheet
product has a maximum R-value (also known as "Lankford
coefficient") in the range of from about 40.degree. to about
60.degree.. In one embodiment, a product produced from the
recrystallized alloy has at least about the same fracture toughness
and at least about the same tensile yield strength as a
compositionally equivalent unrecrystallized alloy of the same
product form and of similar thickness and temper.
[0005] Various aluminum alloys compositions may be useful in
accordance with the instant disclosure. In one embodiment, the
recrystallized aluminum alloy is a 2XXX series aluminum alloy. In
one embodiment, the recrystallized aluminum alloy is a 2199 series
aluminum alloy. In one embodiment, the recrystallized aluminum
alloy includes up to about 7.0 wt % copper. In one embodiment, the
recrystallized aluminum alloy includes up to about 4.0 wt %
lithium.
[0006] The recrystallized aluminum alloy may be utilized in a
variety of industrial applications. In one embodiment, the
recrystallized aluminum alloy is in the form of a sheet product. In
one embodiment, the sheet product is employed in an aerospace
application (e.g., a fuselage product). In other embodiments, the
sheet product is employed in automotive, transportation or other
industrial applications.
[0007] In one embodiment, the recrystallized aluminum alloy is a
2199 series alloy in the form of a sheet product. In this
embodiment, the amount of brass texture exceeds the amount of Goss
texture, and the sheet product has a thickness of not greater than
about 0.35 inch, a LT tensile yield strength of at least about 370
MPa and a T-L fracture toughness (Kapp) of at least about 80
MPa(m1/2).
[0008] In another aspect, method of making recrystallized aluminum
alloy sheet products are provided. In one approach, a method
includes completing a hot rolling and a cold work step on an
aluminum alloy sheet, subjecting the aluminum alloy sheet to a
first recrystallization anneal, completing at least one of (i)
another cold work step; and (ii) a recovery anneal step on the
aluminum alloy sheet, subjecting the aluminum alloy sheet to a
second recrystallization anneal, and aging the aluminum alloy sheet
to produce the recrystallized aluminum sheet product.
[0009] Various ones of the inventive aspects noted hereinabove may
be combined to yield various recrystallized aluminum alloy products
having improved strength and/or toughness qualities, to name a few.
Moreover, these and other aspects, advantages, and novel features
of the invention are set forth in part in the description that
follows and will become apparent to those skilled in the art upon
examination of the following description and figures, or may be
learned by practicing the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1a is a schematic view of a deformed
microstructure.
[0011] FIG. 1b is a schematic view of a recovered
microstructure.
[0012] FIG. 1c is a schematic view of a recrystallized
microstructure.
[0013] FIG. 1d is a schematic view of another recrystallized
microstructure.
[0014] FIG. 1e is a schematic view of another recrystallized
microstructure.
[0015] FIG. 1f is a schematic view of a partially recrystallized
microstructure.
[0016] FIG. 2 is a schematic view of a prior art process for
producing an alloy sheet product.
[0017] FIG. 3 is a schematic map illustrating one embodiment of a
method for producing a recrystallized sheet product.
[0018] FIG. 4 is a schematic map illustrating one embodiment of a
method for producing a recrystallized sheet product.
[0019] FIG. 5 is a schematic map illustrating one embodiment of a
method for producing a recrystallized sheet product.
[0020] FIGS. 6a and 6b are photomicrographs illustrating a
microstructure of a sheet product produced in accordance with an
embodiment of the present disclosure.
[0021] FIGS. 7a and 7b are photomicrographs illustrating a
microstructure of a conventionally processed sheet product.
[0022] FIG. 8 is an OIM scanned image of a sheet product produced
in accordance with embodiments of the present disclosure at the L
plane of the t/2 location.
[0023] FIG. 9 is an OIM scanned image of a conventionally processed
sheet product at the L plane of the /2 location
[0024] FIG. 10 is a graph illustrating the fracture toughness and
tensile yield strength properties for a sheet product produced in
accordance with an embodiment of the present disclosure and a
conventionally produced sheet product.
[0025] FIG. 11 is a graph illustrating Goss texture intensity and
brass texture intensity as a function of thickness for various
conventionally produced sheet products.
[0026] FIG. 12 is a graph illustrating toughness as a function of
thickness for various conventionally produced sheet products.
[0027] FIG. 13 is a graph illustrating strength as a function of
thickness for various conventionally produced sheet products.
[0028] FIG. 14 is a schematic map illustrating one embodiment of a
method for producing a recrystallized sheet product.
[0029] FIG. 15 is a graph illustrating Goss texture intensity and
brass texture intensity as a function of thickness for sheet
products produced in accordance with embodiments of the present
disclosure.
[0030] FIG. 16 is a schematic map illustrating another embodiment
of a method for producing a recrystallized sheet product.
[0031] FIG. 17 is a graph illustrating brass texture intensity and
Goss texture intensity as a function of accumulated cold work for
sheet products produced in accordance with embodiments of the
present disclosure.
[0032] FIG. 18 is a graph illustrating toughness as a function of
thickness for conventionally produced sheet products and sheet
products produced in accordance with embodiments of the present
disclosure.
[0033] FIG. 19 is a graph illustrating strength as a function of
thickness for conventionally produced sheet products and sheet
products produced in accordance with embodiments of the present
disclosure.
[0034] FIG. 20 is a graph illustrating strength as a function of
toughness for conventionally produced sheet products and sheet
products produced in accordance with embodiments of the present
disclosure.
[0035] FIG. 21 is a graph illustrating R-values as a function of
in-plane rotation angle from the L direction for sheets
manufactured in accordance with embodiments of the present
disclosure invention and for conventionally manufactured
sheets.
DETAILED DESCRIPTION
[0036] Aluminum and aluminum alloys are polycrystalline materials
whose characteristics and arrangements can be altered by
deformation of the metal (e.g., rolling, extrusion or forging) or
by the application of heat (e.g., annealing). During deformation of
an aluminum alloy, the free energy of the crystalline material may
be raised by, for example, crystallographic slip. Crystallographic
slip involves the movement of dislocations in certain planes and
directions in each crystal. The occurrence of crystallographic slip
during plastic deformation increases dislocation density and
crystal rotation within the material. Crystal rotation accompanying
deformation is one reason textures, or non-random orientations of
crystals (also called grains), develop within a polycrystalline
material.
[0037] The microstructure of a polycrystalline material, such as an
aluminum alloy, varies depending on its processing history. For
example, aluminum alloys may have a deformed microstructure after
deformation, a recovered microstructure after a recovery anneal,
described in further detail below, and a recrystallized
microstructure after a recrystallization anneal, described in
further detail below. One example of a microstructure including
deformed grains is illustrated in FIG. 1a. In the illustrated
example, the microstructure 1a includes a plurality of deformed
grains 12, each grain having a grain boundary 10. Due to
deformation, the internal areas of the deformed grains 12 include a
high dislocation density, represented in FIG. 1a as shading 14.
[0038] To reduce the free energy of a deformed material, the
material may be annealed. An anneal involves heating the deformed
material at elevated temperature. There are generally two types of
anneals used to treat aluminum alloys: recovery anneals and
recrystallization anneals. With a recovery anneal, an aluminum
alloy is heated to a temperature such that the grain boundary of
the deformed grain is generally maintained, but the dislocations
within the deformed grains 12 move to lower energy configurations.
These lower energy configurations within the grains are called
sub-grains or cells. Thus, the grains produced from a recovery
anneal are generally called recovered grains. One example of a
microstructure including recovered grains is illustrated in FIG.
1b. In the illustrated example, the recovered microstructure 1b
includes recovered grains 22. The recovered grains 22 generally
have the same grain boundary 10 as the deformed grains 12, but, due
to the recovery anneal, sub-grains 16 have formed within the
recovered grains 12.
[0039] With a recrystallization anneal, the aluminum alloy is
heated to a temperature that produces new grains from deformed
grains 12 and/or recovered grains 22. These new grains are called
recrystallized grains. A recrystallization anneal results in the
production of a material having recrystallized grains. Examples of
microstructures including recrystallized grains are illustrated in
FIGS. 1c-1e. In the illustrated examples, microstructure 1c
contains elongated recrystallized grains 32c (FIG. 1c),
microstructure 1d contains large equiaxed recrystallized grains 32d
(FIG. 1d), and microstructure 1e contains small equiaxed
recrystallized grains 32e (FIG. 1e).
[0040] Recrystallization anneal conditions, aluminum alloy sheet
size, and aluminum alloy composition, among others, may be tailored
in an effort to obtain the desired recrystallized grain
configurations. For example, elongated recrystallized grains 32c
may be obtained from anisotropic mechanical deformation (e.g., cold
rolling) and lower recrystallization temperatures. Large equiaxed
recrystallized grains 32d may be obtained from long anneal times.
Small equiaxed recrystallized grains 32e may be obtained from
increased cold work and short anneal times.
[0041] In some circumstances, an anneal may produce a partially
recrystallized material, one example of which is illustrated in
FIG. 1f. In the illustrated example, the partially recrystallized
microstructure if includes a mixture of recovered grains 22 and
recrystallized grains 32.
[0042] The grains of a deformed, recovered, recrystallized or
partially recrystallized polycrystalline materials are generally
oriented in non-random manners. These crystallographically
non-random grain orientations are known as texture. Texture
components resulting from production of aluminum alloy products may
include one or more of copper, S texture, brass, cube, and Goss
texture, to name a few. Each of these textures is defined in Table
1, below.
TABLE-US-00001 TABLE 1 Texture type Miller Indices Bunge (.phi.1,
.PHI., .phi.2) Kocks (.PSI., .THETA., .PHI.) copper {112} 111 90,
35, 45 0, 35, 45 S {123} 634 59, 37, 63 149, 37, 27 brass {110} 112
35, 45, 0 55, 45, 0 Cube {1 0 0} <001> 0, 0, 0 0, 0, 0 Goss
{110} 001 0, 45, 0 0, 45, 0
[0043] Texture is generally measured in polycrystalline materials
using x-ray diffraction techniques to obtain microscopic images of
the polycrystalline materials. Since the images can vary based on
the amount of energy used during x-ray diffraction, the measured
texture intensities are generally normalized by calculating the
amount of background intensity, or random intensity, and comparing
that background intensity to the intensity of the textures of the
image. Thus, the relative intensities of the obtained texture
measurements are dimensionless quantities that can be compared to
one another to determine the relative amount of the different
textures within a polycrystalline material. For example, an x-ray
diffraction analysis may determine a background intensity relative
to a Goss texture intensity or a brass texture intensity, and use
orientation distribution functions to produce normalized Goss
intensities and brass intensities. These normalized Goss and brass
intensity measurements may be utilized to determine the relative
amounts of Goss texture and brass texture for a given
polycrystalline material.
[0044] The crystallographic texture may also be measured using
Orientation Imaging Microscopy (OIM). When the beam of a Scanning
Electron Microscope (SEM) strikes a crystalline material mounted at
an incline (e.g., around 70.degree.), the electrons disperse
beneath the surface, subsequently diffracting among the
crystallographic planes. The diffracted beam produces a pattern
composed of intersecting bands, termed electron backscatter
patterns, or EBSPs. EBSPs can be used to determine the orientation
of the crystal lattice with respect to some laboratory reference
frame in a material of known crystal structure.
[0045] In view of the foregoing, the following definitions are used
herein:
[0046] "Grain" means a crystal of a polycrystalline material, such
as an aluminum alloys.
[0047] "Deformed grains" means grains that are deformed due to
deformation of the polycrystalline material.
[0048] "Dislocation" means an imperfection in the crystalline
structure of the material resulting from the dislocated atomic
arrangement in one or more layers of the crystalline structure.
Deformed grains may be defined by cells of dislocations, and thus
deformed grains generally have a high dislocation density.
[0049] "Recovered grains" means grains that are formed from
deformed grains. Recovered grains generally have the same grain
boundary as deformed grains, but generally have a lower free energy
than deformed grains due to the formation of sub-grains from the
dislocations of the deformed grains. Thus, recovered grains
generally have a lower dislocation density than deformed grains.
Recovered grains are generally formed from a recovery anneal.
[0050] "Recrystallized grains" means new grains that are formed
from deformed grains or recovered grains. Recrystallized grains are
generally formed from a recrystallization anneal.
[0051] "Recrystallized material" means a polycrystalline material
predominately containing recrystallized grains. In one embodiment,
at least about 60% of the recrystallized material comprises
recrystallized grains. In other embodiments, at least about 70%,
80% or even 90% of the recrystallized material comprises
recrystallized grains. Thus, the recrystallized material may
include a substantial amount of recrystallized grains.
[0052] "Recrystallized aluminum alloy" means an aluminum alloy
product composed of a recrystallized material.
[0053] "Unrecrystallized grains" means grains that are either
deformed grains or recovered grains.
[0054] "Unrecrystallized material" means a polycrystalline material
including a substantial amount of unrecrystallized grains.
[0055] "Recovery anneal" means a processing step that produces an
end product having a substantial amount of recovered grains. A
recovery anneal thus generally produces an unrecrystallized
material. A recovery anneal may involve heating a deformed
material.
[0056] "Recrystallization anneal" means a processing step that
produces a recrystallized material. A recrystallization anneal may
involve heating a deformed and/or recovered material.
[0057] "Hot rolling" means a thermal-mechanical process that is
performed at an elevated temperature to deform the metal. Hot
rolling is also known to those skilled in the art as dynamic
recovery. Hot rolling generally does not result in the production
of recrystallized grains, but instead generally results in the
production of deformed grains. In this regard, a hot rolled sheet
product generally exhibits a deformed microstructure, as
illustrated in FIG. 1a, above.
[0058] "Cold work" means deformation processes applied to an
aluminum alloy at about ambient temperatures to deform the metal
into another shape and/or thickness. Deformation processes include
rolling, extrusion and forging. The cold work step may include
cross-rolling or unidirectional rolling.
[0059] "Microstructure" means the structure of a polycrystalline
sample as viewed via microscopic images. The microscopic images
generally at least communicate the types of grains included in the
material. With respect to the present disclosure, microstructures
may be obtained from a properly prepared sample (e.g., see the
preparation technique described with respect to texture intensity
measurements) and with a polarized beam (e.g., via a Zeiss optical
microscope) at a magnification of from about 150.times. to about
200.times..
[0060] "Deformed microstructure" means a microstructure including
deformed grains.
[0061] "Recovered microstructure" means a microstructure including
recovered grains.
[0062] "Recrystallized microstructure" means a microstructure
including recrystallized grains.
[0063] "Texture" means the crystallographic orientation of grains
within a polycrystalline material.
[0064] "Goss texture" is defined in Table 1, above.
[0065] "Brass texture is defined in Table 1, above.
[0066] "Fraction of Goss texture" means the area fraction of Goss
oriented grains of a given polycrystalline sample as calculated
using orientation imaging microscopy using, for example, the OIM
sample procedure, described below.
[0067] "Fraction of brass texture" means the area fraction of brass
oriented grains of a given polycrystalline sample as calculated
using orientation imaging microscopy using, for example, the OIM
sample procedure, described below.
[0068] The "OIM sample procedure" is a follows: the software used
is the TexSEM Lab OIM DC version. 4.0 (EDAX Inc., New Jersey,
U.S.A.), which is connected via FIREWIRE (Apple, Inc., California,
U.S.A.) to a DigiView 1612 CCD camera (TSL/EDAX, Utah, U.S.A.). The
SEM is a JEOL 840 (JEOL Ltd. Tokyo, Japan). OIM run conditions are
70.degree. tilt with a 15 mm working distance at 25 kV with dynamic
focusing and spot size of 1.times.10-7 amp. The mode of collection
is a square grid. Only orientations are collected (i.e., Hough
peaks information is not collected). The area size per scan is 3500
.mu.m.times.600 .mu.m at 5 .mu.m steps at 75X. Four scans per
sample are performed. The total scan area is set to contain more
than 1000 grains for texture analysis. The scans are conducted at
the L plane at the t/2 location. The obtained data are processed
with a multiple-iteration dilation cleanup with a 5.degree. grain
tolerance angle and 3 points per grain minimum grain size (15
.mu.m). The grain boundary map assumes a misorientation angle of
15.degree.. The crystal orientation maps assumes Euler angles of
.phi.1=35.degree. .PHI.=45.degree. .phi.2=0.degree. (.+-.15.degree.
misorientation angle) for the brass texture component and
.phi.1=0.degree. .PHI.=45.degree. .phi.2=0.degree. (.+-.15.degree.
misorientation angle) for the Goss texture component.
[0069] "Texture intensity" means a measured amount of x-ray
diffraction associated with a specific texture for a given
polycrystalline sample. Texture intensity may be measured via x-ray
diffraction and in accordance with "Texture and Anisotropy,
Preferred Orientations in Polycrystals and their Effect on Material
Properties", Kocks et al., pp. 140-141, Cambridge University Press
(1998). The absolute intensity values of texture components
measured may vary among institutes, due to hardware and/or software
differences, and thus the ratios of the texture intensities are
used in accordance with the instant disclosure. Texture intensities
may be obtained as provided by the "Texture intensity measurement
procedure", described below.
[0070] The "texture intensity measurement procedure" is as follows:
samples are prepared by polishing with Buehler Si--C paper by hand
for 3 minutes, followed by polishing by hand with a Buehler diamond
liquid polish having an average particle size of about 3 The
samples are anodized in an aqueous fluoric-boric solution for 30-45
seconds. The texture intensities are measured using a Rigaku
Geigerflex x-ray diffraction apparatus (Rigaku, Tokyo JAPAN), where
the {111}, {200}, and {220} pole figures are measured up to the
maximum tilt angle of 75.degree. by the Schulz back-reflection
method using CuK.alpha. radiation, and then updated pole figures
are obtained after defocusing and background corrections of the raw
pole figure data, and then orientation distribution functions
(ODFs) are calculated from the updated three pole figure data using
appropriate software, such as the "popLA" software, available from
Los Alamos National Laboratory, New Mexico, United States of
America.
[0071] "Goss texture intensity" means the texture intensity
associated with a Goss texture for a given polycrystalline
sample.
[0072] "Brass texture intensity" means the texture intensity
associated with a brass texture for a given polycrystalline
sample.
[0073] "Amount of Goss texture" means either (i) the measured
amount of Goss texture intensity for a given polycrystalline sample
as measured via x-ray diffraction, or (ii) the area fraction of
Goss texture of a given polycrystalline sample as measured using
orientation imaging microscopy (OIM).
[0074] "Amount of brass texture" means either (i) the measured
amount of brass texture intensity for a given polycrystalline
sample as measured via x-ray diffraction, or (ii) the area fraction
of brass texture of a given polycrystalline samples as measured
using orientation imaging microscopy (OIM).
[0075] "Unrecrystallized alloy" means an alloy containing a
substantial amount of unrecrystallized grains, or an alloy
subjected to only a single recrystallization anneal via a solution
heat treatment step.
[0076] Aluminum alloys within the scope of the present disclosure
having a higher amount of brass texture than Goss texture may
exhibit an improved strength to toughness relationship compared to
conventionally produced products. Hence, the present disclosure
relates to recrystallized aluminum alloys having a higher amount of
brass texture than Goss texture. Products produced from the
recrystallized alloys generally have at least about the same
fracture toughness and at least about the same tensile yield
strength as a compositionally equivalent unrecrystallized alloy of
the same product form and of similar thickness and temper.
Mechanical, thermo-mechanical and/or thermal process may be
tailored to produce recrystallized aluminum alloys having a
relatively high amount of brass texture. In one approach, hot
and/or cold work steps (e.g., rolling) are employed in combination
with at least one intermediate recrystallization anneal and a final
recrystallization anneal (e.g., a solution heat treatment step) to
produce recrystallized aluminum alloys having a high amount of
brass texture. Additional tempering operations may be employed
after solution heat treatment to further develop the desired
properties of the recrystallized aluminum alloys.
[0077] The amount of brass texture of the recrystallized aluminum
alloy generally exceeds the amount of Goss texture of the
recrystallized aluminum alloy. In one embodiment, the amount of
brass texture and the amount of Goss texture are determined using
orientation imaging microscopy techniques, as described above. In
one embodiment, the area fraction of brass texture is at least
about 10%. In one embodiment, the area fraction of Goss texture is
not greater than about 5%.
[0078] In one embodiment, the ratio of the amount of brass texture
to the amount of Goss texture in a recrystallized aluminum alloy is
at least about 1, as determined from the area fraction of brass
oriented grains and the area fraction of Goss orientated grains. In
one embodiment, the ratio of the area fraction of brass oriented
grains (BVF) to the area fraction of Goss oriented grains (GVF) in
a recrystallized aluminum alloy is at least about 1.5:1 (BVF:GVF).
In other embodiments, the ratio of brass texture intensity to Goss
texture intensity in a recrystallized aluminum alloy is at least
about 1.75:1 (BVF:GVF), or at least about 2:1 (BVF:GVF).
[0079] In one embodiment, a recrystallized aluminum alloy exhibits
a maximum R-value in the range of from about 40.degree. to
60.degree.. The "R-value", or "Lankford Coefficient" presents the
plastic strain ratio expressed as:
R = e w e t ##EQU00001##
where e.sub.w is the true width strain (in the sheet plane at
90.degree. to the tensile axis) and e.sub.t is the true thickness
strain. R-values may be measured in accordance with ASTM
E517-00(2006)e1, Sep. 1, 2006. Recrystallized aluminum alloy
products exhibiting a maximum R-value in the range of from about
40.degree. to about 60.degree. are generally indicative of products
having a greater amount of brass texture, whereas recrystallized
aluminum alloy products exhibiting an maximum R-value in the range
of about 90.degree. are indicative of products having a greater
amount of Goss texture.
[0080] As noted above, texture intensities may be measured via
x-ray diffraction and in accordance with "Texture and Anisotropy,
Preferred Orientations in Polycrystals and their Effect on Material
Properties", Kocks et al., pp. 140-141, Cambridge University Press
(1998). However, the absolute intensity values of texture
components measured may vary among institutes, due to hardware
and/or software differences. Nonetheless, the relative ratios of
the measured texture intensities may be used to determine the
relative amounts of the two textures within the recrystallized
alloy. Thus, in one embodiment, a recrystallized aluminum alloy
comprises a recrystallized microstructure having a measured brass
texture intensity of at least about 5. In one embodiment, the
measured brass texture intensity is at least about 10. In other
embodiments, the measured brass texture intensity is at least about
15, or at least about 20, or at least about 25, or at least about
30, or at least about 40, or at least about 50. The measured amount
of Goss texture intensity is generally less than the measured
amount of brass texture intensity. In one embodiment,
recrystallized aluminum alloy comprises a recrystallized
microstructure having a measured Goss texture intensity of less
than about 20. In other embodiments, the measured Goss texture
intensity is less than about 15, or less than about 10, or less
than about 5. Thus, In one embodiment, the ratio of the amount of
brass texture to the amount of Goss texture in a recrystallized
aluminum alloy is at least about 1.25:1 (BTI:GTI). In other
embodiments, the ratio of brass texture intensity to Goss texture
intensity in a recrystallized aluminum alloy is at least about
1.5:1 (BTI:GTI), or at least about 2:1 (BTI:GTI), or at least about
3:1 (BTI:GTI), or at least about 4:1 (BTI:GTI), or at least about
5:1 (BTI:GTI), or at least about 6:1 (BTI:GTI), or at least about
7:1 (BTI:GTI), or at least about 8:1 (BTI:GTI), or at least about
9:1 (BTI:GTI), or at least about 10:1 (BTI:GTI). Irrespective of
whether x-ray diffraction or OIM techniques are utilized, specimens
analyzed in accordance with the present application include at
least 1000 grains.
[0081] In one embodiment, the recrystallized aluminum alloy is a
sheet product ("recrystallized sheet product"). As used herein,
"sheet product" means rolled aluminum products having thicknesses
of from about 0.01 inch (.about.0.25 mm) to about 0.5 inch
(.about.12.7 mm). The thickness of the sheet may be from about
0.025 inch (.about.0.64 mm) to about 0.325 inch (.about.8.9 mm), or
from about 0.05 inch (.about.1.3 mm) to about 0.325 inch
(.about.8.3 mm). For many applications such as some aircraft
fuselages, the sheet may be from about 0.05 inch (.about.1.3 mm) to
about 0.25 inch (.about.6.4 mm) thick, or from about 0.05 inch
(.about.1.3 mm) to about 0.2 inch (.about.5.1 mm) thick. The sheet
may be unclad or clad, with cladding layer thicknesses of from
about 1 to about 5 percent of the thickness of the sheet. The sheet
product may comprise various aluminum alloy compositions. Some
suitable alloy compositions include heat-treatable alloys, such as
Al--Li based alloys, including one or more of the 2XXX series
alloys defined by the Aluminum Association 2XXX series alloys, and
variants thereof. One particularly useful alloy is a 2199 series
alloy. In one embodiment, the aluminum alloy includes up to about
7.0 wt % copper. In one embodiment, the aluminum alloy includes up
to about 4.0 wt % lithium. The recrystallized sheet products of the
present disclosure may be utilized in a variety of industrial
applications. For example, the recrystallized sheet products may be
utilized in aerospace applications, such as in the production of a
fuselage product (e.g., an aircraft fuselage section, or a fuselage
sheet), or in transportation, automotive, or other industrial
applications.
[0082] The recrystallized sheet products of the present disclosure
generally exhibit higher tensile yield strengths and fracture
toughness for a given thickness of the recrystallized sheet
product. In one embodiment, a recrystallized sheet product has at
least about the same fracture toughness and about the same tensile
yield strength as a compositionally equivalent unrecrystallized
alloy of the same product form and of similar thickness and temper.
For example, the recrystallized sheet product may have a thickness
of not greater than about 0.35 inch, a LT tensile yield strength of
at least about 370 MPa, and T-L fracture toughness (K.sub.app) of
at least about 80 MPa(m.sup.1/2). As used herein, "LT tensile yield
strength" means the LT tensile yield strength of a recrystallized
sheet measured using ASTM B557M-06 (May 1, 2006). As used herein,
"T-L fracture toughness" (K.sub.app) means the T-L fracture
toughness of the recrystallized sheet product measured using a 16
inch wide M(t) specimen with an initial crack length to width ratio
of 2a/W=0.25 in accordance with ASTM B646-06a (Sep. 1, 2006).
[0083] The recrystallized sheet products of the present disclosure
are generally produced by utilizing at least two recrystallization
anneals, as opposed to conventional sheet production processes. One
conventional process for producing a 2199 aluminum alloy
recrystallized sheet product is illustrated in FIG. 2. In the
illustrated embodiment, the conventional sheet production process
includes a preheat step, a scalping step, and a hot rolling step
(100), a cooling step (110), a recovery anneal (120), a cold work
step (130), another recovery anneal (140), another cold work step
(150), a solution heat treatment step (160) (i.e., a
recrystallization anneal), a cooling step (170) and an aging step
(180).
[0084] With respect to the conventional process illustrated in FIG.
2, the thermo-mechanical processes for conventional 2199 aluminum
alloy recrystallized sheet products comprise alternating cold
rolling and recovery annealing before recrystallization annealing
(in this case in the form of a solution heat treatment). The
recovery anneals may be used to soften materials between cold work
passes, but are not designed to intentionally recrystallize
materials prior to a subsequent cold rolling step. Thus,
conventional sheet production processes generally only include a
single recrystallization anneal, which occurs during the solution
heat treatment step (160).
[0085] Conversely, the recrystallized sheet products of the present
disclosure are generally produced via at least two
recrystallization anneals. One embodiment of a recrystallized sheet
production process is illustrated in FIG. 3. In the illustrated
embodiment, the sheet production process includes a preheat step, a
scalping step and a hot rolling step (200), a cooling step (210), a
recovery anneal (220), a cold work step (230), a first
recrystallization anneal (240), another cold work step (250), and a
solution heat treatment step (260) (i.e., a second
recrystallization anneal), a cooling step (270) and a conventional
aging step (280). Thus, the present process includes at least one
intermediate recrystallization anneal and one subsequent cold work
pass prior to the final solution heat treating step (i.e., a second
recrystallization anneal). The use of two recrystallization steps
during formation of the sheet product may result in the production
of recrystallized sheet products having the above-described brass
texture and Goss texture characteristics (e.g., an amount of brass
texture that exceeds an amount of Goss texture).
[0086] Various steps may be completed between the first
(intermediate) recrystallization anneal and the final
recrystallization anneal (i.e., the solution heat treatment step).
For example, one or more of a recovery anneal and/or cold work step
may be completed between the first and second recrystallization
anneals. By way of illustration, and with reference to FIG. 4, a
sheet production process may include a hot rolling step (310), a
first cold work step (320), a first recrystallization anneal (330),
a second cold work step (340), a first recovery anneal (350), a
third cold work step (360) and a solution heat treating step (370)
(i.e., a second recrystallization anneal).
[0087] In another approach, and with reference to FIG. 5, a sheet
production process may include a hot rolling step (410), a first
cold work step (420), a first recrystallization anneal (430), a
second cold work step (440), a first recovery anneal (450), a third
cold work step (460), a second recovery anneal (470), a fourth cold
work step (480) and a solution heat treating step (490) (i.e., a
second recrystallization anneal). Other variations may also be
completed. In one embodiment, only two recrystallization anneals
are completed in the production of a recrystallized sheet product.
In other embodiments, more than two recrystallization anneals are
completed in the production of a recrystallized sheet product.
[0088] The processing conditions of the first and second
recrystallization anneals may be substantially similar to one
another, or the processing conditions of the first and second
recrystallization anneals may be materially different from one
another. For example, the first recrystallization anneal may
include a heat-up period followed by soaking at temperatures that
facilitate production of recrystallized grains within the alloy
sheet (e.g., a first soaking temperature). The second anneal may
include a heat-up period followed by soaking at temperatures that
facilitate solution heat treatment of the alloy sheet (e.g.,
temperatures higher than the first soaking temperature). In one
embodiment, a 2199 aluminum alloy may be processed by completing a
first recrystallization anneal at temperature of about 454.degree.
C. for about 4 hours. After one or more other steps (e.g., cold
work and/or recovery anneal steps), the 2199 alloy may be further
processed by completing a second recrystallization anneal at a
temperature of about 521.degree. C. for about 1 hour.
[0089] Recrystallized sheet products of aluminum alloy series 2199
may have increased LT (long-transverse) tensile yield strength
and/or T-L (transverse-long) fracture toughness. In one embodiment,
a recrystallized sheet product may have an LT tensile yield
strength of at least about 370 MPa, such as an LT tensile yield
strength of at least about 380 MPa, or an LT tensile yield strength
of at least about 390 MPa, or an LT tensile yield strength of at
least about 400 MPa, or an LT tensile yield strength of at least
about 410 MPa. In a related embodiment, a recrystallized sheet
product may have T-L fracture toughness (K.sub.app) of at least
about 80 MPa(m.sup.1/2), such as a T-L fracture toughness of at
least about 85 MPa(m.sup.1/2), or a T-L fracture toughness of at
least about 90 MPa(m.sup.1/2), or a T-L fracture toughness of at
least about 95 MPa(m.sup.1/2), or a T-L fracture toughness of at
least about 100 MPa(m.sup.1/2), or a T-L fracture toughness of at
least about 105 MPa(m.sup.1/2).
[0090] While the foregoing description predominately relates to
sheet products, it is anticipated that the described methods may
also be utilized with plate products, forged products, and extruded
products. Plate products are distinguished from sheet products in
that plate products have a thickness greater than that of sheet
products (e.g., between about 0.5 inch an 12 inches).
EXAMPLES
Example 1
[0091] Two ingots of a 2199 aluminum alloy are direct chill (DC)
cast. After stress relieving, the ingots are homogenized and
scalped. The ingots are then heated to 950.degree. F. and hot
rolled into sheets having a thickness of 7.2 mm. These sheets are
then recovery annealed by soaking at 371.degree. C. for 4 hours,
followed by soaking at 315.degree. C. for 4 hours, followed by
soaking at 204.degree. C. for 4 hours. These sheets are further
cold rolled with a 30% reduction in thickness. After the first cold
rolling, a first sheet (Sheet 1) is subjected to a
recrystallization anneal at 454.degree. C. for 6 hours (after a 16
hour heat-up period) while a second sheet (Sheet 2) is subjected to
a recovery anneal at 354.degree. C. for 6 hours (after a 16 hour
heat-up period). Subsequently, Sheet 1 and Sheet 2 are then both
cold rolled to a final thickness of 3.5 mm. After cold rolling,
both Sheet 1 and Sheet 2 are solution heat treated at about
521.degree. C. for 1 hour and quenched in water at room
temperature. Sheet 1 and Sheet 2 are then both tempered to a T8
temper using the same tempering conditions.
[0092] The grains and textures of Sheet 1 and Sheet 2 are measured
after the final aging practice. Test samples of these sheets are
prepared by polishing with Buehler Si--C paper by hand for 3
minutes, followed by polishing by hand with a Buehler diamond
liquid polish having an average particle size of about 3 .mu.m. The
samples are anodized in an aqueous fluoric-boric solution for 30-45
seconds. The microstructures are obtained with a polarized beam via
a Zeiss optical microscope at a magnification of from about
150.times. to about 200.times..
[0093] The crystallographic textures of the samples of Sheet 1 and
Sheet 2 are determined using the "texture intensity measurement
procedure", described above, but using internally developed
software. internally developed software. FIG. 6a illustrates a
microstructure of Sheet 1 after solution heat treatment. The
microstructure is fully recrystallized. FIG. 6b illustrates a
microstructure of Sheet 1 taken at transverse direction (LT-ST),
and illustrates a fully recrystallized and pancake shaped
microstructure. FIG. 7a illustrates a microstructure of Sheet 2
after solution heat treatment. FIG. 7b illustrates a microstructure
of Sheet 2 taken at transverse direction (LT-ST), and illustrates a
fully recrystallized and pancake shaped microstructure. As
illustrated in FIGS. 6a, 6b and 7a, 7b, there is no noticeable
difference in grain size between Sheet 1, which was processed with
two recrystallization anneals, and Sheet 2, which was processed
with a single recrystallization anneal.
[0094] The samples of Sheet 1 and Sheet 2 are analyzed with OIM.
The OIM sample procedure, described above, is used to determine the
area fraction of Goss oriented grains and brass oriented grains for
both sheets. FIG. 8. illustrates the OIM scanned image of Sheet 1.
In Sheet 1, the area fraction of brass grains is greater than 10%,
while the area fraction of brass oriented is less than 3%. FIG. 9.
illustrates the OIM scanned image of conventionally processed
sample 2. In Sheet 2, the area fraction of Goss grains is greater
than 25%, while the area fraction of brass oriented is less than
1%.
[0095] Fracture toughness tests are performed on the sheets using a
16 wide M(t) specimen with an initial crack length to width ratio
2a/W=0.25 in accordance with ASTM B646-06a. Tensile testing is
conducted in the LT direction in accordance with ASTM B557M-06 (May
1, 2006) and the tensile results reported are the average of
duplicate tests. As illustrated in FIG. 10, Sheet 1 exhibits
improved properties in combination of long transverse (T-L)
K.sub.app fracture toughness and tensile yield strength (TYS) as
compared to the properties of Sheet 2.
[0096] Table 1, below, contains summary data relating to the
properties of Sheet 1 and Sheet 2. Sheet 1, which is manufactured
with two recrystallization anneals, has a brass texture intensity
nearly 9 times greater than its Goss texture intensity (29.8 for
brass texture intensity, as opposed to 3.4 for Goss texture
intensity). Conversely, Sheet 2, which is manufactured with the
conventional, single recrystallization anneal (i.e., the solution
heat treatment step) has a Goss texture intensity that was about 27
times greater than its brass texture intensity (35.7 for Goss
texture intensity, as opposed to 1.3 for brass texture intensity).
Hence, utilizing two recrystallization anneals during processing of
alloy sheets may result in production of recrystallized alloy
sheets having an amount of brass texture that exceeds the amount of
Goss texture.
TABLE-US-00002 TABLE 1 Sheet 1 Sheet 2 Process Two
recrystallization Single recrystallization anneal steps anneal step
Final Thickness 3.5 mm 3.5 mm Texture after solution Measured
Intensity Measured Intensity heat treatment (SHT) brass texture
29.8 1.3 Goss texture 3.4 35.7 {112}<111> Copper 1.1 2
texture S1 texture 2.4 3.5 Cube texture 0.8 1.8 Area fraction of
brass 11.3% 0.7% texture via OIM Area fraction of Goss 2.4% 26.3%
texture via OIM LT TYS (MPa) 389 358 LT UTS (MPa) 466 454 T-L
K.sub.c (MPa m) 148.36 136.02 T-L K.sub.app (MPa m) 105.73 99.6
Grain Structure Recrystallized Recrystallized after SHT
Example 2
[0097] Various plant produced 2199 alloy recrystallized sheets
(i.e., fabricated with a conventional, single recrystallization
anneal process) are subjected to a variety of tests. For example,
test samples are prepared as described above and both brass texture
intensity and Goss texture intensity are measured as a function of
gauge thickness of the sheet product. FIG. 11 illustrates brass
texture intensity and Goss texture intensity as a function of gauge
thickness for the conventional 2199 sheets. A noticeable trend is
that the Goss intensity increases, but the brass intensity
decreases as the gauge thickness gets thinner. Toughness and
strength tests are also performed on the conventional sheet
products. The sheets are subjected to tensile testing in the LT
direction in accordance with ASTM B557M-06 (May 1, 2006) and T-L
fracture toughness testing using a 16 in. wide M(t) specimen with
an initial crack length to width ratio 2a/W=0.25 in accordance with
ASTM B646-06a. The reported tensile results are the average of
duplicate tests. FIG. 12 and FIG. 13 illustrate the corresponding
T-L fracture toughness (K.sub.app) and ultimate tensile strength,
respectively, as a function of gauge thickness. Reduction in both
toughness and strength is observed with decreasing gauge thickness,
especially for sheets having a thickness below about 4 mm.
Example 3
[0098] A 2199 alloy DC cast ingot having a size of 381
mm.times.1270 mm.times.4572 mm (thickness.times.width.times.length)
is scaled and homogenized. The ingots are then hot rolled to two
different thickness, 5.08 mm and 11.68 mm, and recovery annealed
via a 3-step recovery anneal process, which includes 4 hours of
soaking at 371.degree. C., 4 hours of soaking at 315.degree. C.,
and 4 hours of soaking at 204.degree. C. After this 3-step recovery
anneal, coupons having a size of 50.8 mm.times.254 mm
(width.times.length) from the hot rolled and annealed plates are
produced. As illustrated in FIG. 14, after the 3-step recovery
anneal, a coupon of each thickness (i.e., one 5.08 mm coupon and
one 11.68 mm coupon) is cold roll reduced by one of 30%, 35%, 40%
and 45%, thus producing eight coupons with varying cold work
amounts and thicknesses. Each of these eight coupons is then
processed via a recrystallization anneal at about 454.degree. C. at
4 hours, with a 16 hour heat-up period. Each of the eight coupons
is then cold roll reduced an additional 30%, and then subjected to
a recovery anneal at about 315.degree. C. and 4 hours, with a 16
hour heat-up period. Each of the eight coupons is then cold roll
reduced an additional 30% and then solution heat treated at about
521.degree. C. for 1 hour. After the solution heat treatment, test
samples are prepared as described above and the microstructure of
each sample is measured. FIG. 15 shows the intensities of the Goss
texture and brass texture as a function of hot rolled thickness and
amount of cold work. The results indicate that the two-step
recrystallization process results in sheets having a higher amount
of brass texture than Goss texture in all 8 coupons, thereby
indicating that various amounts of cold work and various
thicknesses can be utilized with the two-step recrystallization
process.
Example 4
[0099] With reference to FIG. 16, a 2199 alloy is hot rolled to a
thickness 5.08 mm and recovery annealed via a 3-step recovery
anneal process, which includes 4 hours of soaking at 371.degree.
C., 4 hours of soaking at 315.degree. C., and 4 hours of soaking at
204.degree. C. After this 3-step recovery anneal, coupons from the
hot rolled and annealed plates are produced. Each of the coupons is
cold roll reduced 30%. Each of these eight coupons is then
processed via a recrystallization anneal at about 454.degree. C.
for 4 hours, with a 16 hour heat-up period. The coupons are then
separately cold roll reduced an additional 35%, 40%, and 45%
respectively. The coupons are then solution heat treated at about
521.degree. C. for 1 hour. After the solution heat treatment, test
samples are prepared as described above and the microstructure of
each sample is measured. The microstructure is fully
recrystallized.
[0100] Another 5.08 mm thick coupon is produced via an initial hot
rolling and 3-step recovery anneal process, as described above, and
is then processed in accordance with the fabrication map
illustrated in FIG. 4. In particular, after the initial cold work,
the coupon is processed via a recrystallization anneal at about
454.degree. C. for 4 hours, with a 16 hour heat-up period. The
coupon is then cold roll reduced an additional 30%. The coupon is
then processed via a recovery anneal at about 315.degree. C. for 4
hours, with a 16 hour heat-up period. The coupon is then cold roll
reduced an additional 30%. The coupon is then solution heat treated
at about 521.degree. C. for 1 hour.
[0101] Another 5.08 mm thick coupon is produced via an initial hot
rolling and 3-step recovery anneal process, as described above, and
is then processed in accordance with the fabrication map
illustrated in FIG. 5. In particular, after the initial cold work,
the coupon is processed via a recrystallization anneal at about
454.degree. C. for 4 hours, with a 16 hour heat-up period. The
coupon is then cold roll reduced an additional 30%. The coupon is
then processed via a recovery anneal at about 315.degree. C. for 4
hours, with a 16 hour heat-up period. The coupon is then cold roll
reduced an additional 30%. The coupon is then processed via another
recovery anneal at about 315.degree. C. for 4 hours, with a 16 hour
heat-up period. The coupon is then cold roll reduced an additional
30%. The coupon is then solution heat treated at about 521.degree.
C. for 1 hour.
[0102] Test samples are prepared as described above and the
microstructure of each sample is measured. FIG. 17 illustrates the
texture intensities as a function of accumulated cold work from at
least some of the above coupons. These, and other results, indicate
that the strength of sheets having recrystallized brass texture in
accordance with the present disclosure can be controlled by
adjusting the amount of cold work after the first intermediate
recrystallization anneal. Furthermore, these and other results
illustrate that the brass texture in recrystallized Al--Li sheets
is attainable by applying intermediate recrystallization anneals
and recrystallization during solution heat treatment. In addition,
the strength of the brass texture in recrystallized sheets can be
controlled by optimizing the thermomechanical process parameters
comprising hot rolling, cold rolling and annealing.
Example 5
[0103] Various ones of the samples produced in Examples 3 and 4 are
selected for mechanical testing. Since aging is a key process to
affect the final properties, the aging is done at the same T8
condition for both the conventionally processed materials and
materials processed via a dual recrystallization process. The
sheets are subjected to tensile testing in the LT direction in
accordance with ASTM B557M-06 (May 1, 2006) and T-L fracture
toughness testing using a 16 in. wide M(t) specimen with an initial
crack length to width ratio 2a/W=0.25 in accordance with ASTM
B646-06a. The reported tensile results are the average of duplicate
tests. FIG. 18 illustrates the average T-L fracture toughness
(K.sub.app) values of the conventionally processed recrystallized
sheets and the recrystallized sheet products of the present
disclosure as a function of gauge thickness. FIG. 19 illustrates
the average LT tensile yield strength of the conventionally
processed recrystallized sheets and the recrystallized sheet
products of the present disclosure as a function of gauge
thickness. As shown in FIGS. 18 and 19, increasing the amount of
brass texture and consequently reducing the amount of Goss texture
in 2199 recrystallized sheets generally results in sheet products
having an improved LT strength and T-L toughness combination
relative to conventionally processed sheets. FIG. 20 illustrates a
strength and toughness plot using the data illustrated in FIGS. 16
and 17.
[0104] FIG. 21 shows R-values of samples produced in accordance
with methods of the present disclosure and the R-values of
conventionally produced samples. The estimated R-values are
obtained as a function of rotation angle from Angle=0.degree.
(where the L direction is parallel to the tension direction) to
Angle=90.degree. (where the L direction is perpendicular to the
tension direction). The variation in R-values as a function of
rotation angle is a direct result of anisotropy in mechanical
behavior due to crystallographic texture. As shown in FIG. 21,
samples produced in accordance with the present disclosure exhibit
maximum R-values between 40.degree. and 60.degree., which is a
classical R-value distribution of a Brass textured sheet, while the
conventionally processed samples exhibit maximum R-values of
90.degree., which is a classical R-value distribution of a Goss
textured sheet.
[0105] While various embodiments of the present invention have been
described in detail, it is apparent that modifications and
adaptations of those embodiments will occur to those skilled in the
art. However, it is to be expressly understood that such
modifications and adaptations are within the spirit and scope of
the present invention.
* * * * *