U.S. patent application number 10/706846 was filed with the patent office on 2005-05-12 for method of manufacturing near-net shape alloy product.
Invention is credited to Addabbo, Michael P., Blake, Sallie L., Gonyer, Amy J., Goodyear, M. Dan, Venema, Gregory B., Witters, Jeffrey J..
Application Number | 20050098245 10/706846 |
Document ID | / |
Family ID | 34552630 |
Filed Date | 2005-05-12 |
United States Patent
Application |
20050098245 |
Kind Code |
A1 |
Venema, Gregory B. ; et
al. |
May 12, 2005 |
Method of manufacturing near-net shape alloy product
Abstract
A method of producing a heat treatable metal product having the
ordered steps of providing an ingot of a heat treatable metal
alloy; rolling the ingot to a flat product; removing material from
the product to achieve a near-net shape of a desired final shape;
and solution heat treating the product. The product is stretched to
the desired final shape and aged to achieve the desired mechanical
properties.
Inventors: |
Venema, Gregory B.;
(Bettendorf, IA) ; Blake, Sallie L.; (Long Grove,
IA) ; Witters, Jeffrey J.; (LeClaire, IA) ;
Goodyear, M. Dan; (Acworth, GA) ; Addabbo, Michael
P.; (Bettendorf, IA) ; Gonyer, Amy J.; (Blue
Grass, IA) |
Correspondence
Address: |
Daniel C. Abeles, Esq.
Eckert Seamans Cherin & Mellott, LLC
Alcoa Inc., Alcoa Technical Center
100 Technical Drive
Alcoa Center
PA
15069-0001
US
|
Family ID: |
34552630 |
Appl. No.: |
10/706846 |
Filed: |
November 12, 2003 |
Current U.S.
Class: |
148/688 |
Current CPC
Class: |
C22F 1/047 20130101;
C22F 1/053 20130101; C22F 1/04 20130101 |
Class at
Publication: |
148/688 |
International
Class: |
C22F 001/04 |
Claims
What is claimed is:
1. A method of producing a heat treatable metal product comprising
the ordered steps of: (a) providing an ingot of a heat treatable
metal alloy; (b) rolling the ingot to a flat product; (c) removing
material from the product to achieve a shape near-net to a desired
final shape; (d) solution heat treating the product; (e) stretching
the product to achieve the desired final shape; and (f) aging the
product.
2. The method of claim 1, wherein the metal alloy is an aluminum
alloy.
3. The method of claim 1, wherein step (c) comprises machining the
product to achieve the near-net shape.
4. The method of claim 2, wherein the aluminum alloy is selected
from the group consisting of AA series 2XXX, 6XXX and 7XXX.
5. The method of claim 2, wherein the flat product is in the F
temper.
6. The method of claim 2, wherein the final product is a component
of an aircraft.
7. The method of claim 6, wherein the component is a wing
panel.
8. The method of claim 7, wherein step (c) comprises machining the
near-net shape of a skin and stiffening members in the wing
panel.
9. A heat treated metal component produced according to the method
of claim 1.
10. The heat treated metal component of claim 9, wherein said
product is a component of an aircraft.
11. The heat treated metal component of claim 10, wherein the
component is a wing panel.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a process for manufacturing
metal alloy plate product in a near-net shape prior to heat
treatment. More particularly, the invention relates to the
production of a metal alloy product in which a metal alloy plate or
sheet is produced in dimensions that are similar to the desired
final dimensions of the product, then heat treated, stretched and
aged.
[0003] 2. Description of Related Art
[0004] Aluminum alloys are extensively used in aircraft and
automobiles as well as other products that benefit from the unique
combination of properties such as low weight (compared to ferrous
alloys), high strength, fracture toughness, and corrosion
resistance. Aircraft and automotive structural components are
typically produced from a sheet or plate to which additional
structural members are attached. For example, the upper and lower
wing panels of an aircraft are typically produced from aluminum
alloy plate (referred to as the skin) which is reinforced by
extruded components (referred to as stringers). The stringers are
fixed to the skin by fasteners such as rivets.
[0005] Aluminum aircraft components produced from flat rolled
products are traditionally manufactured from direct chill cast
ingots that may be several feet thick. The ingot is then hot-rolled
to a preliminary plate or sheet thickness. Subsequent cold rolling
may be performed prior to heat treating, stretching and artificial
or natural aging. Prior to the artificial aging step, the
mechanical properties of the alloy such as yield strength and
fracture toughness are improved by solution heat treating the alloy
at elevated temperatures which alters the microstructure of the
solute components in the alloy. The metal is then quenched to lock
in the microstructure of the alloy achieved during solution heat
treatment. After heat treatment, the material is stretched,
artificially or naturally aged and machined or chemically milled to
its final shape.
[0006] Some final products (e.g. aircraft wing ribs) have
relatively thick cross-sections of up to ten inches thick that are
machined from plate. For these thick gauge applications, the ingot
is hot-rolled, solution heat treated and quenched. Rapid quenching
immediately following solution heat treatment is desirable for
rapid locking of the elements needed for strengthening in the
microstructure. A slow quench rate risks loss of mechanical
properties. However, the quench rate is dependent on the plate
thickness. As the thickness of the plate increases, the quench rate
for the plate decreases which results in lower achievable
mechanical properties. Moreover, some aluminum alloys have
mechanical properties that are readily lost if rapid quenching is
not performed. It would be desirable to produce such alloys in
thick cross-sections utilizing high quench rates to take advantage
of improved mechanical properties. However, the product thickness
has been limited by the quench sensitivity of those alloys and
slower quench rates. Increasing the quench rate or reducing the
cross section thickness, will result in improved mechanical
properties
[0007] Accordingly, a need remains for a method of producing heat
treatable metal product at gauges at which the quench rate is
acceptable.
SUMMARY OF THE INVENTION
[0008] This need is met by the method of present invention for
producing a heat treatable metal product. According to one aspect
of the invention, an ingot of a heat treatable metal alloy such as
aluminum alloy in the F temper (the temper of the alloy as
fabricated) is rolled to a flat product. Material from the flat
product is removed to achieve a shape similar to the desired final
(net) shape, referred to herein as the near-net shape. The near-net
shaped product is solution heat treated and stretched. The
stretching step flattens, stress relieves and brings the shape to
the desired final dimensions. The stretched product is then
artificially aged. Suitable alloys for use in the present invention
are aluminum alloys including alloys of the Aluminum Association
(AA) series 2XXX, 6XXX and 7XXX. The final product may be an
aircraft component such as a wing panel or an automotive
component.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a cross section of a component produced according
to the present invention;
[0010] FIG. 2 is a plot of electrical conductivity for the lower
surfaces of plates produced according to the present invention and
control plates;
[0011] FIG. 3 is a plot of electrical conductivity for the upper
surfaces of plates produced according to the present invention and
control plates;
[0012] FIG. 4 is a plot of tensile strength for plates produced
according to the present invention and control plates;
[0013] FIG. 5 is a plot of fracture toughness for plates produced
according to the present invention and control plates, both in the
T7651 temper; and
[0014] FIG. 6 is a plot of fracture toughness for plates produced
according to the present invention and control plates, both in the
T7451 temper.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0015] The present invention includes a method of producing heat
treatable metal products having a superior combination of
properties and economies of production. The invention may be used
with various alloy systems including aluminum, magnesium, copper
and other alloys which rely on heat treatment for precipitation of
solute for strengthening purposes, referred to herein as a "heat
treatable metal alloy". The present invention is especially useful
for AA 2XXX, 6XXX and 7XXX series aluminum alloys.
[0016] According to the present invention, a heat treatable metal
alloy product is produced as an ingot by direct chill casting or
the like. The term ingot is meant to include other bulk metal
products. The metal alloy ingot is rolled into a flat product.
Material from the flat product is removed resulting in a shape of
the product that is near-net to a desired final shape. By the
phrase "near-net shape" it is meant that the product is
dimensionally similar to the dimensions of the desired final shape.
Material removal may be accomplished by various techniques
including via machining. The near-net shaped product is then
solution heat treated and quenched. Solution heat treatment may be
performed in any type of solution heat treat furnace using either a
spray or an immersion quench system. The orientation of the product
in a solution heat treat furnace may be selected to account for
potential quench distortion and equipment design.
[0017] By removing material so that the product achieves a near-net
shape, the product is thinner and the quench rate for the product
is higher than the quench rate for an ingot or a traditional flat
product. Accordingly, superior properties are achievable in a
product produced according to the present invention due to the
opportunity for high quench rate.
[0018] The solution heat treated product is then stretched to
achieve the desired final dimensions for the product. The phrase
"final dimensions" refers to the dimensions of the product after
practicing the present invention, which may not necessarily be the
ultimate dimensions of a completed component. Further altering of
the product dimensions may occur depending on the end use for the
product. Stretching of a product reduces the residual stresses in
the product, provides flatness to the product and may improve
metallurgical properties of the product in certain alloys. By
removing material so that the product achieves a near-net shape
prior to solution heat treatment, the stretching process is
facilitated due to the smaller volume of the product being
stretched. Typically, stretching decreases the dimensions of the
stretched product by about 1.25% in each of the product thickness
and the product width, i.e. has a target stretch of about 2.5%. The
step of removing material so that the product achieves a near-net
shape should take into account the decrease in the thickness and
width of the product during stretching. For example, the dimensions
of the product in its near-net shape should be 1.25% larger in each
of the product thickness and the product width so that the
stretching step results in the desired the final dimensions.
[0019] Finally, the stretched product which is in its desired final
shape is aged such as via artificial aging. Traditionally,
artificial aging is performed on a plate or sheet product. By
artificially aging a product produced according to the present
invention which has a significantly thinner cross-section than
conventional aged products, the artificial aging process may be
performed more rapidly in both the heat up of the product and the
cool down of the product providing greater control and
consistency.
[0020] Although the invention has been described generally above,
the particular examples give additional illustration of the product
and process steps typical of the present invention.
EXAMPLES
[0021] Two ingots of Aluminum Association alloy 7085 each weighing
approximately 19,000 pounds were randomly selected from existing
commercial stock. The ingots referred to as Ingot A and Ingot B
were chosen from different casting campaigns. Alloy 7085 has the
composition limits shown in Table 1.
1TABLE 1 ELEMENT MIN MAX SILICON -- 0.06 IRON -- 0.08 COPPER 1.3
2.0 MANGANESE -- 0.04 MAGNESIUM 1.2 1.8 CHROMIUM -- 0.04 ZINC 7.0
8.0 TITANIUM -- 0.06 ZIRCONIUM 0.08 0.15 OTHER IMPURITIES, EACH --
0.05 OTHER IMPURITIES, -- 0.15 TOTAL ALUMINUM REMAINDER
[0022] Ingots A and B were scalped and homogenized using standard
fabrication practices and procedures. Both ingots were hot rolled
into plates 3.5 inches thick by 74 inches wide by 600 inches long
using standard hot rolling temperatures and pass schedules. Each of
the two 3.5 inch.times.74 inch plate pieces were cut in half along
its length to yield two sets of two 300 inch long plates. One plate
from Ingot A and one plate from Ingot B were processed according to
the present invention to produce plates having integrally formed
stringers on a web (referred to as ISP plates). The two ISP plates
were machined from the F temper down the full length to produce the
cross section configuration shown in FIG. 1 and are referred to as
ISP A plate and ISP B plate. The other plates from each of Ingots A
and B were processed in their original configurations as control
plates and are referred to as Control A plate and Control B
plate.
[0023] All four plates were solution heat-treated in a horizontal
furnace and spray water quenched in accordance with AMS (American
Metals Society) 2772 guidelines. The ISP plates A and B were
solution heat treated with the stringers oriented up. All plates
were stretched to a target of 2%.
[0024] To check for quench efficiency, the plates were scanned
using eddy current to evaluate the surface electrical conductivity
uniformity. FIG. 2 shows the % IACS (International Annealed Copper
Standard) electrical conductivity across the width (longitudinal
transverse direction) of bottom sides (lower surface during
quenching) of the ISP A and B plates (smooth side, without the
machined stringers) and of the Control plates A and B. FIG. 3 shows
the % IACS electrical conductivity for the top sides of the plates
(upper surfaces during quenching). The data for the top side of the
ISP plates was taken on stringers at the edge of the plates (Edge
Stringer) and on stringers midway across the plates (W/2 Stringer).
The data for the top side of the control plates was taken at
halfway across the width of the plates (W/2). For the bottoms of
the plates and the top sides of the plates, the % IACS electrical
conductivity for the ISP plates was uniformly lower than for the
control plates. Lower % IACS electrical conductivity is indicative
of higher quench rate. As such, product with thinner cross sections
than conventional products can be produced according to the present
invention at higher quench rates.
[0025] Prior to artificial aging the four plate sections, each
plate was again cut in half to yield a piece of plate approximately
150 inches long. The 150 inch plates were aged to each of T7651
type temper and T7451 type temper. Two control plates and two ISP
plates were aged to each temper condition. Upon completion of the
artificial aging, the plates were sectioned for mechanical property
testing. To ensure an accurate comparison between the control plate
properties and the ISP plate properties, special care was taken to
keep all of the test plane references relative to the original
rolled plate thickness. This was important to eliminate variability
in test results associated with chemical composition or grain
structure gradients through thickness. Tensile strength testing was
performed on the webs of the ISP and control plates from each of
Ingots A and B at a plane halfway through the thickness of the
plate web (t/2) at width locations of the plate edge (Edge) and
midway across the plate (W/2). Fracture toughness testing was
performed at planes of halfway through the thickness of the plate
web (Web/2), one quarter through the thickness of the stringer
(t/4) and halfway through the thickness of the stringer (t/2) at
several locations across the plate including the plate edge (Web
Edge), the stringer edge (Stringer Edge), midway across the plate
in the web (Web W/2), and midway across the plate in the stringer
(Stringer W/2). Test locations for the control plates were made in
the locations of the solid (non-machined) plates as if the control
plates had been machined to include stringers and web so that the
comparison between ISP and control plates was referenced from the
same position in the original ingot.
[0026] FIG. 4 shows the longitudinal transverse tensile strength
data in KSI units (ultimate yield strength or UTS and tensile yield
strength or TYS) for the ISP and control plates produced from
Ingots A and B, aged to T7651. The ISP plate strengths are
generally equal to or slightly above the control group.
[0027] FIG. 5 shows the fracture toughness for the ISP and control
plates produced from Ingots A and B aged to T7651, and FIG. 6 shows
similar data for plates aged to the T7451 temper. The ISP plates
generally exhibited 10% to 20% higher fracture toughness than the
control plates in all locations for both tempers.
[0028] It should be appreciated that the present invention allows
for machining (or other material removal) of bulk metal into a
near-net shape prior to solution heat treatment, stretching and
aging with superior properties in the final product compared to
conventionally manufactured product that is machined after
aging.
[0029] The present invention provides economical benefits in the
production of aluminum alloy products. Productivity may be
increased due to higher quench rates and shorter aging practices of
the near-net shape product with concomitant energy savings.
[0030] In addition, certain aluminum alloy products with
complicated shapes have not previously been produced from
flat-rolled wrought products. Extrusion, forging and casting
processes are typically employed to manufacture such products and
those processes do not always impart the mechanical properties
achievable with wrought products. However, by using the method of
the present invention the shapes of extruded, forged or cast
products may be manufactured in a wrought product by removing
material from a flat-rolled (wrought) product to achieve a near-net
shape prior to solution heat treatment.
[0031] Further potential benefits of the present invention include
reduced weight of components and manufacturing cost savings for the
end use customer. The total weight for structural components may be
reduced by manufacturing product according to the present
invention. Fasteners and other related structural members required
for joining components to each other are minimized or avoided when
the product is machined to its near-net shape as an integrally
manufactured product. For example the stiffening members (e.g.
stringers) of an aircraft wing panel may be integrally produced
with the skin using the method of the present invention. The
opportunity for cost savings to the end use customer may include
reduced process time to achieve the final part configuration (e.g.
less machining or chemical milling time) and reduced process
scrap.
[0032] It will be readily appreciated by those skilled in the art
that modifications may be made to the invention without departing
from the concepts disclosed in the foregoing description. Such
modifications are to be considered as included within the following
claims unless the claims, by their language, expressly state
otherwise. Accordingly, the particular embodiments described in
detail herein are illustrative only and are not limiting to the
scope of the invention which is to be given the full breadth of the
appended claims and any and all equivalents thereof.
* * * * *