U.S. patent application number 11/255044 was filed with the patent office on 2007-04-19 for high-strength mechanical and structural components, and methods of making high-strength components.
Invention is credited to Frank Alford, Saket Chadda, Stephane Ferrasse, Janine K. Kardokus, Susan D. Strothers.
Application Number | 20070084527 11/255044 |
Document ID | / |
Family ID | 37947058 |
Filed Date | 2007-04-19 |
United States Patent
Application |
20070084527 |
Kind Code |
A1 |
Ferrasse; Stephane ; et
al. |
April 19, 2007 |
High-strength mechanical and structural components, and methods of
making high-strength components
Abstract
The invention includes components comprising an alloy containing
a base metal and less than or equal to 30% alloying elements. The
material has a grain size of less than or equal to about 30 microns
and an absence of voids and inclusions of a size greater than 1
micron. The components have a yield strength at least 50% greater
than the identical alloy composition in the 0 temper condition.
Where the material is heat treatable, the yield strength is at
least 10% greater than the identical composition in the T6 temper
condition. The invention includes a method of producing components
by casting and initial treatment to form a billet. The billet is
subjected to equal channel angular extrusion and subsequent
annealing at a temperature of less than or equal to 0.85 times the
minimum temperature for inducing growth of submicron grains to over
1 micron.
Inventors: |
Ferrasse; Stephane;
(Veradale, WA) ; Alford; Frank; (Veradale, WA)
; Kardokus; Janine K.; (Veradale, WA) ; Strothers;
Susan D.; (Spokane, WA) ; Chadda; Saket; (San
Jose, CA) |
Correspondence
Address: |
WELLS ST. JOHN P.S.
601 W. FIRST AVENUE, SUITE 1300
SPOKANE
WA
99201
US
|
Family ID: |
37947058 |
Appl. No.: |
11/255044 |
Filed: |
October 19, 2005 |
Current U.S.
Class: |
148/550 ;
148/400; 148/415; 148/437; 148/690 |
Current CPC
Class: |
C22F 1/00 20130101; C22F
1/04 20130101 |
Class at
Publication: |
148/550 ;
148/400; 148/437; 148/415; 148/690 |
International
Class: |
C22C 21/00 20060101
C22C021/00; C22F 1/04 20060101 C22F001/04 |
Claims
1. A high-strength engine component comprising a material
consisting of an alloy containing a base metal alloyed with less
than or equal to 30% of alloying elements, by weight, the material
having an average grain size of less than or equal to about 30
micron, an absence of voids and inclusions having a size greater
than 1 micron, and a yield strength at least 50% greater than the
yield strength of the identical alloy composition in the annealed 0
temper condition.
2. The high-strength engine component of claim 1 wherein the
average grain size is less than or equal to 1 micron.
3. The high-strength engine component of claim 1 wherein the yield
strength is at least 100% greater than the yield of the identical
alloy in the annealed 0 temper condition.
4. The high-strength engine component of claim 1 wherein the
material has a fatigue life at least 5% greater than the fatigue
life of the identical alloy composition in the annealed 0 temper
condition.
5. The high-strength engine component of claim 4 wherein the
material has a fatigue life at least 20% greater than the fatigue
life of the identical alloy composition in the annealed 0 temper
condition.
6. The high-strength engine component of claim 1 wherein the base
metal is selected from the group consisting of Al, Ti, Mg, Be, Ni,
Fe, Cu, Co, W, Ta, Zn, Ag, Sn, Pb, In, Au, Si, Sb, Mo, V, Sc, Cr,
Y, B, Mn, C, Li, P, S, Nb, Zr, Pd, and Cd.
7. The high-strength engine component of claim 1 wherein the alloy
comprises at least one of Al, Ti, Mg, Be, Ni, and Fe.
8. The high-strength engine component of claim 1 wherein the alloy
is an Al alloy selected from the group consisting of 2xxx series,
3xxx series, 4xxx series, 5xxx series, 6xxx series and 7xxx series
Al alloys.
9. The high-strength engine component of claim 1 wherein the alloy
is an Al--Li alloy.
10. The high-strength engine component of claim 1 wherein the alloy
is a Ti--Al--V alloy.
11. The high-strength engine component of claim 1 wherein the base
metal is Mg.
12. The high-strength engine component of claim 1 wherein the
engine component is a wheel.
13. A high-strength engine component comprising a material
consisting of an alloy containing a base metal alloyed with less
than or equal to 0% of alloying elements, by weight, the material
having an average grain size of less than or equal to about 30
micron, an absence of voids and inclusions having a size greater
than 1 micron, soluble second phase precipitates having an average
size of less than 30 micron, and a yield strength at least 10%
greater than the yield strength of the identical alloy composition
in the T6 temper condition.
14. The high-strength engine component of claim 13 wherein the
material has a yield strength at least 30% greater than the yield
strength of the identical alloy composition in the T6 temper
condition.
15. The high-strength engine component of claim 13 wherein the
material has a fatigue life at least 5% greater than the fatigue
life of the identical alloy composition in the T6 temper
condition.
16. The high-strength engine component of claim 13 wherein the base
metal is selected from the group consisting of Al, Ti, Mg, Be, Ni,
Fe, Cu, Co, W, Ta, Zn, Ag, Sn, Pb, In, Au, Si, Sb, Mo, V, Sc, Cr,
Y, B, Mn, C, Li, P, S, Nb, Zr, Pd, and Cd.
17. The high-strength engine component of claim 13 wherein the
alloy comprises at least one of Al, Ti, Mg, Be, Ni, and Fe.
18. The high-strength engine component of claim 13 wherein the
alloy is an alloy selected from the group consisting of 2xxx
series, 3xxx series, 4xxx series, 5xxx series, 6xxx series, and
7xxx series Al alloys, Al--Li alloys, Ti--Al--V alloys and Mg based
alloys.
19. A vehicle structural component comprising a material consisting
of an alloy comprising at least two elements selected from the
group consisting of Al, Ti, Mg, Be, Ni, Fe, Cu, Co, W, Ta, Zn, Ag,
Sn, Pb, In, Au, Si, Sb, Mo, V, Sc, Cr, Y, B, Mn, C, Li, P, S, Nb,
Zr, Pd, and Cd, the alloy containing a base metal alloyed with less
than or equal to 10% of additional alloying elements, by weight,
the material having an average grain size of less than or equal to
about 30 micron, an absence of voids and inclusions having a size
greater than 1 micron, and a yield strength at least 50% greater
than the yield strength of the identical alloy composition in the
annealed 0 temper condition.
20. The vehicle structural component of claim 19 wherein the alloy
is an alloy selected from the group consisting of 2xxx series, 3xxx
series, 4xxx series, 5xxx series, 6xxx series, and 7xxx series Al
alloys, Al--Li alloys, Ti--Al--V alloys, and Mg-based alloys.
21. The vehicle structural component of claim 19 wherein the
structural component is a body panel.
22. A vehicle structural component comprising a material consisting
of an alloy comprising at least two elements selected from the
group consisting of Al, Ti, Mg, Be, Ni, Fe, Cu, Co, W, Ta, Zn, Ag,
Sn, Pb, In, Au, Si, Sb, Mo, V, Sc, Cr, Y, B, Mn, C, Li, P, S, Nb,
Zr, Pd, and Cd, the alloy containing a base metal alloyed with less
than or equal to 30% of additional alloying elements, by weight,
the material having an average grain size of less than or equal to
about 30 microns, an absence of voids and inclusions having a size
greater than 1 micron, soluble second phase precipitates having an
average size of less than 30 micron, and a yield strength at least
10% greater than the yield strength of the identical alloy
composition in the T6 temper condition.
23. The vehicle structural component of claim 22 wherein the alloy
is an alloy selected from the group consisting of 2xxx series, 3xxx
series, 4xxx series, 5xxx series, 6xxx series, and 7xxx series Al
alloys, Al--Li alloys, Ti--Al--V alloys and Mg based alloys.
24. The vehicle structural component of claim 22 wherein the
structural component is a body panel.
25. A method of producing an engine component comprising: providing
a cast alloy; performing an initial treatment comprising at least
one of thermo-mechanical processing and solutionizing to form a
billet; subjecting the billet to at least one pass of equal channel
angular extrusion; and annealing the extruded billet for at least
30 minutes at a temperature of less than or equal to 0.85 T.sub.r,
where T.sub.r is the minimum temperature for which a 30 minute
anneal of the extruded billet will produce growth of grains to over
1 micron.
26. The method of claim 25 wherein the initial processing further
comprises performing at least one pass of equal channel angular
extrusion utilizing heated extrusion die prior to any solutionizing
and quenching.
27. The method of claim 26 wherein the heated extrusion die are at
least 250.degree. C.
28. The method of claim 25 wherein the alloy comprises one or more
elements selected from the group consisting of Al, Ti, Mg, Be, Ni,
Fe, Cu, Co, W, Ta, Zn, Ag, Sn, Pb, In, Au, Si, Sb, Mo, V, Sc, Cr,
Y, B, Mn, C, Li, P, S, Nb, Zr, Pd, and Cd.
29. The method of claim 25 wherein the alloy comprises a base metal
selected from the group consisting of Al, Ti, Mg, and Be.
30. The method of claim 25 wherein the alloy is a heat treatable
alloy.
31. The method of claim 30 wherein the initial treatment comprises
solutionizing sufficiently to dissolve all soluble second phases
followed immediately by quenching.
32. The method of claim 31 further comprising maintaining the
billet at a temperature of less than or equal to about 0.degree. C.
after quenching.
33. The method of claim 31 further wherein the at least one pass of
equal channel angular extrusion is a plurality of passes, and
further comprising quenching the billet between each of the
plurality of passes.
34. The method of claim 31 further comprising refrigerating the
billet between passes of equal channel angular extrusion.
35. The method of claim 30 further comprising artificial
precipitation aging the billet at a temperature below the peak
aging temperature of the billet.
36. The method of claim 25 wherein the alloy is a non-heat
treatable alloy, and wherein the initial treatment lacks
solutionizing.
37. The method of claim 25 further comprising pre-heating prior to
subjecting to equal channel angular extrusion.
38. The method of claim 37 wherein the preheating comprises at
least one of infrared heating and rapid induction heating.
39. The method of claim 25 further comprising heating the billet
between each pass of equal channel angular extrusion.
40. The method of claim 25 further comprising applying a back
pressure on the billet during the at least one pass of equal
channel angular extrusion.
41. A method of forming a vehicle structural component comprising:
forming a billet comprising a heat heat-treatable alloy, the
forming comprising: casting the material; and solutionizing the
material; subjecting the billet to at least one pass of equal
channel angular extrusion; and annealing the extruded billet for at
least 30 minutes at a temperature of less than or equal to 0.85
T.sub.r, where T.sub.r is the minimum temperature for which a 30
minute anneal of the extruded billet will produce growth of grains
to over 1 micron.
42. The method of claim 41 wherein the alloy is an aluminum based
alloy.
43. The method of claim 42 is selected from the 2xxx series of
aluminum alloys.
44. The method of claim 41 wherein the alloy comprises one or more
elements selected from the group consisting of Al, Ti, Mg, Be, Ni,
Fe, Cu, Co, W, Ta, Zn, Ag, Sn, Pb, In, Au, Si, Sb, Mo, V, Sc, Cr,
Y, B, Mn, C, Li, P, S, Nb, Zr, Pd, and Cd.
45. The method of claim 41 wherein the forming the billet further
comprises at least one of hot forging and rolling prior to the
solutionizing.
46. The method of claim 41 wherein the forming the billet further
comprises quenching the billet immediately after solutionizing.
47. The method of claim 41 wherein the forming the billet further
comprises performing at least one pass of equal channel angular
extrusion prior to the solutionizing, wherein at least one of the
billet and extrusion die are heated prior to the at least one
pass.
48. The method of claim 47 wherein an amount of alloying elements
solubilized during the formation of the billet is increased due to
the equal channel angular extrusion performed prior to
solutionizing.
Description
TECHNICAL FIELD
[0001] The invention pertains to high-strength engine components,
vehicle structural components, methods of producing engine
components and methods of forming vehicle structural
components.
BACKGROUND OF THE INVENTION
[0002] Development of lightweight materials which can contribute to
weight reduction of land, air and space vehicles has become
increasingly important. Vehicle weight reduction can result in
increased fuel efficiency and reduced emissions. Lighter weight
materials also offer improved maneuverability and can additionally
reduce manufacturing costs.
[0003] Many of the available lightweight materials lack sufficient
strength for many structural and engine components. Current
materials which are considered to be "lightweight" materials for
use in engine or body components of vehicles include, for example,
magnesium, aluminum, titanium and beryllium metals and alloys.
Optionally, medium-weight materials such as steels are used due to
their relatively high-strength and thermal stability. However,
there is increased drive to reduce the volume of such medium-weight
materials to decrease overall engine and/or vehicle weight.
Accordingly, the overall strength and thermal stability of
components formed of such materials are decreased. Additionally,
many of the available lightweight materials and lower volume medium
weight materials lack sufficient strength to meet engine and/or
vehicle performance standards and safety goals. Accordingly, it is
desirable to develop alternate high-strength lightweight
materials.
SUMMARY OF THE INVENTION
[0004] In one aspect the invention encompasses a high-strength
engine component comprising an alloy which contains a base metal
alloyed with less than or equal to 30% by weight of alloying
elements, where the material has an average grain size of less than
or equal to about 30 microns. The material has an absence of voids
and inclusions of a size greater than 1 micron. The material also
has a yield strength (YS) at least 50% greater than the yield
strength of the identical alloy composition in an annealed 0 temper
condition.
[0005] In one aspect the invention includes high-strength engine
components comprising a material consisting of an alloy having a
base metal alloyed with less than or equal to 30% by weight of
alloying elements. The material has an average grain size of less
than or equal to about 30 microns, an absence of voids and
inclusions of a size greater than 1 micron and contains soluble
second phase precipitates having an average size of less than 30
microns. The material has a yield strength at least 10% greater
than the yield strength of the identical alloy composition in the
T6 temper condition.
[0006] In one aspect the invention includes a vehicle structural
component comprising a material consisting of an alloy comprising
at least two elements selected from Al, Ti, Mg, Be, Ni, Fe, Cu, Co,
W, Ta, Zn, Ag, Sn, Pb, In, Au, Si, Sb, Mo, V, Sc, Cr, Y, B, Mn, C,
Li, P, S, Nb, Zr, Pd, and Cd. The alloy contains a base metal
alloyed with less than or equal to 30% of additional alloying
elements by weight. The material has an average grain size of less
than or equal to about 30 microns, an absence of voids and
inclusions having a size greater than 1 micron, and has a yield
strength at least 50% greater than the yield strength of the
identical alloy composition in the annealed 0 temper condition.
[0007] In one aspect the invention includes a vehicle structural
component comprising material consisting of an alloy of at least
two elements selected from the group consisting of Al, Ti, Mg, Be,
Ni, Fe, Cu, Co, W, Ta, Zn, Ag, Sn, Pb, In, Au, Si, Sb, Mo, V, Sc,
Cr Y, B, Mn, C, Li, P, S, Nb, Zr, Pd, and Cd, the alloy containing
a base metal alloyed with less than or equal to 30 weight % of
additional alloying elements. The material has an average grain
size of less than or equal to 30 microns, has an absence of voids
and inclusions having a size greater than 1 micron, and has soluble
second phase precipitates with an average size of less than 30
microns. The material's yield strength is at least 10% greater than
the yield strength of the identical alloy composition in the T6
temper condition.
[0008] In one aspect the invention includes a method of producing
an engine component. The method includes providing a cast alloy and
performing an initial treatment using at least one of thermal
mechanical processing and solutionizing to form a billet. The
billet is subjected to at least one pass of equal channel angular
extrusion and is subsequently annealed for at least 30 minutes at a
temperature of less than or equal to 0.85 T.sub.r, where T.sub.r is
the minimum temperature for which a 30 minute anneal of the
extruded billet will produce growth of submicron grains to over 1
micron.
[0009] In one aspect the invention encompasses a method of forming
a vehicle structural component. The method includes formation of a
billet of a heat-treatable alloy. The formation of the billet
includes casting and solutionizing the material. The billet is
subjected to at least one pass of equal channel angular extrusion
and is annealed for at least 30 minutes at a temperature of less
than or equal to 0.85 T.sub.r, where T.sub.r is the minimum
temperature for which a 30 minute anneal of the extruded billet
will produce grain growth of submicron grains to over 1 micron.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] Preferred embodiments of the invention are described below
with reference to the following accompanying drawings.
[0011] FIG. 1 is a diagrammatic view of a portion of a mechanical
component in accordance with one aspect of the invention.
[0012] FIG. 2 is a diagrammatic view of a portion of a structural
component of a vehicle in accordance with one aspect of the
invention.
[0013] FIG. 3 is a flowchart diagram illustrating methodology
encompassed by one aspect of the present invention.
[0014] FIG. 4 is a diagrammatic cross-sectional view of a material
being treated with an equal channel angular extrusion apparatus in
accordance with one aspect of the invention.
[0015] FIG. 5 is a diagrammatic view illustrating methodology in
accordance with one aspect of the invention.
[0016] FIG. 6 shows a comparison of yield strength and ultimate
tensile strength for aluminum alloy 6061 processed in accordance
with one aspect of the invention relative to conventional T6 and 0
temper Al 6061.
[0017] FIG. 7 shows a comparison of Brinell hardness for aluminum
6061 processed in accordance with the invention relative to
standard T6 and 0 temper 6061 materials.
[0018] FIG. 8 shows a comparison of yield strength and ultimate
tensile strength for aluminum alloy 2618 materials processed in
accordance with the invention relative to conventional T6 and 0
temper Al 2618 materials.
[0019] FIG. 9 shows a comparison of Brinell hardness for aluminum
alloy 2618 processed in accordance with the invention relative to
conventional T6 and 0 temper Al 2618 materials.
[0020] FIG. 10 shows a comparison of the fatigue properties of Al
2618 material processed in accordance with the invention relative
to conventional Al 2618 T6 material. Arrows indicate testing was
stopped prior to sample failure.
[0021] FIG. 11 shows a comparison of maximum fatigue life for
materials presented in FIG. 10. Arrows indicate testing was stopped
prior to sample failure.
[0022] FIG. 12 shows a comparison of yield strength and ultimate
tensile strength for aluminum alloy 2219 materials processed in
accordance with the invention relative to conventional Al 2219 T6
and 0 temper Al 2219 materials.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0023] This disclosure of the invention is submitted in furtherance
of the constitutional purposes of the U.S. Patent Laws "to promote
the progress of science and useful arts" (Article 1, Section
8).
[0024] One aspect of the invention is production of high-strength
lightweight materials and mechanical and/or structural components
having improved strength and lifetimes. Methods of producing
high-strength lightweight materials, engine components and
structural components according to the invention are described.
[0025] Although lightweight materials have been previously
developed which can be utilized in certain instances, improvement
of strength and fatigue properties of materials can afford
additional safety and an additional decrease in overall weight of
engines, vehicles, and machinery. The invention includes engine and
structural components formed utilizing methods described herein. In
particular instances, the engine or structural component can be
part of a vehicle. Such vehicle can be an air, ground, water or
space vehicle. Exemplary vehicles include automobiles, airplanes,
boats, trains, spacecraft, trucks, bicycles, etc. For purposes of
the present description, an engine component can be any element
comprised by a motor assembly. For example, components in
accordance with the invention can be utilized for motors involved
in transportation, power generation, refrigeration/cooling, etc.
For purposes of the present description, the term structural
component, with reference to a vehicle, can refer to any element
involved in the frame, external or internal body, support
structures, wheels, casings, housings, brakes, landing systems,
etc.
[0026] Although the invention is described primarily with respect
to vehicle engines and vehicle structural components, it is to be
understood that the invention contemplates adaptation of methods
and/or product materials for use in alternative engine applications
and for structural components of devices and constructions other
than vehicles.
[0027] One area of particular importance for which the invention is
particularly applicable is turbomachinery components such as
wheels. For purposes of the present description, the term wheel is
utilized to describe a solid or non-solid disk type structure which
is rotatable, typically by way of a connected rotary shaft.
Exemplary wheels include turbine wheels and compressor wheels.
[0028] Metals and alloys conventionally utilized for components
such as wheels are typically produced by processing methods which
include casting, rolling, forging and in particular instances heat
treatment. The mechanical properties of conventional metals and
alloys are obtained primarily utilizing one or both of two distinct
strengthening mechanisms. These mechanisms are 1) solution or
precipitation strengthening, where size and distribution of second
phase elements is controlled by specific sequences of heat
treatment; and 2) deformation by conventional processing utilizing
rolling and or forging which introduces defects such as
dislocations or specific texture to provide a strengthening effect.
Methods such as rolling or forging can be very inefficient due to
the large change in overall shape of a product during the
processing which inhibits or prevents introduction of high-level
strain into the material. This in turn limits the total level of
deformation that can be introduced into a material thereby limiting
the refinement of structural units such as grain size. Accordingly,
typical grain sizes for conventionally produced materials are
usually greater than 10 microns and more typically greater than 50
microns.
[0029] Conventional methods utilizing rolling and/or forging
additionally result in non-uniform deformation producing
non-homogenous grain size and precipitate distribution. In
particular instances non-uniform stress-strain gradients are
produced between the top surface and a middle thickness of a
resulting billet.
[0030] Various structural parameters including grain size, grain
boundary volume and/or crystalline order can affect strength of
lightweight materials. One option for providing strength
improvement is by creation of amorphous material having an absence
of long range single or polycrystalline order. However, the
additional strength imparted in amorphous materials is typically
gained at the expense of ductility. Accordingly, amorphous
materials may be unsuitable for a variety of applications such as,
for example, fabrication of long panels or wheels with complex
blade geometries. Although amorphous materials can be utilized in
particular instances for specific applications and non-complex
shapes, such materials can typically have low thermal stability.
Further, bulk production of amorphous materials has yet to be
achieved.
[0031] Another mechanism for improvement of mechanical properties
such as strength is grain refinement. Grain refinement to a
sub-micron (100-1000 nm) or nano level (1-100 nm) average grain
size can impart significant strength improvement without
sacrificing ductility. In fact, in particular instances ductility
improvements are obtained simultaneously with increased strength
due to a large increase in the volume of grain boundaries in
materials having extremely small grain size. Resulting materials
can have a wider range of applications relative to amorphous
materials, particularly for applications which rely on ductility
and formability.
[0032] In accordance with the present invention, equal channel
angular extrusion is utilized to achieve grain refinement and
controlled precipitate formation. Equal channel angular extrusion
(ECAE) is a technique which utilizes intense or severe deformation
by simple shear of a material to induce grain refinement. The
resulting refined structures result in an increase in mechanical
properties including tensile strength and hardness. Previously,
ECAE has been utilized specifically for high-purity type materials
and particularly for non heat-treatable materials. For purposes of
the present description heat-treatable materials are those that can
be hardened by heat treatment and non-heat-treatable materials are
those which are not hardenable and/or can loose strength through
thermal treatment. As will be described, the general methodology
and processing in accordance with the invention can be modified and
adapted based on the heat-treatability of the specific material to
be utilized for a particular application.
[0033] In general the present invention pertains to methodology for
strengthening materials by combining severe plastic deformation
techniques such as equal channel angular extrusion with one or more
additional strengthening techniques such as, for example,
solutionizing, precipitation and texture hardening. The combination
of techniques provides materials and products with superior
mechanical properties including, strength, hardness, wear and
fatigue relative to conventional processing and materials.
Materials and products in accordance with the invention can be
particularly useful in applications such as engine and
structural/body components where high-strength lightweight
materials are especially useful.
[0034] The combination of ECAE and heat treatments in accordance
with the invention can advantageously achieve superior mechanical
properties relative to traditional heat treatments alone. These
advantages are most notable in heat-treatable metals and alloys.
ECAE utilization allows strengthening by grain refinement and
additionally allows the rate and extent of precipitation to be
controlled, as well as shape, size and distribution of the
resulting precipitates. Control of precipitate characteristics is
afforded by dynamic precipitation during ECAE. The high strain
during ECAE allows very fine precipitates. In particular instances,
new grain boundaries and/or dislocations are formed simultaneously
with precipitates, the combination of which is responsible for the
most intense improvements in mechanical properties. Due to simple
shear across the thickness of a material undergoing ECAE,
distribution of precipitates is very uniform. The deformation route
(sequence of billet rotation between passes) during ECAE can also
influence the distribution and shape of precipitates.
[0035] Local re-arrangement of atoms during intense strain brought
about by ECAE can increase the solubility limit of some elements
and/or precipitates. The additional solubility can produce a
greater strengthening effect during subsequent heat treatment.
[0036] An additional advantage of utilizing ECAE in combination
with heat-treatment is the increase in rate of static precipitation
during annealing of in ECAE materials. The increase in
precipitation rate is due to the increased area of grain boundaries
which allows efficient diffusion processes in sub-micron
structures. As a result, the time and temperature for achieving
peak-aging or over-aging is reduce thereby reducing overall
fabrication cost.
[0037] One aspect of the invention is described with reference to
FIG. 1. FIG. 1 illustrates an exemplary component 10 comprising a
wheel 12 in association with a rotary shaft 14. Wheel 12 is
illustrated as having an inner radial portion 16, which can be
referred to as a hub portion, and an outer radial portion 18. Wheel
12 as illustrated in FIG. 1 is a solid disk type wheel. However, it
is to be understood that the invention contemplates alternative
wheel types such as, for example, those comprising non-solid disks
where outer portion 18 is alternatively shaped or contoured. For
example, wheel 12 can be configured to have blades, cogs, teeth,
etc. Exemplary wheel types encompassed by the invention include
fans, compressor wheels, impellors, turbine wheels, etc. The
invention additionally contemplates configurations where the hub
portion of the wheel is non-solid.
[0038] The radial distances comprised by inner portion 16 and outer
portion 18 are not limited to particular values, or to any
particular ratio relative to one another. Wheel 12 can be a single
piece or can be fabricated as two or more individual pieces.
Various engines in which component 10 can be a part include but are
not limited to aircraft engines, automobile engines, turbochargers,
superchargers, refrigeration systems and other cooling systems,
spacecraft, trains and other transportation vehicles. The invention
additionally contemplates inclusion of component 10 in accordance
with the invention for additional applications such as, for
example, additional drive train applications and any other
mechanical applications where high-strength lightweight wheels are
desired.
[0039] In operation, wheels can be subjected to high loads and
stresses in a radial direction due to centrifugal forces imparted
by high rotational speeds. Stress can be most severe in the central
disc (hub) section 16 which supports the radial mass of exterior
portion 18. Accordingly, the hub region can be stretched outward
under high tangential stresses. Additionally, component 10 can be
exposed to high thermal gradient end stresses in addition to cyclic
loading. As a result, the blades or outer portion 18 typically
achieve a higher temperature relative to central region 16.
[0040] Depending upon the particular material and fabrication
method, conventional wheels can have a very short finite fatigue
life resulting in failure during operation. In particular
applications the life of the wheel is the limiting component of an
entire engine system. This life limiting aspect is common for
applications such as compressor wheels in turbochargers.
Conventional wheels for such applications are typically fabricated
of cast aluminum or aluminum alloys. Such aluminum materials can be
low cost, lightweight and provide low rotational inertia for rapid
acceleration response during transient loading. However,
conventional casting generates a high degree of metallurgical
imperfection such as voids, inclusions, dendrites and/or
segregation. As a result, cast aluminum wheels can fail in the hub
region resulting in a short life. Although increase in hub
thickness can supply additional stiffness and support, the increase
in thickness also increases the weight. Increased weight in the
disk portion of a rotary component can result in a need for
increase dimension in the rotary shaft portion and/or containment
walls of the engine or other machinery. Such can further add weight
to the overall system.
[0041] In particular applications, conventional aluminum materials
have been replaced by alternative materials such as titanium and
titanium alloys, composite fibers or sintered powders. Titanium
materials and alloys have a higher weight relative to aluminum
materials however, titanium and alloys thereof have additional
strength, thermal stability and fatigue properties relative to
aluminum materials and have similar stiffness and blade natural
frequencies compared to aluminum materials. However, due to the
difficulty in forging and machining of titanium materials, the cost
of such materials and components comprising such materials can be
especially prohibitive to use in many applications.
[0042] Another alternative which has been utilized is a hybrid
wheel design where blades or outer diameter portions are
manufactured separately from the central disk region. The
multi-part wheel is assembled by joining methods such as bolting,
brazing or welding. In these instances the central hub region can
typically comprise wrought aluminum alloy or forged titanium, with
the blades or outer portion comprising cast aluminum or titanium.
Exemplary wrought aluminum alloys utilized for this purpose have
included heat treatable aluminum alloys from the 2xxx and 6xxx
aluminum series (such as Al 2219, Al 2024, Al 2618 and Al 6061).
However, these conventional materials have a limited operating
speed and pressure ratio. Additionally the hybrid design can lack
strength in the joining/bonding region at the interface of inner
and outer radial portions.
[0043] In particular aspects, an entire wheel assembly (inner and
outer radial portions) has been formed from a wrought aluminum
alloy. Conventional fabrication of the unitary design can typically
comprise hot forging to a near net shape followed by precipitation
strengthened heat treatment and machining to a final functional
form. Although having somewhat improved mechanical properties with
low weight and rotational inertia, such materials and components
are unable to meet the ever increasing stringency of service
requirements in many applications.
[0044] The materials and components in accordance with the
invention provide increased strength and mechanical properties
relative to conventional components, have improved manufacturing
and mechanical properties including strength and fatigue, and can
be entirely free of cast defects. The improvement relative to
conventional materials is exemplified by various aluminum alloys as
presented below. Titanium alloy components in accordance with the
invention can also be of particular advantage due to improved
strength, manufacturing, and machining properties relative to
conventional titanium materials.
[0045] Metal component 10 illustrated in FIG. 1 in accordance with
the invention can comprise metals including Al, Ti, Mg, Be, Ni, Fe,
Cu, Co, W, Ta, Zn, Ag, Sn, Pb, In, Au, Si, Sb, Mo, V, Sc, Cr, Y, B,
Mn, C, Li, P, S, Nb, Zr, Pd, Cd and/or alloys of such metals. For
many engine and other mechanical applications, wheel 12 can
preferably comprise a metal or alloy containing at least one of Al,
Ti, Mg, Be, Ni and Fe. Although the invention is not limited to any
particular amount of alloying element content, the most effective
amount of alloying element(s) for purposes of the invention has
been found to be less than or equal to 30% by weight whether the
alloy contains one or multiple alloying elements. In many instances
the total percent of alloying elements is preferably less than or
equal to 10%, and in some instances is preferably less than or
equal to 5%. For purposes of the present description, the term
"base element" can be utilized when referring to a single element
within an alloy having a content which exceeds any other element
within the alloy.
[0046] The invention includes, in addition to wheels and other
mechanical components, metal structures for use in structural
applications. An exemplary structural component 20 in accordance
with the invention is illustrated in FIG. 2. As illustrated,
component 20 can comprise a sheet structure 22 having a height or
thickness `d` which is exceeded by both the length `y` and width
`x` of the sheet. It is to be understood that structural component
20 as illustrated in FIG. 2 is but one exemplary structural shape
encompassed by the invention and that alternative structural
configurations are contemplated. The illustrated sheet type
configuration illustrated can be used in applications such as, for
example, panels for vehicle bodies (i.e. doors, fenders, fuselage,
etc.).
[0047] Exemplary materials and preferred materials for structural
component 20 can be any of the materials and preferred materials
described above with respect to the mechanical component
illustrated in FIG. 10. Since similar or identical materials can be
utilized in formation of the mechanical component 10 illustrated in
FIG. 1 and the structural component 20 illustrated in FIG. 2,
materials and common processing of such materials for formation of
components in accordance with the invention are concurrently
described below. The described materials can undergo additional and
distinct processing to produce the desired configuration for a
particular application.
[0048] Of the materials and alloys indicated above, alloys of
particular interest which can be utilized for either structural or
mechanical components in accordance with the invention include:
aluminum alloys of the 2xxx series (for example, 2618, 2024 and
2219 alloys); aluminum alloys of the 3xxx series; aluminum alloys
of the 4xxx series; aluminum alloys of the 5xxx series; aluminum
alloys of the 6xxx series (for example, Al 6061), aluminum alloys
of the 7xxx series; aluminum lithium alloys; titanium aluminum
alloys (for example, Ti6Al4V); and magnesium based alloys (for
example, ZK60 and AZ31). Processing of such materials in accordance
with the invention can produce structural and engine components
which have superior mechanical properties including strength and
fatigue relative to conventionally produced materials and
components. The additional strength and improved fatigue properties
are achieved utilizing a particular processing sequence which
includes one or more distinct equal channel angular extrusion
(ECAE) treatments at particular processing points, in combination
with various conventional type thermo-mechanical processing and/or
heat treatments. The particular combination and sequence of
processing including severe plastic deformation utilizing ECAE can
produce a substantial strengthening effect and improved fatigue
which markedly exceeds conventional processing abilities. This
improvement in properties imparted by methods of invention can be
achieved for heat-treatable as well as non-heat-treatable
materials.
[0049] Metal parts produced in accordance with the invention such
as wheel 12 depicted in FIG. 1 and panel 20 depicted in FIG. 2 have
an average grain size of less than 30 microns with a uniform grain
size throughout the material. Typically, the uniform average grain
size will be less than 1 micron (also referred to as a submicron
grain size). In most instances the material and component formed
from such material will entirely lack cast defects such as voids
and inclusions having a size of greater than 1 micron. Processing
in accordance with the invention produces a yield and ultimate
tensile strength in resulting materials and components which are at
least 50% higher than the corresponding yield and ultimate tensile
strength for an identical composition in a standard, fully
annealed, 0 temper condition (where all materials are evaluated at
room temperature). For non-heat-treatable materials the yield and
ultimate tensile strength increase relative to fully annealed 0
temper condition in particular applications can be 100% or
more.
[0050] Where the material utilized is a heat-treatable alloy, the
product material or component produced by methodology in accordance
with the invention will also have an average uniform grain size of
less than 30 microns and typically less than 1 micron. The product
will additionally be free of cast defects such as voids and
inclusions having a size greater than 1 micron. Products comprising
the heat-treatable alloys will have an average precipitate size of
soluble second phases of less than 30 microns and typically less
than 1 micron. The yield strength of materials and components
produced from heat treatable alloys will be at least 10% higher
than the corresponding yield strength and ultimate tensile strength
of the identical composition in the standard peak aged T6 condition
(optimal precipitation) evaluated at room temperature. For
particular products, the material or component will have a yield
strength increase of 30% or more relative to standard T6
conditioned material.
[0051] Materials and products in accordance with the invention
additionally have improved fatigue life. For non-heat-treatable
alloys the product fatigue life is improved by at least 5% and
typically 20% or more relative to fully annealed 0 temper condition
for the corresponding alloy (measured under high cyclic stress).
For materials and products produced utilizing heat-treatable
materials, the fatigue life of such products is improved by at
least 5% and typically by 20% or more relative to standard peak
aged T6 condition under high cyclic stress.
[0052] General methodology for processing of heat-treatable and
non-heat-treatable materials in accordance with the invention can
typically include casting of a metal material or alloy, preliminary
processing and extruding utilizing equal channel angular extrusion.
The general processing can also in some instances utilize annealing
at one or more stages of processing of the material. The described
methodology can be utilized for forming high-strength lightweight
materials and products including, but not limited to, mechanical
components and structural components as discussed above.
[0053] Methodology of the invention is described generally with
reference to FIG. 3. An exemplary processing scheme 100 for
treating materials in accordance with the invention is shown. The
general outlined process shown in FIG. 3 can be utilized for both
heat-treatable and non-heat-treatable alloys. Processing of
heat-treatable alloys can typically include additional processing
treatments during the overall processing scheme relative to
non-heat-treatable alloys as described below.
[0054] An initial metal or alloy material can be treated in an
initial process stage 110 which includes casting of the material.
In particular instances, casting of materials can preferably
produce a shaped material, typically rectangular or circular which
has dimensions close to final dimensions of the product.
[0055] The cast material can subsequently be subjected to
preliminary processing step 120. Preliminary processing of
non-heat-treatable materials can preferably comprise
thermo-mechanical processing of the material without solutionizing.
Such processing can include, for example, hot forging, rolling of
the material for homogenization, or a combination thereof. Such
treatment is preferably sufficiently performed to reduce, and in
particular instances, eliminate cast defects and can include
forming of a general shape.
[0056] Where the material or alloy is heat-treatable, preliminary
processing step 120 can further include solutionizing to allow
dissolution of all soluble second phases within the material. Such
solutionizing can preferably be performed at a temperature and for
a sufficient time for complete solublization for the particular
heat-treatable alloy being processed. Where solutionizing is
utilized, such is preferably immediately followed by quenching.
Typically, the quenching will comprise quenching in water and will
be performed to quench as quickly as possible, preferably at a rate
of greater than or equal to 500.degree. F./s and more preferably at
a rate of greater than 1000.degree. F./s.
[0057] The preliminary processing performed in step 120 produces a
billet which will undergo additional processing in accordance with
the invention. The preliminary processing treatment can
additionally include preheating of the billet in preparation for
subsequent treatment. When utilized, the preheating is conducted at
a temperature and for a time below or equal to the temperature and
time for peak aging of the particular alloy being treated. Typical
preheating temperatures for an aluminum material or alloy, for
example, are between 110.degree. C. and 250.degree. C. for a time
of 0.5 hours or greater. In particular instances it can be
advantageous for rapid preheating methods to be utilized such as,
for example, induction heating or infrared techniques. Where rapid
preheating is utilized, the treatment at a temperature of between
110.degree. C. and 250.degree. C. will be less than 1 hour and more
preferably less than 20 minutes. Such preheating conditions can
effectively heat the material to a desired temperature for further
processing while minimizing or avoiding growth of precipitates,
since such growth can result in a loss of precipitate strengthening
ability. It can be advantageous to minimize such loss to allow
optimum strengthening. Accordingly, rapid heating techniques are
advantageous to reduce total preheating time such that soluble
phases do not precipitate and growth of precipitates is
minimized.
[0058] For some heat-treatable alloys (e.g. aluminum alloys of the
7xxx series), precipitation occurs very quickly (within hours or a
few days) even at room temperature. Accordingly, since such
precipitation begins immediately after solutionizing and quenching,
it can be desirable to refrigerate the quenched billet or store the
billet at cryogenic temperatures, preferably less than 0.degree. C.
until the time of further processing. The billet can then undergo
the preheating step (if utilized for the particular material),
preferably by rapid heating techniques immediately prior to plastic
deformation (discussed below).
[0059] Preliminary processing can additionally include artificial
precipitation aging at low temperature over a long period of time
where the temperature and time are less than those corresponding to
conditions for peak aging. Such artificial precipitation aging can
include intermediate aging treatment to stabilize precipitation
(similar to a T7 temper for particular alloys) or even peak aging.
The particular time and temperature will depend upon the
composition of the material being processed. For aluminum alloys a
typical artificial precipitation aging will be conducted at a
temperature of less than 250.degree. C. for less than 20 hours with
preferable conditions being between 100.degree. C. and 200.degree.
C. for a time of greater than 0.5 hours. Where a billet is
refrigerated or stored at cryogenic temperature, the artificial
precipitation can be conducted after such refrigeration and prior
to preheating of the billet in preparation for subsequent plastic
deformation treatment.
[0060] In particular instances whether a heat-treatable or
non-heat-treatable alloy is utilized it can be advantageous to
perform at least one warm or hot equal channel angular extrusion
pass during preliminary processing step 120. Referring to FIG. 4,
such illustrates an exemplary ECAE device 50. Device 50 comprises a
mold assembly or die 52 that defines a pair of intersecting
channels 54 and 56. Intersecting channels 54 and 56 are identical
or at least substantially identical in cross-section with the term
"substantially identical" indicating the channels are identical
within acceptable tolerances of an ECAE apparatus.
[0061] In operation, a material is extruded through channels 24 and
channel 26 resulting in plastic deformation of the material by
simple shear, layer after layer in a thin zone located at the
crossing plane of the channels. Lubrication of the channel walls
and/or billet can assist in achieving uniform simple shear
deformation. Channels 54 and 56 can intersect at an angle of from
about 90.degree. to about 140.degree.. The tool angle (channel
intersect angle) of about 90.degree. can be preferable since an
optimal deformation (true shear strain) can be obtained.
Alternative channel shapes can also be utilized relative to that
illustrated.
[0062] During the preliminary processing stage, the billet of
material 60 as shown in FIG. 4 can be extruded by, for example,
application of sufficient force utilizing a punch 62 where such
force is applied in a downward direction with respect to the
depiction in FIG. 4. A second punch 66 can optionally be provided
to provide an opposing force at the leading edge of billet 60. The
opposing force exerted by second punch 66 is preferably no greater
than half the force exerted by punch 62. The opposing force can
provide back pressure on the billet during ECAE which can
advantageously decrease the risk of crack generation and surface
defects in billets at lower processing temperatures, especially at
high levels of deformation. Application of back pressure can be
especially useful where the material being processed is brittle.
Accordingly, the time and die temperatures for ECAE processing can
be reduced enabling working conditions at temperatures less than
those of peak aging and for a time less than that of peak aging
conditions.
[0063] As an alternative to the second opposing punch technique
depicted in FIG. 4, an alternative technique for providing back
force can be utilized as depicted in FIG. 5. As shown, a slider 70
can be provided along an edge of billet 60 during equal channel
angular extrusion in conjunction with a bar 72 for exertion of back
pressure opposing the direction of extrusion. Further, the degree
of lubrication between interfacing surfaces of the slider and the
die can be utilized to increase the amount of back pressure
encountered by the billet.
[0064] Where one or more passes of ECAE is utilized during
preliminary processing 120, such is preferably performed after
casting and before any heat treatment such as solutionizing. The
inclusion of one or more passes, preferably one or two passes of
ECAE during preliminary processing can advantageously breakdown
cast defects such as voids, pores and dendrites, and aid in
homogenizing the structure prior to subsequent treatments of the
material. In heat treatable alloys the initial ECAE step can
additionally increase the solubility limit of soluble phases within
the material. Such increased solubility can maximize strength
enhancing precipitation that occurs during a subsequent
solutionizing event. Where ECAE is included in the preliminary
treatment, the ECAE die should have a temperature of at least
250.degree. C. and preferably a temperature of at least 350.degree.
C.
[0065] Upon completion of preliminary processing step 120 the
resulting billet, whether of heat-treatable or non-heat-treatable
material, is subjected to a severe plastic deformation treatment
130 as illustrated in FIG. 3. The severe plastic deformation
treatment preferably comprises at least one equal channel angular
extrusion pass and more preferably from one to four passes. Such
passes can be performed by any route; however it can be
advantageous to rotate the billet by 90.degree. between at least
some of the passes. Rotation of the billet between passes allows
strain paths to be achieved and can allow controlling of shape and
structural units including grain size and/or crystallographic
texture.
[0066] ECAE can introduce severe plastic deformation in the
preliminary processed material while leaving the dimension of the
block of material unchanged. ECAE can be a preferred method for
inducing severe strain in a metallic material in that ECAE can be
utilized at low loads and pressures to induce strictly uniform and
homogenous strain. Additionally, ECAE can achieve high deformation
per pass (true strain .epsilon.=1.17); can achieve high accumulated
strains with multiple passes through an ECAE device (at n=4 passes,
.epsilon.=4.64); and can be utilized to create various
textures/microstructures within materials by utilizing different
deformation routes (i.e. by changing an orientation of the billet
between passes through an ECAE device).
[0067] The material being processed by ECAE can be passed through
the ECAE apparatus several times and with numerous routes. ECAE
processing in accordance with the invention will typically include
at least two passes in order to produce a sub-micron structure.
Where intermediate annealing between passes is utilized
(pre-heating of the billet) or where the die are heated during ECAE
passes, the temperature utilized is preferably less than a
temperature which would cause an increase in grain size over 1
micron for the particular material being processed. Although
methods of the invention can be utilized to produce materials
having an average grain size greater than one micron, parameters
will typically be chosen to maintain an average grain size of not
greater than 30 microns.
[0068] Although the invention contemplates ECAE processing under
cold or hot processing conditions, ECAE processing will typically
comprise one or more passes conducted at a temperature below the
peak aging temperature of the particular material. For aluminum
alloys, exemplary temperatures are temperatures less than
300.degree. C., preferably between 110.degree. C. and 225.degree.
C. For titanium materials and alloys, ECAE processing in accordance
with the invention is typically conducted at a temperature of less
than 800.degree. C.
[0069] During the severe plastic deformation treatment,
intermediate preheating of the billet between each pass can be
performed by, for example, rapid heating techniques such as
induction or infrared heating. Preferably, the preheating
temperature and time is less than those corresponding to peak aging
conditions. For aluminum or aluminum alloys preferable temperatures
are between 110.degree. C. and 250.degree. C. for less than or
equal to 0.5 hours. ECAE processing can additionally comprise
quenching of the billet after each ECAE pass with such quenching
preferably being conducted in water. Heating of die and/or billets
for ECAE processing can enhance diffusion mechanisms and thereby
provide better structure homogeneity. Small homogenous and highly
uniform structure achieved by ECAE can afford increased or
maximized material strength.
[0070] Where the material being processed is a non-heat-treatable
alloy the one or more ECAE passes are preferably conducted at the
lowest processing temperature for achieving good surface
conditions. For aluminum alloys which are non heat-treatable, such
processing is preferably conducted at a temperature of less than
300.degree. C. and more preferably at a temperature of from
110.degree. C. to about 225.degree. C. Intermediate preheating of
non-heat-treatable billets between each pass (intermediate
annealing) can additionally be performed preferably by rapid
heating techniques as described above.
[0071] As illustrated in FIG. 3, the resulting extruded billet from
deformation processing event 130 is subjected to a post deformation
anneal per treatment 140 as illustrated in FIG. 3. The post
deformation anneal comprises annealing at a low temperature for
several hours. This anneal can preferably be performed at a
temperature T of less than 0.85 T.sub.r, where T.sub.r is the time
required to grow grains within the material to over 1 micron when
annealed at such temperature for greater than or equal to 30
minutes. (Where the material being annealed has an average grain
size of over 1 micron prior to annealing T.sub.r refers to the
temperature at which grains within a submicron grain material of an
identical composition would grow to a grain size of over 1 micron).
For aluminum alloys the post deformation anneal is preferably
conducted at a temperature of between 100.degree. C. and
200.degree. C. for a time of at least 30 minutes. Typical
treatments can be, for example, a 150.degree. anneal for 1-8 hours.
Performing an anneal at or near T.sub.r for the particular material
can advantageously produce average grain sizes of from about 1
micron to about 30 microns which can facilitate forming.
[0072] Post deformation annealing of materials in accordance with
the invention can result in fine precipitates, the amount of which
can be enhanced by the increased solubility induced by performing
ECAE in preliminary treatments as described above. The post
deformation anneal can advantageously impart improved fatigue
properties relative to conventional materials and relative to
materials not subject to anneal. Additionally, the post deformation
annealing achieves superior fatigue properties at a faster rate
than peak aging treatment.
[0073] Upon completion of the post deformation anneal, the
resulting material can be further processed to produce various
mechanical components such as, for example, the wheel of component
10 depicted in FIG. 1, or structural components such as, for
example, the panel of component 20 shown in FIG. 2. Exemplary
further processing can comprise machining, forming (e.g. by
rolling, stretching, bending, forging, drawing, hyroforming,
superplastic forming, etc.), joining (via mechanical joining,
brazing, solid state bonding, welding, friction stir processing,
etc.), and/or surface treatment (e.g. coating, shot peening). The
resulting components can have the characteristics of properties
described above throughout most or all of their volume.
[0074] Methodology in accordance with the invention enhances
strength of heat-treatable and non-heat-treatable materials
compared to the strongest standard tempered materials of the same
alloying composition. The materials additionally demonstrate
enhanced fatigue properties compared to the corresponding alloy
having standard commercial temper where resistance of such
processed materials in accordance with the invention is also
enhanced relative to conventional temper materials.
EXAMPLE 1
Heat-Treatable Al 6061
[0075] The aluminum alloy designated as Al 6061 is widely used for
structural applications including various aerospace applications.
Conventional Al 6061 T6 temper is produced by solutionizing,
quenching and artificial peak aging at 175.degree. C. for 8 hours.
Such is the strongest temper of this alloy obtainable by
precipitation treatment alone. Standard Al 6061 0 temper is
obtained by fully annealing of the alloy at a temperature of
400-450.degree. C. for several hours. It is the lowest strength
commercially available 6061 material. The yield strength and
ultimate tensile strength of 0 temper and T6 6061 alloys is
presented in FIG. 6 for comparison purposes relative to yield
strength and ultimate tensile strength achieved utilizing
methodology in accordance with the invention.
[0076] Three samples were prepared by processing in accordance with
the invention. The ultimate tensile strength and yield strength of
each of the three samples are presented in FIG. 6. Sample 1 was
prepared by subjecting Al 6061 to solutionizing treatment followed
by quenching. The quenched material was processed through 4 passes
of equal channel angular extrusion and was short term annealed at
150.degree. C. for 1 hour.
[0077] Sample 2 was prepared by solutionizing Al 6061 followed by
immediate quenching and standard artificial peak aging at
175.degree. C. for 8 hours. Aging was followed by 4 passes of equal
channel angular extrusion at a die temperature of less than
170.degree. C.
[0078] Sample 3 was prepared by solutionizing Al 6061 alloy
followed by immediate quenching. The quenched billet was subjected
to 4 passes of equal channel angular extrusion followed by long
term annealing at 150.degree. C. for 8 hours.
[0079] For each of the three samples, the solutionizing was
conducted at 500.degree. C. for several hours and quenching was
performed in water. As illustrated in FIG. 6, equal channel angular
extrusion treatment produces an increase in yield strength of
40-70%, and an increase in ultimate tensile strength of 30-35%
compared to standard 6061 aluminum in T6 condition. A similar
increase in Brinell hardness (30-50%) is also achieved as
illustrated in FIG. 7. It is noted that because Al 6061 T6 is
strengthened relative to 0 temper by precipitation strengthening
only, the additional increase provided in the materials of the
present invention is due to grain refinement achieved during equal
channel angular extrusion. The increase in strength due to ECAE
process is more evident as compared to Al 6061 0 temper with an
increased yield strength of 600-750%, and an increased ultimate
tensile strength and hardness of 200-280%.
[0080] It is noted that Sample 1 has achieved the highest strength
while utilizing the simplest and fastest heat treatment. For Al
6061 the maximum strengthening effect was observed when ECAE
directly follows solutionizing and quenching in accordance with the
invention.
EXAMPLE 2
Heat-Treatable Al 2618 Alloy
[0081] Aluminum alloy having designation Al 2618 has been utilized
for applications such as engine components, for example, compressor
wheels and in turbocharger applications due to its thermal
stability up to 250.degree. C. Standard Al 2618 in T6 condition is
the strongest commercially available temper for the alloy. The
yield strength and ultimate tensile strength of such material is
shown in FIG. 8. The ultimate tensile strength and yield strength
of standard Al 2618 in the 0 temper condition is also shown in FIG.
8.
[0082] Al 2618 was processed in accordance with the invention
combining ECAE processing and heat-treatment. The treatment
included solutionizing the 2618 material followed by ECAE. It was
found that performing ECAE directly after solutionizing and
quenching resulted in the highest strengthening effect. Equal
channel angular extrusion was performed using die temperatures
between 150.degree. C. and 200.degree. C. with intermediate
annealing at similar temperatures.
[0083] After equal channel angular extrusion, the resulting billet
was subjected to low temperature heat-treatment as described in the
methodology section. The yield strength and ultimate tensile
strength of the 2618 materials in accordance with the invention
after 1 pass of ECAE and after 2 passes of ECAE are presented in
FIG. 8. It is noted that only 2 passes of ECAE results in higher
strength than does deformation with additional passes and is
sufficient to produce a sub-micron structure.
[0084] As compared to standard Al 2618 in the T6 condition,
materials processed in accordance with the invention have increased
yield strength and ultimate tensile strength of 10-50% and 10-35%
respectively. As compared to standard Al 2618 in the 0 temper
condition, the increase is more marked with an increase of from
430-650% in yield strength and 175-250% ultimate tensile strength
increase.
[0085] The increase in material hardness for Al 2618 due to
processing in accordance with the invention is presented in FIG. 9.
As shown, the hardness increase achieved by processing in
accordance with the invention is 10-45% as compared to Al 2618 in
the T6 condition. For 1 and 2 passes of equal channel angular
extrusion, superior hardness is achieved for temperatures up to
250.degree. C. This is an advantageous result since the maximum
surface temperature of compressor wheels is typically less than
200.degree. C. The use of rapid heating treatment results in
similar improvements in strength, hardness and fatigue properties
and additionally allows faster processing times.
[0086] Results of fatigue testing are presented in FIGS. 10 and 11.
Material processed in accordance with the invention is compared in
these figures to ECAE Al 2618 in peak aged condition (T6). For
samples processed in accordance with the invention, Al 2618
material was cast, forged, solutionized followed by immediate
quenching and subsequently processed by one pass of equal channel
angular extrusion at a temperature below 200.degree. C. ECAE was
followed by annealing at 150.degree. C. for 6 hours. Fatigue
testing was performed utilizing high cycle fatigue tests conducted
under various stresses (35-60 ksi) at a frequency of 60 Hz. Testing
was performed at room temperature for an R ratio equal to 0.
Samples which were stopped prior to breakage of the sample
(indicated by arrows in the corresponding figures) were concluded
at 10 E7 cycles, with testing of one sample being stopped after 10
E8 cycles without failure.
[0087] Minimum fatigue life (dotted lines FIG. 10) and maximum
fatigue life (solid lines FIG. 10) are presented and indicate a
great improvement in fatigue for ECAE processed Al 2618 as compared
to conventional Al 2618 in T6 condition. For maximum fatigue life
values, fatigue life is improved by a linear factor 6.5x to 66x.
Minimum fatigue life is improved by a linear factor of 7x to 228x.
Accordingly, ECAE deformation in combination with heat-treatment
provides substantial improvement in fatigue life for a wide range
of stresses studied. The increase in tensile strength, hardness and
fatigue indicates that wheels comprising Al 2618 processed in
accordance with the invention can be utilized for higher operating
pressures and rotating frequencies, and can be utilized in
compliance with new environmental regulations. The extra strength
affords more flexibility in the design of a given piece for a
desired fatigue life of a part. These results indicate that Al 2618
processed in accordance with the invention can be used in place of
Ti alloys for compressor wheels in particular applications.
EXAMPLE 3
Heat-Treatable Al 2219
[0088] The aluminum alloy material designated Al 2219 is a more
heavily alloyed material than either Al 2618 or Al 6061. Copper is
its principle alloying element and has a nominal presence of 6.3%,
which is greater than the standard solubility limit of copper in
pure aluminum (around 4.5%). For this alloy, treatment in
accordance with the invention was found to be most beneficial when
hot ECAE step(s) were conducted before solutionizing and quenching
thereby increasing the amount of copper in solution prior to
precipitation as explained above. Referring to FIG. 12, such
presents results of processing of this alloy in accordance with the
invention. FIG. 12 shows the results of equal channel angular
extrusion alone, or as combined with solutionizing and post
deformation annealing, on the yield strength and ultimate tensile
strength relative to standard Al 2219 in the 0 temper condition and
peak aged (T6) condition. As shown, a significant strength increase
is obtained utilizing combination of solutionizing, equal channel
angular extrusion and post deformation annealing relative to ECAE
alone, and relative to precipitation strengthening alone (T6
material). As compared to commercially available T6 grade Al 2219,
material processed utilizing solutionizing/ECAE/annealing results
in a 47% increase in yield strength.
[0089] In compliance with the statute, the invention has been
described in language more or less specific as to structural and
methodical features. It is to be understood, however, that the
invention is not limited to the specific features shown and
described, since the means herein disclosed comprise preferred
forms of putting the invention into effect. The invention is,
therefore, claimed in any of its forms or modifications within the
proper scope of the appended claims appropriately interpreted in
accordance with the doctrine of equivalents.
* * * * *