Patent Application
20070084527
The invention pertains to high-strength engine components, vehicle structural components, methods of producing engine components and methods of forming vehicle structural components.
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.
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.
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.
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.
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.
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.
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 Tr, where Tr is the minimum temperature for which a 30 minute anneal of the extruded billet will produce growth of submicron grains to over 1 micron.
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 Tr, where Tr 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.
Preferred embodiments of the invention are described below with reference to the following accompanying drawings.
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).
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
One aspect of the invention is described with reference to
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.
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.
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.
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.
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.
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.
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.
Metal component 10 illustrated in
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
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
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.
Metal parts produced in accordance with the invention such as wheel 12 depicted in
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.
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.
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.
Methodology of the invention is described generally with reference to
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.
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.
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° F./s and more preferably at a rate of greater than 1000° F./s.
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° C. and 250° 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° C. and 250° 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.
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° 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).
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° C. for less than 20 hours with preferable conditions being between 100° C. and 200° 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.
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
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° to about 140°. The tool angle (channel intersect angle) of about 90° can be preferable since an optimal deformation (true shear strain) can be obtained. Alternative channel shapes can also be utilized relative to that illustrated.
During the preliminary processing stage, the billet of material 60 as shown in
As an alternative to the second opposing punch technique depicted in
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° C. and preferably a temperature of at least 350° C.
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
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 ε=1.17); can achieve high accumulated strains with multiple passes through an ECAE device (at n=4 passes, ε=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).
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.
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° C., preferably between 110° C. and 225° C. For titanium materials and alloys, ECAE processing in accordance with the invention is typically conducted at a temperature of less than 800° C.
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° C. and 250° 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.
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° C. and more preferably at a temperature of from 110° C. to about 225° 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.
As illustrated in
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.
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
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.
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° 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° 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
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
Sample 2 was prepared by solutionizing Al 6061 followed by immediate quenching and standard artificial peak aging at 175° C. for 8 hours. Aging was followed by 4 passes of equal channel angular extrusion at a die temperature of less than 170° C.
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° C. for 8 hours.
For each of the three samples, the solutionizing was conducted at 500° C. for several hours and quenching was performed in water. As illustrated in
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.
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° 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
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° C. and 200° C. with intermediate annealing at similar temperatures.
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
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.
The increase in material hardness for Al 2618 due to processing in accordance with the invention is presented in
Results of fatigue testing are presented in
Minimum fatigue life (dotted lines
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
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.
