This application is related to co-pending U.S. patent application Ser. No. 12/541,071, filed on Aug. 13, 2009, which is incorporated by reference herein in its entirety.
This disclosure generally relates to processes for making shaped metal alloy parts, and deals more particularly with a method of forming features and reducing residual stresses in such parts.
Unitary metallic parts may be fabricated by forging and/or machining a solid block of material. The process of machining blocks, plates or other forms of blanks may be both time consuming and expensive because a relatively large percentage of the blank may become waste material in the form of machining chips. These existing processes may have other issues, including difficulty in achieving maximum material properties from precipitation hardened alloys and/or higher than desired residual stresses present in the blank caused by the processes used to produce the blank, such as, for example and without limitation, precipitation hardening. Additionally, in some cases, existing processes for manufacturing metallic alloy blanks may require larger than desired quantities of relatively high cost metallic alloys.
Accordingly, there is a need for a method of fabricating engineered shapes from metallic alloys that reduces material waste, and reduces or nearly eliminates residual stresses in shaped parts.
The disclosed embodiments provide a method of fabricating engineered shapes from metallic alloys that may substantially reduce material waste while improving material properties, including reducing residual stresses in fabricated metal alloy parts. The method may employ techniques such as incremental forging and/or friction welding to form features or build up blanks into net shaped or near net shaped parts. Plastic deformation of the metallic alloy blanks resulting from shaping techniques may reduce or nearly eliminate residual stresses present in the blanks caused by precipitation hardening or other processes that are used to fabricated the blanks.
According to one disclosed embodiment, a method is provided of manufacturing metallic alloy parts. The method comprises the steps of producing a metal alloy blank and subjecting the blank to a process that introduces residual stresses within the blank. The blank is plastically deformed in order to reduce the residual stresses in the blank. The plastic deformation may be carried out by forming at least one shape or feature in the blank, such as by incremental forging. The process that introduces residual stresses into the blank may include heating the blank and rapidly cooling the heated blank. Plastic deformation of the blank may be performed by age forming a shape into the blank or by incremental forging.
According to another disclosed embodiment, a method is provided of manufacturing an aluminum alloy part. The method comprises subjecting the part to a heat treatment process that introduces residual stresses into the part, and age forming the part in order to shape the part and reduce the residual stresses from the part. The method may further comprise forming a feature on the part by friction welding. The part may be formed by casting a molten aluminum alloy in the general shape of the part, and gauge rolling the cast part to desired dimensions. The method may also include incrementally forging at least one feature into the part. The metal alloy part may comprise one of AlCu, AlZnSc, AlZnCu, and AlMgSi. The heat treatment process may include solution annealing and/or recovery annealing.
According to a further embodiment, a method is provided of manufacturing an aluminum alloy part. The method comprises subjecting the part to a heat treatment process that introduces residual stresses into the part, and incrementally forging at least one feature into the part which reduces the residual stress in the part. The method may further comprise casting a molten aluminum alloy into the general shape of the part, gauge rolling the cast part to desired dimensions, and performing friction welding the part.
According to still another embodiment, a method is provided of introducing residual stresses present in a precipitation hardened alloy part, comprising plastically deforming the part. A plastic deformation may be carried out by friction stir welding and/or incrementally forging features into the part. The plastic deformation may also be carried out by age forming the part.
The disclosed embodiments satisfy the need for a method for fabricating engineered shapes from metallic alloys which reduces material waste while reducing or nearly eliminating residual stresses in the part caused by fabrication processes such as precipitation hardening.
Referring first to
Following the heat treatment step 22, the blank 25 may be plastically deformed at step 24 in order to impart a shape to the blank 27 and/or form one or more features 33 (
The disclosed embodiments may be advantageously employed to produce shaped blanks 25 and similar parts to near net shape using any of a variety of metal alloys including, but not limited to: AlCu, AlZnSc, AlZnCu, AlMgSi and alloys of titanium. The disclosed method may be particularly well suited to fabricating shaped blanks 25 and parts from the above mentioned alloys in which the heat treating performed at step 22 is a form of a process known as precipitation hardening. Precipitation hardening, also sometimes referred to as age hardening, is a heat treatment technique used to increase the yield strength of malleable materials including structural alloys of aluminum and other metals. The precipitation hardening process involves heating the metal alloy to a temperature of at least approximately 90 percent of absolute melting point for several hours, followed by subjecting the hot metal to a cooling medium such as water or glycol, thereby quenching the casting. Precipitation hardening relies on changes in solid solubility with temperature to produce fine particles of an impurity phase, which impede the moment of dislocations or defects in a crystal's lattice. Since dislocations are often the dominate carriers of plasticity, the resulting impurities may serve to harden the alloy material. Unlike ordinary tempering, the metal alloy must be kept at elevated temperature for several hours in order to allow precipitation to take place; this time delay is sometimes referred to as aging.
As will be discussed below, any of several techniques may be employed to plastically deform the heat treated blank 25 as part of step 24 in
The necessary plastic deformation of the blank 25 and formation of the features 33 and/or shaping of the blank 25 may also be carried out by friction stir welding or linear friction welding in which thin strip of metal alloy (not shown) are welded together to form or build up features 33 on the blank 25. Where welding is used to shape and/or form features 33 on the blank 25, it may be advantageous to perform a subsequent heat treatment operation, such as that disclosed in US Patent Publication No. 20060054252 A1 published on Mar. 16, 2006, the entire contents of which are incorporated by reference herein. The process described in this prior patent publication solves the problem of ductility reduction by conducting a thermal exposure treatment prior to solution treatment. This thermal exposure treatment or post-weld annealing may be performed at a temperature below solution heat treatment temperature. The resultant alloy material may have restored mechanical strength with minimal decrease in original ductility. This process may result in material properties that are close to the base metal, however residual stresses in the treated blank 25 may remain.
Attention is now directed to
Next, at step 28, the cast blank 25 may be gauge rolled to a desired thickness or gauge, following which, at step 30, the blank 25 is solution annealed. Solution annealing is a process that involves heating the blank 25 to a temperature above approximately 950 degrees F. and maintaining this temperature for a period of time sufficient for intermetallic phases in the alloy to go into solution. Following this heating, the blank 25 may be quickly cooled to prevent the intermetallic phases from coming out of solution. After the solution annealing 30, the blank 25 may be quenched at 32 by subjecting the hot blank 25 to a cooling medium such as water or glycol. Next, at step 34, the blank 25 may be plastically deformed in order to reduce or substantially eliminate the residual stresses that may be present in the blank 27. After deforming the blank at 34, one or more features 33 may be formed by welding one or more strips (not shown) onto the deformed blank 25, as by friction stir welding or linear friction welding as described in U.S. Pat. Nos. 7,225,967 and 7,156,276, the entire disclosures of which are incorporated by reference herein.
Next, at step 38, the shaped blank 25 may be age formed by heating the blank to a temperature of approximately 250 to 350 degrees F. and applying forces to the deformed blank that urges the deformation to flatten out during the aging process. The age forming performed at step 38 may provide the necessary plastic deformation of the blank 25 that may result in reducing or eliminating residual stresses in the blank introduced by the quenching process at step 32. Finally, at step 40, the welded blank may be machined, if necessary to final dimensions in order to form a finished part. The machining performed at step 40 may be formed on only certain surfaces of the welded blank 25, or on the entire blank 25.
Following solution annealing at 50, the hot blank 25 may be quenched at 52 which may introduce residual stresses into the blank 25. At step 54, in order to reduce or substantially eliminate these residual stresses, the heat treated blank 25 may be age formed back to a flat shape. As previously discussed, age forming is a shaping process for heat treatable metal alloys in which a metal alloy is given an aging treatment while simultaneously being subjected to mechanical shaping loads such as those previously discussed in connection with
During the age forming performed at step 54, the forming loads may be typically lower than the yield stress of the material and the blank shape is obtained due to the low temperature creep that occurs during the aging process. Consequently, there may be less non-uniformity in the microstructure of the part and the parts may have lower residual stresses, and thus better stress corrosion resistance. The method shown in
Attention is now directed to
Another embodiment of the method is shown in
A further form of the method is illustrated in
A further embodiment of the method is illustrated in
Embodiments of the disclosure may find use in a variety of potential applications, particularly in the transportation industry, including for example, aerospace, marine and automotive applications. Thus, referring now to
Each of the processes of method 170 may be performed or carried out by a system integrator, a third party, and/or an operator (e.g., a customer). For the purposes of this description, a system integrator may include without limitation any number of aircraft manufacturers and major-system subcontractors; a third party may include without limitation any number of vendors, subcontractors, and suppliers; and an operator may be an airline, leasing company, military entity, service organization, and so on.
As shown in
The disclosed method may be employed to produce metal alloy parts and components during any one or more of the stages of the production and service method 170. For example, components or subassemblies corresponding to production process 170 may incorporate metal alloy parts that are made according to the disclosed method. Also, one or more method embodiments, or a combination thereof may be utilized during the production stages 178 and 180, for example, by substantially expediting assembly of or reducing the cost of an aircraft 172. Similarly, the disclosed method may be used to produce metal alloy components and parts that are utilized while the aircraft 172 is in service 184.
Although the embodiments of this disclosure have been described with respect to certain exemplary embodiments, it is to be understood that the specific embodiments are for purposes of illustration and not limitation, as other variations will occur to those of skill in the art.
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