Secondary processing of structures derived from AL-RE-TM alloys
A method for processing a metal part includes extruding an Al-RE-TM alloy to form an extruded part, heating the extruded part, and applying a compressive strain greater than about 50% on the heated part.
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Reference is hereby made to co-pending patent application Ser. No. ______ filed on even date (attorney docket U73.12-0108/PA-0002526-US), and entitled “Friction Stir Welded Structures Derived from AL-RE-TM Alloys”; and to co-pending patent application Ser. No. ______ filed on even date (attorney docket U73.12-0110/PA-0002528-US), and entitled “Hollow Structures Formed with Friction Stir Welding”.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENTThe U.S. Government may have certain rights in this invention pursuant to Contract Number F33615-01-2-5217 with the Defense Advanced Research Projects Agency of the U.S. Department of Defense.
BACKGROUNDThe present invention relates to metal structures derived from aluminum—rare earth—transition metal (Al-RE-TM) alloys. In particular, the present invention relates to processing techniques for improving the ductility of metal parts derived from Al-RE-TM alloys.
Al-RE-TM alloys have been considered for structural applications in the aerospace industry. Such alloys have high strengths, and can be formed into a variety of different structures. Furthermore, due to the lower density of aluminum, as compared to well-established alloys such as titanium, Al-RE-TM alloys are also capable of providing significant weight savings.
To obtain good glass-formability, aluminum-based alloys typically include high atomic percentages of rare earth and transition metal elements. However, such alloys accordingly have high volume fractions of intermetallic phases in the devitrified state, which results in alloys having low ductility (e.g., elongations less than 5%). High ductility is desirable for many aerospace applications. As such, there is a need for processing techniques that improve the ductility of Al-RE-TM alloys, while also preserving the strengths of the alloys.
SUMMARYThe present invention relates to a method for processing a metal part. The method includes extruding a Al-RE-TM alloy to form an extruded part having an extrusion axis. The extruded part is then heated and subjected to a compressive strain greater than 50%.
The extrusion system compresses and plastically deforms the billet to form the extruded part with a dense (i.e., substantially non-porous) alloy. The extruded part exits the extrusion system with an extrusion axis that extends along the length of the extruded part. The extruded part has a high strength, but low ductility (e.g., elongations to failure ranging from 1-4%). Suitable yield strengths for the extruded part range from about 620 megaPascals (MPa) (about 90 Ksi) to about 830 MPa (about 120 Ksi).
To increase the ductility of the extruded part, the extruded part is then subjected to secondary processing. This involves heating the extruded part to a temperature that is above the crystallization temperature of the Al-RE-TM alloy (step 14). This causes the Al-RE-TM alloy to form a plastic-like state, thereby allowing the alloy to be plastically deformable. Examples of suitable temperatures for heating the extruded part range from about 300° C. to about 450° C., with particularly suitable temperatures ranging from about 350° C. to about 400° C.
While the extruded part remains heated at the above-discussed temperatures, a compressive strain greater than 50% (i.e., an upset greater than 50%) is applied to the heated extruded part (step 16). In one embodiment, the compressive strain is applied to the heated extruded part in a direction that is substantially parallel to the extrusion axis. For example, the Al-RE-TM alloy may be upset in a direction that is substantially parallel to the extrusion axis to form a variety of parts, such as turbine disks and blades. In an alternative embodiment, the compressive strain is applied to the heated extruded part in a direction that is substantially perpendicular to the extrusion axis. Perpendicular applications are suitable for simple blade forging.
Examples of suitable applied compressive strains include compressive strains greater than about 50%, with particularly suitable compressive strains ranging from about 70% to about 90%. The applied compressive strains may be obtained with strain rates ranging from about 0.0001 seconds−1 to about 1,000 seconds−1. This corresponds to strain rates ranging from slow strain rates of isothermal forging (e.g., for producing disks) to high strain rates of mechanical or hammer forgings (e.g., for producing blades).
The heating and applied compressive strains of steps 14 and 16 may be performed in a variety of secondary processes. Examples of suitable secondary processes for heating and applying the compressive strains to the extruded part include forging operations and hot rolling operations. Suitable forging systems for use with method 10 include thermal forging systems (e.g., systems commercially available from Weber Metals, Inc., Paramount, Calif.), mechanical forging systems (e.g., systems commercially available from Turbine Engine Component Technologies (TECT) Corporation, Newington, Conn.), and hammer forging systems (e.g., systems commercially available from Precision Components International, Inc., Columbus, Ga.). Suitable commercially available hot rolling systems include systems from Oak Ridge National Laboratory, Oak Ridge, Tenn.; and systems from Material Sciences Corporation (Oak Ridge, Tenn.).
In an alternative embodiment, steps 14 and 16 are repeated until a desired strength and ductility are obtained. For example, the extruded part may be heated and upset forged to a compressive strain greater than 50%. The forged metal part is then re-extruded or drawn to a size that fills a desired die dimension, and then close-die forged. During the drawing process, the metal part is desirably drawn using small bites on the outer diameter. Additionally, the drawing and upset forging may be repeated multiple times (e.g., 2-5 times), where each drawing uses small bites on the outer diameter and each upset forging applies a compressive strain greater than 50%.
After steps 14 and 16, the resulting metal part is deformed from the extruded part dimensions due to the applied compressive strain. However, after the secondary process, the metal part substantially retains its pre-secondary process strengths. Examples of suitable yield strengths for the metal parts after the heating and applied compressive strains of steps 14 and 16 include at least about 90% of the yield strength of the extruded part, with particularly suitable yield strengths including at least about 95% the yield strength of the extruded part. The yield strengths are determined pursuant to ASTM E8-04, entitled “Test Methods of Tension Testing of Metallic Materials”.
In addition, the ductility of the resulting metal part substantially increases due to the secondary processing. The secondary processing desirably increases the ductility of the metal part to a value of at least about 5%, where the ductilities are determined as tensile elongations to failure, pursuant to ASTM E8-04. Examples of suitable ductility increases for the metal part include percent increases of at least about 5%, with particularly suitable increases of at least about 10%, where the percent increases are relative to the ductility of the extruded part. The retained yield strengths and substantially-increased ductility allow the metal parts to be used in a variety of structural applications that require high ductility, such as aviation and aerospace applications.
After the secondary processing of steps 14 and 16, the metal part is then incorporated into an assembled structure (step 18). The metal part may also undergo post-processing operations (e.g., cutting, polishing, and painting) before or after incorporation into the assembled structure. Because of the variety of metal parts that may be processed pursuant to method 10, the metal parts may be incorporated into a variety of assembled structures. Examples of suitable assembled structures and assembly techniques involving friction stir welding are disclosed in the co-pending patent application Ser. No. ______ filed on even date (attorney docket U73.12-0108/PA-0002526-US), and entitled “Friction Stir Welded Structures Derived from Al-RE-TM alloys”; and in co-pending patent application Ser. No. ______ filed on even date (attorney docket U73.12-0110/PA-0002528-US), and entitled “Hollow Structures Formed with Friction Stir Welding”, which are hereby incorporated in full by reference.
During the forging process, extruded part 22 and potting block 24 are placed within cavity 28, and are heated pursuant to step 14 of method 10 (shown in
As shown in
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The Al-RE-TM alloys used to form extruded parts during the extrusion process in step 12 of method 10 (shown in
In one embodiment, the Al-RE-TM alloy also includes one or more additional metals, such as magnesium, scandium, titanium, zirconium, iron, cobalt, gadolinium, and combinations thereof. Suitable concentrations of the additional metals in the alloy range from about 0.1% by weight to about 10% by weight, with particularly suitable concentrations ranging from about 1% by weight to about 5% by weight, based on the entire weight of the alloy. An example of a particularly suitable Al-RE-TM alloy for use in forming extruded parts includes an alloy of aluminum-yttrium (Y)-nickel (Ni)-cobalt (Co) (referred to herein as an “Al—Y—Ni—Co” alloy), where yttrium is referred to as a rare earth element.
EXAMPLESThe present invention is more particularly described in the following examples that are intended as illustrations only, since numerous modifications and variations within the scope of the present invention will be apparent to those skilled in the art. Unless otherwise noted, all parts, percentages, and ratios reported in the following examples are on a weight basis.
Examples 1 and 2, and Comparative Examples A and BExtruded rods of Examples 1 and 2 and Comparative Examples A and B were initially formed by extruding an Al—Y—Ni—Co alloy with an extrusion system commercially available from SAPA, Inc., Portland, Oreg.
The extruded rods of Examples 1 and 2 and Comparative Example B were then forged with a forging system. The extruded rod of Comparative Example A was not subjected to the forging process. The forging system used was commercially available from Weber Metals, Inc., Paramount, Calif. The forging involved heating the extruded rods to a temperature of 350° C. (662° F.) and applying a compressive strain to the heated extruded rod in a direction parallel to the extrusion axis. This compressed the lengths of the extruded rods of Examples 1 and 2 and Comparative Example B, thereby shortening the lengths and increasing the diameters. The compressive strain was continuously increased with a strain rate of 0.0002 seconds−1, and until a predetermined compressive strain was reached. The predetermined compressive strain for the heated extruded rods of Comparative Example B and Examples 1 and 2 were 50%, 70%, and 85%, respectively.
Extruded rods of Example 3 and Comparative Example C were formed from an Al—Y—Ni—Co alloy in the same manner as discussed above for Examples 1 and 2 and Comparative Examples A and B. After the extrusion process, the extruded rod of Example 3 was then hot rolled with a hot rolling system commercially available from Material Sciences Corporation, Oak Ridge, Tenn. The hot rolling system heated the metal rod to a temperature of 350° C. (662° F.) and applied a compressive strain of 70% to the extruded rod in a direction perpendicular to the extrusion axis. The extruded rod of Comparative Example C was not hot rolled.
The room temperature yield strengths, tensile strengths, and ductilities of the rods of Example 3 and Comparative Example C were then measured. The yield strengths and the ductilities (i.e., tensile elongations to failure) were each determined pursuant to ASTM E8-04. Table 1 provides the measured yield strengths, tensile strengths, and ductilities for the rods of Example 3 and Comparative Example C.
The data in Table 1 shows that the hot rolling process also allows the metal rod of Example 3 to substantially retain its pre-secondary processing yield strength (i.e., about 91% retention). Additionally, the ductility of the metal rod of Example 3 is substantially increased compared to the ductility of the extruded rod of Comparative Example C. While the forging process discussed above for Examples 1 and 2 provided greater strength retentions and ductility increases, the hot rolling process also increased the ductility of the metal rod to above 5%. As such, the hot rolling process is also suitable for providing metal parts derived from Al-RE-TM alloys that can be used in aviation and aerospace applications.
Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.
Claims
1. A method for processing a metal part, the method comprising:
- extruding a Al-RE-TM alloy to form an extruded part having an extrusion axis;
- heating the extruded part to a temperature above a crystallization temperature of the Al-RE-TM alloy; and
- applying a compressive strain greater than about 50% on the heated part.
2. The method of claim 1, wherein the compressive strain is applied in a direction that is substantially parallel to the extrusion axis.
3. The method of claim 1, wherein the temperature that the extruded part is heated to ranges from about 300° C. to about 450° C.
4. The method of claim 3, wherein the temperature that the extruded part is heated to is in a range from about 350° C. to about 400° C.
5. The method of claim 1, wherein the compressive strain is applied with a strain rate ranging from about 0.0001 seconds−1 to about 1,000 seconds−1.
6. The method of claim 1, wherein the applied compressive strain ranges from about 70% to about 90%.
7. The method of claim 1, wherein the metal part has a tensile strength that is at least 90% of a tensile strength of the extruded part, wherein the tensile strength is measured pursuant to ASTM E8-04.
8. The method of claim 1, wherein the Al-RE-TM alloy comprises an Al—Y—Ni—Co alloy.
9. The method of claim 1, further comprising:
- creating a finished metal part after the heating and applying steps.
10. A method for processing a metal part, the method comprising:
- extruding a Al-RE-TM alloy to form an extruded part, wherein the extruded part has an extrusion axis;
- heating the extruded part to a temperature ranging from about 300° C. to about 450° C.; and
- applying a compressive strain on the heated metal part to provide a ductility increase of at least about 5% relative to a ductility of the extruded part, wherein the ductility is measured pursuant to ASTM E8-04.
11. The method of claim 10, wherein the compressive strain is applied in a direction that is substantially parallel to the extrusion axis.
12. The method of claim 10, wherein the temperature that the extruded metal part is heated to is in a range from about 350° C. to about 400° C.
13. The method of claim 10, wherein the compressive strain is applied with a strain rate ranging from about 0.0001 seconds−1 to about 1,000 seconds−1.
14. The method of claim 10, wherein the applied compressive strain provides a ductility increase of at least about 10% relative to the ductility of the extruded part.
15. The method of claim 10, wherein the Al-RE-TM alloy comprises an Al—Y—Ni—Co alloy.
16. The method of claim 10, further comprising:
- creating a finished metal part after the heating and applying steps.
17. A method for processing a metal part, the method comprising:
- extruding a Al-RE-TM alloy to form an extruded part, wherein the extruded part has an extrusion axis;
- forging the extruded part at a temperature above a crystallization temperature of the Al-RE-TM alloy, and with a compressive strain greater than about 50% in a direction that is substantially parallel to the extrusion axis.
18. The method of claim 17, wherein the temperature that the extruded metal part is heated to ranges from about 300° C. to about 450° C.
19. The method of claim 18, wherein the temperature that the extruded metal part is heated to is in a range from about 350° C. to about 400° C.
20. The method of claim 17, wherein the applied compressive strain ranges from about 70% to about 90%.
21. The method of claim 17, wherein the compressive strain is applied with a strain rate ranging from about 0.0001 seconds−1 to about 1,000 seconds−1.
22. The method of claim 17, wherein the Al-RE-TM alloy comprises an Al—Y—Ni—Co alloy.
Type: Application
Filed: Jun 15, 2007
Publication Date: Dec 18, 2008
Applicants: United Technologies Corporation (Hartford, CT), The Curators of the University of Missouri (Rolla, MO)
Inventors: Thomas J. Watson (South Windsor, CT), Rajiv S. Mishra (Rolla, MO), Yanwen Wang (Rolla, MO)
Application Number: 11/818,764
International Classification: C22F 1/00 (20060101);