Method for Forming Hollow Profile Non-Circular Extrusions Using Shear Assisted Processing and Extrusion (ShAPE)

Abstract

A process for forming extruded products using a device having a scroll face configured to apply a rotational shearing force and an axial extrusion force to the same preselected location on material wherein a combination of the rotational shearing force and the axial extrusion force upon the same location cause a portion of the material to plasticize, flow and recombine in desired configurations. This process provides for a significant number of advantages and industrial applications, including but not limited to extruding tubes used for vehicle components with 50 to 100 percent greater ductility and energy absorption over conventional extrusion technologies, while dramatically reducing manufacturing costs.

Claims

1. A shear assisted extrusion process comprising providing both axial and rotational forces between a billet and a scroll-faced-die to plasticize one end of the billet and provide plasticized billet material through at least one opening in the scroll-face, wherein the billet comprises distinct pieces of material and the pieces of material define spaces between proximate pieces.

2. The process of claim 1 wherein the scroll-face defines spirals as channels or ridges upon the scroll-face.

3. The process of claim 2 wherein the spirals have between 1 and 16 starts.

4. The process of claim 2 wherein the at least one opening of the scroll-face is contiguous with at least one channel of the scroll-face.

5. The process of claim 4 wherein the at least one opening of the scroll-face is contiguous with at least two channels of the scroll-face.

6. The process of claim 4 wherein the scroll-face defines a plurality of openings.

7. The process of claim 6 wherein each of the openings is contiguous with at least one channel.

8. The process of claim 7 wherein each of the channels defines a start.

9. The process of claim 6 wherein the plasticized billet material extends through each of the openings and merges to form a single extrudate.

10. The process of claim 9 wherein the extrudate comprises intermetallic particles.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIG. 1a shows a ShAPE setup for extruding hollow cross section pieces

[0021] FIG. 1b shows another configuration for extruding hollow cross-sectional pieces

[0022] FIG. 2a shows a top perspective view of a modified scroll face tool for a portal bridge die.

[0023] FIG. 2b shows a bottom perspective view of a modified scroll face that operates like a portal bridge die.

[0024] FIG. 2c shows a side view of the modified portal bridge die

[0025] FIG. 3 shows an illustrative view of material separated device and process shown in FIGS. 1-2.

[0026] FIG. 4 a shows a ShAPE set up for consolidating high entropy alloys (HEAs) from arc melted pucks into densified pucks.

[0027] FIG. 4b shows an example of the scrolled face of the rotating tool in FIG. 4a

[0028] FIG. 4c shows an example of HEA arc melted samples crushed and placed inside the chamber of the ShAPE device prior to processing.

[0029] FIG. 5 shows BSE-SEM image of cross section of the HEA arc melted samples before ShAPE processing, showing porosity, intermetallic phases and cored, dendritic microstructure.

[0030] FIG. 6a shows BSE-SEM images at the bottom of the puck resulting from the processing of the material in FIG. 4c,

[0031] FIG. 6b shows BSE-SEM images halfway through the puck

[0032] FIG. 6c shows BSE-SEM images of the interface between high shear region un-homogenized region (approximately 0.3 mm from puck surface)

[0033] FIG. 6d shows BSE-SEM images of a high shear region

DETAILED DESCRIPTION OF THE INVENTION

[0034] The following description including the attached pages provide various examples of the present invention. It will be clear from this description of the invention that the invention is not limited to these illustrated embodiments but that the invention also includes a variety of modifications and embodiments thereto. Therefore, the present description should be seen as illustrative and not limiting. While the invention is susceptible to various modifications and alternative constructions, it should be understood, that there is no intention to limit the invention to the specific form disclosed, but, on the contrary, the invention is to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the invention as defined in the claims.

[0035] In the previously described and related applications various methods and techniques are described wherein the described technique and device (referred to as ShAPE) is shown to provide a number of significant advantages including the ability to control microstructure such as crystallographic texture through the cross sectional thickness, while also providing the ability to perform various other tasks. In this description we provide information regarding the use of the ShAPE technique to form materials with non-circular hollow profiles as well as methods for creating high entropy alloys that are useful in a variety of applications such as projectiles. Exemplary applications will be discussed on more detail in the following.

[0036] Referring first now to FIGS. 1a and 1b, examples of the ShAPE device and arrangement are provided. In an arrangement such as the one shown in FIG. 1 a rotating die 10 is thrust into a material 20 under specific conditions whereby the rotating and shear forces of the die face 12 and the die plunge 16 combine to plasticize the material 20 at the interface of the die face 12 and the material 20 and cause the plasticized material to flow in desired direction. (In other embodiments the material 20 may spin and the die 10 pushed axially into the material 20 so as to provide this combination of forces at the material face.) In either instance, the combination of the axial and the rotating forces plasticize the material 20 at the interface with the die face 12. Flow of the plasticized material can then be directed to another location wherein a die bearing surface 24 of a preselected length facilitates the recombination of the plasticized material into an arrangement wherein a new and better grain size and texture control at the micro level can take place. This then translates to an extruded product 22 with desired characteristics. This process enables better strength and corrosion resistance at the macro level together with increased and better performance. This process eliminates the need for additional heating and curing, and enables the functioning of the process with a variety of forms of material including billet, powder or flake without the need for extensive preparatory processes such as “steel canning”. This arrangement also provides for a methodology for performing other steps such as cladding, enhanced control for through wall thickness and other characteristics.

[0037] This arrangement is distinct from and provides a variety of advantages over the prior art methods for extrusion. First, during the extrusion process the force rises to a peak in the beginning and then falls off once the extrusion starts. This is called breakthrough. In this ShAPE process the temperature at the point of breakthrough is very low. For example for Mg tubing, the temperature at breakthrough for the 2″ OD, 75 mil wall thickness ZK60 tubes is <150 C. This lower temperature breakthrough is believed in part to account for the superior configuration and performance of the resulting extrusion products.

[0038] Another feature is the low extrusion coefficient kf which describes the resistance to extrusion (i.e. lower kf means lower extrusion force/pressure). Kf is calculated to be 2.55 MPa and 2.43 MPa for the extrusions made from ZK60-T5 bar and ZK60 cast respectively (2″ OD, 75 mil wall thickness). The ram force and kf are remarkably low compared to conventionally extruded magnesium where kf ranges from 68.9-137.9 MPa. As such, the ShAPE process achieved a 20-50 times reduction in kf (as thus ram force) compared to conventional extrusion. This assists not only with regard to the performance of the resulting materials but also reduced energy consumption required for fabrication. For example, the electrical power required to extrude the ZK60-T5 bar and ZK60 cast (2″ OD, 750 mil wall thickness) tubes is 11.5 kW during the process. This is much lower than a conventional approach that uses heated containers/billets.

[0039] The ShAPE process is significantly different than Friction Stir Back Extrusion (FSBE). In FSBE, a spinning mandrel is rammed into a contained billet, much like a drilling operation. Scrolled grooves force material outward and material back extrudes around the mandrel to form a tube, not having been forced through a die. As a result, only very small extrusion ratios are possible, the tube is not fully processed through the wall thickness, the extrudate is not able to push off of the mandrel, and the tube length is limited to the length of the mandrel. In contrast, ShAPE utilizes spiral grooves on a die face to feed material inward through a die and around a mandrel that is traveling in the same direction as the extrudate. As such, a much larger outer diameter and extrusion ratio are possible, the material is uniformly process through the wall thickness, the extrudate is free to push off the mandrel as in conventional extrusion, and the extrudate length is only limited only by the starting volume of the billet.

[0040] An example of an arrangement using a ShAPE device and a mandrel 18 is shown in FIG. 1b. This device and associated processes have the potential to be a low-cost, manufacturing technique to fabricate variety of materials. As will be described below in more detail, in addition to modifying various parameters such as feed rate, heat, pressure and spin rates of the process, various mechanical elements of the tool assist to achieve various desired results. For example, varying scroll patterns 14 on the face of extrusion dies 12 can be used to affect/control a variety of features of the resulting materials. This can include control of grain size and crystallographic texture along the length of the extrusion and through-wall thickness of extruded tubing and other features. Alteration of parameters can be used to advantageously alter bulk material properties such as ductility and strength and allow tailoring for specific engineering applications including altering the resistance to crush, pressure or bending.

[0041] The ShAPE process has been utilized to form various structures from a variety of materials including the arrangement as described in the following table.

TABLE-US-00001 TABLE 1 PUCKS Alloy Material Class Precursor Form Bi.sub.2Te.sub.3 Thermoelectric Powder Fe-Si Magnet Powder Nd.sub.2Fe.sub.11B/Fe Magnet Powder MA956 ODS Steel Powder Nb 0.95 Ti 0.05 Fe 1 Sb 1 Thermoelectric Powder Mn-Bi Magnet Powder AlCuFe(Mg)Ti High Entropy Alloy Chunks TUBES Alloy Material Class Precursor Form ZK60 Magnesium Alloy Barstock, As-Cast Ingot AZ31 Magnesium Alloy Barstock AZ91 Magnesium Alloy Flake, Barstock, As-Cast Ingot Mg.sub.2Si Magnesium Alloy As-Cast Ingot Mg.sub.7Si Magnesium Alloy As-Cast Ingot AZ91-1, 5 and 10 wt. % Magnesium MMC Mechanically Al.sub.2O.sub.3 Alloyed Flake AZ91-1, 5 and 10 wt. % Y.sub.2O.sub.3 Magnesium MMC Mechanically Alloyed Flake AZ91-1, 5 and 10 and 5 wt. Magnesium MMC Mechanically % SiC Alloyed Flake RODS Alloy Material Class Precursor Form Al-Mn wt. 15% Aluminum Manganese As-Cast Alloy Al-Mg Mg Al Co-extrusion Barstock Mg-Dy-Nd-Zn-Zr Magnesium Rare Earth Barstock Cu Pure Copper Barstock Mg Pure Magnesium Barstock AA6061 Aluminum Barstock AA7075 High Strength Barstock Aluminum Al-Ti-Mg-Cu-Fe High Entropy Alloy As-Cast Al-1, 5, 10 at. % Mg Magnesium Alloy As-Cast A-12.4TM High Strength Powder Aluminum Rhodium Pure Rhodium Barstock

[0042] In addition, to the pucks, rods and tubes described above, the present disclosure also provides a description of the use of a specially configured scroll component referred by the inventors as a portal bridge die head which allows for the fabrication of ShAPE extrusions with non-circular hollow profiles. This configuration allows for making extrusion with non-circular, and multi-zoned, hollow profiles using a specially formed portal bridge die and related tooling.

[0043] FIGS. 2a-2c show various views of a portal bridge die design with a modified scroll face that unique to operation in the ShAPE process. FIG. 2a shows an isometric view of the scroll face on top of the a portal bridge die and FIG. 2b) shows an isometric view of the bottom of the portal bridge die with the mandrel visible.

[0044] In the present embodiment grooves 13, 15 on the face 12 of the die 10 direct plasticized material toward the aperture ports 17. Plasticized material then passes through the aperture ports 12 wherein it is directed to a die bearing surface 24 within a weld chamber similar to conventional portal bridge die extrusion. In this illustrative example, material flow is separated into four distinct streams using four ports 17 as the billet and the die are forced against one another while rotating.

[0045] While the outer grooves 15 on the die face feed material inward toward the ports 17, inner grooves 13 on the die face feed material radially outward toward the ports 17. In this illustrative example, one groove 13 is feeding material radially outward toward each port 17 for a total of four outward flowing grooves. The outer grooves 15 on the die surface 12 feed material radially inward toward the port 17. In this illustrative example, two grooves are feeding material radially inward toward each port 17 for a total of eight inward feeding grooves 15. In addition to these two sets of grooves, a perimeter groove 19 on the outer perimeter of the die, shown in FIG. 2c, is oriented counter to the die rotation so as to provide back pressure thereby minimizing material flash between the container and die during extrusion.

[0046] FIG. 2b shows a bottom perspective view of the portal bridge die 12. In this view, the die shows a series of full penetration of ports 17. In use, streams of plasticized material funneled by the inward 15 and outward 13 directed grooves described above pass through these penetration portions 17 and then are recombined in a weld chamber 21 and then flow around a mandrel 18 to create a desired cross section. The use of scrolled grooves 13, 15, 19 to feed the ports 17 during rotation—as a means to separate material flow of the feedstock (e.g. powder, flake, billet, etc. . . . ) into distinct flow streams has never been done to our knowledge. This arrangement enables the formation of items with noncircular hollow cross sections.

[0047] FIG. 3 show a separation of magnesium alloy ZK60 into multiple streams using the portal bridge die approach during ShAPE processing. (In this case the material was allowed to separate for effect and illustration of the separation features and not passed over a die bearing surface for combination). Conventional extrusion does not rotate and the addition of grooves would greatly impede material flow. But when rotation is present, such as in ShAPE or friction extrusion, the scrolls not only assist flow, but significantly assist the functioning of a portal bridge die extrusion 17 and the subsequent formation of non-circular hollow profile extrusions. Without scrolled grooves feeding the portals, extrusion via the portal bridge die approach using a process where rotation is involved, such as ShAPE, would be ineffective for making items with such a configuration. The prior art conventional linear extrusion process teach away from the use of surface features to guide material into the portals 17 during extrusion.

[0048] In the previously described and related applications various methods and techniques are described wherein the ShAPE technique and device is shown to provide a number of significant advantages including the ability to control microstructure such as crystallographic texture through the cross sectional thickness, while also providing the ability to perform various other tasks. In this description we provide information regarding the use of the ShAPE technique to form materials with non-circular hollow profiles as well as methods for creating high entropy alloys that are useful in a variety of applications such as projectiles. These two exemplary applications will be discussed on more detail in the following.

[0049] FIG. 4a shows a schematic of the ShAPE process which utilizes a rotating tool to apply load/pressure and at the same time the rotation helps in applying torsional/shear forces, to generate heat at the interface between the tool and the feedstock, thus helping to consolidate the material. In this particular embodiment the arrangement of the ShAPE setup is configured so as to consolidate high entropy alloy (HEA) arc-melted pucks into densified pucks. In this arrangement the rotating ram tool is made from an Inconel alloy and has an outer diameter (OD) of 25.4 mm, and the scrolls on the ram face were 0.5 mm in depth and had a pitch of 4 mm with a total of 2.25 turns. In this instance the ram surface incorporated a thermocouple to record the temperature at the interface during processing. (see FIG. 4b) The setup enables the ram to spin at speeds from 25 to 1500 RPM.

[0050] In use, both an axial force and a rotational force are applied to a material of interest causing the material to plasticize. In extrusion applications, the plasticized material then flows over a die bearing surface dimensioned so as to allow recombination of the plasticized materials in an arrangement with superior grain size distribution and alignment than what is possible in traditional extrusion processing. As described in the prior related applications this process provides a number of advantages and features that conventional prior art extrusion processing is simply unable to achieve.

[0051] High entropy alloys are generally solid-solution alloys made of five or more principal elements in equal or near equal molar (or atomic) ratios. While this arrangement can provide various advantages, it also provides various challenges particularly in forming. While a conventional alloys is typically comprise one principal element that largely governs the basic metallurgy of that alloy system (e.g. nickel-base alloys, titanium-base alloys, aluminum-base alloys, etc.) in an HEA each of the five (or more) constituents of HEAs can be considered as the principal element. Advances in production of such materials may open the doors to their eventual deployment in various applications. However, standard forming processes have demonstrated significant limitations in this regard. Utilization of the ShAPE type of process demonstrates promise in obtaining such a result.

[0052] In one example a “low-density” AlCuFe(Mg) Ti HEA was formed. Beginning with arc-melted alloy buttons as a pre-cursor, the ShAPE process was used to simultaneously heat, homogenize, and consolidate the HEA resulting in a material that overcame a variety of problems associated with prior art applications and provided a variety of advantages. In this specific example, HEA buttons were arc-melted in a furnace under 10.sup.−6 Torr vacuum using commercially pure aluminum, magnesium, titanium, copper and iron. Owing to the high vapor pressure of magnesium, a majority of magnesium vaporized and formed Al1 Mg0.1Cu2.5Fe1Ti1.5 instead of the intended Al1 Mg1Cu1Fe1Ti1 alloy. The arc melted buttons described in the paragraph above were easily crushed with hammer and used to fill the die cavity/powder chamber (FIG. 4c), and the shear assisted extrusion process initiated. The volume fraction of the material filled was less than 75%, but was consolidated when the tool was rotated at 500 RPM under load control with a maximum load set at 85 MPa and at 175 MPa.

[0053] Comparison of the arc-fused material and the materials developed under the ShAPE process demonstrated various distinctions. The arc melted buttons of the LWHEA exhibited a cored dendritic microstructure along with regions containing intermetallic particles and porosity. Using the ShAPE process these microstructural defects were eliminated to form a single phase, refined grain and no porosity LWHEA sample

[0054] FIG. 5a shows the backscattered SEM (BSE-SEM) image of the as-cast/arc-melted sample. The arc melted samples had a cored dendritic microstructure with the dendrites rich in iron, aluminum and titanium and were 15-30 μm in diameter, whereas the inter-dendritic regions were rich in copper, aluminum and magnesium. Aluminum was uniformly distributed throughout the entire microstructure. Such microstructures are typical of HEA alloys. The inter-dendritic regions appeared to be rich in Al—Cu—Ti intermetallic and was verified by XRD as AlCu.sub.2Ti. XRD also confirmed a Cu.sub.2Mg phase which was not determined by the EDS analysis and the overall matrix was BCC phase. The intermetallics formed a eutectic structure in the inter-dendritic regions and were approximately 5-10 μm in length and width. The inter-dendritic regions also had roughly 1-2 vol % porosity between them and hence was difficult to measure the density of the same.

[0055] Typically such microstructures are homogenized by sustained heating for several hours to maintain a temperature near the melting point of the alloy. In the absence of thermodynamic data and diffusion kinetics for such new alloy systems the exact points of various phase formations or precipitation is difficult to predict particularly as related to various temperatures and cooling rates. Furthermore, unpredictability with regard to the persistence of intermetallic phases even after the heat treatment and the retention of their morphology causes further complications. A typical lamellar and long intermetallic phase is troublesome to deal with conventional processing such as extrusion and rolling and is also detrimental to the mechanical properties (elongation).

[0056] The use of the ShAPE process enabled refinement of the microstructure without performing homogenization heat treatment and provides solutions to the aforementioned complications. The arc melted buttons, because of the presence of their respective porosity and the intermetallic phases, were easily fractured into small pieces to fill in the die cavity of the ShAPE apparatus. Two separate runs were performed as described in Table 1 with both the processes' yielding a puck with diameter of 25.4 mm and approximately 6 mm in height. The pucks were later sectioned at the center to evaluate the microstructure development as a function of its depth. Typically in the ShAPE consolidation process; the shearing action is responsible for deforming the structure at interface and increasing the interface temperature; which is proportional to the rpm and the torque; while at the same time the linear motion and the heat generated by the shearing causes consolidation. Depending on the time of operation and force applied near through thickness consolidation can also be attained.

TABLE-US-00002 TABLE 2 Consolidation processing conditions utilized for LWHEA Run Pressure Tool Process Dwell # (MPa) RPM Temperature Time 1 175 500 180 s 2  85 500 600° C. 180 s

[0057] FIGS. 6a-6d show a series of BSE-SEM images ranging from the essentially unprocessed bottom of the puck to the fully consolidated region at the tool billet interface. There appears to be a gradual change in microstructure from the bottom of the puck to the interface. The bottom of the puck had the microstructure similar to one described in FIG. 5. But as the puck is examined moving towards the interface the size of these dendrites become closely spaced (FIG. 6b). The intermetallic phases are still present in the inter-dendritic regions but the porosity is completely eliminated. On the macro scale the puck appears more contiguous and without any porosity from the top to the bottom ¾.sup.th section. FIG. 6c shows the interface where the shearing action is more prominent. This region clearly demarcates the as-cast cast dendritic structure to the mixing and plastic deformation caused by the shearing action. A helical pattern is observed from this region to the top of the puck. This is indicative of the stirring action and due to the scroll pattern on the surface of the tool. This shearing action also resulted in the comminution of the intermetallic particles and also assisted in the homogenizing the material as shown in FIGS. 6c and 6d. It should be noted that this entire process lasted only 180 seconds to homogenize and uniformly disperse and comminute the intermetallic particles. The probability that some of these getting intermetallic particles re-dissolved into the matrix is very high. The homogenized region was nearly 0.3 mm from the surface of the puck.

[0058] The use of the ShAPE device and technique demonstrated a novel single step method to process without preheating of the billets. The time required to homogenize the material was significantly reduced using this novel process. Based on the earlier work, the shearing action and the presence of the scrolls helped in comminution of the secondary phases and resulted in a helical pattern. All this provides significant opportunities towards cost reduction of the end product without compromising the properties and at the same time tailoring the microstructure to the desired properties.

[0059] In as much as types of alloys exhibit high strength at room temperature and at elevated temperature, good machinability, high wear and corrosion resistance. Such materials could be seen as a replacement in a variety of applications. A refractory HE-alloy could replace expensive super-alloys used in applications such as gas turbines and the expensive Inconel alloys used in coal gasification heat exchanger. A light-weight HE-alloy could replace Aluminum and Magnesium alloys for vehicle and airplanes. Use of the ShAPE process to perform extrusions would enable these types of deployments.

[0060] While various preferred embodiments of the invention are shown and described, it is to be distinctly understood that this invention is not limited thereto but may be variously embodied to practice within the scope of the following claims. From the foregoing description, it will be apparent that various changes may be made without departing from the spirit and scope of the invention as defined by the following claims.