Aluminum-carbon metal matrix composite material for fasteners

Abstract

A fastener configured for power distribution applications is disclosed. The fastener includes an aluminum (Al) metal matrix composite (MMC) containing nanoscale carbon particles at a concentration of 0.01 to 2 weight percent (wt%). The nanoscale carbon particles are uniformly distributed throughout the MMC. The fastener is useful for connecting conductors such as busbars, wires, or cables. Also disclosed is a method for manufacturing an aluminum MMC fastener that includes a solid-state deformation process.

Description

Technical Field

[0001] The disclosed teachings relate to a metal composite material for fasteners.

Background Art

[0002] A fastener is a hardware device that mechanically joins or secures two or more objects to each other. Generally, fasteners are used to create non-permanent joints, i.e., joints that can be removed or disassembled without damaging the joining components. Welding is an example of creating a permanent joint. Steel fasteners are typically made from stainless steel, carbon steel, or alloy steel.

[0003] Other alternative methods of joining materials include the use of crimping, welding, soldering, brazing, taping, adhesives, cement, or other adhesives. Forces such as magnets, vacuum (e.g., suction cups), or even friction (e.g., adhesive pads) can also be used. Some types of woodworking joints utilize separate internal reinforcements such as dowels or biscuits, which can be considered fasteners within the scope of a joint system in a sense, but are not general-purpose fasteners in themselves.

[0004] One or more embodiments of the present disclosure are shown by way of example and not limitation in the figures of the accompanying drawings, in which like reference numerals indicate like elements.

Brief Description of the Drawings

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[0006] The various features of the embodiments described herein will become more apparent to those skilled in the art by considering the detailed description in conjunction with the drawings. The embodiments are shown in the drawings by way of example and not limitation, and in the drawings, like reference numerals may indicate like elements. The drawings illustrate various embodiments for purposes of illustration, and those skilled in the art will recognize that alternative embodiments may be employed without departing from the principles of the disclosed technology. Thus, while specific embodiments are shown in the drawings, the technology can accept various modifications.

DETAILED DESCRIPTION OF THE INVENTION

[0007] The disclosed technology relates to a technique for manufacturing an aluminum (Al)-based metal matrix composite (MMC) fastener having a desired strength, thermal stability, and creep resistance without significantly reducing the conductivity below that of pure Al. It is beneficial to create a fine dispersion of reinforcing particles surrounded by an α-Al matrix that is relatively lacking in solute atoms. To achieve this, a metal matrix composite (MMC) additive that has no significant solubility in α-Al is used. Carbon is an ideal candidate as an additive for Al-based MMC fasteners for power distribution applications because its solubility in Al has not been reported and it exists in several nanoscale structures such as carbon nanotubes (CNT) which can be in the form of single-walled carbon nanotubes (SWCNT) or multi-walled carbon nanotubes (MWCNT), graphene nanoplatelets (GNP), fullerenes, and nanodiamonds.

[0008] In one embodiment, the reinforcing particles include carbon in the form of carbon nanotubes (CNT). The CNT may be single-walled CNT, multi-walled CNT, or a combination of the two types.

[0009] In another embodiment, the reinforcing particles include carbon in the form of graphene nanoplatelets (GNP), fullerenes, nanodiamonds, or any combination thereof.

[0010] In another embodiment, the reinforcing particles mainly contain sp 2 or sp 3 hybridized carbon. Examples of mainly sp 2 hybridized carbon include CNT, GNP, and fullerenes. Examples of mainly sp 3 hybridized carbon are nanodiamonds. Amorphous carbon and carbon black are examples of carbon forms that are mixtures of sp 2 and sp 3 hybridized forms.

[0011] The addition of a small amount of carbon (C) nanoscale particles to Al provides an increase in the tensile strength of Al while maintaining substantially the same conductivity, elastic modulus, and coefficient of thermal expansion as compared to Al. For example, a composite product of Al and carbon nanotubes (CNT), or an "Al-CNT" composite product, obtains its tensile strength by processing and dispersion hardening. During cold working by rolling, drawing, or other processes, the grain structure is refined and the CNTs are more uniformly dispersed in the matrix. The tensile strength of Al-CNT increases with the CNT content, but the conductivity decreases slightly. From that perspective, a concentration of 0.1 - 1.0 wt% of CNT is preferred, which maintains a conductivity of about 60% of the International Annealed Copper Standard (IACS).

[0012] The 0.5 wt% CNT extruded aluminum product has been shown to exhibit conductivity similar to that of 1000 series aluminum (60.8% IACS), while showing higher strength and heat resistance compared to standard Al conductors. Strengths above 200 MPa and even above 300 MPa, and thermal stability meeting the requirements of the AT4 level of IEC 62004 "Thermal-resistant aluminum alloy wire for overhead line conductor" have been measured. The mechanical strengthening of the Al-CNT composite by processing and dispersion hardening is achieved by continuously reducing the cross-section of the extruded Al-CNT rod to the desired diameter by cold working (e.g., rolling, drawing). This disclosure includes the applicability of the processed and dispersion-hardened Al-CNT rod for the manufacture of Al fasteners suitable for electrical and / or high-temperature applications.

[0013] To achieve the maximum benefit from the addition of carbon at the nanoscale, a uniform distribution of particles throughout the MMC should be achieved. Depending on the desired production scale and the form of carbon used, a uniform distribution can be achieved in several ways. For example, adding C particles to the Al melt and casting the MMC is one approach, but it is an approach with issues such as surface tension effects, the density difference between C and liquid Al, and the possibility of combustion of the C additive at the Al melting temperature. The second method is to use powder metallurgy techniques to uniformly mix and sinter the Al and nanoscale C powders together into a solid billet. Finally, the third method involves mechanically mixing the nanoscale C additive into the Al substrate by solid-state processing techniques such as friction stir processing, equal-channel angular pressing (ECAP), extrusion, etc.

[0014] The desired resulting MMC product has a carbon particle (e.g., CNT) concentration that is uniformly distributed throughout its entire volume. That is, there are no significant irregular voids or irregular empty spaces between the carbon particles, the carbon particles are not agglomerated (or any agglomeration is negligible), and there are no high or low concentration parts of carbon particles throughout the product volume. The amount of carbon particles in the matrix is essentially the same in all parts of the matrix volume, i.e., within the composite, there are no parts with a distinct difference in carbon particle concentration, e.g., more than 20%, more than 10%, or preferably more than 5%, from any other part.

[0015] In one example, the resulting MMC product has a uniform density and is non-porous. For example, the density may deviate by a maximum of 2% from the theoretical composite density that can be calculated based on the volume of the material, the relative amounts of Al and carbon particles, and their respective densities. The uniform carbon particle concentration in the sample Al-C MMC results in consistent uniform properties such as a uniform conductance throughout the entire volume of the MMC product. The uniform distribution of carbon particles in the sample Al-C MMC product can be verified by high-resolution microscopy.

[0016] Regardless of the technology used to manufacture the Al-C MMC, the final amount of residual stress from processing affects the resulting strength and elongation of the MMC. In the case of fastener applications that require significant elongation or thermal stability, care should be taken to achieve a final state with relatively little residual stress. One way to achieve a final state suitable for this application is by annealing the fastener to relieve residual stress after any necessary cold working procedures have been carried out. Another way is to first manufacture the MMC with nearly final dimensions and geometry using a process (e.g., extrusion) that operates at a high temperature to limit the generation of residual stress. When higher strength is desired and elongation and thermal stability are less important, for example, the introduction of residual stress by the application of cold working is a viable method to increase strength.

[0017] [Fastener for Busbar Applications] Al-C MMC (e.g., Al-CNT MMC) has improved properties compared to common Al alloys. Examples of improved properties include higher strength, higher electrical conductivity, higher heat resistance, and higher creep resistance. As a fastener, the Al-C MMC material provides a highly reliable and efficient connector for electrical applications such as connecting busbars, battery components, or utility wires.

[0018] As used herein, the term "aluminum-based" can refer to pure Al, Al alloys, or Al-based MMCs. Examples of applications of aluminum-based fasteners can be found in the transportation, telecommunications, utility, and power generation industries. For example, it is becoming increasingly important to efficiently mount and connect electrical components to Al busbars within vehicles. The disclosed embodiments provide a practicable solution for fastening aluminum-based busbars to other components in a convenient and consistent safe manner. In electric vehicle / hybrid electric vehicle (EV / HEV) battery module assembly connections, the connectors should have high strength, electrical conductivity (thermal and electrical), and thermal stability. The standard current-carrying capacity of aluminum is about 0.7 A / mm 2 which is sufficient for use in connecting battery modules in EV / HEVs. The power requirements in EV / HEVs continue to increase, as does the need for efficient connections.

[0019] The conductivity of conductor-grade Al alloys such as AA 1350 is 61.2 - 61.8% IACS, and the strength is lower compared to copper (Cu). The addition of alloying elements to Al increases the strength (e.g., alloys of the 2xxx, 5xxx, 6xxx, and 7xxx series), but typically decreases the conductivity. Furthermore, since the strengthening additives used in commercial alloys have relatively high mobility in the Al matrix, the thermal stability of Al alloys is low. For this reason, Al alloys are typically not used in applications exposed to temperatures exceeding 150 °C. However, carbon-reinforced aluminum (Al-C) MMCs, such as aluminum-carbon nanotube (Al-CNT) MMCs, can provide high strength and thermal stability without significant loss of conductivity.

[0020] Al-CNT MMCs have high specific strength and excellent thermal and electrical properties. The amount and distribution of CNTs in the Al matrix are important parameters for achieving the maximum strength of the Al-CNT composite. The length of the CNTs in Al-CNT MMCs may not affect the strength of the composite, but the mechanisms used to strengthen the composite can vary depending on the length of the CNTs. The tendency of CNTs to form aggregates has led to some studies observing lower strength for higher CNT contents due to CNT agglomeration, so a uniform CNT distribution is important for determining specific properties. For example, in one study, 0.1 wt% CNTs were observed to result in higher strength compared to 0.25 wt%, 0.5 wt%, and 1.0 wt% CNTs because the CNTs are uniformly dispersed without agglomeration in the 0.1 wt% CNT MMC compared to MMCs with higher CNT contents (≧0.25 wt% CNT). Another study showed that 0.5 wt% CNTs resulted in improved mechanical properties compared to 1.0 wt% CNTs in the Al-CNT composite due to extensive aggregate formation in the higher content CNT composites. Therefore, higher CNT concentrations are considered beneficial as long as the CNTs are uniformly distributed without significant agglomeration.

[0021] Replacing the Cu busbar with Al results in a significant reduction in weight and cost. However, the transition from a Cu busbar to an Al busbar requires additional changes to compensate for the difference in properties between Al and Cu. For example, Cu busbars are often connected to components by steel fasteners, but the differences in thermal expansion coefficient, creep behavior, and galvanic potential make it risky to connect an Al busbar to a steel fastener. Furthermore, safe power distribution using Al conductors requires care to avoid dangerous conditions that can lead to hot spots and eventual connection failures. Two major causes of these failures are (i) galvanic corrosion and (ii) loosening of connections due to differences in thermal expansion coefficient and creep. Galvanic corrosion occurs between dissimilar metals in the presence of an electrolyte. Al is a strong anode and corrodes vigorously when electrically coupled to Cu or stainless steel. Therefore, connecting a Cu busbar to an Al busbar using stainless steel fasteners can be problematic unless appropriate precautions are taken (such as using a Ni coating, shielding the joint from environmental moisture, etc.). These precautions are costly and can cause failures if applied incorrectly. Loosening of connections due to differences in thermal expansion coefficient and creep behavior can cause failures in Al power distribution systems. In particular, Al conductors expand and contract more quickly with temperature changes compared to the material used to clamp them (e.g., stainless steel fasteners), so a compressive force is always applied to the Al conductor whenever it is heated. Normal use generally causes temperature cycling either through the heat generated by the resistance within the conductor (Joule heating), changes in ambient conditions, or from components surrounding the conductor, and this cyclic loading / unloading can deform the conductor at the connection. Using this deformation, less force is applied at elevated temperatures, but at lower temperatures, electrical contact may be absent or limited.

[0022] The disclosed technology addresses problems associated with joining Al to dissimilar metals. As the number of dissimilar joints decreases, the likelihood of failure decreases. Thus, all-Al joints are an attractive option. For example, connecting two Al busbars with Al bolts and Al nuts avoids the aforementioned failures. Although Al alloy fasteners are commercially available, the disclosed Al-C MMCs (e.g., Al-CNT MMCs) offer distinct advantages over existing alloys for fastener applications. In particular, the disclosed MMC fasteners have improved properties, including higher thermal stability, tensile strength, and electrical conductivity, compared to current Al alloys used in fastener applications.

[0023] Conventional Al fasteners are mainly manufactured from 6000 series alloys (e.g., EN AW 6056). These fasteners reach a maximum ultimate tensile strength (UTS) of approximately 500 MPa, a yield strength of up to 400 MPa, and an elongation of about 7%. The maximum applicable temperature for these fasteners is approximately 150 °C or 180 °C for short periods.

[0024] The disclosed embodiments include Al-MMC fasteners having various combinations of properties in the as-extruded, cold-worked, or cold-worked and annealed states. The combinations of properties include conductivity, UTS, and elongation that are less than, equal to, or greater than a certain value.

[0025] In one embodiment, the Al-C MMC fastener has a conductivity greater than about 50% IACS, a UTS greater than about 80 MPa, and an elongation greater than about 30%. A fastener having such properties can be in the as-extruded state, or a gently cold-worked state, or a cold-worked and annealed state.

[0026] In another embodiment, the Al-C MMC fastener has a conductivity exceeding about 50% IACS, a UTS exceeding about 120 MPa, and an elongation exceeding about 10%. A fastener having such properties can be in the as-extruded state, cold-worked state, or cold-worked and annealed state.

[0027] In another embodiment, the Al-C MMC fastener has a conductivity exceeding about 50% IACS, a UTS exceeding about 200 MPa, and an elongation exceeding about 3%. A fastener having such properties is typically in the cold-worked state or cold-worked and annealed state.

[0028] In another embodiment, the Al-C MMC fastener has a conductivity exceeding about 50% IACS, a UTS exceeding about 300 MPa, and an elongation exceeding about 1%. A fastener having such properties is typically in the cold-worked state or cold-worked and annealed state.

[0029] In a preferred embodiment, the Al-C MMC fastener, either in the cold-worked state or cold-worked and annealed state, has a conductivity exceeding about 55% IACS or exceeding about 58% IACS, a UTS exceeding about 180 MPa, and an elongation exceeding about 10%.

[0030] In one embodiment, the Al-C MMC fastener has excellent creep resistance compared to fasteners made from commercially available aluminum alloys such as 6000 series alloys. The Al-C MMC fastener typically exhibits a total displacement of less than about 5% or less than about 1% when a tensile stress equal to 80% of the room temperature yield strength of the fastener is applied after testing at 150 °C for 100 hours. The Al-C MMC fastener typically exhibits a total creep of less than about 5% or less than about 3% when a tensile stress equal to 80% of the room temperature yield strength of the fastener is applied after testing at 150 °C for 500 hours.

[0031] The Al-CNT MMC fastener provides improved thermal stability, enabling use at temperatures exceeding 200°C. The improved thermal stability provides high creep resistance compared to commercially available Al alloys. Thermal stability is required for the fastener to maintain the necessary pre-tension on the connected parts, and since contact resistance is directly affected by pre-tension, it is important for connections in electrical applications. In electrical applications, the high specific conductivity of Al-CNT is about 60% IACS compared to about 52% IACS of 6000 series alloys, providing an additional advantage.

[0032] [Details of Manufacturing] The disclosed embodiments include techniques for manufacturing Al-C MMC fasteners containing small amounts of nanostructured C additives such as CNT, GNP, fullerene, and / or nanodiamond. In some examples, the amount of nanostructured C additive is 0.01 - 2.0 weight percent (wt%), 0.1 - 1.0 wt%, or 0.2 - 0.8 wt%. In some embodiments, the amount of C additive is about 0.4 wt%, about 0.5 wt%, about 0.6 wt%, about 0.7 wt%, or about 0.8 wt%. The manufacture of Al-C MMC fasteners can be achieved according to different processes including those described in the following examples.

[0033] An exemplary process 100 for manufacturing MMC fasteners is shown in FIG. 1. At 102, a semi-finished MMC product such as a wire, rod, or other profile is produced by extrusion. At 104, the semi-finished MMC product is optionally work-hardened by cold drawing, rolling, etc. At 106, the fastener shaft and head are formed by one or more of various techniques such as milling, flow forming, forging, rolling. At 108, the threads on the fastener are formed by cutting, milling, rolling, or other suitable methods. Thereby, the geometric formation of the fastener is completed. Then, at 110 and 112, optional heat treatment and optional surface treatment are applied respectively.

[0034] The extrusion step 102 can be used to achieve several purposes in the manufacture of Al-C MMC fasteners. One purpose is to produce a specific shape and dimensions of the extruded product. These dimensions may match the target final dimensions required for fastener manufacture if elongation is emphasized more than the strength of the fastener, or may be larger if cold working (e.g., drawing or rolling) is used to increase strength while reducing the cross-sectional area to the target dimensions. In addition to geometric purposes such as size and shape, extrusion using appropriate tools and parameters can be used to increase the uniformity of C additives in the Al-C feedstock that is insufficiently homogenized by other means.

[0035] Increasing the uniformity of Al-C MMC using extrusion can result in significant performance improvements from the viewpoints of strength, thermal stability, etc. Depending on the extrusion process used, the Al-MMC raw material can be in the form of an Al-C rod, bar, granules, compressed powder billet, etc., and multiple passes through the extrusion process can be employed to further improve the uniformity if necessary.

[0036] An optional work hardening step 104 including cold drawing, rolling, etc. can be performed on the Al-C MMC to achieve the target size and dimensions required for fastener manufacture. This process can be carried out at room temperature, and since the residual stress from cold working generally reduces elongation and increases strength, it can be carried out at a high temperature to relieve the internal stress if high elongation is desired in the final fastener product. As an alternative to hot rolling, heat treatment can also be applied after cold rolling as a method of relieving the residual stress after manufacture.

[0037] The forming step 106 is carried out on the semi-finished Al-C MMC product as part of fastener manufacturing. For example, the head and / or shaft of the fastener are created by machining, flow forming, forging, rolling, or other suitable techniques. The ease of forming depends on the structure and amount of C contained in the MMC, as well as the particle size and the amount of residual stress present in the material during forming. To optimize the formability of any particular Al-C MMC, care should be taken to reduce the residual stress during forming by avoiding cold working by manufacturing a material close to the final dimensions or annealing at a temperature high enough to relieve the stress accumulated during cold working procedures. However, if the strengthening provided by the residual stress is required for the characteristics of the final fastener application, some forming can still be carried out with little or no annealing.

[0038] The threads of the fastener are formed in step 108 by machining or forming techniques. Examples of machining techniques include cutting, milling, etc. Examples of forming techniques include rolling, forging, etc. Generally, the forming method is more preferred if possible. The machining step can be used in the case of small batch manufacturing or when the geometric shape of the fastener requires sharp edges or other features that are difficult or impossible with the forming method.

[0039] An optional heat treatment step 108 can be used to impart the desired mechanical, thermal, and / or electrical properties to the finished fastener product. For example, an annealing heat treatment can be used to increase the thermal stability of the product. Such heat treatment can impart other desired properties such as higher elongation, higher conductivity, etc. Heat treatment can also be used to reduce the residual stress accumulated in the product during various forming and / or machining steps in the manufacturing process.

[0040] Using an optional surface treatment step 110, desired surface characteristics can be imparted to the finished fastener product. For example, plating or coating can be applied for corrosion resistance, improved wear characteristics, or lubrication.

[0041] [Geometric Shape of the Fastener] Although a schematic view of an exemplary fastener is shown in FIG. 2, various geometric shapes of the fastener are within the scope of the disclosed embodiments. Depending on the application, the diameter of the fastener shaft can be, for example, from 2 mm to 16 mm. The fastener can conform to metric standards, imperial standards, or any other specifications. The length of the fastener shaft can vary, for example, from 5 to 50 mm to enable fastening a wide range of components having various thicknesses. The thread can cover the entire shaft or only a portion of the shaft.

[0042] The head of the fastener can vary to conform to geometric requirements, to make disassembly easier or less easy, or to adjust the contact area of the fastener against the upper portion of the component being fastened. Variations in the head design can include changes in the overall style. Some possible head styles include bind, fillister, countersunk, flat, hex, oval, pan, round, square, truss, and torque, as well as any variations of those styles. The fastener head can interface with and be designed to be tightened by various tools including torque wrenches, standard wrenches, Allen wrenches, various types and shapes of screwdrivers (e.g., Phillips), and special tool sets designed to prevent unauthorized disassembly.

[0043] [Examples of Al-C MMC Properties with No Significant Residual Stress] (A. Strength and Elongation Behavior of As-Extruded Al-CNT MMC) Figure 3 is a graph showing the beneficial physical properties of as-extruded Al-0.5 wt% CNT (Al-CNT MMC) and drawn Al-0.75 wt% CNT compared to the properties of as-extruded pure Al. More specifically, Figure 3 includes a tensile test showing the properties of an as-extruded Al-0.5% CNT rod with a diameter of 8.3 mm, where the UTS is approximately 120 MPa and the elongation is approximately 24%. Figure 3 also shows the properties of an as-extruded and cold-drawn Al-0.75% CNT rod with a diameter of 8.3 mm, where the UTS is approximately 185 MPa and the elongation is approximately 10%. In contrast, an as-extruded pure Al busbar shows a UTS of approximately 52 MPa and an elongation of approximately 29%. The UTS of the as-extruded MMC busbar at approximately 120 MPa is higher than the UTS of many common Al conductors in the soft state (e.g., Al-1350-O with a UTS of approximately 60 MPa). The UTS of the as-extruded and cold-drawn MMC busbar at approximately 185 MPa is similar to or higher than the UTS of many 6000 series Al alloys used in electrical applications.

[0044] (B. Conductivity of As-Extruded Al-CNT MMC) The conductivity of as-extruded Al-0.5 wt% CNT MMC, measured on wire samples produced in several different production runs, was consistently in the range of 59.5 - 60.5% IACS.

[0045] (C. Creep Behavior of As-Extruded Al-CNT MMC) Figure 4 shows the results of creep tests conducted on an Al-0.75 wt% CNT sample, and for comparison, an Al6101-T6 alloy sample, an A6063-T5 Al alloy sample, and a pure Al (Al99.7) sample. The tests were carried out at 150 °C, and the samples were loaded to 80% of their respective room temperature yield strengths. As shown, the Al-CNT MMC has improved creep properties. Before the test was interrupted at 500 hours, the Al-0.75 wt% CNT did not reach the tertiary creep stage, while the 6063 alloy sample failed completely after about 4 hours, the 6101 sample failed after about 15 hours, and the pure Al sample failed after less than 1 hour.

[0046] [Examples of Al-C MMC properties after cold working to add residual stress] (A. Strength and elongation behavior of cold-worked Al-CNT MMC) The initial extrusion diameter Di of the Al-CNT rod and the final diameter Df of the wire for the desired ultimate tensile strength (UTS) can be calculated from the following relationship.

[0047]

Number

[0048] Here, A and B are constants that depend on the amount of CNT. For an MMC with a nominal CNT content of 0.5 wt%, A and B can be approximately 274 and 34, respectively.

[0049] Figure 5 is a graph showing how cold working affects the strength of Al-0.5 wt% CNT MMC round wires and Al round wires with decreasing cross-sectional area. More specifically, Figure 5 shows plots of the strength improvement due to additional cold working (drawing) for Al-0.5 wt% CNT wires and Al wires.

[0050] Based on the data, in the Al-0.5wt%CNT MMC, due to a sufficient reduction in the cold-worked area, a high strength of about 335 MPa was observed. In contrast, for the pure Al wire, although the strength initially increases upon cold working, the rate is somewhat lower compared to the MMC. Furthermore, the UTS of the pure Al wire reached a plateau at about 140 MPa. The elongation of the MMC remained consistent at 3 - 5% at all levels of cold working. This behavior does not change significantly even when this material is used for busbar applications instead of wires. As an alternative to area reduction, by using a process (such as ECAP) that applies internal stress without changing the cross-sectional area, the strength of the busbar initially produced at the final target dimension or a dimension close to it can be increased.

[0051] (B. Conductivity of Cold-Worked Al-CNT MMC) The conductivity of the cold-worked Al-CNT wire is observed to be in the same range as the wire before cold working, at 59 - 60.5% IACS.

[0052] (C. Thermal Stability of Cold-Worked Al-CNT MMC) To evaluate the thermal stability of the Al-CNT MMC products, heat treatments of the AT4 classification (the highest classification of thermal stability described in IEC62004) were applied to drawn Al 0.5wt%CNT wires to which two different levels of cold working (85% and 98% reduction in cross-sectional area) were applied. Aluminum-based materials that meet the AT4 classification can operate continuously for 40 years at 230°C. To be qualified for AT4 thermal stability, the wires must maintain more than 90% of their UTS after being held at 310°C for 400 hours. They must also maintain more than 90% of their UTS after being held at 400°C for 1 hour. As shown in Figure 6, both of the drawn Al-0.5wt%CNT wires passed this test, demonstrating excellent thermal stability. This behavior extends to fastener applications, provided the same level of cold working is applied.

[0053] For certain applications, Al-CNT MMC fasteners that meet the less stringent AT3 standard for thermal stability described in IEC62004 can still be sufficient while providing substantially better performance compared to commercially available aluminum alloy fasteners. To be qualified for AT3, wire samples must maintain more than 90% of their UTS after being held at 280 °C for 1 hour or after being held at 240 °C for 400 hours. Since it has been shown that the Al-CNT MMCs disclosed herein meet the more stringent AT4 standard, it is also clear that the MMC products meet the less stringent AT3 standard as well.

[0054] [Examples of improving the uniformity of carbon additives in Al-C MMC] (A. Improvement of uniformity in Al-CNT MMC by extrusion) Figure 7 includes images showing the difference in microstructure between two Al 0.5wt% CNT MMCs before and after the increase in uniformity by extrusion. This figure shows the improvement of CNT distribution by solid-phase reprocessing. In the initial MMC702, the aggregated CNTs appear as black spots in the image. After extrusion 704, while the measured C content remains consistent, the number and size of the visible large black spots decrease. More specifically, the images in Figure 7 are cross-sectional micrographs of Al-0.5wt% CNT MMC wires with a high level of undesirable CNT aggregation before (702) and after (704) an additional extrusion process to increase CNT uniformity. The visible black spots are CNT aggregates, and the significant decrease in the size and number density of these spots by extrusion indicates that the process has broken up the aggregates and distributed the CNTs more uniformly. Carbon concentration measurements verify that the C content of these MMCs remained unchanged by this processing. Therefore, the same amount of CNTs is expected to be present in both. From this and other observations, it is clear that the large CNT aggregates are broken and the CNTs are distributed more uniformly by the extrusion process. This has several advantages for the properties of the MMC, as will be explained below.

[0055] (Improvement of Thermal Stability in B.Al-CNT MMC) Improving the uniformity of CNT distribution within the Al-CNT MMC also increases the thermal stability. For example, FIG. 8 shows how the heat treatment (i.e., annealing) of a drawn Al-0.5 wt% CNT MMC wire containing visible CNT aggregates affects the grain size compared to a second drawn Al-0.5 wt% CNT MMC wire having a more uniform CNT distribution. In samples with poorly dispersed CNTs, unconstrained grain growth occurs in some regions of the sample, while in other regions, it resists grain growth. This is due to pockets in the MMC where the amount of CNTs having a thermal stability similar to that of pure Al is relatively low or absent. This phenomenon is not observed in samples with a more uniformly distributed CNT content (e.g., smaller / fewer CNT aggregates having the same C content).

[0056] More specifically, FIG. 8 shows the electron backscatter diffraction (EBSD) images of Al-CNT MMC particles, which demonstrate the advantage of a uniform CNT distribution in a drawn Al 0.5 wt% CNT MMC wire, in contrast to a less uniform CNT distribution. The poorly dispersed sample (802) has a larger initial grain size and shows a non-uniform CNT distribution and excessive grain growth due to drawing and annealing. The sample with a more uniform CNT distribution (804) shows a smaller initial grain size and maintains a relatively consistent and uniform grain size throughout the sample when subjected to the same cold working and heat treatment. As a result of the poorly dispersed CNTs in the Al-0.5 wt% CNT sample, the grains grow freely without being impeded within specific internal regions, and thus, the properties of this sample are significantly less thermally stable than those of an Al-0.5 wt% CNT sample with more uniformly dispersed CNTs.

[0057] Figure 9 shows that an Al-CNT MMC with an insufficient CNT distribution fails the AT4 test according to IEC62004, while a sample with a more uniform CNT distribution passes (see, for example, Figure 6 and the related text). More specifically, Figure 9 shows a plot comparing the thermal stability of as-drawn Al-0.5wt%CNT MMC wires with an insufficient CNT distribution to those with a more uniform CNT distribution. As in Figure 6, samples need to maintain more than 90% of their initial UTS in order to be qualified for AT4 thermal stability. Samples with insufficiently distributed CNTs do not pass the AT4 thermal stability. This comparison emphasizes the importance of breaking up CNT aggregates in Al-CNT MMCs to achieve their full potential.

[0058] [Examples of Al-CNT MMC Fastener Properties Compared with Steel Fasteners] Figures 10A and 10B show the setup for the simulation of a power transmission assembly for bus bar connection. Such connections are found in high-power electrical applications, such as battery connectors for automotive applications. In such applications, aluminum components are more beneficial than currently used copper components due to their significant potential in cost and weight reduction. The requirements for a wide performance range regarding the current-carrying capacity of these conductors and connectors necessitate high thermal stability of the connection system due to resistive heating generated at high electrical loads. Using common steel fasteners for these connections results in an unstable connection state at high temperatures due to the difference in thermal expansion between the aluminum bus bar and the steel fastener. Furthermore, the conductivity of steel is much lower than that of copper, at approximately 3 - 15% IACS. Therefore, connections made with steel fasteners can cause connection loosening and hot spots due to low conductivity.

[0059] Figure 11 is a chart showing a comparison of the pre - tension loss in the busbar connection of an aluminum busbar combined with a stainless - steel fastener against the connection of an Al - CNT MMC busbar combined with an Al - CNT MMC fastener. The connection system was installed with a setting time of 1 hour at 20°C. After setting, the samples were subjected to a thermal cycle of changing from 20°C to 200°C and then back to 20°C. The dwell time at 200°C was 100 hours for each cycle, and 5 cycles were performed. After each cycle, the remaining connection pre - tension was determined.

[0060] Due to the high thermal stability (e.g., AT3 or AT4 level) and equal thermal expansion in all - aluminum (MMC) connections, the measured pre - tension loss is within the range of 30% of the initial installation pre - tension. In the case of aluminum busbars connected by steel fasteners, the pre - tension decreases by almost 90% after the first thermal cycle. This significant decrease nullifies the high initial pre - tension that could be applied to the stronger steel fasteners. Further high - temperature exposure results in a continuous loss of pre - tension down to a poorly defined low pre - tension. Thus, this direct comparison shows the possibility of reliable electrical connections by utilizing Al - CNT MMC fasteners with aluminum - based conductors such as busbars.

[0061] [Remarks] The above description and drawings are illustrative and should not be construed as limiting. Numerous specific details are set forth to provide a complete understanding of the present disclosure. However, well - known details may not be described to avoid obscuring the description. Furthermore, various changes can be made without departing from the scope of the embodiments.

[0062] References to "one embodiment" or "an embodiment" in this specification mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Although the phrase "in one embodiment" appears in various places in this specification, it does not necessarily refer to the same embodiment every time, nor is it an alternative or alternative embodiment mutually exclusive with other embodiments. Furthermore, various features are described that may be shown by some embodiments and not by others. Similarly, various requirements are described that may be requirements for some embodiments but not for others.

[0063] The terms used in this specification generally have their ordinary meanings in the context of the present disclosure and in the particular context in which each term is used. For the particular terms used to explain the present disclosure, additional guidance is provided to practitioners regarding the description of the present disclosure above or elsewhere in this specification. It will be understood that the same thing can be said in multiple ways. For example, it will be recognized that "screw" is a form of "fastener" and these terms can be used interchangeably in some cases.

[0064] Alternative languages and synonyms can be used for any one or more of the terms discussed in this specification, and no special meaning is placed on whether the term is detailed or discussed in this specification. Synonyms are provided for certain terms. The listing of one or more synonyms does not exclude the use of other synonyms. The use of examples throughout this specification, including examples of any of the terms discussed herein, is merely illustrative and is not intended to further limit the scope and meaning of the disclosure or any of the illustrative terms. Similarly, the disclosure is not limited to the various embodiments given in this specification.

[0065] Without intending to further limit the scope of the present disclosure, examples of devices, apparatuses, methods, and their related results according to embodiments of the present disclosure are shown above. For the convenience of the reader, titles or subtitles may be used in the examples, but it should be noted that this should in no way limit the scope of the present disclosure. Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art to which the present disclosure pertains. In case of conflict, the present document including the definitions will prevail.

[0066] From the above, it will be understood that specific embodiments of the present invention are described herein for illustrative purposes, but various changes can be made without departing from the scope of the present invention. Therefore, the present invention is not limited except as by the appended claims.

Claims

**Claim 1** A fastener configured for power distribution purposes, comprising an aluminum (Al) metal matrix composite (MMC) containing nanoscale carbon particles at a concentration of 0.01 to 2 weight percent (wt%), wherein the nanoscale carbon particles are uniformly distributed throughout the Al-MMC. A fastener. **Claim 2** The fastener according to claim 1, wherein the concentration of the nanoscale carbon particles ranges from 0.1 to 1 wt%. **Claim 3** The fastener according to claim 1, wherein the concentration of the nanoscale carbon particles ranges from 0.2 to 0.8 wt%. **Claim 4** The fastener according to claim 1, wherein the nanoscale carbon particles include single-walled carbon nanotubes (CNTs). **Claim 5** The fastener according to claim 1, wherein the nanoscale carbon particles include multi-walled CNTs. **Claim 6** The fastener according to claim 1, wherein the nanoscale carbon particles include graphene nanoplatelets (GNPs), fullerenes, nanodiamonds, or any combination thereof. **Claim 7** The nano-scale carbon particles mainly have sp ２ or sp ３ The fastener according to claim 1, comprising nanoparticles having carbon. **Claim 8** The nanoscale carbon particles are CNTs, GNPs, fullerenes, nanodiamonds, Mainly sp ２ Or sp ３ Nanoparticles having carbon, and any combination thereof selected from the group consisting of. The fastener according to claim 1. **Claim 9** The fastener according to any one of claims 1 to 8, having a conductivity exceeding 50% International Annealed Copper Standard (IACS), an ultimate tensile strength (UTS) exceeding 80 MPa, and an elongation exceeding 30%. **Claim 10** The fastener according to any one of claims 1 to 8, having a conductivity exceeding 50% IACS, a UTS exceeding 120 MPa, and an elongation exceeding 10%. **Claim 11** The fastener according to any one of claims 1 to 8, having a conductivity exceeding 50% IACS, a UTS exceeding 200 MPa, and an elongation exceeding 3%. **Claim 12** The fastener according to any one of claims 1 to 8, having a conductivity exceeding 50% IACS, a UTS exceeding 300 MPa, and an elongation exceeding 1%. **Claim 13** The fastener according to any one of claims 1 to 8, wherein after heating the fastener at either 400 °C for 1 hour or 310 °C for 400 hours, the UTS is at least 90% of its UTS before heating. **Claim 14** The fastener according to any one of claims 1 to 8, wherein after a creep test at 150° C. for 100 hours under an applied load of 80% of the room temperature yield strength, the fastener exhibits a total displacement of less than 5%.

15. The fastener according to any one of claims 1 to 8, wherein after a creep test at 150° C. for 500 hours under an applied load of 80% of the room temperature yield strength, the fastener exhibits a total displacement of less than 5%.

16. The fastener according to any one of claims 1 to 8, wherein the power distribution application includes automotive applications.

17. The fastener according to any one of claims 1 to 8, wherein the fastener is a bolt having a shaft diameter in the range of 2 to 16 mm.

18. The fastener according to any one of claims 1 to 8, wherein the fastener is a bolt having a shaft diameter in the range of 6 to 8 mm.

19. The fastener according to any one of claims 1 to 8, wherein the fastener is a bolt having a shaft length in the range of 5 to 50 mm.

20. The fastener is bind, fillister, dish, flat, hexagonal, elliptical, pan, round, square, truss, and torque a bolt having a head style selected from or related to any of them. The fastener according to any one of claims 1 to 8.

21. The fastener is torque wrench, Allen wrench, standard, Phillips, or special screwdriver, and a tool set configured to prevent unauthorized disassembly The fastener according to any one of claims 1 to 8, including a bolt designed to be tightened using any of the tools.

22. An electrical transmission assembly comprising the fastener according to any one of claims 1 to 21 and a conductor, wherein the conductor is made of pure Al, an Al alloy, or Al - C MMC. The assembly.

23. The assembly according to claim 22, wherein the conductor is a bus bar, a wire, or a cable.

24. A method for obtaining a uniform distribution of nanoscale carbon particles throughout a metal matrix composite (MMC) fastener, comprising obtaining an MMC feedstock material containing a metal matrix and nanoscale carbon particles, A method comprising treating the MMC feedstock material by a solid-state deformation process during or before the manufacture of the MMC fastener, thereby forming the MMC fastener having a uniform distribution of the nanoscale carbon particles throughout the MMC fastener.

25. The method according to claim 24, wherein the solid-state deformation process includes an extrusion process.

26. The method according to claim 24, wherein the solid-state deformation process includes an equal channel angular pressing (ECAP) process.

27. The method according to any one of claims 24 to 26, wherein the MMC feedstock material is an Al-MMC feedstock material.

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