Patent Description:
The present disclosure generally relates to wires formed of an improved <NUM>-series aluminum alloy exhibiting high creep resistance and stress relaxation resistance.

Cable building wire has predominantly been formed of copper due to copper's high electrical conductivity and excellent mechanical properties. Despite these qualities, it would be advantageous to form cable building wire from an aluminum alloy as a consequence of aluminum's higher electrical conductivity, when compared to copper, on a unit weight basis. However, cable wires formed of typical aluminum alloys exhibit low creep resistance and stress relaxation resistance causing cables formed from such alloys to exhibit poor termination performance making such conductors unsuitable for use in buildings. It would be advantageous to form an improved aluminum alloy which balances high electrical conductivity with high creep resistance and stress relaxation resistance. <CIT> discloses an electrical cable comprising an elongate electrically conductive element made of aluminum alloy having aluminum and erbium precipitates and also having an element selected from iron, copper and a mixture thereof. Among the specifically disclosed alloys, one has an erbium content of <NUM>%, a copper content of <NUM>%, an iron content of <NUM>% and an electrical conductivity (IACS) of <NUM>.

In accordance with the present invention, a wire formed from an improved <NUM>-series aluminum alloy is provided, having the features outlined in appended claim <NUM>.

Advantageous features of the wire according to the present invention are disclosed in dependent claims <NUM> to <NUM>.

As will be described herein, aluminum alloys exhibiting a balance of high electrical conductivity as well as high creep resistance and high stress relaxation resistance are disclosed. The aluminum alloys are suitable to form conductors for wires, such as cable building wires. Cables formed from such aluminum alloys can dependably be terminated at building sockets and terminals. Generally, such improved aluminum alloys can be formed through the inclusion of a suitable rare earth element to certain <NUM>-series aluminum alloys to improve the creep resistance and stress relaxation resistance without impairing the electrical conductivity of the standard <NUM>-series aluminum alloy.

As can be appreciated, cable building wire is connected to, and terminated at, receptacles such as power outlets. Termination of cable building wire is typically accomplished by making an electrical connection with the terminal and then using a screw to secure the connection. As can be appreciated, various physical characteristics are important to prevent loosening and failure of a termination over time including the creep resistance and stress relaxation resistance characteristics exhibited by the cable. Creep is the measurement of the rate of change of a material's dimensions over a period of time when subjected to an applied force and controlled temperature. Stress relaxation is the time dependent decrease in stress of a metal under constant strain. Cables formed of metals having low resistance to creep and stress relaxation can deform and can cause undesirable failure of the termination due to loss of electrical contact.

As can be further appreciated, the electrical and mechanical properties of a metal can be influenced through several mechanisms including through the incorporation of additional elements to form alloys and through mechanical and thermal treatment of the metal. Such mechanisms can improve the creep and stress relaxation performance of a metal.

A number of aluminum alloy grades have been standardized by the Accrediting Standards Committee H35 of the Aluminum Association. Standardized aluminum grades are defined by their elemental compositions with the various grades generally intended for specific applications and industries. For example, <NUM>-series aluminum alloys are defined as being high purity aluminum alloys and <NUM>-series aluminum alloys are defined as zinc and magnesium containing alloys. <NUM>-series aluminum alloys are useful in the overhead conductor industry while <NUM>-series aluminum alloys are useful in the aerospace industry. Certain <NUM>-series aluminum alloys have been standardized to provide aluminum alloys useful for the construction of cable wires. <NUM>-series aluminum alloys can include silicon, iron, copper, magnesium, zinc, and boron. Specifically, <NUM>-series aluminum alloys are defined in ASTM B800-<NUM> (<NUM>) titled "Standard Specification for <NUM> Series Aluminum Alloy Wire for Electrical Purposes-Annealed and Intermediate Tempers" and all references herein to <NUM>-series aluminum alloys means aluminum alloys meeting such qualifications.

Specifically, certain <NUM>-series aluminum alloys, such as AA8176 and AA8030, can exhibit improved creep and stress relaxation resistance when compared to conventional aluminum alloys, such as AA1350. However, the creep resistance and stress relaxation resistance of such <NUM>-series alloys is still lower than comparable creep and stress relaxation values for the copper typically used to form cable building wire. This discrepancy can lead to cables formed from <NUM>-series aluminum alloys to experience termination failure. Applicant has discovered that the addition of rare earth elements selected from one or more of erbium and ytterbium to the <NUM>-series alloy AA8030, can allow for the formation of an aluminum alloy which exhibits higher creep resistance and stress relaxation resistance while still maintaining the electrical conductivity of the original alloy.

For example, in certain embodiments, the addition of trace amounts of erbium can increase the creep resistance, increase the stress relaxation resistance, and increase the tensile strength of an AA8030 alloy without reducing the electrical conductivity or elongation at break values of the original alloy.

As can be appreciated, the elongation at break values of the aluminum alloys described herein can be greater than comparable elongation at break values for copper cable building wires. Improved elongation at break values can facilitate the tension forces required to pull cable wire through walls and plenum. In certain embodiments, the aluminum alloys used to form the cable building wires described herein can have an elongation at break value of about <NUM>% to about <NUM>%.

In certain embodiments, the aforementioned rare earth element can be at about <NUM>% by weight of the aluminum alloy, at about <NUM>% by weight of the aluminum alloy, at about <NUM>% by weight of the aluminum alloy, and at about <NUM>% by weight of the aluminum alloy.

AA8030 aluminum alloys are defined by unified number system ("UNS") AA8030 standard and include, by weight, <NUM>% to <NUM>% iron, <NUM>% to <NUM>% copper, <NUM>% or less silicon, <NUM>% or less magnesium, <NUM>% or less zinc, <NUM>% to <NUM>% boron, <NUM>% or less of each other element with a total of less than <NUM>% of each other element, and the balance aluminum. Known AA8030 aluminum alloys can exhibit a tensile creep rate at <NUM> under <NUM> MPa of stress of about <NUM> * <NUM>-<NUM> s-<NUM> and tensile stress relaxation times to reach <NUM>% of an initial tensile stress of <NUM> MPa at room temperature (e.g., at about <NUM>) of about <NUM> seconds.

In certain embodiments that are not part of the present invention, the rare earth element can be added to an AA8176 or an AA8017 aluminum alloy. AA8176 aluminum alloys include, by weight, <NUM>% to <NUM>% iron, less than <NUM>% zinc, <NUM>% to <NUM>% silicon, <NUM>% or less gallium, <NUM>% or less of each other element with a total of less than <NUM>% of each other element, and the balance aluminum. AA8017 aluminum alloys include, by weight, <NUM>% to <NUM>% iron, <NUM>% to <NUM>% copper, <NUM>% or less silicon, <NUM>% or less zinc, <NUM>% or less boron, <NUM>% to <NUM>% magnesium, <NUM>% or less lithium, <NUM>% or less of each other element with a total of less than <NUM>% of each other element, and the balance aluminum.

As can be appreciated, certain aluminum alloys described herein can still satisfy the requirements of standardized aluminum alloy grades. For example, the inclusion of about <NUM>% to about <NUM>%, by weight, of a rare earth element to an AA8030 aluminum alloy is permitted by the AA8030 standard and inventive aluminum alloys AlFe<NUM>Cu<NUM>Si<NUM>Er<NUM>, AlFe<NUM>Cu<NUM>Si<NUM>Er<NUM>, and AlFe<NUM>Cu<NUM>Si<NUM>Er<NUM>, for example, can be considered AA8030 aluminum alloys.

The addition of a rare earth element can increase resistance to tensile creep and resistance to tensile stress relaxation. For example, the addition of about <NUM>% to about <NUM>% erbium to an AA8030 aluminum alloy can lower the tensile creep rate at <NUM> under <NUM> MPa of stress to about <NUM> * <NUM>-<NUM> s-<NUM> to about <NUM> * <NUM>-<NUM> s-<NUM>. As can be appreciated, such improvements can be a 20x to 30x, or even greater, increase in tensile creep resistance as compared to a similar alloy formed without the rare earth element.

Similarly, the tensile stress relaxation resistance of an improved AA8030 aluminum alloy including about <NUM>% to about <NUM>% erbium can improve the tensile stress relaxation time required to reach about <NUM>% of an initial stress of <NUM> MPa, when measured at <NUM>, to about <NUM>,<NUM> seconds to about <NUM>,<NUM> seconds. As can be appreciated, this is about a 2x improvement in stress relaxation times.

As can be appreciated however, the inclusion and modification of the elements in an aluminum alloy can have a dramatic impact on various characteristics of the alloy. For example, the inclusion of about <NUM>% zirconium can improve the creep and stress relaxation properties of an aluminum alloy but can undesirably lower the electrical conductivity of the alloy by about <NUM>% as measured by the International Annealed Copper Standard ("IACS") adopted in <NUM>. Similarly, including an additional <NUM>% copper in an AA8030 alloy containing <NUM>% iron and <NUM>% copper (to form AlFe<NUM>Cu<NUM>) can cause a <NUM>% IACS decrease in electrical conductivity.

Surprisingly, the addition of a rare earth element as described herein can maintain the characteristics of the original alloy, such as electrical conductivity, while improving the creep resistance and stress relaxation resistance of the original alloy. For example, improved AA8030 aluminum alloys including a rare earth element can maintain an IACS value of about <NUM>% to about <NUM>% as compared to an IACS value of about <NUM>% for a standard AA8030 aluminum alloy formed without the rare earth element.

Without being bound by theory, it is believed that the inclusion of a rare earth element can improve the properties of an aluminum alloy by forming structured nano-precipitates which provide strength to reduce creep and stress relaxation. For example, it is believed that the addition of erbium can form Al<NUM>Er (L12 structure) structured nano-precipitates. As can be appreciated, such nano-precipitates are stable at both room temperature and at elevated temperatures and can be effective in impeding the dislocation motion which causes creep and stress relaxation. It is additionally believed that such nano-precipitates can synergistically work with the precipitates (e.g., nano-precipitates or micro-precipitates) formed from the interactions of the iron and copper found in the unmodified <NUM>-series aluminum alloy.

For example, in certain embodiments, iron can be included in an aluminum alloy as described herein at about <NUM>%, by weight, or greater. Such iron loading levels can ensure that the aluminum alloy has sufficient precipitation of Ale(Cu, Fe). As can be appreciated, increasing the loading level of copper can lower the electrical conductivity of an aluminum alloy making it more desirable in certain embodiments to increase the weight percentage of iron.

Generally, the aluminum alloys described herein can be formed in any manner known in the art. For example, the aluminum alloys can be formed by casting an as-cast shape, hot rolling the as-cast shape into a redraw rod, and then drawing the redraw rod into a conductive element, such as a wire. This process can be performed continuously.

Cables formed from the aluminum alloys described herein can be useful as cable building wire. In certain embodiments, the cables can be used with standard building connectors such as connectors which comply with the requirements of UL 486A. Generally, the cable building wires can be used as known in the art. For example, the building cable wires can be installed and used in compliance with NECA/AA <NUM>-<NUM> standards.

The cable building wires can be formed in any suitable manner. For example, the metal alloys described herein can be formed into stranded or solid conductors in various embodiments. Additionally, the cable building wires can be formed of any suitable gauge as determined by the various needs of a particular application. For example, in certain embodiments, building cable wires can be <NUM> American wire gauge ("AWG"), <NUM> AWG, or <NUM> AWG. Additionally, the building cable wire can be coated with an insulator or jacket as known in the art. The building cable wires disclosed herein can weigh less than a copper building cable wire conducting a similar amount of ampacity.

The aluminum alloys described herein can also be used to form alternative articles in certain embodiments. For example, the aluminum alloys can be used to form conductive elements inside of a power receptacle or can be used to form articles which must be resistant to creep.

Table <NUM> depicts the mechanical and electrical properties of several Example aluminum alloys according to the invention; tables <NUM> and <NUM> depict the mechanical and electrical properties of several aluminum alloys which are not part of the present invention. The measured properties include the ultimate tensile strength ("UTS"), the elongation at break, the electrical conductivity as measured by the International Annealed Copper Standard ("IACS"), the tensile creep rate as measured at <NUM> under <NUM> MPa of applied stress, and the tensile stress relaxation time as measured by the time the stress of a sample reaches <NUM>% (Tables <NUM> and <NUM>) or <NUM>% (Table <NUM>) of the initial stress when measured at <NUM>. Ultimate tensile strength was measured in accordance to ASTM B941 (<NUM>); tensile creep was measured in accordance to ASTM E139 (<NUM>); and tensile stress relaxation time was measured in accordance to ASTM E328 (<NUM>).

Table <NUM> depicts examples of AA8017 aluminum alloys, which are not part of the invention. Table <NUM> depicts examples of AA8030 aluminum alloys. Table <NUM> depicts examples of AA8176 aluminum alloys, which are not part of the invention. Additional elements, or impurities, may be present in trace amounts in the disclosed aluminum alloy examples of Tables <NUM> to <NUM>. For example, each of the AA8030 aluminum alloys in Table <NUM> include about <NUM>% silicon. As can be appreciated, such examples remain AA8030 aluminum alloys as the compositions remain with the standards of the named aluminum alloys.

As depicted by Table <NUM>, the inventive examples (Inv. ) exhibited significantly improved tensile creep resistance and tensile stress relaxation resistance as compared to their respective comparative examples (Comp. ) while maintaining electrical conductivity.

The citation of any document is not an admission that it is prior art with respect to any invention disclosed or claimed herein or that it alone, or in any combination with any other reference or references, teaches, suggests, or discloses any such invention.

Claim 1:
A wire formed from an improved <NUM>-series aluminum alloy comprising, by weight:
about <NUM>% to about <NUM>% iron;
about <NUM>% to about <NUM>% copper;
<NUM>% or less magnesium;
<NUM>% to <NUM>% boron;
<NUM>% or less silicon;
<NUM>% or less zinc
about <NUM>% to about <NUM>% of a rare earth element selected from one or more of erbium and ytterbium, and
<NUM>% or less of each other element with a total of less than <NUM>% of each other element,
the balance being aluminum,
wherein the improved <NUM>-series aluminum alloy is an AA8030 aluminum alloy.