High Conductivity Aluminum Alloys

Abstract

A process for obtaining a high conductivity material comprising the providing of a material from the group consisting of commercial purity aluminum and aluminum alloys wherein the alloy contains at least one alloying element in an amount of from 0.1 to 1.5 percent weight, the total not exceeding 3.0 weight percent, cold deforming the material at least 15 percent below 500.degree. F, heating for at least 20 minutes in the range of 400.degree. to 800.degree. F and cooling.

Parent Case Text

This is a continuation, of application Ser. No. 885,315 filed Dec. 15, 1969 now abandoned, which application is a continuation-in-part of co-pending application Ser. No. 715,552, filed Mar. 25, 1968 now abandoned.

Description

The present invention relates to a new and improved electrical conductor. More particularly, the present invention resides in a new and improved aluminum alloy or commercial purity aluminum characterized by improved and surprisingly high electrical conductivity.

High electrical conductivity is essential in electrical conductors since electrical conductivity is the key characteristic of an aluminum conductor.

Specifically, with respect to aluminum conductors, high purity aluminum has an electrical conductivity somewhat in excess of 64 percent IACS; whereas, the industrial minimum conductivity requirement for a commercial purity aluminum, such as EC grade, is about 61 percent IACS, which is substantially lower than for high purity aluminum.

Aluminum base electrical conductor alloys containing varying alloying elements are well-known, such as, for example, aluminum alloy 6201 containing 0.50 to 0.9 percent silicon, 0.6 to 0.9 percent magnesium, and a maximum of 0.06 percent boron, a maximum of 0.50 percent iron, 0.10 percent copper, 0.03 percent manganese, 0.03 percent chromium and 0.10 percent zinc as impurities, other impurities each not exceeding 0.03 percent and totaling less than 0.10 percent, the balance aluminum, and aluminum alloy 5005 containing 0.50 to 1.1 percent magnesium and a maximum of 0.40 percent silicon, 0.7 percent iron, 0.20 percent manganese 0.20 percent copper, 0.10 percent chromium and 0.25 percent zinc as impurities, other impurities each not exceeding 0.05 percent and totaling less than 0.15 percent, the balance aluminum.

These alloys however are in general characterized by electrical conductivity values considerably lower than high purity aluminum. For example, aluminum alloy 6201 wire possesses an electrical conductivity of only about 53 to 55 percent IACS.

It is therefore, highly desirable to conveniently obtain high electrical conductivity values more favorably comparable to high purity aluminum. Conventional mill processing of the aluminum base alloys employed as electrical conductors, e.g., conductor wire, bus bar etc. does not achieve the aforementioned increased conductivity however, and so it is highly desirable that a process be accomplished which meets this goal.

It is also highly desirable to conveniently obtain high electrical conductivity values in combination with high strength in electrical conductors such as wire and strip, for use as, for example, overhead electrical transmission lines in order to reduce the number of supporting line poles or towers. At present it is necessary to employ, for example, strands of EC H-19 temper aluminum wire reinforced with a high strength steel core, or to include additions of varying alloying elements in aluminum in order to achieve the requisite tensile strength but with an attendant loss in electrical conductivity.

It is therefore a principal object of the present invention to provide a process for obtaining commercial purity aluminum or an aluminum alloy with increased electrical conductivity, and the alloy produced thereby.

It is a further object of the present invention to provide a process for obtaining an aluminum alloy having increased electrical conductivity as well as increased strength, and the alloy produced thereby.

It is a further object of the present invention to provide a process to achieve the foregoing objectives simply and conveniently at relatively low cost.

It has now been found that in accordance with the present invention the foregoing objectives may be readily achieved.

In general, the present invention is applicable to the broad class of aluminum alloys in which:

A. the equilibrium solid solubility of the alloying additions is relatively small at room temperature with increasing solubility thereof with increasing temperature;

B. the amounts of the alloying additions in the alloy are above the solubility limit thereof at room temperature

The present invention is also equally applicable to commercial purity aluminum, i.e., at least 99.3 purity, as aforementioned, wherein the electrical conductivity is substantially increased to a value more closely approximating that for high purity aluminum.

Briefly, the process of the present invention comprises:

A. providing a material selected from the group consisting of commercial purity aluminum and aluminum alloys, wherein said alloys contain at least one alloying addition in an amount from 0.1 to 1.5 weight percent, the total thereof not exceeding 3.0 weight percent, wherein said alloying addition is soluble in an amount greater than 0.25 percent in said alloy, and wherein there is no eutectic transformation in said aluminum alloy below 400.degree.F;

B. cold deforming said material to at least 15 percent reduction;

C. heating said material to 400.degree. to 800.degree.F for at least 20 minutes; and

D. cooling said material.

For applications requiring increased strength as well as increased electrical conductivity the alloy, as distinguished from commercial purity aluminum, is further deformed following step(D) at a temperature of from that of room to less than 500.degree.F. This may be accomplished after cooling to room temperature and reheating, or upon or after cooling down from the temperature range of step C. The amount of deformation is naturally dependent upon the strength required and may range up to 99.8 percent or more.

Generally, the more common alloying additions employed in the alloys of the invention are copper, magnesium, silicon, cadmium, antimony, bismuth, tin, zirconium, tantalum, titanium, and/or chromium, although others may also be employed and naturally various elements as impurities may also be present.

The alloy provided may contain the alloying additions substantially in solution prior to the cold deforming step (B), should a direct chill of the billet after casting be employed, although the present invention is equally applicable to alloys wherein the alloying additions are to a degree not in solution. That is, it is immaterial to the present invention whether the alloying substituents are substantially in solution, and hence a direct chill or normal air cool of the casting may be readily employed after casting and/or after homogenizing, should homogenizing be required prior to the practicing of the present invention.

In addition the material provided may readily be in the cast condition or in the wrought condition, i.e., the casting may first be reduced prior to the cold deforming of step (B).

The cold deforming of step (B) normally refers to deformation carried out at room temperature although deformation may also be carried out at higher temperatures so long as the temperature remains below the recrystallization temperatureof the particular alloy being deformed and in general ranges from room up to less than about 500.degree.F. Deforming at temperatures above that of room however, requires amount of reduction in order to provide the requisite internal deformation of the alloy. Although the maximum amount of cold reduction is not critical and may range up to 99.8 percent or more, the minimum amount of reduction required is at 15 percent.

The purpose of the cold deforming of Step (B) and subsequent heating of Step(C) is to effect precipitation of those alloying constituents and impurities which exceed their solubility limit in the alloy at room temperature, and which a portion thereof has remained in solution after a normal air cool, or wherein the substituents have remained substantially in solution due to a rapid cool of the material. Cold deformation of the alloy produces an unstable alloy structure containing these alloying constituents in solid solution. Subsequent heating of the deformed structure at the temperature range of 400.degree. to 800.degree.F of Step (C) and preferably from 400.degree. to 600.degree.F, allows nucleation to occur in the unstable alloy and precipitation to approach equilibrium, whereby electrical conductivity increases.

The initial degree of cold deformation of Step (B) will effect the requisite temperature and the time of the intermediate heat treatment of Step (C) required for any particular alloy and will also determine the resultant level of electrical conductivity and strength. For example, a severely cold deformed alloy will respond at a lower temperature, but will require a longer time at said temperature in order to develop electrical conductivity substantially equal to that of an alloy having a lesser amount of cold deformation and a correspondingly lesser time at a higher heat treating temperature. Although the heating of Step (C) must be for at least 20 minutes the maximum time of heating is not especially critical but generally, although not necessarily, is about 48 hours.

In general, in accordance with the present invention, electrical conductivity values of the alloys of aluminum are raised to within the range of 57 percent to 64 percent IACS, and of commercial purity aluminum to the range of 62.5 to 64 percent IACS.

Following the aforementioned heat treatment of Step (C) and cooling of step (D) the alloy may then be further deformed, or reduced, to the desired gage at room temperature in order to develop the requisite tensile strength e.g., to a range of 37,000 to 55,000 psi., since the alloy is now essentially annealed.

The present invention thus provides for a high conductivity material more nearly comparable to high purity aluminum and, if desired, coupled with improved strength for application wherein high strength is requisite.

The present invention will be more readily apparent from a consideration of the following illustrative examples:

EXAMPLE I

A 2 .times. 2 .times. 7 inches billet containing 0.49 percent copper, 0.17 percent iron, 0.06 percent silicon -- by analysis in weight percent, was cast, solution heat treated at 1150.degree.F for 2 hours and water quenched. The as-cast solution heat treated billet had a conductivity of 57.5 percent IACS measured on a Magnatest FM-100 Conductivity Meter. The as-cast solution heat treated billet was then processed to determine the properties attainable by normal processing, i.e., the billet was then cold rolled down to 3/8 inch diameter redraw rod with the only heating being that which is normally evolved during cold working, and then drawn durther to 0.145 inch diameter wire--a total reduction of 99.6 percent from the casting. At this reduction the wire had a conductivity of only 56.67 percent IACS (measured on a Kelvin Bridge) and a UTS of 47,000 psi.

EXAMPLE II

A 2 .times. 2 .times. 7 inches billet containing 0.48 percent copper, 0.15 percent iron, 0.06 percent silicon -- by analysis in weight percent, was cast, solution heat treated at 1150.degree.F for 2 hours and water quenched. The as-cast solution heat treated billet had a conductivity of 57.5 percent IACS measured on a Magnatest FM-100 Conductivity Meter. The as-cast solution heat treated billet was processed according to the invention as follows: the billet was cold rolled 77 percent in four passes to a hexagonal-shaped rod with a cross sectional area equivalent to a diameter of 1.08 inch. The cold work reduced the conductivity to 55.7 percent IACS. The cold worked rod was then heat treated at 525.degree.F for 25 hours and water quenched. This treatment caused the conductivity to increase to 59.4 percent IACS. After cooling, the alloy was then cold rolled to 3/8 inch diameter redraw rod with the only heating being that which is normally evolved during cold working, and then drawn to 0.145 inch diameter wire and tested.

This wire had a conductivity of 59.96 percent IACS (measured on a Kelvin Bridge) and a UTS of 37,600 psi at this gage.

Additional wire was drawn to 0.064 inch diameter and tested. This data indicates that for a cold reduction of 99.6 percent, i.e., that achieved in reducing a 2.25 inch diameter casting to 0.145 inch diameter wire, the wire had a conductivity of 59.5 percent IACS and a UTS of 47,000 psi.

EXAMPLE III

A 2 .times. 2 .times. 7 inches billet containing 0.40 percent magnesium, 0.10 silicon, 0.18 percent iron -- by analysis in weight percent, was solution heat treated at 1150.degree.F. 2 hours and water quenched. The as cast solution heat treated billet had a conductivity of 56.1 percent IACS measured on a Magnatest FM-100 Conductivity Meter. The as-cast solution heat treated billet was then processed to determine the porperties attainable by normal processing, i.e., the billet was cold rolled to 3/8 inch diameter redraw rod with the only heating being that which is normally evolved during cold working, and then a section was drawn to 0.145 inch diameter wire (a reduction of 99.6 percent) and tested. It had a conductivity of only 55.9 percent IACS (measured on a Kelvin Bridge) and a UTS of 42,400 psi.

EXAMPLE IV

A section of the 3/8 inch diameter redraw rod as described in Example III was then drawn to 0.325 inch diameter rod (97.9 percent reduction from the casting). The drawn 0.325 inch diameter rod had conductivity of 56.40 percent IACS (measured on a Kelvin Bridge). The rod was then further processes according to the invention as follows: the rod was given an intermediate temperature heat treatment of 650.degree.F for 100 minutes and water quenched. This treatment raised the conductivity to 60.12 percent IACS. The rod was then drawn to fine wire (between 0.145 inch and 0.064 inch diameters) and tested. The interpolated data indicates that for a 99.6 percent reduction, the alloy would have a conductivity of 58.7 percent IACS and a UTS of 45,600 psi.

EXAMPLE V

A 2 .times. 2 .times. 7 inches ingot containing 0.18 percent iron, 0.06 percent silicon, 0.015 percent boron, nominal composition in weight percent, balance essentially aluminum was heat treated at 740.degree.F for 4 hours and air cooled before processing according to this invention. After this treatment the ingot had a conductivity of 62.8 percent IACS when measured on a Magnatest FM-100 conductivity meter. The heat treated ingot was then cold rolled to 1.08 inch diameter rod. The conductivity after this 77 percent reduction was 62.3 percent IACS. The rod was then heated at 540.degree.F for 24 hours and cooled. The conductivity was found to increase to 63.9 percent IACS.

EXAMPLE VI

A 2 .times. 2 .times. 7 inches ingot containing 0.10 percent copper, 0.18 percent iron, 0.06 percent silicon nominal composition, in weight percent, balance essentially aluminum, had a conductivity of 60.0 percent IACS in the cast condition, measured on a Magnatest FM-100 conductivity meter. The ingot was homogenized at 1150.degree. F for 2 hours and water quenched. The conductivity after this treatment was 59.8 percent IACS. According to this invention the heat treated ingot was then cold rolled to 1.08 inch diameter rod (a reduction of 77 percent) in which condition it had a conductivity of 59.2 percent IACS. The cold rolled rod was then heat treated at 540 .degree.F for 24 hours. The rod was subsequently rolled and drawn 90 percent to 0.325 inch diameter rod when it had a conductivity of 61.8 percent IACS measured on a Kelvin Bridge.

EXAMPLE VII

A 2 .times. 2 .times. 7 inches ingot containing 0.20 percent magnesium, 0.18 percent iron, 0.6 percent silicon nominal composition in weight percent, balance essentially aluminum, had a conductivity of 58.3 percent measured on Magnatest FM-100 conductivity meter in the cast condition. The conductivity after the ingot was homogenized at 940.degree.F 8 hours and air cooled was 59.1 percent IACS. The heat treated ingot in accordance with this invention was then cold rolled 77 percent to 1.08 inches diameter after which the conductivity was reduced to 59.1 percent IACS. The cold rolled rod was then heat treated at 517.degree.F for 24 hours and subsequently conventionally rolled and drawn 98 percent to 0.145 inch diameter wire where the conductivity was 61.5 percent IACS measured on a Kelvin Bridge.

EXAMPLE VIII

As an example of the prior art for comparison to Example V, a 2 .times. 2 .times. 7 inches ingot of the composition of Example V was heat treated at 750.degree.F for 1/2 hour and then hot rolled in 13 passes without further heating to 3/8inch diameter redraw rod. At this diameter the alloy had a conductivity of 62.4 percent IACS measured on a Kelvin Bridge.

It is thus seen that the present invention readily provides for surprisingly increased electrical conductivity values which more closely approximate that of high purity aluminum as well as high strength, if desired.

This inventon may be embodied in other forms or carried out in other ways without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered as in all respects illustrative and not restrictive, the scope of the invention being indicated by the appended claims, and all changes which come within the meaning and range of equivalency are intended to be embraced therein.

Claims

What is claimed is:

1. A process for forming a high conductivity commercial purity aluminum or aluminum alloy conductor comprising:

A. providing a material selected from the group consisting of commercial purity aluminum and aluminum alloys containing at least one alloying addition in an amount from 0.1 to 1.5 percent, said alloying addition being selected from the group consisting of magnesium, copper, silicon and mixtures thereof, the total amount of said alloying additions not exceeding 3 percent;

B. cold deforming said material to rod at least 15 percent at a temperature below 500.degree.F;

C. heating said material for at least 20 minutes at a temperature from 400.degree.F to 800.degree.F, whereby nucleation occurs in the alloy and electrical conductivity is increased;

D. cooling said material; and

E. further deforming said alloy to wire at a temperature less than 500.degree.F.

2. A process according to claim 1 wherein said material is an aluminum alloy containing magnesium.

3. A process according to claim 1 wherein said material is an aluminum alloy containing copper.

4. A process according to claim 1 wherein said material is an aluminum alloy containing silicon.

5. A process according to claim 1 wherein said material is commercial purity aluminum.

6. A process according to claim 1 wherein said heating step (C) allows precipitation to approach equilibrium.

7. A process according to claim 1 wherein the resultant product has an electrical conductivity of from 57 to 64 IACS.