CA1037742A

CA1037742A - High iron aluminum alloy

Info

Publication number: CA1037742A
Application number: CA203,859A
Authority: CA
Inventors: Enrique C. Chia; Roger J. Schoerner
Original assignee: Southwire Co LLC
Current assignee: Southwire Co LLC
Priority date: 1973-07-23
Filing date: 1974-07-02
Publication date: 1978-09-05
Also published as: FR2238998A1; GB1475587A; DE2435456A1; IT1016955B; JPS5070895A; DE2435456B2

Abstract

ABSTRACT OF THE DISCLOSURE
An aluminium alloy conductor having an electrical conductivity of at least fifty-seven percent (57%) based on the International Annealed Copper Standard having increased ultimate elongation, ultimate tensile strength, creep strength, thermal stability, bendability and fatigue resistance when compared to conventional aluminum conductors. The aluminum alloy conductor can contain intermetallic constitutents consisting of: iron and aluminum and optionally silicon in varying ratios, in a concentration produced by the addition of from more than about 0.99 to about 2.50 weight percent iron to an alloy mass containing less than about 98.83 weight percent aluminum, from more than about 0.18 to about 0.40 weight percent silicon, and trace quantities of conventional impurities normally found within a commercial aluminum alloy.

Description

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BACKGROUND OF THE INVENTION

This invention relates to an aluminum alloy conductor having an acceptable electrical conductivity and improved elongation, bendability ` and tensile strength.
The use of various aluminum alloys (conventionally referred to as EC rod, wire, sheet, foil, plate, tube, and other electrical apparatus and parts) as conductors of electricity is well established in the art.
Such alloys characteristically have conductivities of at least fifty-seven percent (57~0) of the International Annealed Copper Standard (hereinaMer sometimes referred to as IACS) and chemical constituents consisting of a substantial amount of pure aluminum and small amounts of conventional impurities such as vanadium, copper, manganese, magnesium, zinc, boron, gallium, nickel, zirconium, chromium, beryllium and titanium.
The physical properties of prior aluminum alloy conductors have proven less than desirable in many applications. Generally desirable percent elongations have been obtained only at less than desirable tensile strengths and desirable tensile strengths have been obtainable only at less than desirable percent elongations. In addition, the bendability and fatigue resistance OI prior aluminum alloy conductors have been so low that prior conductors have been generally unsuitable for many otherwise desirable end applications.
; . . .Thus is becomes apparent that a need has arisen within the industry for an aluminum alloy electrical conductor which has both improved percent elongatioa and improved tensile strength, and also possesses , the ability to withstand numerous bends at one point and to resist fatigue during use of the conductor. Therefore, it is an object of the present ~.~
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invention to provide an aluminum alloy conductor having novel properties of increased ultimate elongation, ultimate tensile strength, improved bendability, high creep strength, high thermal stability, fatigue resistance, and acceptable electrical conductivity. These and other objects, features and advantages of the present invention will become apparent to those skilled in the art from a consideration of the following description of the invention.

STATEMENT OF THE INVENTION

In accordance with this invention, the present aluminum alloy electrical conductor is prepared from an alloy comprising less than about 98. 83 weight percent aluminum, more than about 0. 99 weight percent iron, and more than about 0.18 weight percent silicon. The aluminum content of the present alloy comprises from about 96. 20 to less than about 98. 83 weight percent with superior results being achieved when from about 97. 20 to about 98. 70 weight percent aluminum is employed. Preferably from about 97. 80 to about 98. 70 weight percent aluminum is employed.
~dvantageously, the iron content of the present alloy comprises from about 2. 50 weight percent to more than about 0. 99 weight percent with particularly superior results being achieved when from about 1.10 weight percent to about 2. 00 weight percent iron is employed. From more than about 0.18 to about 0. 40 weight percent silicon is employed in the present alloy with particularly superior results being achieved when from about 0. 20 weight percent to about 0. 30 weight percent silicon is employed.
The ratio between the percentage iron and the percentage silicon must be 2:1 or greater. Preferably the ratio between the percentage iron and ,.

~7742 the percentage silicon is 8:1 or greater. Thus, if the present aluminum alloy contains an amount of iron within the low area of the present range for iron content, the percentage of aluminum must be increased rather than increasing the percentage of silicon. It has been found that a properly processed conductor having aluminum alloy constituents which fall within the above-specified ranges, possesses acceptable electrical conductivity, improved tensile strength and ultimate elongation and in addition has the novel unexpected properties of surprisingly increased bendability, fatigue resistance, high creep strength and high thermal stability.

PREPARATION OF THE ALLOY
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~; The present aluminum alloy is prepared by initially melting and alloying aluminum with the necessary amounts of iron or other consti-tuents to provide the requisite alloy for processing. Typical impurities or trace elements are also present within the melt, with a total content of from about 0. 005 weight percent to about 0. 40 weight percent.
Advantageously the trace elements are present in a total content of less than 0. 20 weight percent. Preferably the individual impurities or trace elements can be present in amounts of about 0.10 weight percent or less. Of course, when adjusting the amounts of trace elements due consideration must be given to the conductivity of the final alloy since some trace elements affect conductivity more severely than others.
The typical trace elements include vanadium, copper, manganese, magnesium, zinc, boron, gallium, nickel, zirconium, chromium, beryllium, and titanium. If the content of titanium is relatively high .

, ~37742 (but still quite low compared to the alumirluln, ir~n and si]ic~n c~ntent), small amounts of boron may be added t~ ~ie up the excess titanium and keep it from reducing the conductivity of the condu~tor.

PROCESSING OF THE CONDUCTOR

After preparing the melt, the aluminum composition is preferably continuously cast into a continuous bar. The cast bar is then hot-worked in substantially that condition in which it is received from the casting machine. A typical hot-working operation comprises rolling the bar in - a rolling mill substantially immediately after being cast into a bar.
It should be understood that other methods of preparation may be employed to obtain suitable results, but preferable results are obtained with continuous processing. Other methods of preparation include conventional extrusion and hydrostatic extrusion, to obtain rod or wire directly; sintering an aluminum alloy powder to obtain rod, billet, slab, bar, or wire directly; casting rod, billet, slab, bar, or wire directly from a molten aluminum alloy; and conventionally casting aluminum ` alloy billet, slab, and bar which can be subsequently hot-worked to rod and drawn into wire.
One example of a continuous casting and rolling operation capable of producing continuous rod is as follows: A continuous casting machine serves as a means for solidfying the molten aluminum alloy metal to provide a cast bar that is conveyed in substantially the condition in which it solidified from the continuous casting machine to the rolling mill, which serves as a means for hot-forming the cast bar into rod or 1()37'~4Z
another hot-formed product in a manner which imparts substantial movement to the cast bar along a plurality of angularly disposed axes.
The continuous casting machine is of conventional casting wheel type having a casting wheel with a casting groove partially closed by an endless belt supported by the casting wheel and an idler pulley.
The casting wheel and the endless belt cooperate to provide a mold into one end of which the cast bar is emitted in substantially that condition in which it is solidified.
The rolling mill is of conventional type having a plurality of roll stands arranged to hot-form the cast bar by a series of deformations.
The continuous casting machine and the rolling mill are positioned relative to each other so that the cast bar enters the rolling mill substan-tially immediately after solidification and in substantially that condition in which it solidified. In this condition, the cast bar is at a hot-forming temperature within the range of temperatures for hot-forming the cast bar at the initiation of hot-forming without heating between the casting machine and the rolling mill. In the event that it is desired to closely control the hot-forming temperature of the cast bar within the conventional range of hot-forming temperatures, means for adjusting the temperature of the cast bar may be placed between the continuous casting machine and the rolling mill without departing from the inventive concept disclosed herein .
Thus, it will be understood that with this apparatus, cast aluminum alloy rod of an infinite number of different lengths is prepared by simul-taneous casting of the molten aluminum alloy and hot-forming or rolling the cast aluminum bar.

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The rod produced by the casting and rolling operations can be processed in a reduction operation designed to produce wire of various gauges. Preferably the rod can be reduced from about 40 to about 97 percent of its pre-reduction diameter. The unannealed rod (i. e., as rolled to F temper) is cold drawn through a series of progressively constricted dies, without intermediate anneals, to form a continuous wire of desired diameter. At the conclusion of this drawing operation, the alloy wire will have high tensile strength and low ultimate elongation, plus a conductivity that may be less than fifty-five percent (55%) of IACS.
The wire is then annealed or partially annealed to obtain the desired properties and cooled. At the conclusion of the annealing operation, it is found that the annealed alloy wire shows unexpectedly improved percent ultimate elongation, ultimate tensile strength, high creep strength, high conductivity, high thermal stability, bendability and fatigue resistance.
~he annealing operation may be continuous as in resistance annealing, induction annealing, convection annealing by continuous furnaces or radiation annealing by continuous furnaces, or preferably, may be batch annealed in a batch furnace. When continuously annealing, temperatures of about 450F to about 1200F may be employed with annealing times of about five minutes to about 1/10, 000 of a minute. Generally, however, continuous annealing temperatures and times may he adjusted to meet the requirements of the particular overall processing operation so long as the desired physical and electrical properties are achieve~. In a batch annealing operation, a temperature of approximately 310F ~o about 800F is employed with a residence time of about thirty (30) rr~inutes .

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to about twenty-four (24) hours. As mentioned with respect to con-tinuous annealing, in batch annealing the time and temperatures may be varied to suit the overall process so long as the desired properties are obtained. Simply by way of example, it has been found that the following ultimate tensile strengths in the present aluminum wire are achieved with the listed batch annealing temperatures and times.

TABLE I
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Tensile Strength Temperature Time (hrs. ) - (F) 15, 000 - 18, 000 650 3 18,000 - 21,000 550 3 21,000 - 24,000 520 3 24,000- 28,000 480 3 During the casting of this alloy, a substantial portion of the iron present in the alloy precipitates out of solution as constituents of iron and aluminum and optionally silicon; such as FeA13, FeA16, oC-Al-Fe-Si ., and ,B -Al-Fe-Si. A majority of the particles have an average length of from about 0. 30 microns to about 1. 70 microns and an average diameter of from about 0. 05 microns to about 0. 40 microns. Ihus, after casting, the bar contains a dispersion of particulate compounds in a super-saturated solid solution matrix. As the bar is rolled in a hot-working operation the particulate compounds are broken up and dispersed through-out the matrix inhibiting large cell formation. When the rod is drawn to its final gauge size without intermediate anneals the constituents are further dispersed and reduced in size. After aging in a final annealing operation, the tensile strength, elongation, creep strength, thermal - g_ :' :
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stability, fatigue resistance, conductivity and bendability, are increased due to the small cell size and the additional pinning of dislocations by preferential precipitation of the particulate compounds on the dislocation sites. Therefore, new dislocation sources must be activated under the applied stress of the drawing operation and this causes both the strength and the elongation to be further improved.
The properties of the present aluminum alloy conductor are . ~
significantly affected by the size of the particulate compounds in the matrix. Coarse precipitates reduce the percent elongation and benda-bility of the conductor by enhancing nucleation and thus, formation of large cells which, in turn, lowers the recrystallization temperature of the conductor. Fine precipitates improve the percent elongation and bendability by reducing nucleation and increasing the recrystallization temperature. Grossly coarse precipitates generally cause the conductor - to become brittle. Coarse precipitates are clearly visible under an optical microscope, i. e., above about 5000 A. ~,Candf~ FeAlSi are grossly course precipitates, FeA13 and ~eAl6 have particle sizes from about 25 A to about 5000 A.
A typical alloy No. 12 AWG wire of the l~resent invention has ph,ysical properties of at least 16, 000 psi tensile strength, u]timate elongation of 20%, conductivity of at least 58% IACS, and minilmum ~endability of about 15 bends to break. Ranges of physical prc)pertie~ ~ener~lly provided by No. 12 AWG wire prepared from the present alloy include ten~i]~ strengths of about 14, 000 to about 33, ûO0 psi, ultimate elongations ~ about 40% t~
about 5%, conductivities of about 58% to about 62% and number of bends to break of about 38 to 2.

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The aluminum alloy conductor of this invention can be in the form of rod, wire, sheet, foil, tube and the like, and can be used as connector parts in electrical apparatus and can be joined by conventional methods such as crimping, joining by pressure, soldering (with or without heat and flux), welding (with or without flux), ultrasonic welding, ultrasonic soldering, plasma heating, and other methods of joining electrical conductors .
A more complete understanding of this invention will be obtained from the following examples:

EXAMPLE I
A comparison between prior EC aluminum al]oy wire and the present aluminum alloy wire is provided by preparing a prior EC alloy with aluminum content of 99. 73 weight percent, iron content of 0.18 weight per-ent, silicon content of 0. 059 weight percent, and trace amounts of typical impurities. The present alloy is prepared with aluminum content of 98. 28 weight percent, iron content of 1. 40 weight percent, silicon content of 0. 25 weight percent, and trace amounts of typical impurities. Both alloys are continuously cast into continuous bars and hot-rolled into continuous rod in similar fashion. The alloys are then cold-drawn through successively constricted dies to yield #12 AWG continuous wire. Sections of the wire are collected on separate bobbins and batch furnace-annealed at various temperatures and for various lengths of time to yield sections of the prior EC alloy and the present alloy of varying tensile strengths. Several samples of each section are tested in a device designed to measure the .

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: ' number of bends required to break each sample at a particular flexure point. Through uniform force and tension, the device fatigues each sample through an arch of approximately 135. The wire is bent across a pair of spaced opposed mandrels having a diameter equal to that of the wire. The mandrels are spaced apart a distance of about one and one-half times the diameter of the wire. One bend is recorded after the wire is deflected from a vertical disposition to one extreme of the arc, and returned back to the original vertical disposition. The speed of deflec-tion, force and tension are substantially equal for all tested samples.
The results are as follows:

TABLE II
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EC Alloy Present Alloy Tensile No. of bends Ten8ile Average No. of Strength to break Strength bends to break 10,083 43 1/2 16,025 38 12, 788 24 18,500 30 13,480 21 1/2 22,300 22 14, 168 14 25,100 19 15,200 13 3/4 27,700 17 16, 100 11 30,100 12 17,125 9 3/4 33,200 9 18, 186 8 3/4 35, 000 3 23, 069 5 1/2 29, 309 4 As shown in Table II, the present all~y has a surprisingly improved property of bendability over conventional EC alloy.

Several samples of the present alloy #12 AWG wire and EC alloy #12 AWG wire, processed as previously specified, are then tested for .: . -11-:
~037~42 percent ultimate elongation by standard testing procedures. At the instant of breakage, the increase in length of the wire is measured.
The percent ultimate elongation is then figured by dividing the initial length of the wire sample into the increase in length of the wire sample.
The tensile strength of the wire sample is recorded as the pounds per square inch of cross-sectional diameter required to break the wire during the percent ultimate elongation test. The results are as follows:

TABLE II-A
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EC Alloy Present Alloy = .
Tensile Strength Percent Tensile Percent Ultimate Strength Ultimate Elongation Elongation .
10, 000 30. 5 15,500 14 . 12, 700 21. 16, 158 16 13, 500 14. 16,550 15 14, 200 11. 5 17J 200 15 15, 000 8. 18, 270 14 16, 500 3.5 19, 000 12 18, 300 2. 21,480 10 24, 600 7 28, 000 6 38, 000 3 ,.
As shown in Table II-A, the present alloy has a surprisingly improved property of percent ultimate elongation over conventional EC
alloy.
` EXAMPLES 2 THROUGH 7 .:
Six aluminum alloys are prepared with varying amounts of major constituents. Those alloys are reported in the following table:
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TABLE III

Example No. Percent Al Percent Fe Percent Si

2.. ,............. 99.73 0.18 0.059

3................ 98.58 0.99 0.40

4................ 98.39 1.15 0.38

5................ 98.06 1.50 0.33

6................ 97.89 1.79 0.27

7................ 97.70 2.00 0.22

8................ 97.25 2.50 0.18 :
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The six alloys are then cast into six continuous bars and hot-rolled into six continuous rods. The rods are cold-drawn through successively constricted dies to yield #12 gauge wire. The wire produced from the alloys of Examples 2 and 4 are resistance annealed to yield the tensile strengths reported in Table IV. After annealing each of the wires is tested for percent conductivity, tensile strength, and percent ultimate elongation by standard testing procedures for each, except that the procedure specified in Example 1 is used for determining average number of bends to break.
These results are reported in the following table:

TABLE IV

Example No. Conductivity in Tensile % Ultimate percent IACS Strength Elongation -- .
2............ 62. 80 12, 000 20 3............ 60. 08 15, 000 14 4............ 58. 15 14, 800 13 5............ 58. 20 14, 900 12 6............ 59. 90 16, 800 11 7............ 60. 15 16,400 10 8............ 59. 60 18, 000 10 : .. , " .' ' ^~

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From a review of these results, it may be seen that Example 2 falls outside the scope of the present invention in percentage of components.

An aluminum alloy is prepared with an aluminum content of 97. 70 weight percent, iron content of 2. 00 weight percent, silicon content of 0. 27 weight percent and trace amounts of typical impurities. The alloy is cast into a continuous bar which is hot-rolled to yield a continuous rod.
The rod is then cold-drawn through successively constricted dies to yield ~12 AWG wire. ~he wire is collected on a 30 inch bobbin until the collected wire weighs approximately 250 pounds. The bobbin is then placed in a cold General Electric Bell Furnace and the temperature therein is raised to 480F. The temperature of the furnace is held at 480F for three hours after which the heat is terminated and the furnace cools to 40CF.
The furnace is then quick cooled and the bobbin is removed. Under testing it is found that the alloy wire has a conductivity of 58. 8(~o IACS, a tensile strength of 16, 800 psi, a percentage of ultimate elongation of ll(~o and a number of bends to break of 18.
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Example 8 is repeated except the Bell Furnace temperature is raised to 500F, and held for three hours prior to cooling. The annealed alloy wire has a conductivity of 58. 8% IACS, a tensile strength of 16, 000 psi, a percentage of ultimate elongation of 12%, and a number of bends to break of 22.
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EgAMPLE 10 Example 8 is repeated except the Bell E~urnace temperature is raised to 600F and held for three hours prior to cooling. The annealed alloy wire has a conductivity of 59. 2% IACS, a tensile strength of 16,100 psi, a percentage of elongation of 14%, and a number of bends to break of 26.

EXAM PI.E 11 Example 8 is repeated except the Bell Furnace temperature is raised to 600E and held 1 1/2 hours prior to cooling. The annealed alloy has a conductivity of 59. 25% IACS, a tensile strength of 16, 900 psi, a percentage of elongation of 16%, and a number of bends to break of 23.
' ` ~he alloy of Example 8 is cast into a continuous bar which is hot-rolled to yield a continuous F temper rod of 3/8 inch diameter. The rod is then cold-drawn through successively constricted dies to yield #14 AWG wire. The wire is then redrawn on a Synchro Model BG-16 wire drawing machine which includes a Synchro Resistoneal continuous in line annealer. The wire is drawn to #28 AWG at a finishing speed of 3, 300 feet per minute and the in line annealer is operated at 52 volts with transformer tap setting at No. 8. The annealed alloy wire has a conducti-vity of 58. 9% IACS, a tensile strength of 16, 400 psi, and a percentage of ultimate elongation of 18%. Since the wire gauge is so small the number of bends to break is extremely large.

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The alloy of Example 8 is cast into a continuous bar which is hot-rolled to yield a continuous F temper rod of 3/8 inch diameter.
; The rod is then cold-drawn on a Synchro Style No. FX13 wire drawing machine which includes a continuous in line annealer. The rod is drawn to a #12 AWG wire at a finishing speed of 2, 000 feet per minute and the in line annealer voltage at preheater #1 is 35 volts, at pret!eater #2 is 35 volts, and at the annealer is 22 volts. The three transformer taps are set at #5. The annealed alloy wire has a conductivity of 59. 0~0 IACS, ; 10 a tensile strength of 16, 800 psi, and a percentage of ultimate elongation of 17%-- For the purpose of clarity, the following terminology used in this application is explained as follows:
Rod--A solid product that is long in relation to its cross-section.
Rod normally has a cross-section of between three inches and 0. 375 inches.
Wire--A solid wrought product that is long in relation to its cross-section which is square or rectangular with sharp or rounded corners or ; edges, or is round, a regular hexagon or a regular octagon, and whose diameter or greatest perpendicular distance between parallel faces is between 0. 374 inches and 0. 0031 inches.
Foil--Metal in sheet form less than 0. 006 inches in thickness.
Sheet--A flat-rolled metal product of a maximum thickness and minimum width arbitrarily dependent on the type of metal, thinner than plate, thicker than foil.

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1~37 B 42 Plate--A flat-rolled metal product of a minimum thickness and width arbitrarily dependent on the type of alloy and/or application.
While this invention has been described in detail with particular . reference to preferred embodiments thereof, it will be understood that variations and modifications can be effected within the spirit and scope of the invention as hereinbefore described and as defined in the appended claims.
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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An aluminum alloy conductor characterized in having a minimum conductivity of fifty-seven percent (57%) IACS and consisting essentially of from more than about 0.99 to about 2.50 weight percent iron; from more than about 0.18 to about 0.40 weight percent silicon; and from about 0.005 to about 0 40 total weight percent trace elements selected from the group consisting of vanadium, copper, manganese, magnesium, zinc, boron, gallium, nickel, zirconium, chromium, beryllium and titanium; and from about 96.20 to less than about 98.83 weight percent aluminum

2. The aluminum alloy conductor of claim 1 characterized in a preferred form by consisting essentially of from 1.10 to about 2.00 weight percent iron; from about 0.20 to about 0.30 weight percent silicon; and from about 97.20 to about 98.70 weight percent aluminum.

3. The aluminum alloy conductor of claim 1 characterized by having a total trace element content of less than 0.20 weight percent.

4. The aluminum alloy conductor as claimed in Claim 1, 2 or 3 characterized by having less than about 0.10 weight per-cent magnesium, less than about 0.10 weight percent manganese and less than 0.10 total weight percent other associated trace elements.

5. The aluminum alloy conductor as claimed in claim 1, 2 or 3 characterized by the fact that the alloy includes particulate constituents of said aluminum, iron and silicon having an average length of from about 0.30 microns to about 1.70 microns and an average diameter of from about 0.05 microns to about 0.40 microns.

6. The aluminum alloy conductor as claimed in claim 1, 2 or 3 characterized by having less than about 0.108 percent magnesium, less than about 0.108 percent maganese and less than 0.10 total weight percent other associated trace elements while including particulate constituents of said aluminum, iron and silicon having an average length of from about 0.30 microns to about 1.70 microns and an average diameter of from about 0.05 microns to about 0.40 microns.

7. The aluminum alloy conductor as claimed in claim 1, 2 or 3 characterized by the fact that the conductor is cold-drawn to finished wire size without intermediate or preliminary anneals whereby the wire has improved electrical and physical properties.

8. The aluminum alloy conductor as claimed in claim 1, 2 or 3 characterized by having less than about 0.108 percent magnesium, less than about 0.108 percent maganese and less than 0.10 total weight percent other associated trace elements while including particulate constituents of said aluminum, iron and silicon having an average length of from about 0.30 microns to about 1.70 microns and an average diamater of from about 0.05 microns to about 0.40 microns and by the fact that the conductor is cold-drawn to finished wire size without intermediate or preliminary anneals whereby the wire has improved electrical and physical properties.