Note: Descriptions are shown in the official language in which they were submitted.
~4'73~
BACKGROUND OF THE_lNVENTION
The present invention relates to an improved
aluminum alloy electrical conductor, and the continuous
method of production thereof in the form of a rod or wire.
Aluminum base alloys are f inding wider
acceptance in the marketplace of today because of their
light weight and low cost. One area where aluminum alloys
have found increasing acceptance is in the replacement of
copper in the manufacture of electrically con,ductive wire.
Conventional electrically conductive aluminum alloy wire
(referred to as EC) contains a substantial amount of pure
aluminum and trace amounts of impurities such as silicon,
vanadium, iron, copper, manganese, magnesium, zinc, boron,
and titanium.
Even though desirabla in terms of weight and
cost, aluminum alloys have received far less than complete
acceptance in the electrical conductor marketplace. One
of the chief reasons for the lack of complete acceptance
is the range of physical properties available with con-
ventional EC aluminum alloy conductors. If the physical
properties, such as thermal stability, tensile strength,
percent elongation, ductility and yield strength, could be
improved significantly without substantially lessening the
electrical conductivity of the finished product, a very
desirable improvement would be achieved. It is accepted,
however, that addition of alloying elements, as in other
aluminum alloys, reduces conductivity while improving the
phy~ical properties. Consequently, only these additions
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~ID6~ 3~
of elements which improve phy~ical properties without
substantially lessening conductivity will yield an
acceptable and useful product.
In applicant's prior Canadian Patent
ApplicationSerial No. 143~514, Filed May 31J 1972,
there is disclosed a new aluminum alloy electrical con-
ductor which was formulated to yield improved physical
properties with acceptable electrical conductivity. The
aluminum base alloy was prepared by mixing nickel, iron
and optionally other alloying elements with aluminum in
a furnace to obtain a melt having requisite percen*ages
of elements. It was found that suitable results were
obtained with nickel present in a weight percentage of
from about 0.20 percent to about 1.60 percent. Superior
results were achieved when nickel was present in a weight
percentage of from about 0.50 percent to about 1.00 percent
and particularly superior and preferred results were
obtained when nickel was present in a percentage by weight
of from about 0.60 percent to about 0.80 percent.
Suitable results were obtained with iron
present in a weight percentage of from about 0.30 percent
to about 1.30 percent. Superior results were achieved when
iron was present in a weight percentage of from about 0.40
percent to about 0.80 percent and particularly superior
and preferred results were obtained when iron was present
in a percentage by weight of from about 0.45 percent to
about 0.65 percent.
The aluminum content of the alloy of the afore
mentioned patent document could vary from about 97.00 per-
cent to about 99.50 percent by weight with superior resultsbeing obtained with the aluminum content between about
97.~0% and about 99.20% by weight. Since the percentage for
maximum and minimum aluminum did not correspond with the
maximums and minimums for alloying elements, it was apparent
that suitable results were not obtained if the ma~imum
percentages for all alloying elements were employed. If
commercial aluminum was employed in preparing the melt, it
was preferred that the aluminum prior to adding to the melt
in the furnace, contain no more than 0.10 percent total of
trace impurities.
Optionally the alloy of the aforementioned
patent document could contain an additional alloying element
or group of alloying elements. The total concentration of
the optional alloying elements could be up to about 2.00
percent by weight; preferably from about 1.10 percent to
about 1.50 percent by weight. Particularly superior and
preferred results were obtained when from about 0.10 percent
to about 1.00 percent by weight of total additional alloying
elements was employed; particularly if at least one element
is selected from the sub group of magnesium, niobium,
tantalum, silicon and zirconium.
Additional alloying elements included the
following:
ADDITIONAL ALLOYING ELEMENTS
.
Magnesium Cesium Dysprosium
Cobalt ~ttrium Terbium
Copper Scandium Erbium
Silicon Thorium Neodynium
Zirconium Tin Indium
Cerium Zinc Boron
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Niobium Bismuth Thallium
Hafnium Antimony Rubidium
Lanthanum Vanadium ~itanium
Tantalum Rhenium Carkon
Other elements could be present in trace
amounts provided that they did not adversely affect the
mechanical, electrical and physical properties of the
product.
Superior results were obtained with the
following additional elements:
PREFERRED ADDITIONAL ALLOY:l:NG ELEMENTS
Magnesium Zirconium Scandium
Cobalt Niobium Thorium
Copper Tantalum Rare Earth Metals
Silicon Yttrium Carbon
Particularly superior and preferred results
were obtained with the use of cobalt or magnesium as the
additional alloying element. Suitable results were obtained
with magnesium or cobalt in a percentage range of from about
0.001% to about 1.00~ by weight with superior results being
obtained when from about 0.025% to about 0.50~ by weight
was used. Particularly superior and preferred results
were obtained when from about 0.03% ko about 0.10% by weight
of magnesium or cobalt was employed.
While the method of the aforementioned patent
specification yielded an aluminum alloy electrical conductor
product having improved physical properties as compared
with conventional EC aluminum alloy conductors, while main-
~6~'73~3
taining comparable electrical conductivityj it did nothave sufficient ductility to facilitate the continuous
processing steps, nor to yield a finished wire product
having satisfactory elongation characteristics. In par-
ticular, the cast bar would tend to split and crack durinc
the continuous rolling and cold-drawing thereof, and the
wire product often contained intermetallic compound pre-
cipitates which, subsequent to cold-drawing of the product,
exhibited an insufficient ductility.
STATEMENT OF THE INVENTION
In view of the foregoing, it should be
apparent that a need still exists in the art for a method
of preparing an aluminum alloy conductor that will improve
the ductility of the product manufactured by the process
of the aforementioned patent specification, so that such
product can be continuously rolled and cold-drawn without
splitting and cracking,and so that the wire product will
have an elongation of at least 12~ when measured as a
No. 10 A.W.G. wire in the fully annealed condition.
In order to accomplish the foregoing, it has
been determined in accordance with this invention that the
additional alloying elements specified in the aforementioned
patent specification must be very closely controlled, with-
in predetermined limits, specifically the copper, magnesium
and silicon. Thus, there is provided in accordance with
this invention a method of preparing an aluminum alloy
conductor having a minimum conductivity of at least 58
percent IACS, good thermal stability, a tensile strength of
73~
at least 12,000 psi, and a yield strength of at least
8,000 psi when measured as a fully annealed wire, comprising:
(a) Alloying from 0.20 to 1.60 weight
percent nickel, from 0.30 to 1.30 weight percent iron, up
to a total of 2.00 wPight percent of additional alloying
elements including copper, magnesium and silicon, and from
about 97.00 to about 99.50 weigbt percent aluminum with
associated trace elements;
(b) Casting the alloy in a moving mold
formed between a groove in the periphery of a rotating
casting wheel and a metal belt lying adjacent said groove
for a portion of its length;
(c) Hot rolling the cast alloy substan-
tially immediately after casting while the cast alloy is in
substantially that condition as cast to form a continuous
rod; and
(d~ Drawing the rod through wire-drawing
dies, without any preliminary or intermediate anneals
between dies, to form wire of finish gauge size;
characterized in that in order to improve
the ductility of the product the copper content of the alloy
is maintained at less than 0.~5 weight percent, thereby
inhibiting the formation of cuprous oxide particles and
thus permitting continuous rolling and drawing without
splitting and cracking of the product.
The present invention is further characterized
in that in order to further improve the ductility of the
product the magnesium content of the alloy i5 maintained
~ :lt6~3~3
at les than 0.1 weight percent whan the silicon exceeds
0.15 weight percent, thereby yi~lding a wire having an
elongation of at least 12 percent when measured as a
No. lO A.W.G. wire in the fully annealed condition.
As expressed above, it has heen determined
in accordance with this invention that the copper content
must be very closely controlled, within the range specified
above, in order to permit continuous processing of the
product. Although copper is an effective hardening element,
if more than 0.05% copper is present in the alloy of this
invention, it will form extremely hard cuprous oxide par-
ticles that will result in splitting and cracking when the
continuously processed product is rolled and cold drawn.
Since a conventionally processed product can be homogenized
prior to rolling to refine the grain structure, the copper
content thereof need not be so closely controlled. However,
when the product is continuously processed in accordance
with the instant invention, the cast bar is substantially
immediately rolled in the as-cast condition and thus does
not have the benefit of an homogenizing step. Consequently,
the copper content o~ the alloy must be closely controlled
to avoid the brittleness which leads to splitting and crack-
ing of the bar when processed according to the method of
this invention.
Similarly, as expressed above, it has been
determined in accordance with this invention that the sili-
con and magnesium contents must also be very closely
controlled. In particular, when the silicon exceeds 0.15
percent, the magnesium must be limited to less than 0.1
-- 8 --
~36~73~
percent; ot~erwise, the product w~ll exhibit an insufficient
ductility subsequent to cold drawing, if the product was
previously con~inuously cast and rolled.
After preparing the melt in the manner des-
cribed in the aforementioned patent specification, with the
copper, magnesium and silicon controlled in accordance with
the present invention, the aluminum alloy is continuously
cast into a continuous bar by a continuous casting machine
and then substantially immediately thereafter, hot-worked
in a rolling mill to yield a continuous aluminum alloy rod.
An example of a continuous casting and rolling operation
capable of producing continuous rod as specified in this
application is disclosed in the aforementioned patent speci-
fication.
To produce wire of various gau~es, the
continuous rod produced by the casting and rolling operation
is processed in a reduction operation. The unannealed rod
(i.e., as rolled to f temper) is cold-drawn through a series
of progressively constricted dies, without preliminary
or intermediate anneals, to ~orm a continuous wire of
desired diameter. It has been found that the elimination
of intermediate anneals improves the physical properties
of the wire. Processing with intermediate anneals is
acceptable when the requirements for physical properties of
the wire permit reduced values. The conductivity of the
hard-drawn wire is at least 57 percent IACS. If greater con-
ductivity or increased elongation is desired, the wiremay be annealed
or partially annealed after the desired wire size is ob-
tained and cooled. Fully annealed wire has a conductivity
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of at least 58 percent IACS. At the conclusion of the
drawing operation and optional annealing op~ration, it is
found that the alloy wire has the properties of improved
tensile strength and yield strength together with improved
thermal stability, percent ultimate elongation and in-
creased ductility and fatigue resistance as specified previ-
ously in this application. The 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 furnaceO 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 be adjusted to meet
the xequiremenets of the particular overall processing
operation so long as the desired physical properties are
achieved. In a batchannealing operation, a temperature of
approximately 400F to about 750F is employed with resi-
,~,
dence times of about thirty (30) minutes to about twenty-
four (24) hours. As mentioned with respect to continuous
annealing, in batch annealing the times and temperatures
may be varied to suit the overall process so long as the
desired physical properties are obtained.
It has been found that the properties of a No.
10 A.W.G. f~lly annealed soft wire of the present alloy vary
between the following fig~lres:
Tensile ~ield
Conductivity Strength psi Elongation Strength psi
58% - 63~ 12,000~24,000 12~ - 30%8,000-18,000
-- 10 --
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~ more complete understanding of the invention
will be obtained from the following example:
EXAMPLE NO. 1.
Various melts were prepared by adding the re-
~uired amount of alloying elements to 1816 grams of molten
aluminum, containing less than 0.10% trace element ~rities,
to achieve a perc~ntage concentration of elements as shown
in the accompanying table; the remainder being aluminum.
Graphite crucibles are used except in those cases where khe
alloying elements are known carbide formers, in which cases
aluminum oxide crucibles are used. The melts are held for
sufficient times and at sufficient temperatures to allow o
plete solubility of the alloying elements with the base
aluminum. An argon atmosphere is provided over the melt ~o
provide oxidation. Each melt is continuously cast on a con
tinuous casting machine and immediately hot-roll~d through a
rolling mill to 3/8 inch continuous rod. The hard rod was
then cold drawn, without any preliminary or immediate anneals,
into 0~1019 inch, 10 gauge A.W.G. wire. The wire was then
given a final anneal for five hours at 650F resulting in
soft wire.
The types of alloys employed and the results
of the tests performed thereon are as follows:
TABLE 1.
; Ni Fe UTS % Elong. ~ IACS
_
.30 1.00 17,500 12.5 60.40
.80 .70 18,300 25.6 59.73
1.00 .60 17,900 26.1 59.97
. ~
1.50 .40 17,800 24.8 ~3.52
~ r___;~ ~1 ....... . . . . _.. _ _ , _ _ _ __ _
~ 11 ~
3~
% Elong. = Percent Ultimate Elongation
UTS - Ultimate Tensile Strength
% IACS = Conductivity
EX~MPLE NO. 2.
An additional alloy melt was pxepared accord-
: ing to Example No. 1 so that the composition was as follows
in weight percent:
Nickel - 0.60%
Iron - 0.90%
Magnesium - 0.15~
Aluminum - Remainder
The melt was processed to a No. 10 gauge soft wire. The
. physical properties of the wire were as follows:
;~~ Ultimate Tensile Strength - 18,200 psi
~'! Percent Ultimate E:Longation - 25.2%
Conductivity - 59.10% IACS
EXAMPLE NO~ 3.
An additional alloy melt was prepared according
to Example No. 1 so that the composition was as follows in
weight percent:
Nickel - 0.40%
Iron - 1.10%
Aluminum - Remainder
. The melt was processed to a No. 10 gauge soft wire. The
physical properties of the wire were as follows:
Ultimate Tensile Strength - 17,400 psi
Percent Ultimate Elongation - 14.1%
Conductivity - 60.30% IACS
'
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EXAMPLE NO. 4.
An additional ~lloy melt was prepared accord-
ing to Example ~o. 1 so that the composition was as follows
in weight percent:
Nickel - 1.60~
Iron - 0.30%
Aluminum - Remainder
The melt was processed to a No. 10 gauge soft wire. The
physical propertie~ of the wire were as follows:
Ultimate Tensîle Strength - 17,200 psi
Percent Ultimate Elongation - 27.5%
Conductivity - 59.1% IACS
EXAMPLE NO. 5.
~ An additional alloy melt was prepared accord-
: ing to Example No. 1 so that the composition was as follows
in weight percent:
~ Nickel - 0.20%
: Iron - 1.30%
Aluminum - Remainder
,~
The melt was processed to a No. 10 gauge soft wire. The
physical properties of the wire were as follows:
: Ultimate Tensile Strength - 17,500 psi
Percent Ultimate Elongation - 13.5%
Conductivity - 61.05% IACS
EXAMPLE NO. 6.
; An additional alloy melt was prepared accord-
ing to Example No. 1 so that the composition was as follows
in weight percent:
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Nickel - 0.80%
Iron - 0.45~
Cobalt - 0.10%
Aluminum ~ Remainder
The melt was processed to a No. 10 gaug~ soft wire. The
physical properties of the wire were as ~ollows:
Ultimate Tensile Strength - 17,850 psi
Percent Ultimate Elongation - 23.6%
; Conductivity - 59.8 IACS
Thxough testing and analysis of an alloy
containing 0.80 weight percent nickel, 0.30 weight percent
iron, and the remainder aluminum, it has been found that
the present aluminum base alloy after cold working includes
intermetallic compound precipitates. One of the compounds
is identified as nickel aluminate (NiA13) and the other is
identified as iron aluminate (FeA13). The nickel inter-
metallic compound is found to be very stable and e~pecially
so at high temperatures. The nickel compound also has a
.1
low tendency to coalesce during annealing of products
formed from the alloy and the compound is generally inco-
herent with the aluminum matrix. The mechanism of strength-
ening for this alloy is in par~ due to the dispersion of the
nickel intermetallic compound as a precipitate throughout
the aluminum matrix. The precipitate tends to pin disloca-
tion sites which are created during cold working of the
wire formed from the alloy. Upon examination of the nickel
intermetallic compound precipitate in a cold drawn wire, it
is found that the precipitates are oriented in the direction
.,
of drawing. In addition, it is found that the precipitates
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can be rod-like, plate-like, or spherical in configuration.
Other intermetallic compounds may also be
formed depending upon the corstituents of the melt and
the relative concentrations of the alloying elements. Those
intermetallic compounds include the following: Ni2A13,
2 5~ Co2Alg, Co4A113, CeA14, CeA12, VAlll, VA17,
VA16, Val3, Vall2, Zr3Al, Zr2Al, LaA14, A13Ni2, A12Fe5,
Fe3NiA110, Co2A15, FeNiAlg.
The iron aluminate intermetallic compound also
contributes to the pinning of dislocation sites during cold
working of the wire. Upon examination of the iron inter-
metallic compound precipitate in a cold drawn wire, it is
found that the precipitates are substantially evenly dis-
tributed through the alloy and have a particle size of less
than 1 micron. If the wire is drawn without any inter-
mediate anneals, the particle size of the iron intermetallic
compounds is less than 2,000 angstroms.
A charact~ristic of high conductivity aluminum
alloy wires which is not indicated by the historical tests
for tensile strength, percent elongation and electrical
conductivity is the possible change in properties as a
result of increases, decreases, or fluctuations of the tem-
perature of ~he strands. It is apparent that the maximum
operating temperature of a strand or series of strands will
be affected by this temperature characteristic. The charac-
teristic is also quite significant from a manufacturing
viewpoint since many insulation processes require high
temperature thermal cures.
It has been found that the aluminum alloy wire
31 3
of the present invention has a characteristic of thermal
stability which exceeds the thermal stability of convention-
al aluminum alloy wires.
For the purpose of clarity/ the following
terminology used in this application is explained as
follows:
Aluminum alloy rod - A solid product that
is long in relation to its cross-section. Rod normally
has a cross-section of between three inches and 0.375inches.
Aluminum alloy 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.
While this invention has been described in
detail with particu].ar reference to preferred embodiments
thereof, it will be understood that variations and modifi- -
cations can be effected within the spirit and scope of the
invention as described hereinbefore and as defined in the
appended claimS.
., ,~ .
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