Method for manufacturing an aluminum alloy electrical conductor

This disclosure relates to a method and apparatus for manufacturing an aluminum alloy electrical conductor which promote the formation of a wire having a fine, stable subgrain structure of small cell size in the aluminum matrix and a fine dispersion of stable, insoluble intermetallic phase particles. The subgrain structure is improved by closely controlling the thermomechanical processing, particularly the casting rate, deformation parameters and annealing characteristics. After casting, the cast product is substantially immediately hot-formed in a rolling mill wherein the first deformation is more than 30% such that a substantially well defined subgrain structure will be formed in the aluminum matrix, thereby maximizing a refinement of the subgrain structure by permitting breaking-up thereof in each of the subsequent deformations in the rolling mill. After cold-working, without preliminary or intermediate anneals, the product is finally annealed at a temperature not exceeding approximately 700.degree. F.

BACKGROUND OF THE INVENTION 
This invention relates to a method and apparatus for manufacturing an 
aluminum alloy wire that is particularly suitable for use in conducting 
electricity. The wire produced by the method and apparatus of this 
invention has improved properties of yield strength, ultimate tensile 
strength, percent ultimate elongation, ductility, fatigue resistance and 
creep resistance as compared with conventional aluminum alloy electrical 
conductors of similar electrical properties. 
In recent years the use of aluminum as an electrical conductor has 
increased significantly. An electrical grade conductor with a minimum of 
99.45% aluminum was first used for overhead transmission lines in the 
early 1890's and has been used extensively since then with great success. 
There are other electrical applications where aluminum could be used only 
if certain physical and mechanical properties are achieved. These include 
building wire, telephone cable, battery cable, automotive harness wiring, 
aircraft cable, transformer wire, magnet wire and appliance cord. 
Inspection of these uses indicates that a material which possesses high 
strength and a high degree of connectability, coupled with a minimum loss 
in electrical conductivity, would be required for successful performance. 
Electrical Conductor grade aluminum, in the fully annealed condition, 
possesses acceptable ductility and electrical conductivity. However, it is 
seriously handicapped by its poor mechanical properties and thermal 
stability. This precludes its use in applications where a strong, reliable 
connection is required. The connection or termination of the system is one 
of the most critical parts of any electrical system. The termination or 
connection is also the part that is handled by the public, and 
consequently is very often subjected to careless or poor workmanship. An 
ideal system would consist of conductor and termination designed in such a 
way that it would produce a "fool proof" system. 
One of the integral components of the system, the conductor itself, could 
be made stronger and with high thermal stability simply by alloying the 
aluminum with magnesium, silicon, copper, etc., as has been done in the 
past for many structural applications. However, the decrease in electrical 
conductivity associated with the high solubility of these alloying 
additions prohibits their use in electrical conductor aluminum in more 
than very small amounts. Another way that the mechanical properties of the 
aluminum can be increased is to subject it to a certain amount of cold 
work in order to produce extensive work hardening in the matrix. This 
method, however, will render the aluminum unusable as it yields an 
unstable cold worked structure with both low ductility and extremely low 
thermal stability. 
A method for improving the physical properties of an aluminum alloy without 
seriously affecting the electrical properties thereof was disclosed in 
U.S. Pat. No. 3,920,411 of which copending application Ser. No. 632,982, 
abandoned was a continuation-in-part. The method disclosed therein 
consisted of alloying from about 0.35 to about 4.0 weight percent cobalt, 
from about 0.1 to about 2.5 weight percent iron, the remainder being 
aluminum with associated trace elements, and thereafter continuously 
casting, hot-working, cold-working without preliminary or intermediate 
anneals, and thereafter annealing the product to achieve an electrical 
conductivity about 61% IACS and improved mechanical properties as compared 
with conventional electrical conductors. 
It is an object of this invention to yet further improve the mechanical 
properties of an aluminum alloy electrical conductor by more closely 
controlling the thermo-mechanical processing steps broadly disclosed in 
the aforementioned U.S. Pat. No. 3,920,411, thereby obtaining a fine, 
stable cell structure in the aluminum matrix containing a fine dispersion 
of stable, insoluble intermetallic phase particles. 
It has been known for some time that aluminum and its alloys develop a 
well-defined cell structure when subjected to various degrees of 
deformation. This is attributed to the high stacking fault energy of 
aluminum which by the prevention of dislocations splitting into partials, 
aids in the cross-slip process necessary for subgrain formation. During 
deformation, the dislocation density increases and well-defined cells are 
formed until an equilibrium cell size and dislocation density is reached. 
Moreover, the prior art has long recognized that the strength of metal is 
inversely proportional to the size of the grains therein. The effect of 
grain size on the yield strength of metal was first studied by Hall in 
1951 and Petch in 1953 in iron. Their experimental results could be 
described by a relationship of the type 
EQU .sigma.=.sigma..sub.o +k d.sup.-1/2 
where .sigma. is the yield strength, .sigma..sub.o the frictional stress, 
and d the grain size. Several investigations have been carried out on the 
effect of subgrain size on the yield strength of different materials and 
also found it to obey a Hall-Petch type relation. 
Because of the tendency of subgrains to coalesce during recovery and 
recrystallization, thereby growing in size and thus promoting a decrease 
in the yield strength of the metal, the prior art recognized that it would 
be advantageous to provide intermetallic precipitates in the aluminum 
matrix which could pin dislocation sites between adjacent subgrain 
boundaries, thereby immobilizing the grain boundaries by hindering the 
rearrangement of dislocations and therefore inhibiting the movement of the 
recrystallization front. Accordingly, such precipitates, as discussed in 
the aforementioned U.S. Pat. No. 3,920,411, could effectively limit the 
subgrain growth and thus render the physical properties of the metal more 
stable at elevated temperatures. 
As previously mentioned, the conductor of the aforementioned U.S. Pat. No. 
3,920,411 is formulated from an aluminum based alloy prepared by mixing 
cobalt, iron and optionally other alloying elements with aluminum in a 
furnace to obtain a melt having requisite percentages of elements. The 
aluminum content of the alloy could vary from about 93.50 percent to about 
99.65 percent by weight. The optional alloying element or group of 
alloying elements could be present in a total concentration of up to 2.50 
percent by weight, preferably from 0.1 percent to about 1.75 percent by 
weight. 
After preparing the melt, the aluminum alloy was 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. 
As further described in the aforementioned patent, a continuous casting 
machine serves as a means for solidifying 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 
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 in its periphery which is 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 molten metal is poured to solidify and from the 
other 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 substantially 
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 tempertures 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. 
The roll stands each include a plurality of rolls which engage the cast 
bar. The rolls of each roll stand may be two or more in number and 
arranged diametrically opposite from one another or arranged at equally 
spaced positions about the axis of movement of the cast bar through the 
rolling mill. The rolls of each roll stand of the rolling mill are rotated 
at a predetermined speed by a power means such as one or more electric 
motors and the casting wheel is rotated at a speed generally determined by 
its operating characteristics. The rolling mill serves to hot-form the 
cast bar into a rod of a cross-sectional area substantially less than that 
of the cast bar as it enters the rolling mill. 
The peripheral surfaces of the rolls of adjacent roll stands in the rolling 
mill change in configuration; that is, the cast bar is engaged by the 
rolls of successive roll stands with surfaces of varying configuration, 
and from different directions. This varying surface engagement of the cast 
bar in the roll stands function to knead or shape the metal in the cast 
bar in such a manner that it is worked at each roll stand and also to 
simultaneously reduce and change the cross-sectional area of the cast bar 
into that of the rod. 
As each roll stand engages the cast bar, it is desirable that the cast bar 
be received with sufficient volume per unit of time at the roll stand for 
the cast bar to generally fill the space defined by the rolls of the roll 
stand so that the rolls will be effective to work the metal in the cast 
bar. However, it is also desirable that the space defined by the rolls of 
each roll stand not be overfilled so that the cast bar will not be forced 
into the gaps between the rolls. Thus, it is desirable that the rod be fed 
toward each roll stand at a volume per unit of time which is sufficient to 
fill, but not overfill, the space defined by the rolls of the roll stand. 
As the cast bar is received from the continuous casting machine, it usually 
has one large flat surface corresponding to the surface of the endless 
band and inwardly tapered side surfaces corresponding to the shape of the 
groove in the casting wheel. As the cast bar is compressed by the rolls of 
the roll stands, the cast bar is deformed so that it generally takes the 
cross-sectional shape defined by the adjacent peripheries of the rolls of 
each roll stand. 
Thus, it will be understood that with this apparatus, cast aluminum alloy 
rod of an infinite number of different lengths is prepared by simultaneous 
casting of the molten aluminum alloy and hot-forming or rolling the 
cast-aluminum bar. 
According to the method described in the aforementioned patent, the 
continuous rod was cold-drawn through a series of progressively 
constricted dies, without intermediate anneals, to form a continuous wire 
of desired diameter. Thereafter, the wire was annealed or partially 
annealed to obtain a desired tensile strength and cooled. The annealing 
operation was disclosed as being continuous as in resistance annealing, 
induction annealing, convection annealing by continuous furnaces or 
radiation annealing by continuous furnaces, or, preferably, batch annealed 
in a batch furnace. 
In order to produce a product having improved percent ultimate elongation, 
increased ductuity and fatigue resistance, and increased electrical 
conductivity in accordance with the objects of the aforementioned patent, 
it was necessary to anneal at temperatures of about 450.degree. F. to 
about 1200.degree. F. when continuously annealing with annealing times of 
about 5 minutes to about 1/10,000 of a minute. On the other hand, when 
batch annealing, a temperature of approximately 400.degree. F. to about 
750.degree. F. was employed with resident times of about 30 minutes to 
about 24 hours. 
Prior art systems for the continuous production of rod from molten metal, 
i.e., systems where the cast bar is delivered substantially immediately to 
the rolling mill without an intervening homogenizing step such as 
described above, typically provide a reduction of less than 30% in the 
first stand of the rolling mill. Reduction of 20% and 25% are 
conventional. Upon observation, applicants have found that such a cast bar 
does not exhibit a clearly defined subgrain structure after that degree of 
deformation, but rather that the matrix is substantially free of subgrains 
and that at most there is a randomly disposed arrangement of very large 
ragged cells. 
While a well defined subgrain structure will, of course, be formed during 
subsequent deformations in prior art systems, the stock product rolled 
under such conditions is at a disadvantage because the subgrain structure, 
which becomes broken-up and refined when undergoing subsequent 
deformations, is deprived of the refining effects of the initial roll 
stands under which it exhibited an insufficiently-formed subgrain 
structure. Moreover, a stock product which does not exhibit a well defined 
subgrain structure after the first deformation undergoes a lesser degree 
of dynamic recrystallization in the hot-forming process than a stock 
product in which the subgrain structure is formed after the first 
deformation. This phenomenon is attributable to the fact that the product 
is moving at higher speeds and undergoing increased cooling in the latter 
stages of the rolling mill than in the early stages thereof. Consequently, 
if the subgrain structure is not sufficiently formed until after the speed 
and the cooling rate reach critical points, dynamic recrystallization will 
not take place. Accordingly, the ductility of the stock will be diminished 
and the finished product will have a lower elongation than a product which 
undergoes a greater degree of dynamic recrystallization during 
hot-forming. 
It is, therefore, an object of this invention to manufacture an aluminum 
alloy electrical conductor in a system which includes continuous casting 
and hot-forming in a series of deformities, and wherein a sufficient 
degree of deformation is provided in the first of the series of 
deformations so as to therein form a substantially well-defined subgrain 
structure in the stock product which will be broken-up and thus refined in 
subsequent deformations, and which will permit dynamic recrystallization 
of the product during hot-forming, thereby improving the ductility of the 
stock. 
In accordance with this invention, it has been determined that a reduction 
of more than 30% in the first roll stand is necessary to achieve the 
subgrain structure necessary to accomplish the foregoing. In a preferred 
embodiment of the invention the reduction is at least 37%.

SUMMARY OF THE INVENTION 
It has now been found, in accordance with this invention, that the subgrain 
structure of an aluminum alloy electrical conductor can be improved by 
more closely controlling the thermomechanical processing, particularly the 
casting rate, deformation parameters and annealing characteristics. In the 
exemplary embodiment of the invention described hereinafter, this 
processing was performed using an Al-Fe-Co alloy formulated in accordance 
with the following example. In general, however, the aluminum may be 
alloyed with any element or elements that will yield intermetallic 
precipitates and that will not decrease the electrical conductivity below 
58 IACS. Such additional alloying elements include the following: 
______________________________________ 
ADDITIONAL ALLOYING ELEMENTS 
______________________________________ 
Magnesium Yttrium Teribium 
Cobalt Scandium Erbium 
Iron Thorium Neodymium 
Nickel Tin Indium 
Copper Molybdenum Boron 
Silicon Zinc Thallium 
Zirconium Tungsten Rubidium 
Cerium Chromium Titanium 
Niobium Bismuth Carbon 
Hafnium Antimony 
Lanthanum Vanadium 
Tantalum Rhenium 
Cesium Dysprosium 
______________________________________ 
EXAMPLE 
Aluminum ingots with the chemical composition in Table 1 were melted in a 
reverberatory furnace. The metal was heated to 1350.degree. F. prior to 
adding UCAR alloy #1 briquettes containing 41% cobalt-35% iron and 24% 
aluminum to make a 0.5 weight percent cobalt 0.5 weight percent iron 
alloy. The alloy briquettes addition was made in the launder between the 
melter and holding furnaces during the transfer of the metal. The 
necessary amount of briquettes was placed in the trough, with a dam at the 
lower end to prevent the briquettes from being washed into the holding 
furnace without first being taken into solution with the aluminum. The 
metal was stirred after alloying in order to facilitate the homogenization 
of the alloy. After a 30-minute period, the alloy was sampled through two 
doors located on opposite sides of the furnace. The metal temperature in 
the holding furnace was 1350.degree. F..+-.10.degree. F. which resulted in 
a crucible temperature of 1290.degree. F..+-.10.degree. F. 
TABLE 1 
______________________________________ 
CHEMICAL COMPOSITION OF ALUMINUM INGOTS 
(Weight Percent) 
______________________________________ 
Fe Si Cu Mn Mg Cr Ni Zn 
______________________________________ 
0.15 0.04 0.001 0.003 0.008 0.001 0.001 0.02 
______________________________________ 
Ti V Ga B Na Al 
______________________________________ 
0.001 0.005 0.006 0.001 0.001 Balance 
______________________________________ 
It is to be understood that while this invention is described herein in 
connection with the specific Al-Fe-Co alloy described above, the scope of 
the invention is intended to cover all aluminum alloys that similarly 
behave under the same thermomechanical processing steps disclosed herein. 
Accordingly, it has been found that suitable results are obtained with 
cobalt being present in a weight percentage of about 0.2 to about 4.0, and 
iron present in a weight percentage of from about 0.2 to about 2.5. 
Superior results are achieved when cobalt is present in a weight 
percentage of from about 0.35 to about 2.0, and iron is present in a 
weight percentage of from about 0.3 to about 1.5. Particularly superior 
and preferred results are obtained when cobalt is present in a weight 
percentage of from about 0.4 to about 0.95, and iron is present in a 
weight percentage of from about 0.4 to about 0.95. 
The aluminum content of the present alloy may vary from about 93.50 percent 
to about 99.6 percent. If commercial aluminum is employed in preparing the 
present melt, it is preferred that the aluminum, prior to adding to the 
melt in the furnace, contain no more than 0.1 percent total of trace 
impurities. 
Optionally, the present alloy may contain an additional alloying element or 
group of alloying elements. The total concentration of the optional 
alloying elements may be up to 2.50 percent by weight; preferably from 
about 0.1 percent to about 1.75 percent by weight is employed. 
Particularly superior and preferred results are obtained when 0.1 percent 
to about 1.5 percent by weight of total additional alloying elements is 
employed. 
1. Casting Rate 
It has been determined in accordance with this invention that in order to 
produce a final wire product with small, uniformly distributed precipitate 
particles which will serve to limit subgrain growth and pin dislocation 
sites between subgrain boundaries, thereby producing a more stable product 
with improved properties, rapid solidification producing a small 
interdendritic spacing is necessary. To this end, the molten metal is 
preferably cast in a wheel-band type continuous casting machine generally 
designated by the numeral 20 in FIG. 1. 
The casting machine 20 includes a steel mold and is provided with 
sufficient coolant capacity to cool the molten metal at a rate of at least 
311.degree. F./min. 
The rapidly solidified cast bar exhibits well developed pure aluminum 
dendrites with a network of interdendritic eutectic as seen in FIG. 2(a). 
The eutectic consists of an aluminum matrix and Al-Fe-Co compounds. The 
nature of the compounds are, of course, determined by the nature and 
percentage of alloying elements alloyed with the aluminum. In an alloy 
formulated with 0.5 Fe and 0.5 Co according to the above EXAMPLE, the 
intermetallic compounds will be of the type FeAl.sub.3, FeAl.sub.6, 
CoAl.sub.9 and (FeCo).sub.2 Al.sub.9. As will be discussed more fully 
hereinafter, the eutectic compounds will be broken up and distributed 
throughout the aluminum matrix during hot deformation and cold-drawing, 
which results in a further reduction of the inter particle spacing. The 
precipitates act as barriers to the dislocation motion, thereby inhibiting 
subgrain growth and limiting the cell size in the finished wire, thus 
producing excellent mechanical and electrical properties therein. 
The fine eutectic network of the rapidly solidified bar as seen in FIG. 
2(a) can be compared to the as-cast structure of a bar slowly solidified 
at a rate of 28.degree. F./min as seen in FIG. 2(b). The latter structure 
shows patches or colonies of eutectic compound distributed in a matrix of 
primary aluminum. 
The fine eutectic networks formed during rapid solidification can be traced 
through the hot-rolled rod as seen in FIG. 3(a) to the finished wire 
product as seen in FIG. 4(a). On the other hand, the absence of a uniform 
eutectic network in the as-cast structure of the slowly solidified bar can 
be observed also in rod hot-rolled therefrom as seen in FIG. 3(b) as well 
as in its finished wire product as seen in FIG. 4(b). 
The non-uniform distribution of precipitates in products manufactured from 
the slowly-solidified bar results from the slow solidification which 
causes all of the cobalt and iron to precipitate as large particles in 
non-uniformly distributed eutectic colonies. The large areas devoid of 
precipitates cannot resist the movement of the grain boundaries and 
therefore subgrain coalescence takes place during annealing. Accordingly, 
such a product will have inferior properties as compared with the rapidly 
solidified product. 
In view of the foregoing, it should be apparent that rapid solidification, 
such as is obtained with continuous casting, results in a reduction of the 
inter-particle spacing in the eutectic, as compared with the greater 
spacing resulting from slower modification, thereby yielding a finer 
subgrain structure. Moreover, it has been further determined in accordance 
with this invention that if the frequency of nuclei formation can be 
increased during solidification, such as by increasing the degree of 
supercooling or by introducing vibrational energy into the mold, the 
dendritic arm spacing can be further reduced. Consequently, the eutectic 
spacing will be decreased and thus the extent of subgrain growth during 
annealing will be limited by the closely spaced precipitate particles that 
become broken up from the eutectic during subsequent rolling and drawing. 
2. Deformation Parameters 
As seen in FIG. 1, after the cast bar exits from the continuous casting 
machine 20 it is conveyed substantially immediately, in the as-cast 
condition, into a rolling mill 30. The cast bar enters the rolling mill 30 
having a cross-sectional area of 8.24 square inches and it is deformed 
therein in a series of deformations to a 0.375 inch diameter rod. The bar 
enters the rolling mill 30 at a temperature of 1050.degree. F. and exits 
therefrom at a temperature of 750.degree. F. The various rolling 
parameters in each roll stand are presented in Table 2. 
TABLE 2 
______________________________________ 
Rolling Speed Per Pass During Hot Deformation 
Total Reduction 
Speed of Each 
Hot Rolling 
Area of area Roll (Feet/ 
(pass no.) 
(sq. inches) 
(percent) Minute 
______________________________________ 
As-Cast 8.240 0 28 
1 5.150 37.3 45 
2 3.342 59.2 69 
3 2.523 69.2 91 
4 1.794 78.1 129 
5 1.410 82.8 164 
6 0.953 88.4 242 
7 0.712 91.3 324 
8 0.493 94.0 468 
9 0.372 95.5 620 
10 0.263 96.8 877 
11 0.192 97.7 1202 
12 0.148 98.2 1559 
13 0.116 98.6 1989 
______________________________________ 
As discussed above, the hot-forming of the bar into rod in the rolling mill 
30 will convert the aluminum matrix into a fine subgrain structure by 
increasing the dislocation density which facilitates the cross-slip 
process necessary for subgrain formation. Once the subgrain structure is 
formed, the subsequent deformations will break up the subgrains thereby 
refining the same, as well as break up the eutectic compounds and 
distribute them throughout the aluminum matrix. 
As seen in FIG. 5, which is a micrograph of the Al-Fe-Co bar in the as-cast 
condition, the as-cast bar exhibits a complete absence of subgrains in the 
matrix. The eutectic compound 40 is grouped in colonies which have 
precipitated during casting, and there is a negligble dislocation density 
throughout the matrix. However, after the initial reduction in 
cross-section of 37.3% which occurs in the first roll stand 50 of the 
rolling mill 30, a well defined subgrain structure begins to form between 
rows of precipitates as can be seen at 60 in FIG. 6. The formation of this 
structure is further illustrated in FIG. 7. The rows of precipitates 40 
act as dislocation sources during deformation and as initial barriers to 
the motion of dislocations, causing pile-ups and subsequent subgrain 
formation. At this stage, the areas of the matrix devoid of precipitates 
do not show significant subgrain formation. There are, however, 
dislocations randomly dispersed in the matrix and associated with the 
beginning of subgrain formation as seen in FIG. 8. 
The effect of subsequent deformations in the remaining roll stands of the 
mill 30 can be seen by comparing FIGS. 9-18. As seen in FIG. 9, after a 
reduction of 59.2% the bar exhibits a slightly high degree of subgrain 
formation and a higher concentration of dispersed dislocations which in 
some areas appear aligned in a position to form subgrain boundaries. 
The average subgrain size after 59.2 total reduction by hot-working is 5.0 
microns. After a total reduction of 69.2% during hot-rolling, the 
substructure becomes significantly smaller, having an average cell size of 
2.9 microns and becomes uniform throughout the matrix, even in areas 
devoid of precipitates as seen in FIG. 10. The material possesses an 
average cell size of 2.5 microns after 78.1% reduction as seen in FIG. 11 
showing a good cell uniformity throughout. As seen in FIGS. 12-18, as the 
reduction in area increases, the cell size and distribution decreases 
continuously up to a total reduction of 98.6%. 
From FIG. 19, which is a plot of the cell size v. the hot-rolling reduction 
sequence, it can be observed that the cell size decreases progressively 
until the 9th pass (95.5% area reduction), and that thereafter there is no 
further decrease in cell size. 
As discussed above, it has been determined in accordance with this 
invention that it is necessary to provide a sufficient degree of 
deformation in the first roll stand 50 so as to form a substantially 
well-defined subgrain structure in the stock product which will be broken 
up and thus refined in subsequent deformations, and which will permit 
dynamic recrystallization of the product during hot-forming, thereby 
improving the ductility of the product. In accordance with this invention, 
it has been determined that a reduction of more than 30% in the first roll 
stand is necessary to achieve the subgrain structure necessary to 
accomplish the foregoing. In the preferred embodiment of the invention the 
reduction is at least approximately 37%. 
After hot-working, the rod may be cold-worked by drawing through a series 
of wire-drawing dies as designated generally by the numeral 70 in FIG. 1. 
The 0.375 inch diameter rod entering the drawing dies 70 is drawn down 
into 0.105 inch diameter wire without any preliminary or intermediate 
anneals. 
3. Annealing Characteristics 
Annealing the hot-rolled rod before cold-drawing has a detrimental effect 
on the mechanical properties of the finished wire due to the excessive 
growth of the subgrains before cold-work and to the precipitation of the 
compounds before the final anneal. However, by cold-working without any 
preliminary or intermediate anneals as described above, the precipitate 
particles will be uniformly dispersed throughout the aluminum matrix thus 
acting as barriers to the movement of the subgrain boundaries during 
subsequent annealing. 
Annealing after cold-working will dramatically improve the elongation 
characteristics of the wire as well as the electrical conductivity 
thereof. As seen in FIG. 20, which is a plot of electrical conductivity v. 
annealing temperature, the electrical conductivity increases rapidly with 
annealing temperatures above 300.degree. F. and begins to level off at 
annealing temperatures above 530.degree. F. However, as seen in FIG. 21, 
which is a plot of tensile strength v. annealing temperature, it can be 
seen that both the ultimate tensile strength and yield strength decrease 
substantially when the wire is annealed at temperatures above 300.degree. 
F. 
As seen in FIG. 22, which is a plot of subgrain size v. annealing 
temperature, primary recrystallization starts at about 475.degree. F. in 
the cold-rolled Al-0.5% Fe-0.5% Co alloy wire produced from the rapidly 
solidified bar. The onset of recrystallization is marked by the 
coalescence of certain subgrains to form the recrystallization nucleus. 
This is illustrated in FIG. 23. The nucleus grows to form a high-angle 
boundary grain structure with thin, delineated grain walls. During 
recrystallization subgrain growth is inhibited by the presence of the 
precipitate particles which have been formed and uniformly distributed 
according to the thermo-mechanical processing steps disclosed hereinabove, 
and which act as pinning points to the movement of the subgrain 
boundaries. This can be seen most clearly in FIG. 24. Thus, the resulting 
average size of the recrystallized subgrains in the annealed wire is of 
the same magnitude as the average inter particle spacing. 
As further seen in FIG. 22, secondary recrystallization will take place at 
700.degree. F. when the pinning effect of the precipitates is overcome by 
the introduced energy. In FIG. 25 it can be seen that certain subgrains 
have overcome the pinning effect of the particles and have grown into 
other subgrains. In FIG. 26 there is illustrated a large subgrain 80 which 
has formed at the onset of the secondary recrystallization at 700.degree. 
F. It should be apparent, therefore, that the wire manufactured in 
accordance with this invention should not be annealed above 700.degree. 
F., whereupon the average subgrain size will be less than 0.9 microns, 
thereby promoting the improved physical properties described above. 
In view of the foregoing, it should be apparent that there is provided in 
accordance with this invention a novel method and apparatus for 
manufacturing an aluminum alloy conductor whereupon the thermomechanical 
processing steps may be closely controlled so as to obtain a fine subgrain 
structure which will materially improve the physical properties of the 
conductor as compared with electrical conductors manufactured in 
accordance with conventional techniques. Essentially, the wire must be 
manufactured from an aluminum alloy having a sufficient proportion of 
alloying elements added thereto which will yield intermetallic 
precipitates during subsequent thermomechanical processing. The melt must 
be rapidly cast in order to form an interdendritic structure having a 
short arm spacing as well as close inter particle spacing. Thereafter, the 
cast bar must be hot-worked, in the as-cast condition, in a series of 
deformations which includes the steps of increasing the dislocation 
density in the matrix during the first of the series of deformations 
sufficiently to form a substantially well-defined subgrain structure 
therein, thereby maximizing a refinement of the subgrain structure by 
permitting breaking-up thereof in each of the subsequent deformations. 
The hot-rolled product must then be cold-worked, without any preliminary or 
intermediate anneals, to further break up and disperse the particles 
throughout the aluminum matrix. The cold-worked wire is then annealed to 
improve the elongation and electrical conductivity thereof. The wire must 
not be annealed above a temperature at which subgrain coalescence takes 
place. For the alloys specifically disclosed herein, the annealing should 
take place below a temperature of 700.degree. F., and preferably between 
475.degree. F. and 700.degree. F. 
Although only preferred embodiments of the invention have been specifically 
described herein, it is to be understood that minor modifications could be 
made therein without departing from the spirit and scope of the invention 
as defined in the appended claims.