Copper clad aluminum composite wire

A copper-clad aluminum composite wire has a core that is made of an Al-Mg alloy and circumferentially clad with copper or a copper alloy. The aluminum alloy is composed of 1.5 to 10.0 percent by weight of Mg, additives such as Cr and Mn, ordinary impurities, and aluminum whose content is such as to form the rest of the alloy composition. The copper or the copper alloy forms 20 to 40% of the cross-sectional area of the copper-clad aluminum composite wire. Such core material is drawn to reduce the cross-sectional area by 20% or more using a die whose half angle .alpha. is from 15 to 30 degrees to obtain an cladding wire; the cladding wire is further drawn to reduce the cross-sectional area by 70% or more using a drawing die whose half angle .alpha. is from 4 to 15 degrees at least once; and the thus drawn wire is subjected to annealing at temperatures from 200.degree. to 400.degree. C. for from one minute to 24 hours.

BACKGROUND OF THE INVENTION 
The invention relates to lightweight and very strong copper-clad aluminum 
composite wire (hereinafter referred to as "Cu/Al composite wire") and a 
method of manufacturing such Cu/Al composite wire, which is used for 
internal conductors for coaxial cables, electromagnetic shield braided 
wire for coaxial cables, electric wiring cables for airplanes, 
automobiles, electric automobiles, portable VTRs and TV sets, voice coards 
for speakers, magnet wire, and the like. 
FIG. 1 is a sectional view of a Cu/Al composite wire. Reference numeral 1 
designates an aluminum core; and 2, a copper cladding layer around the 
aluminum core 1. 
Having such a makeup, the copper cladding layer in the conventional Cu/Al 
composite wire generally forms from 5 to 20% of the cross-sectional area 
of the composite wire. The aluminum core material is a high-purity 
aluminum alloy whose purity is 99.9% or more or an Al-Fe alloy containing 
0.9 to 2.5 percent iron (see Japanese Patent Unexamined Publication No. 
53-110082). Such Cu/Al composite wire had a conductivity of 60 to 70% IACS 
(International Annealed Copper Standard), a specific gravity of 3.0 to 
3.95, a tensile strength of 10 to 20 kgf/mm.sup.2 (soft-drawn) and 20 to 
35 kgf/mm.sup.2 (hard-drawn) (American Society for Testing Materials 
(ASTM) B566-88). 
As described above, the coverage of the copper cladding layer is from 5 to 
20% at the cross-sectional area. Often the copper cladding layer breaks to 
expose the aluminum core when the composite wire is soldered to printed 
circuits or boards, thus causing defective connections. Also, adjusting, 
stranding, and handling of the wire in thin diameter during the 
intermediate process may cause damage to the copper cladding layer, 
leading to exposure of the aluminum core, which the becomes corroded or 
breaks, etc. 
On the other hand, if the copper clad takes up more than 20% of the total 
cross-sectional area of the wire, the strength of the core against the 
copper clad layer is impaired in the case where the core material is a 
high-purity aluminum alloy material. In this case, the aluminum core may 
break easily when the wire is drawn. Consequently, drawing of wire to 
obtain small sizes is difficult. Also, when high-purity aluminum alloy is 
used, even if the copper forms less than 20% of the cross-sectional area 
of the wire, the tensile strength is small (35 kgf/mm.sup.2 or less). Such 
a wire exhibits insufficient strength which is fatal as a wiring conductor 
when drawn to be 0.15 mm.phi. or less in diameter. In addition, the 
conventional Cu/Al composite wire has exhibited conspicuous inferiority in 
corrosion resistance to salt water at the end faces thereof compared with 
ordinary copper wire. Further, although various types of copper-cladding 
materials are used while utilizing the electromagnetic shielding property 
of copper, no study has been made on the Cu/Al composite wire. 
SUMMARY OF THE INVENTION 
The invention has been made in view of the above circumstances. 
Accordingly, an object of the invention is to provide copper-clad aluminum 
composite wire and a method of manufacturing such wire. 
To achieve the above object, according to a first aspect of the invention, 
a copper-clad aluminum composite wire has a core that is made of an Al-Mg 
alloy and circumferentially clad with copper. The aluminum alloy is 
composed of 1.5 to 10.0 percent by weight of Mg, partial additives such as 
Cr and Mn, ordinary impurities, and aluminum, with the aluminum being in 
such a content as to form the rest of the alloy composition. The copper 
whose purity is 99.9% or more forms from 20 to 40% of the cross-sectional 
area of the wire. 
According to a second aspect of the invention, a method of manufacturing a 
copper-clad aluminum composite wire comprises the steps of: when 
cold-cladding a core material with copper in the above-mentioned 
composition, drawing the copper at a percent reduction of 20% or more 
using a cladding die (see FIG. 6) whose half angle .alpha. is from 
15.degree. to 30.degree. to obtain a cladding wire; drawing the cladding 
wire for elongation at a percent reduction of 70% or more using a drawing 
die whose half angle .alpha. is from 4.degree. to 15.degree. at least 
once; and subjecting the thus drawn wire to an annealing process. 
The diameter of the aluminum alloy core is 6.0 mm.phi. or more. When the 
aluminum alloy core is formed into the cladding wire, the cladding die has 
a half angle .alpha. of from 15.degree. to 30.degree. and the length d of 
the bearing zone is D/6.ltoreq.d.ltoreq.D/4 (where D is the diameter of 
the die). 
The annealing process is carried out at temperatures from 200.degree. to 
400.degree. C. for from one minute to 24 hours. In the method, the drawn 
wire may be further subjected to a cold drawing process for elongation at 
a percent reduction of 50% or more at least once after the annealing 
process. 
The copper-clad aluminum composite wire of the invention uses as an 
aluminum core 1 in FIG. 1 an Al-Mg alloy composed of 1.5 to 10.0 percent 
by weight of Mg, partial additives such as Cr and Mn, ordinary impurities, 
and aluminum, the aluminum being in such a content as to form the rest of 
the alloy composition. Such aluminum core 1 is cladding with copper whose 
purity is 99.9% or more so that the copper forms 20 to 40% of the 
cross-sectional area of the wire. 
In general, the Al-Mg alloy of the present invention includes Zn of about 
0.05 wt %, Cu of about 0.02 wt %, Cr of about 0.05 wt %, Mn of about 0.05 
wt %, Fe of about 0.1-0.2 wt %, and Si of about 0.02 wt % other than Al 
and Mg. 
The inventors have studied the aluminum core material of the Cu/Al 
composite wire and have obtained the following findings. 
(1) If a high-purity aluminum alloy such as described above (JIS1000 Series 
or an aluminum alloy having a high purity of 99.9% or more) is used, 
strength of the core is so low compared with that of the copper cladding 
layer that and breakage originates frequently from the core during the 
drawing process when producing small-diameter wire. The produced wire has 
low bending resistance and low corrosion resistance to salt water. 
(2) Even if an Al-Cu alloy (JIS2000 Series) is subjected first to an 
ordinary softening process in which the alloy is heated to 250.degree. to 
400.degree. C. and cooled, and then a drawing process for elongation, 
strength of the core is so low as to be frequently broken during the 
drawing process to produce small-diameter wire. The bending resistance is 
also low. To improve the strength, the Al-Cu alloy is usually subjected to 
the T6 thermal treatment, in which the alloy is subjected to solution 
treatment and aging treatment. The temperature at which the solution 
treatment is carried out, is 400.degree. C. or more, thus producing 
brittle intermetallic compounds at the boundary between Cu and Al. This 
becomes the cause of breakage of wire, making this alloy unsuitable as a 
core material. The corrosion resistance of the alloy to salt water is 
noticeably poor, making the alloy unsuitable. 
(3) An Al-Mn alloy (JIS3000 Series) may have higher strength depending on 
how much Mg is added, but the strength does not make this alloy suitable 
enough. The addition of Mn disadvantageously increases the softening 
temperature; a Mn-added product (1.2% Mg) requires that the softening 
temperature be 400.degree. C. or more, thereby similarly causing brittle 
intermetallic compounds to be produced at the boundary between Cu and Al. 
However, the corrosion resistance to salt water is fairly improved. 
(4) An Al-Si alloy (JIS4000 Series), exhibiting poor drawability to 
small-diameter wire, is thus unsuitable as a core material. The corrosion 
resistance to salt water is also extremely unsatisfactory. 
(5) An Al-Mg alloy (JIS5000 Series) has been found suitable as a core 
material of the Cu/Al composite wire of the invention. However, if the 
addition of Mg is less than 1.5 percent by weight, strength of the core is 
inadequate and becomes lower than that of the copper cladding layer, which 
may cause the wire to break easily. If Mg is added by 10 percent by weight 
or more, although the strength becomes high, ductility of the core 
material is decreased, exhibiting low drawability to 300 .mu.m or less and 
thus making the alloy unsuitable as the core material. The addition of 1.5 
to 10.0 percent by weight of Mg makes the alloy stronger than the 
circumferentially cladding copper layer, and the softening process can be 
carried out at the temperature from 200.degree. to 400.degree. C. in the 
course of elongation process, so that the drawability to 300 .mu.m or less 
id improved to a remarkable degree. 
(6) An Al-Mg-Si alloy (JIS6000 Series) is unsuitable for its poor strength 
obtained under ordinary heat treatment and drawing processes. A solution 
treatment at 450.degree. C. or more improves the strength but, at the same 
time, brittle intermetallic compounds are similarly produced at the core 
boundary to the copper cladding layer, thus making the alloy unsuitable. 
From the above findings, Al-Mg alloys having 1.5 to 10.0 percent by weight 
of Mg (containing the addition of Cr and Mn) are suitable as a material of 
the aluminum core, particularly, Al-Mg alloys having 4 to 6 percent by 
weight of Mg are optimum. 
The ratio in cross-sectional area of Cu to Al of the Cu/Al composite wire 
will be discussed. If the copper cladding layer forms less than 20% of the 
total cross-sectional area of the wire, the copper cladding layer is 
broken to expose the aluminum core as described previously, causing wire 
breakage and defective connections. Since an Al-Mg alloy used as a core 
material in the Cu/Al composite wire of the invention has low 
conductivity, the makeup of the wire in which the copper cladding layer 
takes up less than 20% may lead to a case where conductivity of the Cu/Al 
composite wire is smaller than 40% IACS, making the wire unsuitable as a 
conductor. On the other hand, if the copper cladding layer forms more than 
40% of the total cross-sectional area of the wire, the specific gravity 
becomes more than 5.2 thus reducing the lightweight advantage making the 
wire unsuitable. Therefore, by setting the ratio in cross-sectional area 
taken up by the copper cladding layer from 20% to 40%, the conductivity 
problem is eliminated, and the specific gravity can be confined to a value 
of less than 5.2, which contributes to the lightweight benefit of the 
wire. 
Considering the electromagnetic shielding property, if the purity of copper 
used in the copper cladding layer is less than 99.9%, the conductivity of 
the wire is decreased together with the shielding property. Also, when the 
copper cladding layer forms less than 20%, particularly less than 10%, of 
the cross-sectional area, the shielding effect tends to decrease greatly, 
while the shielding effect remains unchanged when the copper cladding 
layer forms 40% or more. 
Since purities of copper of the copper cladding layer less than 99.9% 
reduce conductivity of the Cu/Al composite wire, such copper is 
unsuitable. 
Since composite clad wire such as that of the invention is used where a 
size of 100 .mu.m or less is required, the cladding material and the core 
material are preferably bonded metallurgically to some extent. Any 
clearance between these materials makes drawing into thin wire difficult. 
It has been found that success in drawing owes much to three factors: the 
cladding method employed when a core material having a certain thickness 
is clad with a cladding material; to the subsequent drawing method for 
elongation; and to the annealing conditions. A core material, which is an 
aluminum alloy, in the invention preferably has a diameter of 6.0 mm or 
more for satisfactory metallurgical bonding. When the materials are 
passing through a cladding die whose half angle .alpha. is from 15.degree. 
to 30.degree. to prepare cladding wire, the cladding material is elongated 
to thereby generate slide resistance on the core material, i.e., an Al 
alloy, which increases the degree of contact. In contrast thereto, when 
the half angle .alpha. of the die is less than 15.degree., particularly, 
less than 10.degree., the slide resistance is so small that the cladding 
material is not brought into sufficient contact with the core material. If 
.alpha. exceeds 30.degree., particularly, 35.degree. or more, the cladding 
material is drawn so excessively as to be easy to break. Consequently, it 
is preferable to set the half angle .alpha. of the die between 15.degree. 
and 30.degree.. Further, the use of the die whose half angle falls within 
the above range allows a predetermined ratio in cross-sectional area of 
the cladding material to be obtained. In addition, it is important to set 
the length d of the bearing zone of this die between D/6 and D/4 (D is the 
diameter of the die). When d is less than D/6, the surface pressure at the 
time that the cladding material is slid is insufficient, thus causing 
insufficient contact. If d is more than D/4, the die surface is subjected 
to excessive wear, thus not only deteriorating the life of the die but 
also causing breakage of the cladding material, tucking, and the like. 
Still further, in drawing the obtained cladding wire for elongation, it is 
preferable that after the wire is drawn at a percent reduction of 70% or 
more using a drawing die whose half angle .alpha. is from 4.degree. to 
15.degree., the reduced wire is annealed at temperatures from 200.degree. 
to 400.degree. C. to improve the bonding property between the core 
material and the cladding material. Half angles being less than 4.degree. 
cause the die to be worn greatly, while half angles in excess of 
15.degree. cause the cladding layer to be out of position, which is likely 
to result in tucking. Annealing temperatures below 200.degree. C., 
particularly below 150.degree. C., are not enough to induce mutual 
diffusion, while an annealing process at a temperature in excess of 
400.degree. C. for a long time produces brittle intermetallic compounds, 
which leads to easy breakage of wire. Thus, such wire cannot make a 
satisfactory hoop. Further, the annealing time is preferably from one 
minute to 24 hours. Annealing for less than one minute is not enough to 
obtain the effect of mutual diffusion, while annealing that is longer than 
24 hours is too expensive and does not provide performance improvement 
that is commensurate with the expended cost. 
After such annealing, the wire is cold-drawn to reduce the cross-sectional 
area by 50% or more at least once, so that the core material and the 
cladding material can be bonded with no clearance therebetween. The 
strength and bending resistance of the Cu/Al composite wire can thus be 
improved. 
According to such a method, tensile strength of the Cu/Al composite wire is 
30 kgf/mm.sup.2 or more, and even as large as 60 kgf/mm.sup.2. Even if the 
core material is softened at temperatures from 200.degree. to 400.degree. 
C., the tensile strength is between 20 and 35 kgf/mm.sup.2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 2 is a diagram illustrative of an apparatus for manufacturing Cu/Al 
wire. 
An aluminum core material 11 is paid off from a core material supply block 
13 and straightened by a straightener 14. The straightened core material 
is cleaned by a surface cleaning unit 15 and introduced into a casting die 
18. Simultaneously, a copper tape 12 paid off from a copper tape supply 
block 16 is similarly cleaned by a surface cleaning unit 17 and introduced 
into the casting die 18 so as to be laid along the core material 11. The 
thus laid copper tape 12 in the casting die 18 is cast to clad the core 
material 11 concentrically. The side ends of the copper tape 12 to be 
jointed is butt-welded by a TIG welder 20. The thus welded materials are 
then formed into a cladding wire d by a cladding die 21 and rewound by a 
rewinder 24. In the form of cladding wire the aluminum core material 11 
and the copper tape 12 are in intimate mechanical contact with each other. 
In FIG. 2, reference numeral 19 designates a squeeze roller; 22, a 
shielded container for forming nonoxide atmosphere; and 23, a rewinding 
capstan. 
FIG. 3 is a diagram illustrative of an apparatus for manufacturing Cu/Al 
composite wire when a tubular claddingding material is used. 
Cu/Al composite wires in each of which the copper clad layer forms 30% of 
the cross-sectional area of the wire were obtained by cladding and drawing 
while using the apparatus for manufacturing Cu/Al composite wire shown in 
FIG. 2 under the following conditions. The core materials were the 
aluminum alloy wires made of: (a) pure aluminum (JIS1050); (b) Al-Cu alloy 
(JIS2011); (c) Al-Mn alloy (JIS3003); (d) Al-Si alloy (JIS4047); (e) 
Al-Mg-Si alloy (JIS6061); (f) Al-Mg alloy (JIS5056) and (g) Al-Mg alloy 
containing 0.9 percent by weight of Mg (JIS5005) ((f) and (g) were core 
materials of the invention). The diameter of each core wire was set to 8.5 
mm.phi.. The cladding material was a copper tape of 1.0 mm thick and 55 mm 
wide made of oxygen free copper (99.99%). A cladding die whose diameter is 
10.2 mm.phi. and whose half angle .alpha. is 30.degree. was used to clad 
and draw the materials. 
Further, (h) a Cu/Al composite wire in which the copper clad layer takes up 
42% of the cross-sectional area of the wire was produced by cladding and 
drawing the core material Al-Mg alloy (JIS5056) and a cladding material 
copper tape of 1.4 mm thick and 55 mm wide made of oxygen free copper. In 
this case, a cladding die whose diameter was 11.2 mm.phi. and whose half 
angle .alpha. was 25.degree. was used. Still further, a Cu/Al composite 
wire in which the copper cladding layer forms 16.5% of the cross-sectional 
area of the wire was obtained by cladding and drawing the core material 
(JIS5056) and a copper tape of 0.5 mm thick and 40 mm wide made of oxygen 
free copper. In this case, a cladding die whose diameter was 9.3 mm.phi., 
whose half angle .alpha. was 25.degree., and whose bearing length was 1.9 
mm was employed. 
These Cu/Al composite wires were cold-drawn to reduce their diameter to 4.0 
mm.phi. and then annealed at 300.degree. C. for one hour. The annealed 
wires were cold-drawn again so that their diameter was reduced to 1.0 
mm.phi. and annealed again at 300.degree. C. for one hour. The thus 
heat-treated wires were subjected to cold drawing to reduce the diameter 
to as thin as 0.15 mm.phi.. 
While the Cu/Al composite wires using the Al-Cu alloy and the Al-Mg-Si 
alloy as the core materials were subjected to a solution treatment at 
520.degree. C. as an additional heat treatment to improve the strength of 
the 1.0 mm.phi. semi-finished wires, brittle Cu-Al intermetallic compounds 
were produced at the boundary and this caused breakage of the wires. 
Consequently, the treatment was suspended at this point. 
The Cu/Al composite wires whose diameter reached 0.15 mm.phi. without 
breakage were subjected to mechanical property tests such as a tensile 
strength test (kgf/mm.sup.2), a bending resistance test shown in FIGS. 
4(a)-4(b) as well as a soldering test. Further, a salt spray test was 
conducted on these wires in the atmosphere using 5% salt water (pH=6.5 to 
7.2) at 35.degree..+-.1.degree. C. in spraying amounts of from 0.5 to 3.0 
cc/hour. 
FIGS. 4(a) to 4(d) are diagrams illustrative of the bending test. An end of 
a sample piece of Cu/Al composite wire 32 is clamped between a pair of 
steel blocks 31, each having a roundness value of corner (R) of 0.5 mm, 
and a weight 33 weighing 50 g is suspended on the other end (FIG. 4(a)). 
Then, the steel blocks 31 were tilted 90.degree. toward the right as shown 
in FIG. 4(b) to bend the composite wire 32. This operation was counted as 
one bending. The steel blocks 31 were returned in the original position as 
shown in FIG. 4(c) and were then tilted toward the left to give a second 
bending to the composite wire 32 as shown in FIG. 4(d). By repeating this 
operation, the number of bendings was counted until the wire was broken. 
The core material composition, processed states, and mechanical properties 
of the above-mentioned Cu/Al composite wires are shown in Table 1. For 
reference, comparative examples of a single strand of titanium wire, a 
single strand of duralumin wire, and a single strand of tough-pitch wire, 
whose diameter is 0.15 mm.phi., are also presented. 
TABLE 1 
__________________________________________________________________________ 
Type of core material and major element added 
(Wt %) 
JIS Cu coverage Conductivity 
No. No. Cu Si Mn Mg Cr Al (%) Specific gravity 
IACS 
__________________________________________________________________________ 
% 
1 1050 
.ltoreq. 
.ltoreq. 
.ltoreq. 
.ltoreq. 
-- .gtoreq. 
30 4.5 71 
0.05 0.25 
0.05 0.05 99.5 
2 2011 
5.5 0.2 -- -- -- Remaining 
" 4.7 58 
content 
3 2011 
5.5 0.2 -- -- -- Remaining 
" 4.7 58 
content 
4 3003 
1.1 0.2 1.2 -- -- Remaining 
" " 65 
content 
5 4047 
0.1 12 0.1 0.05 
-- Remaining 
" " 55 
content 
6 6061 
0.3 0.6 0.1 1.0 0.2 Remaining 
" " 61 
content 
7 6061 
0.3 0.6 0.1 1.0 0.2 Remaining 
" " 61 
content 
(8) 5056 
0.05 0.1 0.1 5.2 0.10 
Remaining 
30 4.5 52 
content 
(9) 5052 
0.10 0.25 
0.1 2.5 0.20 
Remaining 
25 4.3 52 
content 
10 5056 
0.05 0.1 0.1 5.2 0.10 
Remaining 
16.5 3.7 39 
content 
11 5005 
0.08 0.2 0.1 0.8 -- Remaining 
30 4.5 66 
content 
12 5056 
0.05 0.1 0.1 5.2 0.10 
Remaining 
42 5.3 59 
content 
13 Single-strand titanium wire 4.5 2.2 
14 Single-strand duralumin wire (JIS 2011) 2.8 40 
15 Single-strand tough-pitch copper wire 8.9 100 
__________________________________________________________________________ 
Tensile 
Bending test 
strength at 
(50 g, 0.5 mmR, 
0.15 mm.phi. 
right-angle 
solder- 
500-hour salt spray test 
No. 
Drawability up to 0.15 mm.phi. 
(kgf/mm.sup.2) 
bending) 
ability 
End face Surface 
__________________________________________________________________________ 
1 .DELTA. Frequently broken 
22 35 .largecircle. 
Al core was 
No 
corroded by 8 
corrosion 
2 .DELTA. Frequently broken 
29 39 .largecircle. 
Al core was 
No 
corroded by 35 
corrosion 
3 X No. 2 was subjected to T6 treatment 
Cannot 
Cannot -- -- -- 
(500.degree. C. .fwdarw. water .multidot. cooled .fwdarw. 170.degree. 
C. .times. be be 
10 Hr), but embrittled and broken. 
measured 
measured 
4 .DELTA. Frequently broken 
27 40 .largecircle. 
Al core was 
No 
corroded by 3 
corrosion 
5 .DELTA. Frequently broken 
36 49 .largecircle. 
Al core was 
No 
corroded by 25 
corrosion 
6 .DELTA. Frequently broken 
29 37 .largecircle. 
Al core was 
No 
corroded by 9 
corrosion 
7 X No. 6 was subjected to T6 treatment 
Cannot 
Cannot -- -- -- 
(500.degree. C. .fwdarw. water .multidot. cooled .fwdarw. 170.degree. 
C. .times. be be 
10 Hr), but embrittled and broken. 
measured 
measured 
(8) 
.largecircle. Good drawability 
48 81 .largecircle. 
Al core was 
No 
corroded by 0.8 
corrosion 
(9) 
.largecircle. Good drawability 
47 80 .largecircle. 
Al core was 
No 
corroded by 1.0 
corrosion 
10 .largecircle. Good drawability 
54 98 .DELTA. Cu layer 
Al core was 
No 
easy to 
corroded by 0.8 
corrosion 
break 
11 .DELTA. Frequently broken 
28 40 .largecircle. 
Al core was 
No 
corroded by 4.5 
corrosion 
12 .largecircle. Good drawability, but not light 
40 71 .largecircle. 
Al core was 
No 
corroded by 0.8 
corrosion 
13 X Poor drawability 75 105 X .largecircle. 
No 
corrosion 
14 .DELTA. Frequently broken, T6 treatment done. 
After T6 
69 X Corroded along 
Same as left 
treatment total length with no 
50 trace of original form. 
15 .largecircle. Good drawability, but heavy 
46 40 .largecircle. 
.largecircle. 
No 
corrosion 
__________________________________________________________________________ 
Note: 
Nos. (8) and (9) are Cu/Al composite wires of the invention. 
Nos. 13, 14 and 15 are comparative singlestrand wire samples. 
An ordinary electric conductor whose total cross-sectional area was from 
0.34 to 0.5 mm.sup.2 such as shown in FIG. 5 was prepared by stranding a 
total of 19 single solid conductors of each of the Cu/Al composite wires 
of the invention (Nos. 8 and 9), the Cu/Al composite wires (Nos. 10 and 
12), the duralumin wire (NO. 14) and the tough-pitch copper wire (No. 15) 
as comparative examples. The mechanical properties of these electric wires 
are shown in Table 2. 
While the tensile load (kgf) and soldering test conditions are the same as 
applied to the single wires, the bending test and salt spray test 
conditions were the same except that the weight was 1 kg in the bending 
test and the ends were covered with waterproof caps in the salt spray 
test. 
TABLE 2 
__________________________________________________________________________ 
Conduc- 
Tensile Salt spray 
Outside 
tivity 
load Number character- 
diameter 
(%/ (kgf/ 
Weight 
of Solder- 
istic 
No. Material of conductor 
Makeup (mm) IACS) 
mm.sup.2) 
(g/m) 
bendings 
ability 
(Surface) 
__________________________________________________________________________ 
Wires 8 Cu/Al composite wire 
19 conduc- 
0.76 52 17.8 
1.66 
415 .largecircle. 
.largecircle. 
of tors/0.15 mm.phi. 
the 9 " 19 conduc- 
" " 17.0 
1.59 
403 .largecircle. 
.largecircle. 
inven- tors/0.15 mm.phi. 
tion 
Compara- 
12 " 19 conduc- 
" 60 14.9 
1.96 
360 .largecircle. 
.largecircle. 
tive tors/0.15 mm.phi. 
wires 14 Duralumin 19 conduc- 
" 40 17.5 
1.04 
348 X X 
tors/0.15 mm.phi. 
15 Tough-pitch copper 
19 conduc- 
" 99 16.8 
3.29 
359 .largecircle. 
.largecircle. 
tors/0.15 mm.phi. 
10 Cu/Al composite wire 
19 conduc- 
" 38 19.8 
1.37 
501 .DELTA. 
X 
tors/0.15 mm.phi. 
__________________________________________________________________________ 
As is apparent from Table 1, the Cu/Al composite wire of the invention is 
comparable to titanium wire with respect to the specific gravity. The wire 
of the invention is about half the weight of the single-strand copper wire 
with a satisfactory conductivity that is larger than single-strand 
titanium and duralumin wires. 
The simple heat treatment at below 400.degree. C. and drawing process 
contributes to making strength of the core material greater than that of 
the copper cladding layer, thus providing satisfactory drawability to 
produce wire whose diameter is 0.15 mm.phi.. In addition, the tensile 
strength is increased appropriately while ensuring acceptable bending 
resistance. This means that the composite wire of the invention is 
effective as a conductor used at locations to which bending and bending 
vibration are added. 
Since the composite wire of the invention has such a ratio in 
cross-sectional area of the copper cladding layer to the core as to allow 
soldering heat to be released, thereby ensuring satisfactory soldering 
reliability. 
It is found from Table 2 that the Cu/Al composite wire of the invention has 
the following advantages. Compared with the stranded tough-pitch copper 
wire (No. 15) as the ordinary electric wire in current use, the composite 
wire obtained by the invention not only has greater tensile strength and 
better bending resistance but also is lighter and equal in solderability 
and salt spray characteristic. 
Since the No. 10 stranded Cu/Al composite wire had remarkably low 
conductivity and was thin because of the small Cu layer coverage, the Cu 
layer was damaged during stranding or handling, and the damaged portion 
was locally corroded or broken due to salt water spraying. Thus, this wire 
(No. 15) was unsuitable. The No. 12 stranded Cu/Al composite wire, because 
of the higher Cu layer coverage, is not only inferior to the tough-pitch 
copper wire in current use in terms of tensile load, but also heavier. 
FIG. 7 shows the shield effects of the sample piece wires. It was found for 
the first time that the Nos. 8 and 9 Cu/Al composite wires shown in Table 
1 exhibited a characteristic similar to copper wire in high frequencies. 
Therefore, the Cu/Al composite wire of the invention is extremely effective 
when used in fields such as requiring a small diameter, a certain tensile 
strength, lightness (lighter than copper wire) and soldering reliability 
at end surfaces; e.g., internal conductors of coaxial cables, 
electromagnetic shield braided wire, voice cords for tweeters, wiring 
conductors for airplanes and automobiles, wiring conductors of domestic 
appliances such as portable VTRs and TV sets, magnet wire for motors, and 
the like. 
Since long and continuous wire can be obtained by the invention, the Cu/Al 
composite wire may be used as a filler material for use in TIG (tungsten 
inert gas) and MIG (metal inert gas) cladding by welding.