The focus in this study is therefore on applying a vertical upwards continuous casting (VUCC) mass-production method to the pilot-scale manufacturing of Cu-Zr alloy rods. The microstructure and physical characteristics of these VUCC rods were subsequently investigated and compared with rods produced by CMC. In addition, the wire-drawing capability of the VUCC rods was examined, and the adaptability of the VUCC method to the mass production of hypoeutectic Cu-Zr alloys was fully investigated. 2.

1. Proceeding of the 54th lecture meeting of the Japan Institute of Copper
November 8 – 9, 2014, Yokohama National University, JAPAN
[Re-print in English by NGK]
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Characteristics of Hypoeutectic Cu-Zr Alloy Rods Manufactured by Vertical Upwards Continuous Casting
Naokuni Muramatsu* and Masaaki Akaiwa*
*New Metals Division, NGK Insulators, Ltd., Handa, 475-0825, Japan
1. Introduction
Ideally, copper alloys used in miniaturized electronic devices should exhibit a combination of high strength and high
electrical conductivity. The authors of the present study have previously reported on: (i) the fine dendrite microstructure
of hypoeutectic Cu-x at% Zr (x = 0.5–5) alloys created by copper mold casting (CMC), (ii) the change in this
microstructure with heavy wire-drawing to a lamellar structure of nanometer-scale layers of copper and a Cu/Cu-Zr
intermetallic eutectic phase, and (iii) the good balance between strength and electrical conductivity that these drawn-wires
exhibit1-3)
. Despite this, the mold sizes available for CMC greatly limit the potential for rapid solidification, thus making
CMC unsuitable for mass production.
The focus in this study is therefore on applying a vertical upwards continuous casting (VUCC) mass-production
method to the pilot-scale manufacturing of Cu-Zr alloy rods. The microstructure and physical characteristics of these
VUCC rods were subsequently investigated and compared with rods produced by CMC. In addition, the wire-drawing
capability of the VUCC rods was examined, and the adaptability of the VUCC method to the mass production of
hypoeutectic Cu-Zr alloys was fully investigated.
2. Experimental procedures
Cu-Zr alloy rods were produced by the pilot-scale VUCC at
Rautomead Ltd5)
, which is illustrated schematically in Figure 1.
For this, feedstock specimens were first prepared from 8mm
diameter oxygen free copper (OFC) wires and 13 mm diameter
Cu-50 mass% Zr cored-wires purchased from Affival SAS6)
.
The preparation of this feedstock was controlled by varying the
intermittent-injection speed of each component to given an
alloy composition of Cu-x at% Zr (x = 0.5–5), after which it
was melted in a 500 kg capacity graphite crucible at a constant
temperature of 1300 °C. Oxidation of the molten metal surface
was suppressed by using a graphite flake cover and a flow of
argon gas. Using a water-cooled mold made from a cylindrical
graphite die wrapped in copper tube, continuous casting was
performed by pulling vertically upward. Graphite dies with
inner diameters of 8, 10 and 15 mm were prepared, and their
inner surface was finished to an accuracy of N6 surface
roughness. The cast rod was pulled up by servo-controlled
Molten metal
Crucible
Wire feedstock
(a), (b)
Cast rod
Pinch
roller
Cu mold
Die inserts
Ceramic
cap
Fig. 1 Schematic illustration of vertical upwards
continuous casting (VUCC).

2. Proceeding of the 54th lecture meeting of the Japan Institute of Copper
November 8 – 9, 2014, Yokohama National University, JAPAN
[Re-print in English by NGK]
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pinch rollers with an intermittent cycle; the average upwards-casting speed being 1375 mm/min and the ratio between the
pull and dwell time adjusted within a range of (1:3) to (1:4). More than 200 kg of rod was continuously cast and coiled
for each alloy composition.
Each of the VUCC rods were subsequently drawn down to 0.6 mm in diameter through a combination of hot or cold
swaging, combination-rolling and drawing with cassette roller dies. The draw-ability of each material was then
investigated by further wire-drawing down to an arbitrary diameter using a continuous dice-wire-drawing process.
Chemical analysis of the VUCC rods was conducted using inductively coupled plasma (ICP) spectroscopy.
Microstructural examination was carried out using scanning electron microscopy (SEM) and laser microscopy. Individual
phases in each of the cast rods were identified through X-ray diffraction (XRD). The electrical conductivity of the rod
and wire specimens was determined from their electrical resistivity; a mono-probe used with the rods and a four-probe
technique with the wires. Hardness and ultimate tensile strength were measured using Vickers hardness testing and
multifunctional tensile-testing machines, respectively.
3. Results and discussion
3.1 Appearance and surface characteristics
In the image of the 15 mm diameter VUCC rod given in
Figure 2, oscillation marks consistent with cold shut during
continuous casting are clearly aligned on the rod-surface, and
small cracks can be observed around them. The depth of these
cracks was measured by laser microscopy of vertical
cross-sections and found to be in the order of 0.1–0.8 mm; a
value which can easily be attributed to the hardness of the rod.
Figure 3 shows XRD profiles obtained from transverse
cross-sections of the 8, 10 and 15 mm diameter rods of Cu-5
at% Zr alloy created by VUCC. These profiles indicate that all
of these rods have a dual-phase structure consisting of a Cu
phase and a Cu5Zr intermetallic compound, which is
comparable to the structure of Cu-0.5, Cu-1, and Cu-2 at% Zr
alloys produced by CMC3)
.
3.2 Chemical and microstructural analysis
The ICP analysis results for the Cu-2.5 at% Zr alloy rods
manufactured by VUCC are summarized in Table 1, which
lists: (a) an average of the Zr content at the top and bottom of
each VUCC rod, (b) the average Zr content for all of the rods,
and (c) the standard deviation. It is clearly evident from this
that the alloy composition can be efficiently maintained to
Fig. 2 Appearance of a 15 mm diameter Cu-5
at.% Zr alloy rod produced by VUCC.
Fig. 3 X-ray diffraction patterns of
cross-sections of 8, 10, and 15 mm
diameter Cu-5 at.% Zr alloy rods
produced by VUCC.

3. Proceeding of the 54th lecture meeting of the Japan Institute of Copper
November 8 – 9, 2014, Yokohama National University, JAPAN
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quite a high tolerance during VUCC.
The relationship between the diameter and secondary
dendrite arm spacing (DAS) of Cu-5 at% Zr alloy rods
produced by VUCC is shown in Figure 4 in comparison to
Cu-4 at% Zr alloy rods produced by CMC7)
. We see from this
that both methods produce a very similar hypoeutectic
microstructure, despite the difference in Zr content between the
two alloys. However, a 4 mm diameter rod produced by CMC
has a DAS value of 3 m, whereas the same DAS value can be
obtained in an 11 mm diameter rod using VUCC. This suggests
that VUCC rods solidify at a faster rate, and therefore have a
much finer dendritic microstructure. An estimate of this
solidification rate based on these DAS values will be reported
on the appointed day of the meeting.
3.3 Wire-drawing capability and characteristics of as-drawn wires
Figure 5 shows the appearance of a Cu-2.5 at% Zr alloy wire
13.8 m in diameter, with a 92 m diameter human hair also
shown to provide perspective as to just how thin this wire is.
The fact that it was possible for a 15 mm diameter VUCC rod
to be drawn down to this size certainly confirms it has good
wire-drawing capability, which is considered to be the result of
the fine dendritic microstructure formed by VUCC.
The ultimate tensile strength, total strain to fracture, and
electrical conductivity of this 13.8 m diameter wire were
measured as 1870 MPa, 2.5 %, and 21 %IACS, respectively.
Note that these values are comparable with the 1838 MPa,
2.7%, and 20 %IACS that were reported in a previous study for
a 27m diameter wire drawn from a CMC rod. This suggests
that wires manufactured from VUCC rods possess both high strength and high electrical conductivity.
Serial number 1 2 3 4 5 6 7
Diameter (mm) 10 10 10 8 8 10 15
(a) Ave. Zr (at%) 2.44 2.14 2.43 2.50 2.60 2.94 2.45
(b) Total ave. (at%)
(c) Std. dev. (at%)
2.50
0.23
Table 1 ICP analysis results for 8, 10 and 15 mm diameter Cu-2.5 at% Zr alloy
rods produced by vertical upwards continuous casting (VUCC).
Fig. 4 Secondary dendrite arm spacing (DAS)
versus diameter for a Cu-5 at% Zr alloy
rod manufactured by VUCC in
comparison with a Cu-4at% Zr alloy7)
produced by copper mold casting (CMC).
Fig. 5 (a) Appearance of a 13.8 μm diameter wire
drawn from a 15 mm diameter VUCC rod,
and (b) a sample of human hair for
comparative purposes.

4. Proceeding of the 54th lecture meeting of the Japan Institute of Copper
November 8 – 9, 2014, Yokohama National University, JAPAN
[Re-print in English by NGK]
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4. Summary
(1) The VUCC method provides a higher rate of cooling than CMC, with the resulting dendritic microstructure
expected to contribute to its arm-spacing refinement.
(2) VUCC rods exhibit good wire-drawing capability.
(3) The ultimate tensile strength, total strain to fracture and electrical conductivity of 13.8 μm diameter Cu-2.5 at% Zr
alloy wire drawn from a VUCC rod were found to be 1870 MPa, 2.5 %, and 21 %IACS, respectively.
(4) VUCC has good potential to be adapted to the mass production of hypoeutectic Cu-Zr alloy wires.
REFERENCES
1) N. Muramatsu, N. Ogawa, H. Kimura and A. Inoue: J. JIC 49 (2010), 67-72.
2) N. Muramatsu, H. Kimura and A. Inoue: J. JIC 50 (2011), 199-203.
3) N. Muramatsu, H. Kimura and A. Inoue: J. JIC 51 (2012), 31-36.
4) http://www.rautomead.co.uk/resources/media/1311264032iwcctechnicalseminar_barcelona2009.pdf
5) http://www.rautomead.co.uk
6) http://www.affival.com
7) N. Muramatsu, H. Kimura and A. Inoue: Proceedings of IWCC technical seminar 2009 (Barcelona).