WCN Autumn 2010

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WCN Issue N° 43 29
fails the 1x wrapping test (and was
also observed to fail 3x wrapping test)
for the four weeks condition, whereas
no damage is seen on the Zn5Al
coating.
Figure 17 which shows conditions for
3.4 1083mm samples at 245°C for two
weeks begin to show stronger signs
of peeling.
After five weeks at this temperature
(Figure 18), almost all of the Zn coating
is gone after bending.
However, for this period, the Zn5Al
coatings look identical to those for
225°C, with no coating peeling.
Figure 19 shows similar results for the
1.85mm 1005 wires.
Trials done without aluminium con-
ducting wires present for 245°C,
14 days and 300°C one day show no
differences from those with aluminium
conducting wires present about the
core wires (Figure 18 , 20).
No loss of Zn5Al coating is observed
at 300°C, 1 day, although the Zn coat-
ing on a similarly exposed wire is
completely gone.
Peeling is found to correspond well
with the start of alloy layer growth in
comparing Figure 10 and 11 to the
wrapping tests.
The ability of Zn5Al to withstand
temperatures better than Zn has
also been researched independently
outside of Bekaert.
The Southwire Corporation has
stated in an earlier technical report
that Zn5Al coatings pass wrap tests
after exposures up to 16 weeks for
temperatures as high as 350°C(7).
In comparison, Southwire states that
Zn coatings failed wrapping tests
at 200°C after 5 weeks, 215°C after
1 week and 250°C after 3 days.
Corrosion
Table 1 shows results for 5% dark
brown rust salt spray (average of three
tests) for the 3.4mm 1085 core wires
190°C trials.
A drop for both Zn and Zn5Al coatings
is observed after 30 days, but appears
to hold relatively steady through 185
days.
Probably this drop could be due to
some damage of the coating during
the heating/cooling of the sample.
Salt spray tests were also done for
3.4mm wires exposed at 225°C and
245°C as shown in Table 6.
Again, a small drop in properties is
seen for the galvanised wires, but the
Bezinalized wires appear to actually
have an increase in resistance, perhaps
due to formation of a more protective
oxide layer at the higher temperatures.
The effect of mischmetal
on Zn5Al coatings
In the original patent covering
Galfan(3) by the International Lead and
Zinc Research Organization (ILZRO),
the specification included 0.005-1.0
mischmetal. An optimal composition
was defined as having 4.7 to 5.2%
aluminium, 0.02-0.05% cerium and
0.01 to 0.04% lanthanum.
Coating New 225ºC
2 weeks
225ºC 245ºC
4 weeks 5 weeks
Zn 920 664 792 712
Zn5Al 1856 2304 2304 2120
Coating New 30 days 62 days 121 days 185 days
Zn 920 752 656 792 712
Zn5Al 1856 1368 1424 1488 1415
Table 1 ▼ ▼ : Salt spray results (hours until 5% dark brown rust) for wires exposed at 190°C (averages of
three results)
Table 2 ▼ ▼ : Salt spray results (hours until 5% dark brown rust) for wires exposed at 225 and 245°C (averages of
three results)
Zn
1x
Zn5Al
3x
Zn
Zn5Al
Figure 18 ▲ ▲ : 1x and 3x wrappings for 3.4mm 1083
wires after 245°C, 5 weeks, two magnifications
Figure 19 ▲ ▲ :1x wrapping for 1.85mm 1005 wires
after 245°C, 5 weeks, two magnifications
Figure 20 ▲ ▲ :1x wrapping test for 3.4mm 1083 wires
after 300°C, one day, two magnifications
Zn with Al
conductors
Zn without
Al conductors
Zn5Al with Al
conductors
Zn5Al without
Al conductors