WCN Autumn 2010

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.

1x

Zn with Al conductors

Zn

Zn without Al conductors

Zn5Al

3x

Zn5Al with Al conductors

Zn

Zn5Al

Zn5Al without Al conductors

Figure 18 ▲ ▲ : 1x and 3x wrappings for 3.4mm 1083 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

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.

Figure 19 ▲ ▲ : 1x wrapping for 1.85mm 1005 wires after 245°C, 5 weeks, two magnifications

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,

Table 1 ▼ ▼ : Salt spray results (hours until 5% dark brown rust) for wires exposed at 190°C (averages of three results)

Coating

New

225ºC 2 weeks

225ºC

245ºC

4 weeks

5 weeks

Zn

920

664

792

712

Zn5Al

1856

2304

2304

2120

Table 2 ▼ ▼ : Salt spray results (hours until 5% dark brown rust) for wires exposed at 225 and 245°C (averages of three results)

Coating

New 30 days 62 days 121 days 185 days

Zn

920

752

656

792

712

Zn5Al

1856

1368

1424

1488

1415

29

WCN Issue N° 43 www.iwma.org