WCN Autumn 2010

exemplified for the 3.4mm 1083 wires in Figures 8 - 9 ). A summary of the alloy layer growth at 190°C is shown in Figure 10 for the 3.4mm 1083 and 1.85mm 1005 wires. Figure 11 shows the impact of temperature on the 3.4mm 1083 wires. The results of the trials can be summarised as follows: Growth of the alloy layer in the 1 Zn5Al coated wires could not be observed under any of the trial conditions, only globularising of the aluminium-rich phase No growth of the alloy layer in the 2 Zn coated 3.4mm 1083 ACSR core wires is observed at the 190°C trials; however growth of the alloy layer of the 1.85mm 1005 Zn coated wire was noticed after 120 and 185 days Growth of the alloy layer on the 3 3.4mm Zn coated 1083 ACSR core wire is first observed at 225°C, two weeks as was also seen with coatings on the 1.85mm wires. All higher temperatures also saw similar growth at this time or less. Growth of the alloy layer in the Zn5Al coated 3.4mm 1083 ACSR core wire could not be observed under any of the trial conditions, only globularising of the aluminium-rich phase The greater sensitivity of the 1.85mm 1005 wire to temperature with respect to alloy layer growth is most likely to be

14 days

190ºC 62 days

121 days

28 days

225°C

Figure 8 ▲ ▲ : Microstructures of 3.4mm ACSR core wires after 14 and 28 days at 225°C

185 days

mischmetal) and Zn hot dip coating on 3.4mm 1083 core wires (having a carbon content of about 0.83%) were heated in an oven ( Figure 4 ) on perforated stainless steel shelves with a fan-driven room atmosphere ventilation. Additional 1.85mm AISI 1005 wires coated with similar 270gm 2 coating weights of Zn and Zn5Al (without mischmetal) were also tested at the same time to reveal differences in 34 coating behaviour. Cable/wire lengths were about 20cm. Both ends of the ACSR cables were fixed with pipe clamps to avoid unravelling. Trials were done at the following conditions: 190° C – 15,30, 62, 121 and 185 • days (ACSR 3.4mm 1083 and 1.85mm 1005) 225°C – 14 and 28 days (3.4mm • 1083 without Al conductors and 1.85mm 1005) 245°C – 14 days (ACSR and • 3.4mm 1083 core wires without Al conductors, 1.85mm 1005) and 35 days (ACSR cables and 1.85) 300°C – 1 day (3.4mm 1083 wires • with and without Al conductors, 1.85mm 1005) Microstructures Figures 5 and 6 show microstructures of the ACSR core-wires in the ‘before test’ condition and after 185 days (end of test) at 190°C for the 3.4mm 1083 and 1.85mm 1005 wire coatings, respectively. times up to 185 days at 190°C. Note vacancy formation between alloy layer and zinc top layer. The voids near the surface could also be related to this phenomenon as they were not observed on Zn5Al coated wires Figure 7 ▲ ▲ : Microstructures of 1.85mm Zn-coated wires showing growth in alloy coating at various

245°C, 35 days

Figure 9 ▲ ▲ : 3.4mm ACSR core wire microstructures after 245°C, 35 days

For the 3.4mm wires at 190°C, no significant difference in alloy layer growth can be observed for neither galvanised nor Zn5Al coatings. However, for the 1.85mm 1005 steel, changes in the galvanised coating alloy layer could be could be measured, at 121 and, especially at 185 days ( Figure 7 ). At all temperatures over 200°C, alloy growth was seen in the Zn coatings, but none in the Zn5Al coatings (as

Figure 10 ▼ ▼ : Plot of alloy thickness against time for wires studied

Alloy Layer (µm)

Time (Days)

Figure 11 ▼ ▼ : Plot of alloy thickness as a function of time and temperature for the 3.4mm 1083 wires

Alloy Layer (µm)

Time (Days)

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WCN Issue N° 43 www.iwma.org