Multilayered Zinc—Nickel and Zinc—Cobalt Alloys—Corrosion Resistance under Simulated Conditions and Field Exposure

SUMMARY

Corrosion performance of zinc—nickel and zinc—cobalt alloys prepared as duplex and triplex layers were evaluated by the potentiodynamic polarisation method and a simulated salt spray test. The results were compared with those obtained in the field test under severe tropical marine conditions. The effect of a nickel undercoat was also evaluated. All tests were conducted with electroplated deposits with and without chromate passivation. The results indicate that their corrosion resistance was in the order of Ni/Zn—Co/Zn—Ni>Ni/Zn-Ni/Zn-Co>Zn—Co/Zn—Ni>Zn—Ni/Zn—Co>Ni/Ni—Zn>Ni/Zn—Co. However, in marine testing Ni/Zn-Co/Zn-Ni showed tendency to crack formation.

Keywords:

• duplex/triplex coatings
• field exposure
• multilayer
• potentiodynamic polarization
• zinc alloys