The blistering behavior and mechanisms of various kinds of zinc base coatings having a galvanic protection capability (pure zinc or Zn/Al alloys metallic coatings, zinc-rich coatings and zinc-base coatings with a top coating on the aluminum alloy 5086) were studied in seawater immersion. Pure zinc and Zn/Al alloy metallic coatings exhibited significant blistering on the whole coating surface after 10 months immersion, the zinc-rich coatings were more or less insensitive to the blistering. Although the metallic coatings gave sufficient galvanic protection to the alloy 5086, the zinc-rich coatings did not. Blistering of metallic coatings is due principally to the formation of zinc corrosion products in the coating. Some precipitation of calcareous deposits was found also at the coating-substrate interface. Electrochemical impedance measurements showed the inorganic zinc silicate coating to have an excellent pore blocking effect in the coating.

Subject
Zinc rich coatings, Substrates, Seawater, Corrosion products, Zinc silicates, Metallic coatings, Immersion, Zinc, Aluminum alloys, Blistering, Alloys, Inorganic zinc rich coatings, Thermal spray coatings
Keywords:
blistering, electrochemical impedance, galvanic protection, seawater immersion, zinc-base coatings
NACE International
1992
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