Water vapour corrosion of lamellar, superplastic and cast dendritic Zn-21Al alloy

Corrosion studies were performed on Zn-21Al specimens prepared with three different microstructures: lamellar (furnace cooled), fine grained superplastic (water quenched), and dendritic (cast). As prepared and lightly-deformed (5%25 tension) specimens were exposed an hour per day to boiling water vapor, while held at 40°C, for periods of up to 120 days. All specimens initially gained weight rapidly, but stopped gaining weight after 16-64 days. Non-deformed lamellar material gained the least weight followed by superplastic, deformed lamellar, deformed superplastic, cast and deformed cast. Intergranular corrosion is the most likely mechanism to explain the behavior of each of the microstructures. Preferential corrosion of the zinc rich phase was observed by SEM in all specimens during the early steps of the corrosion process. XPS and AES analyses of specimens corroded for 16 days showed they were covered with an aluminum oxide layer, which apparently passivates the alloy. © 1984.

VIVO