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Assessing corrosion of Zinc plating during salt spray testing

Hello ..My name is Ben and I work for a large manufacturing company in the UK. We buy in many Zinc plated components and as incoming quality check salt spray test them to ASTM B117.

My question is what order would you expect to see corrosion products. White, black then red? And why? I know that red is the corrosion of the base material but why do you see white and black corrosion occurring ?

Ben Smith
Technician - United Kingdom
August 11, 2010

August 13, 2010

Ben,

White corrosion products first, this is corrosion of the zinc. Zinc is sacrificial to steel so corrodes first. The black comes from many sources such as the chromate passivate. Then comes the red corrosion products of the base material.

Brian Terry
Aerospace - Yeovil, Somerset, UK

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