Zinc Plating Without Passivation: Strong White Rust Fix

Summary for zinc plating without passivation Discussion

Zinc plating without passivation is prone to white rust, especially during storage or transit before powder coating. In this thread, Rais Khan asks how to prevent rusting on exported zinc-plated parts that are later powder coated, and whether any passivation can both protect the zinc and still allow good powder-coat adhesion. The discussion notes that zinc plating is nearly always chromate conversion coated because bare zinc is highly susceptible to white rust. Ted Mooney says the ideal pretreatment before powder coating is zinc phosphate, and that zinc surfaces can be zinc phosphated. He adds that this should help deter white rust on the zinc plating, but it is difficult to predict how long parts can safely remain in storage or transit. The thread also notes that powder coating over zinc-plated and chromate-converted surfaces can be problematic, so zinc phosphating the plating or phosphating the steel directly may be preferable.