An improved process for applying a lead-free coating by electrodeposition
to an untreated ferrous metal substrate is provided. The substrate need
not be phosphated prior to treatment. The process includes the following
steps:
a) contacting the substrate surface with a group IIIB or IVB metal compound
in a medium that is essentially free of accelerators needed to form
phosphate conversion coatings; followed by
b) electrocoating the substrate with a substantially lead-free, curable
electrodepositable composition; and
c) curing the electrodepositable composition.
The group IIIB or IVB metal compound is preferably a zirconium compound and
is typically in an aqueous medium.
The process may further include initial steps of cleaning the substrate
with an alkaline cleaner and rinsing with an acidic rinse.
Substrates treated by the process of the present invention demonstrate
excellent corrosion resistance.