Electrocoating process for mixed-metal automotive bodies-in-white

A method of forming a protective conversion coating and an electrocoat on the surfaces of a mixed-metal automotive vehicle body-in white where the surfaces comprise magnesium alloy surfaces and at least one of ferrous metal surfaces, zinc surfaces, and aluminum alloy surfaces;

• the method comprising:
• immersing the body in an aqueous bath comprising a dissolved oxidizing composition comprising cations capable of forming a conversion coating with each of the metal surfaces of the body, the conversion coating comprising elements of the cations and oxygen, the cations reacting with the mixed-metal upon immersion of the body in the bath;
• immersing the cleaned body as a cathode in an aqueous electrocoat bath, the aqueous bath comprising a dispersed polymer for deposition on the mixed-metal surfaces of the cleaned body at a potential of about −100 volts to about −300 volts surfaces;
• and
• subjecting the body-in-white to a potential of about −100 volts to about −300 volts for a period to deposit polymer micelles as a co-extensive coating on the conversion coatings on the mixed-metal surfaces to achieve a coating of desired thickness, the polymer coating comprising cations of the dissolved oxidizing composition.