Patent ID: 8187439

Claim:
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 mixed-metal body-in-white in an aqueous bath comprising a dissolved oxidizing composition comprising cerium cations capable of forming a conversion coating with each of the metal surfaces of the mixed-metal body-in-white, the conversion coatings comprising cerium and oxygen, the cerium cations reacting with each of the metal surfaces of the mixed-metal of the body-in-white upon immersion of the body in the bath to form a conversion coating on the surface of each metal of the mixed- metal body; immersing the body-in-white with its conversion coatings as a cathode in an aqueous electrocoat bath, the aqueous bath comprising a dispersed polymer for deposition on the conversion coatings of the mixed-metal surfaces of the body-in-white at a potential of about −100 volts to about −300 volts; and subjecting the body-in-white to a potential of about −100 volts to about 31 300 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 polymer coating of desired thickness, the polymer coating comprising cations of the dissolved oxidizing composition.