Abstract

The present invention is directed to a process for forming a well visible non-chromate conversion coating on surfaces of magnesium and magnesium alloys, to a composition therefor and to a method of use for such coated articles having surfaces of magnesium or any magnesium alloy. The composition is a solution or dispersion comprising a fluorosilicon acid. The composition is preferably an aqueous solution having a pH in the range from 0.5 to 5 and includes often at least one pH adjustment agent. The thereof formed coating is useful to increase the corrosion resistance and the adhesion of magnesium and magnesium alloys to a paint coating, powder coating, e-coat, fluoropolymer coating, self-lubricant layer and adhesive bonding layer. The conversion coating may favorably be coated with a fluoropolymer coating, coated with a silane based sealing or both. The such formed coating is typically of grey mat non-metallic appearance.

IPC Classes  ?

• C23C 22/34 - Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH < 6 containing fluorides or complex fluorides
• C23C 22/83 - Chemical after-treatment
• C23C 22/78 - Pretreatment of the material to be coated

Abstract

A method for coating, a composition suitable for coating and a coating generated with the method of coating on anodizable metallic surfaces, especially on magnesium rich and aluminum rich surfaces, is disclosed. The composition is an aqueous solution including alkali metal or ammonium cations, phosphorus containing anions and silicon containing anions as well as optionally a peroxide or a compound of Al, Ti, Zr or any mixture of them. Preferably, the anodizing is carried out with a micro-arc oxidation process.

IPC Classes  ?

• C25D 11/02 - Anodisation
• C25D 11/36 - Phosphatising