New Pretreatments and Non-Chromated Chemfilm for Magnesium Alloys

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This work presents the corrosion and paint adhesion properties of a new trivalent chromium-based conversion coating technology along with three different pretreatment methods on AZ92A-T6 cast magnesium alloy.

A new environmentally friendly non-chromated chemfilm with different pretreatments was studied as a replacement to conventional hexavalent chromium-based chemfilm technologies for magnesium alloys. Anti-corrosion and paint adhesion properties of conversion-coated sand-cast AZ92A-T6 magnesium alloy were investigated. Open-circuit potential (Eoc), potentiodynamic polarization, neutral salt spray and gravimetric methods were employed to evaluate the corrosion resistance of this novel conversion coating.
Surface morphology and the presence of the coating were investigated by scanning electron microscopy (SEM) technique. Tape adhesion and pull-off adhesion studies were performed to characterize the paint adhesion properties. Rework along with the Touch-Up application and turbine-oil immersion studies was performed in order to simulate the depot-level maintenance.

The peformance results were compared with the commercial hexavalent chromated magnesium alloy to show that this novel coating technology can replace the conventional chromated conversion coatings.

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