Bilayer coatings for temporary and long–term corrosion protection of magnesium–AZ31 alloy


Phosphate and silane containing organic self–assembled (SA) layers serve as pre–treatments on magnesium alloy sheet materials. A reliable protection was achieved in this work via application of alkyd–based coatings on the pretreated surface. The idea of adopting SA pre–treatments as functional layers at metal–polymer interface is to influence the adhesive properties between solid metal substrate and alkyd–based coating. Hexadecyltrimethoxysilane (HDTMS) deposited metal surfaces exhibit stronger adhesive strength, while a near homogeneous distribution of the octadecylphosphonic acid (ODPA) and perfluorodecylphosphonic acid (PFDPA) exhibit low adhesive phenomenon, when placed as pre–layers in bilayer coatings. Electrochemical impedance results after 168 h of immersion reveal that the organophosphate and organosilane deposited bilayer films demonstrate protective properties with almost no interface defects. Moreover, organophosphate treated bilayer coatings enhance easy peeling of alkyd coat after protecting the surface from corrosive electrolytes. Bilayer coatings developed on AZ31 sheets can confer temporary or long–term corrosion protection depending on further processing strategy and offer efficient alloy protection for both purposes.
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