PROTECTION OF THE AM60B MAGNESIUM ALLOY WITH FABRICATION OF A NOVEL SOL GEL/STRONTIUM PHOSPHATE COMPOSITE COATING

In this work, a composite coating consisting of strontium phosphate conversion coating and hybrid sol-gel layer was prepared on AM60B magnesium alloy. Hybrid sol-gel coating obtained from tetraethylorthosilicate (TEOS) and 3-glycidyloxypropyl-trimethoxysilane (GPTMS) as precursors by the traditional acid catalyzed hydrolysis and condensation, and finally deposition by dip coating techniques. The morphology and the structure of the conversion and sol–gel films were characterized with Scanning Electron Microscopy (SEM). The corrosion protection efficiency of the conversion coated and composite coated alloy samples was evaluated by recording potentiodynamic polarization curves and electrochemical impedance spectra in 0.05M NaCl environment. Results showed that the corrosion resistance of the Mg alloy could be significantly improved by the composite coating. The increased corrosion protection is assumed to be due to the additional layer of sol–gel, which covers pores and/or defects in the bottom conversion layer and prevents corrosive ions from transferring or diffusing to the magnesium alloy substrate.