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Deposition, characterization and electrochemical properties ofsilica-phosphate composite coatings formed over A6092/SiC/17.5paluminum metal matrix composite

Abstract:

This paper investigates the effect of 2.5 wt.% (NH4)3PO4post- treatment after silica treatment on theformation of silica-phosphate (Si-P) composite coatings over A6092/SiC/17.5p aluminum metal matrixcomposite (AMMC). In previous studies, the optimum concentration, treatment time and pH of silicatreatment have been determined. The aim of the current paper is to determine the optimum conditionsunder which Si-P composite coatings can provide a maximum localized corrosion protection to AMMC.The surface morphology of Si-P composite coatings and the ability to protect AMMC substrate from local-ized corrosion in Cl-media were examined as a function of phosphate treatment time (0, 2, 5 and 10 min).Results showed that phosphate post-treatment after silica coating significantly affects the microstruc-ture and the pitting corrosion resistance of the ultimate coated composites. The coating deposited onAMMC post-treated for 2 min provides better pitting corrosion resistance than that post-treated for 5and 10 min. It is largely because the morphologies of the coatings are remarkably different under thethree post-treatment conditions. © 2013 Elsevier Ltd. All rights reserved.