ABSTRACT
Abstract-The prevention of corrosion of aerospace alloys is accomplished using chromate compounds as corrosion inhibitors. Chromate processes have also been shown to prevent the alloys from corrosion fatigue cracking and to enhance their life under conditions of combined corrosive environment and cyclic stress applications. However, the presence of Cr(VI) ions in chromates with the consequent health hazards has led to the restrictions imposed on the use of these systems. Since they are economically competitive, provide excellent corrosion inhibition and possess environmental compatibility, organo-functional silane coatings can be considered as prospective replacements for chromating technology. In this project we have investigated the efficiency with which various bis-type silanes, such as bis-amino, bis-sulfur and bis-ureido silanes, can be used to prevent corrosion fatigue cracking of AA2024-T3 and AA7075-T6 alloys along with prevention of bare corrosion, as already shown in previous research. The testing encompasses loading a dog-bone specimen at 65% of its ultimate tensile strength for a 7075-T6 alloy and at 70% of its ultimate tensile strength for a 2024-T3 alloy. The dog-bone specimens are loaded and alternated with salt spray exposure. This cycle of fatigue loading and salt spray continues until the sample fails. As control specimens we are comparing the silane-coated with chromated samples and uncoated samples. The results indicate that some silanes may increase the corrosion fatigue life for one alloy and not for the other when compared with the chromated counterpart, but when compared to the blank, uncoated ones a positive effect is always observed.
