'Can Surface Treatments Protect Against Corrosion Fatigue Cracking of Al Alloys?'

摘要

Chromate compounds have been used for the prevention of corrosion fatigue cracking (CFC). However the presence of Cr(VI) ions in these chromate conversion coatings poses a consequent health hazards which have led to research to find a replacement. Silanes offer a promise in this regards because of the very good corrosion inhibition, cost competitiveness and environmental compatibility This research investigates the efficiency with which the various bis-type silanes such as bis-amino, bis-sulfur silane, bis-uredo silane can be used to prevent the corrosion fatigue cracking of AA2024 T3 and AA7075 T6 alloys. The methodology includes loading the dog-bone specimen at 65% of its calculated UTS for a 7075 T6 alloy and at 70% UTS for a 2024 T3 alloy. The dog bones are loaded and alternated with salt spray till failure. As a control specimen we are testing the samples against chromate samples and uncoated samples. The results indicate that the silane coatings can be as effective for CFC prevention as the chromate conversion coatings and for some silane systems the performance is better than the chromate coatings.