Mechanisms of Bond Endurance after Surface Treatment of Aluminum for Bonding (STAB) in Nonchromate, Alkaline Solution

Abstract A search for a simple, inexpensive, nonacid, nonchromate surface treatment for aluminum alloys that would produce strong, durable adhesive joints under hydrothermal-stress, evolved from a hot water soak (STAB(1)) to a commercial detergent soak (STAB(2)), to a highly concentrated NaOH room temperature soak (STAB(3)). The first two treatments proved successful on some occasions, but not consistently reproducible. STAB(3) proved to be reproducible and inexpensive; it consists of a room temperature dip in highly concentrated sodium hydroxide (caustic soda will do) followed by a rinse and dry. The mechanisms of endurance failure for some cases of STAB(1) and STAB(2) and the consistent high endurance of STAB(3) are revealed by investigation of surface properties.