A Chromate-Free Process for Preparing Aluminum Substrates for Adhesive Bonding -- A Preliminary Study.
PICATINNY ARSENAL DOVER N J
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A new, non-chromated etchant for preparation of aluminum surfaces for adhesive bonding has been developed. The standard chromated sulfuric acid FPL treatment of aluminum alloy surfaces for adhesive bonding was studied using etching rate determinations, electrochemical monitoring of the reaction, surface resistance measurements, and transmission electron microscopy. The results of these studies were used to develop the new etchant. Limited tests were conducted using a thermosetting film adhesive to bond specimens prepared with a new, non-chromated etchant on two different aluminum alloys, 2024-T3 and 6061-T4. These were subjected to hot water soak and stressed durability testing. These preliminary tests indicate that the new etchant composition resulted in joints with bond strength and short term durability essentially equal to those produced using the standard chromated etchant. The new etchant consisted of an aqueous solution of nitric acid, sodium sulfate, and ferric sulfate.
- Metallurgy and Metallography