The effects of chromate deoxidizer treatment parameter variation on surface morphology and adhesive bonding of 2219-T87 aluminum

Abstract

The shell of the Space Shuttle's External Tank is 2219-T87 aluminum to which an epoxy primer is applied to allow bonding of the Thermal Protection System (TPS). A chromate deoxidizer is used to prepare the aluminum surface for primer bonding. In this study, scanning electron microscopy (SEM) was used to characterize the surface morphology of 2219-T87 aluminum associated with different bond strengths produced by varying the deoxidizer treatment parameters.Eight sets of two 2219-T87 aluminum panels were treated with chromate deoxidizer. One set was used as a control. The second set was subjected to an additional deoxidizer treatment, while the third set received two additional deoxidizer treatments. The fourth, fifth, and sixth sets were held for 5, 10, and 15 minute post deoxidiation and prior to final rinse with demineralized water. The two remaining sets were deliberately contaminated with 25:1 and 100:1 water:deoxidizer solutions, which were allowed to dry on their surfaces.