This report summarizes optimization work for surface preparations and hybrid primers utilizing sol-gel technology on metal alloy substrates. The project focuses on the development and optimization of user-friendly sol-gel methods for preparing metal surfaces for bonding with 250 degrees F-cure and 350 degrees F-cure epoxy adhesives. Several improvements to the Boegel-EPII materials and processes were identified in this work. For example, addition of a surfactant can improve the appearance and uniformity of the sol-gel coatings, but is not critical for achieving good performance on these alloys. Studies indicate that careful choice of abrasive media and tools is required to achieve reproducible performance for the surface preparation of aluminum alloys. Under carefully controlled laboratory conditions, it is possible to yield good performance for many of the abrasive media, but when subjected to conditions that mimic a repair scenario, only a few of the abrasive media gave reproducible performance. Surface contamination on the metal was a result of smeared adhesive, overheating of the abrasive pad or tool, or unacceptable cleaning of the surface. Performance using downselected abrasive media and tools was verified using hot/wet testing, such as the wedge test and double cantilever beam testing. Procedures were documented specifying all of the preferred materials and processes.
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