Development of Corrosion Resistant Surface Treatments for Aluminum Alloys for Spot-Weld Bonding

摘要

The objective of this program was to develop a corrosion resistant spot-weld bonding system for aluminum aircraft primary structures. Anodizing and chemical surface treatment were investigated. Chemical and microscopic techniques indicated that the most suitable corrosion resistant surface on aluminum should be a boehmite surface, alpha Al2O3.H2O. Many anodizing and chemical treatment systems were able to produce this surface oxide; however, most of these systems produced surfaces that either showed poor corrosion resistance or could not be spot-welded. A treatment consisting of the standard FPL etch followed by 90-minute sealing in boiling sodium dichromate solution gave a weldable surface with good corrosion resistance. The best adhesive found was B.F. Goodrich A-1396B. This adhesive was modified by incorporating ZnCrO4 and SrCrO4 to make it more corrosion resistant. The addition of 3% by weight SrCrO4 was found to give an adhesive that could be welded through and had improved corrosion resistance over the unmodified adhesive. The selected spot-weld bonding system is FPL etch with 90-minute dichromate seal and the modified A-1396B adhesive. Tests indicate that this spot-weld bonding system has the strength and corrosion resistance of the best corrosion resistant adhesive systems currently available. (Author)