Corrosion Resistance and Durability of Fasteners in Aircraft Structures

摘要

A corrosion and fatigue evaluation was made to determine whether the rounding of countersunk holes and/or fastener heads would improve the corrosion behavior at the fastener locations or affect the fatigue strength of 7075-T6 aluminum alloy joints assembled with cadmium plated steel countersunk head screws. Test assemblies were prepared with and without corrosion barrier materials, including a MIL-S-8802 polysulfide sealant, in the finishing system. Rounded configurations did not significantly improve corrosion behavior but did improve the fatigue strength of the specimens. The greatest improvement in fatigue properties occurred with a combination of rounded fastener heads and rounded countersunk holes. Of the various corrosion barrier materials tested, only the polysulfide sealant afforded good corrosion protection when used with a paint system overcoat. However, the use of the sealant more than negated the beneficial effect of the rounded configurations on fatigue strength. The use of the sealant lowered the fatigue strength of the control specimens with standard fastener heads and standard countersunk holes by approximately 6%. This loss is counterbalanced by the improvement in corrosion behavior afforded by the sealant to fastener areas. (Author)