An investigation of the effectiveness of a partial cladding pattern on Aluminum 7075 T651

Abstract

One of the primary motivations in developing new materials for the aerospace industry is maximizing specific strength. An often conflicting goal in developing new materials is maximizing corrosion resistance. This is due to the realities of aging aircraft and the rising costs of inspection and maintenance. Currently all aluminum sheet and plate used in the aerospace industry is Alclad to increase corrosion resistance. The Alclad layer can make up 5% of the total plate thickness and does not carry any load. The goal of this work is to show that weight savings in aircraft structures can be achieved by substituting a partial cladding pattern for the continuous Alclad layer while maintaining equivalent corrosion resistance. In this work, the corrosion resistance of aluminum 7075 T651 in the Alclad, partially clad and bare forms were compared after corrosion exposure in an acidic salt spray cabinet test. The degree of corrosion was then evaluated through visual inspection, analysis of cross-sections, tensile test and fatigue tests. Following this, single clad spot panels with varying spot sizes were produced and corroded to investigate if there is a more efficient clad spot size than what was selected for the medium sized test panel. After corrosion exposure, severe to moderate exfoliation corrosion was observed on the unprotected medium sized test panel, light general corrosion was observed on the upper section of the partially clad panel and patches of corrosion not penetrating past the clad layer were observed on the Alclad panel. Tensile and fatigue tests showed that the Alclad and partially clad tests panes resisted degradation of mechanical properties due to corrosion similarly well while outperforming the bare test panel.