Abstract
7055-T7751 Aluminum-Magnesium-Zinc alloy is recently developed alloy in an effort to meet the high performance requirements of compression-dominated airframe applications such as the upper wing structure of the future generation of wide-body aircrafts. This alloy will replace 7075-T651, which is mainly used on the current large commercial aircrafts, because it is claimed to offer an improved fracture toughness and corrosion resistance.
Corrosion behavior of the 7055-T7751 and 7075-T651 aluminum alloys in 3.5% NaCI and artificial seawater were investigated and compared. Testing procedures included electrochemical studies, stress corrosion testing, corrosion fatigue crack propagation rate, and fractography. Optical and scanning electron microscopy were performed to determine the extent of corrosion damage to all samples after each corrosion test. Results showed that 7075 and 7055 were susceptible to stress corrosion cracking (SCC) in 3.5% NaCI, and artificial seawater in a similar manner. In addition, test results indicated that 3.5% NaCI was more aggressive than artificial seawater. Both alloys showed higher crack growth rates in 3.5% NaCI solution and 7055 alloy showed some closure effects at low AK ranges. Finally, fractographic analysis revealed that delamination and intergranular crackings were the dominant failure modes for both alloys.
