Corrosion fatigue crack growth behavior of 7075-T6 under biaxial tension–tension cyclic loading condition

• Experimental biaxial fatigue crack growth data (λ = 1 and 1.5) were developed for salt water and air environments.
• Results showed that increased biaxiality increased crack growth rates.
• The effect of biaxiality on crack growth rates was greater in the salt environment compared to air environment.
• Intergranular cracks were developed along S–T orientation perpendicular to main transgranular fracture in salt water.
• A mechanism based on the observation is presented to explain the biaxial corrosion fatigue.

Biaxial and uniaxial fatigue crack growth of aluminum alloy 7075-T6 was characterized under air and salt water (3.5%) environments. Biaxial fatigue increased crack growth rate in region I relative to uniaxial fatigue under both environments. Biaxial fatigue increased crack growth rate in region II relative to uniaxial fatigue under salt environment. Crack growth rates in region I were comparable in air and salt environments, while they were faster in salt water than air environment in region II. Biaxial fatigue in salt environment exhibited intergranular cracks along with main transgranular fracture. A mechanism for biaxial corrosion fatigue crack growth is proposed.