Corrosion fatigue behavior of 7075 aluminum alloy in saline water environment at different temperatures

Based on high-temperature corrosion fatigue injury problems caused by seawater splash and insolation when aircraft structure material 7075 aluminum alloy servicing at coastal area, the corrosion fatigue life of 7075 aluminum alloy in 35, 55, 75 ℃, 3.5% NaCl saline water is studied by corrosion fatigue life test, and the influence of temperature on corrosion fatigue crack initiation and propagation is discussed by fracture morphology observation using scanning electron microscope (SEM). The results indicate that at the same stress level, corrosion fatigue life decreases with the temperature rising, such as the median fatigue life is respectively 33 001, 30 931, 15 346 cycles while temperature is 35, 55, 75 ℃ at the stress of 300 MPa. There is a competitive relationship between corrosion damage and fatigue damage. When at high stress level, corrosion damage is slight and fatigue damage is the main influencing factor of fatigue life; fatigue source usually initiates from the interface between matrix and Al clad. When the stress level is low, corrosion damage gets severe and fatigue life declines sharply with the temperature rising; fatigue source usually initiates from corrosion pitting. Fracture morphology shows that high-temperature environment influences initiation of fatigue source mainly by accelerating the formation of corrosion pitting, and pitting with deep hole shape is often accompanied by severe stress concentration which does great damage to fatigue property.