Abstract: A study has been made of the fatigue crack growth in an Al-Li alloy 2091 in 3.5%NaCl solu- tion and at an elevated temperature of 130℃.The aging and environmental effects on the crack growth behaviour were examined.It is shown that the fatigue crack growth resistance decreases with aging.The specimen with underaged structures shows the highest resistance to fatigue crack growth due to more deflected crack paths and the resulting high crack closure levels.As compared to laborato- ry air,both 3.5% NaCl solution and elevated tem- perature of 130℃ cause an increase of near-thresh- old crack growth rates and a decrease of threshold levels.The elevated temperature is more effective. The effect of elevated temperature is mainly due to the precipitate coarsening which results in an enhancement of slip irreversibility.Hydrogen embritttlement is supposed to be responsible for the degradation of fatigue crack growth resistance in 3.5%NaCl solution

Key words: fatigue crack growth, AI-Li alloy, precipitate coarsening