关键词: Al-Cu-Li合金, 疲劳裂纹扩展, T₁相, 时效

Abstract: Microstructure and mechanical properties of the Al-Cu-Li alloy aged at 143 ℃ for different time were studied by means of tensile test, fatigue crack propagation rate test, scanning electron microscope(SEM) and transmission electron microscope(TEM). The results show that the strength of the alloy increases rapidly and shows a strong aging response when aged for 25-35 h, while the strength increases slightly and reaches a peak when aged for 65 h. The main precipitates of the Al-Cu-Li alloy after aging at 143 ℃ for 25, 35 and 65 h are T₁ phase. After aging for 25 h, T₁ phases precipitate with fine size, accompanying with precipitation of small amounts of δ′ phase. The alloy aged for 25 h shows a low fatigue crack growth (FCG) rate because the movable dislocations can cut through precipitated phases and undergo reversible slip, increasing fatigue crack deflection and crack closure effects, showing higher crack propagation resistance. With the increase of aging time, the size and number density of T₁ phase increase, and the FCG rate increases. After aging for 65 h, the size of T₁ phase greatly increases, the moving dislocation can only bypass these large phase, resulting in stress concentration, thus the FCG rate increases obviously, the fatigue property of the alloy is the worst.

Key words: Al-Cu-Li alloy, fatigue crack propagation, T₁ phase, aging