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针对不同时效制度下2A97铝锂合金的疲劳裂纹扩展速率进行了研究;并通过光学显微镜、透射电镜和扫描电镜对合金的微观组织和疲劳断口进行了观察分析。结果表明:2A97合金薄板(T3+135℃/12 h)时效态的裂纹扩展速率最低,其次为T3,(T3+135℃/60 h)时效态的扩展速率略低于(T3+135℃/120 h)时效态,T6态的裂纹扩展速率最高。时效制度在较低的ΔK水平下对合金的裂纹扩展速率影响较大,而在较高ΔK水平下影响较小。δ′相及细小的T1相可以促进共面滑移,增加滑移可逆性,降低裂尖应力集中程度及塑性累积水平,同时使裂纹发生偏折,促进裂纹闭合效应,提高裂纹扩展抗力;粗大、密集的T1相及半共格的θ′相抑制共面滑移,易于造成应力集中,降低裂纹扩展抗力;晶界处的无沉淀析出带(PFZ)及平衡相急剧降低晶界强度,极易造成沿晶开裂,使合金裂纹扩展速率迅速提高。
The fatigue crack growth rate of 2A97 Al-Li alloy under different aging regimes was studied. The microstructure and fatigue fracture of the alloy were observed by optical microscope, transmission electron microscope and scanning electron microscope. The results show that the crack growth rate of 2A97 alloy sheet (T3 + 135 ℃ / 12 h) is the lowest, followed by T3 (T3 + 135 ℃ / 60 h) 120 h) aging state, the crack growth rate of T6 state is the highest. The aging regime has a greater effect on the crack propagation rate of the alloy at lower ΔK levels, but less at higher ΔK levels. The δ ’phase and the fine T1 phase can promote the coplanar slip, increase the slip reversibility, reduce the stress concentration and the plastic accumulation level at the crack tip, and at the same time, deflect the crack to promote the crack closure effect and improve the crack propagation resistance. , Dense T1 phase and semi-coherent θ ’phase inhibit coplanar slip, easily lead to stress concentration and reduce crack propagation resistance; grain boundary precipitation zone (PFZ) and the balance phase sharply reduce the grain boundary strength, pole Easily lead to crystal cracking, the rapid expansion of the alloy crack growth rate.