Effect of aging conditios on the fatigue crack propagation rate of 2A97 aluminum-lithium alloy

Abstract:

The fatigue crack propagation（FCP） behaviors of 2A97 aluminum-lithium alloy under different aging conditions were investigated. The microstructures and fracture morphologies were observed and analyzed by TEM 、SEM and OM. The results indicate that （T3 135℃/12h）aging treatment alloy has the minimum FCP rate，followed by T3；（T3 135℃/60h）aging treatment has a slightly slower fatigue crack propagation rate than （T3 135℃/120h）;T6 temper has the maximum FCP rate. Aging conditions have a significant influence on the FCP in low ΔK level，but not in high ΔK level. The δ?and fine T1 phases can enable slip planarity so as to enhance the reversibility of cyclic slip and reduce damage accumulation and stress intensity around the crack tip；slip planarity can also lead to the deflection of crack path and promote the crack closure effect.All these things result in an improvement of crack propagation resistance.Coarse and intensive T1 phase and semi-coherent θ?restrain slip planarity and easily induces stress intensity which can reduce crack propagation resistance.The Precipitation free zone(PFZ) and equilibrium phases at grain boundaries dramaticly reduce the strength of grain boundaries and lead to intergranular fracture ；this arouses greatly improvement in fatigue crack propagation rate.

Key words:2A97 Al-Li alloy;fatigue crack propagation rate;aging treatment;precipitation phase