Effect of creep aging forming on the fatigue crack growth of an AA2524 alloy

Effects of creep aging forming on the microstructural evolution, conventional mechanical properties and fatigue crack propagation (FCP) behavior for 2524 aluminum alloy were studied by tensile and hardness testing, the FCP behavior testing and transmission electron microscopy (TEM) observation. The results show that in the low stress intensity range, the characteristics of precipitates have a significant effect on fatigue performance of the creep-aged aluminum alloy, and the mainly precipitated S″ phases in the alloy creep-aged for 4 h is beneficial to the reversibility of coplanar slip and dislocation slip, and the alloy presents better FCP resistance and relatively lower FCP rate, while the FCP rate increases with increasing aging time. In the Paris regime, effects of microstructure on the FCP rate are no longer obvious, and the FCP rates are almost consistent. Meanwhile, the presence of creep stress significantly accelerates the aging precipitation process. In terms of yield strength σ0.2, hardness and FCP resistance, the 9 h artificial aged alloy is analogous to the 4 h creep aged alloy. The peak strength of the alloy creep-aged for 24 h is the highest, but the fatigue crack growth resistance degraded obviously. It is not comprehensive to determine the optimal process of creep aging only in accordance with the peak strength.