Effect of Fe content on low cycle fatigue behavior of squeeze cast Al-Zn-Mg-Cu alloys

Abstract

Results of different researches prove that Fe content plays a major role on the obtained mechanical properties of the aluminum alloys. Due to the importance of fatigue properties for the application of Al-Zn-Mg-Cu alloys in aviation industry and lack of study on the topic, this research was focused on the effect of Fe content on the low cycle fatigue behavior of these alloys processed by squeeze casting. The experimental alloys processed with different Fe contents of 0.01, 0.33 and 0.55 wt% exhibited similar cyclic behaviorsWhile cyclic hardening, owing to the dislocation multiplication, entanglement, accumulation, interaction with the second phases, and stress induced precipitation, was understood as the ruling mechanism at higher strain amplitudes (0.4%–0.6%), all the studied alloys showed cyclic stabilization at strain amplitudes below 0.4%. The fatigue life of the alloy with 0.33 wt% Fe (B alloy) was better than that of the alloy with 0.55 wt% Fe (C alloy) at all specific strain amplitudes. For the specific strain amplitudes of below 0.5%, the fatigue life of B alloy was much superior to that of the alloy with 0.01 wt% Fe (A alloy). On the other hand, due to the difference existing between the fatigue fracture mechanisms occurred under high strain amplitudes and low strain amplitudes, the fatigue life of A alloy was a little longer than that of B alloy at strain amplitude of 0.6%. It was understood that Fe-rich phases had a great potential to alter the crack propagation path at low strain amplitudes. The crack propagation rate accelerated under conditions that the cyclic stress was large enough to break Fe-rich phases at high strain amplitudes of 0.6%.