The effect of iron content on fatigue lifetime of AlZn10Si8Mg cast alloy

The problem with utilization of the Al-scrap as a material for casting the Al-Si alloys lies in the fact that the scrap, unfortunately as a rule, is contaminated with iron. The current study presents an investigation of the effect of different iron contents (0.150 and 0.559 wt%) on microstructure, porosity and bending fatigue properties in the secondary (recycled) self-hardening AlZn10Si8Mg cast alloy. Rotating bending fatigue tests were realized for a defined number of cycles 3 x 10(6) with a stress asymmetry ratio R = -1 at room temperature. Observation by the optical and SEM microscopy using deep etching and image analysis highlight the role of the plate/needle-like Fe-rich intermetallic (Al5FeSi phase), formed during the solidification process. The quantitative metallography and CT scan was used to quantify the amount of pores.The results show that Al5FeSi phases play an important role in the low cycle region. The higher amounts of needle/plate like Fe-rich particles (Al5FeSi) with increased porosity degraded fatigue lifetime in the short and medium life-time regime ( < 10(6) cycles) and there was no effect or slight increases the fatigue lifetime for long life-time regime (>> 10(6) cycles). In the high cycle's region are the pores more detrimental than Fe-rich phases to the fatigue strength. Fracture surface of the fatigue specimens were analysed by SEM to characterize the micromechanism and the initiation fracture local.