Impact of melt conditioning and filtration on iron-rich β phase in AlSi9Cu3 and its fatigue life studied by μCT

The present study investigates the influence of melt conditioning and filtration on iron-rich phases in AlSi9Cu3 alloy. This method avoids the formation of brittle β phase (Al 4.5 FeSi) and reduces the iron content by sedimentation and subsequent filtration. The comparison of this method to conventional casting (reference) with a higher Fe content is performed by means of scanning electron microscopy, tensile tests, ultrasonic fatigue tests, X-ray diffraction and X-ray microtomography. The reference batch revealed a high proportion of β plates, which are responsible for low strength compared to melt conditioned batch under uniaxial tensile stress. The fatigue properties of melt conditioned batch are significantly improved compared to the reference state. X-ray microtomography scans before and after ultrasonic fatigue tests were evaluated by machine learning algorithms (Trainable Weka Segmentation). The superposition of the segmented fatigue crack with the initial, undeformed state was performed for the first time and showed that the fatigue crack path is strongly influenced by the brittle Fe-rich phases. • Melt conditioning and filtration of secondary AlSi9Cu3 reduces Fe content by 42%. • Formation of α c Chinese script phase instead of β phase increases fatigue limit. • Trainable Weka Segmentation was used for μCT fatigue crack and phase segmentation. • Superposition of fatigue crack with initial condition reveals fatigue crack path.