In cast aluminum alloys used in the automotive industry the microstructure inherited from the foundry process has a strong influence upon the fatigue behavior. In the cylinder heads produced by the Lost Foam Casting process, the microstructure consists of hard intermetallic phases and large gas and microshrinkage pores. In order to study the influence of this complex 3D microstructure on fatigue crack initiation and propagation, an experimental protocol using laboratory and synchrotron tomography, Finite Element simulation and 3D Digital Volume Correlation has been used. Full field measurements at the microstructure scale were performed during a low cycle fatigue test at room temperature performed in situ under synchrotron X-ray tomography (TOMCAT beamline, SLS). Synchrotron tomography allowed characterizing the eutectic Al-Al2Cu, iron based intermetallics phases and above all eutectic Si, which could not be distinguished with laboratory tomography; these constituents were proved a suitable natural speckle for Digital Volume Correlation.The 3D cracks were observed to initiate at large pores and then to propagate along the hard inclusions towards the free surface. The DVC of in-situ fatigue tests allows observing the relations between cracks and displacements discontinuities and strain localizations in measured field. The experimental protocol proposed will be further improved for a validation at a temperature characteristic of in-service conditions of cylinder heads (250°C).
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- Influence of the Lost Foam Casting Microstructure on Low Cycle Fatigue Damage of A319 Aluminum Alloy
Ahmed El Bartali
- Springer International Publishing
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