3D Investigation of Damage During Strain‐Controlled Thermomechanical Fatigue of Cast Al–Si Alloys

The strain‐controlled thermomechanical fatigue behavior is investigated for three cast near‐eutectic Al–Si alloys with different Ni, Cu, and Mg contents. Synchrotron tomography and neutron diffraction experiments are used to correlate 3D microstructural features with damage initiation and evolution. The results show that the alloy with lower Cu, Ni, and Mg concentrations has up to 45% higher thermomechanical fatigue resistance for cooling/heating rates of 5 and 15 K s−1. In addition, this alloy also exhibits damage formation at later stages during thermomechanical fatigue and slower damage accumulation compared to other alloys. This difference in behavior is a consequence of its higher ductility, which is a result of the lower volume fraction and global interconnectivity of the 3D hybrid networks formed by Si and intermetallics and the absence of large primary Si clusters which act as preferred crack initiation sites during the early stages of thermomechanical fatigue. AlSi12Cu3Ni2 alloy with reduced Cu and Mg shows a 45% increase in thermomechanical fatigue (TMF) resistance. 3D investigations reveal preferential crack initiation at large primary Si clusters. AlSi12Cu3Ni2 shows comparatively smaller primary Si clusters and damage initiation and accumulation at later TMF stages. Thermodynamic simulations and sensitivity analysis allow understanding how different microstructures formed and their correlation to TMF resistance.