High resolution cone beam X-ray computed tomography of 3D-microstructures of cast Al-alloys

AlMg5Si7 XCT-data with a voxel size of (0.4 μm)3 show inhomogeneities with brighter grey-values than the Al-matrix identified as elongated Fe-aluminides, and those with lower grey-values identified as pores and Mg2Si-particles with a “Chinese script-like” structure. Higher-absorbing interdendritic Al-Al2Cu-eutectic regions appear brighter than the Al-dendrites in the CT-data of AlCu4Mg1 with (1.1 μm)³/voxel, whereas pores > 4 μm appear darker than the Al-matrix. The size and the 3D-structure of the α-Al dendrite arms with a diameter of 50-100 μm are determined in samples from chill cast billets of AlCu4Mg1 and AlZn6Mg2Cu2 alloys. The irregular interdendritic regions containing eutectic segregations with Cu- and Zn-rich phases are > 5 μm wide. Equally absorbing primary equi-axed Al3(Sc, Zr) particles > 5 μm are distinguished in the centres of the dendrites by the level of sphericity values. The distribution of Ni- and Fe-aluminides in a squeeze cast AlSi12Ni1-alloy is imaged with (0.4 μm)³/voxel, but the Si-phase cannot be segmented.