Morphology of spinels and Al₂O₃ particles in an Al₂O₃/Al-Mg-Si composite material revealed by scanning low energy electron microscopy

In metal matrix composite materials consisting of oxide particles and Al alloys, including Mg as a solute atom, MgAl₂O₄ spinels are formed at the interface between the particles and the matrix. In the present study, the scanning low energy electron microscopy (SLEEM) method has been applied to confirm morphologies of α-Al₂O₃ particles and MgAl₂O₄ spinel crystals grown on the alumina particles in the Al₂O₃/Al-1.0mass% Mg₂Si alloy composite material. The morphology of α-Al₂O₃ particles before fabrication of the composite material was like a facetted barrel with 2 hexagonal (0001} and 6 trapezoidal {1101} planes. Spinels were formed on facets of Al₂O₃ as small particles, and their shape was an octahedron consisting of 8 equiaxial triangles. Spinels and Al ₂O₃ particles keep their orientation relationship which was concluded by our recent TEM study: (111)_MgA12O₄, // (0001)_Al2O₃, [21̄1̄]_MgAl2O ₄ // [21̄1̄0]_Al2O_3, [11̄0] _MgAl2O₄ // [11̄00]_Al2O₃