The solidification microstructure and mechanical properties of Al2O3/A356 metal matrix composites

In the present work, variations in the microstructure, mechanical properties and fracture character with different solidification cooling rate for Al2O3/A356 composites fabricated by squeeze casting were investigated. Experimental results showed that when the solidification cooling rate decreased, the size of crystalline grain of the matrix alloy and eutectic Si phase increased gradually, but the bending strength and the elastic modulus decreased. Meanwhile, the bending strength and elastic modulus of Al2O3/A356 composites were up to 521MPa and 102GPa respectively by appropriate fabrication technology. Actually, for Al2O3/A356 composites fabricated by squeeze casting, the solidification was occurred first in the interstices among particles and the surface of particle was the substrate of the heterogeneous nucleation of eutectic Si phase. Fracture surface of the Al2O3/A356 composites showed character of brittle fracture and the broken and cleavage Al2O3 particles were observed on the fracture surface of the composites. The microcracks were mainly initiated by the cleavage Si phase, and when the load increased the microcracks propagated to the adjacent Al2O3 particles or along the Al2O3/matrix interface.