Microstructure and mechanical properties of Al-base composites by addition of Al-Ni-Co decagonal quasicrystalline particles through a mechanical stirring route

In the present study, the A356Al-base composite materials were fabricated by introducing 2.5, 5, 7.5, 10 mass% of Al-Ni-Co decagonal quasicrystalline particles using the mechanical stirring method. The microstructures, mechanical properties, and Brinell hardness of these composites were investigated in detail by means of scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). It is found that serious compositional diffusion occurs between the Al72Ni12Co16 quasicrystalline particles and the Al melt. Microstructural analysis of all as-cast composites shows that the structure of the quasicrystal disappears and is replaced by the formation of two crystalline phases, Co-rich theta-phase and Ni-rich gamma-phase which all contain Al, Si, Ni, and Co. The particle sizes of the two crystalline phases are much smaller than that of the original decagonal quasicrystalline phase. The composites exhibit improvement of 10.5-24% and 20-25% in yield strength and Brinell hardness, respectively, while the percent elongation decreases obviously. Examination of the fracture surface of the as-cast A356Al-base composites shows that they exhibit typical brittle fracture mode.