Properties of mechanically milled and spark plasma sintered Al–AlB2 and Al–MgB2 nano-composite materials

Air-atomized pure aluminium powder was mechanically alloyed (MA) with AlB2 or MgB2 by using a vibrational ball mill, and MA powders were consolidated by spark plasma sintering (SPS). Solid-state reactions of MA powders have been examined by X-ray diffraction (XRD), and mechanical properties of the SPS materials have been evaluated by hardness measurements and compression tests. The solid-state reactions in both Al–AlB2 and Al–MgB2 composites occurred between the MA powders and stearic acid used as a process control agent after heating at 573–873 K for 24 h. Formation of Al3BC ternary compound occurred in both composites. Formation of γ-Al2O3 was observed in the Al–AlB2 whereas formation of MgAl2O4 occurred in the Al–MgB2. As the result of solid-state reactions in both composites, a hardness increase was observed in MA powders after heating at 573–873 K for 24 h. The full density was attained for the SPS materials from 4 h MA or 8 h MA powders in both composites under an applied pressure of 49 MPa at 873 K for 1 h. The compressive proof strength of the SPS material of the Al–MgB2 was higher than that of the Al–AlB2. The SPS material of Al85(MgB2)15 from 8 h MA powder exhibited the highest compressive proof strength of 846 MPa at room temperature.