In this paper, the hard alloy Al-Si-B has been prepared through melting the precursor, which is obtained by sintering the powders of B, Al, Mg and SiO2 by electron beam. The structure and properties of the final obtained alloy has been studied by X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). The results reveal that the alloy is amorphous. Nano indentor test shows that the average hardness of this alloy is 33.8 GPa. The electrical resistivity measured with a four probe instrument of the alloy is 6.8×10-5 Ω·cm showing a excellent electrical conductivity. Relative friction test shows that this boride has a extremely low friction coefficient of 0.06.