Even though phase diagram of the Al-B system has not been fully understood, it is generally agreed that there are two stable borides, AlB2 and AlB12. It was found from the microsturure that needle shpaed diboride, AlB2, became (Al,Mg)B2 as 1.4wt%Mg is added to Al-3wt%B alloy. The (Al,Mg)B2 phase was formed in the location of inter and intra the Al dendritic region. Both XRD and EPMA results confirmed the precipitation of (Al,Mg)B2 phase. The average composition of the (Al,Mg)B2 diboride, analyzed by EPMA, in at% was Al20.76Mg13.49B65.75.
The hardness and the elastic modulus of (Al,Mg)B2 particles analyzed by nanoindentation are 27 ± 4 GPa and 356 ± 38 GPa. The alloy with Mg addition exhibited higher tensile strength while elongation was decreased.