Ternary phases in Al-B-C system bearing icosahedral boron structures, such as AlB12C2, AlB24C4, Al3B48C2, are of interest due to a possibility to replace rigid purely carbide component of bond between boron icosahedrons in the form of -C-C-C- chains in boron carbide (B12C3) with an elastic metal component by a replacement of carbon atoms by aluminum ones. Ab initio calculations performed on geometric configuration of -C-Al-C- chain between boron icosahedrons in AlB12C2 indicate its change to angular one in comparison with linear chain -C-C-C- in B4C. This suggests that icosahedral aluminum carboborides are less prone to amorphization due to high-energy dynamic loading while maintaining a level of mechanical properties close to boron carbide. Phases formed by interaction of B4C with aluminum vapor in vacuum at temperature 1673K in a wide range of Al concentrations were studied. Thermodynamic calculations as to a possibility of hypothetical reaction 3B4C + 5Al = AlB12 + Al4C3 show its high probability if Al is gaseous. Concentration limits for formation of composite powders of stable composition AlB12C2 85% mass. and Al8B4C7 – 15% mass were determined. This composition has a high technological ability of compaction: at pressure of hot pressing P = 30 MPa and temperature 2103–2123 K hard ceramics with a density of 2.6 g / cm3, Hμ (2H) = 27-28 GPa, Hv (98 H) = 19-20 GPa; K1C = 3.5-4.5 MPa‧m1 / 2 were perennially obtained.