The solid dispersant (graphite) and additional alloying by scandium effects on the intermetallic compound formation in the Al–Mg system under mechanical alloying are studied. As found, the scandium additive significantly accelerates the metastable intermetallic Al$_3$Mg phase formation in (75% at. (Al + 2% wt. Sc)–25% at. Mg)/5% wt. C powder mixture compared to the (75% at. Al–25% at. Mg )/5% wt. C one. The synthesized powder composite, containing metastable Al$_3$Mg phase and solid solution based on aluminium, is consolidated by the spark plasma sintering (SPS) method. The phase composition, structure, and hardness of the SPS sintered samples are determined by X-ray diffraction, scanning electron microscopy, and indentation by the Vickers indenter. The hardness of samples formed after spark plasma sintering is in the range of 175–212 $HV$ and significantly exceeds the hardness of duralumin (124 $HV$).