The effect of modification on the mechanical properties of the secondary aluminum casting alloy (wt.%: 0,528 Mg, 1,124 Cu, 11,539 Si, 84,969 Al, 0,905 Fe, 0,692 Zn, 0,242 Mn) without heat treatment was determined by the introduction of silicon carbide with a particle size of 1-3 μm in the amount of 0.1, 0.2, 0.3 wt. %. Castings were made in steel molds. It is established that the strength of unmodified alloy (σв) is 110 - 120 MPa. When the content of SiC in the alloy from 0.1% to 0.2%, the indicators of σв increase from 130-145 MPa to 155-166 MPa, respectively. Increasing the SiC content to 0.3% leads to a decrease in σв values in the range of 117 - 127 MPa. Hardness indices (HВ): unmodified alloy - 42 - 43, alloy with a content of 0.1% SiC - 43 - 44, with a content of 0.2% SiC - 46 - 47, with a content of 0.3% SiC - 43 - 44. Determination of the density of cast metal obtained in a steel mold and in a sandy-clay form was carried out by the method of hydrostatic weighing of samples in СCl4. It has been established that the density of the alloy of castings with a silicon carbide content of 0.1% is 2761 kg/m3, and that of the unmodified alloy is 2715 kg/m3. With an increase in the silicon carbide content to 0.2%, the density of the metal is 2735 kg/m3. With a SiC content of 0.3 wt.%, the density of the alloy is 2752 kg/m3. The density of the metal of the castings obtained in the sandy-clay form with the modification of 0.1% SiC is 2673 kg/m3, with 0.3% SiC - 2676 kg/m3.