The work presents the effect of strontium and antimony modification on the microstructure and mechanical properties of 226 silumin casts.

The performed research demonstrated that strontium causes high refinement of silicon precipitations in the eutectic present in the microstructure

of the examined silumin and it significantly affects the morphology of eutectic silicon from the lamellar to the fibrous one. Sr

modification also causes an increase of: the tensile strength „Rm” by 12%; the proof stress „Rp0,2” by 5%; the unit elongation „A” by 36%

and the hardness HB by 13%. Antimony did not cause a change in the microstructure of the silumin, yet it caused an increase in Rm and

HB by 5%, in Rp0,2 by 7% and in A by 4%.