*2.1. Materials and Modification Technology*

The object of the study was a eutectic Al-12wt%Si alloy. The chemical compositions of the experimental alloys are presented in Table 1.


**Table 1.** Chemical compositions of experimental alloys.

Salt (RbNO3) was chosen as the compound to add rubidium into the melt. The estimated amounts of rubidium added to the alloy were chosen to be equal to 0.1%, 0.3%, 0.5%, and 1.0% from the weight of the melt. The salt was dried at 150–200 ◦C for 2 h before melting.

Experimental melting was carried out in an electric resistance furnace. The weight of one melt was 1 kg. The melt was previously degassed with argon. Rubidium salt (RbNO3) was added into the melt at the bottom of the crucible at a temperature of 750 ± 5◦ with the help of a "bell". The treatment of the melt with the salt was accompanied by bubbling. Then, the melt stood for 10 min, slag was removed from its surface, and samples of the experimental alloys were poured into a sandy-clay mold at a temperature equal to 710 ± 5 ◦C. Samples were cast separately to determine porosity.

The weight of the melt to determine the duration of the modification effect was equal to 5 kg. The melt was kept at a constant temperature equal to 730 ± 5◦C for up to 240 min. In the process of holding the melt, samples were poured into a sandy-clay mold at the time intervals of 15, 30, 45, 60, 120, 180 and 240 min.
