The Al-Fe-Si system has been the focus of attention of world science for a long time, but there are still unknown scientific areas. A system that provides a fully intermetallic phase composition has been considered, which is a very relevant approach and is of particular interest. In this paper, based on modeling, the phase composition of an alloy rich in silicon and iron has been predicted using commercial starting materials. Heat treatment of the alloy has been carried out using two cooling methods: water and air. It has been found that with accelerated cooling in water, the alpha <-> beta transition is partially suppressed with the formation of a double intermetallic phase theta, with the replacement of some aluminum atoms with silicon atoms. When cooling in air, the dominant phase is the theta phase; the transition theta' with a reduced iron content has been detected.