Aluminum-Silicon-Copper alloys are the most commonly industrially used family of aluminum alloys because of their high specific strength as well as good castability and corrosion resistance. Ductility of aluminum- silicon alloys is a function of the amount of impurities in the alloys and microstructure features particularly morphology and silicon eutectic particle size. strength, ductility and castability of Aluminum- silicon alloys can improve by eutectic modified structure. In this research modification of aluminum-silicon alloys were carried out by in-mold method. Modification were done by salt NaCl 44%wt-KCl 44%wt-NaF 12%wt with various temperature and various weight percentage. It was found combination of sodium and melt of aluminum- silicon alloys offers advantage in initial effectiveness. Tensile properties were increased by about 20% compared with unmodified aluminum- silicon alloys. The TPRE model is the best available model for the growth of plate like silicon. It was found at strontium concentration about 0.02, and with over time about 7 hours, in this condition may be sufficient to suppress completely the TPRE growth. As well as the effect of cooling rate on microstructural features and mechanical properties of AS7U3G alloy was investigated and the modified Hall-Petch equation constants of the alloy were determined. Keywords: aluminum- silicon- copper, modification, in-mold, TPRE, mechanical properties, microstructure
