Abstract: The refinement of the grain size will improve the mechanical properties of AA-356 alloy by propagating ultrasonic vibrations through the die into the melt and adding Al-5Ti-1B master alloy during solidification. Ultrasonic vibrations produces cavitation effect by reducing pores, degassing and formation of more heterogeneous nucleating sites of AA-356 due to the presence of TiAl3 and Bal2 solutes of master alloy. The melt was vibrated at various frequencies and amplitudes with certain interval of time by adding master alloy (Al-5Ti-1B) at different fractions by using Taguchi Technique. From heterogeneous nucleation experimental results shows that the AA-356 structure was changed from columnar dendrite structure into equi-axed globular grain structure with reduction in grain size. The experimental results shows that due to reduced grain size, the mechanical properties like hardness, ultimate tensile strength were increased.