This invention applies ultrasound vibration to molten metal, when it is being cast into a mold, during the entire solidification process. The inventive features correspond to how the vibrations are applied during the solidification. The vibrations are applied in two different ways. Method #1: A through hole is first drilled into the mold wall and the ultrasound probe (that sends the vibrations) is inserted from outside of the mold and through the mold wall. Care is taken that the ultrasound probe does NOT enter into the cavity of the mold and the end that was inserted through the mold wall is flush with the inner wall of the mold. The drilled through hole is just large enough for the ultrasound probe to fit and slide in and out easily, but small enough that the molten metal (from inside the mold) does not leak through from inside to the outside. Thus, when molten metal is poured into the mold, the ultrasonic probe is turned on. As the molten metal starts to solidify in the mold, the molten metal around the probe tip is subjected to ultrasound waves and the solidification process in the local region around the probe continues in the presence of the ultrasound. Gradually, the temperature of the molten metal decreases during solidification, and when the metal in the mold is fully solidified (i.e. temperature everywhere in the metal is below its solidus temperature), ultrasonication can be stopped. Since the ultrasound probe was NOT inserted into the mold cavity , the solidified casting can be removed from the mold independent of the ultrasound probe. Thus, we can fabricate casting in a mold in presence of ultrasound but without the ultrasound probe getting embedded into the casting. Method #2: A hole is drilled into the mold wall but unlike the Method #1, the hole is NOT a through hole. Instead, 3-6 mm worth of wall thickness is retained. Thus, the probe is inserted into the hole so that it touches the hole bottom and a 3-6 mm thick material separates the probe tip from the inside of the mold. During casting, the molten metal is poured into the mold and the ultrasonication is turned on and can be kept on during the entire process of solidification. The ultrasound pulses pass through this 3-6 mm thick wall into the molten metal and improves the local microstructure around it. Gradually, the temperature of the molten metal decreases during solidification, and when the metal in the mold is fully solidified (i.e. temperature everywhere in the metal is below its solidus temperature), ultrasonication can be stopped. Since the ultrasound probe was NOT inserted into the mold cavity and was physically not in contact with molten metal at all, the solidified casting can be removed from the mold independent of the ultrasound probe. Thus, we can fabricate casting in a mold in presence of ultrasound but without the ultrasound probe getting embedded into the casting.