The paper presents an experimental study regarding two Al-Si alloys concerning the influence of ultrasonic treatment on the hardness and microhardness. AlSi12 ultrasound treated function as time hardness important decreases are observed. AlSi7 ultrasound treated function as time hardness easily increases is observed. The contradiction between two measurements was studied by microhardness of AlSi7 grain and eutectic mass materials. Important microhardness decreasing on eutectic mass materials is observed.