A developed approach for fabricating in situ Al3Ti/Al composites via ultrasound assisted direct reaction between solid Ti powers and liquid Al at 780 degrees C was proposed in this research. In situ formed Al3Ti particles were blocky in morphology, and the size of most Al3Ti particles was in the range of 2-7 mu m. The effects of ultrasonic vibration on the microstructure and fabricating process of in situ Al3Ti/Al composites were also discussed by comparing the ultrasonic treated sample and the contrast sample without ultrasonic treatment. In addition, a reaction-peeling model was suggested to explain the formation mechanism of small blocky Al3Ti particles. Crown Copyright (C) 2013 Published by Elsevier B.V. All rights reserved.