Clusters of reinforced particles and long rod-like Al(3)Ti particles are usually present in the matrix of in situ TiC/Al alloy composites fabricated via SHS reaction of the Al-Ti-C system in the molten aluminum alloys. In order to improve the properties of the composites, the above issues should be solved effectively. In our research, high-intensity ultrasonic vibration was introduced into the remelting TiC/Al-12Si composites containing clusters of TiC particles and long rod-like Al(3)Ti phase to optimize the microstructure of the composites. The results of SEM showed that long rod-like Al(3)Ti particles were turned into small blocky ones and large clusters were broken up into small ones. In the meantime, individual TiC particles could be peeled off from the clusters and distributed uniformly in the matrix. An in situ TiC/Al-12Si composite with a homogeneous microstructure was attained successfully. The evolution of the morphology of Al(3)Ti phase and the clusters in the ultrasonic field was also discussed. (C) 2011 Elsevier Ltd. All rights reserved.