Microstructural characterization of in situ TiC/Al and TiC/Al-20Si-5Fe-3Cu-1Mg composites prepared by spray deposition

An innovative spray-deposition technique has been applied to produce in situ TiC/Al and TiC/Al-20Si-5Fe-3Cu-1Mg composites. This technique provides a new route to solve the problems of losses and agglomeration of the reinforcement particles when they are injected into the spray cone of molten droplets during spray forming process. Experimental results have shown that the presence of needle-like Al3Ti and Al-Si-Fe compounds, which are detrimental not only to the fracture toughness, but also to the stability of the microstructure, can be eliminated completely from the final product by using a proper Ti:C molar ratio of 1:1.3 in the Ti-C-Al preforms and adding 5 wt% TiC particles to Al-20Si-5Fe-3Cu-1Mg alloy. Moreover, another major problem of coarsening of silicon particles usually encountered in the hypereutectic A1-Si alloys has also been solved by the technique. The silicon particles in the spray-deposited 5 wt% TiC/Al-20Si-5Fe-3Cu-1Mg composite were much refined (similar to2 mum) compared to those (-5 pm) obtained in the matrix alloy without TiC addition. The formation and elimination mechanisms of Al3Ti phase in TiC/Al composites can be explained based on thermodynamic theory. The modification of the microstructures in the spray-deposited Al-20Si-5Fe-3Cu-1Mg alloy can be interpreted in the light of the knowledge of atomic diffusion. The experimental results also showed that the ultimate tensile strength of the TiC/Al composites was improved over that of the unreinforced Al matrix. (C) 2003 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.