Al-4Cu-xTiB 2 (x = 2.5, 5, 7.5 and 10 wt.%) in situ composites have been successfully prepared by the reaction of mixture of K2 TiF6 and KBF4 with molten alloy. A reaction temperature of 800 °C and a reaction time of 60 min were adopted. A continuous increase in the yield strength and ultimate tensile strength without any significant loss in ductility has been observed with increase in the amount of TiB2 in both as-cast and peak-aged conditions. TiB2 particles enhance the aging kinetics and the time to peak aging at the aging temperature of 170 °C comes down from 40 to 6 h when the TiB2 amount is increased from 0 to 10%. © 2004 Elsevier B.V. All rights reserved.