Influence of TiO2 particles on recrystallization kinetics of Al–2Mg–TiO2 composites

The effect of TiO2 (rutile) particles on recrystallization kinetics of Al–2Mg–TiO2 composites has been studied. These composites were prepared using modified spray forming and conventional stir casting techniques. As cast composites were cold rolled to increase density and subsequently annealed. Results show that recrystallization in composites takes place in the as cast condition without any cold working. The driving force for such phenomenon has been attributed to the generation of thermal stress due to the thermal mismatch between Al and rutile particles. No such transformation was observed in the as spray formed Al–2Mg alloy. Resistivity measurements show a “single hump” in both cold rolled Al–2Mg alloy and cold rolled Al–2Mg–TiO2 composites. The “single hump” is due to the overlapping of recovery and recrystallization. The kinetics of recrystallization is faster in cold rolled Al–2Mg–TiO2 composites as compared to the cold rolled Al–2Mg base alloy and consequently hardness of composites decreases at a faster rate during annealing treatment vis-à-vis the base Al–2Mg alloy. Rapid recrystallization in composites is due to the generation of thermal stresses owing to the thermal mismatch between the Al matrix and TiO2 particles. Thermal stress results in greater dislocation density in the matrix of Al–2Mg–TiO2 composites.