Strengthening in Al alloy nano composites fabricated by ultrasound assisted solidification technique

Effect of temperatures of high power ultrasonic processing (700 °C, 725 °C, 750 °C, and 775 °C) on the distribution of 1 wt% Al2O3 nano-particles in Al6061 alloy melt is studied. From the microstructural examination, it is observed that nano particles are better dispersed in the alloy matrix with increasing ultrasonic processing temperature. Some agglomerated reinforcement particles are seen at lower ultrasonic processing temperature of 700 °C. As compared to the base alloy, mechanical properties like hardness, 0.2% offset yield strength, and ultimate tensile strength increased significantly with processing temperature. This is attributed mainly to the coefficient of thermal expansion mismatch between the alloy matrix and the Al2O3 particles, followed by Orowan strengthening, and to a lesser extent to the Hall-Petch strengthening mechanism.