Numerical simulation and experimental validation of SiC nanoparticle distribution in magnesium melts during ultrasonic cavitation based processing of magnesium matrix nanocomposites.

A two-dimensional coupled model of the temperature field, flow field and pressure field of SiC nanoparticles reinforced AZ91D magnesium composite slurries fabricated by high-intensity ultrasonic stirring method is established. The multiphase flow mixture model is used to simulate the temperature field, flow field and pressure field of the semi-solid slurries. The effects of ultrasonic stirring parameters on the distribution of SiC nanoparticles in AZ91D magnesium alloy melt are simulated by using finite difference method. The simulation results show that the distribution uniformity of SiC nanoparticles in Mg melts is influenced by ultrasonic power and frequency as well as the ultrasonic processing time and depth of ultrasonic probe dipped into the melts, but the ultrasonic power and frequency have greater influence on particle distribution. In the present work, the magnesium matrix composite with uniform dispersion of SiC nanoparticles can be obtained when the ultrasonic power, the ultrasonic frequency, the depth of ultrasonic probe dipped into the melts and ultrasonic processing time are 2 kW, 20 kHz, 20-30 mm and 120 s, respectively. It has been proven that the similar uniform dispersion could be achieved under the optimal ultrasonic processing conditions although SiC particle sizes in the agglomerated SiC-nanoparticles varied between 30 nm and 300 nm in diameter. Moreover, the microstructure and mechanical properties of the SiC nanoparticles reinforced AZ91D magnesium alloy based composites obtained experimentally are improved significantly by using the optimized ultrasonic processing parameters based on numerical simulation.