한국주조공학회

A numerical analysis on the microstructural evolutions of microcellular and cellular α-aluminum phase in the gas-atomized Al-8wt. pct droplets was represented. The 2-dimensional non-Newtonian heat transfer and the dendritic growth theory in the undercooled melt were combined under the assumptions of a point nucleation on droplet surface and the macroscopically smooth solid-liquid interface enveloping the cell tips. It reproduced the main characteristic features of the reported microstructures quite well. It predicted a considerable volume fraction of segregation-free region in a droplet smaller than l0μмm if an initial undercooling larger than 100K is given. The volume fractions of the microcellular region(g_A) and the sum of the microcellular and cellular region(g_a were predicted as functions of the heat transfer coefficient, h and initial undercooling, △T. It was shown that g_A and g_a, in the typical gas-atomization processes with h=0.1-1.0W/cm^2K, are dominated by △T and h, respectively, but for h larger than 4.0W/cm^2K, a fully microcellular structure can be obtained irrespective of the initial undercooling.