PREPARATION OF HOMOGENEITY IMMISCIBLE ALLOY BY MARANGONI CONVECTION
利用Marangoni对流制备均质偏晶合金

A new control casting technique was designed for making homogeneity immiscible alloy in earth gravity field by Marangoni migration of the secondary phase drops in the melting alloy under a temperature gradient. In the technique, the droplet of the secondary phase ahead the solid-liquid interface of the melt of the immiscible alloy will make Stokes movement in gravity field and Marangoni movement in the opposite direction of gravity field in temperature gradient field. As a result, the net velocity of the droplets in the melt will be dependent on the size of the droplets. When the size of the droplets is very small,Marangoni movement of the droplets will dominate, otherwise Stokes movement will dominate. When the net velocity is zero, there will be a critical size of the droplet. By controlling the stability of the solidification process, an ingot with uniform distribution of the dropletscan be obtained. The critical size of the secondary phase droplets was estimated by the following equation Solidification test on Al-Bi and Al-Pb alloy showed that the size of the Bi or Pb particles in Al matrix is roughly the same order of magnitude as that obtained by above equation.Finally, a new conception, precipitation incubation period, was suggested in the discussion.