Abstract

<p indent="0mm">Fluid flow and solidification mechanisms of Al<sub>70</sub>Ag<sub>20</sub>Ge<sub>10</sub> alloy were systematically investigated using electromagnetic levitation, induction, arc, and resistance melting techniques coupled with finite element simulation method. A unique type of vortex-shaped microstructure was formed in these four experiments. This was different from the result under slow solidification conditions. The formation of the vortex-shaped structure was affected by fluid flow and cooling rate of alloy melt. The Lorentz force caused turbulent flow in alloy melt, while the turbulent flow during arc melting was driven by arc force under electromagnetic levitation or induction melting conditions. The surface tension and buoyancy force caused laminar flow in alloy melt during the resistance melting process. Due to rapid flow, the Ag<sub>2</sub>Al phase nucleated ahead of the Al phase, primarily under near-equilibrium conditions. The metastable Ag<sub>2</sub>Al dendrites grew as vortex-shaped morphology and preserved the melt flow pattern during solidification. The increased cooling rate caused a rapid growth of metastable Ag<sub>2</sub>Al dendrites with increased vortex density. The curvature radius of metastable Ag<sub>2</sub>Al dendrites decreased with enhanced melt flow; meanwhile, the more drastic nucleation and growing competition among phases occurred. Finally, irregular Al, Ag<sub>2</sub>Al, and Ge ternary eutectics fully formed inside the vortex-shaped structure.

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