Honglan Xie

Real-Time Observation on Evolution of Droplets Morphology Affected by Electric Current Pulse in Al-Bi Immiscible Alloy

The evolution of Bi-rich droplets morphology in a solidifying Al-Bi immiscible alloy was directly observed using a synchrotron microradiography technique. The electric current pulse (ECP) was applied to control the solidification process of Al-Bi immiscible alloy. It was found that the electromagnetic pinch force and Marangoni force induced by ECP and temperature gradient, respectively, can significantly affect the distribution of Bi-rich droplets. The electromagnetic pinch force drove the droplets from the center to side; meanwhile, the Marangoni force lifted the droplets from the bottom to the top. As a result, the droplets finally distributed with a manner of “inverted triangle.”

Evolution of atomic structure in Al75Cu25 liquid from experimental and ab initio molecular dynamics simulation studies

X-ray diffraction and electrostatic levitation measurements, together with the ab initio molecular dynamics simulation of liquid Al(75)Cu(25) alloy have been performed from 800 to 1600 K. Experimental and ab initio molecular dynamics simulation results match well with each other. No abnormal changes were experimentally detected in the specific heat capacity over total hemispheric emissivity and density curves in the studied temperature range for a bulk liquid Al(75)Cu(25) alloy measured by the electrostatic levitation technique. The structure factors gained by the ab initio molecular dynamics simulation precisely coincide with the experimental data. The atomic structure analyzed by the Honeycutt-Andersen index and Voronoi tessellation methods shows that icosahedral-like atomic clusters prevail in the liquid Al(75)Cu(25) alloy and the atomic clusters evolve continuously. All results obtained here suggest that no liquid-liquid transition appears in the bulk liquid Al(75)Cu(25) alloy in the studied temperature range.

Real time imaging on dendrite morphology evolution during alloy solidification under electric field

The dynamic dendrites growth of metallic alloy during the solidification can not be in-situ observed since the metallic alloy is in optically opaque. It is also not possible to in-situ study the influence of electric current on dendrites growth behaviour. By using synchrotron radiation imaging technique, the evolution of dendrite morphology under an electric current is observed. Results indicate that the direct current can significantly suppress the dendrites growth and the dendrite tip tends to be round from sharp. Increasing the current intensity, the dendrite tip splits due to the current crowding and solute pileup around the round tip. The pulsed electric current can significantly enhance the solidification rate and refine the primary and secondary dendrite arm spaces because of the thermal and mechanical shock around solid/liquid interface.