GRAIN REFINING OF AZ91E ALLOY USING SIC NANOPARTICLES S. Poola, J. Liu, and F. He


Purdue University, West Lafayette, IN, USA Copyright © 2010 American Foundry Society Abstract:


In this paper, ultrasonic vibration was used for dispersing SiC nano-particles into molten metal in order to use these particles as nuclei for grain refinement. Experimental results indicate that small grains can be obtained in metal molds using ultrasonic vibration alone. Nano-particles that


Introduction


Casting microstructure is a key factor in determining the me- chanical and fatigue properties of automotive components. The current methods for grain refining high temperature magnesium alloys are either costly or difficult to control for LPPM casting process1,2


nano-sized particles for grain refining3,4


.This research focuses on the use of . Power ultrasound is


used to disperse a small quantity of nano-sized particles in molten metal for grain refining.


Experimental Procedure


was added into molten metal. Ultrasonic vibration was applied on the molten metal to disperse the individual nano particles from their agglomeration.The molten met- al containing SiC nano particles was then poured into a metal mold to make specimens.The grain structure of the specimens was observed with an optical microscope a us- ing polarized light option and the grain sizes were mea- sured using the linear intercept method described in the ASTM E112-96 standard.


AZ91E alloy was melted and held at 750⁰C in a graph- ite crucible under a protective cover gas mixture of 2.5% SF6+ balance CO2


Results and Discussion


A SEM Image of Commercial SiC Particles Used for Grain Refinement


The size of the individual nano-sized particles is abut 30 to 50 nm (Figure 1). Small nano-sized particles agglom- erate and form clusters about a few microns in size.The voids among the nano-sized particles make it difficult to


Grain Refinement Using Nano Particles Dispersed by Ultrasonic Vibration


. 0.05 wt.% of 30nm sized SiC particles


The average grain size was about 210 µm in the control specimen(Figure 3-(a)) but was smaller than 50 µm in the specimen with an addition of 0.05 wt% SiC(Figure 3-(b)). Spersing nano-sized SiC particles into molten AZ91E al- loy by ultrasonic vibration has shown a significant effect on grain refinement.


Acknowledgment


Research was partly sponsored by a start-up fund pro- vided by the Department of Mechanical Engineering Technology of Purdue University and partly sponsored by the U.S. Department of Energy, Assistant Secretary for Energy Efficiency and Renewable Energy, Office of FreedomCar and Vehicle Technologies, Automotive Lightweighting Materials Transportation Technology Program, the ORNL SHARE user facility, under contract with UT-Battelle, LLC. The authors would like to thank USCAR and Joe Carpenter of the DOE for their financial support of this work.


are dispersed into molten metal using ultrasonic vibration can serve as nuclei for grain refining of Mg alloys.


Keywords: ultrasonic vibration, grain refinement, SiC nano particles, AZ91E alloy


add nano particles into molten metal and wet nano par- ticles by melt.


Individual Nanoparticles Dispersed into the Alloy by Using Power Ultrasound


Power ultrasound creates local high temperature, pressure and shock waves that disperse nanoparticles from their ag- glomerations into molten metal. Ultrasound can also cleanse the surfaces of the particles so that they serve as nuclei for new grains during alloy solidification (Figure 2).


66


International Journal of Metalcasting/Winter 10


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