Figure 3: Hot isostatic processing (HIP) of investment cast 4340+ (silicon modified 4340) showed significant improvements in impact toughness and ductility while austempering showed significant improvements in impact toughness and ductility at the expense of strength. The investment cast Fe-C-W alloy being experimented with has shown superior impact toughness and ductility when compared to the investment cast 4340+ alloy.


GRAIN REFINEMENT OF PURE ALUMINUM USING ULTRASONICS C. Allen and Q. Han


Purdue University, West Lafayette, IN, USA Copyright © 2011 American Foundry Society


ated for microstructure characterization. The etched samples showed significant grain refinement using ultrasonic vibra-


International Journal of Metalcasting/Winter 11


Background The effect of ultrasonic processing during aluminum solidi- fication has been an area of recent interest [Ref.1-4]. To fur- ther the recent work on this subject, the effects of ultrasonic processing were tested on commercial grade pure aluminum. The solidification process of pure aluminum is simpler than alloys. This simplicity is desired to help better understand the mechanism of grain refinement using power ultrasound. The large grain structure of pure aluminum helps for easy comparison of the resulting grain structures. Small samples were created by pouring the melt into an inverted cone cru- cible at different temperatures. Ultrasonic vibration was ap- plied to the melt via the bottom of the crucible (Fig.1). The pouring temperatures used during the experiment were 670, 680, 690, 700, and 710°C. Upon cooling the samples were cut, face milled, and macro etched using a solution of 3HCl + 1HNO3


. The resulting grain structures were then evalu-


tion, even when viewed by the naked eye (Fig. 2). Vibrated samples showed a more uniform, equiaxed grain structure versus the long, columnar structure of their respective con- trol samples. Grain size was also greatly affected by the ul- trasonic processing. On average, the vibrated samples had a mean grain size that was about 7% of the grain size in the control samples (Table 1). Limitations to these experimental results include the presence of residual grain refiners in com- mercial grade pure aluminum, making the grain size in the control sample much smaller. Also, due to the attenuation of ultrasonic vibration in the melt, it is difficult to propagate the ultrasonic wave through large melts. The work is being scaled up to test the feasibility of ultrasonic processing dur- ing the solidification of larger ingots.


Acknowledgments


Research was sponsored by NSF SBIR program (Grant No. IIP-0912132). Aluminum samples were made at Hans Tech Company.


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