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morphology of silicon found in sodium and strontium impurity modified alloys.


3


Procedure Te process involved melt-


ing Al-Si alloys with 6-10% silicon in an argon-rich envi- ronment. A resistance furnace


maintained a temperature of 1,418 F (770 C) for the barium treatment. After which, the resulting melt was poured into a permanent mold that was preheated to 850 F (454 C). Te casting then cooled to room temperature before heat treat- ment. For such treatment, furnace cooled alloys were initially solution treated at 975 F (525 C) for 11 hours and then quenched in water. Te quenched samples were then aged in the same


Results and Conclusions


Te morphology of silicon is similar to that in unmodified Al-Si alloys, but differs signifi- cantly from that of the fibrous


Fig. 3. Heat treatment causes larger silicon particles in the Al-6%Si-1% Ba alloy.


furnace at 356 F (180 C) for 24 hours. Longitudinal and transverse section specimens taken from near the center of the samples were used to determine the microstructure. Visual inspection of the surface revealed negligible amounts of porosity and other casting defects.


Te samples then were subjected to tensile testing. Te microstructure of the alloys was studied using scanning elec- tron microscopy (SEM). Samples were etched to remove surface aluminum and expose the topography and morphology of silicon phase.


48 | MODERN CASTING March 2016


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