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increase in the size of the average pore (Fig. 5). Saleem and Makhlouf deduced that helium flowing in the cross-flow mode passes through the molten alloy, causing more pores. The castings produced via the parallel-flow mode,


3


however, showed fewer pores than those in the cross- flow helium-assisted castings as well as the baseline castings. The researchers believe this is because helium is flowing parallel to the casting surface rather than through the alloy itself. Because of the increase in porosity in the helium-assisted


castings produced with the cross-flow mode, the researches deemed that method not viable and focused on the parallel- flow mode. At a 4-L/minute helium flow rate parallel to each face of the plate, the yield strength increased over the baseline casting from 179 to 241 MPa and the ultimate


Results and Conclusions Micrographs from the helium-assisted castings


made using the cross-flow mode showed more pores than the baseline sand castings, indicating an increased average area of porosity as well as an


Fig. 3. The supply plate is clamped and sealed to the drag for parallel flow helium supply.


Fig. 4. Shown is the location of the thermocouples in the plate casting. 42 | MODERN CASTING December 2012


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