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the melt was degassed to a Reduce Pressure Test sample density of 2.63. Te porosity level was related to the local solidification time and temperature gradient. Because these thermal parameters were readily available from solidification modeling, it was possible to predict the distribution of the porosity (Fig. 9). Samples were cut out at two locations where ther- mocouples had been inserted, i.e. in the feeder tube and in a gate. Te measured porosity in the gate was 0.8%, in reasonable agreement with the predicted results. Te actual porosity level of the aluminum solidified inside the steel tube was 0.4%, much lower than predicted. Te long solidification time (19.2 minutes) of the quiescent liquid melt inside the steel tube is believed to have allowed natu- ral degassing to take place. Figure 10 shows the metallo- graphic aspect of both samples at low magnification. Due to the longer solidification time inside the tube, the


secondary dendrite arm spacing was larger than in the gate (90µm vs 71µm). While low pressure sand casting is not as common


as gravity sand casting or LPPM, it holds a distinct combination of advantages when pouring large cast- ings, including tranquil filling, obtaining metal from underneath the oxidized surface of molten aluminum for higher metallurgical quality, thin wall capability, easy metal handling, and cost efficiency.


Fig. 9. Solidification modeling plots the predicted porosity distribution in the casting (% volume).


Fig. 10. Micrographs of aluminum A356 in the gate (left) and inside the feeding tube is shown.


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