Solidifying


Under Pressure for Improved Properties


Researchers are examining the possibility of applying pressure to aluminum during sand casting to improve component properties.


SANTOSH GHANTI, EDWARD DRUSCHITZ, ALAN DRUSCHITZ AND JOHN GRIFFIN, UNIV. OF ALABAMA AT BIRMINGHAM, BIRMINGHAM, ALABAMA


T


he mechanical properties of aluminum castings can be affected by dissolved


gases and/or shrinkage remaining in a casting after solidification. These defects can be reduced by post processing operations; however, this adds to the cost of the component. Past studies have shown that


applying pressure during solidifica- tion can reduce the size of hydrogen/


gas porosity and improve mechanical properties. Te Castyral R (or pres- sure solidification) process was pat- ented in 1989 and involves pouring a casting inside a pressure vessel and increasing the pressure until solidifi- cation is complete. Mercury Marine produces approximately 20,000 cylin- der blocks per year using this process for lost foam castings. In a previous study, aluminum alloy


A356 lost foam castings solidified under pressure showed a 50-130% increase in elongation but did not show any sig- nificant improvement in tensile or yield strength. Te study showed a reduction in porosity, but no attempt was made to correlate porosity with strength or elongation. A more recent study has examined


solidification under pressure with the nobake sand casting process on an A356


Fig. 2. This pressure vessel was used for the solidification research.


Fig. 1. Shown is a digital rendering of the wedge casting and gating system. At right, the casting dimensions and locations of the thermocouples are indicated (dimensions are in mm).


March 2011 MODERN CASTING | 29


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