Effects of hollow sand mold on the microstructure and mechanical properties of a low pressure aluminum alloy casting

The hollow mold revolutionizes conventional dense mold design as it can optimize the solidification and cooling processes of casting and offer potential to improve performance of castings. In this paper, the effect of hollow mold structures on the microstructure and mechanical properties of a low pressure thin-walled aluminum alloy conical cabin casting was investigated. A hollow mold combined by four sectors with different shell thicknesses was tactfully designed. The hollow mold structures delayed the cooling and solidification of casting. They significantly reduced the pore defect from 0.4 % to 0.03 % at the lower, from 0.68 % to 0.04 % at the middle and from 0.3 % to 0.03 % at the top, compared to dense mold. In the lower and middle areas of casting, improvements of 1.0 % and 1.1 % in mechanical properties were respectively achieved when applying 50 mm-thick-shell hollow sand molds compared with using dense sand mold, while an improvement of 1.1 % was achieved in the upper area of casting with 70 mm-thick-shell. This allows designers to create hollow molds with different shell thicknesses depending on the position in the casting to meet specific needs. For example, thin shell for the bottom to achieve high fluid flow and feeding while thick shell for the top for improved cooling. For castings with wall thickness of 10 mm-20 mm, the most effective shell thickness for the hollow mold is 50 mm-70 mm. The hollow mold provides the feasibility to differentiated semi-quantitatively control the solidification and cooling processes of castings, which can be applied in production of high-end castings in the future.