| Cylindrical lost foam castings were poured using aluminum alloy A356. Chills of three thicknesses and three materials were attached to the bottoms of the patterns to enhance solidification.; Chills reduced the local solidification time within all castings. This effect was most pronounced near the chill. As chill volumetric heat capacity increased, local solidification time decreased.; Modified mold saturation ratio takes into account thermal properties of the chill material, the mold medium, and the molten metal, thus enabling a more sophisticated description of mold heat extraction capacity. There was a good relationship between modified mold saturation ratio and local solidification time for the 25 mm diameter castings. Increases in modified mold saturation ratio led to corresponding decreases in local solidification time for all diameters.; Initial cooling rates increased with the application of chills. This effect was confined to locations adjacent to the chill.; Directional solidification occurred in all castings, even if a chill was not used. The use of a chill enhanced directional solidification.; Secondary dendrite arm spacing varied with local solidification according to: DAS = 10.84t{dollar}rmsbsp{lcub}f{rcub}{lcub}0.294{rcub}.{dollar}; There was a linear relationship between chill volumetric heat capacity and dendrite arm spacing for the 38 mm and 51 mm diameter castings. There was an initial linear relationship and then the dendrite arm spacing reached a constant minimum value of approximately 30 microns for the 25 mm diameter castings.; Increases in modified mold saturation ratio led to decreases in dendrite arm spacing. Despite the assumption of one-dimensional heat transfer, the modified mold saturation ratio provided good indication of the effect of the chill and mold on secondary dendrite arm spacing. (Abstract shortened by UMI.)... |
