Elimination of Solidification Shrinkage Defects in the Casting of Aluminum Alloy

In this study, the analysis is carried out to optimize in-gate position and size of riser for casting mold. The baseline size of riser for the casting of boat propeller is based on geometric modulus and thermal analysis. The riser size is analyzed with thermal-volumetric numerical calculations to predict critical fraction solid (CFS) time and temperature gradient in casting. Simulation predictions are compared with inspection results of actual castings and found good qualitative agreement. The riser reached CFS temperature well before the castings’ cross-sectional transition regions. In feeding the molten metal, the in-gate is placed where the section modulus of casting is higher. However, the tongue of sand at in-gate increases the local cooling rate, resulting in early solidification and blockage of feeding path. The increase in riser size and in-gate position results in elimination of shrinkage cavities. An optical microscopy of the casting critical region is carried out to investigate the effect of numerical measures on internal closed microporosity and microstructure morphology.