円錐シェル型鋳物における Al-Si 系合金の凝固膨張

抄録

  The relationship among interior shrinkage, exterior shrinkage and porosity in conical castings for JIS D12S secondary alloy was investigated in comparison with virgin alloy. The gas contents in the melt were measured by the vacuum fusion extraction method. The relation between expansion and pore generation was also examined to investigate the rise of bottom interior shrinkage cavity observed in high porosity castings. In both secondary and virgin alloys, exterior shrinkage remains constant and interior shrinkage reduces for the increase in porosity. The porosity increases linearly with a gas content in the melt. However, in some secondary alloys different porosities are observed even with the same gas content. The expansion occurs at the initial stage of solidification. This expansion is observed, as well as in some Al-Si binary alloys. Many pores are observed to be uniformly distributed in the entire of the castings. Microstructure of the expansion part shows much more eutectic phases than any other parts. In the case of the solidification under pressurized atmosphere, expansion does not occur and porosity is low in spite of high gas content. These results show that such an expansion may be due to the residual melt pushed upwards by pore generation as the solidification advances.