Feeding and Distribution of Porosity in Cast Al-Si Alloys as Function of Alloy Composition and Modification

Unmodified, Na-modified, and Sr-modified castings of Al-7 pct Si and Al-12.5 pct Si alloys were cast in molds in which it was possible to create different cooling conditions. It is shown how solidification influences the distribution of porosity at the surface and the center of the castings as a function of modification and Si content in sand- and chill-cast samples. Eutectic modification, Si content, and cooling conditions have a great impact on the distribution of porosity. Unmodified and Na-modified castings are more easily fed with porosity tending to congregate near the centerline of the casting, while Sr-modified castings solidify in a mushy manner that creates a more homogeneous distribution of porosity in the casting. The amount of porosity was highest in the Sr-modified alloys, lower in the Na-modified alloys, and lowest in the unmodified alloys. The size of the porosity-free layer and the effectiveness of the feeders were greater in the castings made with the steel chills due to the increased thermal gradients and consequent increase in the directionality of solidification

SYNTHESIS OF ZR-BASED GLASSY ALLOY FOAMS

The present basically concerns with the synthesis of foamy structured amorphous Zr-based alloy, Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 (Vit-1), by liquid state processing. In this method, melt was injected in to the evacuated interstitial voids of the NaCl crystals placed in a copper mould. The casting has been subsequently washed with a jet of water to ensure the removal of NaCl entrapped in the casting, thus resulting in a porous structured casting. It shows the possibility of synthesizing amorphous metal foams with large dimensions using salt infiltration technique.11Nsciescopu