The Effect of Sr-Modification on Porosity, Volumetric Shrinkage, Melt Hydrogen and Inclusion Content of A356 Alloy

摘要

The effect of Sr addition on porosity formation was investigated using a directional solidification technique. The results indicate that Sr-modifkation increases both the pore size and the pore number density of A356 alloy significantly. In an attempt to understand the nature of this problem, this study investigated the effect of Sr on the melt inclusion content, volumetric shrinkage and melt hydrogen content of A356 alloy. Using LIMCA apparatus, the melt inclusion content was monitored before and after Sr addition. The results indicate that Sr increased both the melt inclusion content and the average inclusion size. The solid and liquid densities were measured to calculate the volumetric shrinkage of A356 alloy. It was observed that Sr does not change the liquid density but increases the solid density, and therefore Sr increases the volumetric shrinkage of A356 alloy. In addition, hydrogen measurements were performed by taking Ransley samples and analyzing them by the nitrogen carrier fusion technique. It was seen that the melt hydrogen content before and after Sr addition remained essentially constant, and Sr treatment did not introduce hydrogen into the melt. In addition, strontium does not affect the rate of hydrogen pick-up by molten Al-Si alloys.