INFLUENCE OF HYDROGEN CONTENT AND BIFILM INDEX ON FEEDING BEHAVIOUR OF Al-7Si

摘要

The relationship between 'hydrogen-porosity' and 'Sr modification-porosity' has long been investigated. In this study, this phenomenon has been investigated in terms of bifilm content. A feeding test with deliberately inadequate feeding to promote some degree of shrinkage porosity has been used to compare feeding and porosity of Al-7Si alloy in gravity die casting. A melt with three different hydrogen contents was prepared by degassing first and then upgassing to low, mid and high hydrogen levels (0.1, 0.2 and 0.3 respectively) with Ar-10%H_2 mixture. Reduced pressure test samples were taken for bifilm index calculation and 10 tensile test bars were cast into sand moulds for mechanical testing. The results showed that feedability was increased with B-grain refining (SiBloy alloy) than the conventional Ti-B grain refined. However, pore distribution was scattered in both cases when the alloys were Sr-modified.