Effect of Sr modification on nucleation and growth of microporosity during the solidification of al-7%Si foundry alloy

摘要

A quench-during-solidification method was used to study the nucleation and growth characteristics of microporosity in unmodified and strontium-modified Al- 7%Si (A356)foundry alloy. The method consisted of quenching samples of solidifying metal at different fractions of solid in order to track the change in percent porosity during freezing. Several different melt hydrogen contents were studied. The results indicate that there is usually a greater amount of porosity in modified alloys, and that modified alloys need less hydrogen than unmodified alloys to nucleate pores. In addition, the nucleation of pores occurs at a lower fraction solids in modified alloys than in unmodified alloys. It is probable that the increased amount of porosity found in modified alloys is due to the earlier nucleation of porosity in these alloys.