Impurity effects on the solidification of primary Al3(Sc,Zr) phase in Al alloys

Abstract

The nucleation and growth of primary Al3Sc phase has been investigated in high purity Al alloys and commercial purity Al alloys, with a special focus on the impurity effects. In the case of high purity Al alloys, most primary Al3Sc phases were pushed to grain boundaries during moving solidification front. Such type of primary Al3Sc phase does not contribute to the heterogeneous nucleation and thereby no significant grain refinement of Al alloys was observed, although some Al3Sc particles remain the same orientation with the Al matrix. In the case of commercial purity Al alloy, the presence of impurities, e.g. Ti, Fe and Si, enhances the heterogeneous nucleation of primary Al3Sc phase. Most primary Al3Sc phases are located within the Al matrix, and keep the same orientation with the Al matrix. Furthermore, the presence of impurities also changes the growth mode of primary Al3Sc phase. In the case of commercial purity Al alloy, a layer by layer growth was observed. This investigation demonstrates that impurities have important effects on the nucleation and growth of primary Al3Sc phases in Al based alloys.