科研之友
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摘要
The enhanced grain refining efficiency of B in treating hypoeutectic Al-Si alloys has been identified for more than 30 years. However, its exact underlying mechanism remains to be explored. Here, we report that AIB(2) could be a highly efficient nucleating substrate for alpha-Al in Al-Si alloys with high Si concentrations. The addition of AlB2 alone without the presence of Si does not result in a significant grain refinement. The enhanced grain refining efficiency can be mainly attributed to the enhanced heterogeneous nucleation of AlB2 caused by Si. It is proposed that the creation of a layer of SiB6 at the interface between AlB2 and Al may reduce the crystallographic mismatch, which can significantly improve the nucleating, potency of AlB2. Furthermore, the formation of SiB6 layer may occur for only a limited span of time in Al-Si melt, and it may further transform to other stable phase (e.g. Si). This investigation reveals the nucleating behavior of AlB2 influenced by solute Si and thereby sheds some novel insights on the grain refinement mechanism of Al alloy.
