La、B元素联合变质对Al-Si合金中初生相形核的影响

Effect of Combined Modification of La and B on Nucleation of Primary Phase in Al-Si Cast Alloys

采用扫描电镜(SEM)、X射线衍射仪(XRD)和透射电镜(TEM)等测试手段,研究了La、B元素联合变质对Al-Si合金中初生相形核的影响。结果表明,在亚共晶Al-Si合金熔体中,LaB6的形成对凝固过程中初生α-Al相具有细化作用,但这种作用会因Ti与B生成TiB2而受到抑制。在过共晶Al-Si合金熔体中,LaB6的形成对初生Si相以及共晶Si相形核存在促进作用;TEM分析显示,LaB6相的{110}晶面与初生Si相的{111}晶面有着良好的晶体学位相关系,可作为初生Si相的非均质形核核心。

The effects of the combined modification of La and B composite modification on the primary phase of Al-Si alloys were investigated by means of SEM, XRD and TEM. The results reveal that the primary α-Al phase in hypoeutectic Al-Si cast alloys can be effectively refined with the combinative addition of La and B since the LaB6 phase was formed in Ai-Si alloy melt, while the process can be suppressed by the addition of Ti due to the formation of TiB2 phase. In the hypereutectic Al-Si alloys, the close-packed plane({110}) of LaB6 crystal has a good crystallographic relationship with the close-packed plane({111}) of Si crystal, which means LaB6 may act as the heterogeneous nuclei to promote the nucleation of Si phase.