Mg-TiB_2中间合金和Ce对AZ91D镁合金显微组织的细化

Grain Refinement of AZ91D Magnesium Alloy by Mg-TiB_2 Master Alloy and Ce

采用SEM、EDS和XRD等测试手段,研究了Mg-50%TiB2中间合金和稀土元素Ce对AZ91D镁合金显微组织的细化效果。结果表明,加入1.4%的中间合金可以显著细化AZ91D镁合金的枝晶组织和晶粒,α-Mg的平均晶粒尺寸由240μm下降至50μm。在此基础上,复合添加0.2%Ce后,枝晶组织和晶粒进一步细化,同时,β相由粗大骨骼状转变为岛状和细小的粒状,且产生新相Al4Ce。通过能谱分析及面错配度计算证实,TiB2可作为初生α-Mg的良好异质核心。加入稀土元素Ce引起合金成分过冷度增加,从而激活固液界面前沿潜在的TiB2核心,提高TiB2的形核率。

The microstructure of AZ91D magnesium alloy with Mg-50%TiB2 and Ce was studied by SEM, EDS and XRD. It was found that the addition of 1.4% （Mg-50%TiB）2 master alloy to AZ91D magnesium alloy led to the α-Mg grain size decreasing from 240 μm to 50 μm. Combining addition of 1.4% （Mg-50%TiB）2 master alloy and 0.2%Ce resulted in better grain refining effect, the β phase morphology obviously changing from the bulk skeletal structure to island and fine granular structure. Furthermore a small amount of needle-like compound Al4Ce was found. Based on the EDS test results and calculation of the planar disregistry between TiB2 and α-Mg, TiB2 particles can act as the heterogeneous nucleus of primary α-Mg phase. The addition of Ce can increase the degree of undercooling of primary α-Mg phase, and activate the potential TiB2 particles in the solid-liquid interface.