新型Mg-50%Al_4C_3-6%Ce中间合金的制备及其对AZ91D合金的细化机制(英文)

Fabrication of a New Mg-50%Al_4C_3 -6%Ce Master Alloy and Its Refinement Mechanism on AZ91D Alloy

采用粉末原位合成工艺成功制备新型Mg-50%Al4C3-6%Ce中间合金,并利用X射线衍射(XRD)仪、扫描电镜(SEM)及能谱(EDS)分析对其进行物相鉴别和形貌分析。结果显示,中间合金主要由层片状Al4C3和细杆状Al4Ce以及Mg基体组成。在AZ91D镁合金熔体中加入Mg-50%Al4C3-6%Ce中间合金可明显细化枝晶组织,枝晶形貌由六重对称的树枝状演变为花瓣状,当加入量为1.2%(质量分数)时,平均晶粒尺寸由基体合金的360μm降至65μm。晶粒细化机制可归结为Al4C3颗粒作为初生α-Mg的异质晶核,Ce富集于固液界面,引起成分过冷,从而激活固液界面前沿潜在的Al4C3核心,提高Al4C3的形核率。

Mg-50%AI4C3-6%Ce master alloy has been prepared by powder in-situ synthesis process. Phases compositions, micro-morphology and micro-area composition were analyzed by XRD （X-ray diffraction）, SEM （scanning electron microscope） and EDS （energy dispersive spectrometer）. The results show that the master alloy mainly contains lamellar Al4C3, rod-shaped Al4Ce and Mg. The microstructure of AZ91D alloy is obviously refined after Mg-50%Al4C3-6%Ce master alloy addition. The dendritic morphology of a-Mg evolves from a characteristic six-fold symmetrical shape to a petal-like shape. After adding 1.2wt% master alloy to AZ91D magnesium alloy, the average grain size is obviously decreased from 360 to 65μm. The mechanism of grain refinement is ascribed to the Al4C3 particles acting as heterogeneous crystal nucleus of primary a-Mg and Ce can activate the potential Al4C3 particles on the solid-liquid interface.