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研究稀土Nd和冷却速度对AZ91镁合金共晶组织及β相形貌的影响,分析了Nd和冷却速度与合金组织之间的相关规律。结果表明:加Nd变质对β相分布、形貌的影响效果随着冷却速度的减小而增大。Nd的作用机理主要通过改变树枝晶α-Mg枝晶的间距,进而影响β相的数量和分布形貌,而对α-Mg的晶粒尺寸影响不大。β相的显微硬度为344HV,为基体α-Mg的4.5倍。由于β相的存在,造成两相材料的变形不协调,在界面附近产生应力集中,从而在界面处易诱发裂纹源。在铸型冷却能力较小时,加入Nd进行变质处理可以减少共晶β相的数量,增大其分散度。此外,Nd的加入还可在基体中形成杆状Al11Nd3金属间化合物。
The effect of rare earth Nd and cooling rate on the eutectic microstructure and β phase morphology of AZ91 magnesium alloy was studied. The correlation between Nd and cooling rate and alloy microstructure was analyzed. The results show that the effects of Nd modification on the distribution of β phase and the morphology increase as the cooling rate decreases. The mechanism of Nd mainly affects the grain size of α-Mg by changing the spacing of dendritic α-Mg dendrites, thereby affecting the number and distribution of β-phase. β-phase microhardness of 344HV, 4.5 times the matrix α-Mg. Due to the presence of β phase, the deformation of the two-phase material is not coordinated and stress concentration occurs in the vicinity of the interface, thereby easily inducing crack sources at the interface. In the cooling capacity of the mold is small, adding Nd for modification can reduce the number of eutectic β phase and increase its dispersion. In addition, the addition of Nd also forms a rod-shaped Al11Nd3 intermetallic compound in the matrix.