【摘要】 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。更多还原

【Abstract】 The effects of neodymium and cooling rate on the morphology of eutectic structure and β phase in AZ91HP magnesium alloy were studied,and the influence mechanism of neodymium addition and cooling rate on its microstructure was also analyzed.The results indicate that the effects of neodymium modification on morphology and distribution of β phase increase with cooling rate decreasing.The rare-earth neodymium influences the dendritic spacing of α-Mg dendrite,and thus influences the amount and distribution of β phase and that of a little effect on the grain size of α-Mg dendrite is observed.The microhardness of β phase is 344 HV,which is 4.5 times that of α-Mg matrix.Due to the existence of β phase in the matrix,the incoordinate deformation between β phase and the matrix leads to stress concentration at interface of the two phases.Consequently,cracks are easily induced at the interfaces.When the mold with lower cooling rate,the amount of eutectic β phase is decreased and the dispersity of β phase increases with neodymium addition.In addition,a kind of rod-like intermetallic compound Al₁₁Nd₃ forms in the matrix.更多还原