半固态A356-Nd合金中Nd_XAl_Y化合物对凝固组织细化的影响

Effects of Nd_XAl_Y Compound on the Refinement of Solidified Microstructure in Semisolid A356-Nd Alloy

研究了Nd对半固态A356铝合金凝固组织细化的影响。在铝熔体中随着Nd添加量由0.1%～0.8%变化,会先后生成NdAl_2、NdAl_3、Nd_3Al_(11)、NdAl四种稀土铝化物,并且按照(块状-小豆状)-(颗粒状-短棒状)-(针状-条状)-(板状)进行形貌演变。通过不同维度的错配度计算,在形核基底(Nd_XAl_Y)与初生相的不同匹配关系里,Nd_XAl_Y按照NdAl_2(半共格)-NdAl_3(11.53%)-Nd_3Al_(11)(6.13%),依次呈现出有效形核-中等有效形核-(接近)最有效形核的特质,因此NdAl_2、NdAl_3、Nd_3Al_(11)均可以作为有效形核质点,而NdAl与铝基体严重分离,不宜作为有效形核质点。借助OM、SEM、EDS、XRD,分析出不同的Nd添加量对初生相的细化侧重点不同,结合对应生成Nd_XAl_Y的物化特性、形貌演变过程及有效性高低,阐明了在0.3%Nd和0.6%Nd添加量时,对应拟合曲线获得最值的原因,并优选出0.6%Nd时生成的共晶产物Nd_3Al_(11)是初生相最有效的异质形核基底。实验表明,在A356铝合金中添加0.6%Nd,并在650℃浇注625℃保温1 min后水淬,对应晶粒平均等积圆直径为79.828μm,形状因子为0.605,有效初生相个数为86,获得的初生相细化效果最好。

The effect of Nd on the solidification microstructure refinement of A356 alloy was studied.In aluminum melt,with the change of Nd content from 0.1%~0.8%,four kinds of rare earth aluminide,NdAl2,NdAl3,Nd3Al11 and NdAl,would be generated successively,and the morphology would evolve according to(block-small bean)-(particle-short rod)-(needle-strip)-(plate).By calculating the mismatch degree of different dimensions between nucleation base(NdXAlY)and primary phase,NdXAlY,in accordance with NdAl2(semi-coherent)-NdAl3(11.53%)-Nd3Al11(6.13%),presented the characteristics of the effective nucleation-medium effective nucleation-(near)the most effective nucleation.Therefore,NdAl2,NdAl3 and Nd3Al11 could all be used as effective nucleation particles.However,NdAl was severely decoupled from the aluminum matrix and should not be used as an effective nucleation particle.With the help of OM,SEM,EDS and XRD,the emphasis of different Nd additions on the refinement of the primary phase was analyzed.Combining with the physical and chemical properties,the evolution process and the effectiveness of the corresponding NdXAlY,the extreme value reason for the corresponding fitting curve of 0.3%Nd and 0.6%Nd was illuminated,and the eutectic product Nd3Al11 produced by 0.6%Nd was the most effective heterogeneous nucleation substrate of the primary phase.Experiments show that the addition of 0.6%Nd in A356 alloy,pouring in 650℃and isothermal holding for 1 min,after 625℃water quenching mold release,the corresponding average grain equal-area circle diameter is 79.828μm,the shape factor is 0.605,the number of effective primary phase is 86,and the best refinement effect of the primary phase is obtained.