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首页> 中文期刊> 《铸造》 >试验确定AZ91/SiC复合材料异质形核模型中决定于SiC质量分数和过冷度的晶粒密度函数

试验确定AZ91/SiC复合材料异质形核模型中决定于SiC质量分数和过冷度的晶粒密度函数

         
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镁合金及其复合材料作为重要的轻质材料在汽车和航空工业中的应用一直引人注目.由于镁不能形成任何稳定的碳化物,SiC颗粒被大量用于增强镁基复合材料.AZ91/SiC复合材料凝固后固态晶粒密度Nv是合金液态最大过冷度AT的函数.这类函数决定于异质形核位置特征与合金中存在的SiC数量.本文的目的是为描述初生相晶粒密度与过冷度关系的模型选择参数.这一模型与基于化学元素扩散和晶界动力学的结晶模式有关,能够用于预测铸件质量及其显微组织.形核模型通常有未知确切值的参数,甚至其物理意义都是待讨论的,对试验数据进行分析之后可以获得这些参数.制备了SiC强化的AZ91合金基复合材料,其中SiC颗粒含量分别为0、1%、2%、3%和4%(质量分数).把这种复合材料铸造成具有4种厚度的试验板.从热电偶测温点附近获取数据,分析不同复合材料与不同厚度试板的过冷度及其对晶粒尺寸的影响.显微组织和热分析给出的一套数据建立了晶粒尺寸与SiC颗粒质量分数及过冷度联系,这些数据用于近似形核模型的参数调节.获得的模型在模拟复合材料显微组织方面是非常有用的.%Magnesium a Iloys and their composites have been attracting attention as an important lightweight material and are being utilized in the automobile and aerospace industries.In terms of the reinforcement in magnesium-based composites, the SiC particles are extensively used because magnesium can not form any stable carbide.The grain density in the solid state Nv after solidification of AZ91/SiC composite is a function of maximum undercooling of a liquid alloy ΔT.This type of function depends on the characteristics of heterogeneous nucleation sites and number of SiC present in the alloy.The aim of this paper was selection of parameters for the model describing the relationship between the grain density of primary phase and undercooling.This model in connection with model of crystallisation, which is based on chemical elements diffusion and grain interface kinetics, can be used to predict casting quality and its microstructure.Nucleation models have parameters, which exact values are usually not known and sometimes even their physical meaning is under discussion.Those parameters can be obtained after mathematical analysis of the experimental data.The composite with 0, 1％, 2％, 3％ and 4 wt.％ of SiC particles were prepared.The AZ91 alloy was a matrix of the composite reinforcement SiC particles.This composite was cast to prepare four different thickness plates.They were taken from the region near to the thermocouple, to analyze the undercooling for different composites and thickness plates and its influence on the grain size.The microstructure and thermal analysis gave set of values that connect mass fraction of SiC particles, and undercooling with grain size.These values were used to approximate nucleation model adjustment parameters.Obtained model can be very useful in modelling composites microstructure.

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