颗粒增强Al－4％Mg复合材料中显微孔隙的分析

探讨了Ａｌ２Ｏ３、ＳｉＣ、ＳｉＯ２等三种颗粒增强Ａｌ－４％Ｍｇ复合材料凝固组织中显微孔隙的形成规律．结果表明：前者显微孔隙是由Ａｌ２Ｏ３颗粒加入导致熔体粘度增加、颗粒堵塞枝晶间的补缩流动通道以及颗粒与基体合金的热膨胀系数的差异三种因素所引起；第二种材料由于气孔易在ＳｉＣ颗粒表面形核，或者ＳｉＣ颗粒与基体结合较弱，使得该复合材料比前者易形成显微孔隙；第三种复合材料，是由于ＳｉＯ２颗粒与基体间发生了界面反应，一定量的Ｓｉ溶入了基体，增大了基体的凝固潜热，从而提高了基体合金凝固时的补缩流动能力，所以ＳｉＯ２ｐ／Ａｌ－４％Ｍｇ复合材料的凝固组织比同样条件下Ａｌ２Ｏ３ｐ／Ａｌ－４％Ｍｇ和ＳｉＣｐ／Ａｌ－４％Ｍｇ复合材料致密。

Investigation of Microporosities in Particulates Reinforced Al-4%Mg Composites

The generation mechanism of microporosities in particles reinforced Al-4%Mg composites was investigated. The microporosities in solidification structure of Al2O3 particle reinforced Al-4%Mg composites were caused by increased viscosity due to particle incorporation,particle blocking interdendritic flow tunnel and mismatch of thermal expansion between particle and matrix. Microporosities were more likely to form in SiC particle reinforced Al -4%Mg composites than in Al2O3 particle reinforced Al-4%Mg composites because they nucleated more easily in this type of composites or SiC particles and matrix wer weakly bonded. For SiO2 particle reinforced Al-4%Mg composite,Some amount of Si dissolved in matrix due to chemical reaction,and fluidity of the composites was improved because it had higher solidification latent heat. This was why SiO2 particle reinforced Al-4%Mg composites had sounder structure than the other two types of composites.