Creep mechanism and creep constitutive model of aluminum silicate short-fiber-reinforced magnesium matrix composite

By the constant stress tensile creep test method, creep tests were performed on aluminum silicate short fiber-reinforced AZ91D magnesium matrix composite with volume fraction of 30% and its matrix alloy AZ91D under different temperatures and stresses. The results indicate that the composite and the matrix have the same true stress exponent and true activation energy for creep, which are 3 and 144.63 kJ/mol, respectively. The creep of the composite is controlled by the creep of its matrix, which is mainly the controlling of viscous slip of dislocation, and the controlling of grain boundary slippage as a supplement. The creep constitutive model obtained from the experiment data can well describe the creep deformation pattern of the composite.

Al2_O_3-SiO_(2(sf))/AZ91D复合材料的蠕变微观组织和变形机理

在温度为473-573 K、外加应力为30-100 MPa下,对硅酸铝短纤维增强AZ91D镁基(Al2O3-SiO2(sf)/AZ91D)复合材料及AZ91D镁合金进行拉伸蠕变实验。通过SEM和TEM检测方法对其蠕变微观组织变化和变形规律进行研究。结果表明,当两种材料的真应力指数n=3时,蠕变速率受位错的黏滞性滑移控制;复合材料的门槛应力增大、短纤维有效的承载和传载作用导致复合材料的蠕变抗力显著增大。短纤维表面上的MgO保护层增大了短纤维的承载和传载作用;短纤维的存在阻碍了复合材料的蠕变变形,降低了蠕变变形速率,控制着整个蠕变变形过程。

界面对硅酸铝短纤维增强AZ91D镁基复合材料蠕变性能的影响

界面对复合材料蠕变性能的影响很大。在试验分析的基础上建立了硅酸铝短纤维增强AZ91D镁基复合材料理论分析模型,利用三维有限元分析方法,系统研究了界面特性、界面上应力应变分布和短纤维位向变化对硅酸铝短纤维增强AZ91D镁基复合材料蠕变性能的影响。研究表明:界面特性,如厚度、模量,均对纤维最大轴应力和稳态蠕变速率有影响,当界面厚度增加,纤维最大轴应力减小而稳态蠕变速率增大;当界面模量增大,纤维最大轴应力增大而稳态蠕变速率减小,但当界面模量高于基体模量时,纤维最大轴应力和稳态蠕变速率均保持不变;纤维位向也影响轴应力分布和稳态蠕变速率,纤维在其末端界面上存在较大的应力和应变,此处容易产生微裂纹而使材料抗蠕变能力下降;界面对硅酸铝短纤维增强AZ91D镁基复合材料的蠕变曲线和蠕变断裂机制也有影响,其影响程度还与纤维位向有关。