泡沫镁宏微观结构表征及压缩性能研究

Macro-micro Structure Characterization and Compressive Properties of Magnesium Foams

摘要:

针对熔体发泡法制备泡沫镁存在的困难，使用包覆发泡剂及改进工艺成功制得泡孔均匀的泡沫镁试样。利用OM、SEM、EDS及XRD等分析手段对试样进行宏微观结构表征，结果表明：泡沫镁试样宏观孔以典型的闭孔结构为主，但也存在一些连通孔及少量大孔，它们多是宏观裂纹的产生及扩展位置。泡孔内壁存在一些褶皱缺陷，且弥散分布着许多反应产生的MgO和CaO颗粒，压缩变形过程中，这些部位易产生应力集中，促进微裂纹的形成与扩展。孔壁上主要分布着碳化硅颗粒及生成的Mg2Ca相。测试分析了孔隙率和孔径对泡沫镁压缩力学性能和能量吸收性能的影响，并深入研究其压缩破坏机理，研究发现：随着孔隙率的降低，泡沫镁弹性变形增大，屈服强度升高；随着孔径的增大，泡沫镁屈服强度及平台应力明显减小，表现出显著的孔径效应。随着孔隙率的升高或孔径的增大，泡沫镁的能量吸收性能显著降低。泡沫镁的破坏为解理脆性断裂，这与孔壁组织及镁基体性质有很大的关系。

Abstract:

Magnesium foams are fabricated by melt foaming method using coated CaCO3 as blowing agent. Macro-micro structure characteristics of magnesium foams are investigated by OM, SEM, EDS and XRD methods. The results show that the macro pores are given priority to with closed-cell structure. Meanwhile it contains some communicated pores and big pores, these positions usually generate macro cracks during compression. Fold defects and reaction products MgO and CaO particles diffusely distribute on the pore inner walls, create stress concentration and cause micro cracks. Pore walls are mainly composed of SiC particles introduced at the thickening stage and second phases Mg2Ca. Furthermore, compressive properties and energy absorption performances are tested and the fracture mechanism is studied. Elastic deformation and yield strength increase with decreasing porosity. Yield strength and plateau stress reduce dramatically with increasing pore size, namely magnesium foam shows an evident aperture effect. Besides, energy absorption performances significantly decrease with increasing porosity or pore size. And magnesium foam shows cleavage fracture during compression due to the micro structure of pore walls and the characteristic of magnesium substrate.