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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Mg_2Ca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。
In view of the difficulty of preparing foamed magnesium by melt foaming method, the foamy magnesium sample with uniform cell was successfully obtained by using the coating foaming agent and the improved technology. The samples were characterized by OM, SEM, EDS and XRD. The results show that the macropores of magnesium foam samples are dominated by closed-cell structures, but some interconnected pores and a few macropores exist, which are mostly macro-cracks. There are some folds in the inner wall of the cell wall, and there are many MgO and CaO particles dispersedly distributed in the cell walls. During the compressive deformation, stress concentration is likely to occur in these areas, which promotes the formation and propagation of microcracks. The hole wall is mainly distributed with silicon carbide particles and the generated Mg_2Ca phase. The effects of porosity and pore size on compressive mechanical properties and energy absorption of magnesium foam were analyzed and the mechanism of compression failure was investigated. The results show that with the decrease of porosity, the elastic deformation of the foam magnesium increases and the yield strength increases. With the increase of the pore size, the yield strength of the foam magnesium and the stress of the platform decrease obviously, showing a significant pore size effect. As porosity increases or pore size increases, the energy absorption capacity of foamed magnesium decreases significantly. The destruction of foamed Mg is responsible for the cleavage of brittle fracture, which has a great relationship with the properties of pore wall structure and magnesium matrix.