Fabrication And Characterization Of Magnesium-based Matrix Composites By In-situ Reaction And Self-assembly Growth

Magnesium-based matrix composites (Mg-MMCs) have many excellent properties, such as high specific strength, fine damping and shock absorption, electron-magnetic shielding and perfect recycle capability, Mg-MMCs are ideal candidates for aeronautics, automobile, electronic packaging and other high-tech fields. Therefore, it is called that Mg-MMCs are the most worthy and exploitative"Green Engineering Materials"with greatly potential applications in 21st century.In this work, the fabrication and characterization of the Mg-MMCs were reported. The composites were fabricated by in-situ self-assemble growth method, which combined with in-situ chemical reaction and self-assemble transformation. All the reinforcements were found to be distributed in the Mg matrix uniformly.According to the experimental results, some important conclusions were given as follows:The differential scanning calorimetry (DSC) was conducted on Mg-Al₂O₃ and Mg-Al(NO₃)₃ samples, it is identified that the chemical reactions of the samples took place at 300-400℃and the MgO nanowires and Al was in-situ formed. When the samples sintered to 550℃and cooled down, the two-phase Mg-Mg₁₇Al₁₂ eutectic was obtained by self-assemble transformation. In the Mg-MnO₂ sample, the reaction took place at about 400℃, with the formation of MgO nanowires and Mn.The decomposition of Al(NO₃)₃, sol-gel method for Al₂O₃ and ordinary Al₂O₃ powder were checked in this work. The influences on the microstructure of sintered samples in different milling process were presented, and the observations of scanning and transmission electron micrograph (SEM and TEM) showed that the samples made by ultrasonic stirring were compact and fine. Vickers hardness tests identified that the Vickers hardness of ultrasonically stirred sample is 25 percent higher than that made by generally stirring. The growth mechanisms of MgO nanowires and Mg-Mg₁₇Al₁₂ eutectic were discussed.The development of MgO nanowires followed a vapor-solid mechanism (VS). The self-assemble transformation growth mechanism of Mg-Mg₁₇Al₁₂ eutectic was analyzed in detail. The chemical and solidifying reactions in both heating and cooling processes were studied in this work. The products can be applied for electronic, biomedical and military industries.