## 2 Materials and Methods  
### MIMC Composites Fabrication  
Previously, our team used a three-dimensional network of Si\({}_{3}\)N\({}_{4}\) ceramic structure and pressure-assisted and vacuum-driven permeation technique to reinforce magnesium matrix composites (Si\({}_{3}\)N\({}_{4}\)-Mg) [26]. The preparation process was as follows: a porous ceramic skeleton was prepared from high-purity \(\beta\)-Si\({}_{3}\)N\({}_{4}\) powder (97% of Si\({}_{3}\)N\({}_{4}\) and less than 100 \(\upmu\)m in diameter, Shanghai Silicon Materials Plant, Shanghai, China). The porous reticulated polyurethane (PU) was selected as the original framework, and the porous prefabricated parts were prepared through the replication process. Figure 1a shows the porous network of Si\({}_{3}\)N\({}_{4}\) ceramic skeleton after impregnation and sintering. Then, it was heated in a nitrogen-filled muffle furnace (SQFL-1700, Shanghai, China) until it reached the desired processing temperature of 750 \({}^{\circ}\)C, at which time, the liquid magnesium alloy was infiltrated into the preform skeleton by means of pressure-assisted and vacuum-driven permeation techniques. Figure 1b shows a Si\({}_{3}\)N\({}_{4}\)-Mg metal matrix composite, in which zone \"1\" is the Si\({}_{3}\)N\({}_{4}\) three-dimensional network skeleton, and zone \"2\" is the Mg matrix. Figure 1c shows the schematic diagram of the infiltration device, and the mechanical properties of Si\({}_{3}\)N\({}_{4}\)-Mg matrix composite are shown in Table 1, which indicates that the ceramic network reinforcement significantly enhances the elastic modulus, rockwell hardness, and tensile strength of the matrix, while the elongation is decreased [27; 28].  
Recently, however, our team tried a new and simple process to fabricate the magnesium matrix composites. The network skeleton of the reinforcement designed by three-dimensional weaving technology was shown in Figure 2a, and the model of the metal matrix composite of the infiltrated reinforcement was shown in Figure 2b. The reinforcement skeleton materials were chosen as stainless steel (Fe-18 Cr-9 Ni), titanium alloy (Ti-6 Al-4V), and aluminum alloy (Al-5 Mg-3 Zn), respectively, while magnesium matrix was selected as AZ31(Mg-3.31 Al-1.05 Zn). The skeleton was fabricated using the three-dimensional weaving techniques, and measured by Archimedes measurements (ASTM C373), with a reinforcement volume fraction of approximately 15%. Unlike the preparation of Si\({}_{3}\)N\({}_{4}\)-Mg matrix composites, the MIMC composites' fabrication processing was applied pressure infiltration technology, which is shown in Figure 2c. The entire experiment was carried out under an inert gas argon atmosphere. Firstly, in the inert atmosphere of a mixture of CO\({}_{2}\) and SF\({}_{6}\), the furnace temperature was set to 720 \({}^{\circ}\)C to melt the AZ31 alloy. Then, the molten magnesium alloy liquid was poured into an infiltration mold having a temperature of 650 \({}^{\circ}\)C and, finally, the pressure head started to be pressed. At last, the magnesium matrix composites interpenetrated by stainless steel reinforcement (MISC), the magnesium matrix composites interpenetrated by titanium alloy reinforcement (MITC), and the magnesium matrix composites interpenetrated by aluminum alloy reinforcement (MIAC), were fabricated successfully.