## 1 Introduction  
In last two decades, in situ metal matrix composites, as a branch of discontinuous reinforced metal matrix composites, have been attracting many researchers interest and have made notable achievements [1]. The word \"in situ composite\" comes from \"in situ crystallization\". The concept of in-situ composite was proposed by Soviet scientist [PERSON] et al., where they synthesized TiB\({}_{2}\) reinforced Cu based functional gradient materials by Self-Propagating High-temperature Synthesis in 1987 [2; 3; 4]. High quality in situ aluminum-matrix and titanium-matrix composites have been developed for various applications in vehicles, aerospace, and the machinery industries [5; 6]. However, the research on in situ metal matrix composites and its current research investment, are far from meeting the urgent needs of the high-tech development of modern industry and the military [7; 8]. Therefore, it is of great importance to conduct more in-depth research on in situ metal matrix composites, for applications in leading-edge manufacturing and innovation areas, such as alloy material design theory, amorphous nano-crystalline matrix inoculation and refinement mechanism, and ceramic nano-particulate reinforcement. The goal is to make major breakthroughs rapidly in nano-fabrication technology and basic theoretical research in new types of metal matrix composite materials, so as to contribute to the transformation and upgrade of the traditional metal material industry [9; 10; 11]. The advantages of aluminum-based composite materials include high specific strength, excellent corrosion resistance, and outstanding electrical conductivity [12]. The primary purpose of adding reinforcement to the aluminum matrix, is to compensate for the low strength, inferior high-temperature performance, and poor wear resistance of aluminum. For aluminum matrix composites, the most effective particulate reinforcements are mostly ceramic particles. These particles can be divided into two types, one is directly formed in the matrix and the other is added after artificial synthesis. In addition to the high specific strength and specific modulus, these reinforcements have superior high-temperature performance; they are therefore widely used in the production of composite materials [13; 14]. Table 1 shows the property parameter of the compound, which can be used as a particle enhancer. In recent decades, studies on TiC, TiB\({}_{2}\), ZrB\({}_{2}\), AlN or its biphasic particle composite reinforced aluminum matrix composites have been increasing. TiC particles, as the reinforced phase of in-situ aluminum matrix composites, show many excellent properties: high hardness, high melting point, high elastic modulus, low thermal conductivity, and good wettability and thermodynamic stability in molten aluminum [15]. TiB\({}_{2}\) has been intensively investigated in modern engineering materials, due to its high melting point, superior hardness, and excellent corrosion resistance, as well as good thermal and electrical conductivity. At present, TiB\({}_{2}\) is widely applied in the field of high-temperature electrodes, armor, cutting tools, and other structural materials [16]. TiC and TiB\({}_{2}\) are usually synthesized in situ by Al-Ti-C and Al-Ti-B systems. At present, the most commonly used reinforcements in the industry are Al-Ti-C and Al-Ti-B reinforcements [20; 21]. Table 2 shows the characteristics of various reinforcements [22; 23; 24; 25; 26]. Researches have been fully developed and widely used in industrial production. However, Al-Ti-C as well Al-Ti-B, have some disadvantages in the application process, where Al-Ti-B contains TiB\({}_{2}\) which tends to accumulate in molten aluminum, decreasing the refining effect. In addition, Al\({}_{3}\)Ti particulates contained in Al-Ti-C and Al-Ti-B refinements have low refinement efficiency and degrade the matrix properties because of its needle-like appearance.