The preparation methods of composite materials mainly include the following: 1) melting and casting; 2) impregnation; 3) powder metallurgy; 4) vacuum hot pressing; 5) rapid cooling/jet deposition.
3) Powder metallurgy
The main process of the powder metallurgy method is to uniformly disperse a certain proportion of aluminum powder and silicon powder and a binder. The powder is mixed and formed by dry pressing, injection, and the like. Finally, sintering is performed under a protective atmosphere to form a denser material. The method solves the problems of poor wettability of silicon particles and aluminum matrix, difficulty in adding silicon particles to the melt, and the material can be formed at one time, and less cutting processing is performed, which overcomes the disadvantages of metal matrix composite materials that are difficult to process. However, this method has a complicated process, and it is difficult to carry out precise control, the pressure pattern is not dense, and the cost is high.
4) Vacuum hot pressing
The vacuum hot pressing method refers to a sintering process carried out simultaneously with pressure forming and pressure sintering. The advantages are: 1 The powder is easily plastically flowed and densified; 2 The sintering temperature and sintering time are short; 3 The high density is high. The general process is as follows: Under vacuum, the powder is placed in a mold cavity, the powder is heated while being pressurized, and compact and uniform material is formed after a short time of pressurization. However, due to its complex process and poor operability, the application of this technology in the preparation of high-silicon aluminum alloys is limited.
5) Rapid cooling/spray deposition
Rapid cooling/spray deposition technology is a rapid solidification technology that has been developed to overcome the problems of complicated processes, serious oxidation, and the countermeasures against powder metallurgy and other technologies. Because this process has advantages that other processes cannot match, it has developed rapidly in recent years. Rapid cooling/spray deposition has the following advantages: 1) No macro-segregation; 2) Fine and uniform equiaxed grain microstructure; 3) Fine primary precipitate phases; 4) Low oxygen content; 5) Improved hot workability.