Melt-casting method is the most widely used method to prepare alloy materials because of its simple equipment, low cost and large-scale industrial production. The Si distribution of high-silicon aluminum alloy by conventional casting is extremely uneven, and it is easy to produce cracks during processing, with serious composition segregation, coarse grains and poor mechanical properties, which makes it difficult to carry out subsequent processing such as machining. With the increase of silicon content in the alloy, this problem is more prominent, and it is difficult to prepare high-silicon aluminum alloy materials by conventional casting.
2) Permeation method
Infiltration method is divided into pressure infiltration method and pressureless infiltration method. Pressure infiltration method is to infiltrate the matrix metal melt into the gap of the reinforcement by mechanical pressurization or compressed gas pressurization, which can solve the problem of incomplete infiltration caused by the non-wetting of the reinforcement material and metal liquid, but its application and development are limited because of the relatively complex pressurization system.
3) Powder metallurgy
The main process of powder metallurgy is to evenly disperse a certain proportion of aluminum powder, silicon powder and binder, mix the powder by dry pressing, injection and other methods, and finally sinter in a protective atmosphere to form a relatively dense material. This method solves the problems of poor wettability between silicon particles and aluminum matrix, and it is difficult for silicon particles to join melt. Moreover, the material can be formed at one time by less cutting, which overcomes the disadvantage that metal matrix composites are difficult to process. However, this method is complex, difficult to control accurately, compact and costly.
4) vacuum hot pressing method
Vacuum hot pressing method refers to the sintering process of pressure forming and pressure sintering at the same time. Its advantages are: ① powder is easy to flow and plastic is compact; ② Short sintering temperature and time; ③ High density. The general process is: under the vacuum condition, put the powder into the mold cavity, heat the powder while pressurizing, and form a dense and uniform material after a short period of pressurization. However, due to its complex process and poor operability, the application of this technology in the preparation of high silicon aluminum alloy is limited.
5) rapid cooling/spray deposition
Rapid cooling/spray deposition technology is a rapid solidification technology developed in competition with powder metallurgy and other technologies in order to overcome the problems of complex working procedures and serious oxidation. This process has developed rapidly in recent years because of its incomparable advantages over other processes. Rapid cooling/spray deposition has the following advantages: 1) no macrosegregation; 2) Fine and uniform equiaxed crystal structure; 3) Fine initial sedimentation stage; 4) Low oxygen content; 5) The hot workability is improved. (1) Sub-crystalline silicon-aluminum alloy contains 9% ~ 12% silicon.
2 * * * crystalline silicon-aluminum alloy contains silicon 1 1% ~ 13%.
(3) The silicon content of the hypercrystalline silicon-aluminum alloy is above 12%, mainly in the range of 15% ~ 20%.
(4) The aluminum alloy with silicon content exceeding 22% is called high-silicon aluminum alloy, of which 25%-70% is the main one, and the highest silicon content in the world can reach 80%.