Basis of rheo squeeze casting technology for aluminum alloy

Green environmental protection is the theme direction of today’s social development. With the innovation and development of new technologies and new processes, aluminum alloy, especially wrought aluminum alloy, has been widely used in aerospace, ship, weapon, automobile and household appliances industries due to its high strength and light weight. It is an indispensable structural material in modern manufacturing. With the upgrading of industrial products, the demand for energy-saving and low-carbon environment-friendly materials is increasing, and the consumption of aluminum alloy is also increasing year by year.

Semi solid metal processing technology is a new metal forming technology invented by American professor Flemings in 1970s. Semi solid processing is to process the solid-liquid mixture containing spherulite or near spherulite solid in the range of solidification temperature. Because of its good fluidity, it is easy to be formed by conventional processing technologies such as extrusion, die forging and die casting. The results show that the forming temperature of semi-solid parts is in the mixed zone of solid and liquid phase, the shrinkage and forming force are reduced, the dimensional accuracy and forming performance are improved, and the near net forming can be realized. Semi solid metal processing technology combines the advantages of plastic processing and traditional metal solidification forming technology. The deformation resistance is lower than that of solid processing, and the processing temperature is lower than that of liquid metal. It can realize the processing of large deformation metal parts with complex shape, high quality and precision requirements. It is known as one of the most promising near net forming and new material preparation technologies in the 21st century.

Squeeze casting, also known as liquid die forging, is a kind of processing technology that applies greater mechanical pressure on the liquid or solid-liquid coexisting metal alloy poured into the mold to make it solidify under the pressure and obtain the parts. It is a liquid forming method based on casting and combined with forging technology. The typical process flow of squeeze casting is as follows: pouring metal or alloy melt into the open mold cavity, then closing the mold with the punch or upper mold down, using the pressure of the punch or upper mold on the metal or alloy melt to produce filling flow, and gradually solidifying to reach the shape and size of the part; then continuing to apply high pressure on the punch or upper mold to solidify the part The remaining UN solidified metal or alloy melt is subjected to isostatic pressure and solidified under pressure to obtain the required parts. Compared with the conventional casting methods such as pressure casting and gravity casting, squeeze casting can refine the alloy grain, effectively eliminate the micro shrinkage and macro shrinkage, and make the casting have good mechanical properties and surface quality. Squeeze casting technology is an efficient and accurate forming technology, which does not need riser feeding. The process is simple, and the metal utilization rate is high. The casting not only has high surface quality, but also can manufacture complex parts. Its shape quality and mechanical properties are close to or reach the level of conventional forgings.

Semi solid processing and squeeze casting are combined to form a new material forming method, which is called semi-solid squeeze casting. Whether the semi-solid metal slurry can be directly rheoformed or not can be divided into two types: rheo squeeze casting and thixo squeeze casting. Rheo squeeze casting is a new metal forming process, which integrates semi-solid forming and squeeze casting, makes full use of the rheological properties of semi-solid metal slurry to fill the mold, and then solidifies under high static pressure. At home and abroad, the direct forming technology of semi-solid metal melt includes rheo extrusion, rheo die casting, rheo squeeze casting and rheo rolling. Rheo squeeze casting combines the dual advantages of semi-solid rheological properties and squeeze casting process. It can produce structural and functional parts with high density and strong safety performance, which is an important process for the development of rheo forming technology. Therefore, it is of great economic and social significance to carry out the experimental research and theoretical exploration of rheo squeeze casting technology.