Treatment On The Squeezed State Of High-silicon Aluminum Alloy, Primary Silicon Form

Hypereutectic aluminum-silicon alloys have low density, high strength, high wear resistance and low thermal-expansion coefficient. However, the casting of hypereutectic Al-Si alloys always present relatively coarser and brittle primary silicon particles with shape angle which degrade significantly mechanical properties, and limit the further applications of these alloys. At present, several processing methods have been applied in fining and modifying the morphologies of primary silicon, such as addition of modifiers, semi-solid metal processing (SSM), and levitation casting, which is either not as efficient as expected, nor cannot be realized in industry production due to sophisticated technology & facility, and high expense. In hypereutectic aluminum-silicon alloys, the most primary silicon's organizations are the board strip, and distribute non-uniform. In this work, in order to obtain the tiny crystal grain, the extrusion is carried on to Al-25%Si as well as the Al-30%Si alloy; in order to obtain the spherical primary silicon, diffusion treatment and reheating treatment are carried on to them, and the effects of different components have been contrasted.Study shows that: extrusion deformation can significantly fine the morphologies of primary silicon. Before the extrusion, there are primary silicon with shrinkage, overlapping primary silicon, five-star-shaped primary silicon. In the extrusion process, they will collide with each other and get fractured, and the primary silicon will grow up at the same time. With more thick primary silicon, Al-30% Si alloy is superior to Al-25% Si alloy in the grain refining effect. When processed by diffusion treatment, with the improvement of the heating temperature or holding time, the primary silicon will grow up and crest truncation. However, too longer holding time will deteriorate morphologies of primary silicon because primary silicon will overlap each other. In the reheating treatment process, the organization of hypereutectic aluminum-silicon alloys go through the following stages: eutectic silicon phase fuse, a small amount of liquid form in the gap of a phase, liquid expansion and encompass a phase, a phase completely melt and co-exist with the primary silicon, and in the process, primary silicon spheroidization occurred. The reheating treatment is better than diffusion treatment in spheroidization effect of primary silicon, and reheating treatment on top of diffusion treatment is in favor of the primary silicon' spheroidization. Therefore, reheating treatment on top of diffusion treatment is the best solution.In this work, by using extrusion deformation, diffusion treatment, reheating treatment, the primary silicon become small and spheroidization, and the solution have a practical value. The solution need the less demanding of equipment, and the method is simple feasible and good effect. It is a new train of thought to fine and modify the morphologies of primary silicon after all.