Experimental and simulation study for rewelding defects during the flow process of Semi-solid die casting

摘要

Semi-solid die casting process due to its advantages of compact process, high performance and low cost is widely applied in automobile, communication and other industries for the preparation with high performance aluminum alloy castings. Compared with liquid metal melt, the filling behavior is laminar flow for semi-solid metal melt with higher apparent viscosity. In the process of semi-solid die casting, the semi-solid metal melt from different directions came together, it will lead to "rewelding" defects if with insufficient fusion or uneven slurry state. In this paper, the formation reasons and forms of flow "rewelding" defects are analyzed. By numerical simulation and experimental analysis, the flow state of semi-solid metal melt at the junction of filling frontier is represented, and the state of "rewelding" defect is characterized. The effect of eliminating defects is analyzed by modifying the mold structure, such as redesigning overflow and venting systems at the confluence position. The results show that the microstructure of the "rewelding" defects in the confluence position of the semi-solid metal melts is the segregati12on of solid and liquid phase, gas, oxidation inclusions and other defects. Different semi-solid die casting process will affect the flow state and defect size at the location of different semi-solid metal melt coming together. By means of the process control and the mold structure optimization, "rewelding " defects can be removed from the product cavity. The aluminum alloy semi-solid die-casting products with high performance are obtained finally.