Microstructure evolution of A356 alloy in a novel rheocasting approach

A novel approach, was designed to obtain thixotropic structure of equiaxed or non-dendrtic grains for rheocasting, and demonstrated experimentally using A356 aluminum alloy. The circumstance in bulk liquid metal, which would burst into copious nucleation, and at the same time create homogeneous distribution of temperature and solute, was constructed by combined utilization of rotating magnetic fields and a cooling tube. Both the solidified microstructures in metal mold and sand mold exhibited non-dendritic characteristic. Analyses of the rheocasting A356 microstructure indicated that high density of nuclei occurred by inserting a cooling tube into rotating slurry at liquidus temperature. In the case of slow cooling rate, mushy slurry obtained with high nuclei density kept non-dendritic morphology of primary particles with holding time, accompanying grain particles’ coarsening and spheroidizing; moreover, the eutectic silicon got coarsening with retaining time.