Study on Formation of Microstructure in Rheo-Diecastings of Semi-Solid A380 Aluminum Alloy Slurry

Abstract

The formation of the microstructure in the rheo-diecastings were studied by the experiment of rheo-diecasting with semi-solid A380 Aluminum alloy slurry. The results show that the grain diameter and shape factor of primary α-Al grains decreased and increased along the rheo-diecasting direction, respectively, making the primary α-Al grains gradually distributing uniformly. The combination of injection pressure and narrow gate of the runner and ingate was the main reason for the evolution of the primary α-Al grains, moreover, the collision and friction among primary α-Al grains during the filling were helpful for the refinement and spheroidization of the primary α-Al grains. The residual liquid solidified into the secondary solidification microstructure accompanied by the evolution of the primary α-Al grains. The accumulation of the fragments of the primary α-Al grains, the secondary α2-Al nuclei or grains which formed in previous positions, the effective nucleation rate of the residual liquid, and the collision and fraction among the secondary α2-Al grains and between the secondary α2-Al grain and the primary α-Al grains made the secondary solidification microstructure of the residual liquid present multiplex and complicate characteristics. In this paper, the formation of the microstructure in the rheo-diecastings were studied by the experiment of rheo-diecasting. During the rheo-diecasting, the grain diameter and shape factor of primary α-Al grains decreased and increased, respectively along the rheo-diecasting direction, which made the primary α-Al grains gradually distribute uniformly. The drifting of the fragments of the primary α-Al grains and secondary α2-Al nucleus, and the effective nucleation rate of the residual liquid played an important effect on the morphology of the secondary solidification structure.