Improving Microstructure and Mechanical Properties for Large-Diameter 7075 Aluminum Alloy Ingots by a Forced Convection Stirring Casting Process

A simple process so-called forced convection stirring casting (FCSC) was proposed to prepare large-diameter 7075 Al alloy ingots. The flow behavior, temperature, and composition fields of the melt in the FCSC process were simulated. The macromorphology, macrosegregation, microstructure, and mechanical properties of the ingots prepared by the FCSC were studied and compared with those prepared by normal casting (NC). The results showed that in the FCS device, the strong convection caused by the axial flow and circular flow rapidly promoted the uniformity of the temperature and composition fields of the melt. Microstructures of the FCSC ingots from the edge to the center were all nearly spherical grains, which were much finer and more uniform than that of the NC ingots. The rotation speed played an important role in the microstructure of the FCSC ingots, and the grains became finer and rounder as the speed increasing. The FCSC process effectively eliminated cracks, improved macrosegregation, and decreased the eutectic phase area fraction and the average grain boundary thickness of ingots. Mechanical properties of the ingots prepared by the FCSC are far better than that of the NC ingots.