STUDY ON THE REHEATING AND THIXOFORMING OF 7075 ALUMINUM ALLOY CAST BY LIQUIDUS SEMI- CONTINUOUS CASTING

The liquid fraction of liquidus semi-continuous casting (LSC) 7075 alloy at different temperatures, evolution of the reheating microstructures at different reheating temperatures, thixo- formability and the mechanical properties of thixoforming products were studied. The results show that the best thixoforming temperature is 600-620 ℃ and the liquid fraction 30%-50%. Reheating can turn the rosette-shaped grains into spheroids which are suitable for thixoforming. The best re- heating microstructures can be obtained at about 580 ℃ and the holding time about 15-30 min, or near 600 ℃ and 5-15 min. The good thixoformability of the billet corresponds to 600 ℃ reheating for 15 min. The ultimate strength of products forged in mould is 357.9 MPa, and 468 MPa after T6 treatment. Therefore, Liquidus semi-continuous casting is an efficient way for semi-solid slurry making, and together with its thixioforming are very hopeful for industralization.