Abstract:The semi-solid 2024 alloy billets were isothermally reheated at 620, 630, 640 and 650 ℃, respectively. The effect of isothermal temperature on the microstructure of semi-solid billet during partial remelting was studied by optical microscopy and metallographic image analysis system. The results show that the higher the isothermal temperature is, the quicker the formation rate of liquid phase is and the finer the grains are. The grains of semi-solid billet isothermally reheated over liquidus temperatures 640 and 650 ℃ are much finer than those at solidus-liquidus zone temperatures 620 and 630 ℃, but the spheroidization degree is slightly lower. It is indicated that through the analysis of microstructural evolution mechanism, the restraining of grains coalescence and the shortening of holding time by accelerating the formation rate of liquid phase are the reasons of grains refinement, and the shortening of holding time is the reason of grains spheroidization degree lowering.

Key words: semi-solid metal; partial remelting; isothermal temperature; microstructural evolution