Die design method for thin plates by indirect rheo-casting process and effect of die cavity friction and punch speed on microstructures and mechanical properties

Abstract

Thin plates with a thickness of 1.2mm are fabricated from semi-solid A356 alloy through an indirect rheo-casting process both with and without an electromagnetic stirrer (EMS). The thin die cavity for forming is designed with the fluid analysis software MAGMA. A semi-solid slurry with a solid fraction of 40% is prepared and then injected into the die of a 200t hydraulic press. Forming tests are performed on the thin plates at two punch speeds (30 and 300mm/s) and two cavity friction conditions (mf=0.4 and mf=0.9). The formability, mechanical properties, and microstructure are then evaluated. The semi-solid slurry obtained with an EMS contains fine and globular solid particles; the semi-solid slurry produced without an EMS reveals rosette particles and coarser globular solid particles. At high friction (mf=0.9), the cavity is mainly filled with the liquid phase. At a higher punch rate, the thin plates show better formability and a microstructure with fine and even solid particles. The tensile strength and elongation of the thin plate formed with a punch speed of 300mm/s in the cavity with graphite lubrication (mf=0.9) are 216MPa and 10%, respectively. These values are 57MPa and 5.5% higher, respectively, than those of the thin plate formed at a punch speed of 30mm/s.