Evaluation of the Rheological Behavior of a Semi-Solid Al�CSiC Composite using a Parallel-Plate Drop-Forge Viscometer

Abstract

This paper presents of studies performed to assess the effect of rheological behavior on the near-net shape forming of an Al-20 vol% SiC composite of Duralcan F3A.20S and of the mother aluminum alloy A356 for comparison. Isothermal experiments were conducted using results of a parallel-plate drop-forge viscometer in a temperature range from 849 K (576 ºC) to 862 K (590 ºC). Each experiment indicated that the viscosity decreased in the early increasing shear rate stage and subsequently increased with decreasing shear rate. The overall relationship between the viscosity, µ [Pa . s], and the shear rate, ɺ γ γ -1.5 for A356. The power-law index was the same for both materials, whereas the power-law constant of Duralcan was two times greater than that of the A356 mother alloy because of the distribution of 20 vol% SiC particles. The decrease in the viscosity that accompanied an increase in the shear rate depended on both the temperature and the applied force. The viscosities of 32 kPa . s for both Duralcan and A356 at the maximum effective duration of deformation, which obtained from the plot as a function of the viscosity, appeared to be the points at which the dominant factor governing the visco-plastic flow process transitions from plastic forming to casting. The viscosity must also represent optimum semi-solid forming conditions, as indicated by the achievement of both a moderate working time and an adequate deformation. The optimum operating temperature for both materials can be ranged from 855 K (582 ˚C) to 857 K (584 ˚C), which is just above the melting point.