Rheological behavior of semi-solid Al-Si alloys: Effect of morphology

Abstract

Swirled enthalpy equilibration device (SEED) technology was used to cast semi-solid metal, SSM, billets of A356 Al-Si alloy. The deformation behavior of the SSM billets was studied using parallel plate compression viscometry. The compression tests were carried out at different applied pressures and solid phase morphologies. The rheological studies were conducted assuming the SSM slurry behaving like Newtonian or non-Newtonian fluid. The calculated viscosity numbers confirmed psuedoplastic behavior of the SSM billets and were correlated to the morphology, average aspect ratio, and shear rate to highlight the effect of metallurgical and process parameters on the viscosity and thus "rheological behavior" of SSM alloys. An empirical equation is proposed to correlate viscosity with average aspect ratio and shear rate:log η = - 1.85 + 4.9 over(AR, -) - (0.255 over(AR, -) + 0.03) log over(γ, {ring operator}), 1.4 < over(AR, -) < 1.8. This equation is valid for the shear rates less than 0.01 s-1. © 2007 Elsevier B.V. All rights reserved.