The influence of shearing conditions on the rheology of semi-solid magnesium alloy

The influence of the shearing conditions on the rheology of semi-solid magnesium slurry was investigated by a Couette type viscometer. As the stirring time increased, the apparent viscosity first decreased until reaching a minimum value, and then gradually increased. The phenomena might be affected by the destruction of the dendritic structure (resulting in a decreasing curve) and particle coarsening (resulting in an increasing curve). The apparent viscosity was also influenced by the solid fraction, pre-stirring time, and resting time. When the pre-stirring time was fixed, particle coalescence might lead to an increase in the apparent viscosity as the resting time increased at higher solid fraction. At lower solid fraction, the release of entrapped liquid by Ostwald ripening might cause the apparent viscosity to decrease with increased resting time. When the solid fraction was fixed and the resting time increased, the apparent viscosity might increase due to particle coalescence (for a shorter pre-stirring time) and Ostwald ripening might make the apparent viscosity decrease by releasing entrapped liquid (for a longer pre-stirring time). (C) 2007 Elsevier B.V. All rights reserved.