A comparative characterization of near-equiaxed microstructures as produced by spray casting, magnetohydrodynamic casting and the stress induced, melt activated process

The near-equiaxed microstructure of wrought and cast aluminum alloys as produced by the most common methods used to provide material for subsequent semisolid processing, is examined. More specifically, the grain size and degree of spheroidization of alloys produced by spray casting, magnetohydrodynamic (MHD) casting and the stress induced, melt activated (SIMA) process are characterized and compared. It is shown that the microstructure of alloys with the same composition differs significantly when produced by the three methods, showing the influence of the production method. Spray casting and the SIMA process result in a microstructure with perfectly equiaxed grains that is inherently suitable for semisolid processing, while MI-ID-cast alloys exhibit a non-uniform initial microstructure, with dendritic features dominant at the perimeter of the casting. Finally, the mechanisms responsible for the formation of near-equiaxed microstructure for each method are investigated. (C) 2000 Elsevier Science S.A. All rights reserved.