Spray forming of silicon added AZ91 magnesium alloy and its workability

Si was added to AZ91 Mg alloy to improve the mechanical properties of the AZ91 Mg alloy. Spray forming was employed to refine the primary phases during solidification by means of rapid solidification generated at atomization and droplet flight stages. The process parameters of spray forming were varied to reduce the porosity level and improve the morphology of the billet preforms. As-spray-formed microstructures were characterized using optical microscope (OM), scanning electron microscope/energy dispersive spectrometer (SEM/EDS), and X-ray diffraction (XRD), which were compared with as-cast microstructures. Workability of spray-formed materials was studied, which was compared with that of cast materials. In the workability study, cylindrical specimens were extruded by simple direct extrusion with various ram speeds at various temperatures. Extrusion pressure and ram displacement were recorded and analyzed. Material flow patterns and macrostructures of extrusion, and surface conditions and microstructures of extruded specimens were analyzed using stereoscope, OM, and SEM. The effects of extrusion temperatures and ram speeds on the workability of spray-formed and cast materials were studied and compared. The extrusion operating conditions of spray-formed and cast materials were determined. (C) 2004 Elsevier B.V. All rights reserved.