Microstructural features induced by spray processing and hot extrusion of an Al-18% Si-5% Fe-1.5% Cu alloy

An inert gas atomization technique was employed to produce spray deposits of an Al-18Si-5Fe-1.5Cu (wt.%) alloy. The spray-deposited alloy was subsequently hot extruded with a reduction ratio of 6:1 and extrusion temperature of 480 °C. The microstructural features of the as-spray-deposited and extruded alloys were examined using optical, scanning electron and transmission electron microscopy techniques, and chemical analyses of phases were carried out using energy dispersive X-ray analysis and spectroscopic methods. The microstructure of the spray-deposited alloy revealed the presence of a cellular and plate-like morphology of β-Al5SiFe phase coexisting with δ-Al4Si2Fe phase in contrast to the presence of only δ-Al4Si2Fe phase in atomized powder particles. The formation of the β-Al5SiFe phase is suggested to arise as a result of phase transformation of δ-Al4Si2Fe phase during slow cooling of the spray deposit. The hot extrusion of the alloy resulted in fragmentation of both intermetallic phases and Si into nano-sized particles. The microstructure evolution during spray deposition and hot extrusion of the alloy is discussed.