Analytical electron microscopy of spray formed and hot extruded Al-18%Si–5%Fe-1.5%Cu alloy

Abstract

A spray atomization and deposition technique has been employed to produce spray – deposits of an Al-18Si-5Fe-1.5Cu (wt.%) alloy. Subsequently the alloy was hot extruded with a reduction ratio of 6:1 and extrusion temperature of 480 °C. The microstructural features of as spray - deposited and extruded alloy has been examined using SEM and TEM techniques and chemical analyses of phases by spectroscopic method. Samples for TEM study were initially prepared by a tripod mechanical polishing followed with an ion beam milling. The microstructure of spray – deposited alloy exhibited the presence of a cellular and plate – like morphology of β-Al 5 SiFe co-existing with δ-Al 4 Si 2 Fe. The formation of β-Al 5 SiFe phase is suggested to arise as a result of phase transformation of δ-Al 4 Si 2 Fe phase during slow cooling rate of the spray – deposit. The hot extrusion of the alloy resulted in fragmentation of both intermetallic phases and Si and revealed the dislocations present inside the Al-grains / grain boundaries along with broken pieces of Si and intermetallics at nano-scale in the matrix. A systematic approach has been persuaded to understand the evolution of microstructure and phase formation during inert gas atomization, spray deposition and hot extrusion of this alloy.