Influence of Mn addition on microstructure and phase formation of spray-deposited Al-25Si-xFe-yMn alloy

The hypereutectic Al-25Si-xFe-yMn alloys (with the ratio of Mn to Fe (y/x) between 0 and 1 wt.%) were synthesized by spray forming. The microstructure of the spray-deposited preforms as well as the over-sprayed powders was investigated. The addition of Mn was aimed to improve the mechanical properties of the alloys through forming the particulate α-Al15(Fe,Mn)3Si2 phase to replace the acicular δ-Al4FeSi2 and β-Al5FeSi phases formed in the alloy without Mn. XRD results revealed that, for alloy with y/x = 0, almost single acicular δ-Al4FeSi2 phase presented in the over-sprayed powders, whereas the spray-deposited preform consisted of both δ-Al4FeSi2 and β-Al5FeSi phases. For alloy with y/x = 0.625, the particulate α-Al15(Fe,Mn)3Si2 phase began to appear in the deposited preform. When y/x increased to 1.0, δ-Al4(Fe,Mn)Si2, β-Al5(Fe,Mn)Si and α-Al15(Fe,Mn)3Si2 phases coexisted in the over-sprayed powders, whereas only particulate α-Al15(Fe,Mn)3Si2 phase could be observed in the deposited preform. These results can be explained with schematics for transformation of the intermetallics in light of the phase forming mechanisms involved during spray deposition.