Microstructure modification and related mechanism of spray‐formed Fe‐bearing hypereutectic Al‐Si alloys

Abstract

AbstractThe Fe‐bearing hypereutectic Al‐Si alloys with/without Cr/(Cr+Mn) addition have been prepared by Spray Forming (SF) process. With 2 wt.% Cr addition, the short‐rod β‐Al5FeSi phase in spray‐formed Al‐25Si‐5Fe‐3Cu (wt.%, denoted as 3C) alloy can be substituted by particulate α‐Al(Fe,Cr)Si phase with sizes less than 5–6 μm. But small quantity of blocky β‐Al5(Fe,Cr)Si phase still appears in Cr‐added hypereutectic Al‐Si alloy. When (2Cr+1Mn) (wt.%) are added simultaneously into 3C alloy, almost all the short‐rod β‐Al5FeSi phase or blocky β‐Al5(Fe,Cr)Si phase disappear, instead, the α‐Al(Fe,Cr,Mn)Si phase become the only Fe‐bearing phase. During heat treatments, the other two spray‐formed hypereutectic Al‐Si alloys (besides SF‐3C alloy) are thermodynamically stable for the appearance of high thermodynamically stable particulate α‐Al(Fe,Cr)Si/α‐Al(Fe,Cr,Mn)Si phase. Also the phase transformation occurred during the heating/cooling process of the present hypereutectic Al‐Si alloys are investigated and the mechanism of microstructural formation of the spray‐formed alloys are discussed.