A eutectoid phase transformation for the primary intermetallic particle from Alm(Fe,Mn) to Al3(Fe,Mn) in AA5182 alloy

The size and morphology evolution of the primary intermetallic particles in a DC-cast AA5182 alloy during homogenization at 470 and 520 degreesC has been studied. A eutectoid phase transformation of the primary particles Al-m(Fe,Mn) --> Al-3(Fe,Mn) --> Al is observed by field emission gun scanning electron microscopy (FEG-SEM) and transmission electron microscopy (TEM). After the transformation, Al-m(Fe,Mn) particles become a lamellar mixture of Al-3(Fe,Mn) and Al, which is believed to be beneficial to the break-up of the large primary particles during hot rolling. The transformation mechanism and the transformation kinetics have been studied. During isothermal treatment at 520 degreesC, the fractional transformation rate is mainly controlled by nucleation. At 470 degreesC, the phase transformation is controlled by both nucleation and growth of Al-3(Fe,Mn) in Al-m(Fe,Mn) phase. (C) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.