Correlative characterization of primary Al-3(Sc,Zr) phase in an Al-Zn-Mg based alloy

摘要

Three-dimensional electron backscatter diffraction, focused ion beam, transmission electron microscopy and energy filtered transmission electron microscopy were employed to investigate the structural information of primary Al-3(Sc,Zr) phase, i.e. size, shape, element distribution and orientation relationship with the alpha-Al matrix. It was found that (i) most primary Al-3(Sc,Zr) phases have a cubic three-dimensional morphology, with a size of about 6-10 pm, (ii) most primary Al-3(Sc,Zr) phases are located within the alpha-Al matrix, and exhibit a cube to cube orientation relationship with the alpha-Al matrix, and (iii) a layer by layer growth was observed within primary Al-3(Sc,Zr) phases. Al, Cu, Si and Fe are enriched in the alpha-Al matrix between the layers of cellular eutectic Al-3(Sc,Zr) phase, while Sc,Ti and Zr are enriched in small Al-3(Sc,Zr) phases. A peritectic reaction and subsequent eutectic reaction between Al3Sc and Al was proposed to interpret the observed layer by layer growth. This paper demonstrates that the presence of impurities (Fe, Si, Cu, Ti) in the diffusion field surrounding the growing Al-3(Sc,Zr) particle enhances the heterogeneous nucleation of Al-3(Sc,Zr) phases. (C) 2015 Elsevier Inc. All rights reserved.