Study on diffusion behavior and microstructural evolution of Al/Cu bimetal interface by synchrotron X-ray radiography

Synchrotron X-ray radiography was used to in situ study the interface diffusion behavior and microstructural evolution during the melting and solidification of Al/Cu bimetal. During the solidification, the dendritic growth around the interface is mainly dominated by the variation of Cu concentration and thermal field. Four transition zones of solute profile around the interface were identified to be I (α-Al), II (Al + Al2Cu), III (Al2Cu) and IV (AlCu, Al3Cu4 and Al2Cu3), respectively. During the melting, the concentration variations of Al and Cu around the interface were quantitatively analyzed through the extraction of gray level from sequenced X-ray images. The diffusion coefficients of Cu in liquid Al were calculated from the known concentration variations by an inverse method based on Fick's second law. The diffusion coefficients of Cu in Al were found to follow linear Arrhenius equation dependencies with the pre-exponential factor of 2.83 × 10−5 m2 s−1 and the activation energy of 96.0 kJ mol−1 in a temperature range of 893-970 K.