3D X-Ray Diffraction Characterization of Grain Growth and Recrystallization in Rolled Braze Clad Aluminum Sheet

Braze clad on aluminum (Al) sheets has enabled fast and convenient brazing assembly of complex heat exchangers. However, there are details in the brazing process that are not fully understood. Herein, 3D X-ray diffraction (3DXRD) is used to investigate the grain position, size, and orientation before and after controlled atmosphere brazing (CAB). The outcomes are presented as maps of center-of-mass positions with relative grain size distribution and color-coded grain orientations. The results show that, for braze clad Al sheets exposed to CAB simulation, it is possible to distinguish grains from the solidified Al-Si alloy from those in the core Al alloy. It is also possible to distinguish new grains obtained through recrystallization during CAB. Hence, the study shows that stretching of the rolled Al sheet by 6% provides enough stored energy in the core material so that recrystallization occurs during CAB and, in addition, provides conditions for Al-Si alloy grain growth into the core material. While the phenomenon is well known, it is poorly understood for processes in connection with brazing of mechanically formed Al alloy components in heat exchanger assemblies, and these results demonstrate the potential for gaining deeper insights through 3DXRD. (Less)