3D characterisation of grain orientation induced braze alloy wetting

Purpose and goal

An application problem when brazing aluminium is that molten braze alloy may penetrate into the bulk, which reduces the corrosion resistance and, thus, increases the risk for leakages in, e.g., heat exchangers. The phenomenon is poorly understood, but according to a new hypothesis the molten braze alloy penetration depends on the wetting of grains with different orientation compare to neighboring grains. Hence, the study aims to find out, through synchrotron radiation based 3D imaging, if braze alloy penetration into aluminium is dependent on the grain orientation mismatch.

Expected results and effects

Through phase-contrast tomography we have recorded 3D images of aluminium sheet materials with different stages of braze alloy penetration. Characteristic signs of braze alloy penetration has been identified in the 3D images and together with 3D X-ray diffraction, for crystal orientation information, and 3D X-ray diffraction contrast imaging, for grain shape information, the braze alloy penetration process is captured step by step. The project has provided new perspectives on the braze alloy penetration process and further analysis expects to support or reject the hypothesis.

Planned approach and implementation

Heat treatments with a temperature gradient over rolled aluminium sheet samples were performed at Gränges. Further sample preparations were performed at Lund University. Optical microscopy and laboratory based phase contrast tomography gave practice prior to the synchrotron radiation based experiments, which were performed at the BL14B2 beamline at SPring-8 and the Swedish beamline (P21-2) at PETRA-III. Both beamtimes were applied through open calls. Data treatments and analysis were, and still are, performed at Kobe University and Lund University. The data volume is massive.