Characterisation of Ga-coated and Ga-brazed aluminium

This work is devoted to the brazing of aluminium using liquid gallium. Gallium was deposited on aluminium samples at ~ 50 °C using a liquid gallium “polishing” technique. Brazing was undertaken for 30 min at 500 °C in air. EDS (Energy Dispersive X-ray Spectroscopy) and AES (Auger Electron Spectroscopy) characterisation of Ga-coated samples has shown that the Ga surface layer thickness is of ten (or a few tens of) nanometres. Furthermore, aluminium oxide layer (Al2O3) was shown to be “descaled” during Ga deposition, which ensures good conditions for further brazing.Cross-section examination of Ga-coated samples shows that liquid gallium penetrates into the aluminium grain boundaries during deposition. The thickness of the grain boundary gallium film was measured using an original EDS technique and is found to be of a few tens of nanometres. The depth of gallium grain boundary penetration is about 300 μm at the deposition temperature.The fracture stress of the brazed joints was measured from tensile tests and was determined to be 33 MPa. Cross-section examination of brazed joints shows that gallium has fully dissolved into the bulk and that the joint is really autogenous.

► Aluminium can be brazed using liquid gallium deposited by a “polishing” technique.
► The aluminium oxide layer is “descaled” during liquid Ga “polishing” deposition.
► EDS can be used for determination of surface and grain boundary Ga film thickness.
► The surface and grain boundary Ga film thickness is of a few tens of nm.
► Surface and grain boundary gallium dissolves in the bulk during brazing.