Clad Melting and Joint Formation in Aluminum Brazing Under Severe Alterations of the Background Atmosphere: A Superior New Brazing Sheet Material Vs. a Traditional Brazing Sheet

The paper summarizes a comparative in situ and in real time study of the onset of melting, clad flow, and joint formation of a novel aluminum brazing sheet material vs. a traditional material. The key adverse impact considered involves a change of the oxygen content of the nitrogen background atmosphere. A series of hot stage microscopy studies of the brazing process evolution have been performed  within the range of ~2 ppm to 20,000 ppm of oxygen (i.e., ~2, 200, 500, 2000, and 200000 ppm). Both series of tests with and without added potassium fluoroaluminate flux were performed. Standard set of brazing parameters was selected and kept as constant, so that an adverse impact of the atmosphere can be registered. A remarkable consistency of the clad flow and joint formation in case of a newly developed material without added flux was documented for up to 2000 ppm Oxygen A partial joint formation, without added flux, has been repeatedly registered even in air. Digital, real time video clips of all the stages of brazing (melting, reactive flow, joint formation and solidification) will be presented. The study is supported by a detailed analysis of joint formation and documented in terms of selected metrix.