Flux-Free Brazing of Aluminum Alloys under Ultra-Low Oxygen Partial Pressure through a Zirconia Oxygen Pump

Flux-free brazing of aluminum alloys was carried out under high purity nitrogen gas with ultra-low oxygen partial pressure prepared by zirconia oxygen pump. The flux-free brazability of the aluminum alloys was improved by adding a small amount of magnesium into the sample, which was more effective in the core alloy than in the brazing filler alloys. Higher heating rate of the sample increased a fillet length. When the oxygen partial pressure of atmospheric gas was much reduced to the order of 10−25 Pa through a zirconia oxygen pump, a long fillet was obtained, comparable to that formed by flux brazing. The reason for the improvement of the brazability was discussed from the viewpoint of the fine segmentation of the oxide film caused by the combined effects of reduction of the oxide film, thermal expansion at melting the filler alloy, and gas phase formation reaction from the molten filler alloys.