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

Abstract

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 the fillet length. When the oxygen partial pressure of atmospheric gas was much reduced to the order of 10⁻²⁵ Pa using a zirconia oxygen pump, a long fillet, comparable to that formed by flux brazing, was obtained. The reason for the improved brazability was discussed from the viewpoint of the fine segmentation of the oxide caused by the combined effects of reduction of the oxide, thermal expansion at melting the filler alloy, and gas phase formation reaction from the molten filler alloys.

 

This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 85 (2021) 352–358. Figure 6 is modified, and eq. (9) is added.

Fig. 6 Schematic of the fragmentation progress of oxide film on the brazing filler alloy during flux-free brazing of aluminum alloy under ultra-low oxygen partial pressure.