Effect of Flux on Void Formation During Copper Alloy Brazing

Abstract

In general, a flux is used to braze a copper alloy. Defects （mainly voids） are formed when spreading a molten brazing filler metal in the joint gaps owing to such factors as the brazing conditions, vaporized flux and its residue. Previous studies have confirmed that the gap shape and the gap size affect void formation. Furthermore, it was confirmed that the behavior of the flux （gas and residue, which are generated from the flux） affected the void formation. Therefore, in this study, we conducted the brazing experiment in which the amount of flux was varied in order to suppress the generation of gas and residue and reduce the void ratio.

Using C3604 as a base metal, two specimen shapes and three gap sizes were prepared. The specimen was heated in an electric furnace, X–rays were irradiated onto the side surface of the test piece during the temperature increase, and a video was taken. From the X–ray transmission images, it was found that the void ratio decreased as the flux decreased at the gap 500 µm and the gap 800 µm. Further, it was confirmed from the video that the gas generated from the flux decreased with the decrease in the flux, and that the void formation was suppressed. It was also found that the void ratio increased as the flux decreased at the gap 100 µm. From these results, between the gap 100 µm to 500 µm, it was considered that the void formation factor changes from the flux to the size of the gap.