Discussion on apparent chromaticity and surface composition evolution of copper-phosphorus brazing filler metal

In this paper, the application and development on processing technology of copper-phosphorus brazing filler metal were described. Combined with the actual production, the apparent chromaticity and surface composition of copper-phosphorus brazing filler metal were tested during thermal processing. The apparent chromaticity was introduced to predict the microficial composition of copper-phosphorus brazing filler metal, and the relationship between composition and chromaticity was discussed. To BCu89AgP and BCu91AgP, two kinds of copper-phosphorus brazing filler metals as typical representative, the results of chromaticity and surface microstructural evolution were measured under different process conditions, while the discoloration mechanism of copper-phosphorus brazing filler metal was analyzed. The results showed that the apparent color of copper-phosphorus brazing filler metal was closely related to the surface composition. Meanwhile, the correspondence between chroma and composition was proved, which provided an important reference for production and application. Aiming at the evolution of chromaticity and the law of composition evolution, several copper-phosphorus brazing filler metal extrusion and drawing processes were proposed. Finally, the color range of copper-phosphorus brazing filler metal in the hope of "rose red" in the actual production was calibrated, and the recommendations of extrusion temperature and drawing temperature were given.