Brazing properties of silver based filler metal with different carbon contents

Brazing properties of silver based brazing filler metal with different carbon contents obtained by different rolling technologies were researched using optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), etc. The results showed that the carbon-containing layer was about 0.5~7.0 μm on the surface of brazing filler metal rolled with oil; the existing forms of carbon on the surface were mainly free carbon molecules, ZnC₈ and C₂CdO₄; with the carbon content increasing from 0% to 1.1%, the wetting area decreased from 356.8 to 65.3 mm², and the tensile strength decreased from 387.2 to 89.5 MPa. The carbon content in the brazing filler metal should be controlled below 0.005%. There were several existing forms for surface carbon-containing layer after brazing. Some carbon molecules which had no enough time to rise to the surface were wrapped inside the brazing filler metal; some carbon molecules which floated with the melt of brazing filler metal were around the brazing filler metal, and then were pushed to the spreading forefront to form an annular ring; some diffused into the steel matrix to form carbides with Cr, Ni, Fe, etc.