Effect of sulphur on silver filler metal and brazing properties

The properties of sulphurized silver based solder were studied by optical microscope,scanning electron microscopy and other analytical tools. The experimental results indicate that the tensile strength of sulphurized filler metal decreased significantly, and then to a certain extent until not varied. The difference of wettability was obvious at different sulphurizing time. The wetting area was reduced by nearly half at the sulphurizing time of 30 min,but the wetting area of brazing filler metal would change little if the sulphurizing time further lasted. Relative dense sulphurized layer was formed on the surface of brazing filler metal and its thickness was about 10 μm. The distribution of Zn and Cu in the sulphurizing layer and the internal brazing filler metal is relatively uniform,while the Ag element is distributed periodically. Sulfur existed in the form of Ag₂S,Cu₂S,CuS and ZnS in the brazing filler metal. The melting points of Ag₂S, Cu₂S,CuS and ZnS were relatively high,and their existence would affect the welding properties severely.