STUDIES INTO NEW, ENVIRONMENTALLY FRIENDLY Ag-Cu-Zn-Sn BRAZING ALLOYS OF LOW SILVER CONTENT

The paper present selected results of the research conducted for elimination of toxic cadmium from silver based brazing alloys of Ag-Cu-Zn-Cd type. The investigations were conducted with nine new alloys of constant, low silver content (25%) and diversified copper (38.8-46%), zinc (19-32%) and tin (3-10%) contents. Tin was selected as potentially the best cadmium substitute basing on literature review and analysis of equilibrium systems. For examinations and tests a series of ingots in laboratory scale was manufactured, as well as some ingots in pilot scale for the selected, most promising alloys. Complex metallographic examinations of the brazing alloys samples produced in various conditions were made as well as analyses of their phase composition. Also mechanical properties of the samples both in ambient and in elevated temperatures were examined, and physical and technological properties and usability of the alloys were determined. The last stage of the study covered laboratory trials of brazing using the selected alloys. Basing on the results it can be said that there is a possibility to substitute selected cadmium containing silver-based alloys with environmentally friendly alloys of Ag-Cu-Zn-Sn type of relatively low silver content. Low range of melting point was reached, as preliminary assumed. Mechanical properties of the studied alloys strongly depend on temperature, and present limited plasticity in room temperature, while at high temperature (over 500 degrees C) present superplasticity. The examined alloys show good spreadability and the brazing tests confirmed their good reactions both with copper and brass base in a wide temperature range.