Quantitative characterization of brazability for Sn-plated Ag brazing filler metals based on entropy model

Two types of Sn-plated AgCuZnSn brazing filler metals were prepared by a combinative process of electroplating and thermal diffusion using BAg50CuZn and BAg34CuZnSn brazing filler metal. The comprehensive thermal analyzer, wetting test furnace and universal tensile testing machine were applied to analyze the melting temperature range, wetting area and tensile strength. The mathematical model of the filler metals wetting entropy and the joint strength entropy were established, and compared with the traditional brazing filler metal prepared by melting alloying under the same condition of Sn content. The wetting entropy of the Sn-plated Ag brazing alloys are smaller than the traditional brazing filler metals, and its joint strength entropy value is slightly higher than the latter. The wetting entropy value of the Sn-electroplated brazing alloys and traditional filler metal are similar to the change trend of the wetting area for those filler metals on the surface of the 316LN stainless steel. The change trend of the brazed joint strength entropy value with those filler metals are basically the same as the tensile strength of the 316LN stainless steel joint with the increase of the Sn content. The experimental results show that the mathematical model of the wetting entropy and the joint strength entropy can quantitatively predict the brazing process and mechanical properties of the Sn-electroplated Ag brazing alloys to a certain extent.