Thermodynamics Analysis of Melting Characteristics for SilverBrazing Alloys with Electroplating Tin

Abstract:

Silver brazing alloys with electroplating tin were prepared using the combination process of electroplating and heat diffusion based on BAg50CuZn substrate. By revealing the thermodynamic properties of silver brazing alloys with electroplating tin, the melting temperature of silver brazing alloys were observed by differential scanning calorimeter (DSC), the phase transformation thermodynamic characteristic of silver brazing alloys were analyzed with the thermal analysis kinetics of non-isothermal differential and integral methods. The microstructure and phase composition of wetting interface between 304 stainless steel and silver brazing alloys were investigated by optical microscope and XRD, respectively. The results show that the phase transformation temperature range of silver brazing alloys from solid to liquid would be narrower with the increase of Sn content, and the phase transformation activation energy of silver brazing alloys is gradually increased by non-isothermal differential and integral method. When Sn content is 7.2 %, the activation energy and pre exponential factor reach to the maximum, which are 555.56 kJ/mol and 1.41×10₃₂, respectively. The phase transformation rate equation of silver brazing alloys with electroplating tin is deduced as k=1.41×10₃₂exp(-5.56×10₅/RT). Silver brazing alloys of 7.2 % Sn content is melted on the surfae of 304 stainless steel, the microstructure of wetting interface are composed of Ag phase, Cu phase, CuZnphase, Cu₅Zn₈ phase, Cu₄₁Sn₁₁ phase and Ag₃Sn phase.

Key words:silver brazing alloys with electroplating tin; melting characteristic; activation energy; phase transformation rate; DSC