Microstructure and melting properties of Ag–Cu–In intermediate-temperature brazing alloys

The microstructure and melting properties of ternary Ag–Cu–In intermediate-temperature alloys (400–600 °C) prepared by electric arc melting were investigated in this work. The melting properties, phase compositions, microstructure and hardness were characterized by differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM) and micro-hardness tester, respectively. The results show that the melting properties, phase compositions, microstructure and hardness of Ag–Cu–In brazing alloys are substantially different when adding different levels of indium. Indium element could effectively reduce the melting temperatures of (Ag–Cu₂₈)–xIn alloys, and the melting temperatures of (Ag–Cu₂₈)–25In alloy are located at 497.86 and 617.48 °C. When the indium content varies from 5 wt% and 10 wt%, the dominant phases in the alloys are Ag-rich and Cu-rich phases, and their granular crystals are smaller than 0.5 µm. When the indium content is higher than 15 wt%, the phase compositions of the alloy are Ag₄In and Cu₁₁In₉, and the microstructure exhibits dendritic crystals with a uniform distribution. The hardness of (Ag–Cu₂₈)–xIn alloy decreases first and then increases with the content of indium increasing, and the highest hardness of (Ag–Cu₂₈)–25In alloy is HV 266.0.