Continuous strip casting, microstructure, and performance of Ag-Cu brazing alloy

This study sought to examine the suitability of the continuous strip casting process as a new fabrication method for the Ag-Cu brazing alloy. Several continuous strip casting processes such as planar flow casting, melt dragging, and twin roll strip casting were applied to the manufacture of the Ag-32%Cu strip. In particular, twin roll strip casting was found to realize the best strip shaping ability and microstructural homogeneity. The effect of aging heat treatment on the microstructure and mechanical properties of a Ag-Cu strip was also investigated through tensile test, hardness test, X-ray diffraction (XRD), scanning electron microscopic (SEM) observations, and electron probe microanalysis (EPMA). Tensile results showed gradually decreasing strengths and simultaneously increasing elongation with longer aging time. An appropriate TS strength of 283 MPa and a significantly enhanced plasticity of 41% were realized with aging condition of 670°C/2hrs. Finally, twin-rolled strips 1 mm thick could be cold-rolled to a very thin strip (80-100 μm thickness). The microstructural evolution and crystalline morphologies of Ag-Cu metastable strips were also investigated and related to the mechanical properties.