Abstract:In order to explain the reason why the columnar crystal precious metal has excellent ultra-fine wire processing property and high resistance, three kinds of Ag-28Cu-0.75Ni alloy bars, columnar crystal of 20 μm×60 μm, equiaxed crystal of 10 μm, and tri-crystal zone with surface fine crystal of 5 μm + columnar crystal with length diameter ratio of around 3 + core equiaxed crystal of 30 μm, were obtained by horizontal continuous casting, water-cooled copper die casting, and graphite die casting, respectively. The effects of grain morphology and size on the ultra-fine wire processability and resistivity of Ag-28Cu-0.75Ni alloy bars were studied. The results show that, compared with the equiaxed crystal bar and the tri-crystal zone bar, the columnar crystal bar has the lower dislocation density (1.78×1015 m-2), the lowest ratio of micro-hardness change (33.3%), and no cleavage step after the tensile test, thus, it presents the lowest work hardening rate. Besides, the axial tensile strength of as-cast columnar crystal bar is up to 384.6 MPa. Therefore, the ultra-fine wire with the diameter of 0.05 mm and the length of 100 meters or more can be obtained by the high-efficiency continuous wire drawing of the columnar crystal bar. The resistivity of processed and annealed Ag-28Cu-0.75Ni alloy ultra-fine wires that drawn from the columnar crystal bar are higher, after two times continuous annealing, the resistivity of columnar crystal Ag-28Cu-0.75Ni alloy ultra-fine wire is up to 3.68 μΩ.cm, which is related to the lower dislocation density and work hardening rate.