Effect of multiple forging on the microstructure and properties of an as-cast Cu-Ni-Si alloy with high Ni and Si contents

A Cu-Ni-Si alloy with high Ni and Si contents was prepared by the traditional melting and casting method, and then multiple forging and ageing were conducted to investigate their effect on the microstructure and properties. The results show that reticular Ni31Si12 phases are located on the grain boundaries of the dendritic alpha-Cu(Ni, Si) solution matrix in the as-cast Cu-Ni-Si alloy because of the high Ni and Si contents, and some rice-like Ni2Si phases precipitate in the interior of alpha-Cu(Ni, Si) grains during cooling. With increasing number of forging passes, the morphology of the alpha-Cu(Ni, Si) matrix changes from dendrites to elongated dendrites and then equiaxed grains, the Ni31Si12 phase changes from reticular to irregular and then particle-like, while the Ni2Si phase gradually disappears. As a result, the hardness increases continuously up to 18 forging passes, while the electrical conductivity first increases and then decreases significantly. The hardness and electrical conductivity achieve the highest values with 18 forging passes and a subsequent ageing treatment at 450 degrees C for 4 h, and the corresponding microstructure comprises an equiaxed alpha-Cu(Ni, Si) matrix with microscale Ni31Si12 particles and sub-microscale Ni2Si precipitates.