Abstract: The Ag-50wt%Cu hypereutectic alloy was solidified in a 3m drop tube. It is .revealed that with the decrease of droplet size, the strnctural morphology transformed from the dendrites with long trunk and thin short secondary arms to fine dendritic structures.The calculations based on LKT dendritic growth model indicate that dendritic growth is dominantly controlled by solute diffusion within the whole undcreooling regime.However, the influence of thermal diffusion-controlled growth becomes stronger above a critical undercooling about 268K. The refinement of dendritic structure is caused by large amounts of nuclei within droplet. Moreover, it is estimated that when droplet diameter is smaller than 300μm, the undercooling and growth velocity are fanger than 268K and 290mm/s respectively, while the solute impping effect may occur. Compared with Ag-15wt%Cu hypoeutectic alloy, there is no evident feature of dendritic-toequiaxed transition for Ag-50wt%Cu hypereutectic alloy, which is consistent with the calculation results of dendritic breakap time.Keuwords: Ag-Cu alloy; rapid solidification; undercooling; dendritic growth

Key words: Ag-Cu alloy, rapid solidification, undercolling, dendritic growth