Abstract:The liquid/solid interface morphologies and cellular/dendrite spacing adjustment of Al-4%Cu (mass fraction) alloy were studied during directional solidification. The results show that the primary dendrite arm spacing adjustment mechanisms are overgrowth at low growth rate of v=30 μm/s, and dendrite tip splitting at higher growth rate as v=300 μm/s, which is instead of the growth of tertiary arm at higher growth rate. The tip radius interacts with primary dendrite spacing, and increases as primary spacing becoming larger in stable primary dendrite arm spacing. It is analyzed with LMK theory that the variation of dendrite tip concentration results in tip radius change, which leads to tip splitting. According to diffusion model, the relation of primary spacing and interface concentration is also obtained, and it shows that for dendrite it could reduce constitutional undercooling with adjusting primary spacing automatically.

Key words: Al-Cu alloy; directional solidification; dendrite spacing; tip splitting