Al_Cu合金定向凝固枝晶尖端开裂及间距调整机制.pdf

18 10 2008 10 Vol.18 No.10 The Chinese Journal of Nonferrous Metals Oct. 2008 1004-0609(2008)10-1813-06 Al-Cu ( 710072) Al-4%Cu()/v=30 µm/s v=300 µm/s LMK Al-Cu TG 113.1; TG 115.21 A Dendrite tip splitting and primary spacing adjustment mechanism of Al-Cu alloy during directional solidification QU Min, LIU Lin, TANG Feng-tao, ZHANG Wei-guo, HUANG Tai-wen, FU Heng-zhi (State Key laboratory of Solidification Processing, Northwestern Polytechnical University Xi’an 710072, China) 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 / [7] CBr -X