EFFECT OF AN ABRUPT GROWTH RATE ON PRIMARY Al2Cu PHASE IN DIRECTIONAL SOLIDIFICATION OF Al–40%Cu HYPEREUTECTIC ALLOY
QUAN Qiongrui; LI Shuangming; FU Hengzhi
State Key Laboratory of Solidification Processing; Northwestern Polytechnical University; Xi’an 710072
Cite this article:
QUAN Qiongrui LI Shuangming FU Hengzhi. EFFECT OF AN ABRUPT GROWTH RATE ON PRIMARY Al2Cu PHASE IN DIRECTIONAL SOLIDIFICATION OF Al–40%Cu HYPEREUTECTIC ALLOY. Acta Metall Sin, 2010, 46(4): 500-505.
Intermetallics combining metal and ceramic properties exhibit colorfully complicated growth morphologies in solidification. Different from the solidus phase solidification, intermetallic solidification remains less understanding of the correlation between processing parameters and microstructure morphologies. In this paper, considering that the intermetallic compound Al2Cu phase has well–known thermophysical properties available for the theoretical and experimental research, we carried out the directional solidification experiments and focused on an Al–Al2Cu hypereutectic alloy, where the Al2Cu phase was solidified as a primary phase. The primary Al2Cu phase growth behavior in the experiments included phase competition growth between coupled eutectic and primary phase, faceted phase transition and its change in growth morphology. By using a high thermal gradient directional solidification apparatus, the directionally solidified microstructures of Al–40%Cu (mass fraction) hyereutectic alloy were investigated and discussed based on the competition growth model. As the growth rate was changed abruptly from 10 μm/s to 2 μm/s, the microstructure transition from a primary Al2Cu dendrite plus interdendritic eutectic to an entirely coupled eutectic occurred due to the interface growth temperature of the coupled eutectic exceeding that of the primary Al2Cu dendrite. Also, the alloy liquid composition ahead of the solid/liquid interface approaching the eutectic point caused this microstructure transition. Simultaneously, in the changing–growth rate experiments, the primary Al2Cu dendrites were firstly broken into small ones and then became the eutectic microstructure; it was interpreted rather by the decrease in liquid solute concentration ahead of the solid/liquid interface tan by te effect of the thermal–solutal convection. Moreover, the morphology change iphase growth from faceted primary Al2Cu phase to non–faceted phase was observed by reducing abruptly the growtrate from 10 μm/s to 2 μm/s, which can be explained by the Jackson fctor α decreasing with increasig the interface growth temperature of primary Al2Cu pase.
Supported by National Natural Science Foundation of China (No.50971101), Program for New Century Execllent Talents in University (No.NCET–07–0692) and the Fund of the State Key Laboratory of Solidification Processing in NWPU (No.34–TP–2009)
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