Abstract:The large and small sized Cu (solid)/Al (liquid) couples were prepared to investigate the directional growth behavior of primary α(Al) phase during a concentration-gradient-controlled solidification process under various static magnetic fields (SMFs). The results show that in the large couples, the α(Al) dendrites reveal a directional growth character whether without or with the SMF. However, the 12 T magnetic field induces regular growth, consistent deflection and the decrease of secondary arm spacing of the dendrites. In the small couples, the α(Al) dendrites still reveal a directional growth character to some extent with a SMF of ?5 T. However, an 8.8 T SMF destroys the directional growth and induces severe random deflections of the dendrites. When the SMF increases to 12 T, the α(Al) dendrites become quite regular despite of the consistent deflection. The directional growth arises from the continuous long-range concentration gradient field built in the melt. The morphological modification is mainly related to the suppression of natural convections and the induction of thermoelectric magnetic convection by the SMF.

Key words: α(Al) dendrite; diffusion couple; concentration gradient field; static magnetic field; directional growth; thermoelectric magnetic convection