Abstract: The relationship between primary arm spacing of Al-4.5%Cu alloy and withdrawal rate during unidirectional solidification was investigated when the withdrawal rate is in the range of 20−220 μm/s. The result shows that the primary arm spacing decreases along with increasing withdraw rate. The primary arm spacing decreases sharply with withdrawal rate below 100 μm/s, and decreases more gently with a withdrawal rate beyond 100 μm/s. Through the comprehensive consideration of the difference between withdrawal rate and interface growing rate, temperature gradient and etc, the function between primary arm spacing and withdrawal rate is founded, which could predict the variation of primary arm spacing exactly when the withdrawal rate is in the range of 100−220 μm/s. It is hoped that the function can be helpful to obtain a good match of experimental parameters during unidirectional solidification.

Key words: Al-4.5%Cu alloy; unidirectional solidification; primary dendrite arm spacing; withdrawal rate; heat transfer