EFFECT OF WITHDRAWAL RATE ON DENDRITIC INTERFACIAL CHARACTERISTIC FOR A1-4%Cu ALLOY DURING DIRECTIONAL SOLIDIFICATION

Directional solidification experiments were carried out on Al-4%Cu alloy under with- drawal rates varying from 100μm/s to 600μm/s.It is showed that the primary dendrite arm spacing decreases with increasing withdrawal rate.The shape of quenched solid/liquid interface in dendrite growth morphology appears as unevenness where some dendrite trunks grow as convex parts.The ex- tent of protrusion is inconspicuous at lower withdrawal rates.With withdrawal rate increasing,those protrusions are then reinforced and finally almost faded.Dendrite interface temperature is also first increased and then decreased with increasing withdrawal rate.The KGT model and non-equilibrium effect were used to determine the dendrite interface temperature,tip undercooling and composition and the formula to describe dendrite tip undercooling was also obtained.It is found that the unevenness of interface is related to the tip undercooling and compositions.