デンドライトの1次枝間隔に及ぼす凝固条件の影響

Abstract

To examine the relationship between the primary dendrite arm spacing and solidification conditions, experiments were performed with Al-2.0%Cu, Al-4.0%Cu, Al-6.0%Cu, and Al-2.0%Si alloys which were unidirectionally solidified in three ways, i.e., by rapid cooling, by slow cooling, and by alternating rapid and slow cooling. The results are summarized as follows:(1) When the average cooling rate V ranged between 1.6 K/s and 12.6 K/s, the primary dendrite arm spacing Z1 (10−3 m) was proportional to (G2R)−1⁄4 which was expected from Hunt’s theory, G (103 K/m) is the temperature gradient in liquid and R (10−3 m/s) is the growth rate.(2) When the average cooling rate V for most of the slowly cooled specimens was lower than 1.6 K/s, the value n in the equation Z1∝(G2R)−n became smaller than 1⁄4.(3) When the temperature gradient in the solid-liquid coexisting region was expressed as Gs (103 K/m), the primary dendrite arm spacing Z1 was proportional to Gs−0.70R−0.35 for all the specimens.(4) For the specimens solidified by rapid cooling and slow cooling, the relationship between Z1 and the cooling rate V was expressed as Z1∝V−1⁄2. But for the ones solidified by alternating rapid and slow cooling, Z1 was not proportional to V−1⁄2.(5) For all the specimens, Z1 was proportional to (GsR)−1⁄2.