抄録
The structure in Al-Zr alloys solidified under various cooling conditions were investigated. A relation between crystallization of the metastable Al3Zr and grain sizr of solidified crystals is discussed. A complete solid solution is attained in the alloys solidified at a high cooling rate or in the alloys containing smaller amounts of Zr. The metastable phase Al3Zr with L12 type crystal structure or the equilibrium phase Al3Zr with DO23 type crystallizes primarily with decreasing cooling rate and with increasing Zr content. The metastable Al3Zr grows into fine dendritical shape followed by solidification of α-aluminum. An angular structure is, therefore, observed within a grain. The dendritical metastable Al3Zr grows in the <111> Al3Zr (=Al) direction differently from aluminum. The average grain size of angular structure decreases with increasing cooling rate. The number of grains including the angular structure increases, and the average grain size of solidified crystals decreases with increasing Zr content at the same cooling rate. The dendritical metastable Al3Zr acts as an effective nucleus for crystallization of α-aluminum and has a grain refining effect.
