일방향 응고시킨 Al-Co 합금의 특성에 관한 연구

Abstract

일방향 응고시킨 Al-Co 공정합금의 기계적 성질 및 조직을 연구하였다. Al-Co 공정합금은 결정성장속도(R) 1~10cm/hr, 고-액 계면에서 열적온도구배(G)은 32℃로 유지하며 일방향 응고하였다. 공정합금의 미세조직은 성장조건(G/R)에 따라서 다양해진다. 즉 G/R 의 비가 8.5×103℃/㎠/sec 보다 크면 라멜라 조직이 형성되며, G/R 의 비가 8.5×103℃/㎠/sec 보다 작으면 콜로니 조직이 형성된다. 라멜라조직내의 층상간격(λ)은 λ²· R = constant 의 관계식을 통해서 결정성장속도에 따라 다르다는 것을 발견할 수 있었다. 성장조건에 따른 인장성질을 비교하면 콜로니 조직의 층상간격이 라멜라조직의 층상간격보다 작을수록 층상간격은 증가하였다. 같은 샘플에서 항복응력은 층상간격에 따라 변하지 않았다. 핵형성 방법은 응고방법에 따라고-액계면에 의해 결정되는 작용이 발견되지 않았다. 공정합금의 미세경도는 층상간격이 증가할수록 증가하였다.|The structures, the mechanical properties of the unidirectionally solidified Al-Co eutectic alloy were investigated. Al-Co eutectic alloy was unidirectionally solidified with growth rates(R) between 1cm/hr and 10cm/hr at induction furnace maintaining the thermal gradient (G) at solid-liquid interface, 32℃/cm The eutectic microstructure was varied according to the growth condition(G/R ratio). When G/R ratio was larger than 8.5×103℃/cm2/sec, the lamellar structure was formed, when G/R ratio was smaller than 8.5×103℃/cm2/sec, the colony structure was formed. It was found that the interlamellar spacing(λ) was dependent on the growth rate(R) through the relationship, λ²·R = constant. The tensile properties in as-grown condition increased with the decrease of interlamellar spacing and the values corresponding to the colony structure are lower than those corresponding to the lamellar structure with the same lamellar spacing. The Yield stress for samples in aged condition did not change with the interlamellar spacing. The mechanism of nuclei formation was found out that whose operation was determined by a type of the solid-liquid interface formed during solidification. The microhardness of this eutectic alloy increased with the growth rate increase.