ECAP 강가공에 의한 5083 Al 합금의 초소성 변형

Abstract

초기 결정립 크기가 200 μm인 상업용 5083 Al 합금에서 equal channel anglar pressing(ECAP) 강가공에 의하여 결정립을 초미세화 시킬 수 있었다. ECAP는 200℃에서 수행되었고, 반복 passes시 180˚ 회전을 주면서 같은 시편에 8 passes까지 강가공을 가하였다. 미세조직 특징은 1 pass후 평균 0.2 μm의 폭과 0.8 μm의 길이를 갖는 연신된 평행한 bands가 균일하게 형성 되었고, 4 passes후 결정립 크기가 약 0.3 μm인 등축의 초미세 결정립이 얻어졌다. 이러한 초미세 결정립을 갖는 5083 Al 합금에서 저온 초소성 성질이 얻어졌는데, 약 0.5 μm의 결정립 크기를 갖을 때 250℃이하의 온도에서 연신율이 200 %이상인 초소성 거동을 나타내었다.

An ultrafine grained structure was introduced into a commercial 5083 Al alloy with the initial grain size of ∼200 μm using the equal channel angular pressing technique. Equal channel angular pressing was successfully conducted at 200℃ and the results showed that the microstructure was reasonably homogeneous after single passage and consisted of parallel bands of elongated substructure having the average width of 0.2 μm and the average length of 0.8 μm. Repetitive passes were conducted on the same sample up to total 8 passes through the die so that the sample was rotated 180˚ around its longitudanal axis between passes. An equiaxed ultrafine grained structure of ∼0.3 μm was obtained in the present alloy after 8 passes. It was found that a 5083 Al alloy with the grain size of ∼ 0.3 μm exhibited a superplastic-like behavior with elongation to failure in excess of 200% below.