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Korean Journal of Metals and Materials > Volume 56(1); 2018 > Article
Korean Journal of Metals and Materials 2018;56(1): 40-48. doi: https://doi.org/10.3365/KJMM.2018.56.1.40
Al 첨가가 Mg-7Sn-1Zn 합금 압출재의 미세조직과 인장 및 굽힘 특성에 미치는 영향
김상훈1, 이종언1, 김예진1, 최재옥1,2, 이정훈3, 박성혁1
1경북대학교 신소재공학부
2재료연구소 실용화연구단
3한국생산기술연구원 울산지역본부
Effect of Al Addition on the Microstructure, Tensile Properties, and Bendability of Extruded Mg-7Sn-1Zn Alloy
Sang-Hoon Kim1, Jong Un Lee1, Ye Jin Kim1, Jae Ok Choi1,2, Jeong-Hun Lee3, Sung Hyuk Park1
1School of Materials Science and Engineering, Kyungpook National University, Daegu 41566, Republic of Korea
2Implementation Research Division, Korea Institute of Materials Science, Changwon 51508, Republic of Korea
3Ulsan Regional Division, Korea Institute of Industrial Technology, Ulsan 44413, Republic of Korea
Correspondence  Sung Hyuk Park ,Tel: +82-53-950-5565, Email: sh.park@knu.ac.kr
Received: 21 August 2010;  Accepted: 31 October 2017.  Published online: 1 January 2018.
ABSTRACT
The effect of Al addition on the microstructure and mechanical properties of extruded Mg-Sn based alloy is investigated by adding 1 wt% Al to the Mg-7Sn-1Zn alloy and indirectly extruding the billets with and without the Al addition. The Al addition promotes dynamic recrystallization (DRX) behaviour during hot extrusion, which results in an increase in the area fraction of dynamically recrystallized (DRXed) grains and a decrease in the width of unDRXed grains of the extruded alloy. In addition, dynamic precipitation during extrusion is also accelerated by the Al addition owing to the decrease in Sn solubility in the Mg matrix, thereby increasing the amount of Mg2Sn precipitates and decreasing their size. The increased amount of fine precipitates, and the reduced amount of coarse unDRXed grains, lead to a reduction in the average grain size of the extruded alloy. The Al addition significantly improves tensile properties (i.e., strength and ductility) and 3 point bending strength of the extruded alloy. The improvement in the tensile and bending strengths is attributed to the combined effects of grain-boundary hardening by the reduced grain size, precipitation hardening by more abundant precipitates, and solid-solution hardening by dissolved Al atoms. The increase in the tensile elongation results from the decrease in the amount and size of the coarse unDRXed grains because {10-11} contraction and {10-11}-{10-12} double twins, which can act as initiation sites of microcracks, easily occur under tension along the extrusion direction in the coarse grains. However, the increased amount of precipitates and the reduced grain size accelerate the formation of shear bands and suppress the activation of {10-12} twinning in the upper side of the bending sample, which consequently results in a deterioration in the bending formability of the extruded alloy.
Keywords: magnesium alloy, extrusion, recrystallization, precipitation, tensile properties
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