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Vol.56, No.1, 40 ~ 49, 2018
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| Title |
| Effect of Al Addition on the Microstructure, Tensile Properties, and Bendability of Extruded Mg-7Sn-1Zn Alloy |
| 김상훈 Sang-hoon Kim , 이종언 Jong Un Lee , 김예진 Ye Jin Kim , 최재옥 Jae Ok Choi , 이정훈 Jeong-hun Lee , 박성혁 Sung Hyuk Park |
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| 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.
(Received August 21, 2017; Accepted October 31, 2017) |
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| Key Words |
| magnesium alloy, extrusion, recrystallization, precipitation, tensile properties |
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