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Sung Hyuk Park - One of the best experts on this subject based on the ideXlab platform.
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variation in dynamic deformation behavior and resultant yield asymmetry of Az80 Alloy with extrusion temperature
Journal of Materials Science & Technology, 2020Co-Authors: Sanghoon Kim, Ha Sik Kim, Sangwon Lee, Byoung Gi Moon, Sung Hyuk ParkAbstract:Abstract In this work, variation in the dynamic recrystallization (DRX) and dynamic precipitation behavior of Az80 Alloy during extrusion due to changes in extrusion temperature was investigated, and the resultant microstructure and yield asymmetry were analyzed. As the extrusion temperature increases from 250 °C to 350 °C, the primary DRX mechanism changes from twin-induced DRX to discontinuous DRX, resulting in an increase in the DRX area fraction and unDRXed grain size. In addition, as the extrusion temperature rises, Mg17Al12 precipitation during extrusion decreases sharply throughout the extruded material. The reduction in the compressive yield strength (CYS) with increasing extrusion temperature is more pronounced than it is for the tensile yield strength (TYS), which ultimately increases the yield asymmetry of the extruded material. The higher extrusion temperature has less of an influence on the TYS due to the promotion of certain hardening effects. On the other hand, the greater reduction in the CYS is attributed to the increased fraction and size of regions in which { 10 1 ¯ 2 } twins predominantly form and the lower amount of precipitates, which effectively facilitates { 10 1 ¯ 2 } twinning.
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effects of cold pre forging on microstructure and tensile properties of extruded Az80 Alloy
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2017Co-Authors: Ye Jin Kim, Sanghoon Kim, Jong Un Lee, Jae Ok Choi, Ha Sik Kim, Youngmin Kim, Yongjin Kim, Sung Hyuk ParkAbstract:Abstract This study investigates the effects of cold pre-forging (CPF) on the extrusion load during hot extrusion and on the microstructure and mechanical properties of extruded Az80 Alloy. For this purpose, a billet is forged to 10% strain at room temperature and then subjected to indirect extrusion at 200 °C. The CPF process causes the formation of a large amount of deformation twins and an increase in the dislocation density of the billet. The cold-forged Az80 billet exhibits a higher extrusion load during extrusion than an unforged Az80 billet, owing to the occurrence of twin-boundary hardening and enhanced strain-hardening effects in the former. The initial twins introduced by the CPF process promote dynamic recrystallization behavior during extrusion because they act as nucleation sites for recrystallization. As a result, the CPF process increases the area fraction of fine recrystallized grains and the microstructural homogeneity of the extruded Alloy. The Az80 Alloy extruded after CPF shows a higher tensile strength and ductility than the Az80 Alloy extruded without CPF. The improvement in strength is attributed mainly to the decrease in the average grain size caused by an increased recrystallization fraction. The increased ductility is due to the reduced area fraction of coarse unrecrystallized grains, in which microcracks occur during tensile plastic deformation.
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Evolution of tension and compression asymmetry of extruded Mg-Al-Sn-Zn Alloy with respect to forming temperatures
Materials & Design, 2016Co-Authors: Sangik Lee, Sung Hyuk Park, Jung Seok Kim, Sung-jun Park, Jonghun YoonAbstract:Abstract Substantial strength of as-extruded and as-forged ATZ842 Alloys is attributed to precipitation strengthening due to the presence of fine Mg 2 Sn and Mg 17 Al 12 particles in the Alloys. Because Mg Alloys inevitably undergo dynamic recrystallization during the warm forging that is required for their net-shape processing, it is important to examine microstructural evolution in as-forged samples. The appropriate forging temperature was found to range from 250 to 300 °C; average grain size started to increase at temperatures over 350 °C due to abnormal grain growth and a reduction in the fraction of second-phase particles. The ATZ842 Alloy showed mechanical properties superior to those of the Az80 Alloy, including yield and ultimate strengths in both tensile and compressive deformations. Remarkably, the tension and compression asymmetry in plastic flow of ATZ842 forged at 250 °C was characterized by a yield ratio of about 1.02, compared to the yield ratio of 0.88 for the Az80 Alloy.
Sanghoon Kim - One of the best experts on this subject based on the ideXlab platform.
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variation in dynamic deformation behavior and resultant yield asymmetry of Az80 Alloy with extrusion temperature
Journal of Materials Science & Technology, 2020Co-Authors: Sanghoon Kim, Ha Sik Kim, Sangwon Lee, Byoung Gi Moon, Sung Hyuk ParkAbstract:Abstract In this work, variation in the dynamic recrystallization (DRX) and dynamic precipitation behavior of Az80 Alloy during extrusion due to changes in extrusion temperature was investigated, and the resultant microstructure and yield asymmetry were analyzed. As the extrusion temperature increases from 250 °C to 350 °C, the primary DRX mechanism changes from twin-induced DRX to discontinuous DRX, resulting in an increase in the DRX area fraction and unDRXed grain size. In addition, as the extrusion temperature rises, Mg17Al12 precipitation during extrusion decreases sharply throughout the extruded material. The reduction in the compressive yield strength (CYS) with increasing extrusion temperature is more pronounced than it is for the tensile yield strength (TYS), which ultimately increases the yield asymmetry of the extruded material. The higher extrusion temperature has less of an influence on the TYS due to the promotion of certain hardening effects. On the other hand, the greater reduction in the CYS is attributed to the increased fraction and size of regions in which { 10 1 ¯ 2 } twins predominantly form and the lower amount of precipitates, which effectively facilitates { 10 1 ¯ 2 } twinning.
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effects of cold pre forging on microstructure and tensile properties of extruded Az80 Alloy
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2017Co-Authors: Ye Jin Kim, Sanghoon Kim, Jong Un Lee, Jae Ok Choi, Ha Sik Kim, Youngmin Kim, Yongjin Kim, Sung Hyuk ParkAbstract:Abstract This study investigates the effects of cold pre-forging (CPF) on the extrusion load during hot extrusion and on the microstructure and mechanical properties of extruded Az80 Alloy. For this purpose, a billet is forged to 10% strain at room temperature and then subjected to indirect extrusion at 200 °C. The CPF process causes the formation of a large amount of deformation twins and an increase in the dislocation density of the billet. The cold-forged Az80 billet exhibits a higher extrusion load during extrusion than an unforged Az80 billet, owing to the occurrence of twin-boundary hardening and enhanced strain-hardening effects in the former. The initial twins introduced by the CPF process promote dynamic recrystallization behavior during extrusion because they act as nucleation sites for recrystallization. As a result, the CPF process increases the area fraction of fine recrystallized grains and the microstructural homogeneity of the extruded Alloy. The Az80 Alloy extruded after CPF shows a higher tensile strength and ductility than the Az80 Alloy extruded without CPF. The improvement in strength is attributed mainly to the decrease in the average grain size caused by an increased recrystallization fraction. The increased ductility is due to the reduced area fraction of coarse unrecrystallized grains, in which microcracks occur during tensile plastic deformation.
Gaofeng Quan - One of the best experts on this subject based on the ideXlab platform.
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Eutectic phase strengthening and strain rate sensitivity behavior of Az80 magnesium Alloy
Materials Science and Engineering: A, 2020Co-Authors: Ren Lingbao, Mingyang Zhou, Lu Tianhui, Fan Lingling, Yangyang Guo, Yuwenxi Zhang, Carl J. Boehlert, Gaofeng QuanAbstract:Abstract A Mg–8Al-0.5Zn-0.2Mn wt.% (Az80) Alloy, containing a high volume percent of the β eutectic phase, was prepared using extrusion without a homogenization pretreatment (EX-II(F)). The β-eutectic-phase contributions to grain refinement, texture tailoring, and plastic behavior were discussed. Microstructure characterization was presented along with a strengthening mechanism analysis. The β-eutectic-phase strengthening contributions to the yield strength were estimated according to the thermal mismatch, Orowan looping, load transfer, and Hall-Petch mechanisms. In addition, the temperature and strain dependence for strain rate sensitivity (SRS) were investigated, and the influence of aging on the SRS evolution was discussed. The SRS exponent, m, of the EX-II(F) was measured at 298–573 K using strain rate jumps between 10−4 s−1-10−3 s−1. The m-value increased with increasing strain and temperature, and decreased with grain coarsening and Al solute depletion. Aging precipitation exhibited a softening effect on the 473–573 K flow stress and resulted in higher m-values. The β eutectic phase cracking decreased with increasing test temperature, which was attributed to the high deformability of the β eutectic phase above 573 K. Overall, this work has shown that the β eutectic phase can serve as a means to strengthen extruded Az80.
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Effect of Y Addition on the Semi-Solid Microstructure Evolution and the Coarsening Kinetics of SIMA Az80 Magnesium Alloy
Metals, 2017Co-Authors: Qi Tang, Mingyang Zhou, Gaofeng QuanAbstract:Semi-solid feedstock of Az80 magnesium Alloy modified by trace rare-earth Y element (0, 0.2, 0.4, 0.8 wt. %) was fabricated by strain-induced melting activation (SIMA) in the form of extrusion and partial remelting. The effect of Y addition on the microstructure evolution of the extruded and isothermally heat treated Alloy was observed by using an optical microscope (OM), scanning electron microscope (SEM), X-ray diffraction (XRD) and quantitative analysis. The results show that the Y addition can refine the microstructure and make the β-Mg17Al12 phases agglomerate. During the subsequent isothermal treatment at 570 °C, the average solid grain size, shape factor and liquid fractions increased with the prolonged soaking time. The smaller spheroidal solid grains and larger shape factor were obtained in the semi-solid microstructure due to Y addition. The coalescence and Ostwald ripening mechanism operated the coarsening process of solid grains simultaneously. The coarsening rate constants of Az80M1 (0.2 wt. % Y addition) of 164.22 μm3 s−1 was approximately four times less than the un-modified Az80 Alloy of 689.44 μm3 s−1. In contrast, the desirable semi-solid structure featured, with fine and well globular solid grains, an appropriate liquid fraction, and shape factor was achieved in Az80M1 Alloy treated at 570 °C for 20–30 min.
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plastic behavior of Az80 Alloy during low strain rate tension at elevated temperature
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2014Co-Authors: Lingbao Ren, Gaofeng QuanAbstract:Abstract The plastic behavior of Az80 Mg Alloy has been investigated at 573–673 K and at a strain rate of 10 −4 –10 −2 s −1 . The apparent activation energy has been calculated by the sine constitutive equation. The results show that the stress exponent is close to 2.7±0.3, and the activation energy is approximately 172 kJ/mol. This fact implies that the non-basal slip would have been activated at high temperatures with increased activation energy by dislocation climb and grain rotation.
Ha Sik Kim - One of the best experts on this subject based on the ideXlab platform.
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variation in dynamic deformation behavior and resultant yield asymmetry of Az80 Alloy with extrusion temperature
Journal of Materials Science & Technology, 2020Co-Authors: Sanghoon Kim, Ha Sik Kim, Sangwon Lee, Byoung Gi Moon, Sung Hyuk ParkAbstract:Abstract In this work, variation in the dynamic recrystallization (DRX) and dynamic precipitation behavior of Az80 Alloy during extrusion due to changes in extrusion temperature was investigated, and the resultant microstructure and yield asymmetry were analyzed. As the extrusion temperature increases from 250 °C to 350 °C, the primary DRX mechanism changes from twin-induced DRX to discontinuous DRX, resulting in an increase in the DRX area fraction and unDRXed grain size. In addition, as the extrusion temperature rises, Mg17Al12 precipitation during extrusion decreases sharply throughout the extruded material. The reduction in the compressive yield strength (CYS) with increasing extrusion temperature is more pronounced than it is for the tensile yield strength (TYS), which ultimately increases the yield asymmetry of the extruded material. The higher extrusion temperature has less of an influence on the TYS due to the promotion of certain hardening effects. On the other hand, the greater reduction in the CYS is attributed to the increased fraction and size of regions in which { 10 1 ¯ 2 } twins predominantly form and the lower amount of precipitates, which effectively facilitates { 10 1 ¯ 2 } twinning.
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effects of cold pre forging on microstructure and tensile properties of extruded Az80 Alloy
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2017Co-Authors: Ye Jin Kim, Sanghoon Kim, Jong Un Lee, Jae Ok Choi, Ha Sik Kim, Youngmin Kim, Yongjin Kim, Sung Hyuk ParkAbstract:Abstract This study investigates the effects of cold pre-forging (CPF) on the extrusion load during hot extrusion and on the microstructure and mechanical properties of extruded Az80 Alloy. For this purpose, a billet is forged to 10% strain at room temperature and then subjected to indirect extrusion at 200 °C. The CPF process causes the formation of a large amount of deformation twins and an increase in the dislocation density of the billet. The cold-forged Az80 billet exhibits a higher extrusion load during extrusion than an unforged Az80 billet, owing to the occurrence of twin-boundary hardening and enhanced strain-hardening effects in the former. The initial twins introduced by the CPF process promote dynamic recrystallization behavior during extrusion because they act as nucleation sites for recrystallization. As a result, the CPF process increases the area fraction of fine recrystallized grains and the microstructural homogeneity of the extruded Alloy. The Az80 Alloy extruded after CPF shows a higher tensile strength and ductility than the Az80 Alloy extruded without CPF. The improvement in strength is attributed mainly to the decrease in the average grain size caused by an increased recrystallization fraction. The increased ductility is due to the reduced area fraction of coarse unrecrystallized grains, in which microcracks occur during tensile plastic deformation.
Jonghun Yoon - One of the best experts on this subject based on the ideXlab platform.
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Evolution of tension and compression asymmetry of extruded Mg-Al-Sn-Zn Alloy with respect to forming temperatures
Materials & Design, 2016Co-Authors: Sangik Lee, Sung Hyuk Park, Jung Seok Kim, Sung-jun Park, Jonghun YoonAbstract:Abstract Substantial strength of as-extruded and as-forged ATZ842 Alloys is attributed to precipitation strengthening due to the presence of fine Mg 2 Sn and Mg 17 Al 12 particles in the Alloys. Because Mg Alloys inevitably undergo dynamic recrystallization during the warm forging that is required for their net-shape processing, it is important to examine microstructural evolution in as-forged samples. The appropriate forging temperature was found to range from 250 to 300 °C; average grain size started to increase at temperatures over 350 °C due to abnormal grain growth and a reduction in the fraction of second-phase particles. The ATZ842 Alloy showed mechanical properties superior to those of the Az80 Alloy, including yield and ultimate strengths in both tensile and compressive deformations. Remarkably, the tension and compression asymmetry in plastic flow of ATZ842 forged at 250 °C was characterized by a yield ratio of about 1.02, compared to the yield ratio of 0.88 for the Az80 Alloy.
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warm forging of magnesium Az80 Alloy for the control arm in an automobile
Proceedings of the Institution of Mechanical Engineers Part D: Journal of Automobile Engineering, 2015Co-Authors: Jonghun Yoon, Sangik LeeAbstract:With the growing environmental concerns surrounding transportation machines, magnesium Alloy, which has an excellent specific strength, good vibration damping and a high electromagnetic shielding capability, is increasingly being used in automobile body parts in order to reduce the carbon emissions and to increase the energy efficiency through a reduction in the mass. However, forming techniques with magnesium Alloy at room temperature pose considerable difficulty owing to its strong plastic anisotropy of tension and compression. In this study, a control arm, which is a complex-shaped part in the suspension system of a vehicle, was warm forged with Mg–8 mass % Al–0.5 mass % Zn (Az80) Alloy to reduce the mass. To validate the applicability of the magnesium Alloy control arm in the automobile, its microstructure and its mechanical properties were analysed.
