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Influence of bi addition on dynamic recrystallization and precipitation behaviors during hot extrusion of pure Mg

Journal of Materials Science & Technology 2020年第9期44卷 62-75页

作者： Jongbin Go Jong Un Lee Hui Yu Sung Hyuk Park School of Materials Science and Engineering Kyungpook National UniversityDaegu41566Republic of Korea School of Materials Science and Engineering Hebei University of TechnologyTianjin300130China

Low material cost and high extrudability for ensuring price competitiveness with Al alloys,as well as excellent mechanical properties,are essential for expanding the application range of Mg *** is a promising alloying element for developing extruded Mg alloys that satisfy such *** is inexpensive,exhibits a high solubility limit,and forms a thermally stable Mg3bi2 phase,which improves the commercial viability and enables the high-speed extrusion of Mg–bi *** this study,the effects of bi addition on the dynamic recrystallization(DRX)and dynamic precipitation behaviors during hot extrusion of a pure Mg and the resultant microstructure and mechanical properties of the extruded materials were *** addition of 6 wt%and 9 wt%bi to a pure Mg yielded numerous fine Mg3bi2 precipitates during the early stage of hot ***,the area fraction of dynamic recrystallized(DRXed)grains decreased because of DRX-behavior suppression by the Zener pinning ***,the DRXed grain size was substantially reduced through the grain-boundary pinning *** size and number of undissolved Mg3bi2 particles in the homogenized billets increased when the bi content was increased,which resulted in increased DRX fractions owing to the enhanced levels of particle stimulated *** addition yielded considerable strength improvement of the extruded pure ***,the extruded Mg–bi binary materials were less ductile than the extruded pure Mg *** lower ductility resulted from the cracking at twins formed in the coarse unDRXed grains of the Mg-6bi material and the cracking at large undissolved Mg3bi2 particles in the Mg-9bi material.

关键词： Magnesium bi addition Extrusion Recrystallization Precipitation

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Effect of bi on graphite morphology and mechanical properties of heavy section ductile cast iron

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China Foundry 2014年第2期11卷 125-131页

作者： Song Liang Guo Erjun Tan Changlong School of Materials Science and Engineering Harbin University of Science and Technology

To improve the mechanical properties of heavy section ductile cast iron, bismuth(bi) was introduced into the iron. Five castings with different bi content from 0 to 0.014 wt.% were prepared; and four positions in the casting from the edge to the center, with different solidifi cation cooling rates, were chosen for microstructure observation and mechanical properties test. The effect of the bi content on the graphite morphology and mechanical properties of heavy section ductile cast iron were investigated. Results show that the tensile strength, elongation and impact toughness at different positions in the fi ve castings decrease with a decrease in cooling rate. With an increase in bi content, the graphite morphology and the mechanical properties at the same position are improved, and the improvement of mechanical properties is obvious when the bi content is no higher than 0.011wt.%. But when the bi content is further increased to 0.014wt.%, the improvement of mechanical properties is not obvious due to the increase of chunky graphite number and the aggregation of chunky graphite. With an increase in bi content, the tensile fracture mechanism is changed from brittle to mixture ductile-brittle fracture.

关键词： heavy section ductile cast iron bi addition cooling rate graphite morphology mechanical properties

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Effect of bi modification treatment on microstructure,tensile properties,and fracture behavior of cast Al-Mg_2Si metal matrix composite

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China Foundry 2013年第1期10卷 18-23页

作者： Wu Xiaofeng Wang Zhe Zhang Guangan Wu Fufa School of Materials Science and Engineering Liaoning University of Technology

bi has a good modification effect on the hypoeutectic Al-Si alloy, and the morphology of eutectic Si changes from coarse acicular to fine fibrous. Based on the similarity between Mg2Si and Si phases in crystalline structure and crystallization process, the present study investigated the effects of different concentrations of bi on the microstructure, tensile properties, and fracture behavior of cast Al-15wt.%Mg2Si in-situ metal matrix composite. The results show that the addition of the proper amount of bi has a significant modification effect on both primary and eutectic Mg2Si in the Al-15wt.%Mg2Si composite. With an increase in bi content from 0 to lwt.%, the morphology of the primary Mg2Si is changed from irregular or dendritic to polyhedral shape; and its average particle size is significantly decreased from 70 to 6 μm. Moreover, the morphology of the eutectic Mg2Si phase is altered from flake-like to very short fibrous or dot-like. When the bi addition exceeds 4.0wt.%, the primary Mg2Si becomes coarse again. However, the eutectic Mg2Si still exhibits the modified morphology. Tensile tests reveal that the bi addition can improve the tensile strength and ductility of the material. Compared with those of the unmodified composite, the ultimate tensile strength and percentage elongation after fracture with 1.0wt.% bi increase 51.2% and 100%, respectively. At the same time, the bi addition changes the fracture behavior from brittle to ductile.

关键词： AI/Mg2Si composites casting bi addition microstructural characterization tensile properties

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