Evolutions of the Micro- and Macrostructure and Tensile Property of Cu-15Ni-8Sn Alloy During Electromagnetic Stirring-As
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THE Cu-Ni-Sn alloys are expected to replace the CuBe alloys and have been widely used for electrical switchgear, springs, and connectors due to their high corrosion resistance, high thermal conductivity, and excellent electric conductivity after aging heat treatment.[1–3] Continuous casting is an excellent method for producing aluminum alloys[4,5] and copper alloys[6,7] with high manufacturing efficiency. However, the traditional continuous casting method also presents some difficult technical problems such as highly columnar macrostructure,[8] severe segregation,[9] and shrinkage porosity.[10] These problems will result in weak hot working performance during the forging or rolling process, thereby yielding poor mechanical properties. Grain refinement is an effective way to improve the
ZHE SHEN, BANGFEI ZHOU, JIE ZHONG, YUNBO ZHONG, TIANXIANG ZHENG, LICHENG DONG, YONG ZHAI, WEILI REN, ZUOSHENG LEI, and ZHONGMING REN are with the State Key Laboratory of Advanced Special Steel & Shanghai Key Laboratory of Advanced Ferrometallurgy & School of Materials Science and Engineering, Shanghai University, Shanghai 200072, China. Contact emails: yunboz@staff.shu.edu.cn, [email protected] Manuscript submitted April 5, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS B
deformability and tensile strength of the alloys. The adjustments of casting parameters, such as the cooling rate and pouring temperature, the addition of grain refinement agents, and mechanical stirring, are common methods used to achieve grain refinement. However, these methods either have limited effects on grain refinement or give rise to impurities. Electromagnetic stirring (EMS) has been used to modify the columnar to equiaxed transition (CET)[11,12] and then to refine the grain size.[13,14] Many studies on the CET and refinement mechanism have been reported. Willers et al.[15] found the CET in the unidirectional solidification of Pb-Sn alloys under a rotating magnetic field and suggested that the forced convection leads to a reduction in the temperature gradient ahead of the solidification front and then induces the remelting of the dendrites at certain locations because of the remarkable temperature fluctuations in the mushy zone. Campanella et al.[16] found that the efficiency of EMS depends strongly on the penetration of the liquid in the mushy zone and developed a dendrite fragmentation criterion to explain the grain refinement. Moreover, the forced convection induced by EMS can also influence the dendritic growth. Dendritic morphology undergoes a significant transformation from the dendrite to rosette structure due to its rotation under streamlined flow or a periodic change in the fluid flow direction around the growing solid.[17] In addition, the improvement in the
strength can be obtained by the fine-grain strengthening according to the Hall–Petch relationship.[18,19] However, the tensile strength is also affected by the dendrite. Kato[20] showed that the tensile property in the growth direction is controlled by dendritic solute segregation that depends on the primary arm spaci
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