Microstructure, Element Distribution, and Mechanical Property of Cu9Ni6Sn Alloys by Conventional Casting and Twin-Roll C
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As high-performance copper alloys, Cu-Ni-Sn alloys are widely used, such as in elastic mechanical parts and electronic connectors, due to their high strength, stiffnesses, corrosion resistance, and conductivities.[1–4] CuNi-Sn alloys are considered to be one of the most promising types of alloys to replace Cu-Be alloys.[5–7] Cu-Ni-Sn alloys are often strengthened by spinodal decomposition during aging.[8–10] Nearly all the Sn atoms are dissolved in the solid solution of Cu and Ni (a
DELIN TANG, LIN WANG, JING LI, and HAILIANG YU are with the State Key Laboratory of High Performance Complex Manufacturing, Central South University, Changsha 410083, China and with the College of Mechanical and Electrical Engineering, Central South University, Changsha 410083, China and also with the Light Alloys Research Institute, Central South University, Changsha 410083, China. Contact e-mails: [email protected], [email protected] ZHAOFEI WANG is with the Technology Center, Yantai Wanlong Vaccum Metallurgy Co., Ltd, Yantai 264006, China. CHARLIE KONG is with the Electron Microscope Unit, University of New South Wales, Sydney, NSW 2052, Australia. Manuscript submitted August 6, 2019. Article published online February 5, 2020 METALLURGICAL AND MATERIALS TRANSACTIONS A
phase) after solution treatment. A modulated structure consisting of Sn-rich and Sn-poor regions subsequently forms because of the spinodal decomposition at the first stage of the aging treatment.[11] Metastable c¢ precipitates are generated from the modulated structure with further aging treatment, while the alloy performance is remarkably improved. Finally, stable c precipitates with cellular structures form and constitute the final phase composition with the a phase. Although the homogeneous aged Cu9Ni6Sn alloy has excellent properties, Sn segregation severely affects the performance of alloys formed by conventional casting (CC), especially for alloys high in Sn (e.g., Cu15Ni8Sn and Cu9Ni6Sn).[12–14] Thus, homogenization treatment or severe plastic deformation[15] is required to reduce the segregation of Sn rather than eliminate it. Some methods have been developed to eliminate elemental segregation, such as hyporapid solidification (HS)[16–18] and rapid solidification (RS).[19–21] HS (temperature drop rate 104 K/s) can effectively restrain element segregation. As a typical HS technique, the twin-roll casting (TRC) process has been extensively studied in recent decades because of its short process times, low-energy consumption, and lack of generated pollution. Tripathi et al.[22] prepared an Mg alloy strip by TRC, and they found that there was a bimodal grain size in the produced strip. Kikuchi et al.[23] investigated the surface quality of Mg-Al alloy strips by TRC. Another TRC strip with a dimension of 1000 9 110 9 2 mm was produced, and the microstructure of the strip was analyzed by Xu et al.[24] There were columnar crystals in the surface layer and fine equiaxed crystals with severe Al segregation in the center layer. Heo et al.[25] investigated the tensile p
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