Enhanced Mechanical and Electrical Properties of a Cu-Ni-Si Alloy by Thermo-mechanical Processing
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THE emergence of very-large-scale and super-large-scale integrated circuits, driven by rapid advances in modern information technology, is exerting more stringent requirements on the strength and electrical conductivity of copper alloys used in lead frames. Presently, Cu-Fe-P,[1] Cu-Ni-Si,[2] and Cu-Cr-Zr[3] alloys have great application potential in lead frames. Among these three alloy systems, Cu-Fe-P alloys are most widely used but suffer from poor peeling resistance, low strength, and magnetism. Cu-Cr-Zr alloys possess both excellent strength (> 500 MPa) and electrical conductivity (~ 80 pct IACS), but the high oxidation tendency of the Zr element makes the fabrication of these alloys rather
LEI JIANG, HUADONG FU, CHANGSHENG WANG, and JIANXIN XIE are with the Beijing Laboratory of Metallic Materials and Processing for Modern Transportation, Institute for Advanced Materials and Technology, University of Science and Technology Beijing, Beijing 100083, P.R. China. Contact e-mail: [email protected] WEIDONG LI is with the Department of Materials Science and Engineering, The University of Tennessee, Knoxville, TN 37996. Manuscript submitted March 7, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
challenging, largely restricting their large-scale applications. However, these limitations do not exist in Cu-Ni-Si alloys, which are also proven to have high strength and good electrical conductivity. Therefore, Cu-Ni-Si alloys are regarded as a family of alloys that have greatest application potential in lead frames. Current research efforts in Cu-Ni-Si alloys mainly focus on the improvement of their mechanical and electrical properties, by a variety of approaches. One of the approaches is to add minor elements, such as P, Cr, Zr, Al, Mg,[4–8] into the alloys to customize microstructure, and therefore tune the properties. P can improve the alloy’s properties through promoting grain refinement and the precipitation of second phases.[4] Likewise, adding Al and Mg[7] into the Cu-Ni-Si alloys can induce precipitation hardening as well as refine grains. The addition of Cr in Cu-Ni-Si alloys results in the precipitation of Cr and Cr3Si, thereby benefiting the strength too.[5] Another approach is to severely deform alloys so that ultrafine grains can be attained to improve the strength.[9–11] For instance, applying equal channel angular pressing (ECAP) to a Cu-Ni-Si alloy produced an average grain size of 0.9 lm, which significantly improved the alloy strength while not appreciably compromising its electrical conductivity.[9] Lastly, the
tensile strength and electrical conductivity of Cu-Ni-Si alloys can also be enhanced by thermo-mechanical treatments.[12–14] For example, a Cu-Ni-Si alloy with a tensile strength of 1158 MPa and electrical conductivity of 25.2 pct IACS was made with a series of aging treatments.[13] Also, 65 pct cold rolling followed by the aging treatment at 450 C for 4 hours led to a Cu-Ni-Si-Zn alloy with a tensile strength of 745 MPa and electrical conductivity of 42.7 pct IACS.[14] In general, the reported w
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