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1/8/04

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Correlation of the Microstructure and Mechanical Properties of Oxide-Dispersion-Strengthened Coppers Fabricated by Internal Oxidation JONGSANG LEE, YONG CHAN KIM, SUNGHAK LEE, SANGHO AHN, and NACK J. KIM This study was aimed at the correlation of the microstructure and mechanical properties of oxidedispersion-strengthened (ODS) coppers fabricated by internal oxidation. Atomized copper powders mixed with Cu2O oxidant powders were internally oxidized and then hot extruded to fabricate ODS coppers without defects. In order to sufficiently oxidize copper powders, oxidant powders should be added in amounts 30 pct in excess of the stoichiometrically calculated amount. In the extruded ODS coppers, very fine Al2O3 dispersoids of 10 nm in diameter were homogeneously distributed inside copper grains of 1 m in size. The volume fraction of Al2O3 dispersoids increased as the Al content in atomized copper powders increased. With increasing volume fractions of Al2O3 dispersoids, the yield and tensile strengths increased, while the elongation and electrical conductivity decreased, and all the properties of the ODS coppers were sufficiently above the required properties of electrode materials for spot welding. To understand the mechanism responsible for the improvement of the yield strength of the ODS coppers, yield strength was interpreted using the Orowan’s strengthening model, which was fairly consistent with the experimental results.

I. INTRODUCTION

AS the demand for automated production lines in electronic and automotive industries is currently rising, it is increasingly important to develop electrode materials for spot welding, which are critical for the automation of welding lines. These electrode materials are required to have excellent room- and high-temperature strength as well as the properties that copper conventionally has, such as high electrical and thermal conductivity and excellent corrosion resistance and formability. High-quality copper alloys meeting these requirements can largely be divided into precipitation-hardened and oxide-dispersion-strengthened (ODS) types. The precipitation-hardened copper alloys, represented by Cu-Be, Cu-Ti, and Cu-Cr alloys, show high strength, since fine phases are precipitated inside a copper matrix during heat treatment.[1–3] As Cu-Be and Cu-Ti alloys have poor electrical conductivity despite their high strength, Cu-Cr alloys are mainly used for electrode materials. However, the Cu-Cr alloys, whose precipitates are coarsened at temperatures above 473 K, abruptly deteriorate in strength, hardness, and wear resistance. Thus, when they are used for electrode materials, productivity can decrease because the welding tip is readily worn out. Weldability can also diminish during spot welding, as alloying occurs between the weld metal and welded material. This may stop the manufacturJONGSANG LEE, Manager, is with the PDP Division, Samsung SDI Co., Ltd., Chungnam, 330-300 Korea. YONG CHAN KIM, Research Assistant, is with the Center for Advanced Aerospace Materi