Tensile anisotropy in Cu-Ni-Mn-Sn-Al alloys
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1/8/04
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Tensile Anisotropy in Cu-Ni-Mn-Sn-Al Alloys SEUNGZEON HAN, KEUNYONG SOHN, CHANGJOO KIM, and SANGSHIK KIM In the present study, the tensile anisotropy of age-hardened Cu-6Ni-2Mn-2Sn-2Al, Cu-6Ni-2Mn-2Sn2Al, and Cu-6Ni-2Mn-5Al alloy sheets, either perpendicular or parallel to the rolling direction, was examined. It was found that age-hardened Cu-Ni-Mn-Sn-Al alloys have higher tensile strength along the T orientation than L orientation at high rolling ratios. Such a trend was most notable in the high Al containing Cu-6Ni-2Mn-5Al alloy among the alloys studied. At high rolling ratios, well-developed deformation bandlike structures were observed to be mostly aligned perpendicular to the rolling direction for each alloy. These deformation bandlike structures appeared to be responsible for the higher tensile strength along the T orientation. The transmission electron microscopy (TEM) examination demonstrated that the deformation bandlike structures consisted of tangled dislocation networks, which were further thickened with the addition of Al or the reduction of Sn. The stacking fault energy (SFE) of Al and Sn, as related to the ease of cross-slip, is believed to be responsible for the present observation.
I. INTRODUCTION
THE interest in high-strength Cu alloys has been revived because of the increasing demand of high-strength connector materials with high conductivity in the electronics industry.[1–12] Among the high-strength Cu alloys, Cu-Ni-Sn alloys have gathered strong attention as possible low-cost substitutes for Cu-Be alloys.[1–12] The Cu-Ni-Sn alloys contain a relatively high amount of expensive Ni and Sn, which acts as a barrier for the wide spread use of the alloys. The low hot workability further limits the application.[8] At present, it is impracticable to produce sheet products of high Sncontaining Cu-Ni-Sn alloys, including Cu-9Ni-6Sn alloy, due to a severe cracking during hot working caused by the Sn-rich segregates formed during solidification.[8] Considerable research activities have been directed toward solving the hot cracking problem, including the powder metallurgy technique and the lowering of Sn content.[9] For the reduction of the product cost, the study was carried out to partially replace Ni and Sn by the less expensive elements, such as Mn and Al. The Mn has a high solubility to Cu, and can partially replace expensive Ni, which is known to improve the castability and tensile strength in Cu-Ni-Sn alloys. The addition of Al, which is a strong solid solution strengthener in Cu, may compensate the reduced tensile strength as a result of lowering Sn content. Previously, the authors reported that Cu-6Ni-2Mn-2Sn-2Al alloy was hot workable with a reduced production cost and reasonable physical properties compared to Cu-9Ni-6Sn alloys.[8] While conducting previous research, it was found that Cu-Ni-Mn-Sn-Al alloys have a unique texture-tensile property relationship. At present, the effect of texture developed during cold rolling on the tensile behavior of Cu-Ni-MnSn-Al alloys
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