A Grain Boundary Engineering Approach to Promote Special Boundaries in a Pb-base Alloy
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A Grain Boundary Engineering Approach to Promote Special Boundaries in a Pb-base Alloy D.S. Lee, H.S. Ryoo and S.K. Hwang∗ School of Materials Science and Engineering, Inha University, #253, Yonghyun-Dong, Nam-Gu, Incheon, 402-751, Korea ∗ Jointly appointed by the Center for Advanced Aerospace Materials, Pohang University of Science and Technology, Pohang, Korea ABSTRACT A grain boundary engineering approach was employed to improve the microstructure of a commercial Pb-base alloy for better performance in automobile battery application. Through a combination of cold working, recrystallization and subsequent thermomechanical-processing, it was possible to increase the fraction of the low Σ coincidence site lattice boundaries up to 91% in addition to the substantial grain refinement. A preliminary electrochemical evaluation indicated a better corrosion resistance in the experimental material laden with the special boundaries. The high frequency of the coincidence site lattice boundaries in the specimens was interpreted in terms of the ‘Σ3 regeneration’ model proposed in previous works. INTRODUCTION Pb-base alloys are extensively used for automobile batteries. Like many other secondary batteries, those made with Pb-alloy lose charge/discharge efficiency during usage, which originates from material degradation. With the recurrence of PbO2 ↔ PbSO4 reaction, a volume change occurs at the anode, which results in intergranular corrosion in the Pb-alloy [1]. The alloy design approach of adding elements such as Ca, Sn, Ag and Ba [1-4] is only partly successful in alleviating the problem and also is not readily amenable for materials recycling. Recently, a grain boundary engineering approach was proposed to improve the material properties related to the grain boundary character distribution (GBCD) [5]. Improvement of the mechanical properties as well as the electrochemical properties has been reported in Ni-base alloys [6] and Pb-base alloys [7-9] through promotion of the coincidence site lattice (CSL) boundaries. Motivated by these prior arts, the present work was designed to seek the means to maximize the frequency of the CSL boundaries in a commercial Pb-base alloy by a unique combination of the thermomechanical processing parameters. EXPERIMENTAL PROCEDURE A commercial Pb-0.09Ca-1.8Sn (all in wt.%) alloy for the anodic plate in automobile batteries was used as experimental material. The plate was continuously cast into a thickness of 10mm. In the initial condition, the strip cast plates were heavily cold rolled to 80% or 90% reduction and then recrystallized at 270°C/10min. Subsequent processing consisted of a light cold rolling and the identical recrystallization heat treatment. This process, termed as TMP, was
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