A Grain Boundary Engineering Approach to Promote Special Boundaries in a Pb-based Alloy

초록

Grain boundary engineering was employed as a means to promote special boundaries in a commercial Pb-base alloy used for positive electrode grids in automobile batteries that are vulnerable to intergranular corrosion, cracking and creep. The present approach was adopted as a new alternative to the conventional alloy design methodology of grain refining or alloying with minor additions Ca, Sn or Ag, etc., which is either costly or ineffective for the creep resistance. With an aim to increase the fraction of the special boundaries, a unique TMT processing route was developed that consisted of strip rolling and recrystallization annealing heat treatment. More than 80% strip rolling followed by annealing increased the portion of the CSL (Coincidence Site Lattice) boundaries significantly above the level of commercial grid materials. With repeated TMT the CSL boundaries of sigma3-sigma9, analyzed by EBSD method, steadily increased and reached to 90% of the total boundary areas. The TMT-treated specimens exhibited numerous annealing twins identified as sigma3n boundaries, supporting the reproduction mechanism of the sigma3 boundaries.