Effects of thermo-mechanical iterations on the grain boundary character distribution of Pb–Ca–Sn–Al alloy

Recrystallized Pb–0.05%Ca–1.5%Sn–0.026%Al (mass fraction) alloy, with an averaged grain size of 20–30 μm, special grain boundary (Σ1–Σ29) fraction of less than 40% and the general high angle boundary (HAB) network of fully connected, was subjected to 1–4 cycles of thermo-mechanical processing (TMP) of rolling at ambient temperature followed by annealing at 270 °C (0.9Tm). Electron back-scatter diffraction (EBSD) techniques were employed to determine the grain boundary character distribution (GBCD) of the processed samples. The results indicated that 1-, 3- and 4-cycle TMP has very strong but nearly identical effects on the GBCD, the fraction of special boundaries enhanced to 80%, and the connectivity of general high angle boundary (HABs) network is interrupted sufficiently by the so-called special boundaries; However, 2-cycle TMP exerts slight impacts on the GBCD, the fraction of special boundaries is only increased to 59.2% and the connectivity of HABs network is not interrupted substantially. Further discussion pointed out the effects of 1-, 3- and 4-cycle TMP might be attributed to the migration and interactions of incoherent Σ3 (Σ3ic) and its variants Σ9 and Σ27 boundaries, while that of 2-cycle TMP may be caused by an enhanced recrystallization.