Effects Of High-temperature Recovery Treatment After Large Strain On The Grain Boundary Character Distributions Of Subsequently Cold Rolled And Annealed Pb-Ca-Sn-Al Alloy

Electron back scatter diffraction (EBSD) was used to study the effects of recovery treatment after cold rolling on the grain boundary character distributions (GBCD) of subsequently strain-annealed Pb-0.05Ca-1.5Sn-0.026Al (mass fraction, %) alloy. The results indicated that strong texture of single {001}<110> (rotated cubic) component developed in the specimen treated by 90% cold rolling ( thickness reduction) and subsequent recovery treatment at 250℃for 3 minutes. When this specimen was further subjected to 30% cold rolling and annealing at 270℃for 10 minutes, there appeared a large number of special boundaries (SBs) such as∑3,∑9 and∑27 boudnareis. The fraction of total SBs was approaching 80%, in which the fraction of (∑9+∑27) boundaries reached 20%, and the connectivity of general high angle boundary (HABs) network was interrupted substantially by these SBs. It implied that such two-step specific thermal mechanical treatment was a very effective method to obtain an optimized GBCD. The statistical EBSD measurement indicated that averaged fraction of special boundaries (SBs) mainly consisting of∑3,∑9 and∑27 boundaries was higher than 72% in the samples mentioned above. The EBSD-reconstructed GBCD observation showed that curved incoherent∑3 boundaries were the major part of∑3 boundaries.Three typical specimens which were GBE processed (sample A), recrystallized (sample B) and cast (sample C) were exposed to sulfuric acid solution at 25℃for 600h. The after-corrosion morphology of the surfaces and cross-sections of the samples were observed by SEM. The cross-section views indicated that the penetration of intergranular corrosion path from the surface into the interior is arrested in sample A, which had the highest total SBs fraction (77.8%) and the most effective interruption of general high angle boundary (HABs) network connectivity.Further discussion pointed out that the presence of a strong single texture component of {001}<110> (rotated cubic) in the sample after first large strain cold rolling plus high temperature recovery had a beneficial effect on GBCD optimization. That is, this type of preferred texture promotes the formation of incoherent∑3 interface. Those incoherent∑3 boundaries migrated and interacted and then produced high fraction of SBs such as∑9 and∑27 boudaries.