Grain-scale origins of PLC banding in Al-9Mg sheet revealed by in-situ EBSD and DIC

High-Mg containing aluminum alloy sheet (Al-9 Mg) was produced by horizontal twin-roll casting (TRC), yielding a ∼ 6 m strip with uniform thickness and a centerline segregation-free microstructure. After homogenization, 75% cold rolling, and full annealing, the sheet exhibited a fully recrystallized grain structure (∼40 μm) and an excellent strength-ductility balance (YS ≈ 162 MPa, UTS ≈ 343 MPa, elongation ≈ 25%). Serrated flow was investigated by correlative full-field DIC and in-situ tensile EBSD. PLC activity initiated at ε ≈ 0.13 and manifested as propagating B-type stretcher-strain marks inclined ∼ 55–60° to the rolling direction. In-situ EBSD revealed that macroscopic PLC bands originate from intragranular shear bands (∼45° traces) that preferentially developed in grains oriented between 〈001〉 and 〈101〉, where {111}〈110〉 slip showed high Schmid factor, low Taylor factor, and low initial KAM/GND. Progressive straining produced strong substructure refinement: the LAGB boundary-length density (2–15°) increased from 3.34 to 153.29 mm −1 and the mean KAM rose from ∼ 0.18° to ∼ 0.39°, while GOS classification shifted from fully recrystallized to predominantly deformed. Texture changes remained modest (PF max 4.28 → 4.34 m.r.d.; ODF max 15.6 → 17.5 m.r.d.), indicating that PLC deformation is governed primarily by orientation-dependent slip localization and was accommodated by rapid substructure refinement.