Evolution of Near-Surface Deformed Layers on AA3104 Aluminium Alloy

The present work studied the microstructure of near-surface deformed layers and their evolution from the transfer slab to the cold rolled final gauge sheet of an AA3104 aluminium alloy. Electron microscopy of ultramicrotomed cross-sections revealed two types of near-surface deformed layers, i.e. type A and type B, both with different microstructures to the underlying bulk alloy. A typical feature of the deformed layers is the nano-sized ultrafine grains, with diameters <= 200 nm for the type A and <= 500 nm for the type B deformed layer. Electron energy loss spectroscopy (EELS) indicated that oxide particles are present along grain boundaries within the type A deformed layer, while the type B deformed layer is free of oxide particles. The type A deformed layer is mainly generated at elevated temperatures during the early stages of hot rolling. Its thickness is non-uniform across the surface, with a maximum of similar to 4 mu m on the transfer slab, similar to 1 mu m on the re-roll gauge sheet and similar to 0.8 mu m on the final gauge sheet. While the surface of the hot rolled sheet is mainly covered by the type A deformed layer, the surface undergone cold rolling is alternately covered by the type A and the type B deformed layers.