A combined TEM and SKPFM investigation of the surface layers on rolled AA5050 aluminium alloy using ultra‐microtomy

This article studies the evolution of near‐surface morphology as a function of various thermo‐mechanical treatments along the fabrication line of rolled AA5050 aluminium alloy. Ultra‐microtomy has been used to prepare cross‐sectional thin foils for transmission electron microscopy (TEM) and proper surfaces for scanning Kelvin probe force microscopy (SKPFM) analysis. A slight increase in the Volta potential difference (between the inter‐metallics and the matrix) between the as‐cast surface and the surface obtained after the first hot‐mill pass, emphasized that the changes in surface micro‐structure, which in turn affect the corrosion and electrochemical properties of the finished product, had already occurred at that stage. The Volta potential difference during the subsequent hot‐mill pass remained relatively constant. As far as the near‐surface morphology was concerned, hot‐rolling resulted in the formation of a heavily deformed surface layer. Annealing of the hot‐rolled aluminium sheet resulted in partial re‐crystallization of the surface layer. Subsequent cold‐rolling re‐introduced deformation in the near‐surface region. Copyright © 2008 John Wiley & Sons, Ltd.