Anodisation of aluminium alloy AA7075-Influence of intermetallic particles on anodic oxide growth


Zhang F., Ornek C. , Nilsson J., Pan J.

CORROSION SCIENCE, vol.164, 2020 (Journal Indexed in SCI) identifier identifier

  • Publication Type: Article / Article
  • Volume: 164
  • Publication Date: 2020
  • Doi Number: 10.1016/j.corsci.2019.108319
  • Title of Journal : CORROSION SCIENCE
  • Keywords: Intermetallic particles, Anodization, SKPFM, In-situ EC-AFM, Operando EIS, Localised dissolution, ELECTROCHEMICAL IMPEDANCE SPECTROSCOPY, IN-SITU, DISSOLUTION PHENOMENA, LOCALIZED CORROSION, BEHAVIOR, EVOLUTION, PHASES, MICROSTRUCTURE, INFORMATION, AA2024-T3

Abstract

Microstructure and Volta-potential analyses were conducted to characterise intermetallic-particles (IMPs) in AA7075-T5. EIS and AFM were applied under operando-conditions to investigate anodisation processes. IMPs have pronounced influence on the growth of anodic aluminium oxide (AAO) films resulting in low charge transfer resistance. Cu-bearing constituents show cathodic-character, whereas Mg2Si and MgZn2 particles show anodic-character. During anodisation, Al7Cu2Fe remain stable with peripheral-dissolution around boundary. De-alloying of S-phase particles leads to the detachment. Mg2Si undergoes de-alloying at low potential, and re-passivation at high potential. MgZn2 dissolves entirely upon anodization. Localised-dissolution in large-IMPs boundaries or nanometre-sized IMPs facilitates bubble evolution, confirming local breakdown of barrier-layer.