Microstructure and corrosion behaviour of low copper 7xxx aluminium alloy

Abstract

High strength aluminium alloys provide benefits in vehicle efficiency and energy consumption. Weldable, lean 7xxx aluminium alloys are currently being developed for body‐in‐white production. In the present study, the influences of thermomechanical history on microstructure and, consequently, on the corrosion behaviour of lean 7xxx aluminium alloys have been investigated. Accelerated corrosion testing has been carried out to assess the corrosion behaviour of the alloys. Conventional electron microscopy, together with electron energy loss spectroscopy, was employed to characterise the alloy microstructure in the as‐fabricated condition, and to examine the microstructural changes after corrosion testing, with the aim of identifying the microstructural features associated with the propagation of corrosion in the alloys. Further, alloys before and after EXCO corrosion testing were examined using a newly developed SEM nanotomography approach; it was demonstrated that the degradation of the microstructure, in particular sub‐surface cracking advancing along the rolling plane is related to thermomechanical processing. Further, this may be associated with the distribution of fine η phase AlMgZn2 particles at elongated grain boundaries; additionally, the η phase distribution is associated with thermomechanical history. Copyright © 2013 John Wiley & Sons, Ltd.