Corrosion behaviour and mechanism of new aerospace Al–Zn–Mg alloy friction stir welded joints and the effects of secondary Al 3 Sc x Zr 1− x nanoparticles

•Investigate corrosion behaviour and microstructure of new Al–Zn–Mg friction stir weld joints.•Establish relationship between microstructure, property and corrosion behaviour of weld joints.•Clarify corrosion mechanism of Al–Zn–Mg weld joints with and without 0.10Sc and 0.10Zr (wt.%).•Reveal mechanism for the improved corrosion resistance caused by secondary Al3ScxZr1−x nanoparticles.