Corrosion behaviour and mechanism of new aerospace Al-Zn-Mg alloy friction stir welded joints and the effects of secondary Al3ScxZr1−x nanoparticles

Corrosion behaviour, residual stress, intermetallics and microstructure of friction stir welded aerospace Al-Zn-Mg and Al-Zn-Mg-0.10Sc-0.10Zr (wt.%) alloys were investigated comparatively and in detail. The thermo-mechanically affected zones adjacent to weld nugget are most susceptible to corrosion in two weld joints. In addition to the enrichment of coarse Si and Fe intermetallics, wide precipitate free zones (in Al-Zn-Mg weld joint) and high tensile residual stress are the key factors. Secondary Al3ScxZr1−x nanoparticles can effectively improve stress corrosion cracking resistance and decrease exfoliation corrosion rates of Al-Zn-Mg weld joints by restraining the formation of precipitate free zones and refining grains.