Fig. 1 Photograph of a segment of the as-received AA2024 alloy thin wall structure fabricated by the combination of WAAM and HPIR

Fig. 2 A representative SEM micrograph showing the general view of the AA2024 alloy thin wall structure (corresponding to surface A in Fig. 1)

Fig. 3 Grain structure of the AA2024 alloy thin wall structure (corresponding to surface A in Fig. 1): a, b grain orientation distributions in inverse pole figure colouring and Euler’s colour; c-e grain orientation distributions in Euler’s colour for MPZ, MPB and HAZ, respectively; f-h grain-stored energy distributions in grey scale for MPZ, MPB and HAZ, respectively, with the average values inset

Fig. 4 Grain orientation distributions in IPF colouring and the corresponding distributions of misorientations higher than 1.5°: a, b MPZ; c, d MPB; e, f HAZ

Fig. 5 Representative SEM micrographs of AA2024 alloy thin wall structure after electropolishing (corresponding to surface A in Fig. 1): a general view; b-d MPZ, MPB and HAZ; e-g typical areas and corresponding EDX maps for MPZ, MPB and HAZ

Fig. 6 Representative SEM micrographs of the AA2024 alloy thin wall structure after mechanical polishing (corresponding to surface A in Fig. 1): a MPZ; b MPB; c HAZ; d framed area in c at an increased magnification

Fig. 7 TEM analysis of fine precipitates in MPB: a representative HAADF micrograph, showing a multi-phase intermetallic particle in MPB; b EDX maps of the framed area in a; c, d representative HAADF micrographs showing precipitates in arrays or as cellular structures

Fig. 8 Representative HAADF micrographs of typical fine precipitates across the AA2024 alloy thin wall structure: a, b MPZ; c, d HAZ

Fig. 9 Electrochemical analysis of distinctive areas across the thin wall structure: a OCP evolution with the immersion period; b potentiodynamic polarization curves; c, d Nyquist and Bode plots; e equivalent circuit model

Fig. 10 A representative optical micrograph of AA2024 alloy thin wall structure after 30 min immersion in a 3.5 wt% NaCl solution (corresponding to surface A in Fig. 1)

Fig. 11 Representative SEM micrographs of AA2024 alloy thin wall structure after 30 min immersion in a 3.5 wt% NaCl solution (corresponding to surface A in Fig. 1): a general view; b the framed area in a at an increased magnification; c the typical morphology of MPB; d the framed area in c at an increased magnification; e, f framed areas in d at increased magnifications

Fig. 12 Representative SEM micrographs of the cross section in MPB after 30 min immersion in a 3.5 wt% NaCl solution: a general view; b, c framed areas 1-2 in a at increased magnifications

Fig. 13 a A representative HAADF micrograph of a typical cross section in MPB of the AA2024 alloy thin wall structure after 30 min immersion in a 3.5 wt% NaCl solution; b, c grain orientation distribution in inverse pole figure colouring and the corresponding grain-stored energy distribution in grey scale (the brighter, the higher stored energy and vice versa); d framed area 1 in a at an increased magnification; e framed area in d at an increased magnification; f framed area 2 in a at an increased magnification; g-i framed areas 1-3 in e at increased magnifications

Fig. 14 A representative optical micrograph of AA2024 alloy thin wall structure after 12 h immersion in a 3.5 wt% NaCl solution (corresponding to surface A in Fig. 1)

Fig. 15 Representative SEM micrographs of AA2024 alloy thin wall structure after 12 h immersion in a 3.5 wt% NaCl solution (corresponding to surface A in Fig. 1): a general view; b, c framed areas 1-2 in a at increased magnifications; d another general view; e framed area in d at increased magnifications

Fig. 16 A representative optical micrograph of AA2024 alloy thin wall structure after 24 h immersion in a 3.5 wt% NaCl solution (corresponding to surface A in Fig. 1)

Fig. 17 Representative SEM micrographs of AA2024 alloy thin wall structure after 24 h immersion in a 3.5 wt% NaCl solution (corresponding to surface A in Fig. 1): a general view; b framed area in a, using a lower accelerating voltage of 1.5 kV; c a typical localized corrosion site; d, e framed areas in c at increased magnifications

Fig. 18 Schematic diagram showing the localized corrosion development of the AA2024 alloy thin wall structure during the immersion in a 3.5 wt% NaCl solution. In the diagram, the distribution of grain-stored energy is displayed in grey scale with a higher brightness representing a higher stored energy and vice versa. The magnified view exhibits the role of S phase precipitates and interdendritic intermetallics during the localized corrosion development