Fig. 1. Sample preparation for micro-tensile testing. (a) Disk with 3 mm in diameter and a thickness of ～10 µm, (b) enlarged FIB image showing the micro-tensile sample taken from the center area of the disk marked by the rectangular frame in (a), (c) high-magnification FIB image showing the gauge length (L), width (W), and thickness (t), LD and TD represent the loading direction and the transverse direction of the micro-tensile sample respectively.

Fig. 2. Engineering stress-strain (SS) curves of the alloy in as-fabricated (AF) and heat-treated (HT) conditions (300 °C/6 h). Their local yield regions, as marked by dashed-line frames, are enlarged and inserted for clarity.

Fig. 3. Strain monitoring by DIC method of an HT specimen during tensile deformation. (a) Five overall strain levels (marked by dashed-lines) selected for DIC images, (b) illustration in the specimen gauge showing the virtual extensometer set for measuring the overall strain (OS) and localized strain (LS), (c-g) DIC maps showing strain fields forming within the gauge at different strain levels, (h) the evolution of stress with time, (i) the corresponding evolution of OS and LS with time.

Fig. 4. Typical bimodal grain structure in the HT sample. (a) EBSD inverse pole figure (IPF) map showing alternating FG and CG regions. The samples for micro-tensile testing are also shown, the IPF map is generated by choosing build direction (BD) as the projection axis, ND is the direction normal to BD. (b, c) Corresponding pole figures from CG and FG regions, respectively. (d, e) Grain size distribution of CG and FG regions respectively.

Fig. 5. Stress-strain curves from the micro-tensile testing. (a) Engineering stress-strain curves of the FG, SCG, LCG micro-tensile specimens, (b) close-up view at the tensile stress level beyond 500 MPa.

Fig. 6. Intermetallic particles in FG and CG regions. SEM-BSE image taken from (a) FG and (b) CG regions of an HT sample, showing a high number density of intermetallic particles forming in both areas. (c, d) 3D visualization reconstructed from the FIB slice-and-view images showing the intermetallic particles in the FG region and CG region, respectively.

Fig. 7. APT 3D reconstructed composition maps from an FG region of the HT sample.

Fig. 8. Secondary precipitates in the matrix of HT sample. (a) HAADF-STEM image taken along <001>α displaying a high number density of nano-sized precipitates finely dispersed in the HT sample. Corresponding FFT pattern inserted showing the diffraction spots from these precipitates, indicated by holy arrows. (b) Enlarged image showing the L12 structure (a = 0.42 nm) of the precipitate marked by yellow-color dashed-line frame in (a).

Fig. 9. BF-STEM images of HT sample with 5% tensile strain revealing the dislocation structure inside (a, b) two different grains in FG region, and (c) a grain in CG region. Beam directions in (a-c) are parallel to <110>Al.

Fig. 10. HT sample strained to fracture. (a) SEM image of tensile fracture surface showing micro cracks occurring in FG and interface delamination, (b) enlarged image from red-color dashed-line rectangle frame in (a) showing the nucleation of microvoids due to grain boundary particles decohesion followed by progressive linkage of microcracks propagating along the grain boundary, (c) SEM image showing a crack blunting at the CG region.