Hydrothermal surface modification of Al5X1 alloy powder for enhanced mechanical and corrosion properties after spark plasma sintering

This study describes a novel hydrothermal method for modifying the surface of Al5X1 alloy powder using synthesized ZrScOx nanoparticles, followed by spark plasma sintering (SPS). This process transforms the original oxide film on the surface of the untreated powder into the active core–shell interface. The alloy material obtained after SPS process increasing interparticle bonding, grain boundaries stability, mechanical strength, and corrosion resistance. To obtain a stable ZrScOx colloidal dispersion, the sol–gel method was used, which provided the formation of nanoparticles with the average size of 3.8 nm by DLS and 2.5–4 nm by HR-TEM analysis, whereas a zeta potential equal to 43.2 mV testified for high stability of the suspension. After the hydrothermal synthesis at 160 °C for 60 min, a dense acicular layer of oxides was created with the surface content of zirconium and scandium equal to 2.8 at% and 1 at%, correspondingly. Using cross-sectional SEM/EDS analysis, the core-shell structure was confirmed, which consisted of an aluminum-rich core and the uniform distributed ZrScOx particles. As a result of SPS, the modified alloy showed the finer microstructure in comparison with the original one. The average grain size decreased from 36.3 μm to 29.1 μm, and hardness increased from 79.2 ± 0.3 HV to 88.4 ± 0.5 HV. The compression test showed that the yield strength was increased from 153.7 to 283.4 MPa (~84%). Corrosion tests showed that after modification, polarization resistance increased almost threefold compared to the unmodified sample. This improvement is attributed to the stable Al–O–Zr/Sc interfacial bond, inhibition of grain growth, stronger particle bonding, and the barrier effect of the ZrScO_x shell.