Effect of Y and Er microalloying on microstructure and corrosion behaviour of AA7085/Al2O3+ZrB2 composites

Résumé fourni par la source

Rare-earth elements Yttrium (Y) and Erbium (Er) have been applied as micro-alloying additions to aluminium to enhance corrosion resistance through grain-boundary restructuring. However, their role in reinforced AA7085 remained insufficiently understood. In this work, hot-rolled AA7085/Al 2 O 3 +ZrB 2 composites (AC) in T74 condition, with and without Y or Er additions, were systematically investigated using electrochemical testing, immersion corrosion experiment, microstructural characterization, and surface chemistry analysis. Both Y and Er reduced the corrosion current density and corrosion rate in 3.5wt % NaCl solution compared with the unmodified composite. The corrosion current density decreased from 2.0 μA·cm -2 for AC to 1.37 μA·cm -2 and 1.16 μA·cm -2 for AC-Y and AC-Er composites, respectively. Microstructural observation indicated that Y and Er additions modified grain boundary precipitates characteristics, precipitate-free zone morphology, and intermetallic phase distribution. Compared with the AC composite, the AC-Er composite exhibited a more discontinuous corrosion morphology, and the lowest measured IGC penetration depth, indicating a change in corrosion path development during chloride exposure. XPS analysis further revealed differences in the composition of the surface oxide layer after corrosion. The observed corrosion behaviour is associated with rare-earth-induced modifications of the grain-boundary environment, surface-film chemistry, and intermetallic phase distribution, which collectively alter corrosion-path development during chloride exposure. Despite these benefits, the Al 8 Cu 4 Er phase can initiate shallow pitting, revealing a microstructural trade-off. The corrosion kinetics and intergranular corrosion resistance followed the trend AC-Er > AC-Y > AC. However, long-term EIS monitoring showed a continuous decrease in the polarization resistance of AC-Er, whereas the AC composite exhibited an extreme increase in Rp at 48h, attributed to corrosion product accumulation rather than actual passivation. Thus, the above ranking reflects differences in corrosion kinetics and corrosion mode rather than superior long-term interfacial-film stability. These findings provide a clear perspective for designing corrosion-resistant, high-strength aluminium composites via targeted microalloying.

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