Layered double hydroxides on additively manufactured Al–Si alloy: Growth mechanism, microstructure and corrosion performance

Additive manufacturing (AM) of Al–Si alloys has been targeted as a cutting-edge technology for producing complex-shaped components in the aerospace and automotive industries. However, their limited corrosion resistance in aggressive environments hampers their implementation in mass-production engineering. On this basis, surface treatments, such as Layered double hydroxides (LDH), have recently shown promising results for conventionally processed Al alloys. This research presents a pioneering investigation on the study of Zn–Al Layered Double Hydroxide (LDH) coatings on AlSi10Mg alloys fabricated via Laser Powder Bed Fusion (L-PBF). In detail, the LDH synthesis was performed in ambient conditions and different treatment times (0–360 min) on the Al–Si AM samples (considering two planes: one following the building direction XZ and one parallel to the building platform XY) and a conventional cast Al–Si substrate of similar chemical composition (included as reference). The main characterization results (SEM/EDS) reveal the formation of a well-defined and thicker coating on the cast alloy (∼2.5 µm) compared to the AM alloy (∼1.5–2 µm) after 60 min of treatment. The lower coating growth rate on the AM sample was attributed to the finer Si distribution. This feature hampered the aluminium dissolution and the Zn–Al-LDH layer formation. However, despite being thinner, the LDH coating on the AM alloy was more compact (also associated with the fine underlying Si distribution), which contributed to its better corrosion resistance.