Plasma sprayed dense Al-B₄C composite coating for corrosion prevention

Achieving dense atmospheric plasma-sprayed (APS) aluminum-based composite coatings is challenging due to interconnected pores in the conventional coatings that create pathways for corrosive media to penetrate, limiting long-term anti-corrosion performance. In this study, a homogeneously reinforced Al-40 vol% B₄C composite feedstock is developed through mechanical alloying to achieve a homogenously reinforced dense APS deposited coating in the as-sprayed state, which eliminates costly post-deposition processing for densification. The relatively high B₄C content can enable multifunctionality in the coating, as previous studies have shown that increased B₄C content results in enhanced radiation shielding. The coating was deposited on AZ31B Mg alloy for electrochemical evaluation and on Al7075 alloy for mechanical testing. The deposition, microstructure characterization, electrochemical behavior, and cohesive strength of the coating is studied. Results indicate that the Al-B₄C coating appears pore-free and has a uniform distribution of B₄C. The open circuit potential (OCP) of Al-B₄C coating is −0.76 V, closely matching bulk Al, which is higher than pure APSed porous Al coating (OCP −1.42 V). Negligible open pores and resemblance of OCP with bulk Al indicate that the Al-B₄C coating is dense. While the corrosion potential (E_corr) of Al-B₄C coating is higher than that of pure Al coating, the converse is observed for the corrosion current (I_corr), indicating higher corrosion rates in the former on corrosion initiation due to micro-galvanic interactions between B₄C and the Al matrix. Failure at the glue joint during tensile tests suggests that Al-B₄C coating has a minimum cohesive strength of 60 MPa. The combination of near pore-free microstructure, corrosion resistance, strong interfacial bonding, and high B₄C loading highlights the potential of the APSed Al-B₄C coating as a lightweight multifunctional protective layer for marine, aerospace, and nuclear applications requiring both environmental durability and radiation shielding capability.