To enhance the surface protection of exposed moving parts made from magnesium alloys, this study focuses on developing high-performance micro-arc composite (MCC) coatings on AZ80 wrought magnesium alloy substrate. AZ80 alloys were fabricated through forging at different temperatures (250 °C, 350 °C, and 450 °C) to investigate the influence of thermal deformation on substrate properties. Subsequently, micro-arc oxidation (MAO) coatings and MCC coatings were applied to the forged alloys. Comprehensive analyses—including microstructural characterization, salt spray corrosion tests, and stress corrosion cracking (SCC) evaluations—were conducted under both static and stress conditions. Among the forging temperatures, 250 °C produced substrates with refined grains and a favorable distribution of β-Mg₁₇Al₁₂ precipitates, resulting in improved baseline corrosion resistance. MAO coatings offered moderate protection, primarily delaying corrosion initiation and crack propagation under stress environments. Building upon this foundation, MCC coatings—fabricated by electrostatic spraying to form an inner-embedded and outer-wrapped structure over the MAO layer—demonstrated significantly superior protective performance. Under both static and stress corrosion scenarios, the MCC coatings effectively suppressed SCC initiation and progression, highlighting their potential for robust surface protection in demanding service environments.

Nickel-based superalloys are extensively used in fabricating high-temperature gas turbine components, owing to their superior high-temperature strength, excellent structural stability, and remarkable hot corrosion resistance. The influence of impurity sulfur content on their hot corrosion performance is a core scientific issue in hot-end component compositional design and smelting. This study investigated chromium (Cr)-rich nickel-based superalloys with sulfur (S) contents of 3 ppm, 16 ppm, and 42 ppm via XRD, SEM, and an EPMA, focusing on their hot corrosion behavior under a 100% Na₂SO₄ deposit at 900 °C. The results indicated that their hot corrosion products were basically identical, forming a Cr-dominated outer oxide layer rich in Ti, Co, and Ni, an Al₂O₃-based inner corrosion zone, and a CrS_x-dominated sulfide layer. With increasing sulfur content, the outer layer thickness decreased from approximately 30 μm to less than 20 μm, pores in the outer oxide layer increased in quantity and size, and internal sulfides and nitrides accumulated. The average depth of spallation increased from 55 μm for the S3 alloy to 80 μm for the S16 alloy, with the S42 alloy showing even more extensive spallation. The alloy’s hot corrosion performance deteriorated notably with increasing S content. The mechanism of sulfur’s effect on hot corrosion behavior is that sulfur in the alloy segregates at oxide film defects, enhancing defect stability and increasing their quantity and size. These defects serve as rapid diffusion channels for corrosive media, thereby accelerating the alloy’s hot corrosion rate.