Surface Corrosion Phenomenon and Mechanism Analysis of SiC Particle-Reinforced Aluminum Matrix Composite Forgings After Anodization

This study investigates the abnormal black spots observed on the surface of SiC-reinforced aluminum matrix composite in helicopter lift systems after anodization. Systematic analysis was conducted using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), white-light interferometry, metallographic examination, and micro-nano CT three-dimensional characterization. The results indicate that the black spots correspond to corrosion pits caused by incomplete anodized layers, with an average depth of 20 μm. Localized intergranular corrosion features were observed at the bottom of some pits, extending to depths of 60 μm. EDS detected trace element Cl (0.27 wt%) in corroded regions, confirming the critical role of chloride ion infiltration in corrosion initiation. Metallographic cross-sections revealed corrosion propagation along grain boundaries, while 3D micro-nano CT demonstrated no significant inward corrosion penetration and no abnormal distribution of SiC particles. The study concludes that localized anodized layer failure is the root cause of black spot defects, providing critical insights for optimizing manufacturing processes and quality control of aerospace aluminum matrix composite components.