Corrosion Behavior of Detonation Gun Sprayed Al Coating on Sintered NFeB

Pure Al coating was prepared by a detonation gun (D-gun) spraying process to protect sintered NdFeB magnets. The detonation gun sprayed coating is very uniform and has a low porosity of 0.77%. The thickness of the Al coating is approximately 16 μm. The corrosion current density for the coated sample was 1.30 × 10⁻⁵ A/cm² immediately after immersion in 3.5% NaCl solution, compared to 6.54 × 10⁻⁵ A/cm² for the uncoated sample. X-ray photoelectron spectrometry results indicate that the formation of Al₂O₃ film contributes to the increased corrosion resistance of Al coating. Meanwhile, electrochemical impedance spectroscopy with equivalent electrical circuit was used to ascertain the corrosion process of the Al coatings. Results show the corrosion procedure consists of two stages which agree with the potentiodynamic polarization test. It can be concluded that the Al coating deposited by the D-gun spray process can improve the corrosion resistance of sintered NdFeB.