Preparation and Evaluation of Corrosion Resistance for Perhydropolysilazane-Converted Al Coatings on NdFeB Magnets

Abstract

The advancement of metal protective coatings on NdFeB magnets has been constrained by environmental pollution concerns, particularly in electroplating and conversion coating processes. This study introduces an environmentally friendly Al coating on NdFeB magnets fabricated through physical vapor deposition and perhydropolysilazane (PHPS) conversion. The impact of PHPS pyrolysis temperature on the structural characteristics and corrosion resistance of Al(PHPS)/NdFeB coatings is comprehensively analyzed. Corrosion resistance is evaluated using neutral salt spray tests, electrochemical polarization measurements, and impedance spectroscopy analysis. Compared with conventional Al/NdFeB, the corrosion resistance of Al(PHPS)/NdFeB specimens is markedly improved, in which the optimized Al(PHPS)/NdFeB-300 obtained with pyrolysis temperature at 300℃ achieves a neutral salt spray test duration of 336 hours, a corrosion potential of -0.557 V, and a corrosion current density of 3.44×10-9 A/cm². The enhanced corrosion performance is attributed to the formation of Si and Al composite oxides on the surface of the Al coating.