Corrosion behavior of Al100 − xCux (15 ≤ x ≤ 45) doped Nd–Fe–B magnets

The corrosion behavior of Al100 − xCux (x = 15, 25, 35, 45 at.%) doped Nd–Fe–B magnets has been investigated in 0.005 M H2SO4 solution using potentiodynamic polarization and electrochemical impedance spectroscopy techniques. It was found that the corrosion resistance first improves with the increase of copper content, reaches a maximum at x = 35 and thereafter decreases. The existence of optimal corrosion resistance in the Al65Cu35 doped magnets is attributed to both the increase of chemical stabilization and the optimization of distribution/morphologies of (Pr, Nd)-rich intergranular phases. Addition of Al55Cu45 shows poorer corrosion resistance mainly due to coarsening of intergranular phases that, in turn, led to increasing the amount of active reaction channel at the triple junction of the matrix phase.