The chemical conversion film containing, at least as the constituent components
thereof, (a) at least one of the metals selected from molybdenum, zirconium, vanadium,
and tungsten; (b) a rare earth metal constituting the magnet; and (c) oxygen, which
is formed on the surface of a rare earth metal-based permanent magnet according
to the present invention, contains a composite metal oxide provided on the surface
of the R-rich phase having a lower oxidation-reduction potential through a preferential
reaction of the metallic ions that are present in the form of complex ions or oxide
ions, such as of molybdenum, contained in the treatment solution, with the rare
earth metals that elute from the magnet. Thus formed composite metal oxide reduces
the difference in corrosion potential as to realize a uniform surface potential,
and effectively suppresses the corrosion based on potential difference. Furthermore,
the chemical conversion film thus formed exhibits excellent corrosion resistance
even if it is provided as a thin film. The production method thereof can be implemented
at low cost and by a simple process comprising treating the surface of the magnet
by using a treatment solution containing a molybdate and the like.
