Surface treatment for iron-based permanent magnet including rare-earth element

A surface treatment for a R--TM--X type of permanent magnet material comprising:

• mechanically working said permanent magnet to form a magnet substrate;
• degreasing said magnet substrate;
• removing a surface layer of said magnet substrate, whose quality is changed in the step of mechanically working, by a first etching, using from 0.2 to 10 vol % of a nitric acid, and a second etching, using a mixture of 0.2 to 10 vol % oxygenated water and from 10 to 30 vol % of an acetic acid;
• forming a non-bright nickel-plating, of from about 5 to about 25 .mu.m thickness, on said magnet substrate;
• forming a copper layer on said magnet substrate prior to the step of forming said non-bright nickel layer;
• forming a semi-bright nickel plating, of from about 1 to about 15 .mu.m thickness, on said non-bright nickel plating;
• forming a chromate layer, of from about 0.0001 to about 10 .mu.m thickness, on said semi-bright nickel plating;
• said step of forming a chromate layer includes a chromate treatment comprising dipping said magnet in a chromate solution, wherein said chromate solution is acidic consisting essentially of at least one of chromic acid anhydride and dichromic acid with a chrome concentration of at least 0.01 mol/l;
• and
• neutralizing said chromate layer using alkalines;
• said step of neutralizing said chromate layer includes immersing said magnet in a deliquescent solution containing at least one of a sodium hydroxide and potassium hydroxide;
• where R is at least one of about 5 to 40 wt % of an element and a mixture of Nd, Pr, and Dy, TM comprises of iron and one of from about 0.5% to about 15 wt % of Co and from about 0.5 wt % of Al, and X is at least one of about 0.2 to 8 wt % of an element and a mixture of elements comprising B and N.