Effects of post-machining heat treatment on the magnetic properties and the corrosion of NdDyFeB magnets

The post-machining heat treatment of NdDyFeB sintered magnets in the temperature range of 600°C to 1000°C in a small amount of oxygen atmosphere has been studies. In this process, demagnetization characteristics of the magnets which have deteriorated during the machining, recover to a good magnetic condition and very thin oxidation layer, approximately 0.3 μm thick, have formed on the surface of the machine finished magnets. After exposing the finished magnets covered with such thin oxidation layer, in 60°C,90% R.H. for 100 hours, no corrosion have been observed.