The impact of post-processing heat treatment on the magnetic properties of additively manufactured Nd-Fe-B magnets

The effect of post-process heat treatment on magnetic properties by laser powder bed fusion (LPBF) additively manufactured Nd-Fe-B magnets was studied in dependence of heat treatment temperature and as built condition. The magnets show very different magnetic performance in the as built condition, which depends on the adjusted LPBF process parameters. Heat treatments subsequent to LPBF processing lead to a remarkable change in the magnetic properties, whereby the response characteristics of the magnets depend on the as built condition and magnets with low initial coercivity show a large potential of improvement in case of low temperature heat treatments. Crystallization of amorphous constitutes in the microstructure, whose volume fraction depends on the LPBF manufacturing parameter, is responsible for this improvement. Exceeding the optimal heat treatment temperatures leads to the precipitation of α-Fe and deteriorates coercivity but enhances remanence of the magnets. Magnets with low initial coercivity require higher heat treatment temperatures to obtain optimal magnetic performance and show an increased stability against overaging.