2016 Volume 57 Issue 10 Pages 1789-1793
In general, the manufacturing process of NdFeB sintered magnets is as follows: preparing the starting alloys, crushing and pulverizing into fine powders, press-forming in magnetic fields for alignments, sintering, aging, crushing and cutting. It is well known that microstructure of starting alloys affect the ease of pulverization, press-forming for alignments in the magnetic field and sintering. A single roll casting process (hereinafter referred to as strip-casting) is a beneficial method for obtaining starting alloys with suitable microstructure. For this reason, strip-casting is regarded as a de-facto standard process for the production of starting alloys for NdFeB magnets. With this method, strips of 100–500 μm thickness are formed by pulling up from a melt by a single roll. For this reason, it is important to control primary crystal growth. In this study, we investigated primary crystal growth in starting alloys. First, Nd15.66Febal.B5.52 (atomic %) alloys were prepared using a strip-casting furnace. A batch size was 500 kg and roll diameter was 500 mm. Microstructures of obtained strip-casting samples were observed by electron probe micro-analyzer (EPMA). In this measurement, we focused on the morphologies of primary crystal growth and the distribution of constituent elements. Next we investigated the relation between the surface roughness of the rolls and frequencies of nucleation at the surface contacting a roll. The alloys were prepared using a strip-casting furnace. A batch scale was 5 kg and roll diameter was 300 mm. The alloy composition was Nd10.35Dy3.88Febal.B5.96 (atomic %). In this study, we also reviewed the method of reducing segregations of chill crystals existing in the microstructures of the starting alloys.
This Paper was Originally Published in Japanese in J. JFS 88 (2016) 154–159.