Effect of hydrogen pressure on hydrogenation and pulverization behavior of Sm(CoFeCuZr)z ingot and strip casting flake

Abstract

Effect of hydrogen pressure on hydrogenation and pulverization behavior of Sm(CoFeCuZr)7.6 alloy prepared by plate mold (PM) and strip casting (SC) has been systematically investigated. Increasing hydrogen pressure can improve the hydrogenation ability. Both the PM and SC have the similar hydrogen absorption process, which can be divided into two stages. The first stage follows the Sieverts’ law (1–5 MPa) while the second one deviates from the Sieverts’ law (5–10 MPa). Rietveld refinement shows that the hydrogen absorption causes different lattice distortion of different phases without changing the phase structure. The internal stress caused by such lattice distortion is the primary reason that accelerates the pulverization of the alloys, and increasing hydrogen pressure can lead to the decrease of particle size of the PM and SC alloys. The hydrogen decrepitation (HD) process are studied in detail based on these results. The hydrogen absorption mechanism of Sm(CoFeCuZr)7.6 alloy can be regarded as a hydrogen dissolution process without phase transformation. In addition, the existence of a large amount of fine grains in the SC has an adverse effect on the alignment, which can be optimized by taking effective methods to reduce the overcooling rate. This work proves that the SC, HD and jet milling process can be a promising new approach to powder preparation for high-performance Sm(CoFeCuZr)z sintered magnets.