Effect of Processing Parameters on the Magnetic Properties and Macrotexture of a Nd_13.5Fe_73.8Co_6.7B_5.6Ga_0.4Alloy Processed by Equal Channel Angular Pressing With Back Pressure

Abstract

Equal channel angular pressing (ECAP) is a well-established thermo-mechanical processing technique which could induce c-axis texture of Nd2Fe14B in a melt-spun Nd13.5Fe73.8Co6.7B5.6Ga0.4 alloy. However, the effects of ECAP processing parameters such as temperature, backward-pressure and multiple-pass ECAP routes remain unknown for this alloy. In this work we have investigated the effects of these processing parameters on the c-axis texture formation. It is found by xray diffraction macrotexture analysis that the maximum intensity of 001 pole figures for the tetragonal-Nd2Fe14B phase (Imax) shows an increase from 2.7 to 4.1 m.r.d. (multiples of random distribution) by increasing the ECAP temperature from 723 to 823 K, while the difference in remanent magnetization between easy and hard directions (ΔMr ) rises from 24.0 Am 2 /kg to 41.5 Am 2 /kg. When the back-pressure was increased from 0.25 to 0.5 GPa at 823 K, Imax showed an increase from 2.8 to 4.1 m.r.d. However, Imax saturated for back-pressures above 0.5 GPa, suggesting that back pressure has limited effect on the texture formation, although it is necessary for compaction of the alloy powders. Two multiple-pass ECAP routes conventionally known as route-A and -C were employed for two-pass ECAP at 823 K. It is found that the route A processing is effective in enhancing the texture formation while the texture is lost by a subsequent pressing when adopting route C. Therefore, compaction of Nd13.5Fe73.8Co6.7B5.6Ga0.4 alloy powder using route A ECAP passes with 0.5 GPa backpressure at 823 K results in pronounced texture, which is beneficial for anisotropic hard magnetic properties.

Manufacturing Processes for Permanent Magnets: Part II—Bonding and Emerging Methods

“…51 While over 95% green density was achieved, the texture formation was less than ideal, and the (BH) max was estimated at about 1 MGOe, far less than the 7 MGOe achieved with the conventional method. 52 Onal et al 53 studied the effects of ECAP process variables on the magnetic properties of commercial meltspun Nd-Fe-Ga-Co-B powder (MQU-F1). The goal was to achieve high texture without significant grain growth.…”