Magnetic properties and microstructures of hydrogenation-disproportionation-desorption-recombination processed Nd-Fe-B powders by grain boundary diffusion of Nd-Cu-Al

•Low melting point Nd80Cu10Al10 (wt.%) ternary alloy is employed as the source for grain boundary diffusion.•Coercivity of HDDR anisotropic magnetic powders is enhanced after grain boundary diffusion.•In the range of 770-870℃, the coercivity increases at first and then decrease as the temperature exceeds 820 °C.•The maximum of the coercivity of Hcj = 1321.29 kA∙m-1 is obtained with 6 wt% Nd-Cu-Al.