Effect of cooling rates on the microstructure and magnetic properties of MnAl permanent magnetic alloys

•The pure τ phase MnAl was obtained by tuning the copper roller speed of 5 m/s.•A high magnetization of 118.2 emu/g was achieved in the as-spun MnAl ribbon.•The phase transformation and magnetic performances were tailored by the copper roller speed. In this work, the microstructure, phase transformation and magnetic properties of MnAl permanent magnetic alloys prepared by the melt-spinning technique were systematically investigated by tuning the cooling rate. It was shown that the MnAl microstructure, phase transformation and magnetic properties can be tailored by the copper roller speed. With increasing of the roller speed, the phase transformation from the γ2, β phases to the ε phase was observed. In addition, the variation of magnetic properties was attributed to the phase content and microstructure of the ferromagnetic τ phase in the MnAl alloys, being controlled by the cooling rate. As a result, the high-purity τ phase MnAl was obtained at a copper roller speed of 5 m/s, which exhibited a high magnetization of 118.2 emu/g. Therefore, this work can provide a method for the direct fabrication of the high-purity ferromagnetic τ phase MnAl alloy.