Preparation, Microstructure And Magnetic Properties Of Non-rare Earth MnAl Based Permanent Magnetic Materials

With the decline in rare earth reserves of China and the drastic increase in the price of RE metals,non-rare-earth permanent magnetic materials have attracted great attention due to theirs good hard magnetic properties: low cost,good corrosion resistance,etc..The ferromagnetic ?-MnAl phase with a tetragonal structure in the MnAl alloys is a metastable phase,forming from the high temperature ? phase by anneealing under 550?.How to achieve high purity ? phase is the key to studying the magnetic properties of MnAl alloys.In this Paper,the structure and magnetic properties of the MnAl alloys by doping Cu?Ga ?C elements were investigated.Different heat treatments before ball milling were also investigated.The MnAl based flakes were prepared using surfactant-assisted ball-milling method.The structure and magnetic properties of the as-milled MnAl powders were investigated.The main results are summarized as follows:?1?Doping Cu in MnAl alloys can stabilize the structure of ? phase and increase the content of ? phase.The Mn₅₀Al₄₆Cu₄C₃ sample has a high purity magnetic phase,and the optimal coercivity of the as-milled powders is 7 times higher than the coercivity of bulk alloys.The heat treatment temperature and heat treatment time also have some influences on the stability of ? phase.It is found that the ? phase is more easily formed when the heat treatment temperature is above 1100?.The coercivity of Mn₅₀Al₄₆Cu₄C₃ /Fe powders were less than coercivity of the as-milled Mn₅₀Al₄₆Cu₄C₃ powders,but the remanent magnetization were higher than the remanent magnetization of the as-milled Mn₅₀Al₄₆Cu₄C₃ powders.After quenching at 500? for 3min,the coercivity decreased,the remanent magnetization increased obviously.The morphology of the as-milled Mn₅₀Al₄₆Cu₄C₃ powders was flakes in scanning electron microscope.The as-milled powders were oriented in magnetic field and measured in perpendicular and parallel to the magnetic field direction.It was found that the remanence and coercivity of the oriented samples were quite different,in different direction,which indicating that the Mn₅₀Al₄₆Cu₄C₃ samples have a large anisotropy.?2?Doping a certain amount of Ga can improve the content of ? phase in the alloys.The optimal coercivity of as-milled Mn₅₀Al₄₆Ga₄C₃ is 2.2kOe.The Ga-doped MnAl alloys have ? phase and non-magnetic phases after heat-treated at 1000?,which indicated that the heat treatment temperature affected the stability of ? phase.