Effect Of High-Energy Ball Milling And Subsequent Heat Treatment On The Microstructure And Magnetic Properties Of Mn-Ga Alloys

In the current development of science and industry technology,permanent magnet materials are more and more widely used,although the current rare earth permanent magnet materials are still mainstream products,but because the development and production of rare earth metals will seriously pollute the environment,while the improvement of magnetic material performance also needs to develop new varieties of magnetic materials.Mn-Ga alloy is a magnetic material with great performance potential,especially with greater stubborn advantages,through component optimization and preparation process optimization,revealing the different ball grinding conditions,heat treatment conditions and the role of the applied magnetic field on the nano-phase composition and magnetic properties of Mn-Ga alloy,which can help to provide reference for the development of new magnetic materials of Mn-Ga series.In this paper,Mn-Ga alloy powder is prepared by high-energy ball milling process to make its grain size reach nanometer level.After pressing the Mn-Ga powder into a block,an annealing heat treatment under a magnetic field and without a magnetic field is performed to obtain the desired sample.The main phase components are Mn3Ga phase,Mn0.85Ga0.15 phase,MnO phase and a small amount of MnGa phase analyzed by X-ray diffraction pattern.The grain size is between 50-500 nm.The structure is characterized by scanning electron microscopy.The large particles in the Mn-Ga alloy structure are protruding,and the small particles are mostly distributed in the pits.The area of large particles contains more elements of Mn,Ga and O,and the area of small particles contains Mn and O elements.The content is less.The distribution difference between Mn element and Ga element in large particles and small particles is obviously smaller than that of O element.The proportion of Ga in the Mn-Ga alloy has a significant effect on the structure and properties of the alloy.The Mn-25at%Ga alloy has the smallest grain size,uniform distribution,better coupling,and the largest coercive force.The refinement of the grain size is beneficial to the improvement of the coercivity of the alloy.With the increase of ball milling time,the grain size of Mn-25at%Ga alloy gradually increases.The coercivity of the alloy after 2 hours of ball milling reached the maximum value of 15.7 kOe,and the residual magnetism was as small as 6.26 emu/g;after 3.5 hours of ball milling,the alloy remanence reached the maximum value of 9.46 emu/g.When the annealing temperature is 300℃-400℃,Mn0.85Ga0.15 phase precipitates in Mn-Ga alloy,and when the temperature rises to 500℃,Mn0.85Ga0.15 phase transforms into D022-Mn3Ga phase.With the increase of the annealing temperature and the extension of the annealing time,the grain size gradually increases.When the annealing temperature is 500℃and the holding time is 5 h,although the coercivity does not reach the highest value,the remanence is significantly improved and the overall magnetic performance is the best.The coercivity,remanence,and maximum energy product of Mn-25at%Ga alloy are 14.99 kOe,7.4 emu/g,and 13.2 MGOe,respectively.Annealing under the condition of magnetic field can make the grains refined and evenly distributed.Compared with the condition of no magnetic field,the coercive force of the alloy annealed in a strong magnetic field of 12 T increases,and the remanence decreases.For the 12 T strong magnetic field heat treatment sample,the method of extended annealing without magnetic field can significantly improve the remanence of the alloy while keeping the coercivity unchanged.The overall performance is the best when the coercive force is extended for 2 h.Remanence and maximum energy product are 8.72 kOe,8.29 emu/g and 16.38 MGOe,respectively.However,the coercive force and remanence of the 3 T/9 T high magnetic field heat treatment sample are reduced,and the magnetic performance is reduced.Other elements are added to the Mn-Ga alloy.When the additive is FeB,the coercivity and remanence of Mn70X5Ga25 alloy are the highest,which are 7.85 kOe and 1.25 emu/g,respectively.When Fe5B is added,the coercivity and remanence are reduced to 4.45 kOe and 0.54 emu/g,respectively.When Fe,FeCo and Fe5Co are added,the magnetic properties are poor.