Study On Microstructure And Properties Of MnGa Alloy By Mechanical Alloying And Strong Magnetic Field Heat Treatment

With the development of science and technology,high performance permanent magnets play a very important role in technological progress and innovation.At present,sintered NdFeB permanent magnet is widely used.But production of rare-earth metals has been limited by overproduction,high prices and environmental pollution,forcing scholars to look for alternatives.Among the potential rare-earth free magnetic materials,Mn-Ga binary alloy has become a better choice due to its potential excellent magnetic properties.It is characterized by high coercivity,simple preparation process,and the ability to combine with soft magnetic materials with the characteristics of soft and hard magnetic phase.It is expected to become the next generation of magnetic materials with excellent magnetic properties.In this study,the grain size of Mn-20at%Ga alloy annealed after mechanical alloying can reach nanometer level,and the average grain size is between 10 nm and 20 nm.The main phase components of the alloy are Mn3Ga phase,Mn0.85Ga0.15 phase and a small amount of MnGa phase,as well as a small amount of MnO phase caused by oxidation in the process of ball grinding and heat treatment.After mechanical alloying,the elements in the samples were evenly distributed and there was no obvious area of element concentration.The annealing process has a significant effect on the microstructure and magnetic properties of Mn-20at%Ga alloy.With the increase of annealing temperature,the precipitation amount of Mn3Ga phase first increased and then decreased,while the ratio of Mn3Ga phase to Mn0.85Ga0.15 phase directly determines the magnetic properties of Mn-20at%Ga alloy.When the annealing temperature is 385? the grain size of the alloy is smaller,the shape is more regular,and the size distribution is even.At this time,the proportion of Mn3Ga phase and Mn0.85Ga0.15 phase is the largest,which effectively improves the coercivity of the alloy.The extension of annealing time has little effect on Mn3Ga phase,but it can affect the precipitation of Mn0.85Ga0.15 phase.With the increase of annealing time,Mn0.85Ga0.15 phase precipitation first increased and then decreased,reaching the maximum precipitation when the annealing time was 5 h.At the same time,a small amount of MnGa phase was also included in the alloy.At this time,the shape of the alloy was regular and the size distribution was relatively uniform.Strong magnetic field heat treatment can effectively refine the grain size of Mn-20at%Ga alloy to make its grain shape more regular and size distribution even.It has a negative effect on the texture formation of Mn0,85Ga0.15 phase,but has little effect on Mn3Ga phase.Strong magnetic field can significantly improve the remanence and maximum magnetic energy product of the alloy and effectively improve the magnetic property of the alloy.With the increase of magnetic field strength,the grain size of Mn-20at%Ga alloy decreases gradually and increases when the magnetic field strength is 9T.The strong magnetic field promotes the even distribution of grains in Mn-20at%Ga alloy after heat treatment.After 3T magnetic field heat treatment,the remanence of the alloy increased by 40.48%and the maximum magnetic energy product increased by 93.6%,indicating that the magnetic property of the alloy could be significantly improved by magnetic field heat treatment with appropriate intensity.