Preparation,Phase Structure And Magnetic Properties Of MnAl-based Permanent Magnet Alloys With Low Mn Content

MnAl-based permanent magnet alloys with tetragonal structure have attracted wide attention due to their excellent properties.But,the magnetic ?-MnAl phase in the alloy is metastable.Therefore,how to prepare permanent magnet alloys with high purity ?-MnAl magnetic phase is one of the urgent problems to be solved.?-MnAl phase can be obtained by cooling after heat treatment of high temperature epsilon phase.Doping C element and excessive Mn in MnAl can increase the stability of magnetic phase,but excessive Mn can lead to antiferromagnetic coupling between Mn-Mn atoms,which leads to the decrease of saturation magnetization.In this paper,low Mn content MnAl-based permanent magnet alloys doped with Zr,Sn,Si and C elements were prepared by arc furnace melting.The effects of different heat treatment processes,such as temperature,heat treatment at different pressures and cooling way,on the phase structure and magnetic properties of MnAl-based alloys were studied.The main results are summarized as follows:(1)Cooling way has an important effect on the formation of magnetic phase and magnetic properties of MnAl alloy.For Mn50Al50-xZrx(x=1,2,3,4),when x=1,the samples obtained by air-cooling have high purity magnetic phase.When x=2?4,the quenched samples have better magnetic properties.When x=3,the sample obtained a single ?-MnAl phase structure directly after quenching.(2)The phase structure and magnetic properties of MnAl alloy are greatly affected by different heat treatment temperatures.For Mn50Al50-xSnx(x=1,2,3,4)samples obtained by quenching,no magnetic phase was observed when the heat treatment temperature was 1050?.The content of ? phase is positively correlated with the content of Sn when the heat treatment temperature is 1100?.When the annealing temperature is 1150?,all the samples have magnetic phases and the content of magnetic phases is higher than that of the first two temperatures.(3)The phase structure and magnetic properties of MnAl alloys are greatly affected by heat treatment at different pressures.The magnetic phase content of MnsoAl49Zr ingot decreases with the increase of pressure,the remanence and saturation magnetization of the sample decrease gradually,and the coercivity increases gradually.When the pressure is 1.4×102 Pa,the coercivity of the sample reaches 4.45 kOe.(4)The samples of Mn50Al50-xSixC3(x=1,2,3,4)were studied.After quenching at 1100? for 16h and quenching at 500? for half an hour,the decomposition of high temperature epsilon phase disappears and the proportion of ?-MnAl magnetic phase increases.It can be seen that heat treatment at 500? is beneficial to the transformation of the epsilon-MnAl phase into the ?-MnAl magnetic phase in MnAl alloy.