Study On NdFeB Magnetism By Selective Laser Melting

Among rare earth magnets,Nd Fe B alloy is the most superior due to its high magnetic energy product and coercive magnetic force.This alloy is widely used in high-density magnetic recorders,audio equipment,automotive starting motors,and medical equipment.However,the traditional Ndfeb powder metallurgy process has several drawbacks such as the addition of a binder resulting in high porosity,internal hysteresis loss,low residual magnetic flux,low magnetic energy product,and high-temperature sintering process of grain size,resulting in insufficient coercive magnetic force.Selective laser melting forming has a high cooling rate,which usually results in small grain size for common aluminum alloy,titanium alloy,stainless steel,and other materials forming.Through the selective laser melting forming of Nd Feb material,better magnetic characteristics may be achieved.However,there is a lack of literature on the selective laser melting forming of Nd Feb,and the effect of process parameters on sample molding quality and magnetic properties is unclear.Therefore,this paper aims to explore the effect of selective laser melting on the magnetic properties of Nd Feb.The experiment utilized a self-developed selective laser melting platform.CW laser and PULSE laser were output by controlling fiber laser,and combined with single light path and spectrophotometer path to form different mode selective laser melting processes.The effects of scanning distance,scanning speed,powder thickness,and other process parameters on the molding quality,microstructure,and magnetic properties of the samples were investigated.The main research results are as follows:（1）The optimized CW laser beam splitting process mode forming Nd Feb process parameters are as follows:single spot power 53W,spot diameter 59μm,spot spacing 80μm,scanning spacing 420μm,scanning speed 50mm/s,powder layer thickness 40μm.The Ndfeb sample has a better solid block forming effect.There is moreα-Fe soft magnetic phase in the tissue of the formed Ndfeb sample,and less Nd₂Fe₁₄B hard magnetic phase.There is a large massive neodymium-rich phase and a small amount of neodymium oxide at the grain boundary.The maximum magnetic property is BHmax≈0,and the sample has almost no magnetism.（2）The process parameters of forming Nd Feb under the optimized PULSE laser spectrophotometer path process mode are as follows:single spot power 53W,laser frequency&pulse width 10k Hz（60us）,spot diameter 59μm,spot spacing 48μm,scanning spacing 120μm,scanning speed 160mm/s,powder layer thickness 40μm.The Ndfeb sample has a better solid block forming effect.There are more Nd₂Fe₁₄B hard magnetic phases and lessα-Fe soft magnetic phases in the tissue of the formed Ndfeb sample.There are thin layer neodymium-rich phases and a small amount of neodymium oxide at the grain boundary.The maximum magnetic property is BHmax=1.1MGOe.（3）The process parameters of forming Nd Feb in the optimized PULSE laser single-light path process mode are as follows:single spot power 160W,laser frequency 10k Hz,pulse width 60us,spot diameter 96μm,overlap rate 25%,scanning speed 250mm/s,powder layer thickness 25μm.The Ndfeb sample has the best molding quality and the best magnetic properties,BHmax=1.3MGOe.（4）In the hybrid laser single-light optical path molding process of Nd Fe B,it was found that although the overall structural strength,density,and magnetic characteristics of the hard magnetic area of the molded sample were slightly weaker,it was possible to achieve magnetic control in different parts that traditional sintered magnets cannot achieve.This preliminary result verifies the feasibility of the selective laser melting process in forming Nd Fe B samples with locally different magnetic properties.