Research On Additive Manufacturing Of Soft Magnetic Alloy For Complex Magnetic Shielding Structure Via Selective Laser Melting

Soft magnetic materials and magnetic shielding structures are widely used in the fields of power engineering,aerospace,nuclear power,microelectronics and other industrial products,and based on the requirements of which,complex 3D magnetic shielding structures are employed in some important or special applications.Compared with traditional manufacturing methods,Additive Manufacturing has the advantage of high flexibility,no mold,short cycles,no restrictions on structures and materials,which provides new ideas for the "Design-Manufacture integration" and "Structure-Function interation" of lightweight,functional and complex shaped metal components.Aiming at the engineering requirements of additive manufacturing and lightweight design of soft magnetic alloyed magnetic shielding structure,based on Selective Laser Melting(SLM),experimental studies focusing on 1J85 alloy(Ni-15Fe-5Mo Permalloy)were carried out on the SLM preparation process,microstructures,mechanical properties,magnetic performance and the design of lightweight structures in this article.The main research contents and key conclusions are as follows:(1)Process optimization:Bulk samples were prepared with gas-atomized Ni-15Fe-5Mo Permalloy powder.An optimized SLM process window was established by means of the studying of the changing rules and influencial mechanism at different laser power,scanning speed and hatching space for relative density and surface roughness.And then a magnetic shielding structure for FOG was prepared using the optimized process parameters.The results show that the increase of laser power at high laser scanning speed tends to improve the relative density,meanwhile,the increase of laser power leads to the surface roughness decreasing first and then increasing.Taking into account the relative density and surface roughness,the optimized SLM parameters of 1J85 alloy,which was employed for the additive manufacturing of magnetic shielding structure,follow as:laser power(P)200 W,scanning speed(v)400 mm/s,hatching space(h)80?m,and layer thickness(t)35?m.(2)Microstructures and Properties:The microstructures,which consists of element composition and distribution,morphology of the molten pool,phase,grain size and orientation,grain boundary characteristics,of the as-printed and subsequently annealed 1J85 soft magnetic alloy were characterized and analyzed by OM,XRD,FE-SEM,EDS,EBSD and other methods.The influence of microstructures evolution on mechanical and magnetic properties was discussed.The typical hierarchical characteristic of microstructures could be observed in the as-printed samples which mainly include the coexisted grains of dendritic and equiaxial ones with grain boundaries and the micron-and submicron-scaled cellular substructures with cellular walls.The elimination of the anisotropy of mechanical properties was attributed to the homogenization of the microstructures after annealing.The soft magnetic performance of as-printed samples was further enhanced by recrystallization annealing(e.g,,the saturation magnetization increased from 60?64 emu/g to 78 emu/g,and the coercivity decreased from 2.5 Oe to 1.5 Oe),which was believed to be due to the residual-stress relief,the increased proportion of coarsened grains,the reduction of low angle grain boundary density,the elimination of cellular walls,and the re-homogenization of elemental compositions.The obstruction of domain wall movement by grain boundary density and grain boundary arrangement in different directions explains the existence of magnetic anisotropy,which has been improved after annealing but still exists.(3)Lightweight thin-walled structures:Thin-walled structures and thin-walled honeycomb structures with different horizontal angle and thickness were printed.The formability,microstructures and tensile properties of thin-walled structures with different structural characteristics were compared and analyzed,and the compression behavior of the thin-walled honeycomb structures was further researched then via experiment and numerical simulation,which might provide technical support for designing the magnetic shielding structure of 3D printed FOG filled with lightweight structures.It could be concluded that the relative density of thin-walled structures decreases as the angle increases.Compared with the bulk samples,the relative density and surface roughness affects the mechanical properties of SLMed thin-walled structures.As the angle increases,the compressive performance of thin-walled honeycomb structures was gradually improved,and the angle between the cells where the stress is concentrated was the starting point for structural failure.The differences between the experimental verification and numerical simulation results of the compression process indicates that the forming quality(surface roughness,micro-forming defects,etc.)are critical to meeting the mechanical performance service requirements of lightweight magnetic shielding structures.This research might provide support for the applications of "Structure-Function integration"and "Design-Danufacture integration" additive manufacturing technology for soft magnetic alloy and complex magnetic shielding structures in such important fields as power mechanical and electrical equipment,nuclear power equipment,aviation and aerospace equipment.