Patent Publication Number: US-2019180896-A1

Title: Aluminum alloy particle with a permanent magnet core

Description:
BACKGROUND 
     Many directed energy deposition processes use metallic powders/particles as the feedstock material. In these processes, a thin layer of powder is distributed across a build platform and subjected to an energy input from a laser (or other energy source) to fuse the layer. The process is repeated until the desired component is formed. Manufactured components are often subjected to post-manufacturing processes like machining to further refine the component. 
     When permanent magnetic materials are used in a feedstock, the resulting components can be brittle and difficult to machine. Adding aluminum alloys to the feedstock can improve the workability of a manufactured component, but the reflectivity of some aluminum alloys can interfere with the laser during manufacturing. 
     SUMMARY 
     A particle for use in a powder-based additive manufacturing process includes a magnetic core having a first magnetic permeability, and an aluminum alloy coating surrounding the magnetic core. The aluminum alloy coating has a second magnetic permeability lower than the first magnetic permeability. 
     A three-dimensional magnetic component includes an aluminum alloy matrix, and a plurality of particles dispersed throughout the matrix. Each of the particles includes a magnetic core having a first magnetic permeability, and an aluminum alloy coating surrounding the magnetic core. The aluminum alloy coating has a second magnetic permeability lower than the first magnetic permeability. 
     A method of making a three-dimensional magnetic component includes applying a layer of a feedstock to a build substrate, and fusing the layer using an energy source. The feedstock includes a plurality of magnetic particles having a permanent magnetic core and an aluminum alloy coating surrounding the permanent magnetic core. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-section of a particle suitable for use in a powder-based additive manufacturing process. 
         FIG. 2  is a magnified cross-section of a portion of a magnetic component. 
         FIG. 3  is a cross-section of a magnetic component. 
         FIG. 4  is a cross-section of an alternative magnetic component. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention is directed to particles for use as a feedstock for manufacturing magnetic components. The particles include a magnetic core coated with an aluminum-silicon alloy. The particles can further include an optional outer silicon coating. The particles can be included in a feedstock used to produce a magnetic component. An aluminum alloy powder can be added to the feedstock to enhance an aluminum matrix surrounding the fused particles. The resulting components have a more robust microstructure and can be formed with more complex geometries than those produced using current manufacturing methods and materials. 
       FIG. 1  is an enlarged cross-section of magnetic particle  10 . Particle  10  includes magnetic core  12  and aluminum-silicon coating  14  surrounding core  12 . Particle  10 , as shown, also includes coating  16 , although exemplary embodiments of particle  10  do not require coating  16 . Core  12  is formed from a sintered powder of magnetic material. The material can be a permanent magnetic material formed from rare earth elements. For example, core  12  can be formed from an alloy of samarium or neodymium. Other suitable permanent magnet materials, such as ceramics, ferrites, and manganese bismuth are contemplated herein. 
     Coating  14  is an aluminum alloy of a composition that is considered suitable for welding added to enhance the material properties of particle  10 . For example, such alloys experience less solidification cracking than other materials. Suitable alloys for coating  14  can be Al12Si, AlSi10Mg, Aluminum 356.0, or Aluminum 357.0, to name a few, non-limiting examples. Other alloys, such as a 6000 series aluminum alloy, are contemplated herein. Coating  14  has low magnetic permeability (μ) compared to core  12 , such that coating  14  does not interfere with a magnetic field generated within core  12 . 
     Coating  14  can be applied to core(s)  12  using a fluidized bed powder coating process, during which heated cores  12  are immersed in a container of an aluminum-silicon alloy powder, or are passed through a cloud of electrically charged powder. Coating  14  can alternatively be applied using a mechanical dry coating process, such as ball milling. Other suitable coating techniques are contemplated herein. 
     Coating  16  is a silicon-based coating that can be applied to increase the silicon content of particle  10 . For example, a 6000 series aluminum alloy has a lower silicon content (compared to other coating  14  materials), so an embodiment using such an alloy for coating  14  can benefit from the addition of coating  16 . Coating  16  can be applied using one of the methods described above with respect to coating  14 . Alternatively, coating  16  can be applied using a chemical vapor deposition (CVD) process. Coatings  14  and/or  16  can, but do not always, coat the entire surface of core  12 /coating  14 . The extent to which each coating  14  and/or  16  covers the underlying surface will depend on, for example, surface imperfections or the coating process used. 
     Particle  10  can have a spherical or near-spherical shape in order to optimize particle packing when forming a component. Particle  10  can have a diameter (d) ranging from 15 μm to 150 μm. The diameter can range from 40 μm to 45 μm in an exemplary embodiment. The diameter of particle  10  depends on such factors as the number and thickness of coatings applied over core  12 , or the build parameters for the desired component. 
       FIG. 2  is a magnified, three-dimensional cross-section showing a portion of magnetic component  18 , formed as an aluminum metal matrix composite. As can be seen in  FIG. 2 , particles  10  are contained within matrix  20 . Matrix  20  is an aluminum matrix that can be formed by adding a supplemental aluminum powder material to the feedstock containing particles  10 . It is also considered that the supplemental aluminum powder can be introduced into component  18  separately, but concurrent with particles  10 . The supplemental powder material can be formed from an aluminum alloy, such as the aluminum-silicon alloys used to form coating  14 . Other suitable aluminum alloys are contemplated herein. 
     The density (p) of component  18  (the number or particles  10  per cubic volume) can be tailored depending on the requirements of component  18 . Density can range from, for example, 25% to 74%, depending on factors such as particle distribution and size, as well as the magnetic material used and the magnetic field requirements of component  18 . For example, if component  18  needs only to be weakly magnetic, it can be made to be less dense than components for other applications. In an exemplary embodiment, particles  10  can be of uniform size and distribution. In other embodiments, however, particles  10  can be arranged in a less ordered fashion, and/or can vary in size, depending on the desired mechanical properties or the manufacturing process used. 
     Component  18  can be formed using a powder-based, directed energy deposition process, using a feedstock of particles  10  and the supplemental aluminum alloy powder. The feedstock is deposited as a thin layer onto a build substrate, and a laser (or other energy source) fuses the layer. The process is repeated to form component  18 . Component  18  can be formed to have various geometries, and can include straight or curved sides. For example, a cross-sectional shape of component  10  can be rectangular or crescent shaped, as is shown in  FIGS. 3 and 4 , respectively. Other cross-sectional shapes, such as a circle, ellipse, star, or polygon are contemplated herein. Component  18  can undergo post-manufacturing machining to smooth edges, create surface enhancements, etc. Finally, component  18  can be magnetized using an electric current. Component  18  can be incorporated into, for example, a permanent magnetic generator. 
     The disclosed particles can be used to form components having improved mechanical properties, and can allow for the manufacture of components having complex geometries. The disclosed components can be used in a variety of applications, including aerospace, automotive, and other transportation industries. 
     Discussion of Possible Embodiments 
     The following are non-exclusive descriptions of possible embodiments of the present invention. 
     A particle for use in a powder-based additive manufacturing process includes a magnetic core having a first magnetic permeability, and an aluminum alloy coating surrounding the magnetic core. The aluminum alloy coating has a second magnetic permeability lower than the first magnetic permeability. 
     The particle of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     The above particle can further include a silicon-based coating surrounding the aluminum alloy coating. 
     In any of the above particles, the magnetic particle can have a spherical or near-spherical shape. 
     In any of the above particles, a particle diameter can range from 15 μm to 150 μm. 
     In any of the above particles, a particle diameter can range from 40 μm to 45 μm. 
     In any of the above particles, the magnetic core can be formed from a permanent magnetic material. 
     In any of the above particles, the permanent magnetic material can include a rare earth element. 
     In any of the above particles, the aluminum alloy coating can include a material selected from the group consisting of Al12Si, AlSi10Mg, C356, C357, and combinations thereof. 
     A three-dimensional magnetic component includes an aluminum alloy matrix, and a plurality of particles dispersed throughout the matrix. Each of the particles includes a magnetic core having a first magnetic permeability, and an aluminum alloy coating surrounding the magnetic core. The aluminum alloy coating has a second magnetic permeability lower than the first magnetic permeability. 
     In the above component, a density of the particles within the matrix can range from 25% to 74%. 
     In any of the above components, the aluminum alloy matrix and the aluminum alloy coating can be formed from the same material. 
     Any of the above components can further include a silicon-based coating surrounding the aluminum alloy coating. 
     In any of the above components, a cross-sectional shape of the component can include a straight portion. 
     In any of the above components, a cross-sectional shape of the component can include a curved portion. 
     A method of making a three-dimensional magnetic component includes applying a layer of a feedstock to a build substrate, and fusing the layer using an energy source. The feedstock includes a plurality of magnetic particles having a permanent magnetic core and an aluminum alloy coating surrounding the permanent magnetic core. 
     The above method can further include repeating the steps of applying the layer and fusing the layer to form the three-dimensional component. 
     Any of the above methods can further include machining the three-dimensional component. 
     Any of the above methods can further include magnetizing the three-dimensional component using an electric current. 
     In any of the above methods, the feedstock can further include an aluminum alloy powder. 
     In any of the above methods, each of the particles can further include a silicon-based coating surrounding the aluminum alloy coating. 
     While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.