阅读说明：本技术 一种基于激光选区熔化的合金增材制造控制系统及方法 (Alloy additive manufacturing control system and method based on selective laser melting ) 是由 杨永强 周瀚翔 于佳明 刘子欣 宋长辉 樊胜杰 于 2021-09-27 设计创作，主要内容包括：本发明公开了一种基于激光选区熔化的合金增材制造控制系统及方法,其中控制系统包括：激光发射模块,用于输出激光；成型室,包括用于制造所需工件的成型缸；绕组模块,用于向所述成型缸提供交变磁场。本发明提供一种基于交变磁场的合金激光选区熔化增材制造细晶强化的方案,通过复合场作用抑制铝合金枝晶沿热扩散方向的织构,阻断外延生长,实现晶粒细化和定向凝固,从而对组织性能进行强化。本发明可广泛应用于激光熔化技术领域。(The invention discloses an alloy additive manufacturing control system and method based on selective laser melting, wherein the control system comprises: the laser emission module is used for outputting laser; a forming chamber including a forming cylinder for manufacturing a desired workpiece; and the winding module is used for providing an alternating magnetic field for the forming cylinder. The invention provides a scheme for manufacturing fine crystal reinforcement by selective melting and material increase of an alloy laser based on an alternating magnetic field, which inhibits the texture of aluminum alloy dendrite along the thermal diffusion direction through the action of a composite field, blocks epitaxial growth, and realizes grain refinement and directional solidification, thereby reinforcing the texture performance. The invention can be widely applied to the technical field of laser melting.)

1. An alloy additive manufacturing control system based on selective laser melting, comprising:

the laser emission module is used for outputting laser;

a forming chamber including a forming cylinder for manufacturing a desired workpiece;

and the winding module is used for providing an alternating magnetic field for the forming cylinder.

2. The laser selective melting based alloy additive manufacturing control system of claim 1, wherein the alloy comprises at least one of a copper alloy, an aluminum alloy, or an aluminum magnesium alloy.

3. The laser selective melting-based alloy additive manufacturing control system according to claim 1, wherein the winding module comprises an electromagnet winding and a control circuit;

the control circuit is used for controlling the electromagnet winding to output an alternating magnetic field with a preset waveform;

the preset waveform is a square wave, a triangular wave, a triangle-like waveform or a sine wave.

4. The system of claim 3, wherein the predetermined waveform is a triangle-like waveform;

the control circuit comprises a first waveform input circuit and a second waveform input circuit which have the same circuit structure;

a first square wave is input into the input end of the first waveform input circuit, the first output end of the first waveform input circuit is connected with the first end of the electromagnet winding, and the second output end of the first waveform input circuit is connected with the second end of the electromagnet winding;

a second square wave is input into the input end of the second waveform input circuit, the first output end of the second waveform input circuit is connected with the second end of the electromagnet winding, and the second output end of the second waveform input circuit is connected with the first end of the electromagnet winding;

the first square wave and the second square wave differ by half a period.

5. The alloy additive manufacturing control system based on selective laser melting of claim 4, wherein the first waveform input circuit comprises an optical coupler device and an NMOS tube;

the first square wave is used as the input of the optical coupler, the output of the optical coupler is connected with the grid electrode of the NMOS tube, the drain electrode of the NMOS tube is connected with the first end of the electromagnet winding, and the source electrode of the NMOS tube is connected with the second end of the electromagnet winding.

6. The system of claim 3, wherein the installation angle of the electromagnet winding is adjustable according to the crystal texture direction of the alloy.

7. An alloy additive manufacturing control method based on selective laser melting is applied to an alloy additive manufacturing control system based on selective laser melting according to any one of claims 1 to 6, and is characterized by comprising the following steps of:

controlling a laser emitting module to generate laser to melt the alloy;

and controlling the winding module to generate an alternating magnetic field to the forming cylinder, acting in the molten pool, so as to inhibit the texture of the alloy dendrite along the thermal diffusion direction, block epitaxial growth and realize grain refinement and directional solidification.

8. The alloy additive manufacturing control method based on selective laser melting according to claim 7, wherein the control winding module generates an alternating magnetic field to the forming cylinder to act on the molten pool, and the method comprises the following steps:

the alternating magnetic field acts on the molten pool to generate induction current in the molten pool;

generating a lorentz force on the alloy dendrite based on the induced current;

and changing the texture of the dendritic crystal along the thermal diffusion direction based on the Lorentz force, and blocking the growth of the dendritic crystal.

9. The method for controlling the additive manufacturing of the alloy based on the selective laser melting as claimed in claim 8, wherein the induced current is distributed not perpendicular to the magnetic field direction but close to perpendicular to the easy magnetization axis direction of the crystal due to the influence of the crystal magnetic anisotropy in the alloy.

10. The method of claim 8, wherein the Lorentz force changes the alignment of fine crystals in the melt to make the direction of the easy axis of the crystals parallel to the direction of the alternating magnetic field.

Technical Field

The invention relates to the technical field of laser melting, in particular to an alloy additive manufacturing control system and method based on selective laser melting.

Background

Selective Laser Melting (SLM) is a major technical approach in the additive manufacturing of metallic materials. The technology selects laser as an energy source, scans layer by layer on a metal powder bed layer according to a planned path in a three-dimensional CAD slicing model, achieves the effect of metallurgical bonding by melting and solidifying the scanned metal powder, and finally obtains the metal part designed by the model.

During the solidification of the melt, the crystals are all solidified along the direction of the thermal gradient to form elongated columnar crystals or dendrites. In the additive manufacturing, due to the fast cooling speed, the main temperature gradient is along the construction direction (layer-by-layer stacking direction), which may cause the crystal to grow along the construction direction, which is not favorable for the improvement of the mechanical property. Such as: in the case of aluminum alloy, the aluminum alloy is a face-centered cubic crystal, so that it is aligned along the <100> crystal direction when grown in the structural direction, which is disadvantageous in improving the performance.

Disclosure of Invention

To at least some extent solve one of the technical problems in the prior art, it is an object of the present invention to provide a system and a method for controlling additive manufacturing of an alloy based on selective laser melting.

The technical scheme adopted by the invention is as follows:

a laser selective melting based alloy additive manufacturing control system comprising:

the laser emission module is used for outputting laser;

a forming chamber including a forming cylinder for manufacturing a desired workpiece;

and the winding module is used for providing an alternating magnetic field for the forming cylinder.

Further, the alloy includes at least one of a copper alloy, an aluminum alloy, or an aluminum magnesium alloy.

Further, the winding module comprises an electromagnet winding and a control circuit;

the control circuit is used for controlling the electromagnet winding to output an alternating magnetic field with a preset waveform;

the preset waveform is a square wave, a triangular wave, a triangle-like waveform or a sine wave.

Further, the preset waveform is a triangle-like waveform;

the control circuit comprises a first waveform input circuit and a second waveform input circuit which have the same circuit structure;

a first square wave is input into the input end of the first waveform input circuit, the first output end of the first waveform input circuit is connected with the first end of the electromagnet winding, and the second output end of the first waveform input circuit is connected with the second end of the electromagnet winding;

a second square wave is input into the input end of the second waveform input circuit, the first output end of the second waveform input circuit is connected with the second end of the electromagnet winding, and the second output end of the second waveform input circuit is connected with the first end of the electromagnet winding;

the first square wave and the second square wave differ by half a period.

Further, the first waveform input circuit comprises an optical coupler device and an NMOS tube;

the first square wave is used as the input of the optical coupler, the output of the optical coupler is connected with the grid electrode of the NMOS tube, the drain electrode of the NMOS tube is connected with the first end of the electromagnet winding, and the source electrode of the NMOS tube is connected with the second end of the electromagnet winding.

Further, the installation angle of the electromagnet winding can be adjusted according to the crystal texture direction of the alloy.

The other technical scheme adopted by the invention is as follows:

an alloy additive manufacturing control method based on selective laser melting is applied to the alloy additive manufacturing control system based on selective laser melting, and comprises the following steps:

controlling a laser emitting module to generate laser to melt the alloy;

and controlling the winding module to generate an alternating magnetic field to the forming cylinder, acting in the molten pool, so as to inhibit the texture of the alloy dendrite along the thermal diffusion direction, block epitaxial growth and realize grain refinement and directional solidification.

Further, the control winding module generates an alternating magnetic field to the forming cylinder to act on the molten pool, and comprises:

the alternating magnetic field acts on the molten pool to generate induction current in the molten pool;

generating a lorentz force on the alloy dendrite based on the induced current;

and changing the texture of the dendritic crystal along the thermal diffusion direction based on the Lorentz force, and blocking the growth of the dendritic crystal.

Further, due to the influence of crystal magnetic anisotropy in the alloy, the distribution of the induced current is not perpendicular to the direction of the magnetic field, but approaches to be perpendicular to the direction of the easy magnetization axis of the crystal.

Further, the Lorentz force changes the arrangement of fine crystals in the fusant, so that the direction of the easy magnetization axis of the crystals is parallel to the direction of the alternating magnetic field.

The invention has the beneficial effects that: the invention provides a scheme for manufacturing fine crystal reinforcement by selective melting and material increase of an alloy laser based on an alternating magnetic field, which inhibits the texture of aluminum alloy dendrite along the thermal diffusion direction through the action of a composite field, blocks epitaxial growth, and realizes grain refinement and directional solidification, thereby reinforcing the texture performance.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following description is made on the drawings of the embodiments of the present invention or the related technical solutions in the prior art, and it should be understood that the drawings in the following description are only for convenience and clarity of describing some embodiments in the technical solutions of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to these drawings without creative efforts.

FIG. 1 is a schematic structural diagram of an alloy additive manufacturing control system based on selective laser melting according to an embodiment of the present invention;

FIG. 2 is a circuit diagram of a control circuit according to an embodiment of the present invention;

FIG. 3 is a schematic diagram illustrating the mechanism of action of an alternating magnetic field on long-branched crystals in the embodiment of the present invention;

FIG. 4 is a schematic diagram of an embodiment of the present invention after an alternating magnetic field has acted on the dendrites;

FIG. 5 is a schematic diagram showing the effect of an alternating magnetic field on fine crystal orientation in an embodiment of the present invention.

Detailed Description

Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the accompanying drawings are illustrative only for the purpose of explaining the present invention, and are not to be construed as limiting the present invention. The step numbers in the following embodiments are provided only for convenience of illustration, the order between the steps is not limited at all, and the execution order of each step in the embodiments can be adapted according to the understanding of those skilled in the art.

In the description of the present invention, it should be understood that the orientation or positional relationship referred to in the description of the orientation, such as the upper, lower, front, rear, left, right, etc., is based on the orientation or positional relationship shown in the drawings, and is only for convenience of description and simplification of description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus, should not be construed as limiting the present invention.

In the description of the present invention, the meaning of a plurality of means is one or more, the meaning of a plurality of means is two or more, and larger, smaller, larger, etc. are understood as excluding the number, and larger, smaller, inner, etc. are understood as including the number. If the first and second are described for the purpose of distinguishing technical features, they are not to be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated or implicitly indicating the precedence of the technical features indicated.

In the description of the present invention, unless otherwise explicitly limited, terms such as arrangement, installation, connection and the like should be understood in a broad sense, and those skilled in the art can reasonably determine the specific meanings of the above terms in the present invention in combination with the specific contents of the technical solutions.

As shown in fig. 1, the present embodiment provides an alloy additive manufacturing control system based on selective laser melting, including:

the laser emission module is used for outputting laser;

a forming chamber 1 including a forming cylinder 2 for manufacturing a desired workpiece;

and the winding module is used for providing an alternating magnetic field for the forming cylinder 2.

In the system of the embodiment, the texture of the alloy dendrite along the thermal diffusion direction is inhibited through the action of a composite field (the energy field of laser and an alternating magnetic field), the epitaxial growth is blocked, the grain refinement and the directional solidification are realized, and the texture performance is enhanced. The system is suitable for metal materials with high-temperature conductivity, such as aluminum alloy, copper alloy, aluminum magnesium alloy and the like.

The laser emitting module generates laser and emits the laser to the metal powder in the forming cylinder to melt the metal powder. Referring to fig. 1, the laser module includes a galvanometer, a collimator, a field lens, a fiber laser, and the like, and these devices may be implemented by using existing apparatuses, which are not described herein again. Referring to fig. 1, a forming cylinder 2, a powder cylinder, a lifting device and a scraper are arranged in a forming chamber 1, the powder cylinder is used for placing metal powder, the lifting device enables the metal powder in the powder cylinder to overflow a preset surface through upward movement, and the scraper is controlled to push the overflowing metal powder to a preset position in the forming cylinder. The selective laser melting additive manufacturing is layered manufacturing, namely, firstly laying a layer of powder, then carrying out laser processing, then laying a layer of powder, then carrying out laser processing, and repeating the steps in such a way to finally obtain the required workpiece.

The laser acts on the metal powder to melt the metal powder and form a molten pool. The alternating magnetic field acts on the molten pool, the texture of the dendritic crystal along the thermal diffusion direction is changed through the Lorentz force generated by induced current around the dendritic crystal arm of the alloy, the growth of the dendritic crystal is blocked, and the fine-grained nucleation in the molten pool is facilitated. Due to the influence of crystal magnetic anisotropy, the distribution of induced current is not completely perpendicular to the direction of the magnetic field, but approaches to be perpendicular to the direction of the easy magnetization axis of the crystal. Lorentz force generated by the induction current changes the arrangement of fine crystals in the melt, so that the direction of the easy magnetization axis of the crystals is parallel to the direction of the alternating magnetic field. In some optional embodiments, in the laser selective melting additive manufacturing, a vertical alternating magnetic field is applied, so that fine-grain strengthening and directional solidification of alloy forming can be completed, and a desired microstructure is obtained.

Referring to fig. 2, in some alternative embodiments, the waveform of the alternating magnetic field is a triangle-like waveform, and the winding module includes an electromagnet winding and a control circuit; the control circuit is used for controlling the electromagnet winding to output an alternating magnetic field with a preset waveform.

The control circuit comprises a first waveform input circuit and a second waveform input circuit which have the same circuit structure;

the input end of the first waveform input circuit inputs a first square wave, the first output end of the first waveform input circuit is connected with the first end of the electromagnet winding, and the second output end of the first waveform input circuit is connected with the second end of the electromagnet winding; the input end of the second waveform input circuit inputs a second square wave, the first output end of the second waveform input circuit is connected with the second end of the electromagnet winding, and the second output end of the second waveform input circuit is connected with the first end of the electromagnet winding; the first square wave and the second square wave differ by half a period.

The first waveform input circuit comprises an optical coupler device and an NMOS tube; the first square wave is used as the input of the optical coupler, the output of the optical coupler is connected with the grid of the NMOS tube, the drain of the NMOS tube is connected with the first end of the electromagnet winding, and the source of the NMOS tube is connected with the second end of the electromagnet winding.

As shown in fig. 2, the control circuit includes two waveform input circuits with the same structure, and the main devices of the waveform input circuits include an optocoupler, an NMOS transistor, and the like. Two groups of positive-zero square waves (with a half period difference, see fig. 2, waveforms a and B on the middle and left sides) are used for controlling a driving power supply of the electromagnet, and the obtained waveforms are similar to triangular waves (theoretically, near simple harmonics, because of magnetizing and demagnetizing processes, the front half section of the simple harmonics is an approximate straight line, so that the two waveforms are overlapped to form an approximate triangular waveform, see fig. 2, C waveform on YC, and YC is an electromagnet winding).

In some alternative embodiments, the installation angle of the electromagnet winding can be adjusted according to the crystal texture direction of the alloy; the direction of the magnetic field, i.e. the direction of the windings, changes the texture direction when the crystal solidifies.

The system implementation mechanism comprises two parts: 1) the fine grain strengthening, the acting force acting on the fine grain strengthening is electromagnetic force (Lorentz force), the electromagnetic force is generated by the interaction of induction current and magnetic field, but not generated by thermoelectric current and magnetic field in static magnetic field mode, so the induction current distribution plane is basically vertical to the magnetic field, the force acts on the dendrite of the alloy, the thick dendrite can be deflected, the stability of the top of the surface crystal can be damaged, the epitaxial growth can be blocked, and fine cell crystal nucleus can be easily formed in the molten pool, thereby realizing the purpose of fine grain strengthening. Moreover, the triangular wave represents a periodic change in the direction of the magnetic field, and can improve anisotropy, change the initial directional solidification state, and suppress the <100> crystal plane index, thereby enhancing performance. The mechanism is schematically shown in fig. 3 and 4; in fig. 3, when the alternating magnetic field is not applied, the crystal is solidified in the direction of the thermal gradient, i.e., in the vertically upward direction, and when the alternating magnetic field is added, an induced current and lorentz force are generated, thereby changing the direction of solidification, as shown in fig. 4.

2) Realize the shaping of materials with special function reinforcement, such as strength, electric conductivity or thermal conductivity. The crystal arrangement along the characteristic crystal direction brings special performance, taking mechanical properties as an example, the preferred arrangement of the face-centered cubic crystal along the <101> direction has performance advantages compared with the <100>, and the strength is greatly increased. When an alternating magnetic field acts on a molten pool, the induced current distribution plane is influenced by an easy magnetization axis, a certain included angle exists between an equivalent current loop and the plane perpendicular to the magnetic field, and the free crystal grains can be deflected by electromagnetic force, so that the plane is perpendicular to the magnetic field, and transient balance is achieved. Referring to fig. 5, this effect is primarily on the free fine crystals, which can be seen in fig. 4 with irregularly shaped free cells, without significantly affecting the (long) dendrites.

The operation of the above system is explained in detail with reference to specific embodiments.

1) Overview of the Equipment

The additive manufacturing completes the manufacturing of the metal part in a layer-by-layer stacking mode, and the rapid forming of the complex structural part can be realized. The laser is combined with the auxiliary magnetic field, so that the epitaxial growth of crystal branches can be blocked, and an ideal microstructure and performance can be obtained. The application of the method is realized by means of a selective laser melting device, and a vertical alternating magnetic field generator is modified on the basis of the selective laser melting device, and the schematic diagram is shown in figure 1. The alternating magnetic field is controlled by a pulse signal given by the singlechip and is driven by an optical isolation and NMOS tube. The two sets of control pulse control signals are both positive-zero level, and differ by 1/2 cycles, and generate positive and negative levels after passing through the control circuit (as shown in fig. 2). And measuring the alternating magnetic induction intensity by a Gaussian magnetometer and an oscilloscope. Due to the existence of the iron core in the winding, the obtained alternating magnetic field is triangular wave, and the frequency is consistent with the frequency of the control signal. When the frequency of the input control signal is 300Hz, the obtained alternating magnetic field has an amplitude of 0.4mT and an effective value of 0.2 mT.

2) Directional solidification and fine grain strengthening

Due to the rapid cooling of the molten pool in the selective laser melting manufacturing process, the dendrites in the structure can be directionally solidified along the direction of the thermal gradient, and a texture with a <100> crystal orientation can be formed when the metal material is in a cubic structure. The long-branched crystal epitaxially grown along the <100> crystal orientation can significantly affect the mechanical properties of the part and reduce the reliability of the part. Meanwhile, fine structures are difficult to obtain in the manufacturing process of the aluminum alloy, and the strength of parts is limited. The Lorentz force generated by the alternating magnetic field can strengthen the convection of the molten mass, reduce the temperature gradient and control the thickening of crystal grains in the solidification process, thereby obtaining a sample with excellent performance.

According to the faraday's law of electromagnetic induction, when the magnetic flux through the molten pool changes, an equivalent induced current is generated. The magnitude of the induced current is related to the electric field strength and the conductivity. In the mushy zone of the molten bath, the electric field strength E can be determined from the maxwell equation:

wherein B is the magnetic induction intensity, and the right equation is the magnetic induction intensity change rate.

Current density J_IEThis can be obtained from equation 2:

J_IE＝σ_sE (2)

wherein sigma_sFor solid conductivity, E is the electric field strength. Since the solid phase and the liquid phase exist in the mushy zone at the same time, and the electrical conductivity of the solid is much greater than that of the liquid, it can be considered that the current density of the solid dendrite region is much greater than that of the molten region. Lorentz force F under the action of induced current and magnetic field_IEThe plane on which the equivalent current is applied is obtained from equation 3. Unlike the distribution of the thermoelectric current along the direction of the thermal gradient, F_IECan act on the bottom and the top of the dendritic crystal at the same time and is far greater than the thermoelectric magnetic force F_TE When the induced current acts on a single dendrite, the Lorentz force borne by the dendrite is in an equilibrium state; when the induced current acts on a plurality of dendrites, the Lorentz force borne by the dendrites is in an unbalanced state, and the direction can be judged by a left-hand rule and is perpendicular to the current direction and the magnetic field direction.

WhereinIs the effective magnetic induction (vector).

The parameters of the aluminum alloy used are shown in Table 1.

TABLE 1

In casting and additive manufacturing, the metal is directionally solidified along the direction of thermal gradient, which is generally considered when the Lorentz force is greater than 1 × 10⁵N/m³It is sufficient to change the direction and morphology of the dendrite solidification. The lorentz force (induced electromagnetic force) generated by the induced current obtained according to equation 3 can be 1 × 10⁶N/m³The deflection, the crushing and the thinning of the dendrite can be completed. In the SLM additive manufacturing process, the dendrite of the aluminum alloy in the molten pool is along the direction of the thermal gradient<100>Crystal orientation and significant epitaxial growth occurs. The induced electromagnetic force can make the fine crystal of the molten pool mushy zone free to be easy to nucleate after the dendrite is broken. When the orientation of the free crystal is not aligned with the growth direction of the dendrite, the growth of the dendrite is also blocked, and thus the grains in the structure can be effectively refined. By inhibition<100>Epitaxial growth of crystal orientation, enhancement<101>The crystal face index of the aluminum alloy can effectively improve the strength and the plasticity of the aluminum alloy. The action schematic is shown in fig. 3 and fig. 4. Due to the magnetocrystalline anisotropy, the induced current is not distributed exactly perpendicular to the magnetic field but at a small angle. When the induced electromagnetic force acts on the small crystal unit, the crystal unit is forced to rotate, and when the plane where the induced current is located is vertical to the direction of the magnetic field, the stress balance is achieved, so that the directional solidification of fine grains is realized, and the action mechanism is shown in fig. 5.

The embodiment also provides an alloy additive manufacturing control method based on selective laser melting, which is applied to the alloy additive manufacturing control system based on selective laser melting, and comprises the following steps:

s1, controlling the laser emitting module to generate laser to melt the alloy;

s2, controlling the winding module to generate an alternating magnetic field to the forming cylinder, acting on the molten pool to inhibit the texture of alloy dendrite along the thermal diffusion direction, blocking epitaxial growth, and realizing grain refinement and directional solidification.

As a further alternative, the winding module is controlled to generate an alternating magnetic field to the forming cylinder, and the alternating magnetic field acts on the molten pool, and the method comprises the following steps:

the alternating magnetic field acts on the molten pool to generate induction current in the molten pool;

generating a lorentz force on the alloy dendrite based on the induced current;

based on Lorentz force, the texture of the dendritic crystal along the thermal diffusion direction is changed, and the growth of the dendritic crystal is blocked.

Further as an alternative embodiment, the distribution of the induced current is not perpendicular to the direction of the magnetic field, but approaches perpendicular to the direction of the easy axis of the crystal due to the influence of the crystal magnetic anisotropy in the alloy.

Further as an alternative embodiment, the lorentz force changes the arrangement of fine crystals in the melt so that the direction of the easy magnetization axis of the crystals is parallel to the direction of the alternating magnetic field.

The embodiment discloses a method for manufacturing and forming materials with high-temperature conductivity, such as copper, aluminum and the like by applying an alternating magnetic field to selective laser melting additive manufacturing. The texture of the aluminum alloy dendrite along the thermal diffusion direction is inhibited through the action of the composite field, the epitaxial growth is blocked, and the grain refinement and directional solidification are realized, so that the texture performance is enhanced. The method is suitable for metal materials with high-temperature conductivity, such as aluminum alloy, copper alloy, aluminum magnesium alloy and the like. The alternating magnetic field acts on the molten pool, and the texture of the dendritic crystal along the thermal diffusion direction is changed through the Lorentz force generated by the induced current around the dendritic crystal arm, so that the growth of the dendritic crystal is blocked, and the fine-grained nucleation in the molten pool is facilitated. Due to the influence of crystal magnetic anisotropy, the distribution of induced current is not completely perpendicular to the direction of the magnetic field, but approaches to be perpendicular to the direction of the easy magnetization axis of the crystal. Lorentz force generated by the induction current changes the arrangement of fine crystals in the melt, so that the direction of the easy magnetization axis of the crystals is parallel to the direction of the alternating magnetic field. Therefore, in the selective laser melting additive manufacturing, a vertical alternating magnetic field is applied, so that the fine-grain strengthening and directional solidification of aluminum alloy forming can be completed, and an ideal microstructure is obtained.

In the foregoing description of the specification, reference to the description of "one embodiment/example," "another embodiment/example," or "certain embodiments/examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

While embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that: various changes, modifications, substitutions and alterations can be made to the embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

While the preferred embodiments of the present invention have been illustrated and described, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.