Method for improving interfacial bonding quality of heterogeneous material gradient composite structure in additive manufacturing

Abstract

The present invention provides a method for improving the interfacial bonding quality of a gradient composite structure of heterogeneous materials in additive manufacturing, including: printing a first metal material on a substrate using a first heat source to obtain a first metal layer; printing a second metal material on the surface of the first metal layer using a second heat source to obtain a composite structure of the second metal layer and the first metal layer; heating the surface of the second metal layer using a third heat source to raise the temperature of the interface between the first metal layer and the second metal layer to an expected temperature, and synchronously rolling the surface of the second metal layer using a rolling mill; printing the second metal material on the surface of the second metal layer after the above rolling until a target component is formed. This method does not introduce new intermetallic compounds at the interface of the gradient composite structure, introduces a new third heat source to heat and control the temperature of the second metal layer, and uses a rolling mill to synchronously roll the surface of the second metal layer, effectively eliminating the pore and crack defects at the interface of the heterogeneous material gradient composite structure.

Description

Technical Field

[0001] The present invention relates to the technical field of additive manufacturing, and particularly to a method for improving the interfacial bonding quality of a gradient composite structure of heterogeneous materials in additive manufacturing. Background Art

[0002] With the continuous and rapid development of fields such as China's aerospace, shipbuilding and marine, and automotive industries, the performance requirements for related components, especially main load-bearing components, have been gradually improved, the structures have become increasingly complex and integrated, and single metals or alloys are difficult to meet their requirements for comprehensive material properties. A gradient composite structure refers to a whole structural component made of two metal materials with different properties. By designing the layout of different materials in the structural component, the active regulation of the performance of the gradient composite structure can be achieved. The preparation technologies and processes of the gradient composite structure mainly include laser welding, friction stir welding, explosion welding, diffusion welding, rolling, and additive manufacturing, etc. Additive manufacturing, also known as "3D printing", is a technology for manufacturing components by rapidly forming raw materials under the heating of a focused heat source and accumulating materials layer by layer. Using additive manufacturing technology, objects with complex and customized geometric shapes that cannot be produced by traditional methods can be quickly manufactured. In addition, additive manufacturing can achieve customized regulation of the microstructure and mechanical properties of different regions of the target component.

[0003] There are significant differences in the physical properties of heterogeneous materials such as melting point, thermal conductivity, and thermal expansion coefficient. During the bonding process of heterogeneous materials, defects such as cracks and pores and residual stresses are easily generated; it is difficult to avoid the formation of a large number of brittle intermetallic compound phases during the bonding of heterogeneous materials, which will weaken the mechanical properties of the gradient composite structure. Due to the extremely large temperature gradient in the molten pool during the additive manufacturing process, the micro-region temperature distribution is uneven, and it is easy to form large-area columnar crystal structures and defects such as pores and cracks. The repeated heat input and high cooling rate during the additive manufacturing process result in high residual stresses in the printed parts, which further promotes the generation of interface cracks in the gradient composite structure, making it more difficult to form the gradient composite structure.

[0004] In the prior art, through the method of optimizing process parameters, the interface defects of the additive manufacturing gradient composite structure are reduced; usually, intermediate layers or alloy partitions are prepared between heterogeneous materials by means of welding, laser cladding, hot dip plating, flame wire spraying, etc., to avoid direct contact between different materials, regulate the type of intermetallic compounds at the bonding interface, and inhibit the growth of brittle phases. However, the gradient composite structure prepared only by optimizing process parameters still has problems such as uneven microstructure, anisotropic mechanical properties, and relatively large tensile residual stresses; the addition of intermediate layers or partitions also introduces new intermetallic compounds at the interface of the heterogeneous material gradient composite structure, and the interface composition is still mainly composed of brittle phases, and the problems of defects, uneven organization, and residual stresses cannot be solved. Summary of the Invention

[0005] In view of this, the present invention proposes a method for improving the interfacial bonding quality of additive manufactured heterogeneous material gradient composite structures to solve the problems in the above-mentioned background technology, such as the gradient composite structures prepared only by optimizing process parameters still having problems such as non-uniform microstructure, mechanical property anisotropy, and large tensile residual stress; and the addition of an intermediate layer or partition also introduces new intermetallic compounds at the interface of the heterogeneous material gradient composite structure, the interface composition is still mainly composed of brittle phases, and the problems of defects, non-uniform microstructure, and residual stress cannot be solved.

[0006] The technical solution of the present invention is realized as follows:

[0007] The present invention provides a method for improving the interfacial bonding quality of additive manufactured heterogeneous material gradient composite structures, including:

[0008] Using a first heat source to print a first metal material on a substrate to obtain a first metal layer, where the main elements of the first metal material and the substrate are the same;

[0009] Using a second heat source to print a second metal material on the surface of the first metal layer to obtain a composite structure of the second metal layer and the first metal layer, where the melting point of the second metal material is lower than that of the first metal material, and the main elements of the second metal material and the first metal material are different;

[0010] Using a third heat source to heat the surface of the second metal layer to raise the temperature of the interface between the first metal layer and the second metal layer to an expected temperature, and using a rolling mill to synchronously roll the surface of the second metal layer;

[0011] Using the second heat source to print the second metal material on the surface of the rolled second metal layer until the target component is formed.

[0012] Based on the above technical solutions, preferably, the use of the third heat source to heat the surface of the second metal layer to raise the temperature of the interface between the first metal layer and the second metal layer to an expected temperature specifically includes:

[0013] If an intermetallic compound phase with a melting point lower than the melting points of the two is formed between the main elements of the first metal material and the second metal material, the expected temperature is above the melting point of the intermetallic compound phase but lower than the melting point of the second metal material;

[0014] If the melting point of the intermetallic compound phase formed between the main elements of the first metal material and the second metal material is higher than the melting point of the second metal material, the expected temperature is above 0.3 times the melting point of the intermetallic compound phase but lower than the melting point of the second metal material.

[0015] Based on the above technical solutions, preferably, the use of the rolling mill to synchronously roll the surface of the second metal material includes: under the action of the rolling mill, the surface deformation amount of the second metal layer reaches 5% - 60% of the single-layer printing thickness of the second metal material.

[0016] On the basis of the above technical solutions, preferably, the roll moves synchronously with the third heat source, and the distance between the roll and the third heat source is 2 - 6 cm.

[0017] On the basis of the above technical solutions, preferably, heating the surface of the second metal layer using the third heat source includes: when the third heat source moves, it performs a fast scan synchronously, and the scanning direction is perpendicular to the moving path.

[0018] On the basis of the above technical solutions, preferably, the moving path of the third heat source is the same as or opposite to that when the second heat source prints the second metal material; the moving speed of the third heat source is 2 - 30 mm / s.

[0019] On the basis of the above technical solutions, preferably, the effective heating range of the third heat source is 0.8 - 5 times the width of a single pass when printing the second metal material, and the width of the roll is 0.8 - 1 times the effective heating range of the third heat source.

[0020] On the basis of the above technical solutions, preferably, the first heat source, the second heat source, and the third heat source are moving focused heat sources, and a single heat source or a combined heat source among laser, arc, plasma arc, and ion beam is adopted.

[0021] On the basis of the above technical solutions, preferably, the first metal material is one of nickel and nickel-based alloys, cobalt and cobalt-based alloys, titanium and titanium-based alloys, steel, copper and copper-based alloys, and aluminum and aluminum alloys; the second metal material is one of nickel and nickel-based alloys, cobalt and cobalt-based alloys, titanium and titanium-based alloys, steel, copper and copper-based alloys, aluminum and aluminum alloys, and magnesium and magnesium alloys.

[0022] On the basis of the above technical solutions, preferably, the printing raw material forms of the first metal material and the second metal material are wire or powder.

[0023] The method for improving the interfacial bonding quality of the additive manufacturing heterogeneous material gradient composite structure of the present invention has the following beneficial effects compared with the prior art:

[0024] (1) By printing a second metal material on the surface of the first metal layer using a second heat source, a composite structure of the second metal layer and the first metal layer is obtained. By regulating the interfacial structure between the first metal layer and the second metal layer, the bonding quality between the two is improved, and no new intermetallic compounds are introduced at the interface of the gradient composite structure. The surface of the second metal layer is heated using a third heat source to raise the temperature at the interface between the first metal layer and the second metal layer to the desired temperature. During the additive manufacturing process, a new heat source is introduced to heat and control the temperature at the interface of the heterogeneous material gradient composite structure, fully improving the absorption efficiency of different materials for the heat source. At the same time of heating, a rolling mill is used to synchronously roll the surface of the second metal layer, which can refine and homogenize the interfacial structure while eliminating interfacial defects, eliminate the anisotropy of the mechanical properties at the interface of the gradient composite structure, realize the improvement of the bonding performance at the interface of the additive manufactured heterogeneous material gradient composite structure, effectively eliminate the pore and crack defects at the interface of the heterogeneous material gradient composite structure, and introduce compressive residual stress to inhibit interface cracking;

[0025] (2) If an intermetallic compound phase is formed between the main elements of the first metal material and the second metal material with a melting point lower than the melting points of the two, the desired temperature is above the melting point of the intermetallic compound phase but lower than the melting point of the second metal material, ensuring that the intermetallic compound phase can melt while the second metal layer does not melt;

[0026] When the melting point of the intermetallic compound phase formed between the main elements of the first metal material and the second metal material is higher than the melting point of the second metal material, the desired temperature is above 0.3 times the melting point of the intermetallic compound phase but lower than the melting point of the second metal material, that is, the desired temperature is above the recrystallization temperature of the intermetallic compound phase, ensuring that the intermetallic compound can recrystallize while the second metal layer does not melt, reducing strain;

[0027] Through the above setting of the desired temperature, after synchronously rolling the surface of the second metal layer using a rolling mill, it is possible to refine and homogenize the interfacial structure while eliminating interfacial defects, eliminate the anisotropy of the mechanical properties at the interface of the gradient composite structure, and realize the improvement of the bonding performance at the interface of the additive manufactured heterogeneous material gradient composite structure;

[0028] (3) Under the action of the rolling mill, the surface deformation of the second metal layer reaches 5% - 60% of the single-layer printing thickness of the second metal material to eliminate interfacial defects and densify the structure, and introduce compressive residual stress to the interface or cause the interfacial structure to recrystallize under the action of thermal deformation;

[0029] (4) By synchronously performing rapid scanning when the third heat source moves, and the scanning direction is perpendicular to the moving path, thereby increasing the effective heating range of the third heat source for the interface;

[0030] (5) The effective heating range of the third heat source is 0.8 to 5 times the width of a single pass during the printing of the second metal material, and the width of the rolling mill is 0.8 to 1 times the effective heating range of the third heat source, ensuring that the area rolled by the rolling mill is within the heating range of the third heat source, improving the synchronization of rolling and heating, and enhancing the reliability and stability of the device. Description of the Drawings

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0032] Figure 1 It is a flowchart showing the method for improving the interfacial bonding quality of an additive manufactured heterogeneous material gradient composite structure in an embodiment of the present invention;

[0033] Figure 2 It is a schematic diagram showing the principle of the method for improving the interfacial bonding quality of an additive manufactured heterogeneous material gradient composite structure in an embodiment of the present invention;

[0034] Figure 3 It is a schematic diagram showing the principle of the method for improving the interfacial bonding quality of an additive manufactured aluminum / magnesium gradient composite structure in Application Example 1 of the present invention;

[0035] Figure 4 It is a schematic diagram showing the principle of the method for improving the interfacial bonding quality of an additive manufactured titanium / aluminum gradient composite structure in Application Example 2 of the present invention. Detailed Embodiments

[0036] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0037] Refer to Figures 1-4 As shown, an embodiment of the present invention proposes a method for improving the interfacial bonding quality of an additive manufactured heterogeneous material gradient composite structure, including:

[0038] Step S1: Use a first heat source to print a first metal material on a substrate to obtain a first metal layer, where the main elements of the first metal material and the substrate are the same;

[0039] In step S1, specifically, a first heat source is used to print a first metal material on a substrate to a certain thickness, as shown in (a), (b), and (c) of Figure 2 . The first heat source is a moving focused heat source, and a single heat source or a combined heat source among laser, arc, plasma arc, and ion beam is used. The first metal material is one of nickel and nickel-based alloys, cobalt and cobalt-based alloys, titanium and titanium alloys, steel, copper and copper-based alloys, and aluminum and aluminum alloys. The process parameters used by the first heat source to form the first metal layer are the optimized process parameters when there are no pores and cracks. Figure 2 Before step S1, the following preparatory work is also required: The surface of the substrate is polished successively with 80-mesh, 240-mesh, 500-mesh, and 1000-mesh sandpapers, and then the substrate is fixed on the printing platform through a fixture.

[0040] Before step S1, the following preparatory work is also required: The surface of the substrate is polished successively with 80-mesh, 240-mesh, 500-mesh, and 1000-mesh sandpapers, and then the substrate is fixed on the printing platform through a fixture.

[0041] Step S2: Use a second heat source to print a second metal material on the surface of the first metal layer to obtain a composite structure of the second metal layer and the first metal layer. The melting point of the second metal material is lower than that of the first metal material, and the main elements of the second metal material and the first metal material are different.

[0042] In step S2, specifically, a second heat source is used to print a layer of the second metal material on the surface of the first metal material to obtain the second metal layer, as shown in (d) of Figure 2 . The second metal material is one of nickel and nickel-based alloys, cobalt and cobalt-based alloys, titanium and titanium alloys, steel, copper and copper-based alloys, aluminum and aluminum alloys, and magnesium and magnesium alloys. The second heat source is a moving focused heat source, and a single heat source or a combined heat source among laser, arc, plasma arc, and ion beam is used. The process parameters used by the second heat source to form the second metal material are the optimized process parameters when there are no pores and cracks. Figure 2 In step S2, specifically, a second heat source is used to print a layer of the second metal material on the surface of the first metal material to obtain the second metal layer, as shown in (d) of Figure 2 . The second metal material is one of nickel and nickel-based alloys, cobalt and cobalt-based alloys, titanium and titanium alloys, steel, copper and copper-based alloys, aluminum and aluminum alloys, and magnesium and magnesium alloys. The second heat source is a moving focused heat source, and a single heat source or a combined heat source among laser, arc, plasma arc, and ion beam is used. The process parameters used by the second heat source to form the second metal material are the optimized process parameters when there are no pores and cracks.

[0043] Step S3: Use a third heat source to heat the surface of the second metal layer to raise the temperature of the interface between the first metal layer and the second metal layer to the expected temperature, and use a rolling mill to perform synchronous rolling on the surface of the second metal layer.

[0044] In step S3, as shown in (e) of Figure 2 , the third heat source is a moving focused heat source, and a single heat source or a combined heat source among laser, arc, plasma arc, and ion beam is used. Figure 2 In step S3, as shown in (e) of Figure 2 , the third heat source is a moving focused heat source, and a single heat source or a combined heat source among laser, arc, plasma arc, and ion beam is used.

[0045] Step S4: Use the second heat source to print the second metal material on the surface of the second metal layer after rolling until the target component is formed. The operations in step S4 are as shown in (f), (g), and (h) of Figure 2 . Figure 2 In step S4, the operations are as shown in (f), (g), and (h) of Figure 2 .

[0046] In some embodiments, in step S3, heating the surface of the second metal layer with the third heat source to raise the temperature of the interface between the first metal layer and the second metal layer to the expected temperature specifically includes: If an intermetallic compound phase is formed between the main elements of the first metal material and the second metal material and the melting point of the intermetallic compound phase is lower than the melting points of both of them, the expected temperature is above the melting point of the intermetallic compound phase but lower than the melting point of the second metal material. By setting the expected temperature as above, it is ensured that the intermetallic compound phase can be melted while the second metal layer will not be melted. After synchronously rolling the surface of the second metal layer with a rolling mill, it is possible to refine and homogenize the interface structure while eliminating interface defects, eliminate the anisotropy of the mechanical properties of the gradient composite structure interface, and achieve an improvement in the interface bonding performance of the additive manufacturing heterogeneous material gradient composite structure.

[0047] In other embodiments, in step S3, heating the surface of the second metal layer with the third heat source to raise the temperature of the interface between the first metal layer and the second metal layer to the expected temperature specifically includes: When the melting point of the intermetallic compound phase formed between the main elements of the first metal material and the second metal material is higher than the melting point of the second metal material, the expected temperature is above 0.3 times the melting point of the intermetallic compound phase but lower than the melting point of the second metal material. That is, the expected temperature is above the recrystallization temperature of the intermetallic compound phase, ensuring that the intermetallic compound can undergo recrystallization while the second metal layer will not be melted, reducing strain. After synchronously rolling the surface of the second metal layer with a rolling mill, it is possible to refine and homogenize the interface structure while eliminating interface defects, eliminate the anisotropy of the mechanical properties of the gradient composite structure interface, and achieve an improvement in the interface bonding performance of the additive manufacturing heterogeneous material gradient composite structure.

[0048] In some embodiments, in step S3, synchronously rolling the surface of the second metal material with a rolling mill includes: Under the action of the rolling mill, the surface deformation of the second metal layer reaches 5% - 60% of the single-layer printing thickness of the second metal material. By setting the deformation amount as above, it is possible to eliminate interface defects and densify the structure, introduce compressive residual stress to the interface or cause the interface structure to undergo recrystallization under the action of thermal deformation, inhibit interface cracking, and improve the quality of the gradient composite structure interface.

[0049] In some embodiments, the rolling mill moves synchronously with the third heat source, and the distance between the rolling mill and the third heat source is 2 - 6 cm. The rolling mill is behind the third heat source, and the second metal layer is first heated and then rolled by the rolling mill. Through the distance between the rolling mill and the third heat source, a spacing is formed between the rolling mill and the third heat source, but the spacing is not too large to cause the temperature at the corresponding position to not meet the requirements when the rolling mill reaches the third metal layer, improving reliability and stability.

[0050] In some embodiments, heating the surface of the second metal layer using the third heat source includes: when the third heat source moves, it synchronously performs rapid scanning, and the scanning direction is perpendicular to the moving path. For the case where the interface area between the first metal layer and the second metal layer is large, when the third heat source moves, it synchronously performs rapid scanning, and the scanning direction is perpendicular to the moving path, thereby increasing the effective heating range of the third moving heat source on the interface and improving the heating efficiency.

[0051] In some embodiments, the moving path of the third heat source is the same as or opposite to that of the second heat source when printing the second metal material; the moving speed of the third heat source is 2 - 30 mm / s. Through the setting of the above parameters, the third heat source can uniformly heat the second metal layer while ensuring the heating efficiency and improving the stability and reliability.

[0052] In some embodiments, the effective heating range of the third heat source is 0.8 - 5 times the width of a single pass during the printing of the second metal material, and the width of the rolling mill is 0.8 - 1 times the effective heating range of the third heat source. Through the setting of the above parameters, it is ensured that the second metal layer can be covered by the effective heating range of the third heat source, the entire second metal layer can be heated by the third heat source, the heating uniformity is good, it is ensured that the area rolled by the rolling mill is within the heating range of the third heat source, the synchronization of rolling and heating is improved, and the reliability and stability of the device are improved.

[0053] In some embodiments, the printing raw materials of the first metal material and the second metal material are in the form of wires or powders. The form of the printing raw materials can be wires or powders, which has good compatibility with the form, a wider applicable range, and improved applicability.

[0054] In some embodiments, the first heat source, the second heat source, and the third heat source can be the same heat source during actual use, or can be reasonably selected according to the absorption efficiency of the heat source by the printing material.

[0055] Application Example 1

[0056] This embodiment provides a method for improving the interfacial bonding quality of an additive manufacturing aluminum / magnesium gradient composite structure, as combined with Figure 3 shown, including the following steps:

[0057] Step S11: Use 80 - mesh, 240 - mesh, 500 - mesh, and 1000 - mesh sandpapers to polish the surface of the Al 6061 aluminum alloy substrate in sequence, and then fix the substrate on the printing platform through a fixture;

[0058] Step S12: Print multiple layers of AlSi10Mg aluminum alloy blocks on the substrate using a first laser heat source. The melting point of AlSi10Mg aluminum alloy is 660 °C. The printing raw material AlSi10Mg aluminum alloy is powder with a powder diameter between 5 and 78 μm. The laser power is 275 W, the laser spot diameter is 110 μm, the scanning speed is 1500 mm / s, the scanning pitch is 0.09 mm, and the layer thickness is 0.03 mm;

[0059] Step S13: Print a layer of ZK60 magnesium alloy on the surface of AlSi10Mg aluminum alloy using a second laser heat source, as shown in (a) of Figure 3 . The melting point of ZK60 magnesium alloy is 649 °C. The printing raw material ZK60 magnesium alloy is powder with a powder diameter between 10 and 90 μm. The laser power is 80 W, the laser spot diameter is 80 μm, the scanning speed is 600 mm / s, the scanning pitch is 0.06 mm, and the layer thickness is 0.03 mm. Two kinds of Al-Mg intermetallic compound layers, Al3Mg2 and Al12Mg17, are formed at the interface between AlSi10Mg aluminum alloy and ZK60 magnesium alloy. The melting points of the two Al-Mg intermetallic compound phases, Al3Mg2 and Al12Mg17, are 453 °C and 460 °C respectively. Due to the uneven temperature distribution at different positions of the printed part during the additive manufacturing process and the difference in solidification time in each region of the molten pool, holes exist, and there are different degrees of deformation at different positions of the printed part, resulting in the existence of residual stress. And the Al-Mg intermetallic compound is a brittle phase and will crack under the action of residual stress, as shown in (a) and (b) of Figure 3 ;

[0060] Step S14: Heat the surface of ZK60 magnesium alloy using a third laser heat source. The laser spot diameter is 3 mm, the laser power is 100 W, the scanning speed is 5 mm / s, and the temperature range of the aluminum / magnesium interface layer corresponding to the effective laser heating area is between 460 and 649 °C, so that the Al3Mg2 and Al12Mg17 Al-Mg intermetallic compound layers formed at the interface between AlSi10Mg aluminum alloy and ZK60 magnesium alloy are melted, but the ZK60 magnesium alloy does not melt, as shown in (c) of Figure 3 . Synchronously use a rolling mill to perform hot deformation on the surface of ZK60 magnesium alloy. The reduction amount is 60% of the single-layer thickness of the printed ZK60 magnesium alloy, which is 0.018 mm, and the width of the rolling mill is 3 mm. Under the action of the third laser heat source, the Al-Mg intermetallic compound layer at the interface layer is melted, and the hole and crack defects are reduced and eliminated. Combining the rolling mill pressure to generate hot deformation in the acting area, the hole and crack defects are further eliminated, making the interface structure densified. And during the hot deformation process, the interface structure undergoes recrystallization and is refined and homogenized. In addition, the tensile residual stress in the hot deformation area under the action of the rolling mill pressure is eliminated, and the residual stress state changes to a compressive stress state. Thus, the interface bonding quality of the additive manufacturing aluminum / magnesium gradient composite structure is improved;

[0061] Step S15: Subsequently, continue the additive manufacturing process on the surface of the rolled ZK60 magnesium alloy using the second laser heat source in Step S13 until the component is formed.

[0062] Application Example 2

[0063] This embodiment proposes a method for improving the interfacial bonding quality of an additive manufactured titanium / aluminum gradient composite structure. As shown in Figure 4 the following steps are included:

[0064] Step S21: Use 80-mesh, 240-mesh, 500-mesh, and 1000-mesh sandpapers to polish the surface of the pure titanium substrate in sequence, and then fix the substrate on the printing platform through a fixture;

[0065] Step S22: Use an electron beam heat source to print multiple layers of Ti6Al4V titanium alloy blocks on the substrate. The melting point of Ti6Al4V titanium alloy is 1668 °C. The printing raw material Ti6Al4V titanium alloy is powder with a powder diameter between 50 and 105 μm. The electron beam current is 18 mA, the scanning speed is 2400 mm / s, the scanning spacing is 0.12 mm, and the layer thickness is 0.1 mm;

[0066] Step S23: Use a laser heat source to print a layer of AA5087 aluminum alloy on the surface of Ti6Al4V titanium alloy. The melting point of AA5087 aluminum alloy is 589 °C. As shown in (a) of Figure 4 , the printing raw material AA5087 aluminum alloy is wire with a wire diameter of 1 mm. The laser power is 4000 W, the laser spot diameter is 1.6 mm, the wire feeding speed is 10 m / min, the scanning speed is 1 m / min, the scanning spacing is 1.7 mm, and the layer thickness is 2.4 mm. Three titanium-aluminum intermetallic compound layers of Al3Ti, TiAl, and TiAl3 are formed at the interface between Ti6Al4V titanium alloy and AA5087 aluminum alloy. The melting point of the TiAl phase, which has the highest melting point among the three titanium-aluminum intermetallic compound phases of Al3Ti, TiAl, and TiAl3, is 1456 °C. Due to the uneven temperature distribution at different positions of the printed part during the additive manufacturing process and the difference in solidification time in each region of the molten pool, holes exist, and there are different degrees of deformation at different positions of the printed part, resulting in the existence of residual stress. And the titanium-aluminum intermetallic compound is a brittle phase and will crack under the action of residual stress, as shown in (a) and (b) of Figure 4 ;

[0067] Step S24: Heat the surface of AA5087 aluminum alloy with a laser heat source. The laser spot diameter is 3 mm, the laser power is 500 W, and the scanning speed is 3 mm / s. The temperature range of the effective laser heating area is between 0.3 times the melting point of the titanium-aluminum intermetallic compound phase (437 °C) and the melting point of AA5087 aluminum alloy (589 °C), that is, above the recrystallization temperature of the titanium-aluminum intermetallic compound phase. As shown in (c) of Figure 4 , simultaneously use a rolling mill to perform hot deformation on the surface of AA5087 aluminum alloy. The reduction is 50% of the single-layer thickness of the printed AA5087 aluminum alloy, which is 1.2 mm, and the width of the rolling mill is 3 mm. Under the action of the laser heat source and the rolling mill pressure, thermal deformation and recrystallization occur at the interface between the titanium alloy and the aluminum alloy, and pore and crack defects are reduced or eliminated, and the interface structure becomes denser and more uniform. In addition, the tensile residual stress in the thermally deformed area under the action of the rolling mill pressure is eliminated, and the residual stress state changes to a compressive stress state. Thereby improving the interface bonding quality of the additive manufacturing titanium / aluminum gradient composite structure;

[0068] Step S25: Subsequently, use the laser heat source in Step S23 to continue the additive manufacturing process on the surface of the rolled AA5087 aluminum alloy until the component is formed.

[0069] In summary, a method for improving the interface bonding quality of an additive manufacturing heterogeneous material gradient composite structure provided by the present invention can eliminate pore and crack defects at the interface of the additive manufacturing heterogeneous material gradient composite structure, introduce compressive residual stress to inhibit interface cracking, and specifically control the temperature and thermal deformation of the interface of the heterogeneous material gradient composite structure, which can refine and homogenize the interface structure while eliminating interface defects, eliminate the anisotropy of the mechanical properties of the gradient composite structure interface, and achieve the improvement of the interface bonding performance of the additive manufacturing heterogeneous material gradient composite structure.

[0070] The above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. Method for improving interfacial bonding quality of heterogeneous material gradient composite structure in additive manufacturing, characterized in that, Including: Printing a first metal material on a substrate using a first heat source to obtain a first metal layer, where the main elements of both the first metal material and the substrate are the same; Printing a second metal material on the surface of the first metal layer using a second heat source to obtain a composite structure of the second metal layer and the first metal layer, where the melting point of the second metal material is lower than that of the first metal material, and the main elements of the second metal material and the first metal material are different; Heating the surface of the second metal layer using a third heat source to raise the temperature at the interface between the first metal layer and the second metal layer to an expected temperature, and simultaneously rolling the surface of the second metal layer using a roller; the expected temperature is lower than the melting point of the second metal material; the expected temperature specifically includes: if an intermetallic compound phase with a melting point lower than the melting points of both is formed between the main elements of the first metal material and the second metal material, the expected temperature is above the melting point of the intermetallic compound phase but lower than the melting point of the second metal material; if the melting point of the intermetallic compound phase formed between the main elements of the first metal material and the second metal material is higher than the melting point of the second metal material, the expected temperature is above 0.3 times the melting point of the intermetallic compound phase but lower than the melting point of the second metal material; Printing the second metal material on the surface of the second metal layer after the above rolling using the second heat source until the target component is formed.

2. The method for improving the interfacial bonding quality of the additive manufacturing heterogeneous material gradient composite structure according to claim 1, wherein The simultaneous rolling of the surface of the second metal material using the roller includes: under the action of the roller, the surface deformation amount of the second metal layer reaches 5% - 60% of the single-layer printing thickness of the second metal material.

3. The method for improving the interfacial bonding quality of the gradient composite structure of heterogeneous materials in additive manufacturing according to claim 1, wherein The roller moves synchronously with the third heat source, and the distance between the roller and the third heat source is 2 - 6 cm.

4. The method for improving the interfacial bonding quality of the gradient composite structure of heterogeneous materials in additive manufacturing according to claim 3, wherein The heating of the surface of the second metal layer using the third heat source includes: the third heat source performs rapid scanning synchronously during movement, and the scanning direction is perpendicular to the movement path.

5. The method for improving the interfacial bonding quality of the additive manufacturing heterogeneous material gradient composite structure according to claim 4, wherein The movement path of the third heat source is the same as or opposite to that when the second heat source prints the second metal material; the movement speed of the third heat source is 2 - 30 mm / s.

6. The method for improving the interfacial bonding quality of the additive manufacturing heterogeneous material gradient composite structure according to claim 5, characterized in that The effective heating range of the third heat source is 0.8 - 5 times the single-pass width when the second metal material is printed, and the width of the roller is 0.8 - 1 times the effective heating range of the third heat source.

7. The method for improving the interfacial bonding quality of the gradient composite structure of heterogeneous materials in additive manufacturing according to claim 1, wherein The first heat source, the second heat source, and the third heat source are moving focused heat sources, and a single heat source or a combined heat source among laser, arc, plasma arc, and ion beam is adopted.

8. The method for improving the interfacial bonding quality of the gradient composite structure of heterogeneous materials in additive manufacturing according to claim 1, characterized in that, The first metal material is one of nickel and nickel-based alloys, cobalt and cobalt-based alloys, titanium and titanium-based alloys, steel, copper and copper alloys, aluminum and aluminum alloys; the second metal material is one of nickel and nickel-based alloys, cobalt and cobalt-based alloys, titanium and titanium-based alloys, steel, copper and copper alloys, aluminum and aluminum alloys, magnesium and magnesium alloys.

9. The method for improving the interfacial bonding quality of the gradient composite structure of heterogeneous materials in additive manufacturing according to any one of claims 1-8, characterized in that, The printing raw material forms of the first metal material and the second metal material are wire or powder.

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