A friction extrusion deposition solid-phase additive aluminum alloy and its preparation method

Abstract

The present invention relates to a friction extrusion deposition solid-phase additive aluminum alloy and a preparation method thereof. Among them, the preparation method of the friction extrusion deposition solid-phase additive aluminum alloy includes the following steps: preparing a composite powder from aluminum alloy powder and carbon nanotubes; performing cold pressing treatment on the composite powder to obtain a preform; using the preform as a raw material to perform friction extrusion deposition additive manufacturing to obtain an additive part; and performing heat treatment on the additive part to obtain the friction extrusion deposition solid-phase additive aluminum alloy. The present invention is mainly used for preparing a friction extrusion deposition solid-phase additive aluminum alloy with high grain boundary thermal stability, avoiding abnormal grain growth of the additive part during heat treatment, and thus improving the tissue uniformity of the friction extrusion deposition solid-phase additive aluminum alloy.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum alloy preparation, and particularly to a friction extrusion deposition solid-phase additive aluminum alloy and a preparation method thereof. Background Art

[0002] The 6xxx series aluminum alloy has the advantages of high specific strength, good corrosion resistance, easy formability, etc., and is widely used in industries such as aviation, railway, shipbuilding, and automobile. The traditional manufacturing methods are difficult to meet the manufacturing requirements of the 6xxx series aluminum alloy structural parts with gradually increasing complexity, large size, and integrity. Additive manufacturing (AM), due to its unique free-form forming ability, can greatly meet the requirements of high-end equipment and components for high integration, multi-functionality, lightweight, and integration, and is considered a disruptive technology in the manufacturing field. Therefore, it has received great attention and preliminary application in fields such as aerospace.

[0003] Additive friction extrusion deposition (AFED) is a new type of solid-state additive manufacturing technology developed on the basis of additive friction stir deposition (AFSD). Among them, the schematic diagram of the principle of AFSD is as shown in Figure 2 Figure (a) in. AFSD transports raw materials 1 in the form of rods, chips, or powders through a rotating hollow tool 4. The material pushed out from the rotating hollow tool 4 is violently rubbed against the substrate 6 or the deposited material 5 under the action of the axial upsetting force. The raw materials are softened under the action of frictional heat and deformation heat. When the material is extruded to the required width, the shoulder starts to move laterally to form a layer of deposited material. A three-dimensional component is fabricated by selectively adding subsequent deposited layers on the previous deposited layers. And AFED (the schematic diagram of the principle is as shown in Figure 2As shown in Figure (b) therein, first, the raw material 2 in the form of bars, chips, powders, etc. is filled into the non-rotating cavity 3. Under the action of the axial upsetting force, the raw material and the rotating die 7 undergo rapid friction, causing the raw material at the bottom of the cavity to reach the viscoplastic rheological state due to friction and deformation heat. The softened material is extruded like "squeezing toothpaste" at the opening position and deposited on the substrate 9 along a predetermined route, thereby forming the additive layer 8. By depositing layer by layer, the required sample is prepared. During the AFSD and AFED processes, the metal does not melt, which can avoid the formation of solidification defects in the component. The prepared component is dense and has a uniform structure, and has the potential to obtain better mechanical properties than the forged component of the same composition. Compared with AFSD, AFED transfers the friction surface to between the raw material and the rotating die, softens the raw material before it contacts the deposited layer, has stronger tissue regulation ability, and has a smaller acting pressure on the deposited layer, making it more suitable for the additive manufacturing of weak-rigidity complex structures. At the same time, AFED has a larger plastic deformation amount and is more suitable for promoting the uniform distribution of strengthening phases in aluminum-based materials.

[0004] During the AFED process of 6xxx series aluminum alloys, the peak temperature can reach 400 - 580 °C, causing the main strengthening phases to coarsen and re-dissolve, resulting in serious softening of the prepared additive components. The tensile strength is only 50 - 70% of the peak-aged base material. Therefore, solution aging treatment must be carried out after additive manufacturing to improve the mechanical properties of the additive component materials. Due to the fine grains of the additive material, the grain boundary storage energy is relatively high, and during the solution process, the strengthening phase particles dissolve, reducing the pinning effect on the grain boundaries, resulting in abnormal grain growth, which significantly reduces the comprehensive mechanical properties of the additive component. Therefore, the problem of abnormal grain growth during the solution heat treatment process of 6xxx series aluminum alloys after AFED needs to be solved urgently.

[0005] Friction stir welding, AFSD, and AFED technologies are all technologies that achieve deformation during the friction stir process of materials. Currently, the main methods for controlling the stability of the nugget structure in friction stir welding of aluminum alloys at home and abroad mainly include adjusting welding process parameters, adding post-welding deformation processes, and adding elements such as scandium and zirconium to form second-phase particles that can hinder grain boundary movement. However, adding a deformation process after additive manufacturing seriously weakens the near-net-shape forming advantage of the additive technology. And different from traditional friction stir welding and friction stir deposition additive manufacturing, the shear deformation of materials during the AFED process is more significant, and the trend of abnormal grain growth during the subsequent solution process is more obvious. Existing methods are difficult to completely avoid the abnormal grain growth that occurs during the solution treatment process of AFED materials. In addition, 6xxx series aluminum alloys have the highest solution temperature among heat-treatable aluminum alloys, and the trend of abnormal grain growth is more significant.

[0006] Therefore, there is an urgent need to develop methods that can significantly improve the thermal stability of grain boundaries in friction extrusion deposition solid-phase additive 6xxx series aluminum alloys. Summary of the Invention

[0007] In view of this, the present invention provides a friction extrusion deposition solid-phase additive aluminum alloy and a preparation method thereof, mainly aiming to improve the grain boundary thermal stability of the friction extrusion deposition solid-phase additive aluminum alloy.

[0008] To achieve the above object, the present invention mainly provides the following technical solutions:

[0009] On the one hand, an embodiment of the present invention provides a preparation method of a friction extrusion deposition solid-phase additive aluminum alloy, which includes the following steps:

[0010] Step of preparing composite powder: Prepare composite powder from aluminum alloy powder and carbon nanotubes (Carbon nano-tube, CNT); wherein, the mass percentage content of CNT in the composite powder is not less than 0.5wt.% and not more than 5wt.%.

[0011] Step of cold pressing treatment: Perform cold pressing treatment on the composite powder to obtain a preform.

[0012] Step of friction extrusion deposition additive manufacturing: Use the preform as raw material to perform friction extrusion deposition additive manufacturing to obtain an additive part.

[0013] Step of heat treatment: Perform heat treatment on the additive part to obtain a friction extrusion deposition solid-phase additive aluminum alloy.

[0014] Preferably, in the step of preparing composite powder: the aluminum alloy powder is 6xxx series aluminum alloy powder; and / or the aluminum alloy powder includes alloy powder and / or elemental powder; and / or the particle size of the aluminum alloy powder is 10 - 120μm.

[0015] Preferably, in the step of preparing composite powder: the carbon nanotube CNT includes single-walled CNT and / or multi-walled CNT; and / or the diameter of the carbon nanotube is 10 - 80nm and the length is 2 - 50μm; the mass percentage content of CNT in the composite powder is not more than 3wt.%.

[0016] Preferably, use mechanical ball milling and powder mixing method to prepare composite powder from aluminum alloy powder and carbon nanotube CNT; preferably, control the process parameters of mechanical ball milling and powder mixing as follows: the ball milling speed is 200 - 600rpm, the ball milling time is 4 - 10h, and the ball-to-powder ratio is 5:1 - 15:1.

[0017] Preferably, in the step of cold pressing treatment: load the composite powder into a mold and perform cold pressing under a pressure greater than 30MPa to obtain a preform; and / or the preform is in block or rod shape.

[0018] Preferably, in the friction extrusion deposition additive manufacturing step: using the preform as raw material, the preform is fed by a feeding mechanism into a rotating extrusion deposition die. Friction occurs between the preform and the inner surface of the extrusion deposition die. When it reaches the viscoplastic rheological state under the action of friction and deformation heat, it is advanced axially under the action of the feeding mechanism and deposited on the surface of the substrate. After traversing along a predetermined additive path and reciprocating multiple times, an additive part is obtained.

[0019] Preferably, in the friction extrusion deposition additive manufacturing step, the peak temperature needs to satisfy the following formula:

[0020]

[0021] wherein, T is the peak temperature during the additive manufacturing process, with the unit of K; x is the mass fraction of carbon nanotubes CNT in the composite powder; v1 is the feeding speed of the preform, with the unit of mm / min; ω is the rotational speed of the extrusion deposition die, with the unit of rpm; d is the width of the deposition layer, with the unit of mm; v2 is the traversing speed of the extrusion deposition die, with the unit of mm / min; τ is the thickness of a single deposition layer, with the unit of mm; a is a correction factor, and its value range is 1×10 -3 -1.1×10 -3 K / mm 2 ·rpm.

[0022] Preferably, the process parameters of the friction extrusion deposition additive manufacturing step are set as follows: the feeding speed v1 of the preform is 5 - 100 mm / min, preferably 20 - 70 mm / min; the rotational speed ω of the extrusion deposition die is 200 - 1000 rpm, preferably 300 - 600 rpm; the traversing speed v2 of the extrusion deposition die is 20 - 500 mm / min, preferably 100 - 300 mm / min; the thickness τ of a single deposition layer is 0.3 - 3 mm, preferably 0.5 - 1.5 mm.

[0023] Preferably, for the process parameter setting in the friction extrusion deposition additive manufacturing step, the peak temperature of the friction extrusion deposition additive manufacturing should be below 540 °C, preferably 100 - 540 °C.

[0024] Preferably, the heat treatment step includes:

[0025] Solution treatment: heating the additive part to 500 - 540 °C, holding for 0.2 - 5 hours, and then quenching in water to room temperature to obtain the additive part after solution treatment;

[0026] Artificial aging treatment: heating the additive part after solution treatment to 100 - 240 °C, holding for 1 - 30 hours, and then cooling to room temperature to obtain the friction extrusion deposition solid-phase additive aluminum alloy.

[0027] In another aspect, an embodiment of the present invention provides a friction extrusion deposition solid-phase additive aluminum alloy, wherein the friction extrusion deposition solid-phase additive aluminum alloy is prepared by the preparation method of the friction extrusion deposition solid-phase additive aluminum alloy described in any one of the above.

[0028] Preferably, the average grain size range of the friction extrusion deposition solid-phase additive aluminum alloy is 0.5 - 15 μm.

[0029] Preferably, in the friction extrusion deposition solid-phase additive aluminum alloy: the carbon nanotubes have a complete structure and are evenly distributed; the precipitation phases are mainly needle-shaped nano-precipitation phases β″. It should be noted here that: the complete structure and even distribution of the carbon nanotubes contribute to improving the thermal stability.

[0030] Preferably, the average tensile strength of the friction extrusion deposition solid-phase additive aluminum alloy reaches 300 - 450 MPa.

[0031] Compared with the prior art, a friction extrusion deposition solid-phase additive aluminum alloy and its preparation method of the present invention have at least the following beneficial effects:

[0032] On the one hand, an embodiment of the present invention provides a preparation method of a friction extrusion deposition solid-phase additive aluminum alloy, which mainly includes the following steps: preparing a composite powder from aluminum alloy powder and carbon nanotubes CNT; wherein, the mass percentage content of carbon nanotubes CNT in the composite powder is not less than 0.5 wt% and not more than 5 wt%; performing cold pressing treatment on the composite powder to obtain a preform; using the preform as a raw material to perform friction extrusion deposition additive manufacturing to obtain an additive part; performing heat treatment on the additive part to obtain a friction extrusion deposition solid-phase additive aluminum alloy. Regarding the above scheme, it should be noted that: by adding CNT to the preparation raw materials of the AFED aluminum alloy additive part, the dispersed CNT pins the grain boundaries, improving the thermal stability of the grain boundaries and avoiding the phenomenon of abnormal grain growth in the AFED aluminum alloy part during subsequent heat treatment, and improving the material tissue uniformity; in addition, the addition of an appropriate amount of flexible CNT does not affect the mechanical processing performance of the aluminum alloy itself and can cooperate with existing subtractive manufacturing means to realize the forming of the final component. Compared with directly performing AFED on the powder, by adding a mixing and cold pressing step before AFED, the effective dispersion of CNT in the additive part is realized, and the process controllability and process stability of AFED are effectively improved; compared with directly using commercial CNT / aluminum alloy bars for AFED, the hot pressing and extrusion processes for bar preparation are omitted, with a shorter process and lower cost.

[0033] Furthermore, an embodiment of the present invention provides a method for preparing a friction extrusion deposition solid-phase additive aluminum alloy. In the friction extrusion deposition additive manufacturing step: The following formula can more intuitively guide the AFED preparation process of aluminum alloys with different CNT contents, avoid a large number of experiments using the trial-and-error method, and avoid the generation of harmful phase Al4C3 caused by the AFED peak temperature being higher than 540 °C (the peak temperature is the key parameter determining whether harmful phase Al4C3 is generated in the additive sample); in addition, the grains are significantly refined by providing nucleation sites and hindering grain growth through CNTs, improving the mechanical properties of the material. The formula is as follows:

[0034]

[0035] where T is the peak temperature during the additive process, in K; x is the mass fraction of carbon nanotubes CNT in the composite powder; v1 is the feeding speed of the preform, in mm / min; ω is the rotational speed of the friction extrusion deposition die, in rpm; d is the width of the deposition layer, in mm; v2 is the transverse movement speed of the friction extrusion deposition die, in mm / min; τ is the thickness of a single deposition layer, in mm; a is a correction factor, with a value range of 1×10 -3 -1.1×10 -3 K / mm 2 ·rpm. On the other hand, an embodiment of the present invention provides a friction extrusion deposition solid-phase additive aluminum alloy, which is specifically prepared by the above-mentioned method for preparing a friction extrusion deposition solid-phase additive aluminum alloy; wherein, the average grain size range of the friction extrusion deposition solid-phase additive aluminum alloy is 0.5 - 15 μm; the structure of the carbon nanotubes is complete and evenly distributed; the precipitated phases are mainly needle-shaped nano-precipitated phases β″. Under the combined strengthening effect of fine grains, carbon nanotubes, and nano-precipitated phases, the average tensile strength of the aluminum alloy reaches 300 - 450 MPa. It can be seen that the friction extrusion deposition solid-phase additive aluminum alloy prepared by the present invention has the advantages of being dense, having a uniform structure, fine grains, and excellent mechanical properties.

[0036] The above description is only an overview of the technical solution of the present invention. In order to be able to understand the technical means of the present invention more clearly and implement it according to the content of the specification, the following takes the preferred embodiments of the present invention and describes them in detail in conjunction with the accompanying drawings as follows. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is a schematic diagram of the preparation process of a method for preparing a friction extrusion deposition solid-phase additive aluminum alloy provided by an embodiment of the present invention;

[0038] Figure 2 is a schematic diagram of the principles of friction stir deposition additive manufacturing technology and friction extrusion additive manufacturing technology, where Figure 2Figure (a) in it is the schematic diagram of friction stir deposition additive manufacturing technology; Figure 2 Figure (b) in it is the schematic diagram of friction extrusion deposition additive manufacturing;

[0039] Figure 3 It is the physical diagram of the additive part prepared in Example 1 of the present invention;

[0040] Figure 4 It is the microstructural diagram of the additive part sample prepared in Example 1 of the present invention; among them, Figure 4 Figure (a) in it is the metallographic diagram of the additive part sample before solution treatment; Figure 4 Figure (b) in it is the metallographic diagram of the additive part sample after solution treatment; Figure 4 Figure (c) in it is the EBSD grain morphology diagram of the additive part sample after solution treatment;

[0041] Figure 5 It is the TEM diagram of the additive part sample after solution aging heat treatment prepared in Example 1 of the present invention; among them, Figure 5 Figure (a) in it shows the distribution and morphology of CNT; Figure 5 Figure (b) in it is the bright field image obtained along the <100> zone axis, showing the distribution and morphology of the precipitated phase

[0042] Figure 6 It is the microstructural diagram of the additive part sample prepared in Comparative Example 1 of the present invention; among them, Figure 6 Figure (a) in it is the metallographic diagram of the additive part sample before solution treatment; Figure 6 Figure (b) in it is the metallographic diagram of the additive part sample after solution treatment; Figure 6 Figure (c) in it is the EBSD grain morphology diagram of the additive part sample after solution treatment;

[0043] Figure 7 It is the macroscopic morphology diagram of the additive part sample prepared in Comparative Example 3;

[0044] Figure 8 It is the TEM diagram of the additive part sample prepared in Comparative Example 4. Detailed implementation manners

[0045] To further elaborate on the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following combines the drawings and preferred embodiments to detail the specific implementation manners, structures, features and their effects of the application according to the present invention. In the following description, different "one embodiment" or "embodiment" do not necessarily refer to the same embodiment. In addition, the specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0046] The present invention provides a friction extrusion deposition solid-phase additive aluminum alloy and a preparation method thereof, aiming to solve the problem that current friction extrusion deposition solid-phase additive aluminum alloys (such as 6xxx series aluminum alloys) are prone to abnormal grain growth during the solution treatment process. Existing means are difficult to completely avoid the problem of abnormal grain growth during the solution treatment of AFED materials. The present invention proposes a method to improve the thermal stability of the grain boundaries of friction extrusion deposition solid-phase additive aluminum alloys. CNTs are introduced into the aluminum alloy matrix. Under the intense stirring action of AFED, the CNTs are dispersed, pinning the grain boundaries, enhancing the thermal stability of the grain boundaries, significantly suppressing the abnormal grain growth during the solution process, and obtaining AFED additive components with fine and uniform microstructure and excellent mechanical properties.

[0047] It should be noted here that: The specific surface area of CNTs is extremely large, and they have a large aspect ratio, which makes CNTs prone to agglomeration, difficult to be effectively dispersed, and hinders the exertion of their pinning effect. Therefore, before AFED, CNTs must be added to the aluminum alloy powder by mixing to form a composite powder, and the pre-dispersion of CNTs must be achieved. Before AFED, preparing the composite powder into a bulk preform can avoid the problems of difficult process parameter control and unstable process during direct AFED of the composite powder.

[0048] The introduction of CNTs makes the fluidity of the aluminum alloy during the AFED process worse. To ensure good fluidity and formability of the deposited material, AFED generally needs to be carried out under a higher heat input. However, a higher heat input will exacerbate the interfacial reaction between CNTs and the Al matrix, generating a brittle and easily hydrolyzed Al4C3 phase. Therefore, it is necessary to strictly control the AFED heat input to achieve stable and good forming of the CNT-containing phase aluminum alloy at a lower AFED peak temperature.

[0049] The specific scheme of the present invention is as follows:

[0050] The present invention provides a preparation method of a friction extrusion deposition solid-phase additive aluminum alloy, as Figure 1 shown, mainly including the following steps:

[0051] Step of preparing composite powder: Prepare a composite powder from aluminum alloy powder and CNTs.

[0052] Among them, the aluminum alloy powder can be alloy powder and / or elemental powder.

[0053] The aluminum alloy powder is 6xxx series aluminum alloy powder. Correspondingly, the alloy powder includes aluminum alloy powders such as 6061, 6063, 6082, etc. with Al, Mg, Si as the main alloying elements and intermediate alloy powders constituting the 6xxx series aluminum alloy; correspondingly, the elemental powder includes elemental powders composed of elements contained in the 6xxx series aluminum alloy such as Al powder, Mg powder, Si powder, Cu powder, etc.

[0054] The diameter of the aluminum alloy powder is 10 - 120 μm. The CNT is single-walled CNT, multi-walled CNT, or a combination of the above materials; wherein, the mass fraction of CNT in the composite powder is not less than 0.5 wt.%, and not more than 5 wt.%, preferably not more than 3 wt.%; the diameter of the CNT is 10 - 80 nm, and the length is 2 - 50 μm.

[0055] The composite powder is obtained by mechanical ball milling. Among them, the ball milling speed is 200 - 600 rpm, the ball milling time is 4 - 10 h, and the ball-to-material ratio is 5:1 - 15:1.

[0056] Cold pressing treatment step: cold press the composite powder to obtain a preform.

[0057] Specifically, load the composite powder into a steel mold and perform cold pressing treatment under a pressure greater than 30 MPa to obtain a preform (the preform is block-shaped or rod-shaped).

[0058] Friction extrusion deposition additive manufacturing step: using the preform as a raw material, perform friction extrusion deposition additive manufacturing to obtain an additive part.

[0059] The preform is deposited layer by layer on the surface of the substrate by friction extrusion deposition additive manufacturing. It can be understood that according to the different shapes and sizes of the additive part, the traveling path of the corresponding mold for friction extrusion deposition additive manufacturing is also different. The specific operation can be as follows: use the preform as a raw material and send it into a non-rotating cavity. Under the action of the feeding mechanism, the preform is sent to a high-speed rotating extrusion deposition mold. The preform and the inner surface of the extrusion deposition mold undergo high-speed friction. The preform near the extrusion deposition mold reaches the viscoplastic rheological state due to friction and deformation heat, and is axially advanced under the action of the feeding mechanism and deposited on the surface of the substrate. It is laterally translated along a predetermined additive path and reciprocated multiple times to obtain an AFED component.

[0060] The process parameters are reasonably matched according to the following formula to control the AFED peak temperature below 540 °C to reduce the generation of the Al4C3 phase. The formula is as follows:

[0061]

[0062] Among them, T is the peak temperature during the additive manufacturing process, with the unit of K, x is the mass fraction of carbon nanotube CNT in the composite powder; v1 is the feeding speed of the preform, with the unit of mm / min; ω is the rotation speed of the extrusion deposition mold, with the unit of rpm; d is the width of the deposition layer, with the unit of mm; v2 is the lateral translation speed of the extrusion deposition mold, with the unit of mm / min; τ is the thickness of a single-layer deposition layer, with the unit of mm; a is a correction factor, and its value range is 1×10 -3 -1.1×10 -3 K / mm2 · rpm.

[0063] Among them, the feeding speed is controlled at 5 - 100 mm / min, preferably 20 - 70 mm / min; the rotation speed of the deposition mold is controlled at 200 - 1000 rpm, preferably 300 - 600 rpm; the transverse movement speed of the deposition mold is controlled at 20 - 500 mm / min, preferably 100 - 300 mm / min; the thickness of a single deposition layer is 0.3 - 3 mm, preferably 0.5 - 1.5 mm.

[0064] Heat treatment step: Heat-treat the additive manufactured part to obtain a friction extrusion deposition solid-phase additive manufactured aluminum alloy.

[0065] Perform subsequent solution treatment and artificial aging treatment on the additive manufactured part. The solution heat treatment is specifically heating to 500 - 540 °C and holding for 0.2 - 5 hours, and then quenching in water to room temperature; after the solution treatment, perform artificial aging treatment: heating to 100 - 240 °C for artificial aging treatment for 1 - 30 hours, and then cooling to room temperature.

[0066] In summary, a friction extrusion deposition solid-phase additive manufactured aluminum alloy and its preparation method proposed by the present invention, by adding an appropriate amount of CNT to the aluminum alloy raw material powder, the dispersed CNT pins the grain boundaries, improves the thermal stability of the grain boundaries, avoids abnormal grain growth during the subsequent heat treatment process of the AFED additive manufactured part, and improves the material structure uniformity. Compared with directly performing AFED on the mixed powder, by adding a mixing and cold pressing step before AFED, the effective dispersion of CNT in the additive manufactured part is achieved, and the process controllability and process stability of AFED are effectively improved; compared with directly using commercial CNT / aluminum alloy bars for AFED, the hot pressing and extrusion processes for bar preparation are omitted, the process is shorter and the cost is lower. A prediction formula for the AFED peak temperature of 6xxx series aluminum alloy containing CNT is proposed to guide the adjustment of AFED process parameters. By controlling the AFED peak temperature below 540 °C, the formation of Al4C3 phase is inhibited; and the grains are significantly refined by the way that CNT provides nucleation sites and hinders grain growth, improving the mechanical properties of the material. Compared with adding elements such as Sc and Zr to 6xxx aluminum alloy, CNT has higher thermal stability and stronger pinning ability, which can effectively avoid abnormal grain growth of AFED aluminum alloy parts; compared with adding hard ceramic particles such as SiC and B4C to aluminum alloy, the addition of CNT will not significantly reduce the elongation and machining properties of AFED aluminum alloy materials, and can cooperate with existing subtractive manufacturing means to realize the forming of the final component.

[0067] The following further illustrates the present invention through specific experimental examples:

[0068] Example 1

[0069] In this embodiment, a friction extrusion deposition solid-phase additive manufacturing aluminum alloy is prepared, which mainly includes the following steps:

[0070] Step of preparing composite powder: Take 990 g of 6061 aluminum alloy powder with a mesh size of 300 (where the composition of the 6061 aluminum alloy powder is as follows: Al-1.04Mg-0.67Si-0.33Cu, wt.%) and 10 g of multi-walled CNTs with a diameter of 10 - 15 nm and a length of 2 - 5 μm for ball milling and powder mixing. Among them, the ball milling speed is 300 rpm, the ball milling time is 8 h, and the ball-to-powder ratio is 5:1. After ball milling and powder mixing, a composite powder with a CNT content of 1.0 wt.% (CNT / 6061Al composite powder) is obtained.

[0071] Cold pressing treatment step: Load the composite powder into a steel mold and cold press it into a blank under a pressure of 50 MPa to obtain a preform.

[0072] Friction extrusion deposition additive manufacturing step: Use the preform as the raw material for AFED. Feed the preform into a non-rotating cavity. Under the action of the feeding mechanism, the preform is fed towards a high-speed rotating extrusion deposition die, and high-speed friction occurs between the preform and the upper surface of the extrusion deposition die, causing the preform near the extrusion deposition die to reach the viscoplastic flow state due to friction and deformation heat. The material in the flow state is advanced axially under the action of the feeding mechanism. The rotation speed of the extrusion deposition die, the transverse movement speed of the extrusion deposition die, and the feeding speed of the preform are 520 rpm, 300 mm / min, and 30 mm / min respectively. The thickness of a single deposition layer is 1.4 mm. The material is extruded at the opening of the extrusion deposition die and deposited on a substrate made of matrix alloy along a predetermined route to form a deposition layer. Repeat multi-layer additive manufacturing to obtain an additive manufactured part.

[0073] Heat treatment step: Put the additive manufactured part into a heat treatment furnace for solution heat treatment at a temperature of 530 °C for 2 hours, and then quickly quench the additive manufactured part in water to reduce its temperature to room temperature; put the additive manufactured part cooled to room temperature into a heat treatment furnace for artificial aging treatment at a temperature of 170 °C for 6 hours, and then air cool it to room temperature to obtain the friction extrusion deposition solid-phase additive manufacturing aluminum alloy.

[0074] The macroscopic morphology of the additive manufactured part sample in this embodiment is as Figure 3 shown. The width of the deposition layer is 30 mm, the forming of the additive manufactured part is good, and no obvious holes and crack defects are observed in the additive manufactured part sample.

[0075] The enlarged cross-sectional view of the additive manufactured part sample in this embodiment is as Figure 4 shown in Figure (a). It can be seen that the cross-section of the additive manufactured part sample shows dense bonding between layers and no obvious additive manufacturing marks, which proves that dense 6061 aluminum alloy samples can be produced using this technology.

[0076] Calculations were performed using the AFED peak temperature prediction formula, where x is 1.0 wt.%, v1 is 30 mm / min, ω is 520 rpm, d is 30 mm, v2 is 300 mm / min, τ is 1.4 mm, and a is 1×10 -3 -1.1×10 -3 K / mm 2 ·rpm. The peak temperature T of the AFED process in this example was calculated to be 735 - 808 K, equivalent to 462 - 535 °C, and the measured peak temperature was 522 °C. In the AFED material (i.e., the additive sample), the CNT structure was intact and evenly distributed, and no generation of the Al4C3 phase was observed (see Figure 5 (a) of Figure 4 . After solution heat treatment of the additive sample, no abnormal grain growth was observed, and the average grain size was 1.2 μm (see Figure 5 (b) and (c) of

[0077] . The tensile strengths of the friction extrusion deposition solid-phase additive aluminum alloy obtained after heat treatment along the additive length, width, and height directions were 377 MPa, 378 MPa, and 301 MPa, respectively. The average tensile strength was 352 MPa, and the average elongation was 12.5%.

[0078] Example 2

[0079] The main differences between this example and Example 1 are as follows:

[0080] In the step of preparing the composite powder: The composition of the 6061 aluminum alloy powder is Al - 1.2Mg - 0.6Si - 0.2Cu (wt.%). The ball milling and mixing process is as follows: Take 975 g of 1000-mesh commercial pure Al powder, 12 g of 200-mesh commercial pure Mg powder, 6 g of 200-mesh commercial pure Si powder, 2 g of 400-mesh commercial pure Cu powder, and 5 g of multi-walled CNTs with a diameter of 40 - 60 nm and a length of 5 - 10 μm for ball milling and mixing. The ball milling speed is 300 rpm, the ball milling time is 8 h, and the ball-to-material ratio is 10:1 to obtain a composite powder with a CNT content of 0.5 wt.% (CNT / 6061Al composite powder).

[0081] In the friction extrusion deposition additive manufacturing step: The rotational speed of the extrusion deposition die, the transverse movement speed of the extrusion deposition die, and the feeding speed of the preform are 300 rpm, 200 mm / min, and 30 mm / min, respectively. The single-layer additive thickness is 1.3 mm.

[0082] Others are the same as in Example 1.

[0083] The additive part of this embodiment is well-formed, and the width of the deposited layer is 30 mm.

[0084] Calculations are carried out using the AFED peak temperature prediction formula, where x is 0.5 wt.%; v1 is 30 mm / min; ω is 300 rpm; d is 30 mm; v2 is 200 mm / min; τ is 1.3 mm; a is 1×10 -3 -1.1×10 -3 K / mm 2 ·rpm. The peak temperature T during the AFED process of this embodiment is calculated to be 690 - 759 K, which is equivalent to 417 - 486 °C, and the measured peak temperature is 455 °C. The CNT structure in the AFED material (i.e., the additive part sample) is complete and evenly distributed, and the formation of the Al4C3 phase is not observed. After solution heat treatment of the additive part sample, no abnormal grain growth phenomenon is observed, the average grain size is 0.9 μm, and the needle-like nano-precipitation phase β″ is evenly distributed. After aging treatment, the average tensile strength of the friction stir deposition solid-phase additive aluminum alloy reaches 391 MPa, and the average elongation is 8.0%.

[0085] Example 3

[0086] The main difference between this embodiment and Example 1 is that:

[0087] In the step of preparing the composite powder: the CNT content in the composite powder is 5 wt.%. At the same time, the AFED process in the friction stir deposition additive manufacturing step is fine-tuned: the rotation speed of the extrusion deposition die, the transverse movement speed of the extrusion deposition die, and the feeding speed of the preform are 640 rpm, 300 mm / min, and 30 mm / min respectively, and the single-layer additive thickness is 1.3 mm.

[0088] Others are the same as in Example 1.

[0089] The additive part of this embodiment is well-formed without defects, and the width of the deposited layer is 30 mm. However, due to the high CNT content, the fluidity of the material becomes poor, and it needs to be formed under a higher heat input, resulting in a non-smooth surface of the additive part.

[0090] Calculations are carried out using the AFED peak temperature prediction formula, where x is 5.0 wt.%; v1 is 30 mm / min; ω is 640 rpm; d is 30 mm; v2 is 300 mm / min; τ is 1.3 mm; a is 1×10 -3 -1.1×10 -3 K / mm 2· rpm. The peak temperature T of the AFED process in this embodiment is calculated to be 738 - 811 K, which is equivalent to 465 - 539 °C, and the measured peak temperature is 535 °C. In the AFED material (i.e., the additive part sample), the CNT structure is complete and evenly distributed, and no generation of Al4C3 phase is observed. After solution heat treatment of the additive part sample, no abnormal grain growth is observed, the average grain size is 1.4 μm, and the needle-like nano-precipitation phase β″ is evenly distributed. The tensile strength of the friction extrusion deposition solid-phase additive aluminum alloy obtained after aging treatment reaches 431 MPa, and the average elongation is 4.1%.

[0091] Example 4

[0092] The main difference between this embodiment and Example 1 is that the CNT used in the step of preparing the composite powder is single-walled CNT with a diameter of 1 - 3 nm.

[0093] Others are the same as those in Example 1.

[0094] The formed additive part obtained in Example 4 is in good shape, and the width of the deposition layer is 30 mm.

[0095] Calculation is carried out using the AFED peak temperature prediction formula, where x is 1.0 wt.%; v1 is 30 mm / min; ω is 520 rpm; d is 30 mm; v2 is 300 mm / min; τ is 1.4 mm; a is 1×10 -3 - 1.1×10 -3 K / mm 2 · rpm. The peak temperature T of the AFED process in this embodiment is calculated to be 735 - 808 K, which is equivalent to 462 - 535 °C, and the measured peak temperature is 520 °C. In the AFED material (i.e., the additive part sample), the CNT structure is complete and evenly distributed, and no generation of Al4C3 phase is observed. After solution heat treatment of the additive part sample, no abnormal grain growth is observed, the average grain size is 1.2 μm, and the needle-like nano-precipitation phase β″ is evenly distributed. The average tensile strength of the friction extrusion deposition solid-phase additive aluminum alloy obtained after aging treatment in all directions reaches 340 MPa, and the average elongation is 10.4%.

[0096] Comparative Example 1

[0097] The main difference between this comparative example and Example 2 is that 0.4 wt.% of CNT is added in the step of preparing the composite powder.

[0098] Others are the same as those in Example 2.

[0099] The formed additive part obtained in Comparative Example 1 is in good shape (see Figure 6 (a) figure of

[0100] Calculated using the AFED peak temperature prediction formula, where x is 0.4 wt.%, v1 is 30 mm / min, ω is 300 rpm, d is 30 mm, v2 is 200 mm / min, τ is 1.3 mm, and a is 1×10 -3 -1.1×10 -3 K / mm 2 ·rpm. The peak temperature T of the AFED process in this example was calculated to be 691 - 760 K, equivalent to 418 - 486 °C, and the measured peak temperature was 460 °C. However, due to the too low CNT content, the grain boundary migration could not be effectively hindered, and abnormal grain growth occurred in the additive parts after solution heat treatment (see Figure 6 (b) and (c) of

[0101] Comparative Example 2

[0102] The main difference between this comparative example and Example 1 is that in the step of preparing the composite powder, the CNT content in the composite powder is 6 wt.%; other steps are the same as in Example 1.

[0103] In Comparative Example 2, due to the too high CNT content, the flow resistance of the material during the AFED process was large, the material extrusion was not smooth, resulting in too high extrusion pressure and poor formability of the material. No abnormal grain growth was found in the additive parts after solution heat treatment. The average tensile strength of the friction extrusion deposition solid-phase additive aluminum alloy obtained after aging heat treatment was 456 MPa, and the average elongation was only ~1%, which was difficult to meet the requirements of engineering applications.

[0104] Comparative Example 3

[0105] The main difference between this example and Example 1 is that the cold pressing pressure in the cold pressing treatment step is 25 MPa.

[0106] Others are the same as in Example 1.

[0107] In Comparative Example 3, due to insufficient cold pressing pressure, the powder was loose, the formability of the additive parts was poor, and there were a large number of non-deposited areas on the surface (see Figure 7 shown).

[0108] Comparative Example 4

[0109] The main difference between this comparative example and Example 1 is that

[0110] In the friction extrusion deposition additive manufacturing step, the rotation speed of the extrusion deposition die, the transverse movement speed of the extrusion deposition die, and the feeding speed of the preform are 400 rpm, 200 mm / min, and 26 mm / min respectively, and the single-layer additive thickness is 1.3 mm.

[0111] Others are the same as in Example 1.

[0112] The additive part in Comparative Example 4 was well formed, and the width of the deposited layer was 30 mm.

[0113] Calculations were carried out using the AFED peak temperature prediction formula, where x was 1.0 wt.%; v1 was 26 mm / min; ω was 400 rpm; d was 30 mm; v2 was 200 mm / min; τ was 1.3 mm; a was 1×10 -3 -1.1×10 -3 K / mm 2 ·rpm. The peak temperature T of the AFED process in this example was calculated to be 791 - 871 K, which is equivalent to 518 - 598 °C, and the measured peak temperature was 560 °C. Here, due to the excessively high peak temperature, CNTs in the AFED material (i.e., the additive part sample) were damaged, generating a large amount of Al4C3 phase (see Figure 8 shown). No abnormal grain growth was found in the additive part after solution heat treatment, and the needle-like nano-precipitation phase β″ was evenly distributed. The average tensile strength of the friction stir extrusion deposited solid-phase additive aluminum alloy after aging heat treatment was 316 MPa, and the average elongation was 10.7%. The weakening of the Al4C3 phase would affect the corrosion resistance of the material and it was difficult to meet the requirements of engineering applications.

[0114] Comparative Example 5

[0115] The main difference between this comparative example and Example 1 is that:

[0116] An aluminum alloy with 0.2 wt.% Sc and 0.1 wt.% Zr added on the basis of 6061 aluminum alloy was used as the raw material for AFED.

[0117] Other steps are the same as in Example 1.

[0118] The additive part of Comparative Example 5 was well formed, but the addition of Sc and Zr elements did not significantly improve the grain boundary thermal stability of the AFED aluminum alloy, and abnormal grain growth still existed after solution heat treatment. The average tensile strength of the material after aging treatment was 383 MPa, and the average elongation was 7.2%.

[0119] Table 1 Comparison of performance indexes of materials prepared in Example 1 - Example 4 and Comparative Example 1 - 5

[0120]

[0121] Table 1 shows the comparison of the mechanical properties of the AFED components obtained by selecting different matrix components, different CNT contents, and different raw material preparation methods in the specific implementation manner, and performing AFED and subsequent solution aging treatment, and whether abnormal grain growth occurs during the solution heat treatment process. It can be seen that: compared with the aluminum alloy material without CNT, the AFED aluminum alloy material obtained by the present invention has significantly improved strength and elongation, effectively solves the problem of abnormal grain growth during the solution treatment of the AFED material, and by controlling the AFED peak temperature below 540 °C, the generation of Al4C3 phase is effectively avoided. The aluminum alloy material prepared by the present invention has the characteristics of good strength-plasticity matching and fine and uniform structure, and can break through the size and performance limitations of the aluminum alloy prepared by the traditional method, and has important potential application value in important structural parts such as aviation and aerospace.

[0122] The above is only a preferred embodiment of the present invention, and does not impose any form of limitation on the present invention. Any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A preparation method of a friction extrusion deposition solid-phase additive aluminum alloy, characterized in that, It includes the following steps: Step of preparing composite powder: Prepare composite powder from aluminum alloy powder and carbon nanotube CNT; wherein, the mass percentage content of CNT in the composite powder is not less than 0.5wt.% and not more than 5wt.%; Step of cold pressing treatment: Perform cold pressing treatment on the composite powder to obtain a preform; Step of friction extrusion deposition additive manufacturing: Use the preform as raw material to perform friction extrusion deposition additive manufacturing to obtain an additive manufactured part; Step of heat treatment: Perform heat treatment on the additive manufactured part to obtain friction extrusion deposition solid phase additive aluminum alloy; Wherein, in the step of friction extrusion deposition additive manufacturing, the peak temperature satisfies the following formula: where T is the peak temperature of the additive process, in K, is the mass fraction of carbon nanotubes CNT in the composite powder; is the feeding speed of the preform, in mm / min; is the rotational speed of the extrusion deposition die, in rpm; is the width of the deposition layer, in mm; is the transverse movement speed of the extrusion deposition die, in mm / min; is the thickness of a single deposition layer, in mm; is the correction factor, with a value range of 1×10 -3 -1.1×10 -3 K / mm 2 ·rpm.

2. The preparation method of the friction extrusion deposition solid-phase additive aluminum alloy according to claim 1, characterized in that In the step of preparing composite powder: The aluminum alloy powder is 6xxx series aluminum alloy powder; and / or The aluminum alloy powder includes alloy powder and / or elemental powder; and / or The particle size of the aluminum alloy powder is 10 - 120μm.

3. The preparation method of the friction extrusion deposition solid-phase additive aluminum alloy according to claim 1, characterized in that, In the step of preparing composite powder: The carbon nanotube CNT includes single-walled CNT and / or multi-walled CNT; and / or The diameter of the carbon nanotube is 10 - 80nm and the length is 2 - 50μm; The mass percentage content of CNT in the composite powder is not more than 3wt.%.

4. The preparation method of the friction extrusion deposition solid-phase additive aluminum alloy according to claim 1, characterized in that, Prepare the composite powder from aluminum alloy powder and carbon nanotube CNT by mechanical ball milling and powder mixing method.

5. The preparation method of the friction extrusion deposition solid-phase additive aluminum alloy according to claim 4, characterized in that, The process parameters of mechanical ball milling and powder mixing are controlled as follows: the ball milling speed is 200 - 600rpm, the ball milling time is 4 - 10h, and the ball-to-powder ratio is 5:1 - 15:

1.

6. The preparation method of the friction extrusion deposition solid-phase additive aluminum alloy according to claim 1, characterized in that, In the step of cold pressing treatment: Load the composite powder into a mold and perform cold pressing under a pressure greater than 30MPa to obtain a preform; and / or The preform is in block shape or rod shape.

7. The preparation method of the friction extrusion deposition solid-phase additive aluminum alloy according to claim 1, wherein In the step of friction extrusion deposition additive manufacturing: Use the preform as raw material. Under the action of the feeding mechanism, the preform is fed into the rotating extrusion deposition mold. When the preform undergoes friction with the inner surface of the extrusion deposition mold and reaches the viscoplastic flow state under the action of friction and deformation heat, it advances axially under the action of the feeding mechanism and is deposited on the surface of the substrate. After traversing and reciprocating multiple times along the preset additive manufacturing path, an additive manufactured part is obtained.

8. The preparation method of the friction extrusion deposition solid-phase additive aluminum alloy according to claim 1, characterized in that The process parameters of the friction extrusion deposition additive manufacturing step are set as follows: the feeding speed of the preform is 5 - 100 mm / min; the rotation speed ω of the extrusion deposition die is 200 - 1000 rpm; the transverse movement speed of the extrusion deposition die is 20 - 500 mm / min; the thickness of a single deposition layer is 0.3 - 3 mm.

9. The method for preparing friction extrusion deposition solid phase additive aluminum alloy according to claim 8, wherein The feeding speed of the preform is 20 - 70 mm / min; The rotation speed ω of the extrusion deposition mold is 300 - 600rpm; The transverse movement speed of the extrusion deposition die is 100 - 300 mm / min; The thickness of the single-layer deposition layer is 0.5 - 1.5 mm.

10. The preparation method of the friction extrusion deposition solid-phase additive aluminum alloy according to claim 1, wherein, The process parameters in the step of friction extrusion deposition additive manufacturing are set such that the peak temperature of the friction extrusion deposition additive manufacturing is below 540°C.

11. The preparation method of the friction extrusion deposition solid-phase additive aluminum alloy according to claim 10, characterized in that, The peak temperature of the friction extrusion deposition additive manufacturing is 100 - 540°C.

12. The preparation method of the friction extrusion deposition solid-phase additive aluminum alloy according to claim 1, characterized in that, The heat treatment step includes: Solution treatment: Heat the additive manufactured part to 500 - 540°C, hold for 0.2 - 5 hours, and then water quench to room temperature to obtain the additive manufactured part after solution treatment; Artificial aging treatment: Heat the additive manufactured part after solution treatment to 100 - 240°C, hold for 1 - 30 hours, and then cool to room temperature to obtain friction extrusion deposition solid phase additive aluminum alloy.

13. A friction extrusion deposition solid-phase additive aluminum alloy, characterized in that, The friction extrusion deposition solid phase additive aluminum alloy is prepared by the method for preparing friction extrusion deposition solid phase additive aluminum alloy according to any one of claims 1 - 12.

14. The friction extrusion deposition solid-phase additive aluminum alloy according to claim 13, wherein, The average grain size range of the friction extrusion deposition solid-phase additive aluminum alloy is 0.5 - 15 μm.

15. The friction extrusion deposition solid-phase additive aluminum alloy according to claim 13, wherein In the friction extrusion deposition solid-phase additive aluminum alloy: the carbon nanotubes have a complete structure and are evenly distributed.

16. The friction extrusion deposition solid-phase additive aluminum alloy according to claim 13, wherein The average tensile strength of the friction extrusion deposition solid-phase additive aluminum alloy reaches 300 - 450 MPa.

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