Electrode arc additive manufacturing method for aluminum alloy grain refinement based on double-wire composition synergistic regulation

Abstract

The application discloses a kind of based on double wire component synergistic regulation and control electric arc additive aluminum alloy grain refinement method, belong to electric arc additive manufacturing technical field.The method includes: the component height is zoned along deposition direction;Target element content in two wires is determined and deposition component is calculated according to transfer coefficient;Set constant total mass flow, change the proportion of control wire by the complementary adjustment of substrate wire and control wire wire feed amount, so that total flow fluctuation does not exceed ±8%;Real-time acquisition interlayer temperature or molten pool area and dynamically increase the proportion of control wire, synchronously reduce the proportion of substrate wire;Different wire feeding strategies are respectively executed in arc starting, stable and arc closing sections.The application realizes the dynamic matching of deposition component with thermal state, ensures the forming size accuracy, effectively inhibits columnar crystal growth, promotes equiaxed crystal transformation, and improves the uniformity of component organization and mechanical properties.

Description

Technical Field

[0001] This invention relates to the field of materials processing, and specifically to a method for refining the grain size of aluminum alloys produced by arc additive manufacturing based on the synergistic regulation of dual-wire composition. Background Technology

[0002] When aluminum alloys are manufactured by electric arc additive manufacturing (WAAM), the molten pool repeatedly undergoes directional heat dissipation and interlayer reheating along the component direction, which easily forms coarse columnar crystals that penetrate multiple layers, leading to increased anisotropy of the microstructure, susceptibility to hot cracking, and tendency for local segregation.

[0003] Existing grain refinement methods mainly fall into three categories: ① using special welding wires containing Ti, B, Sc, and Zr; ② adding particle-reinforcing phases to the molten pool; ③ applying auxiliary energy fields such as ultrasonic and electromagnetic fields. However, the composition of special welding wires is fixed and cannot be dynamically adjusted according to the differences in heat accumulation at the bottom, middle, and top of the component; adding too few particles or refining elements will result in insufficient effect, while adding too many will form coarse second phases; auxiliary energy fields require additional special devices, and parameter matching is complex.

[0004] Dual-wire arc additive manufacturing can deliver the matrix wire and the control wire separately, but existing methods mostly use a fixed wire feed ratio. As the build-up height increases, the melt pool volume, element burn-off, and solidification rate all change, making it difficult to obtain suitable refining element content in each layer with a fixed ratio. Directly increasing the control wire feed rate will synchronously increase the total deposition amount, causing fluctuations in layer height and wall width, affecting dimensional accuracy. In addition, when the droplet points and arrival times of the two wires are unreasonable, the refining components are prone to local enrichment or incomplete melting, reducing refining efficiency.

[0005] In summary, the existing technology has three main defects: (1) the single wire or fixed double wire ratio cannot adjust the deposition composition according to the thermal state; (2) the change in the control wire ratio is coupled with the change in the total deposition amount, which affects the dimensional accuracy of the component; (3) when the droplet drop point and timing are unreasonable, the distribution of the fine components is uneven and the utilization rate is low. Summary of the Invention

[0006] To address the aforementioned technical problems in existing technologies, the present invention aims to provide a method for refining the grain size of aluminum alloys in arc additive manufacturing based on the synergistic regulation of dual-wire composition. This method involves independently metering and feeding the substrate wire and the control wire, and dynamically changing the ratio of the two wires while maintaining a relatively stable total wire feed mass flow rate. This allows the deposition composition and grain refinement capability to be matched with the interlayer temperature, molten pool state, and component height, thereby achieving uniform grain refinement of the aluminum alloy component along the component direction. Simultaneously, by limiting the distance between the molten droplet landing points and the arrival time sequence of the two wires, the method promotes the uniform mixing of refining components in the molten pool and improves the utilization rate of refining elements.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A method for refining the grain size of aluminum alloys in arc additive manufacturing based on the synergistic regulation of dual-wire composition involves simultaneously feeding a matrix wire and a control wire into the same molten pool during the arc additive manufacturing process. The matrix wire provides the main alloy composition of the component, while the control wire provides grain refinement components. The two wires are controlled by independent wire feeding mechanisms and their mass flow rate is calculated and synergistically adjusted by a controller. The method includes the following steps: Step 1: Based on the 3D model of the component, perform layer slicing and path planning, and divide the construction height along the deposition direction into the substrate influence zone, the stable construction zone, and the heat accumulation zone; Step 2: Determine the mass fraction of the target grain-refining element in the matrix wire and the control wire, and determine the transfer coefficient of each element from the wire to the deposited metal through preliminary experiments. The deposition content of the target grain-refining element j is calculated according to the following formula: C j =(η 1j C 1j m1+η 2j C 2j m2) / (m1+m2); Where m1 and m2 are the mass flow rates of the matrix filament and the control filament, respectively, in g / s; C 1j and C 2j η represents the mass fraction of target element j in the matrix filament and the control filament, respectively, in wt.%; 1j and η 2j , respectively, are the transfer coefficients of target element j in the matrix filament and the control filament, %; Step 3: Set the total mass flow rate M = m1 + m2, and the control wire ratio r = m2 / M; determine the initial control wire ratio r according to the target deposition composition and equation (1), and make complementary adjustments through m1 = M·(1-r) and m2 = M·r so that the fluctuation of the total mass flow rate M does not exceed ±8% when the control wire ratio r changes; Step 4: During the deposition process, collect at least one of the following process characteristic parameters in real time: interlayer temperature, melt pool area, melt pool surface temperature, or build-up height. When the interlayer temperature exceeds the target upper limit or the melt pool area increases relative to the reference value, increase the proportion of control wire within the target composition upper limit range. When the control wire is not fully melted, reduce the control wire feed rate or adjust the droplet landing point. Step 5: The arc section adopts a gradual wire feeding method, the stable section implements closed-loop component adjustment, the corner and arc end sections reduce the total mass flow rate and maintain the target component ratio, the oxide film is cleaned after each layer is deposited, and the next layer is deposited after the interlayer temperature returns to the set range.

[0008] Furthermore, the matrix wire is selected from Al-Cu, Al-Mg, Al-Mg-Si, or Al-Zn-Mg-Cu aluminum alloy wires with a wire diameter of 0.8 mm to 1.6 mm; the control wire is selected from Al-Ti-B, Al-Sc-Zr, Al-Zr, or aluminum-based composite wires containing TiB2 particles with a wire diameter of 0.8 mm to 1.6 mm.

[0009] Furthermore, the two wires are fed into the same molten pool from both sides or front and back of the welding torch, with an included angle of 10° to 80° and a distance of 0mm to 4mm between the molten droplets of the two wires.

[0010] Furthermore, the total wire feed speed is 2m / min to 16m / min, the control wire mass ratio is 2% to 28%, the welding current is 60A to 260A, the arc voltage is 12V to 28V, the travel speed is 2mm / s to 15mm / s, the interpass temperature is 40℃ to 220℃, and the shielding gas flow rate is 12L / min to 35L / min.

[0011] Furthermore, both wires are electrically fused wires, or one is an arc main wire and the other is a cold-filled wire or a hot wire.

[0012] Furthermore, the control wire is made of homogeneous alloy wire, cored wire, particle-reinforced composite wire, or surface-coated wire.

[0013] Furthermore, the dynamic adjustment described in step 4 employs a hierarchical method, a lookup table method, a threshold control method, a proportional-integral method, or a model predictive control method.

[0014] Furthermore, the substrate-affected region is the 1st to 10th layers close to the substrate, the stable construction region is the intermediate region from the substrate-affected region to the heat accumulation region, and the heat accumulation region is the last 10th to 20th layers close to the top of the component.

[0015] Furthermore, the included angle between the two wires is 20° to 45°, the distance between the molten droplets is 1mm to 3mm, and the molten droplet of the control wire is located behind the molten droplet of the base wire.

[0016] Furthermore, the target upper limit of the interlayer temperature mentioned in step 4 is 130℃~150℃. When the interlayer temperature exceeds the target upper limit but is lower than the pause threshold, the control filament feeding speed is increased by 0.03m / min~0.10m / min, and the matrix filament feeding speed is reduced by the corresponding amount. When the interlayer temperature reaches the pause threshold, the deposition is paused, and deposition continues after the interlayer temperature drops to the recovery temperature.

[0017] The advantages and positive effects of this invention are: 1. Dynamic composition control: The deposition composition can be dynamically adjusted according to the construction height and thermal accumulation state, avoiding insufficient or excessive fine components in different areas of the fixed composition filament.

[0018] 2. Decoupling of composition and deposition rate: The complementary control of total mass flow rate and control wire ratio is adopted to adjust the composition without significantly changing the deposition rate per unit length, thereby reducing the fluctuation of layer height and wall width.

[0019] 3. Improve component utilization: By limiting the landing point and arrival position of the twin wires, the control components are brought into the high-temperature convection zone of the molten pool, thereby improving the uniformity of melting and dispersion.

[0020] 4. Wide range of applications: It can be used by combining general-purpose matrix wires with a small amount of high-concentration control wires, and is suitable for a variety of aluminum alloy systems.

[0021] 5. Compared with single-wire deposition, this method can reduce the average grain size of ER2319 aluminum-copper alloy from about 391 μm to about 64 μm and increase the equiaxed grain area fraction from 28.8% to 88.3%. Attached Figure Description

[0022] Figure 1 These are the grain sizes at different locations in Example 1 of this invention; Figure 2 These are the transverse and longitudinal stretching curves of the deposited state in Example 1 of this invention; Figure 3 The grain size is shown at different locations in Comparative Example 1; Figure 4 The grain size is shown at different locations in Comparative Example 2. Detailed Implementation

[0023] The present invention will be further described below with reference to the embodiments and accompanying drawings, but this is not intended to limit the scope of protection of this application.

[0024] The method of the present invention includes the following steps: Step 1: Based on the 3D model of the component, perform layer slicing and path planning, and divide the construction height along the deposition direction into the substrate influence zone, the stable construction zone, and the heat accumulation zone; Step 2: Determine the mass fraction of the target grain-refining elements in the matrix wire and the control wire, and determine the transfer coefficient of each element from the wire to the deposited metal through preliminary experiments. For the target grain-refining element j, its deposition content is calculated according to the following formula: C j =(η 1j C 1j m1+η 2j C 2j m2) / (m1+m2, Where m1 and m2 are the mass flow rates of the matrix filament and the control filament, respectively, in g / s; C 1j and C 2j η represents the mass fraction of target element j in the matrix filament and the control filament, respectively, in wt.%; 1j and η 2j , respectively, are the transfer coefficients of target element j in the matrix filament and the control filament, %; Step 3: Set the total mass flow rate M = m1 + m2, and the control wire ratio r = m2 / M; determine the initial control wire ratio r according to the target deposition composition and equation (1), and make complementary adjustments through m1 = M·(1-r) and m2 = M·r so that the fluctuation of the total mass flow rate M does not exceed ±8% when the control wire ratio r changes.

[0025] Step 4: During the deposition process, collect at least one of the following process characteristic parameters in real time: interlayer temperature, melt pool area, melt pool surface temperature, or build-up height. When the interlayer temperature exceeds the target upper limit or the melt pool area increases relative to the baseline value, increase the proportion of control wire within the target composition upper limit range; when the control wire shows insufficient melting, reduce the control wire feed rate or adjust the droplet landing point position.

[0026] Step 5: In the arc initiation phase, a gradual wire feeding method is used to ensure a smooth establishment of the molten pool; in the stabilization phase, closed-loop composition adjustment is implemented to maintain the target composition stability; in the corner and arc termination phases, the total mass flow rate is reduced while maintaining the target composition ratio. After each layer is deposited, the oxide film is cleaned, and the next layer is deposited only after the interlayer temperature returns to the set range.

[0027] The recommended process range for the method of this invention is as follows: total wire feed speed 2m / min~16m / min, control wire mass ratio 2%~28%, welding current 60A~260A, arc voltage 12V~28V, travel speed 2mm / s~15mm / s, interpass temperature 40℃~220℃, and shielding gas flow rate 12L / min~35L / min.

[0028] Alternative solutions to the present invention include, but are not limited to, the following forms: both wires can be electrically fused wires, or a combination of an arc main wire and a cold-filled wire or a hot wire can be used; the control wire can be a homogeneous alloy wire, a core wire, a particle-reinforced composite wire, or a surface-coated wire; the dynamic adjustment strategy can be the layering method, table lookup method, threshold control method, proportional-integral method, or model predictive control method in the prior art.

[0029] Example 1 This embodiment uses the method of the present invention to prepare ER4043 aluminum-silicon alloy thin-walled components. The specific implementation process is as follows.

[0030] S1. Materials used: The matrix wire is made of ER4043 aluminum alloy wire with a diameter of Φ1.2mm and a nominal composition of Al-5.3Si-0.15Mg-0.15Ti (mass fraction, %). The Ti element in the matrix wire serves as the basic source of grain refinement elements.

[0031] The control wire is an Al-5Ti-1B master alloy wire with a diameter of Φ1.2mm (mass fraction, %), in which the mass fraction of Ti element is 5% and the mass fraction of B element is 1%. The Ti and B elements in the control wire react in the molten pool to generate TiB2 particles and Al3Ti particles, which serve as a heterogeneous nucleation substrate for α-Al and promote the formation of equiaxed crystals.

[0032] The substrate is a 2219-T87 aluminum alloy plate with dimensions of 300mm×150mm×20mm. Before deposition, the oxide film on the substrate surface is removed with a wire brush, and then the surface oil is cleaned with anhydrous ethanol to ensure good metallurgical bonding between the substrate and the first deposition layer. The printed component is a single-pass multi-layer thin-walled part with a length of 180mm, a target width of 8mm, and a target height of 100mm. Based on the component's geometry and the preset layer height, the single-layer lift is set to 1.8mm, and a total of 56 layers are deposited.

[0033] S2, Basic Process Parameters: The pulsed gas metal arc welding power source is used, with an average current of 145A, a peak current of 210A, a base current of 65A, a pulse frequency of 80Hz, and an arc voltage of 18V. The purpose of using pulsed current is to stir the molten pool through the periodically changing arc force, thereby promoting the uniform distribution of refined components.

[0034] The welding torch travel speed is set to 7.0 mm / s; since it is a single-pass multi-layer straight-wall component, there is no need for lateral oscillation, so the welding torch oscillation amplitude is set to 0 mm; the shielding gas is high-purity argon with a purity of 99.999% and a gas flow rate of 22 L / min; the distance from the nozzle to the workpiece is set to 15 mm to ensure arc stability and prevent spatter from clogging the nozzle; the interlayer temperature is controlled within the range of 90℃ to 130℃; after each layer is deposited, an infrared thermometer is used to measure the temperature of the substrate or the surface of the deposited layer; the next layer is deposited when the temperature drops below 130℃.

[0035] S3, Dual-wire feed parameters: Two wires are symmetrically fed in from the left and right sides of the welding torch's forward direction, with each wire making a 35° angle with the central axis of the welding torch. The substrate wire's molten droplet falls in front of the center of the molten pool, while the control wire's molten droplet falls behind the substrate wire's molten droplet, with a 2mm distance between the two drops. This configuration allows the control wire's molten droplet to enter the high-temperature convection zone of the molten pool formed by the substrate wire's molten droplet, utilizing the Marangoni convection of the molten pool and the arc force to achieve rapid dispersion of TiB2 and Al3Ti particles.

[0036] The total wire feeding speed of the two wires is set to be constant at 6.0 m / min to meet the requirement that the total mass flow rate fluctuation does not exceed ±8% in this invention. According to the thermal state differences of different height areas of the component, different control wire ratios are set in different sections, and the total wire feeding speed is kept constant by adjusting the reverse synchronous adjustment of the base wire feeding speed.

[0037] Layers 1 to 10 are the substrate-affected zone: the substrate wire feed speed is set to 5.88 m / min, the control wire feed speed is set to 0.12 m / min, the total wire feed speed is 6.0 m / min, and the control wire mass ratio is 2%. Since this area is close to the substrate, the substrate has a significant thermal conductivity effect, the melt pool cools quickly, the high temperature dwell time is short, and the burning loss of Ti and B elements is less. Therefore, a lower control wire ratio can meet the fineness requirements.

[0038] Layers 11 to 46 are the stable build-up region: the substrate wire feed speed is set to 5.79 m / min, the control wire feed speed is set to 0.21 m / min, the total wire feed speed is 6.0 m / min, and the control wire mass ratio is 3.5%. As the build-up height increases, the thermal conductivity of the substrate weakens, and lateral heat dissipation becomes the main heat dissipation path. The molten pool cooling rate decreases, and the burn-off of Ti and B elements increases slightly. Therefore, the proportion of control wire is appropriately increased to 3.5%. Layers 47-56 are the heat accumulation zone: the substrate wire feeding speed is set to 5.70 m / min, the control wire feeding speed is set to 0.30 m / min, the total wire feeding speed is 6.0 m / min, and the control wire mass ratio is 5%. The top region has the most severe heat accumulation, the molten pool exists for a long time, the burning loss of Ti and B elements increases, and the solidification rate of the molten pool decreases. Stronger compositional supercooling and more heterogeneous nucleation particles are required to suppress columnar crystal growth. Therefore, the proportion of control wire is further increased to 5%.

[0039] In the three sections mentioned above, the substrate filament feed rate and the control filament feed rate exhibit complementary changes: for every 0.09 m / min increase in the control filament feed rate, the substrate filament feed rate decreases by 0.09 m / min simultaneously, maintaining a total feed rate of 6.0 m / min for both filaments. This complementary control method ensures a relatively constant deposition mass per unit length, avoiding fluctuations in layer height and wall width caused by changes in the control filament ratio.

[0040] S4. Dynamic Correction Rules: Infrared thermometers were used to monitor the interlayer temperature in real time before each layer was deposited, and the upper limit of the interlayer temperature control target was set at 130℃.

[0041] When the interlayer temperature is detected to be higher than 130℃ but lower than 150℃, it indicates that the heat accumulation exceeds the target range but has not yet reached a dangerous level. In this case, the following corrective action is taken: the control wire feed speed is increased by 0.06 m / min from the current section's baseline value, while the matrix wire feed speed is simultaneously decreased by 0.06 m / min from the current section's baseline value, maintaining the total wire feed speed at 6.0 m / min. The principle behind this corrective action is that an increase in interlayer temperature means an increase in molten pool superheat and high-temperature residence time, leading to increased burn-off of refining elements and a decrease in nucleation driving force. Therefore, additional refining elements are needed to increase the number of nucleation particles.

[0042] When the interlayer temperature reaches 150°C, the deposition operation is paused, and deposition continues only after the interlayer temperature naturally cools down to 120°C. The principle behind this pause protection measure is that when the interlayer temperature exceeds 150°C, the molten pool becomes severely overheated, and even increasing the proportion of control wires cannot compensate for the loss of refinement effect. Furthermore, prolonged high temperatures will exacerbate the coarsening of the already deposited layer. Therefore, it is necessary to actively interrupt the deposition process to restore a suitable thermal state.

[0043] When the projected area of ​​the molten pool increases by 15% relative to the average value of the stable region, it is determined that the molten pool size has increased abnormally, and the following correction operation is performed: the travel speed is increased from 7.0 mm / s to 7.5 mm / s for a duration of 1.5 s. The principle of this operation is that, under the condition of constant heat input, increasing the travel speed can shorten the arc action time per unit length, reduce the molten pool size, and shorten the high-temperature residence time, thereby mitigating the adverse effects of heat accumulation on the refining effect.

[0044] The rate of change of the control wire feed speed is limited to 0.03 m / (min·s), meaning that the change in the control wire feed speed per second shall not exceed 0.03 m / min. This limitation aims to prevent sudden changes in the control wire feed speed that could lead to droplet transfer instability and arc disturbance.

[0045] S5. Sampling and Testing and Effect Analysis: After deposition, metallographic samples were taken from three heights: 10 mm (representing the bottom region), 50 mm (representing the middle region), and 90 mm (representing the top region) from the substrate. Grain size, equiaxed grain area fraction, Ti / B element distribution, layer width variation, and tensile properties were measured. 1) Grain size and equiaxed grain ratio: like Figure 1As shown, the average grain size at 10 mm from the substrate is 72 μm, with an equiaxed grain area fraction of 84.6%; the average grain size at 50 mm from the substrate is 63 μm, with an equiaxed grain area fraction of 88.9%; and the average grain size at 90 mm from the substrate is 58 μm, with an equiaxed grain area fraction of 91.5%. The average grain size at all three height positions is less than 100 μm, and the equiaxed grain area fraction is greater than 80%.

[0046] The above results show that the method of the present invention achieves a significant grain refinement effect across the entire height range of the component. From bottom to top, the grain size shows a slight decreasing trend, while the equiaxed grain fraction shows a slight increasing trend. This may be related to the higher proportion of control wires (5%) in the top region and the fewer subsequent thermal cycles experienced by the top deposited layer. Overall, the grain size difference among the three heights is small (58μm~72μm), and the microstructure is uniform.

[0047] The mechanism of the aforementioned grain refinement effect is analyzed as follows: During the arc additive manufacturing process, after the Al-5Ti-1B control wire droplet enters the molten pool, Ti and B elements react in the molten pool to generate TiB2 particles and Al3Ti particles. The TiB2 particles have a low lattice mismatch with α-Al, which can serve as an effective heterogeneous nucleation substrate, reducing the nucleation energy barrier and promoting the earlier nucleation of α-Al at higher temperatures. Al3Ti particles can also serve as nucleation particles during the solidification process of the molten pool. With the formation and dispersion of a large number of nuclei in the molten pool, the growth space of each nucleus is mutually restricted, thereby effectively refining the grain size. At the same time, the enrichment of Ti elements at the solid-liquid interface front produces compositional supercooling, which inhibits the preferred growth of columnar crystals and promotes the formation of equiaxed crystals. When the interlayer temperature rises and causes the molten pool to overheat, this method increases the proportion of control wire to supplement more TiB2 nucleation particles and Ti solute elements, thereby compensating for the adverse effects of reduced nucleation efficiency and increased burn-off at high temperatures.

[0048] 2) Element distribution: The average content of Ti in the deposited metal was 0.27 wt.%, and the average content of B was 0.026 wt.%. The standard deviation of Ti content along the height direction was 0.025 wt.%, and the standard deviation of B content along the height direction was 0.006 wt.%, indicating that Ti and B elements were uniformly distributed at different heights of the component, without obvious local enrichment or segregation. This demonstrates that the present invention effectively compensates for the differences in element burn-off in different height regions by setting the proportion of control wires in different sections and combining it with interlayer temperature feedback correction. At the same time, by reasonably limiting the droplet spacing of 2 mm and the included angle of the two wires of 35°, the refining components were fully and uniformly mixed in the molten pool.

[0049] 3) Layer width and height accuracy: The average layer width of the component is 8.07 mm, the layer width fluctuation range is 7.72 mm to 8.43 mm, the maximum width deviation is ±0.43 mm, and the deviation from the target width of 8 mm is +5.4% to -3.5%, which meets the general requirements for the forming accuracy of arc additive manufacturing.

[0050] After deposition, the total height of the component was 100.8 mm, with a cumulative height deviation of +0.8 mm relative to the target height of 100 mm. The high-precision control of layer width and height is achieved thanks to the constant total mass flow rate control strategy of this invention. That is, when the control filament ratio changes, the matrix filament feed speed is adjusted synchronously in the opposite direction to keep the total filament feed speed of the two filaments constant at 6.0 m / min, thereby ensuring the consistency of deposition quality per unit length of each layer.

[0051] 4) Analysis of mechanical property test results: like Figure 2 As shown, the longitudinal tensile strength of the sedimentary sample is 199 MPa, the transverse tensile strength is 196 MPa, and the difference between the longitudinal and transverse tensile strengths is 1.5% (the absolute value of the strength difference is 3 MPa divided by the average value, 197.5 MPa). The longitudinal elongation is 8.7%, and the transverse elongation is 7.9%.

[0052] For aluminum alloy components manufactured by arc additive manufacturing, a difference in longitudinal and transverse tensile strength of less than 10% is generally considered an indicator of effective anisotropy control. In this embodiment, a strength difference of 1.5% indicates that the component's anisotropy has been significantly suppressed, which is consistent with the microstructure characteristics dominated by equiaxed grains.

[0053] Example 2 This embodiment uses the method of the present invention to prepare Al-Zn-Mg-Cu series aluminum alloy thin-walled components. The specific implementation process is as follows.

[0054] S1. Materials used: The base wire is an Al-6.2Zn-2.3Mg-1.6Cu alloy wire with a diameter of Φ1.2mm (mass fraction, %), which belongs to the Al-Zn-Mg-Cu series of high-strength aluminum alloys. This alloy has high strength after aging treatment, but this series of alloys has high requirements for solidification structure control, obvious tendency of columnar grain coarsening, and strong sensitivity to hot cracking.

[0055] The control wire is an Al-2Sc-1Zr alloy wire with a diameter of Φ1.2mm (mass fraction, %), in which the mass fraction of Sc is 2% and the mass fraction of Zr is 1%. During the solidification of the molten pool, Sc and Zr form Al3Sc and Al3Zr particles. These particles have an L12 ordered structure and are coherent or semi-coherent with the α-Al matrix, which can efficiently promote the heterogeneous nucleation of α-Al. In addition, Al3Sc and Al3Zr particles can exist stably during subsequent heat treatment, and produce a pinning effect on grain boundaries, inhibiting recrystallization and grain growth.

[0056] The substrate is a 7075 aluminum alloy plate with dimensions of 250mm×120mm×15mm. The oxide film is removed and the plate is cleaned with anhydrous ethanol before deposition.

[0057] The printed component is a single-pass multi-layer thin-walled part with a length of 150mm, a target width of 10mm, and a target height of 80mm. The single-layer lift is set to 2.0mm, and a total of 40 layers are deposited.

[0058] S2, Process Parameters: The welding power source uses a gas metal arc welding (GMAW) system with an average current of 155A, an arc voltage of 19V, and a travel speed of 6.0mm / s. The shielding gas is high-purity argon with a flow rate of 25L / min. The nozzle-to-workpiece distance is 16mm, and the interpass temperature is controlled within the range of 100℃ to 150℃.

[0059] The total feed rate of the two wires was set to 5.5 m / min and kept constant throughout the deposition process. Different control wire ratios were set for different sections based on the division of different construction zones. Layers 1 to 8 are the substrate-affected zone: the substrate wire feed speed is 5.39 m / min, the control wire feed speed is 0.11 m / min, the total wire feed speed is 5.5 m / min, and the control wire ratio is 2.0%.

[0060] Layers 9 to 25 are the stable construction zone: the matrix filament feeding speed is 5.31 m / min, the control filament feeding speed is 0.19 m / min, the total filament feeding speed is 5.5 m / min, and the control filament ratio is 3.5%.

[0061] Layers 26 to 40 are the heat accumulation zone: the matrix filament feeding speed is 5.23 m / min, the control filament feeding speed is 0.27 m / min, the total feeding speed is 5.5 m / min, and the control filament ratio is 5.0%.

[0062] In the three sections, the feed speed of the matrix filament and the feed speed of the control filament are complementary, and the total feed speed of the two filaments is always kept at 5.5m / min.

[0063] Infrared thermometers are used to monitor the interlayer temperature in real time, and the target control range for the interlayer temperature is set to 100℃~150℃.

[0064] When the interlayer temperature exceeds 145℃, the feed rate of the control yarn is increased by 0.055 m / min from the current section's baseline value, while the feed rate of the matrix yarn is simultaneously decreased by 0.055 m / min from the current section's baseline value, maintaining a total feed rate of 5.5 m / min. This operation continues until the interlayer temperature returns to the target range.

[0065] When the interlayer temperature is below 110℃, restore the baseline control filament ratio and matrix filament feeding speed of the construction zone.

[0066] S3. Post-deposition heat treatment: After deposition, the components are subjected to T6 heat treatment: solution treatment is carried out at 470℃±5℃ for 1 hour, followed by water quenching, and then aging at 120℃±3℃ for 24 hours.

[0067] The purpose of T6 heat treatment is to allow Sc and Zr elements to fully dissolve into the α-Al matrix during the solution treatment process, and to precipitate as nano-sized Al3Sc and Al3Zr particles during the aging process, thereby further improving the strength and thermal stability of the component. At the same time, the recrystallization behavior during the heat treatment process is suppressed by the pinning effect of Sc and Zr elements, which is beneficial to maintaining a fine-grained structure.

[0068] S4. Sampling, Testing, and Effect Analysis After heat treatment, samples were taken from the bottom, middle and top of the component to test the Sc and Zr content, grain size, texture strength and longitudinal and transverse tensile properties.

[0069] 1) The test results show that the Sc content in the bottom region is 0.046 wt.% and the Zr content is 0.024 wt.%; the Sc content in the middle region is 0.061 wt.% and the Zr content is 0.036 wt.%; and the Sc content in the top region is 0.073 wt.% and the Zr content is 0.048 wt.%.

[0070] The maximum difference in Sc content at the three height positions was 0.027 wt.%, which is less than the control limit of 0.03 wt.%, indicating that the method of the present invention maintained a stable distribution of Sc and Zr elements along the construction direction during the process of adjusting the proportion of control fibers from 2.0% to 5.0%, and no local deviation from the target range occurred.

[0071] The contents of Sc and Zr increased from bottom to top, consistent with the design of increasing the proportion of control wire from 2.0% to 5.0%. The standard deviations of Sc and Zr were both small, indicating that the proportion of control wire set in different sections effectively compensated for the differences in element burn-off and dilution at different heights.

[0072] 2) Metallographic examination results show that the average grain size in the bottom region is 68 μm and the equiaxed crystal area fraction is 82.3%; the average grain size in the middle region is 55 μm and the equiaxed crystal area fraction is 87.6%; and the average grain size in the top region is 51 μm and the equiaxed crystal area fraction is 89.1%.

[0073] The average grain size at all three height positions is less than 80 μm, and the equiaxed crystal area fraction is higher than 80%, indicating that in the Al-Zn-Mg-Cu alloy system, the dynamic ratio control of the Sc-Zr control wire can also achieve uniform grain refinement across the entire height range.

[0074] The grain size decreases from bottom to top, which may be related to the increasing content of Sc and Zr: more Sc and Zr elements mean more Al3Sc and Al3Zr nucleation sites, providing more nucleation sites during solidification, thereby further refining the grains. This result also verifies the effectiveness of the dynamic adjustment strategy of this invention—in the top region where heat accumulation is more severe, appropriately increasing the content of refining elements helps to compensate for the reduction in nucleation driving force caused by the slowdown in cooling.

[0075] 3) Texture Intensity Analysis: The maximum texture intensity at the bottom is 3.8, the maximum texture intensity at the middle is 3.5, and the maximum texture intensity at the top is 3.7, all less than 5. Texture intensity is a quantitative indicator characterizing the degree of preferred orientation of crystals; the lower the value, the more random the grain orientation distribution and the lower the risk of anisotropy. In this embodiment, the texture intensity at all three height positions is less than 5, indicating that the continuous growth of columnar crystals is effectively suppressed, and equiaxed crystal structure dominates.

[0076] 4) Tensile property analysis: After heat treatment, the longitudinal tensile strength is 526 MPa, the transverse tensile strength is 501 MPa, and the difference between longitudinal and transverse tensile strength is 4.8%; the longitudinal yield strength is 455 MPa, the transverse yield strength is 434 MPa; the longitudinal elongation is 7.8%, and the transverse elongation is 7.4%.

[0077] After T6 heat treatment, the strengthening of the Al-Zn-Mg-Cu alloy mainly comes from the synergistic strengthening of the MgZn2 (η' phase) precipitated during aging and Al3Sc / Al3Zr nanoparticles. The high-density Al3Sc / Al3Zr particles not only provide grain refinement but also improve the alloy strength through dispersion strengthening and grain boundary pinning effect. The longitudinal and transverse strength difference is only 4.8%, which is much lower than the anisotropy level in the comparative example, indicating that the component prepared by the method of the present invention has good isotropy in mechanical properties.

[0078] To verify the advantages of the technical solution of this invention over the prior art, the following comparative examples are set up: Comparative Example 1: ER4043 matrix filament monofilament deposition ER4043 aluminum alloy monofilament was used for deposition without the addition of control filament; the average current, travel speed and total wire feed speed were kept consistent with those in Example 1; the monofilament feed speed was 6.0 m / min and no composition adjustment was performed.

[0079] Comparative Example 2: Deposition of ER4043 matrix filament and Al-5Ti-1B control filament at a fixed ratio The same ER4043 matrix wire and Al-5Ti-1B control wire as in Example 1 were used. The total wire feed rate was kept constant at 6.0 m / min: the matrix wire feed rate was fixed at 5.79 m / min, the control wire feed rate was fixed at 0.21 m / min, and the control wire ratio was kept constant at 3.5%. No adjustments were made based on interlayer temperature, build-up height, or melt pool state throughout the deposition process, and no dynamic correction rules were implemented. Other process parameters were consistent with those in Example 1.

[0080] Comparative Example 2 reflects the grain refinement effect of dual-wire arc additive manufacturing with a fixed wire feed ratio in the prior art. Compared with the single-wire deposition in Comparative Example 1, the fixed-ratio dual-wire deposition can obtain a finer grain structure in the middle and bottom regions by continuously introducing refining elements. However, due to the inability of the fixed ratio to adapt to the problem of increased burn-off of refining elements and decreased nucleation efficiency when the heat accumulation at the top intensifies, the grain refinement effect in the top region is significantly deteriorated.

[0081] like Figure 3 As shown, the test results of Comparative Example 1 indicate that the average grain size in the bottom region is 315 μm, with an equiaxed crystal area fraction of 35.2%; the average grain size in the middle region is 386 μm, with an equiaxed crystal area fraction of 28.7%; and the average grain size in the top region is 472 μm, with an equiaxed crystal area fraction of 22.4%. From bottom to top, the grain size shows a continuous coarsening trend, the proportion of equiaxed crystals continuously decreases, and the columnar crystal coarsening characteristics are obvious.

[0082] like Figure 4 As shown, the test results of Comparative Example 2 indicate that the average grain size in the bottom region is 78 μm, with an equiaxed crystal area fraction of 85.1%; the average grain size in the middle region is 69 μm, with an equiaxed crystal area fraction of 87.3%; and the average grain size in the top region is 118 μm, with an equiaxed crystal area fraction of 76.6%. The grain refinement effect in the bottom and middle regions is comparable to that of Example 1, but the top region suffers from insufficient refinement due to heat accumulation, resulting in an average grain size increase to 118 μm, a 71% increase compared to the middle region, and a decrease in the equiaxed crystal ratio to 76.6%. Furthermore, the layer width fluctuation range of Comparative Example 2 is 7.58 mm to 8.52 mm (maximum deviation ±0.47 mm), slightly higher than that of Example 1.

[0083] The comparison between Comparative Example 1 and Example 1 shows that single-filament deposition results in significantly coarse grain size and severe anisotropy due to the lack of sufficient heterogeneous nucleation points and compositional supercooling effect. The comparison between Comparative Example 2 and Example 1 shows that while a fixed dual-filament ratio can achieve good grain refinement in the relatively thermally stable bottom and middle regions, it cannot solve the problem of insufficient grain refinement caused by heat accumulation at the top. In contrast, this invention, by setting and controlling the filament ratio in zones and implementing interlayer temperature feedback correction, allows the top region to receive more sufficient refinement elements than the bottom and middle regions, thereby achieving uniform grain refinement across the entire height range.

[0084] The embodiments given above are preferred examples for implementing the present invention, and the present invention is not limited to the above embodiments. Any non-essential additions or substitutions made by those skilled in the art based on the technical features of the present invention are within the protection scope of the present invention.

Claims

1. A method for refining the grain size of aluminum alloys produced by arc additive manufacturing based on the synergistic regulation of dual-wire composition, characterized in that, In the process of arc additive manufacturing, a matrix wire and a control wire are simultaneously fed into the same molten pool. The matrix wire provides the main alloy composition of the component, and the control wire provides grain refinement components. The two wires are controlled by independent wire feeding mechanisms and their mass flow rate is calculated and coordinated by a controller. The process includes the following steps: Step 1: Based on the 3D model of the component, perform layer slicing and path planning, and divide the construction height along the deposition direction into the substrate influence zone, the stable construction zone, and the heat accumulation zone; Step 2: Determine the mass fraction of the target grain-refining element in the matrix wire and the control wire, and determine the transfer coefficient of each element from the wire to the deposited metal through preliminary experiments. The deposition content of the target grain-refining element j is calculated according to the following formula: C j =(η 1j C 1j m1+η 2j C 2j m2) / (m1+m2) ; Where m1 and m2 are the mass flow rates of the matrix filament and the control filament, respectively, in g / s; C 1j and C 2j η represents the mass fraction of target element j in the matrix filament and the control filament, respectively, in wt.%; 1j and η 2j , , respectively, are the transfer coefficients of target element j in the matrix filament and the control filament, , %; Step 3: Set the total mass flow rate M = m1 + m2, and the control wire ratio r = m2 / M; determine the initial control wire ratio r according to the target deposition composition and equation (1), and make complementary adjustments through m1 = M·(1-r) and m2 = M·r so that the fluctuation of the total mass flow rate M does not exceed ±8% when the control wire ratio r changes; Step 4: During the deposition process, collect at least one of the following process characteristic parameters in real time: interlayer temperature, melt pool area, melt pool surface temperature, or build-up height. When the interlayer temperature exceeds the target upper limit or the melt pool area increases relative to the reference value, increase the proportion of control wire within the target composition upper limit range. When the control wire is not fully melted, reduce the control wire feed rate or adjust the droplet landing point. Step 5: The arc section adopts a gradual wire feeding method, the stable section implements closed-loop component adjustment, the corner and arc end sections reduce the total mass flow rate and maintain the target component ratio, the oxide film is cleaned after each layer is deposited, and the next layer is deposited after the interlayer temperature returns to the set range.

2. The method for grain refinement of aluminum alloys based on synergistic control of dual-wire composition in arc additive manufacturing according to claim 1, characterized in that, The matrix wire is selected from Al-Cu, Al-Mg, Al-Mg-Si or Al-Zn-Mg-Cu aluminum alloy wires with a wire diameter of 0.8mm to 1.6mm; the control wire is selected from Al-Ti-B, Al-Sc-Zr, Al-Zr or aluminum-based composite wires containing TiB2 particles with a wire diameter of 0.8mm to 1.6mm.

3. The method for grain refinement of aluminum alloys based on synergistic control of dual-wire composition in arc additive manufacturing according to claim 1, characterized in that, Two wires are fed into the same molten pool from both sides or front and back of the welding gun. The angle between the two wires is 10° to 80°, and the distance between the droplets of the two wires is 0mm to 4mm.

4. The method for grain refinement of aluminum alloys based on synergistic control of dual-wire composition in arc additive manufacturing according to claim 1, characterized in that, The total wire feed speed is 2m / min to 16m / min, the control wire mass ratio is 2% to 28%, the welding current is 60A to 260A, the arc voltage is 12V to 28V, the travel speed is 2mm / s to 15mm / s, the interpass temperature is 40℃ to 220℃, and the shielding gas flow rate is 12L / min to 35L / min.

5. The method for grain refinement of aluminum alloys based on synergistic control of dual-wire composition in arc additive manufacturing according to claim 1, characterized in that, Both wires are electrically fused wires, or one is an arc main wire and the other is a cold-filled wire or a hot wire.

6. The method for grain refinement of aluminum alloys based on synergistic control of dual-wire composition in arc additive manufacturing according to claim 1, characterized in that, The control wire is made of homogeneous alloy wire, cored wire, particle-reinforced composite wire, or surface-coated wire.

7. The method for grain refinement of aluminum alloys based on synergistic control of dual-wire composition in arc additive manufacturing according to claim 1, characterized in that, The dynamic adjustment described in step 4 employs a stratified method, a lookup table method, a threshold control method, a proportional-integral method, or a model predictive control method.

8. The method for grain refinement of aluminum alloys based on synergistic control of dual-wire composition in arc additive manufacturing according to claim 1, characterized in that, The substrate-affected region is the 1st to 10th layers closest to the substrate, the stable construction region is the intermediate region between the substrate-affected region and the heat accumulation region, and the heat accumulation region is the last 1st to 10th layers closest to the top of the component.

9. The method for grain refinement of aluminum alloys based on synergistic control of dual-wire composition in arc additive manufacturing according to claim 3, characterized in that, The included angle between the two wires is 20° to 45°, the distance between the molten droplets is 1 mm to 3 mm, and the molten droplet of the control wire is located behind the molten droplet of the base wire.

10. The method for grain refinement of aluminum alloys based on synergistic control of dual-wire composition in arc additive manufacturing according to claim 1, characterized in that, The target upper limit of the interlayer temperature mentioned in step 4 is 130℃~150℃. When the interlayer temperature exceeds the target upper limit but is lower than the pause threshold, the control yarn feeding speed is increased by 0.03m / min~0.10m / min, and the matrix yarn feeding speed is reduced by the corresponding amount. Deposition is paused when the interlayer temperature reaches the pause threshold, and continues after the interlayer temperature drops to the recovery temperature.

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