Low-heat-input rotary friction welding and rapid aging integrated process for high-strength aluminum alloy component

Abstract

The invention provides a low-heat-input rotary friction welding and rapid aging integrated process for a high-strength aluminum alloy component, and belongs to the technical field of metal material welding. Comprising the following steps that firstly, the to-be-welded end faces of two high-strength aluminum alloy workpieces are treated and clamped on a rotating main shaft and a movable clamp of rotary friction welding equipment correspondingly, and it is ensured that the two high-strength aluminum alloy workpieces are centered; and secondly, the high-strength aluminum alloy workpiece on the rotating side is made to rotate, ultrahigh preset pressure P1 is applied at the same time, and P1 = K * sigma s. Plastic flowing of the material is actively triggered through ultrahigh preset friction pressure, the material is extruded out in a flash mode at the low temperature at which the strength is not obviously reduced, low-heat-input low-temperature welding is achieved, meanwhile, high dislocation density can be used as a rapid diffusion channel and a preferable nucleation point position for rapid aging, and the welding quality is improved. And a dispersed and fine strengthening phase is formed through induction within an extremely short time, so that the joint strength is efficiently recovered.

Description

Technical Field

[0001] This invention belongs to the field of metal material welding technology, specifically relating to an integrated process for low heat input rotary friction welding and rapid aging of high-strength aluminum alloy components. Background Technology

[0002] Heat-treatable aluminum alloys are widely used in high-end equipment manufacturing such as aerospace and rail transportation due to their excellent specific strength and mechanical properties. Traditional rotary friction welding is based on a two-step process principle. Stage 1 (frictional heat generation): Under relatively low frictional pressure and high rotational speed, the interface temperature slowly rises to the material's high thermoplasticization temperature due to prolonged frictional heat generation between the workpieces. This process is usually accompanied by significant heat accumulation and diffusion. Stage 2 (upsetting): After the interface material is fully thermoplasticized, an upsetting pressure higher than the frictional pressure but much lower than the room temperature yield strength of the base material is rapidly applied to achieve the interaction and metallurgical bonding of the interface materials.

[0003] This welding method, employing low friction pressure and prolonged high-speed friction in the initial stage, leads to a significant accumulation of heat at the interface and in the heat-affected zone, causing severe microstructure overheating. The peak temperature typically approaches or even exceeds 500°C. At this high temperature, the nanoscale precipitates of strengthening phases obtained through heat treatment in the aluminum alloy base material will dissolve significantly or coarsen substantially, fundamentally weakening the precipitation strengthening effect. Furthermore, prolonged high temperatures also cause the formation of coarse-grained structures in the weld zone and heat-affected zone, as well as the recovery and annihilation of existing high-density dislocations in the base material. This microstructural deterioration collectively results in a significant reduction in the strength and hardness of the joint area, typically only 50%-65% of the base material's properties, forming a distinct "softening zone" in mechanical properties. Simultaneously, for joints severely softened due to microstructure overheating, the entire component requires a time-consuming, energy-intensive, and potentially deformable reprocessing involving solution quenching and artificial aging; otherwise, it is impossible to effectively rebuild the high-strength aluminum alloy microstructure. Summary of the Invention

[0004] (1) Technical problems to be solved In view of the shortcomings of the prior art, the purpose of this invention is to provide an integrated low heat input rotary friction welding and rapid aging process for high-strength aluminum alloy components, so as to solve the fundamental problem that existing welding technologies, due to their inherent process sequence, are insufficient in controlling heat input and maintaining microstructure stability when welding high-strength aluminum alloy components.

[0005] (2) Technical solution To address the aforementioned technical problems, this invention provides an integrated low-heat-input rotary friction welding and rapid aging process for high-strength aluminum alloy components, comprising the following steps: Step 1: Process the end faces of the two high-strength aluminum alloy workpieces to be welded, and clamp them on the rotating spindle and moving fixture of the rotary friction welding equipment respectively to ensure that the two high-strength aluminum alloy workpieces are aligned. Step 2: Rotate the high-strength aluminum alloy workpiece on the rotating side while applying an ultra-high preset pressure P1, where P1 = K × σs. When the shortening of the high-strength aluminum alloy workpiece reaches the welding endpoint, the equipment stops. Step 3: Within 24 hours after welding is completed, perform rapid aging treatment on the welded joint.

[0006] Preferably, the initial state of the high-strength aluminum alloy workpiece is a heat-treated state with a high dislocation density.

[0007] Preferably, the end face of the high-strength aluminum alloy workpiece to be welded is machined before welding to ensure a smooth surface.

[0008] Preferably, after the turning process, acetone is used for ultrasonic cleaning to remove oil stains.

[0009] Preferably, the rotational speed of the high-strength aluminum alloy workpiece on the rotating side is 300-1500 rpm.

[0010] Preferably, σs is the yield strength of the high-strength aluminum alloy workpiece at room temperature, and K is a coefficient.

[0011] Preferably, the value of K ranges from 0.75 to 1.0.

[0012] Preferably, the rapid aging treatment specifically involves placing the welded high-strength aluminum alloy workpiece in a circulating air furnace and holding it at a temperature of 180–250°C for 1–20 minutes, followed by water cooling.

[0013] Preferably, the welding endpoint is a shortening of 2-8 mm for the high-strength aluminum alloy workpiece.

[0014] Preferably, the method further includes performing Vickers hardness testing and room temperature static tensile testing on the treated welded joint to evaluate its mechanical properties.

[0015] (3) Beneficial effects Compared with the prior art, the beneficial effects of the present invention are as follows: In the above solution, the plastic flow of the material is actively triggered by ultra-high preset friction pressure, so that the material is extruded in the form of flash at a low temperature before the strength (rheological stress) has decreased significantly. This achieves "heat generation on demand" and "instant heat dissipation", which physically limits the heat input and significantly reduces the peak temperature by 100-250°C. Compared with the existing method of relying on long-term frictional heat generation with low pressure and high speed, passively waiting for the material near the interface to soften as a whole, resulting in serious heat accumulation and high peak temperature, this invention achieves low-heat-input low-temperature welding.

[0016] The above-mentioned low-heat-input welding method not only introduces a large number of dislocations during the welding process through low-temperature-high-strain-rate plastic deformation, but also maximizes the preservation of nano-reinforcing phases, high dislocation density, and high solute supersaturation in the base material. The resulting weld microstructure is not a deteriorated area that needs repair, but rather an ideal precursor that can be rapidly strengthened later. Compared with the existing high-heat-input method that leads to the dissolution of reinforcing phases, coarse grains, and a sharp drop in dislocation density, forming a softened "precipitate-depleted region", this method achieves the active design and control of the weld microstructure.

[0017] In the above scheme, based on the special weld structure rich in solute and dislocations, rapid aging can utilize the high dislocation density as a rapid diffusion channel and preferred nucleation site to induce the formation of a diffuse and fine strengthening phase in a very short time (1-20 minutes), thereby efficiently restoring the joint strength. Compared with the existing technology, where softened joints are difficult to restore performance due to solute loss and insufficient non-uniform nucleation sites, traditional T6 aging is difficult to restore performance and requires time-consuming and energy-intensive resolution treatment + artificial aging, the performance restoration under the technology of this invention is more efficient.

[0018] The above solution innovatively couples welding (ultra-high pressure) and heat treatment (rapid aging) into an integrated high-performance manufacturing process. This not only simplifies the process but also allows the two stages to work together. Low heat input welding creates ideal preconditions for rapid aging, while rapid aging can effectively release the potential of the weld structure, achieving a synergistic strengthening effect of "1+1>2".

[0019] The above scheme makes full use of the base material state, clearly defining the preferred base material state with high dislocation density (such as T3 / T8 state), so that the initial strengthening effect of the base material can be fully preserved in welding and further utilized in subsequent heat treatment. It unifies the base material state, welding, and heat treatment into the same strengthening logic, thereby maximizing the exploitation of material potential. Attached Figure Description

[0020] Figure 1 This is a schematic diagram comparing the new process of this invention with the traditional process.

[0021] Figure 2This is a schematic diagram illustrating the microstructure evolution mechanism during the welding process and rapid post-weld aging of the present invention.

[0022] Figure 3 This is a comparison chart of the welding temperature curves of the new process of this invention and the traditional process.

[0023] Figure 4 This is a comparison chart of the joint hardness distribution curves of the embodiment and the comparative example.

[0024] Figure 5 This is a comparison chart of the mechanical performance data of the joints in the example and the comparative example.

[0025] As shown in the figure, specific structures and devices are labeled in the figure to clearly illustrate the structure of the embodiments of the present invention. However, this is only for illustrative purposes and is not intended to limit the present invention to the specific structure, device and environment. Those skilled in the art can adjust or modify these devices and environments according to specific needs, and such adjustments or modifications are still included in the scope of the appended claims. Detailed Implementation

[0026] The following is a detailed description of an integrated low-heat-input rotary friction welding and rapid aging process for high-strength aluminum alloy components provided by the present invention, with reference to the accompanying drawings and specific embodiments. It should be noted that, to make the embodiments more detailed, the following embodiments are the best and preferred embodiments; for some known technologies, those skilled in the art can also use other alternative methods to implement them; and the accompanying drawings are only for more specific description of the embodiments and are not intended to specifically limit the present invention.

[0027] It should be noted that the use of terms such as "an embodiment," "an embodiment," "an exemplary embodiment," and "some embodiments" in the specification indicates that the described embodiment may include a specific feature, structure, or characteristic, but not every embodiment necessarily includes that specific feature, structure, or characteristic. Furthermore, when a specific feature, structure, or characteristic is described in connection with an embodiment, implementing such a feature, structure, or characteristic in conjunction with other embodiments (whether explicitly described or not) should be within the knowledge of those skilled in the art.

[0028] Generally, terms can be understood at least partly from their use in context. For example, depending at least partly on the context, the term "one or more" as used herein can be used to describe any feature, structure, or characteristic in a singular sense, or a combination of features, structures, or characteristics in a plural sense. Additionally, the term "based on" can be understood not necessarily to convey an exclusive set of factors, but rather, alternatively, depending at least partly on the context, to allow for the presence of other factors that are not necessarily explicitly described.

[0029] It is understood that the meanings of “on”, “above” and “above” in this disclosure should be interpreted in the broadest sense, such that “on” means not only “directly on” something, but also includes something with an intermediary feature or layer, and that “above” or “above” means not only “on” something, but also includes something “above” or “above” without an intermediary feature or layer.

[0030] Furthermore, spatially related terms such as “below,” “under,” “lower,” “above,” and “upper” are used herein for convenience to describe the relationship of one element or feature to one or more other elements or features, as illustrated in the accompanying drawings. Spatially related terms are intended to cover different orientations in the use or operation of the device other than those depicted in the accompanying drawings. The device may be oriented in other ways, and the spatially related descriptive terms used herein can be interpreted similarly.

[0031] Embodiments of the present invention provide an integrated low-heat-input rotary friction welding and rapid aging process for high-strength aluminum alloy components, comprising the following steps: Step 1: Pre-welding preparation and assembly: The welding end faces of the two high-strength aluminum alloy workpieces are processed, including turning, to ensure a smooth surface. After turning, the workpieces are ultrasonically cleaned with acetone to remove oil stains. They are then clamped onto the rotating spindle and moving fixture of the rotary friction welding equipment to ensure that the two high-strength aluminum alloy workpieces are aligned. Step 2, "One-step" friction welding under ultra-high preset pressure: Rotate the high-strength aluminum alloy workpiece on the rotating side at a speed of 300-1500 rpm, and apply an ultra-high preset pressure P1, where P1=K×σs. When the shortening of the high-strength aluminum alloy workpiece reaches the welding endpoint, the equipment stops. The welding endpoint is when the shortening of the high-strength aluminum alloy workpiece is 2-8mm. σs is the yield strength of the high-strength aluminum alloy workpiece at room temperature, and K is a coefficient with a value ranging from 0.75 to 1.0. Its mechanism of action is as follows: Under this ultra-high preset pressure P1, the welding process no longer relies on prolonged frictional heat generation to fully soften the material, allowing it to undergo upsetting deformation under a lower pressure to form a metallurgical bond. As friction continues, the interface temperature rises, leading to a decrease in the material's yield strength. Once its instantaneous flow stress falls below P1, the interface material can undergo instantaneous plastic flow and be extruded in the form of flash. This process forms an adaptive and continuous "micro-area plasticization-extrusion" cycle, enabling the material to deform continuously at a lower temperature. Frictional heat is promptly removed, making it less likely for heat accumulation to occur at the interface or for heat diffusion to occur along the workpiece. This achieves low heat input and low-temperature welding overall. The low-temperature-high strain rate material deformation during the welding process can also introduce a large number of new dislocations. Step 3, rapid aging treatment after welding: Within 24 hours after welding, the welded joint is subjected to rapid aging treatment. Specifically, the welded high-strength aluminum alloy workpiece is placed in a circulating air furnace and held at a temperature of 180–250℃ for 1–20 minutes, followed by water cooling. The strengthening mechanism lies in the fact that the special weld microstructure obtained in step two, containing high solute atom concentration, high dislocation density, and fine grain structure, provides an ideal prerequisite for rapid aging. The high solute atom concentration ensures sufficient precipitate-forming elements, while the high dislocation density and high grain boundary density provide a large number of sites for the heterogeneous nucleation of the strengthening phase and significantly accelerate the atomic diffusion rate. This allows for the induction of a large number of fine, dispersed strengthening phases in a short time, achieving a simultaneous improvement in joint strength and toughness.

[0032] like Figure 4 and Figure 5 As shown, in this embodiment, the initial state of the high-strength aluminum alloy workpiece is a heat-treated state with a high dislocation density; for example, the T3 state (solution + cold working), the T8 state (solution + cold working + artificial aging), or the pre-deformed T7 state. This initial high dislocation density is largely retained during the low heat input welding process in step two. Furthermore, the low-temperature, high-strain-rate material deformation during welding can introduce a large number of new dislocations. These dislocations act as preferential nucleation sites and rapid diffusion channels during the rapid aging process in S3, further promoting the dispersed precipitation of the strengthening phase, thereby creating a more significant strengthening effect.

[0033] Example 1 Commercial AA6061-T6511 aluminum alloy rods with a diameter of 20mm were selected as the base material to be welded, with a room temperature yield strength σs=298 MPa.

[0034] Step 1: Before welding, the end faces of the workpieces to be welded are machined to ensure a smooth surface, followed by ultrasonic cleaning with acetone to remove oil stains. After cleaning, the workpieces are clamped onto the rotating spindle and moving fixture of the continuous drive friction welding machine, ensuring precise alignment.

[0035] Step 2: During the welding process, the spindle speed is set to 750 rpm. Simultaneously with the start of rotation, the control system immediately applies a preset friction pressure calculated using the formula P1=K×σs, where K=0.84, resulting in an actual applied ultra-high friction pressure of P1=250MPa. Under this pressure, after the welding process begins, flash forms rapidly and continuously and is stably extruded, with the entire welding process smooth and free from abnormal vibration. The welding endpoint is reached when the workpiece shortening reaches 6 mm, at which point the equipment automatically stops, eliminating the need for the upsetting stage in traditional processes and successfully achieving low-heat-input, low-temperature welding.

[0036] Step 3: After welding, the sample is placed in a circulating air furnace for rapid aging treatment. The specific process is as follows: hold at 210 °C for 10 minutes, then quickly remove and water-cool. Finally, the treated weld joint is subjected to Vickers hardness testing and room temperature static tensile testing to evaluate its mechanical properties.

[0037] Comparative Example 1 Commercial AA6061-T6511 aluminum alloy rods with a diameter of 20mm were selected as the welding base material, with a room temperature yield strength σs=298 MPa.

[0038] Step 1: Before welding, the end faces of the workpieces to be welded are machined to ensure a smooth surface, followed by ultrasonic cleaning with acetone to remove oil stains. After cleaning, the workpieces are clamped onto the rotating spindle and moving fixture of the continuous drive friction welding machine, ensuring precise alignment.

[0039] Step 2: During the welding process, the spindle speed is set to 750 rpm. Simultaneously with the start of rotation, the control system applies a preset frictional pressure P1 = 20 MPa, initiating the frictional heating stage. After welding begins, flash forms slowly, and the entire welding process remains stable without significant vibration. When the shortening reaches the set value of 6 mm, the control system immediately increases the pressure to the upsetting pressure P2 = 100 MPa, causing a rapid and substantial formation of flash. After holding the pressure for 10 seconds, the equipment automatically stops, completing the welding process.

[0040] Step 3: After welding, the sample is placed in a circulating air furnace for rapid aging treatment. The specific process is as follows: hold at 210 °C for 10 minutes, then quickly remove and water-cool. Finally, the treated weld joint is subjected to Vickers hardness testing and room temperature static tensile testing to evaluate its mechanical properties.

[0041] The technical solution provided by this invention, specifically the low heat input weld joint obtained in Example 1, exhibits a tensile strength of 301.5 MPa, which further increases to 334.2 MPa after rapid aging, reaching 98.6% of the base material strength. The hardness distribution curve (see attached figure) is also shown. Figure 4The results showed no obvious softening zone in the joint area, and the uniformity of mechanical properties was significantly better than that of the traditional process. In contrast, Comparative Example 1, which used the traditional friction welding process, had a welded joint tensile strength of only 235 MPa. Even after the same aging treatment (210 ℃ / 10 minutes), the strength remained almost unchanged (238 MPa), which was much lower than that of Example 1 of the present invention, indicating that its microstructure had undergone irreversible deterioration during the welding process.

[0042] Combined with appendix Figure 3 The process thermal cycling curves shown clearly illustrate the underlying mechanism of this invention: due to the use of ultra-high preset friction pressure, the peak welding temperature is effectively controlled at approximately 378°C, far lower than the 517°C of Comparative Example 1. This low heat input welding environment allows a large amount of the original high dislocation density and strengthening phase in the base material to be retained. The low-temperature, high-strain-rate material deformation during the welding process can even introduce a large number of new dislocations, forming a special weld structure rich in solute atoms and crystal defects. This structure not only possesses high strength but also provides ideal precipitation heat and kinetic conditions for subsequent rapid aging. That is, the high-density dislocations not only store additional distortion energy, effectively reducing the energy barrier (nucleation activation energy) required for the nucleation of the strengthening phase, but also the dislocation network provides short-circuit diffusion channels for the rapid transport of solute atoms. This synergistic effect of thermo-kinetic conditions enables the nanoscale strengthening phase to overcome the energy barrier at a lower temperature and in a shorter time, achieving diffuse precipitation with a high nucleation rate, thereby achieving a high-performance connection with joint strength nearly equal to that of the base material. In summary, the present invention aims to achieve low heat input welding through ultra-high pressure, fundamentally suppressing overheating and softening of the joint structure, and utilizing the special weld structure obtained thereby to efficiently restore and improve the mechanical properties of the joint through a rapid aging treatment.

[0043] This invention encompasses any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of this invention. To provide the public with a thorough understanding of this invention, specific details have been described in detail in the above preferred embodiments; however, those skilled in the art will fully understand the invention even without these details. Furthermore, to avoid unnecessary misunderstanding of the essence of this invention, well-known methods, processes, procedures, components, and circuits have not been described in detail.

[0044] Those skilled in the art will understand that all or part of the steps in the methods of the above embodiments can be implemented by a program instructing related hardware, and the program can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc.

[0045] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A low-heat-input rotary friction welding and rapid aging integrated process for high-strength aluminum alloy components, characterized in that, Includes the following steps: Step 1: Process the end faces of the two high-strength aluminum alloy workpieces to be welded, and clamp them on the rotating spindle and moving fixture of the rotary friction welding equipment respectively to ensure that the two high-strength aluminum alloy workpieces are aligned. Step 2: Rotate the high-strength aluminum alloy workpiece on the rotating side while applying an ultra-high preset pressure P1, where P1 = K × σs. When the shortening of the high-strength aluminum alloy workpiece reaches the welding endpoint, the equipment stops. Step 3: Within 24 hours after welding is completed, perform rapid aging treatment on the welded joint.

2. The integrated low-heat-input rotary friction welding and rapid aging process for high-strength aluminum alloy components according to claim 1, characterized in that, The initial state of the high-strength aluminum alloy workpiece is a heat-treated state with a high dislocation density.

3. The integrated low-heat-input rotary friction welding and rapid aging process for high-strength aluminum alloy components according to claim 1, characterized in that, Before welding, the end face of the high-strength aluminum alloy workpiece to be welded is machined to ensure a smooth surface.

4. The integrated low-heat-input rotary friction welding and rapid aging process for high-strength aluminum alloy components according to claim 3, characterized in that, After the turning process, the oil stains are removed by ultrasonic cleaning with acetone.

5. The integrated low-heat-input rotary friction welding and rapid aging process for high-strength aluminum alloy components according to claim 1, characterized in that, The rotational speed of the high-strength aluminum alloy workpiece on the rotating side is 300-1500 rpm.

6. The integrated low-heat-input rotary friction welding and rapid aging process for high-strength aluminum alloy components according to claim 5, characterized in that, σs represents the yield strength of the high-strength aluminum alloy workpiece at room temperature, and K is a coefficient.

7. The integrated low-heat-input rotary friction welding and rapid aging process for high-strength aluminum alloy components according to claim 6, characterized in that, The value of K ranges from 0.75 to 1.

0.

8. The integrated low-heat-input rotary friction welding and rapid aging process for high-strength aluminum alloy components according to claim 1, characterized in that, The rapid aging process specifically involves placing the welded high-strength aluminum alloy workpiece in a circulating air furnace and holding it at 180–250°C for 1–20 minutes, followed by water cooling.

9. The integrated low-heat-input rotary friction welding and rapid aging process for high-strength aluminum alloy components according to claim 1, characterized in that, The welding endpoint is defined as a shortening of 2-8 mm for the high-strength aluminum alloy workpiece.

10. The integrated low-heat-input rotary friction welding and rapid aging process for high-strength aluminum alloy components according to claim 1, characterized in that, It also includes Vickers hardness testing and room temperature static tensile testing of the treated welded joints to evaluate their mechanical properties.

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