High-quality aluminum alloy resistant to intergranular corrosion and its manufacturing method and application

Abstract

The application discloses a high-quality aluminum alloy with intergranular corrosion resistance and a manufacturing method and application thereof, and belongs to the technical field of high-quality aluminum alloy materials and processing and welding thereof. The manufacturing method comprises the following steps: step one, gradient equal-channel angular pressing (ECAP) processing: 4-6 passes of ECAP processing are performed on a cast alloy blank at a gradient temperature, the first pass is at 320 DEG C, and the temperature is lowered by 10 DEG C for each pass; step two, multi-pass room-temperature rolling; step three, two-stage T6 heat treatment; and step four, ultrasonic-assisted friction stir welding (FSW). The pretreatment + ultrasonic-assisted friction stir welding technology of the application significantly improves the comprehensive performance of the welded alloy, such as strength, toughness, corrosion resistance and the like, and has a wide application prospect in industrial production, especially in the fields of marine engineering, high-humidity environment, aerospace, automobile manufacturing and the like which have strict requirements on the performance of welded joints.

Description

Technical Field

[0001] This invention relates to a high-quality aluminum alloy resistant to intergranular corrosion for 7xxx series aluminum alloys, its pretreatment process and application, and is particularly suitable for scenarios where structural connections need to be achieved through welding and where there are strict requirements for intergranular corrosion resistance, such as aerospace engineering, rail transit engineering, marine engineering, and structural components in high humidity environments. It belongs to the field of high-quality aluminum alloy materials and their processing and welding technology. Background Technology

[0002] 7xxx series aluminum alloys, as high-performance aluminum alloys, possess advantages such as high strength and good machinability, and have broad application prospects in aerospace, rail transportation, and marine engineering. However, during industrial production and welding processes, their microstructure is prone to changes, leading to a decrease in resistance to intergranular corrosion and limiting their engineering applications.

[0003] In the prior art, friction stir welding (FSW), as a solid-state welding method, can achieve better electrochemical corrosion resistance. However, due to the formation of continuously distributed fine MgZn2 phases at the grain boundaries during the welding process, the intergranular corrosion depth is significantly increased (up to 40 μm), resulting in poor resistance to intergranular corrosion.

[0004] Ultrasonic-assisted friction stir welding (UaFSW), as a modified FSW technology, has been proven by scholars at home and abroad to improve weld formation, joint performance, reduce welding load, and improve welding efficiency and quality. It is a very promising modified FSW technology.

[0005] Equal channel corner extrusion (ECAP), as a severe plastic deformation (SPD) process, can refine the grains of the parent material to the submicron or even nanoscale through multiple shear deformation passes, significantly improving the strength and toughness of the material. Simultaneously, it can break down the original coarse second phases (such as MgZn2 and Al2CuMg in the 7xxx series), reducing compositional segregation and laying a uniform microstructure foundation for subsequent processes. Rolling, as a subsequent plastic processing step, can further adjust the grain orientation after ECAP (forming a more reasonable texture) and reduce material anisotropy. At the same time, compression deformation eliminates any micropores that may remain after ECAP, increasing material density and reducing potential corrosion sources (such as localized electrochemical corrosion at pores).

[0006] T6 treatment allows the strengthening phase in 7xxx series aluminum alloys to precipitate uniformly within the refined grains, achieving a synergistic effect of "fine grain strengthening + precipitation strengthening," which significantly improves the tensile strength and yield strength of the base material.

[0007] Therefore, it is necessary to develop a corrosion-resistant and toughening process that combines "gradient ECAP-rolling-T6 heat treatment + ultrasonic-assisted FSW", which takes into account the performance control of material preparation and bonding processes and has clear engineering application value. Summary of the Invention

[0008] The purpose of this invention is to provide a method for manufacturing a high-quality aluminum alloy resistant to intergranular corrosion. This method involves constructing a synergistic control system of gradient ECAP + rolling + dual-stage T6 heat treatment, and combining it with ultrasonic-assisted friction stir welding to achieve the connection, thereby solving the problem of severe intergranular corrosion in conventional friction stir welding.

[0009] Meanwhile, the present invention provides a high-quality aluminum alloy resistant to intergranular corrosion.

[0010] Meanwhile, this invention provides an application of a method for manufacturing a high-quality aluminum alloy resistant to intergranular corrosion.

[0011] Meanwhile, this invention provides an application of a high-quality aluminum alloy resistant to intergranular corrosion.

[0012] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: The matrix is ​​pretreated with gradient ECAP (4-6 passes, gradient cooling) + rolling (50-80% reduction) + two-stage T6 pretreatment; ultrasonic-assisted FSW welding is introduced to promote the uniform distribution of the second phase at the grain boundaries and suppress the continuous distribution of the MgZn2 phase at the grain boundaries, ultimately reducing the weld corrosion depth to ≤25μm (a reduction of 37.5%), refining the microstructure, and restoring mechanical properties.

[0013] The aluminum alloy is a 7xxx series aluminum alloy, with a zinc content of 4%-15wt%, a magnesium content of 1-3wt%, a manganese content of 0.1%-0.6wt%, a copper content of 0.5-2.5wt%, an iron content of ≤0.5wt%, and the remainder being aluminum.

[0014] A method for manufacturing a high-quality aluminum alloy resistant to intergranular corrosion includes the following steps: Step 1, Gradient ECAP processing: The cast alloy billet is subjected to 4-6 passes of ECAP processing at a gradient temperature, with the first pass at 320℃ and each subsequent pass decreasing by 10℃.

[0015] ECAP process parameters: path Bc, single-pass strain 1.0-1.2.

[0016] Step 2, multi-pass room temperature rolling: The alloy obtained in Step 1 is subjected to multi-pass room temperature rolling with a total reduction of 50%-80% and a single reduction of no more than 5% of the sample thickness to prepare a large-size plate with dimensions of 200mm×100mm×10mm.

[0017] Step 3, double-stage T6 heat treatment: The sheet obtained in Step 2 is first subjected to solution treatment (460-480℃×1h, water quenching), then subjected to the first stage of artificial aging (115-125℃×6h), and then subjected to the second stage of artificial aging (155-165℃×6h) to obtain the finished product.

[0018] Step 4, Ultrasonic Assisted Friction Stir Welding: The friction stir welding tool is made of WC-Co based steel and has a concave shoulder (12mm in diameter) and a columnar pin (4mm in diameter and 1.9mm in height). The welding speed is 80-120mm / min, the rotation speed is 800-1200r / min, the tilt angle is 3°~5°, the axial pressure is 0.7-1.0t, the ultrasonic frequency is 20-30kHz, and the amplitude is 10-20μm.

[0019] In this invention, steps one through three are pretreatment processes for friction stir welding.

[0020] After step one, a large number of layered dislocation structures with different orientations are formed in the alloy.

[0021] After step two, the RD-TD surface microstructure of the parent material contains uniformly distributed equiaxed crystals (approximately 2.5 μm in size) and strip-shaped crystals, with the total grain size controlled between 2.5 and 4 μm.

[0022] After step three, a small number of MgZn2 precipitates with a size of 2-4 μm and a spacing of 2.8-4 μm are formed at the grain boundaries of the parent material, and they are scattered.

[0023] The high-quality aluminum alloy resistant to intergranular corrosion obtained by this invention has an average MgZn2 phase size of 2-4 μm and a discontinuous distribution at the grain boundaries; the intergranular corrosion depth in 3.5 wt.% NaCl solution is ≤25 μm.

[0024] The high-quality aluminum alloy resistant to intergranular corrosion obtained by this invention has R p The value is 32100-37500 The alloy has a tensile strength of 518-535 MPa, a yield strength of 497-510 MPa, and an elongation of 9-10%.

[0025] Application of a method for manufacturing a high-quality aluminum alloy resistant to intergranular corrosion in lightweight, long-service-life materials. This invention provides a method for manufacturing a high-quality aluminum alloy resistant to intergranular corrosion in lightweight, long-service-life materials.

[0026] The lightweight, long service life materials include materials for aerospace, rail transportation, marine engineering, and structural components for high humidity environments.

[0027] Marine engineering and structural components in high-humidity environments include ship hull frames, deck support beams, etc.

[0028] The beneficial effects of adopting the above technical solution are as follows: This invention provides a method for manufacturing a high-quality aluminum alloy resistant to intergranular corrosion. This method can effectively improve the alloy's resistance to intergranular corrosion while maintaining good mechanical properties, and mainly has the following advantages: (1) The present invention has excellent resistance to intergranular corrosion. The intergranular corrosion depth of the welded parts is ≤25μm, which is significantly lower than the 40μm of conventional friction stir welding. The reason is that the MgZn2 precipitates at the weld are large in size and scattered in distribution, which avoids the expansion of corrosion paths caused by continuous fine phases.

[0029] (2) The mechanical properties of the present invention are well maintained. The tensile strength of the welded parts is ≥518MPa, the yield strength is ≥497MPa, and the elongation is 9-10%. The decrease is small compared with the base material, which meets the requirements of engineering applications.

[0030] (3) The present invention has strong industrial applicability. The rolling process can prepare large-size plates, and the T6 heat treatment is a conventional process in the metal industry, which is easy to scale up production.

[0031] Compared to conventional friction stir welding, ultrasonic-assisted friction stir welding effectively refines the grains of the weld joint, reduces defects, and results in a more uniform and dense microstructure of the weld alloy. Ultimately, the pretreatment + ultrasonic-assisted friction stir welding technology of this invention significantly improves the overall performance of the weld alloy, such as strength, toughness, and corrosion resistance, and has broad application prospects in industrial production, especially in fields with stringent requirements for weld joint performance, such as marine engineering, high-humidity environments, aerospace, and automotive manufacturing.

[0032] In summary, this invention presents a high-quality aluminum alloy resistant to intergranular corrosion, along with its manufacturing method and applications. The processed alloy weld exhibits excellent comprehensive mechanical properties. Furthermore, the experimental scheme is simple and easy to operate, and it does not contain expensive or rare alloying elements, significantly reducing production costs. This invention has important applications in the field of industrial profiles where cost-effectiveness is a critical factor. Attached Figure Description

[0033] Figure 1 This is a flowchart of the ECAP pretreatment process of the present invention; Figure 2 This is a comparison diagram of the distribution of precipitated phases in the weld seam under different processes in this invention; Figure 3 This is a diagram showing the intergranular corrosion morphology of the weld seam in this invention. Detailed Implementation

[0034] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. The following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Example 1

[0035] Prepare a 200mm×100mm×10mm board.

[0036] The aluminum alloy is a 7xxx series aluminum alloy with a zinc content of 10wt%, a magnesium content of 2wt%, a manganese content of 0.3wt%, a copper content of 1.5wt%, an iron content of 0.3wt%, and the remainder being aluminum.

[0037] like Figure 1 As shown, a method for preparing a high-quality aluminum alloy resistant to intergranular corrosion is as follows: (1) Gradient ECAP processing: The cast alloy billet is subjected to 5 passes of ECAP processing at a gradient temperature. The first pass is 320℃ and the last pass is 280℃, with a temperature drop of 10℃ for each pass. The ECAP path is Bc, and the strain per pass is 1.1. (2) Multi-pass room temperature rolling: The above extruded sample was subjected to multi-pass room temperature rolling, with a single pass reduction of 5% and a total reduction of 80%; a large-size plate with dimensions of 200mm×100mm×10mm was prepared, and no obvious microcracks were generated on the sample surface. (3) Two-stage T6 heat treatment: First, solution treatment is carried out at 470℃ for 1 hour, followed by first-stage artificial aging at 120℃ for 6 hours, and then second-stage artificial aging at 160℃ for 6 hours; (4) Ultrasonic-assisted friction stir welding: rotation speed 1000rpm, welding speed 100mm / min, tilt angle 3°, axial pressure 0.8t, ultrasonic vibration frequency 25kHz, amplitude 15μm.

[0038] In the microstructure of this sample, the MgZn2 phase at grain boundaries is approximately 3.0 μm in size and 3.5 μm in spacing. The MgZn2 precipitates at the weld are larger and more scattered, preventing corrosion path propagation caused by continuous fine phases. The corrosion depth reaches 20 μm, R p The value is 35200 The alloy has a tensile strength of 535 MPa, a yield strength of 510 MPa, and an elongation of 9%, which is only slightly lower than that of the base material, meeting the requirements of engineering applications.

[0039] This embodiment describes the application of a method for manufacturing a high-quality aluminum alloy resistant to intergranular corrosion in lightweight, long-service-life materials.

[0040] The application of the high-quality aluminum alloy resistant to intergranular corrosion obtained in this embodiment in lightweight, long-service-life materials.

[0041] The lightweight, long service life materials include materials for aerospace, rail transportation, marine engineering, and structural components for high humidity environments.

[0042] Marine engineering and structural components in high-humidity environments include ship hull frames, deck support beams, etc.

[0043] like Figure 2 The image shown is a comparison of weld precipitation under different processes: Figure 2 (a) In the parent material of this embodiment, the precipitated phases are uniformly distributed along the rolling direction at the grain boundaries; Figure 2 (b) After pretreatment and ultrasonic-assisted FSW in this embodiment, the size of the precipitated phase increased and the distribution became uneven. This is because heat input during the welding process caused some of the precipitated phases to dissolve and then reprecipitate during the cooling process to form larger particles. Figure 2 (c) In conventional FSW (i.e. Comparative Example 1), the precipitate particles are significantly finer and more uniformly distributed. This is because the intense plastic deformation during the welding process promotes the breakage and redistribution of the precipitate, thereby improving the strength and toughness of the weld. Figure 2 (d) is the heat-affected zone of a conventional FSW (i.e., Comparative Example 1). Due to the uneven temperature distribution, the morphology and degree of precipitation of the precipitated phase are also different. Figure 2 (e) and (f) are respectively Figure 2 (d) at point A Figure 2 (b) The EDS energy spectrum at point B shows that the elemental composition of the precipitated phases at the weld varies under different processes, resulting in different effects on the weld performance. Specifically, point A in Comparative Example 1 contains a higher content of Fe and a lower content of Zn. Fe in aluminum alloys often forms brittle and hard phases (such as Al-Fe intermetallic compounds), which can fracture the matrix and reduce plasticity and toughness. Insufficient Zn will weaken the strengthening effect. However, point B in Example 1 of this invention does not contain Fe, indicating that the dissolution of Fe impurities or the removal of Fe impurities is effectively suppressed during ultrasonic-assisted friction stir welding. It also contains a higher content of Zn, which improves the strength and corrosion resistance of the alloy, resulting in superior welding alloy performance of this invention.

[0044] like Figure 3 The image shows the intergranular corrosion morphology of welds under different processes: Figure 3 (a) Pitting corrosion mainly occurred in the base material area, with a corrosion depth of 8.6 μm. Figure 3 (b) In this embodiment, pretreatment + ultrasonic-assisted FSW resulted in intergranular corrosion in the weld area of ​​the base material, with a corrosion depth of 20 μm; Figure 3 (c) is a conventional FSW (i.e., Comparative Example 1), where severe intergranular corrosion caused exfoliation corrosion with a corrosion depth of 40 μm. Example 2

[0045] Prepare a 200mm×100mm×10mm board.

[0046] The aluminum alloy is a 7xxx series aluminum alloy with a zinc content of 4 wt%, a magnesium content of 1 wt%, a manganese content of 0.1 wt%, a copper content of 0.5 wt%, an iron content of 0.5 wt%, and the remainder being aluminum.

[0047] Its manufacturing method is as follows: (1) Gradient ECAP processing: The cast alloy billet is subjected to four ECAP processing passes at a gradient temperature. The first pass is 320℃ and the last pass is 290℃, with a temperature drop of 10℃ for each pass. The ECAP path is Bc, and the strain per pass is 1.0. (2) Multi-pass room temperature rolling: The above extruded sample was subjected to multi-pass room temperature rolling, with a single pass reduction of 4%; the total reduction reached 60%; and no obvious microcracks were generated on the sample surface. (3) Two-stage T6 heat treatment: First, a solution treatment is performed at 460℃ for 1 hour, followed by a first-stage artificial aging at 115℃ for 6 hours, and then a second-stage artificial aging at 155℃ for 6 hours. (4) Ultrasonic-assisted friction stir welding: rotation speed 800 rpm, welding speed 120 mm / min, tilt angle 5°, axial pressure 0.7t; ultrasonic vibration frequency 20 kHz, amplitude 10 μm.

[0048] This embodiment describes the application of a method for manufacturing a high-quality aluminum alloy resistant to intergranular corrosion in lightweight, long-service-life materials.

[0049] The application of the high-quality aluminum alloy resistant to intergranular corrosion obtained in this embodiment in lightweight, long-service-life materials.

[0050] The lightweight, long service life materials include materials for aerospace, rail transportation, marine engineering, and structural components for high humidity environments.

[0051] Marine engineering and structural components in high-humidity environments include ship hull frames, deck support beams, etc.

[0052] In the microstructure of this sample, the grain boundary MgZn2 phase has a size of 2.0 μm, a spacing of 2.8 μm, and a corrosion depth of 25 μm. p The value is 32100 The alloy has a tensile strength of 518 MPa, a yield strength of 497 MPa, and an elongation of 10%. Example 3

[0053] Prepare a 200mm×100mm×10mm board.

[0054] The aluminum alloy is a 7xxx series aluminum alloy with a zinc content of 15wt%, a magnesium content of 3wt%, a manganese content of 0.6wt%, a copper content of 2.5wt%, an iron content of 0.1wt%, and the remainder being aluminum.

[0055] Its manufacturing method is as follows: (1) Gradient ECAP processing: The cast alloy billet is subjected to 6 passes of ECAP processing at a gradient temperature. The first pass is 320℃ and the last pass is 270℃, with a temperature drop of 10℃ for each pass. The ECAP path is Bc, and the strain per pass is 1.2. (2) Multi-pass room temperature rolling: The above extruded sample was subjected to multi-pass room temperature rolling, wherein the single-pass reduction was 5%; the total reduction was 70%; and no obvious microcracks were generated on the sample surface. (3) Two-stage T6 heat treatment: First, a solution treatment is performed at 480℃ for 1 hour, followed by a first-stage artificial aging at 125℃ for 6 hours, and then a second-stage artificial aging at 165℃ for 6 hours. (4) Ultrasonic-assisted friction stir welding: rotation speed 1200rpm, welding speed 80mm / min, tilt angle 3°, axial pressure 1.0t; ultrasonic vibration frequency 30kHz, amplitude 20μm.

[0056] This embodiment describes the application of a method for manufacturing a high-quality aluminum alloy resistant to intergranular corrosion in lightweight, long-service-life materials.

[0057] The application of the high-quality aluminum alloy resistant to intergranular corrosion obtained in this embodiment in lightweight, long-service-life materials.

[0058] The lightweight, long service life materials include materials for aerospace, rail transportation, marine engineering, and structural components for high humidity environments.

[0059] Marine engineering and structural components in high-humidity environments include ship hull frames, deck support beams, etc.

[0060] In the microstructure of this sample, the grain boundary MgZn2 phase has a size of 4.0 μm, a spacing of 4.0 μm, and a corrosion depth of 19 μm. p The value is 37500 The alloy has a tensile strength of 521 MPa, a yield strength of 502 MPa, and an elongation of 10%.

[0061] Comparative Example 1

[0062] Prepare a 200mm×100mm×10mm board.

[0063] The only difference between this comparative example and Example 1 is that: (1) No pretreatment was performed; (2) Friction stir welding: rotation speed 1000 rpm, welding speed 100 mm / min; The difference between this comparative example and Example 1 is that no pretreatment was performed; the MgZn2 phase size at the grain boundaries of the alloy obtained in this comparative example is 0.8 μm, the spacing is 0.8 μm, and the corrosion depth reaches 40 μm. p The value is 26711 The alloy has a tensile strength of 361 MPa.

[0064] Comparative Example 2

[0065] The only difference between this comparative example and Example 1 is that: (1) No pretreatment was performed; (2) Direct ultrasonic-assisted friction stir welding.

[0066] The difference between this comparative example and Example 1 is that no pretreatment was performed; the alloy grain boundary MgZn2 phase size obtained in this comparative example is 0.8 μm, the spacing is 1.0 μm, and the corrosion depth reaches 40 μm. p The value is 27890 The alloy has a tensile strength of 370 MPa.

[0067] Comparative Example 3

[0068] The only difference between this comparative example and Example 1 is that the gradient ECAP process is replaced by direct ECAP extrusion of the alloy at the homogenization temperature.

[0069] Specifically, Its manufacturing method is as follows: (1) The alloy was directly subjected to 4 passes of ECAP extrusion at a homogenization temperature of 320℃. (2) Multi-pass room temperature rolling: The above extruded sample was subjected to multi-pass room temperature rolling, with a single pass reduction of 5% and a total reduction of 80%; a large-size plate with dimensions of 200mm×100mm×10mm was prepared, and no obvious microcracks were generated on the sample surface. (3) Two-stage T6 heat treatment: First, solution treatment is carried out at 470℃ for 1 hour, followed by first-stage artificial aging at 120℃ for 6 hours, and then second-stage artificial aging at 160℃ for 6 hours; (4) Ultrasonic-assisted friction stir welding: rotation speed 1000rpm, welding speed 100mm / min, tilt angle 3°, axial pressure 0.8t, ultrasonic vibration frequency 25kHz, amplitude 15μm.

[0070] In the microstructure of this sample, the MgZn2 phase at grain boundaries is 1.0 μm in size and 1.5 μm in spacing, remaining a continuous fine phase, with a corrosion depth of 35 μm.p The value is 28525 The alloy has a tensile strength of 420 MPa.

[0071] Comparative Example 4

[0072] The only difference between this comparative example and Example 1 is that only one T6 heat treatment was performed.

[0073] Specifically, Its preparation method is as follows: (1) Gradient ECAP processing: The cast alloy billet is subjected to 5 passes of ECAP processing at a gradient temperature. The first pass is 320℃ and the last pass is 280℃, with a temperature drop of 10℃ for each pass. The ECAP path is Bc, and the strain per pass is 1.1. (2) Multi-pass room temperature rolling: The above extruded sample was subjected to multi-pass room temperature rolling, with a single pass reduction of 5% and a total reduction of 80%; a large-size plate with dimensions of 200mm×100mm×10mm was prepared, and no obvious microcracks were generated on the sample surface. (3) T6 heat treatment: first, solution treatment at 470℃ for 1 hour, followed by artificial aging at 120℃ for 12 hours; (4) Ultrasonic-assisted friction stir welding: rotation speed 1000rpm, welding speed 100mm / min, tilt angle 3°, axial pressure 0.8t, ultrasonic vibration frequency 25kHz, amplitude 15μm.

[0074] In the microstructure of this sample, the MgZn2 phase at grain boundaries has a size of 1.0 μm and a spacing of 1.6 μm, remaining a continuous fine phase, with a corrosion depth of 37 μm. p The value is 28651 The alloy has a tensile strength of 418 MPa.

[0075] Comparative Example 5

[0076] The only difference between this comparative example and Example 1 is that ultrasonic-assisted friction stir welding is replaced with conventional friction stir welding.

[0077] Specifically, Its preparation method is as follows: (1) Gradient ECAP processing: The cast alloy billet is subjected to 5 passes of ECAP processing at a gradient temperature. The first pass is 320℃ and the last pass is 280℃, with a temperature drop of 10℃ for each pass. The ECAP path is Bc, and the strain per pass is 1.1. (2) Multi-pass room temperature rolling: The above extruded sample was subjected to multi-pass room temperature rolling, with a single pass reduction of 5% and a total reduction of 80%; a large-size plate with dimensions of 200mm×100mm×10mm was prepared, and no obvious microcracks were generated on the sample surface. (3) Two-stage T6 heat treatment: First, solution treatment is carried out at 470℃ for 1 hour, followed by first-stage artificial aging at 120℃ for 6 hours, and then second-stage artificial aging at 160℃ for 6 hours; (4) Friction stir welding: rotation speed 1000rpm, welding speed 100mm / min, tilt angle 3°, axial pressure 0.8t.

[0078] In the microstructure of this sample, the MgZn2 phase at grain boundaries has a size of 1.1 μm and a spacing of 1.7 μm, remaining a continuous fine phase, with a corrosion depth of 34 μm. p The value is 29012 The alloy has a tensile strength of 460 MPa.

[0079] Comparative Example 6

[0080] The only difference between this comparative example and Example 1 is that in the gradient ECAP process, the temperature is reduced by 5°C for each pass.

[0081] In the microstructure of this sample, the MgZn2 phase at grain boundaries is 1.5 μm in size and 2.0 μm in spacing, remaining a continuous fine phase, with a corrosion depth of 32 μm. p The value is 29589 The alloy has a tensile strength of 475 MPa.

[0082] Comparative Example 7

[0083] The only difference between this comparative example and Example 1 is that in the gradient ECAP process, the temperature is reduced by 15°C per pass.

[0084] In the microstructure of this sample, the MgZn2 phase at grain boundaries has a size of 1.3 μm and a spacing of 1.8 μm, remaining a continuous fine phase, with a corrosion depth of 34 μm. p The value is 29124 The alloy has a tensile strength of 465 MPa.

[0085] Main testing methods: Electron backscatter diffraction (EBSD) analysis: Samples used for EBSD testing must possess good conductivity and have clean, smooth, and stress-free surfaces. During sample preparation, the samples are first mechanically polished until the surface is bright and scratch-free, followed by electropolishing. The electropolishing solution consists of 10% HClO4 + 90% C2H5OH, with the temperature set at -20℃, the voltage constant at 32 V, and the electropolishing time at 60 s. After electropolishing, the sample is immersed face down in a beaker containing anhydrous ethanol for ultrasonic cleaning, then dried with a warm air blower, placed in a sample box, packaged, and vacuum-sealed, awaiting testing. The EBSD equipment used in this experiment is a Hitachi S-3400N. The results are then processed and analyzed using HKL-CHANNEL5 software to obtain data such as microstructure, MgZn2 phase size, and spacing.

[0086] Intergranular corrosion performance test: Intergranular corrosion tests were conducted according to GB / T 7998-2005. The etching solution was prepared as follows: 1 L NaCl solution (57 g NaCl + 1 L deionized water) + 10 mL H2O2. The sample was suspended in the etching solution by a plastic thread, and the ratio of the sample surface area to the volume of the etching solution was less than 20 mm². 2 / mL, the experimental temperature was maintained at 35±2℃ in a constant temperature water bath. After corrosion for 6 h, the sample was taken out, cleaned with alcohol and blown dry. The sample cross section was cut and the corrosion morphology and corrosion depth were observed under a Japanese Olympus BX51M metallographic microscope.

[0087] Electrochemical performance testing: Electrochemical performance was measured using a CHI660E electrochemical workstation (Shanghai Chenhua Instrument Co., Ltd.). A three-electrode system was employed, with the test sample as the working electrode and a working area of ​​10 mm². 2 The counter electrode was a platinum electrode, the reference electrode was a calomel electrode (saturated KCl solution), and the electrolyte was a 3.5 wt.% sodium chloride solution (500 mL).

[0088] Open-circuit potential (OCP) AC impedance and dynamic polarization potential were measured for each sample. The OCP scan time was 3600 s, the AC impedance spectrum (EIS) frequency range was 10 mHz to 10 kHz, and the perturbation amplitude was 10 mV. The potentiodynamic polarization (PDP) curve was measured at a scan rate of 0.5 mV / s from a position 0.25 V lower than the OCP towards the positive direction. The scan was stopped when the breakdown voltage reached -2 ​​to -3 V. The polarization resistance value Rp was obtained from the equivalent circuit parameters.

[0089] Mechanical property testing: Tensile strength of the samples was obtained by room temperature tensile testing on a universal testing machine at a tensile rate of 0.36 mm / min. Tensile tests of all room temperature rolled samples were performed using samples taken from the RD-TD (Transverse direction, TD) surface.

[0090] Finally, it should be noted that the above embodiments are only for illustrating the technical concept and features of the present invention and are not intended to limit it. Different preparation methods can still be modified according to this technical solution, and the modified technical solution cannot deviate from the spirit of the technical solution of the present invention.

[0091] It should be understood that, in order to simplify this disclosure and aid in understanding one or more of the various aspects of the invention, features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof in the above description of exemplary embodiments of the invention. However, this method of disclosure should not be interpreted as reflecting an intention that the claimed invention requires more features than expressly recited in each claim. Rather, as reflected in the claims, inventive aspects lie in fewer than all the features of the foregoingly disclosed embodiments. Therefore, the claims, following the detailed description, are hereby expressly incorporated into that detailed description, wherein each claim itself is a separate embodiment of the invention.

[0092] Although the invention has been described with reference to a limited number of embodiments, those skilled in the art will understand from the foregoing description that other embodiments are conceivable within the scope of the invention described herein. Furthermore, it should be noted that the language used in this specification has been chosen primarily for readability and instructional purposes, and not for the purpose of interpreting or limiting the subject matter of the invention. Therefore, many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the appended claims. The disclosure of the invention is illustrative and not restrictive, and the scope of the invention is defined by the appended claims.

[0093] 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 method for manufacturing a high-quality aluminum alloy resistant to intergranular corrosion, characterized in that: Includes the following steps: Step 1, gradient ECAP processing: The cast alloy billet is subjected to 4-6 passes of ECAP processing at a gradient temperature, with the first pass at 320℃ and each subsequent pass decreasing by 10℃. Step 2, multi-pass room temperature rolling: The alloy obtained in Step 1 is subjected to multi-pass room temperature rolling, with a total reduction of 50% to 80%, and the reduction in a single pass not exceeding 5% of the sample thickness; Step 3, two-stage T6 heat treatment: first, solution treatment at 460-480℃ for 1 hour, then first-stage artificial aging at 115-125℃ for 6 hours, and then second-stage artificial aging at 155-165℃ for 6 hours. Step 4, Ultrasonic-assisted FSW welding: Perform ultrasonic-assisted FSW welding on the pretreated substrate; The aluminum alloy is a 7xxx series aluminum alloy, with a zinc content of 4%-15wt%, a magnesium content of 1-3wt%, a manganese content of 0.1%-0.6wt%, a copper content of 0.5-2.5wt%, an iron content of ≤0.5wt%, and the remainder being aluminum.

2. The manufacturing method according to claim 1, characterized in that: In step one, the ECAP process parameters are: path Bc, single-pass strain 1.0-1.

2.

3. The manufacturing method according to claim 1, characterized in that: In step four, the ultrasonic-assisted FSW welding process is as follows: rotation speed 800-1200 rpm, welding speed 80-120 mm / min, tilt angle 3°~5°, axial pressure 0.7-1.0t, ultrasonic frequency 20-30 kHz, amplitude 10-20 μm.

4. The manufacturing method according to claim 1, characterized in that: In step four, the machining tool for FSW welding is made of WC-Co based steel, and the tool has a concave shoulder with a diameter of 12 mm and a columnar pin with a diameter of 4 mm and a height of 1.9 mm.

5. The manufacturing method according to claim 1, characterized in that: After step one, a large number of layered dislocation structures with different orientations are formed in the alloy; after step two, equiaxed crystals and strip-shaped crystals are uniformly distributed in the alloy, and the total grain size is controlled at 2.5-4μm. After step three, MgZn2 precipitates with a size of 2-4 μm and a spacing of 2.8-4 μm are formed at the grain boundaries of the alloy and are scattered.

6. The high-quality aluminum alloy resistant to intergranular corrosion obtained by welding according to any one of claims 1 to 5, characterized in that: The average size of the MgZn2 phase at the grain boundaries of the aluminum alloy is 2-4 μm and it is discontinuously distributed; the intergranular corrosion depth in 3.5 wt.% NaCl solution is ≤25 μm.

7. The high-quality aluminum alloy resistant to intergranular corrosion according to claim 6, characterized in that: R of aluminum alloy p The value is 32100-37500 The alloy has a tensile strength of 518-535 MPa, a yield strength of 497-510 MPa, and an elongation of 9-10%.

8. The application of the high-quality aluminum alloy resistant to intergranular corrosion as described in claim 6 in aerospace materials, rail transportation materials, marine engineering materials, and materials for high-humidity environments.

9. The application of the manufacturing method according to any one of claims 1 to 5 in aerospace materials, rail transit materials, marine engineering materials, and materials for high humidity environments.

10. The application according to claim 9, characterized in that: Materials used in marine engineering and high-humidity environments include ship hull frames and deck support beams.

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