Welding methods and weld joints for 5XXX series aluminum alloy thick plates

Abstract

This invention provides a welding method and welded joint for 5XXX series aluminum alloy thick plates. The welding method includes: machining the weldable sides of two 5XXX series aluminum alloy thick plates into double V-grooves; performing pre-weld laser cleaning and assembly on the double V-grooves; linearly increasing the horizontal gap between the weld joints along the welding direction; performing MIG welding on the weld joints, with the first pass being a straight pass and the subsequent passes being figure-eight sway welding; except for the last pass, performing at least one interlayer laser cleaning on the corresponding weld bead after each pass. This invention effectively improves weld porosity, thermal deformation, and grain coarsening problems by designing high-magnesium welding wire that matches the base material, optimizing the groove structure, co-processing pre-weld and interlayer laser cleaning, asymmetric gap assembly based on thermal deformation prediction, and synergistic grain refinement through the integration of interlayer laser cleaning and figure-eight sway welding, achieving Class I weld quality and a high weld joint strength coefficient.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of aluminum alloy welding manufacturing, in particular to a 5XXX series aluminum alloy thick plate welding method and welding joint. BACKGROUND

[0002] 5XXX series aluminum alloy is widely used in structures requiring lightweight and resistance to marine climate due to its good corrosion resistance, formability and weldability. However, as the thickness increases (≥15mm), the welding difficulty increases exponentially, mainly facing the following challenges: first, porosity sensitivity: the moisture absorption of the aluminum alloy surface oxide film is the main source of welding porosity, and the thick plate needs multi-pass welding, which further increases the probability of porosity; second, severe deformation: large heat input welding will cause uneven thermal cycle in the thick plate, accumulating huge internal stress in the thick plate rigid structure, causing difficult-to-correct warping and angular deformation; third, microstructure degradation: the weld metal is prone to epitaxial growth along the base material grain to form coarse columnar crystals during solidification, resulting in a significant decrease in the plasticity and toughness of the welding joint, becoming a weak link of the structure.

[0003] The prior art focuses on the improvement of a single link, such as replacing the welding wire brand, adjusting the welding parameters or introducing post-heat treatment, lacking the coordinated design and control of the whole chain of "composition-structure-purification-process", and it is difficult to systematically solve the above common problems. Therefore, there is an urgent need for a universal and integrated welding technology solution for 5XXX series aluminum alloy thick plates. SUMMARY

[0004] The main purpose of the present application is to provide a 5XXX series aluminum alloy thick plate welding method and welding joint to solve the problems of large welding porosity, severe thermal deformation and coarse grains in the welding of 5XXX series aluminum alloy thick plates in the prior art.

[0005] In order to achieve the above-mentioned purpose, according to one aspect of the present application, a 5XXX series aluminum alloy thick plate welding method is provided, comprising the following steps: step S1, preparing a 5XXX series aluminum alloy thick plate and a 5XXX series aluminum alloy welding wire; the thickness of the 5XXX series aluminum alloy thick plate is 15-30mm, and the difference between the weight percentage of Mg in the 5XXX series aluminum alloy thick plate and the weight percentage of Mg in the 5XXX series aluminum alloy welding wire is ≤1.2%; step S2, processing the welding sides of two 5XXX series aluminum alloy thick plates into double-V type grooves, and performing laser cleaning before welding on the double-V type grooves to obtain a pre-welding cleaning body; the double-V type groove has a middle blunt edge; step S3, assembling the pre-welding cleaning body to obtain a welding joint to be welded; along the welding direction, the horizontal gap of the welding joint to be welded linearly increases, the horizontal gap at the welding starting point is denoted as J min , and the horizontal gap at the welding ending point is denoted as J max , 1mm≤J maxJ min ≤3mm; step S4, preheating the to-be-welded joint to 60-100℃, and sequentially performing single-layer multi-pass MIG welding on the front and back surfaces of the to-be-welded joint in a protective gas environment; the total pass number of the single-layer multi-pass MIG welding is denoted as n, the welding form of the first pass is straight welding, and the welding form of the second pass to the nth pass is 8-shaped weaving; the welding current of the straight welding is less than the welding current of the 8-shaped weaving, and the difference is 0-10A; wherein, when performing single-layer multi-pass MIG welding on the front surface of the to-be-welded joint, at least one interlayer laser cleaning is performed on the corresponding weld after each pass welding; when performing single-layer multi-pass MIG welding on the back surface of the to-be-welded joint, at least one interlayer laser cleaning is performed on the corresponding weld after each pass welding from the first pass to the n-1th pass; the laser power of the pre-welding laser cleaning is less than the laser power of the interlayer laser cleaning, and the difference is 50-100W.

[0006] Further, in step S1, the weight percentage content of Mg in the 5XXX series aluminum alloy thick plate is less than the weight percentage content of Mg in the 5XXX series aluminum alloy welding wire, and the difference is 0.1-0.5%; and / or the 5XXX series aluminum alloy thick plate comprises, in terms of weight percentage, Mg 4.0-4.9%, Mn 0.4-1.0%, Cr 0.05-0.25%, Si≤0.4%, Fe≤0.4%, Cu≤0.14%, Zn≤0.25%, Ti 0.01-0.15%, the balance being Al and unavoidable impurities, single impurity≤0.05%, and total impurities≤0.15%.

[0007] Further, in step S1, the 5XXX series aluminum alloy welding wire comprises, in terms of weight percentage, Mg 4.3-5.2%, Mn 0.4-1.0%, Cr 0.02-0.25%, Si≤0.4%, Fe≤0.4%, Cu≤0.1%, Zn≤0.25%, Ti≤0.15%, the balance being Al and unavoidable impurities, single impurity≤0.05%, and total impurities≤0.15%; and / or the diameter of the 5XXX series aluminum alloy welding wire is 1-1.5mm.

[0008] Further, in step S2, the single-side bevel angle of the double-V-shaped groove close to the to-be-welded side of the 5XXX series aluminum alloy thick plate is 26°-34°; and / or the thickness of the intermediate blunt edge is 0-1mm; and / or the laser power of the pre-welding laser cleaning is 50W-100W, and the cleaning speed is 4-20mm / s.

[0009] Further, the laser power of the interlayer laser cleaning is 100W-200W, and the cleaning speed is 4-20mm / s; and / or the total cleaning depth of the interlayer laser cleaning in each weld is 0.2-0.5mm.

[0010] Further, in step S3, 1mm≤J min ≤3mm; and / or, 2mm≤J max ≤6mm.

[0011] Further, in step S4, the shielding gas comprises argon and / or helium; and / or the flow rate of the shielding gas is 20-30 L / min; and / or 2≤n≤8; and / or the weaving frequency of the 8-shaped weaving is 2-4 Hz, and the weaving amplitude is 2-5 mm.

[0012] Further, in step S4, the welding current of the straight welding is less than the welding current of the 8-shaped weaving, and the difference is 2-8 A; and / or the welding current of the straight welding is 250-270 A, and the welding speed is 55-65 cm / min; and / or the welding current of the 8-shaped weaving is 260-270 A, and the welding speed is 50-60 cm / min.

[0013] According to another aspect of the present application, a welded joint is provided, which is obtained by using the above-mentioned welding method of the 5XXX series aluminum alloy thick plate.

[0014] Further, the tensile strength of the welded joint is 295-305 MPa, and the welding coefficient is 0.95-0.98; and / or the average grain size of the weld zone of the welded joint is 90-110 μm.

[0015] By using the technical solution of the present application, a closed-loop technical system from material matching, structure design to whole-process control of welding is constructed for the 5XXX series aluminum alloy thick plate with a thickness of more than 15 mm. By designing the 5XXX series welding wire with high magnesium content matched with the base material, optimizing the double-V groove structure, cooperating with the laser interlayer purification before welding, assembling based on the asymmetric gap predicted by the thermal deformation, and fusing the laser interlayer cleaning with the 8-shaped weaving for grain refinement, the core problems including welding porosity, thermal deformation and grain coarsening are systematically solved, the I-grade weld quality is obtained, the strength coefficient of the welded joint is high, and the uniform and fine equiaxed crystal structure can be formed in the weld zone. The method of the present application has strong universality, and is especially suitable for the high-strength and high-quality welding manufacturing of the thick plate aluminum alloy structure in the fields of ship, ocean engineering and rail transportation. BRIEF DESCRIPTION OF DRAWINGS

[0016] The accompanying drawings, which form a part of the present application, are used to provide further understanding of the present application, and the illustrative embodiments of the present application and their description serve the purpose of explaining the present application. In the drawings:

[0017] Figure 1 A simulated schematic diagram of a welded joint according to an embodiment of the present application is shown.

[0018] Figure 2A sequence diagram of interpass laser cleaning according to Embodiment 1 of the present application is shown;

[0019] Figure 3 A weld X-ray detection diagram (I level) of a welded joint according to Embodiment 1 of the present application is shown;

[0020] Figure 4 A weld grain structure diagram of a welded joint according to Embodiment 1 of the present application is shown;

[0021] Figure 5 An equiaxed crystal structure of a weld zone of a welded joint according to Embodiment 1 of the present application is shown;

[0022] Figure 6 A structure of a base material zone of a welded joint according to Embodiment 1 of the present application is shown;

[0023] Figure 7 A post-tensioning photograph of a welded joint according to Embodiment 1 of the present application is shown.

[0024] Among them, the above-mentioned drawings include the following reference signs:

[0025] 1, interpass laser cleaning of the first pass on the front surface; 2, interpass laser cleaning of the second pass on the front surface; 3, interpass laser cleaning of the back bevel; 4, interpass laser cleaning of the first pass on the back surface; A, single-sided bevel angle; B, intermediate land thickness. DETAILED DESCRIPTION

[0026] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to the drawings and in combination with the embodiments.

[0027] As described in the background art of the present application, there are problems of large welding porosity, serious thermal deformation and coarse grains in the welding of 5XXX series aluminum alloy thick plates in the prior art. In order to solve the above problems, in a typical embodiment of the present application, a welding method for a 5XXX series aluminum alloy thick plate is provided, comprising the following steps: step S1, preparing a 5XXX series aluminum alloy thick plate and a 5XXX series aluminum alloy welding wire; the thickness of the 5XXX series aluminum alloy thick plate is 15-30 mm, and the difference between the weight percentage of Mg in the 5XXX series aluminum alloy thick plate and the weight percentage of Mg in the 5XXX series aluminum alloy welding wire is ≤1.2%; step S2, processing the to-be-welded side of the two 5XXX series aluminum alloy thick plates into a double-V type groove, and performing pre-welding laser cleaning on the double-V type groove to obtain a pre-welding cleaning body; the double-V type groove has an intermediate land; step S3, assembling the pre-welding cleaning body to obtain a to-be-welded joint; along the welding direction, the horizontal gap of the to-be-welded joint linearly increases, the horizontal gap at the welding starting point is denoted as J min , and the horizontal gap at the welding ending point is denoted as Jmax ,1mm≤J max -J min ≤3mm; Step S4: Preheat the head to be welded to 60~100℃. Under a protective gas environment, perform single-sided multi-layer multi-pass MIG welding on the front and back sides of the head to be welded sequentially. The total number of passes in the single-sided multi-layer multi-pass MIG welding is denoted as n. The first pass is a straight pass weld, and the second to nth passes are figure-eight sway welds. The welding current for straight passes is ≤ the welding current for figure-eight sway welds, with a difference of 0~10A. When performing single-sided multi-layer multi-pass MIG welding on the front side of the head, at least one interlayer laser cleaning is performed on the corresponding weld after each pass. When performing single-sided multi-layer multi-pass MIG welding on the back side of the head, at least one interlayer laser cleaning is performed on the corresponding weld after each pass from the first to the (n-1)th pass. The laser power for pre-welding laser cleaning is < the laser power for interlayer laser cleaning, with a difference of 50~100W. In single-sided multi-layer multi-pass MIG welding, one layer corresponds to one welding pass.

[0028] This invention is a high-strength welding method for 5XXX series aluminum alloy thick plates based on the synergy of composition, structure, process and purification. It integrates a systematic solution for specific composition materials, bevel and gap structure, welding process parameters and laser purification throughout the pre-weld and inter-layer processes.

[0029] [Ingredient Synergy]

[0030] This invention strictly limits the chemical composition of the base material (i.e., 5XXX series aluminum alloy thick plate) and the welding wire (i.e., 5XXX series aluminum alloy welding wire), especially controlling the relationship between the Mg content of the base material and the welding wire. This ensures the strength compensation capability of the welding wire for the base material, which is the material basis for achieving a high weldability coefficient in the welded joint. Preferably, the weight percentage of Mg in the 5XXX series aluminum alloy thick plate is 4.0~4.9%, and the weight percentage of Mg in the 5XXX series aluminum alloy welding wire is 4.3~5.2%.

[0031] [Structural Collaboration]

[0032] The weldable sides of two 5XXX series aluminum alloy thick plates are machined into double V-shaped bevels with a blunt edge in the middle. The two plates are then assembled to form a weld joint, creating an asymmetrical linear gradient gap along the welding direction, with the gap difference between the starting and ending points being smaller than 1mm. max -J min ≤3mm.

[0033] A schematic diagram of a simulated welded joint according to one embodiment is shown below. Figure 1The upper right part is an enlarged view of the horizontal plane, and the joint gap forms an asymmetric linear gradient along the welding direction; the lower right part is an enlarged view and a further enlarged view of the double V-shaped groove area, which has a certain single-sided groove angle A and a middle blunt edge thickness B.

[0034] The double V-shaped groove structure is the basis of optimizing heat input and ensuring penetration, and based on this, the joint to be welded is further provided with an asymmetric linear gradient gap, because the inventors unexpectedly found in the research process that uneven thermal shrinkage during welding can cause joint deformation when using traditional equal gap assembly. This deformation continuously interferes with the formation of the molten pool and the weld, ultimately leading to incomplete penetration defects. Therefore, the present application presets a linearly changing gap to match the welding thermal shrinkage rule, realizes "active, accurate and feedforward" control of welding deformation, and together with the double V-shaped groove structure forms a "structural defense line" to control deformation.

[0035]

Full purification coordination

[0036] The present application uses pre-welding laser cleaning and purification to eliminate the generation of hydrogen pores from the source, replacing mechanical polishing and chemical cleaning which are easy to introduce pollution. At the same time, interlayer laser cleaning is set to perform laser interlayer purification, which can not only continuously ensure cleanliness during multi-pass welding, but also further "activate the surface" of the weld through moderate energy input, creating favorable nucleation conditions for subsequent grain refinement. Pre-welding laser purification and interlayer laser purification together form a full, non-contact, physical purification channel from the beginning of welding to the welding process, which is used to systematically eliminate the generation of hydrogen pores and activate the weld surface. The laser power of pre-welding laser cleaning is less than that of interlayer laser cleaning, so that the surface oxide film and passivation film can be removed in stages. The present application replaces traditional mechanical or chemical cleaning through laser full-process purification technology, fundamentally avoids the introduction of foreign inclusions and chemical reagent pollution, reduces the hydrogen pore rate to a very low level, and significantly improves the welding organization cleanliness and weld quality.

[0037]

Welding process coordination

[0038] After preheating the joint to be welded to 60~100℃, the front and back of the joint to be welded are respectively subjected to single-sided multi-layer multi-pass MIG welding in a protective gas environment. During the welding process, in addition to the first pass on the front and the first pass on the back using straight welding, the other passes all use 8-shaped weaving. The complex motion trajectory of 8-shaped weaving can produce strong mechanical stirring and thermal disturbance to the molten pool, and has strong grain refinement effect. The interlayer laser cleaning provides the "seed" for fine grain nucleation, and the 8-shaped weaving provides the "environment" for fine grain growth. The two work in succession during the welding process and jointly intervene in the solidification process of the weld, thereby strongly promoting the formation of equiaxed crystals and fundamentally improving the microstructure and mechanical properties of the weld. The welding current of straight welding is < the welding current of 8-shaped weaving, so that the fusion quality of the base weld is ensured while providing sufficient heat input for subsequent weaving to maintain molten pool stirring, thereby synergistically promoting grain refinement and equiaxed crystal formation.

[0039] The present application first deeply couples four dimensions of composition, structure, purification and process to form a synergistic effect of "1+1+1+1>4", which is a technology system of mutual correlation, mutual support, ring after ring, and mutual enhancement. Through closed-loop collaborative design of multiple technology modules, the common problems of aluminum alloy thick plate welding are systematically solved, and the bottleneck of single technology optimization is broken. The welding joint prepared has extremely low porosity (up to I level), high strength, small deformation, excellent microstructure, good process repeatability, stable welding joint quality, and the strength coefficient of the welding joint is as high as 0.95 or more. In addition, the welding method of the present application is easy to realize automation, and has wide application prospect in the fields of ships, ocean engineering, etc.

[0040] To achieve the best match between the thick plate base material and the welding wire, further reduce the welding porosity and thermal deformation during welding, promote the formation of equiaxed crystals in the weld area, and improve the tensile strength of the welding joint, in a preferred embodiment, in step S1, the weight percentage of Mg in the 5XXX series aluminum alloy thick plate is < the weight percentage of Mg in the 5XXX series aluminum alloy welding wire, and the difference is 0.1~0.5%; and / or the 5XXX series aluminum alloy thick plate comprises, by weight percentage, Mg 4.0~4.9%, Mn 0.4~1.0%, Cr 0.05~0.25%, Si≤0.4%, Fe≤0.4%, Cu≤0.14%, Zn≤0.25%, Ti 0.01~0.15%, the balance being Al and unavoidable impurities, single impurity≤0.05%, total impurities≤0.15%.

[0041] Based on similar reasons, in a preferred embodiment, in step S1, the 5XXX series aluminum alloy welding wire comprises, in terms of weight percentage, Mg 4.3-5.2%, Mn 0.4-1.0%, Cr 0.02-0.25%, Si≤0.4%, Fe≤0.4%, Cu≤0.1%, Zn≤0.25%, Ti≤0.15%, the balance being Al and unavoidable impurities, single impurity≤0.05%, total impurities≤0.15%; and / or the diameter of the 5XXX series aluminum alloy welding wire is 1-1.5 mm.

[0042] In a preferred embodiment, in step S2, the single-side groove angle of the double-V groove near the to-be-welded side of the 5XXX series aluminum alloy thick plate is 26°-34°; and / or the thickness of the intermediate root face is 0-1 mm; and / or the laser power of the pre-welding laser cleaning is 50 W-100 W, and the cleaning speed is 4-20 mm / s. In some embodiments, the form of the pre-welding laser cleaning includes: performing non-contact scanning cleaning in a straight line or a spiral along the welding direction; and / or the double-V groove and the groove extension area are subjected to pre-welding laser cleaning to obtain a pre-welding cleaning body; the groove extension area is an area 0-60 mm away from the double-V groove.

[0043] Controlling the single-side angle of the double-V groove in the above range is beneficial to improving the stability and fluidity of the molten pool, promoting the full fusion of the materials in the welding process, and at the same time, moderately reducing the heat input of the weld, so as to effectively inhibit the grain coarsening and enhance the microstructure and mechanical properties of the weld. The above intermediate root face can improve the welding efficiency while maintaining the penetration and weld forming quality, and reduce the stress concentration and crack risk caused by excessive fusion between the welds. Controlling the parameters of the pre-welding laser cleaning in the above range is beneficial to promoting the effective removal of the oxide film, reducing the excessive thermal effect on the base material, maintaining its original physical and chemical properties, and thoroughly purifying the welding area to prevent the generation of hydrogen pores, thereby further improving the cleanliness of the welding structure and the weld quality.

[0044] Based on similar reasons, preferably, the laser frequency of the pre-welding laser cleaning is 15-25 kHz, and the laser emission speed is 7000-9000 mm / s.

[0045] In a preferred embodiment, the laser power of the interpass laser cleaning is 100-200 W, and the cleaning speed is 4-20 mm / s; and / or the total cleaning depth of the interpass laser cleaning in each weld bead is 0.2-0.5 mm. In some embodiments, the form of the interpass laser cleaning includes full-width cleaning. The power of the interpass laser cleaning is higher than that of the pre-welding laser cleaning, which helps to form a clean and activated surface on the subsequent weld bead, provides favorable conditions for the formation of fine grains, and thus improves the performance of the welded joint at the micro level and improves the crack resistance and corrosion resistance of the weld. Under the above conditions, the interpass cleaning can promote good bonding between the weld beads and reduce the adverse effects on the underlying weld bead, achieving uniform and refined microstructure in the weld zone.

[0046] For the purpose of further improving the geometric accuracy of the welded structure, in a preferred embodiment, in step S3, 1 mm≤J min ≤3 mm; and / or, 2 mm≤J max ≤6 mm. When the asymmetric linearly tapered gap of the to-be-welded joint is within the above range, it is more conducive to accurately control the welding deformation and further reduce the warping and angular deformation caused by the accumulation of thermal stress between the plates.

[0047] To reduce the oxidation and contamination that may be introduced during welding, and to optimize the thermodynamic conditions in the weld forming process, thereby providing stable and reliable protection for high-quality welding, in a preferred embodiment, in step S4, the shielding gas includes argon and / or helium; and / or the flow rate of the shielding gas is 20-30 L / min; and / or 1≤n≤8. The above conditions are conducive to fine control of the heat input and cooling rate of each pass welding, which can promote sufficient fusion of the molten pool and reduce abnormal grain growth, achieve more uniform and refined microstructure of the weld, and improve the comprehensive mechanical properties of the welded joint. In some embodiments, the total number of layers of single-sided multi-layer multi-pass MIG welding is denoted as m, m=n.

[0048] In a preferred embodiment, in step S4, the welding current of the straight welding is less than that of the 8-shaped weaving, and the difference is 2-8 A; and / or the welding current of the straight welding is 250-270 A, and the welding speed is 55-65 cm / min; and / or the welding current of the 8-shaped weaving is 260-270 A, and the welding speed is 50-60 cm / min. Under the above conditions, the complex disturbance of the welding heat source in the molten pool can further promote the refinement of the grains and create favorable conditions for the formation of equiaxed grains. The difference in current and speed between the straight welding and the 8-shaped weaving is conducive to promoting the deep fusion of the first weld bead and the sufficient filling and refinement of the subsequent weld bead, which collectively improves the weld porosity, thermal deformation, and grain coarsening problems, and achieves I-grade weld quality.

[0049] Preferably, when the front surface of the to-be-welded joint is subjected to single-sided multi-layer multi-pass MIG welding, 3-8 times of inter-pass laser cleaning are performed on the corresponding weld pass after each pass welding; when the back surface of the to-be-welded joint is subjected to single-sided multi-layer multi-pass MIG welding, 3-8 times of inter-pass laser cleaning are performed on the corresponding weld pass after each pass welding from the 1st pass to the n-1th pass.

[0050] Preferably, the front surface of the to-be-welded joint is first subjected to single-sided multi-layer multi-pass MIG welding, at least one time of inter-pass laser cleaning is performed on the corresponding weld pass after each pass welding; then the back surface of the to-be-welded joint is subjected to single-sided multi-layer multi-pass MIG welding, at least one time of inter-pass laser cleaning is performed on the corresponding weld pass after each pass welding from the 1st pass to the n-1th pass.

[0051] In another typical embodiment of the present application, a welded joint is also provided, which is obtained by using the above-mentioned welding method of the 5XXX series aluminum alloy thick plate, and based on the improved welding method, the welding porosity is significantly reduced, the thermal deformation is alleviated, the I-grade weld quality can be obtained, the strength coefficient of the welded joint is as high as 0.95 or more, and a uniform and fine equiaxed crystal structure can be formed in the weld zone, which is suitable for high-strength and high-quality welded manufacturing of thick plate aluminum alloy structures in the fields of ships, ocean engineering and rail transportation.

[0052] Specifically, in a preferred embodiment, the tensile strength of the welded joint is 295-305 MPa, and the welding coefficient is 0.95-0.98; and / or the average grain size of the weld zone of the welded joint is 90-110 μm, and the microstructure is equiaxed crystal.

[0053] Typically but not limitedly, the thickness of the 5XXX series aluminum alloy thick plate is 15 mm, 18 mm, 20 mm, 22 mm, 25 mm, 28 mm, 30 mm or any range value consisting of any two of the above values.

[0054] Typically but not limitedly, the diameter of the 5XXX series aluminum alloy welding wire is 1 mm, 1.1 mm, 1.2 mm, 1.3 mm, 1.4 mm, 1.5 mm or any range value consisting of any two of the above values.

[0055] Typically but not limitedly, the difference between the weight percentage of Mg in the 5XXX series aluminum alloy thick plate and the weight percentage of Mg in the 5XXX series aluminum alloy welding wire is 0%, 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.2% or any range value consisting of any two of the above values.

[0056] Typically but not exclusively, the difference between the weight percent of Mg in the 5XXX series aluminum alloy thick plate and the weight percent of Mg in the 5XXX series aluminum alloy welding wire is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, or a range defined by any two of these values.

[0057] Typically but not exclusively, the 5XXX series aluminum alloy thick plate includes, by weight percent, Mg 4.0%, 4.2%, 4.5%, 4.8%, 4.9%, or a range defined by any two of these values, Mn 0.4%, 0.5%, 0.6%, 0.8%, 1.0%, or a range defined by any two of these values, Cr 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, or a range defined by any two of these values, Si 0%, 0.1%, 0.2%, 0.3%, 0.4%, or a range defined by any two of these values, Fe 0%, 0.1%, 0.2%, 0.3%, 0.4%, or a range defined by any two of these values, Cu 0%, 0.02%, 0.05%, 0.1%, 0.12%, 0.14%, or a range defined by any two of these values, Zn 0%, 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, or a range defined by any two of these values, Ti 0.01%, 0.02%, 0.05%, 0.1%, 0.15%, or a range defined by any two of these values, with the balance being Al and unavoidable impurities.

[0058] Typically but not exclusively, the 5XXX series aluminum alloy welding wire includes, by weight percent, Mg 4.3%, 4.5%, 4.8%, 5.0%, 5.2%, or a range defined by any two of these values, Mn 0.4%, 0.5%, 0.6%, 0.8%, 1.0%, or a range defined by any two of these values, Cr 0.02%, 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, or a range defined by any two of these values, Si 0%, 0.1%, 0.2%, 0.3%, 0.4%, or a range defined by any two of these values, Fe 0%, 0.1%, 0.2%, 0.3%, 0.4%, or a range defined by any two of these values, Cu 0%, 0.02%, 0.05%, 0.08%, 0.1%, or a range defined by any two of these values, Zn 0%, 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, or a range defined by any two of these values, Ti 0%, 0.05%, 0.1%, 0.15%, or a range defined by any two of these values, with the balance being Al and unavoidable impurities.

[0059] Typically but not exclusively, the J min1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, or any range value formed by any two of the numerical values. max 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, or any range value formed by any two of the numerical values. max -J min 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, or any range value formed by any two of the numerical values.

[0060] Typically but not limitedly, the laser power of the pre-weld laser cleaning is less than the laser power of the interlayer laser cleaning, and the difference is 50 W, 60 W, 70 W, 80 W, 90 W, 100 W, or any range value formed by any two of the numerical values.

[0061] Typically but not limitedly, n is 2, 3, 4, 5, 6, 7, 8, or any range value formed by any two of the numerical values.

[0062] Typically but not limitedly, the welding current of the straight welding is less than the welding current of the 8-shaped weaving, and the difference is 0 A, 2 A, 5 A, 8 A, 10 A, or any range value formed by any two of the numerical values.

[0063] The application will be further described in detail below in combination with specific examples, which cannot be understood as limiting the scope of the application claimed.

[0064] Example 1 Welding of a 20 mm thick 5083 aluminum alloy plate for shipbuilding

[0065] Step S1, prepare 5083-O aluminum alloy plate as 5XXX series aluminum alloy thick plate, state O, tensile strength 309 MPa, size 20 mm thick; at the same time, prepare 5XXX series aluminum alloy welding wire with a diameter of 1.2 mm; the composition of the thick plate and the welding wire is shown in Table 1.

[0066] Step S2, process the welding sides of the two 5XXX series aluminum alloy thick plates into double V-shaped grooves, the single side groove angle A = 30°, and the middle blunt edge thickness B = 1 mm; along the welding direction, use a 200 W pulsed fiber laser (parameter setting: power 70 W, frequency 20 kHz, laser emission speed 8000 mm / s) to perform linear non-contact scanning cleaning on the processed double V-shaped grooves and the two sides 30 mm area, the cleaning speed is 5 mm / s, and a pre-weld cleaning body is obtained.

[0067] Step S3, assemble the pre-weld cleaning body to obtain a to-be-welded joint; along the welding direction, the horizontal gap of the to-be-welded joint linearly increases, the horizontal gap J min 1 mm, the horizontal gap J max2 mm, J max - J min = 1 mm, forming a linearly graded gap.

[0068] Step S4, preheat the joint to be welded to 80°C, the protective gas is 99.99% argon, the flow rate is set to 25 L / min, and the front and back of the joint to be welded are sequentially welded by single-sided 2-layer 2-pass MIG welding:

[0069] a. First pass welding on the front: straight welding is used, the current is 260 A, and the speed is 60 cm / min. Immediately after welding, 3 times of interlayer laser cleaning are performed.

[0070] b. Second pass welding on the front: 8-shaped weaving is used, the current is 265 A, the speed is 55 cm / min, the weaving frequency is 2 Hz, and the weaving amplitude is 3 mm. Immediately after welding, 3 times of interlayer laser cleaning are performed.

[0071] c. Back bevel depth cleaning: flip the workpiece, and perform 3 times of interlayer laser cleaning on the back bevel until the fusion metal of the front weld is exposed.

[0072] d. First pass welding on the back: straight welding is used, the current is 260 A, and the speed is 60 cm / min. Immediately after welding, 3 times of interlayer laser cleaning are performed.

[0073] e. Second pass welding on the back: 8-shaped weaving is used, the current is 265 A, the speed is 55 cm / min, the weaving frequency is 2 Hz, and the weaving amplitude is 3 mm. The welding is completed.

[0074] The above interlayer laser cleaning includes: using a 200W pulsed fiber laser (parameter settings: power 150W, frequency 20kHz, laser emission speed 8000mm / s) to clean the weld with full width, and the total cleaning depth of each weld is about 0.3mm. The sequence diagram of single-sided 2-layer 2-pass MIG welding and interlayer laser cleaning of Example 1 is shown in Figure 2 , which sequentially includes interlayer laser cleaning 1 of the first pass weld on the front, interlayer laser cleaning 2 of the second pass weld on the front, interlayer laser cleaning 3 of the back bevel, and interlayer laser cleaning 4 of the first pass weld on the back.

[0075] Examples 2 to 5

[0076] The difference from Example 1 is that in step S1, the composition and thickness of the 5XXX series aluminum alloy thick plate, and the composition and diameter of the 5XXX series aluminum alloy welding wire are different, as shown in Table 1.

[0077] Examples 6 to 7

[0078] The difference from Example 1 is that the double V-shaped groove and the horizontal gap of the joint to be welded are different, as shown in Table 2.

[0079] Examples 8-9

[0080] The difference from Example 1 is that the parameters of laser cleaning are different, see Table 3 for details.

[0081] Examples 10-11

[0082] The difference from Example 1 is that the parameters of welding are different, see Table 4 for details.

[0083] Comparative Example 1

[0084] The difference from Example 1 is that in step S3, the horizontal gap of the joint to be welded is constant at 2 mm along the welding direction. The constant gap assembly will cause uneven thermal shrinkage during welding, causing joint deformation, continuous interference with the formation of the molten pool and the weld bead, resulting in incomplete penetration of the welded joint.

[0085] Comparative Example 2

[0086] The difference from Example 1 is that in step S4, all straight bead welding is used, and the second layer is welded in two passes to fill the double V groove. In the multi-pass welding process, straight bead welding cannot produce strong mechanical stirring and thermal disturbance to the molten pool, the grain refinement effect is poor, the weld has more pores, and even cannot meet the requirements of III-grade weld.

[0087] Comparative Example 3

[0088] The difference from Example 1 is that interlayer laser cleaning is not performed. The absence of interlayer laser cleaning, which has cleaning and activating effects, results in serious interlayer inclusion in the obtained weld, and there are many pores, and even cannot meet the requirements of III-grade weld.

[0089] Performance test:

[0090] The welded joints prepared in the above examples and comparative examples were detected, and the results are shown in Table 5.

[0091] Welding seam level: non-destructive testing was carried out according to CB / T 3747-2013 by X-ray technology.

[0092] Weld microstructure: metallographic analysis was carried out using a metallographic microscope.

[0093] Tensile strength: detected according to GB / T 228.1-2021 by using an electronic tensile testing machine.

[0094] Welding coefficient: the calculation formula is welding coefficient = tensile strength of welded joint ÷ tensile strength of base material.

[0095] Table 1

[0096]

[0097] Table 2

[0098]

[0099] Table 3

[0100]

[0101] Table 4

[0102]

[0103] Table 5

[0104]

[0105] The X-ray detection image of the weld joint of Example 1 is shown in Figure 1. Figure 3 It can be seen that the method of the present application can obtain a Grade I weld. The grain structure image of the weld joint of Example 1 is shown in Figure 2. Figure 4 It can be seen that the grain structure is uniform and fine. The equiaxed crystal structure of the weld zone of the weld joint of Example 1 is shown in Figure 3. Figure 5 The equiaxed crystal structure of the base material zone is shown in Figure 4. Figure 6 It can be seen that the central zone of the weld is a typical equiaxed crystal with an average grain size of about 100 μm, and the base material zone is a typical rolling fiber structure. The post-tensioning photograph of the weld joint of Example 1 is shown in Figure 5. Figure 7 .

[0106] As can be seen from the above, compared with the comparative examples, the embodiments of the present application construct a closed-loop technical system from material matching, structure design to the whole process control of welding for the 5XXX series aluminum alloy thick plate with a thickness of more than 15 mm. By designing the 5XXX series welding wire with high magnesium content matched with the base material, optimizing the double-V groove structure, pre-welding and interlayer laser collaborative purification, asymmetric gap assembly based on hot deformation prediction, and grain refinement synergy of fusion laser interlayer cleaning and 8-shaped weaving, the core problems of welding porosity, hot deformation and grain coarsening are systematically solved, Grade I weld quality is obtained, the strength coefficient of the weld joint is high, and uniform and fine equiaxed crystal structure can be formed in the weld zone. The method of the present application is versatile, and is especially suitable for high-strength and high-quality welding manufacturing of thick plate aluminum alloy structures in the fields of ships, ocean engineering and rail transportation.

[0107] In addition, it can be seen that when each process parameter is within the preferred range of the present application, the comprehensive effect is better.

[0108] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method of welding a 5XXX-series aluminium alloy plate, characterized in that, The method comprises the following steps: Step S1, preparing a 5XXX series aluminum alloy thick plate and a 5XXX series aluminum alloy welding wire; the thickness of the 5XXX series aluminum alloy thick plate is 15-30 mm, and the difference between the weight percentage of Mg in the 5XXX series aluminum alloy thick plate and the weight percentage of Mg in the 5XXX series aluminum alloy welding wire is ≤1.2 %; Step S2, processing the welding sides of two pieces of the 5XXX series aluminum alloy thick plate into double-V-shaped grooves, and performing laser cleaning before welding on the double-V-shaped grooves to obtain a cleaning body before welding; the double-V-shaped grooves have an intermediate blunt edge; Step S3, assembling the pre-weld cleaning body to obtain a to-be-welded joint; along a welding direction, a horizontal gap of the to-be-welded joint linearly increases, and the horizontal gap at a welding starting point is recorded as J min , the horizontal gap at a welding ending point is recorded as J max , 1mm≤J max -J min ≤3mm; Step S4, preheating the welding joint to be welded to 60-100 DEG C, and sequentially performing single-layer multi-pass MIG welding on the front and back of the welding joint to be welded in a protective gas environment; the total pass number of the single-layer multi-pass MIG welding is denoted as n, the welding form of the first pass is straight welding, and the welding form of the second pass to the n-th pass is 8-shaped weaving; the welding current of the straight welding is ≤ the welding current of the 8-shaped weaving, and the difference is 0-10 A; wherein, when the single-layer multi-pass MIG welding is performed on the front of the welding joint to be welded, the corresponding welding bead is subjected to at least one interlayer laser cleaning after each pass welding; when the single-layer multi-pass MIG welding is performed on the back of the welding joint to be welded, the corresponding welding bead is subjected to at least one interlayer laser cleaning after each pass welding in the first pass to the n-1-th pass; the laser power of the laser cleaning before welding is < the laser power of the interlayer laser cleaning, and the difference is 50-100 W.

2. The method of welding a 5XXX-series aluminum alloy plate according to claim 1, characterized by, In the step S1, the weight percentage of Mg in the 5XXX series aluminum alloy thick plate is < the weight percentage of Mg in the 5XXX series aluminum alloy welding wire, and the difference is 0.1-0.5 %; and / or According to the weight percentage, the 5XXX series aluminum alloy thick plate comprises Mg 4.0-4.9 %, Mn 0.4-1.0 %, Cr 0.05-0.25 %, Si ≤0.4 %, Fe ≤0.4 %, Cu ≤0.14 %, Zn ≤0.25 %, Ti 0.01-0.15 %, the balance being Al and inevitable impurities, single impurity ≤0.05 %, and total impurities ≤0.15 %.

3. The welding method of a 5XXX-series aluminum alloy thick plate according to claim 1 or 2, characterized by, In the step S1, According to the weight percentage, the 5XXX series aluminum alloy welding wire comprises Mg 4.3-5.2 %, Mn 0.4-1.0 %, Cr 0.02-0.25 %, Si ≤0.4 %, Fe ≤0.4 %, Cu ≤0.1 %, Zn ≤0.25 %, Ti ≤0.15 %, the balance being Al and inevitable impurities, single impurity ≤0.05 %, and total impurities ≤0.15 %; and / or The diameter of the 5XXX series aluminum alloy welding wire is 1-1.5 mm.

4. The welding method of the 5XXX-series aluminum alloy thick plate according to claim 1 or 2, characterized by, In the step S2, the single-side groove angle of the double-V-shaped groove close to the welding side of the 5XXX series aluminum alloy thick plate is 26-34 DEG; and / or the thickness of the intermediate blunt edge is 0-1 mm; and / or the laser power of the laser cleaning before welding is 50-100 W, and the cleaning speed is 4-20 mm / s. 5.The welding method of the 5XXX series aluminum alloy thick plate according to claim 1 or 2, characterized in that, the laser power of the interlayer laser cleaning is 100 W to 200 W, and the cleaning speed is 4 to 20 mm / s; and / or the total cleaning depth of the interlayer laser cleaning in each of the welding beads is 0.2 to 0.5 mm.

6. The welding method of the 5XXX-series aluminum alloy thick plate according to claim 1 or 2, characterized by, In the step S3, 1 mm ≤ J min ≤ 3 mm; and / or, 2 mm ≤ J max ≤ 6 mm.

7. The method of welding a 5XXX-series aluminum alloy plate according to claim 1 or 2, characterized in that, in the step S4, the shielding gas comprises argon and / or helium; and / or the flow rate of the shielding gas is 20 to 30 L / min; and / or 2≤n≤8; and / or the swing frequency of the 8-shaped weaving is 2 to 4 Hz, and the swing amplitude is 2 to 5 mm.

8. The method of welding a 5XXX-series aluminum alloy plate according to claim 1 or 2, characterized in that, in the step S4, the welding current of the straight bead welding is < the welding current of the 8-shaped weaving, and the difference is 2 to 8 A; and / or the welding current of the straight bead welding is 250 to 270 A, and the welding speed is 55 to 65 cm / min; and / or the welding current of the 8-shaped weaving is 260 to 270 A, and the welding speed is 50 to 60 cm / min.

9. A welded joint, characterized by obtained by using the welding method of the 5XXX series aluminum alloy thick plate according to any one of claims 1 to 8. 10.The welded joint according to claim 9, characterized in that, the tensile strength of the welded joint is 295 to 305 MPa, and the welding coefficient is 0.95 to 0.98; and / or the average grain size of the weld zone of the welded joint is 90 to 110 μm.

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