Laser welding method for high-strength metal

Abstract

The invention relates to the field of high-strength metal welding, in particular to a laser welding method for high-strength metal. The method comprises the steps that (1) a set of high-strength metal workpieces are provided and assembled to form a to-be-welded assembly with a to-be-welded welding line; 2) providing a first laser heat source to irradiate the welding line to form a first main laser melting zone and a first heat affected zone; 3) executing at least one progressive laser treatment process, each process comprising: providing a kth laser heat source to irradiate a (k-1) th heat affected zone formed in the previous process, k > = 2, and forming a kth heat affected zone; wherein the parameter control meets the following conditions: the heat input of the kth laser heat source is less than the heat input of the (k-1) th laser heat source; and the irradiation area of the kth laser heat source is less than or equal to the irradiation area of the (k-1) th laser heat source. According to the method, the width of the heat affected zone of the final welding joint is gradually reduced by repeatedly melting the previous welding heat affected zone through laser, so that the strength of the welding joint is improved.

Description

Technical Field

[0001] This invention relates to the field of high-strength metal welding, and more specifically to a laser welding method for high-strength metals. Background Technology

[0002] Fusion welding is a general term for welding processes, including arc welding and laser beam welding. It relies on melting to join materials with similar compositions and melting points. Due to the inherent high-temperature phase transformation in fusion welding, the areas on both sides of the weld where the solid base material undergoes significant changes in microstructure and properties under the welding thermal cycle are called the heat-affected zone (HAZ). To ensure the quality of the weld joint, the microstructure and properties of the HAZ must also meet the requirements. With the increasing use of various high-strength steels, stainless steels, heat-resistant steels, and some special materials (such as aluminum alloys, titanium alloys, nickel alloys, composite materials, and ceramics) in production, the problems existing in the HAZ have become more complex, making it a weak point in weld joints.

[0003] The microstructure of the heat-affected zone (HAZ) in a weld is uneven, resulting in uneven properties. Unlike the weld itself, where performance requirements can be met by adjusting the chemical composition and employing appropriate welding techniques, the HAZ's properties cannot be altered through compositional changes. Its inhomogeneity arises from the welding thermal cycle. For typical welded structures, the primary considerations are the HAZ's hardening, embrittlement, toughening, and softening, as well as its overall mechanical properties, corrosion resistance, and fatigue performance.

[0004] Weld softening refers to the phenomenon where the hardness or strength of a metal material decreases in the heat-affected zone (HAZ) under the influence of welding thermal cycles. Cold-worked or heat-treated metals or alloys generally experience varying degrees of softening in the HAZ. This is most typical in high-strength steels that have undergone tempering and alloys with precipitation and dispersion strengthening, which soften or lose strength in the HAZ after welding. Softening in cold-worked metals or alloys is caused by recrystallization. To address weld softening, current methods primarily include more efficient laser welding and electron beam welding, post-weld heat treatment, post-weld mechanical treatment, and strict control of heat input during the welding process to mitigate the effects of HAZ softening.

[0005] The invention patent application No. 201410806107.5 discloses a method for improving the mechanical properties and corrosion resistance of weld zones using ultrasonic and electrical pulse coupling. This method involves introducing pulsed current to the weld surface and the surface of the heat-affected zone of the metal part for electroplastic treatment, while simultaneously using an ultrasonic impact device to sequentially ultrasonically impact the surface of the working area through its high-hardness impact indenter. This method requires very complex equipment and processes, resulting in high costs and low efficiency.

[0006] CN117548807B discloses a method that uses ultrasonic impact equipment during welding to strengthen the welded joint by applying ultrasonic impact immediately after welding. However, this method uses complex ultrasonic equipment, which is inefficient and costly.

[0007] CN 102658416 A discloses a mixed gas shielded welding process for precipitation-strengthened high-strength steel. This process employs mixed gas shielded welding and single / double welding with double-sided forming techniques to weld precipitation-strengthened high-strength steel with a tensile strength of 600 MPa, effectively reducing the softening width of the heat-affected zone. Optimized welding process parameters are used, employing an 80% Ar + 20% CO2 mixed gas, a welding current of 90-140 A, and a heat input of 7-12 kJ / cm. Precipitation strengthening and grain refinement are achieved through Ti(C,N), and the tested weld joint tensile strength reaches 710 MPa. This method primarily reduces the heat-affected zone width through the optimization of various shielding gases and process parameters; however, it is only applicable to 600 MPa grade high-strength steel, limiting its applicability, and the process control is complex.

[0008] CN112458243A discloses a method for improving the softening of the heat-affected zone (HAZ) in arc welding of ultra-high strength QP steel. This patent primarily employs laser hardening technology to effectively address the softening problem in the HAZ during arc welding of thin ultra-high strength QP steel plates, thereby increasing the hardness of the weld HAZ. The patent mainly describes the laser hardening technology, determining the softening width of the weld HAZ, and setting the power and scanning speed of the laser spot. However, this technology has high equipment requirements and is excessively costly.

[0009] CN111069738B discloses a method for improving softening in aluminum alloy welding. By adding a forced cooling device during the welding process to constrain the spread of welding heat in the transverse direction of the sheet metal, the extent and degree of heat's influence on the aluminum alloy are reduced, thereby decreasing the degree and width of softening in the heat-affected zone. However, this method requires complex forced cooling equipment, is not applicable to all working conditions, and is complex and costly.

[0010] CN108637532B discloses a method for solving the softening problem of the heat-affected zone after welding by injecting compressed gas into the heat-affected zone of electroslag welding through a directional cooling device. Although this method can improve the softening problem to some extent, it requires high control of the injected compressed gas and is costly.

[0011] As can be seen, current methods for addressing the softening problem of the heat-affected zone (HAZ) in high-strength metal welding mainly involve forced cooling during welding, post-weld mechanical treatment, and optimization of process parameters. All of these methods are complex, costly, and inefficient. Therefore, there is an urgent need for a simple, low-cost, and highly efficient welding method to overcome the softening problem in the HAZ of high-strength metal welding. Summary of the Invention

[0012] This invention provides a highly efficient and simple laser welding method to overcome the softening problem of the heat-affected zone (HAZ) in high-strength metal welding, significantly reducing the width of the HAZ and improving its strength and hardness. By repeatedly remelting the HAZ formed in the previous laser pass using laser heat, and utilizing the narrow range of subsequent laser heat sources, the width of the HAZ is gradually reduced, thereby improving its performance. Specifically, the technical solution of this invention is as follows:

[0013] This invention provides a laser welding method for high-strength metals, comprising the following steps:

[0014] 1) Provide a set of high-strength metal workpieces to be assembled into a welding assembly, wherein the welding assembly has a welding line to be welded;

[0015] 2) Provide a first laser heat source to irradiate the welding line to form a first main laser melting zone and a first heat-affected zone adjacent to the melting zone;

[0016] 3) Perform at least one progressive laser processing step, each step including:

[0017] Provide the (k-1)th heat-affected zone formed in the previous process before the kth laser heat source irradiation, where k≥2, and melt the entire region or a part of the adjacent melting zone to form a region with a width B. k The kth thermally affected zone;

[0018] The parameter control satisfies the following conditions: the heat input of the k-th laser heat source is less than the heat input of the (k-1)-th laser heat source, where the heat input Q = P / v, v is the welding speed, and P is the power of the laser heat source; and the irradiation area of ​​the k-th laser heat source is less than or equal to the irradiation area of ​​the (k-1)-th laser heat source.

[0019] Preferably, the parameter control satisfies: the power of the k-th laser heat source ≤ the power of the (k-1)-th laser heat source. More preferably, the parameter control satisfies: 0.2P k-1 ≤P k ≤P k-1 And P2≤0.6P1, P k P k-1 , respectively, are the power of the k-th and (k-1)-th laser heat sources.

[0020] Preferably, the parameter control satisfies: the welding speed of the k-th laser heat source ≥ the welding speed of the (k-1)-th laser heat source. More preferably, the parameter control satisfies: 1.4v k-1 ≥v k ≥v k-1 v k v k-1 , respectively, are the welding speeds of the k-th and (k-1)-th laser heat sources.

[0021] Preferably, the parameter control satisfies: 0.2Q k-1 ≤Q k ≤0.7Q k-1 Q k Q k-1 These are the heat inputs of the k-th and (k-1)-th laser heat sources, respectively.

[0022] Preferably, the parameter control satisfies: 0.01S k-1 ≤S k ≤S k-1 S k S k-1 , respectively, are the spot areas of the k-th and (k-1)-th laser heat sources.

[0023] Preferably, the parameter control satisfies the following: the center of the laser spot of the k-th laser heat source is located in the (k-1)-th heat-affected zone, and the distance between it and the edge of the melting zone generated by the irradiation of the (k-1)-th laser heat source is 0.1B. k-1 ~0.3B k-1 B k-1 denoted as the width of the (k-1)th heat-affected zone.

[0024] When the spot area and shape are the same in each process, such as being circular or square, the spot size D of the k-th laser heat source is controlled. k <Spot size D of the (k-1)th laser heat source k-1 This allows for the achievement of a light spot area S. k <S k-1 The (k-1)th heat-affected zone is the heat-affected zone formed by the (k-1)th laser heat source irradiation.

[0025] Using this method, the width of each new heat-affected zone is smaller than the width of the previous heat-affected zone, i.e., B. k <B k-1 For example, B3 < B2 < B1, ultimately achieving a gradual decrease in the width of the heat-affected zone.

[0026] For example, the assembly form of the metal workpiece is any one of butt joint, lap joint, or corner joint.

[0027] Preferably, the final heat-affected zone width Bn of the welded joint formed in step 3) is ≤0.5mm and less than 60% of the initial width. The initial width is the width B1 of the first heat-affected zone.

[0028] For example, the equivalent circular diameter of the spot area of ​​the first laser heat source is 0.4-0.5 mm, and the equivalent circular diameter of the spot area of ​​the second laser heat source is no more than 0.3 mm, and more narrowly, no more than 0.2 mm. Further, a progressive laser processing step is performed, and the equivalent circular diameter of the spot area of ​​the third laser heat source is no more than 0.1 mm, and more narrowly, no more than 0.05 mm.

[0029] Preferably, the beam quality of the k-th laser heat source performing the progressive laser processing step satisfies M. 2 ≤1.3.

[0030] Furthermore, two k-th laser heat sources are symmetrically distributed on both sides of the weld formed by the melting of the first laser heat source, and the area of ​​the heat-affected zone formed by the melting of the (k-1)-th laser heat source is more than 50%, and the area of ​​the melted zone formed by the melting of the (k-1)-th laser heat source is less than 50%.

[0031] For example, the first laser heat source can be used for various forms of laser welding, such as single laser welding, laser filler wire welding, and laser composite welding.

[0032] Preferably, the number of times n of the progressive laser processing step is executed satisfies 1≤n≤5.

[0033] Preferably, all laser heat sources act simultaneously on the assembly to be welded at the same welding speed. The irradiation spot of the k-th laser heat source and the (k-1)-th laser heat source maintain a preset distance in the welding direction. This preset distance is set such that when the k-th laser heat source irradiates the target area of ​​the (k-1)-th heat-affected zone formed in the previous process, the molten zone formed by the (k-1)-th laser heat source in the target area and adjacent to the target area has solidified. By reasonably setting this preset distance, heat accumulation can be effectively avoided and subsequent laser treatment can be performed only after the previous molten zone has solidified. In this way, all laser heat sources are completed in one welding process, improving efficiency and reducing the number of thermal cycles. Preferably, all laser heat sources are integrated into a single laser processing device.

[0034] Compared with the prior art, the beneficial effects of the present invention are:

[0035] 1) The integrated multi-laser heat source is used to realize the manufacturing of the overall welded joint, which can precisely control the welding range and melting area, and realize the precise manufacturing of the welded joint; by optimizing the arrangement and energy output of the multi-laser heat source, a variety of materials can be applied, with a wide welding range and strong adaptability.

[0036] 2) This method only requires controlling parameters such as the output energy and relative positions of the laser heat source, and does not involve other equipment such as forced water cooling, so the manufacturing cost of the whole method is lower;

[0037] 3) In this method, the synergistic effect of multiple laser heat sources can optimize weld formation, avoid the formation of defects such as undercut and spatter, and obtain a welded joint with better forming quality.

[0038] 4) This method can achieve the preparation of higher strength welds by simultaneously feeding welding wire and other welding materials during the welding process and by designing different welding material compositions. It can also adapt to various conditions with gaps, misalignments, etc., and has a wide range of applications.

[0039] 5) This method utilizes a high-beam-quality laser beam for welding, which can significantly improve melting efficiency, increase manufacturing efficiency, and reduce costs. Attached Figure Description

[0040] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0041] Figure 1 The diagram shown is a schematic diagram of the workpiece docking assembly involved in this invention;

[0042] Figure 2 The figure shown is a schematic diagram of the workpiece overlap angle assembly involved in this invention;

[0043] Figure 3 The diagram shown is a schematic diagram of the workpiece overlapping assembly involved in this invention;

[0044] Figure 4 The diagram shown is a schematic of the welding laser heat source arranged on the top surface of the assembly in this invention.

[0045] Figure 5 The diagram shown is a schematic diagram of the joint cross-section formed by the first laser heat source acting on the workpiece during docking, as described in this invention.

[0046] Figure 6 The diagram shown is a schematic of the second laser heat source irradiating the top surface of the connector in this invention.

[0047] Figure 7 The figure shown is a schematic diagram of the cross-section of the joint after irradiation by the second laser heat source involved in this invention;

[0048] Figure 8 The diagram shown is another schematic diagram of the cross-section of the joint after irradiation by the second laser heat source involved in this invention;

[0049] Figure 9The diagram shown is a schematic of laser filler wire welding involved in this invention;

[0050] Figure 10 The diagram shown is a schematic representation of the top surface of the connector involved in this invention.

[0051] Figure 11 The image shown is a metallographic diagram of the joint cross-section formed in Comparative Example 1 of this invention;

[0052] Figure 12 The image shown is a metallographic diagram of the joint cross-section formed by a single laser remelting in Embodiment 1 of this invention;

[0053] Figure 13 The image shown is a metallographic diagram of the joint cross-section formed by secondary laser remelting in Embodiment 2 of this invention;

[0054] Figure 14 The image shown is a metallographic diagram of the joint cross-section formed in Comparative Example 2 of this invention;

[0055] Figure 15 The image shown is a metallographic diagram of the joint cross-section formed by a single laser remelting in Example 4 of this invention.

[0056] In the attached diagram, 111-first metal workpiece, 112-second metal workpiece, b0-assembly gap, 1111-welding line; 11-first main laser irradiation spot; 21-second laser irradiation spot, 31-third laser irradiation spot, 122-first main laser melting zone, 121-first heat-affected zone, B1-width of the first heat-affected zone, 130-second laser melting zone, 131-second heat-affected zone, B2-width of the second heat-affected zone, 3-welding wire, 110-first main laser beam, d1-distance between the second laser irradiation spot and the first main laser irradiation spot in the welding travel direction, t1-width of the first main laser melting zone, t2-width of the second laser melting zone, 140-third laser melting zone, 141-third heat-affected zone. Detailed Implementation

[0057] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the present invention is further described below in conjunction with specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, the accompanying drawings are schematic diagrams; therefore, the apparatus and device of the present invention are not limited by the size or scale of the schematic diagrams.

[0058] It should be noted that in the claims and specification of this patent, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one" does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0059] This invention provides a laser welding method for high-strength metals, the method comprising the following steps:

[0060] 1) Provide a set of high-strength metal workpieces to be assembled into a welding assembly, wherein the welding assembly has a welding line to be welded;

[0061] 2) Provide a first laser heat source to irradiate the welding line to form a first main laser melting zone and a first heat-affected zone adjacent to the melting zone;

[0062] 3) Perform at least one progressive laser processing step, each step including:

[0063] Provide the (k-1)th heat-affected zone formed in the previous process before the kth laser heat source irradiation, where k≥2, and melt the entire region or a part of the adjacent melting zone to form a region with a width B. k The kth thermally affected zone;

[0064] The parameter control satisfies the following conditions: the heat input of the k-th laser heat source is less than the heat input of the (k-1)-th laser heat source, where heat input Q = P / v, v is the welding speed, and P is the power of the laser heat source; the spot area of ​​the k-th laser heat source is less than or equal to the spot area of ​​the (k-1)-th laser heat source. The preferred parameter control satisfies the following conditions: the power of the k-th laser heat source is less than or equal to the power of the (k-1)-th laser heat source; and the welding speed of the k-th laser heat source is greater than or equal to the welding speed of the (k-1)-th laser heat source.

[0065] In step 1), the high-strength metal workpiece is a metal material that softens upon heating. It can be a metal or alloy material that has undergone various cold-work strengthening or heat treatment strengthening processes. Its original state can be an alloy strengthened by solid solution strengthening, dispersion strengthening, or phase transformation strengthening; for example, martensitic steel with an initial fully martensitic microstructure, cold-rolled steel that has undergone varying degrees of cold work hardening, stainless steel, steel strengthened by heat treatment, and aluminum-magnesium alloys. In this invention, it is generally a test plate with a certain thickness, and its surface can have a coating composed of one or more elements such as zinc, aluminum, and tin. The thickness of the workpiece is generally between 0.2-10 mm, preferably 0.5-5 mm. Typically, two workpieces are assembled to form a welding assembly, wherein the first metal workpiece is 111 and the second metal workpiece is 112, and the thicknesses of the two workpieces can be the same or different. Figure 1 The diagram shows a cross-sectional view of the assembly formed by the butt joint of two workpieces. The assembly gap formed by the butt joint is b0, which ranges from 0 to 2 mm. Furthermore, the assembly of the two workpieces can be a corner joint, such as... Figure 2 As shown, the lap corner position is the welding position, i.e., welding line 1111; the other two workpieces can also be joined in an overlapping manner, such as... Figure 3 As shown, the welding position at this time is the lap line from top to bottom in the diagram, which is welding line 1111. The number of laps in the assembly to be welded can also be more than 3 layers of workpieces.

[0066] The invention will now be described using butt welding as an example. (See reference...) Figure 4-9 A first metal workpiece 111 and a second metal workpiece 112 are joined to form a weldable assembly, with the weld line being the welding position. A first main laser beam 110 is provided, and the light spot area formed by its irradiation on the top surface of the weldable assembly is the first main laser irradiation spot 11. The first main laser irradiation spot 11 travels along the weld line at a certain speed, and the laser heats and melts the weldable assembly, causing the weld line position to melt and solidify, forming a first main laser melting zone 122 and a first heat-affected zone 121. The width of the first heat-affected zone is B1 (i.e., the initial width). Subsequently, a second laser heat source irradiates the first heat-affected zone 121, and a second laser irradiation spot 21 is formed in the first heat-affected zone on each side, as shown below. Figure 6 As shown; under the action of the second laser heat source, at least a portion of the first heat-affected zone 121 melts and resolidifies to form a new second heat-affected zone 131 and a second laser melting zone 130; at this time, there are two cases: when the second laser melting zone 130 does not exceed the area of ​​the first heat-affected zone 121, such as Figure 7As shown; at this time, the inner side of the second laser melting zone 130 is fused with the first main laser melting zone 122 of the previous stage, while the outer area does not exceed the outer boundary of the first heat-affected zone 121. The final second heat-affected zone 131 includes a portion of the first heat-affected zone 121 of the previous stage, satisfying that the width B2 of the second heat-affected zone is less than the width B1 of the first heat-affected zone. When the second laser melting zone 130 exceeds the area of ​​the first heat-affected zone 121, refer to... Figure 8 At this point, the second laser melting zone 130 completely covers the first heat-affected zone 121, forming a new second heat-affected zone 131, satisfying B2 < B1. After performing the second laser heat source treatment, a third laser heat source can be used to continue processing the second heat-affected zone 131, forming a third laser irradiation spot 31 within each side of the second heat-affected zone 131. Through the same processing method, a third heat-affected zone (with a width of B3) is finally obtained, satisfying B3 < B2. Performing at least one progressive laser processing step results in a final weld joint with a heat-affected zone width ≤ 0.5 mm and less than 60% of B1.

[0067] It is worth mentioning that in each processing step, the laser heat source is distributed within the heat-affected zone of the previous pass, ensuring that the heat-affected zone of the previous pass is at least partially melted and fused with the melted zone of the previous pass. Two axisymmetrically arranged k-th laser heat sources (k≥2) form a laser beam. The two k-th laser heat sources are located on both sides of the weld formed by the melting of the first laser heat source, with the weld centerline as the axis of symmetry. The equivalent circle diameter of the spot area of ​​the first laser heat source on the surface of the composite bond is generally 0.4-0.5 mm, and the equivalent circle diameter of the spot area of ​​the k-th laser heat source on the surface of the assembly does not exceed 0.3 mm, preferably not exceeding 0.2 mm, more narrowly not exceeding 0.1 mm, and more preferably 0.05 mm. Generally, as the number of welding passes increases, the irradiation area of ​​the laser heat source in each subsequent pass gradually decreases, thereby reducing the width of the melted zone and the heat-affected zone. In order to achieve efficient melting, the laser heat source has a high power density, and a beam quality factor (M) can be used. 2 This is accomplished using a relatively good single-mode laser, typically M. 2 ≤1.3, preferably M 2 <1.1. The energy distribution of each group of laser beams can be uniform, Gaussian, or other variations. The shape of the irradiated area on the surface of the assembly by each group of laser beams can be circular, rectangular, annular, or a combination of various straight lines and curves.

[0068] Generally, each group of laser beams arranged symmetrically in subsequent configurations has the same wavelength, ranging from 0.3 to 10 μm, particularly emitted by infrared lasers with wavelengths of 0.5 to 3 μm, and more commonly, wavelengths of 900 to 1100 nm, which is common in laser processing. The laser beams are typically emitted by lasers, which can be of various types, such as solid-state lasers or gas lasers. Specifically, they can include fiber lasers, disk lasers, semiconductor diode lasers, and Nd:YAG type solid-state lasers, or CO2 gas lasers. Other types are also possible, as long as they can generate laser beams and create keyholes and molten weld pools. Each group of two laser beams can be emitted by the same laser or by multiple independent lasers. Multiple laser beams can be generated from a single laser and then split into multiple beams by a beam splitter within an integrated laser processing head. The beam splitter achieves this through any internal optical element or combination thereof, such as prisms or mirrors. A laser system controller can be connected to the beam splitter to control the energy distribution and irradiation area size of the two beams, as well as the coordinated output during processing, such as power level, relative position distance, and defocusing. The generation of multiple laser beams is generally achieved through optical elements or combinations thereof within the laser processing head. These can consist of completely fixed optical elements forming a laser beam with fixed beam characteristics, or they can include internal movable and deflectable optical elements, allowing the irradiation area formed by the laser beam on the raw material surface to be variable. During processing, the beam's movement and deflection can achieve high-speed scanning in space. During the welding process, the laser beam can travel along the welding direction in a fixed or synchronous high-speed motion, including oscillations. The oscillation shape can include various forms such as circles, broken lines, figure-eights, and infinity symbols. The oscillation frequency is generally 50-500 Hz, and the oscillation amplitude is between 0.2-1.5 mm. Multiple single or mixed shielding gases, such as Ar, N2, and He, can be added during the welding process, or the welding can be performed without a shielding gas. The power of each laser beam is generally 500W-5KW, preferably 800W-3KW; and the travel speed of the laser beam relative to the workpiece assembly is generally 1-10 m / min, preferably 1.5-8 m / min.

[0069] It is worth mentioning that during the laser welding process of the first main laser beam 110 at the foreground, the laser heat source can be a multimode laser or a single-mode laser. Generally, when facing large assembly gaps, it can also have a large equivalent circular spot diameter. During the welding process, methods such as oscillation are used to enhance connectivity and reduce the negative impact of the gap. Simultaneously, synchronous solder feeding can be used for the main welding process to achieve tolerance of large gaps and control of the microstructure and properties of the molten zone. The solder can be in the form of powder, wire, or rod; when it is wire, it is the laser filler wire welding well-known in the field. Figure 9 The diagram shows the simultaneous addition of welding wire 3 during welding. Observed along the welding direction, welding wire 3 is generally placed at the front, with its end positioned at the center of the first main laser beam 110. The distance between the point where it intersects with the first main laser beam 110 and the top surface of the assembly is 0-1 mm. During laser welding, the first main laser beam 110 heats and melts the welding wire using laser energy, causing it to fuse with the workpiece to form a molten pool. The wire feeding device can be replaced by, for example, MAG (metal active gas), MIG (metal inert gas), or TIG (tungsten inert gas). The welding wire 3 can be a solid welding wire or a flux-cored welding wire. The solder addition method can also be a combination of two different devices, for example, using two filling devices to deliver different solders, one delivering solder with a certain composition and the other delivering solder with a different composition. By combining the two solders, the final solder delivered into the molten pool has the required proportion of composition. Alternatively, the solder can also be added through multiple steps or multiple components. During the welding process, the wire feeding speed of welding wire 3 is generally 1-5 m / min, and its ratio to the welding speed is between 0.3 and 1.5. In addition, the main laser welding process can be a composite welding process using the first main laser beam 110 and other forms of heat sources, such as a composite with MIG, MAG, TIG and other arcs.

[0070] In this invention, the core principle is to continuously reduce the width of the heat-affected zone through multiple laser thermal melting processes, thereby improving joint performance. Therefore, the time difference between the action of subsequent laser beams and the laser beams in the previous process can be achieved through simultaneous action in a single welding operation, or through remelting in multiple subsequent processes. That is, all melting processes can be performed in a single step or in multiple steps. When completed in one operation, all laser beams can be considered integrated into a single laser processing device. During a single laser welding process, all laser beams act simultaneously. At this time, the positions of all laser beams have a preset spacing. Taking the relative positions of the second laser heat source and the first laser heat source (i.e., the first main laser beam) as an example, let's now refer to... Figure 10The width of the first main laser melting region 122 formed by the melting of the first main laser irradiation spot 11 is the width t1 of the first main laser melting region, and the width of the first heat-affected region 121 is the width B1 of the first heat-affected region; the width of the second laser melting region 130 formed by the melting of the second laser irradiation spot 21 within the first heat-affected region 121 is the width t2 of the second laser melting region; where B2 < B1; and the second laser irradiation spot 21 must melt at least a portion of the first heat-affected region 121 and fuse it with the first main laser melting region 122 to form a new second heat-affected region 131. Therefore, the thermal effect range of the second laser irradiation spot 21 covers at least a portion of the first heat-affected zone 121. The distance d1 between the second laser irradiation spot 21 and the first main laser irradiation spot 11 in the welding travel direction satisfies the following: during the solidification process after the formation of the first main laser melting zone 122, its temperature is at least lower than the solid temperature of the molten metal, that is, the second laser heat source is applied at least when the first main laser melting zone 122 adjacent to the target area of ​​the first heat-affected zone 121 is in a solid state. The larger d1 is, the better, at least d1 > 5 mm, preferably d1 > 10 mm. The second laser irradiation spot 21 and the first main laser irradiation spot 11 maintain a preset offset in perpendicular to the welding travel direction. This offset is set based on experience or based on the measured value of the actual welded heat-affected zone width of the test sample. Generally speaking, the offset for steel is 0.05-0.5 mm, and the offset for aluminum alloy is 0.2-1.0 mm. Furthermore, the interaction between the 3rd (4th, 5th...) laser heat source and the 2nd (3rd, 4th...) laser heat source is similar and will not be described further here. At this time, all laser heat sources act on the assembly to be welded simultaneously at the same welding speed.

[0071] When the laser heat sources do not act simultaneously on the components to be welded, i.e., they act separately, this can be understood as performing multiple laser remelting processes independently after the initial welding. In this case, the power parameters and welding speed of each laser heat source can be adjusted individually. Similarly, the irradiation spots formed by each group of laser beams, such as the second laser irradiation spots 21 on both sides, can also act separately. The interval between laser heat sources can be such that the next laser remelting is applied only after the previous welding pass is completed, gradually reducing the width of the heat-affected zone. Furthermore, each group of laser heat sources can be independent or integrated into a single system. The power parameters and beam quality of each laser heat source can be adjusted or fixed independently. Simultaneously, the melting form of each group of laser beams can be deep penetration welding or heat conduction welding, preferably deep penetration welding. The penetration depth of each laser beam can be either through the workpiece or without penetration (melting through) depending on specific needs.

[0072] Generally, the heat input of subsequent laser heat sources is lower than the heat input of the laser in the previous process, that is, the heat input Q of the k-th laser heat source. k<The heat input Q of the (k-1)th laser heat source k-1 Where the heat input Q = P / v, P: power of the laser heat source (W), v: welding speed (m / min), meaning that subsequent laser heat sources have higher melting efficiency; when all laser heat sources are multimode lasers, the power of subsequent lasers does not exceed the power of the previous laser, and its focused spot size is not larger than that of the previous laser, and its welding speed is not lower than that of the previous laser. When the k-th laser heat source is a single-mode laser, its laser power does not exceed 60% of the power of the 1st laser heat source, and its laser power does not exceed the power of the previous laser, its focused spot size is not larger than that of the previous laser, and its welding speed is not lower than that of the previous laser.

[0073] Example 1

[0074] The base material used for the butt joint was 1.5mm thick 301-3 / 4H cold-rolled hardened stainless steel, which is strengthened through cold work. Welding was first performed using a conventional laser at a speed of 3.0m / min, a laser power of 2.5kW, and a laser spot size of 0.5mm. The resulting laser-welded joint exhibited severe softening in the heat-affected zone, reaching a width of 0.56mm, with a minimum hardness of 240HV, only 57.14% of the base material (average hardness of 420HV).

[0075] Figure 12 The figure shows the cross-sectional morphology of the laser-welded joint after a second laser remelting in the heat-affected zone; the remelting laser beam used is a single-mode laser (beam quality M). 2 =1.3), the irradiation spot diameter is 0.05mm, the welding speed is 3.0m / min, the laser power is 600w, the center of the spot is located in the heat-affected zone of the previous process, and the distance between the spot and the edge of the melting zone generated in the previous process is 0.17mm; it can be seen that after the heat-affected zone is remelted, the heat-affected zone outside the original first main laser melting zone 122 is remelted to form a new second laser melting zone 130 and a new second heat-affected zone 131, the softening degree is significantly reduced, and the width of the heat-affected zone is reduced; the width of the heat-affected zone is reduced to 0.30mm, and the minimum hardness of the heat-affected zone is 280HV, which is 66.67% of the base material.

[0076] Example 2

[0077] The base material used for the butt joint was 1.5mm thick 301-3 / 4H cold-rolled hardened stainless steel, which is strengthened through cold work. Welding was first performed using a conventional laser at a speed of 3.0m / min, a laser power of 2.5kW, and a laser spot size of 0.5mm. The resulting laser-welded joint exhibited severe softening in the heat-affected zone, reaching a width of 0.56mm, with a minimum hardness of 240HV, only 57.14% of the base material (average hardness of 420HV).

[0078] Figure 13 The figure shows the cross-sectional morphology of the laser-welded joint after the first and second laser remelting in the heat-affected zone; the laser beam used for the first remelting was a single-mode laser (beam quality M). 2 =1.3), the irradiation spot diameter is 0.05mm, the welding speed is 3.0m / min, the laser power is 600w, the spot center is located in the heat-affected zone of the previous process, and the distance between the spot center and the edge of the molten zone generated in the previous process is 0.17mm; the second remelting laser beam is also a single-mode laser (beam quality M 2 =1.3), the irradiation spot diameter is 0.05mm, the welding speed is 4.2m / min, the laser power is 600w, the center of the spot is located in the heat-affected zone of the previous process, and the distance between it and the edge of the melting zone generated in the previous process is 0.03mm; it can be seen that after the heat-affected zone is remelted, the heat-affected zone outside the original first main laser melting zone 122 is remelted to form a new second laser melting zone 130 and a third laser melting zone 140 formed by the second remelting, and finally a new third heat-affected zone 141 is formed. Its softening degree is significantly reduced and the width of the heat-affected zone is reduced; the width of the heat-affected zone is reduced to 0.24mm, and the minimum hardness of the heat-affected zone is 300HV, which is 71.42% of the base material.

[0079] Example 3

[0080] The base material used for the butt joint was 1.5mm thick 301-3 / 4H cold-rolled hardened stainless steel, which is strengthened through cold work. Welding was first performed using a conventional laser at a speed of 3.0m / min, a laser power of 2.5kW, and a laser spot size of 0.5mm. The resulting laser-welded joint exhibited severe softening in the heat-affected zone, reaching a width of 0.56mm, with a minimum hardness of 240HV, only 57.14% of the base material (average hardness of 420HV).

[0081] The cross-sectional morphology of the laser-welded joint after the first and second laser remelting in the heat-affected zone was examined; the laser beam used for the first remelting was a single-mode laser (beam quality M). 2=1.3), the irradiation spot diameter is 0.05mm, the welding speed is 3.0m / min, the laser power is 1.5kw, the spot center is located in the heat-affected zone of the previous process, and the distance between the spot center and the edge of the molten zone generated in the previous process is 0.17mm; the second remelting laser beam is also a single-mode laser (beam quality M 2 =1.3), the irradiation spot diameter is 0.05mm, the welding speed is 4.2m / min, the laser power is 600w, the center of the spot is located in the heat-affected zone of the previous process, and the distance between the spot center and the edge of the molten zone generated in the previous process is 0.17mm.

[0082] Results: After remelting the heat-affected zone, a new third heat-affected zone was formed, which significantly reduced the degree of softening and the width of the heat-affected zone. The width of the heat-affected zone was reduced to 0.32 mm, and the minimum hardness of the heat-affected zone was 291 HV, which is 69.28% of that of the base material.

[0083] Example 4

[0084] The base material used for the butt joint was 2.0mm thick 7075-T6 aluminum alloy. Welding was first performed using a conventional laser at a speed of 3.0m / min, a laser power of 4kW, and a laser spot size of 0.4mm. The resulting laser-welded joint exhibited severe softening in the heat-affected zone, reaching a width of 0.9mm, with a minimum hardness of 120HV, only 75% of the base material's (average hardness is approximately 160HV).

[0085] Figure 15 The figure shows the cross-sectional morphology of the laser-welded joint after a second laser remelting on the right side of the heat-affected zone; the remelting laser beam used is a single-mode laser (beam quality M). 2 =1.2), the irradiation spot diameter is 0.05mm, the welding speed is 3.0m / min, the laser power is 1500w, the center of the spot is located in the heat-affected zone of the previous process, and the distance between the spot and the edge of the melting zone generated in the previous process is 0.27mm; it can be seen that after the heat-affected zone is remelted, the heat-affected zone outside the original first main laser melting zone 122 is remelted to form a new second laser melting zone 130 and a new second heat-affected zone 131. Its softening degree is significantly reduced, and its width is significantly reduced compared with the original heat-affected zone on the left; the width of the heat-affected zone is reduced to about 0.5mm, and the minimum hardness of the heat-affected zone is 135HV, which is 84.4% of the base material.

[0086] Comparative Example 1

[0087] The base material used for the butt joint workpiece is 1.5mm thick 301-3 / 4H cold-rolled hardened stainless steel, which is strengthened by cold work hardening. Figure 11The figure shows the cross-sectional morphology of the joint after welding using a conventional laser. The welding speed was 3.0 m / min, the laser power was 2.5 kW, and the laser irradiation spot size was 0.5 mm. It can be seen that the heat-affected zone softened severely after welding, with a width of 0.56 mm and a minimum hardness of 240 HV, which is only 57.14% of that of the base material (the average hardness of the base material is 420 HV).

[0088] Comparative Example 2

[0089] The base material used for the mating workpiece is 2.0mm thick 7075-T6 aluminum alloy. Figure 14 The figure shows the cross-sectional morphology of the joint after welding with a conventional laser. The welding speed was 3.0 m / min, the laser power was 4 kW, and the laser irradiation spot size was 0.4 mm. It can be seen that the heat-affected zone softened severely after welding, with a width of 0.9 mm and a minimum hardness of 120 HV, which is only about 75% of that of the base material (the average hardness of the base material is about 160 HV).

[0090] Comparative Example 3

[0091] The laser-welded joint obtained after welding in Comparative Example 1 underwent another laser remelting in the heat-affected zone. The remelting laser beam used was a single-mode laser (beam quality M). 2 =1.3), the irradiation spot diameter is 0.05mm, the welding speed is 4.2m / min, the laser power is 400w, the center of the spot is located in the heat-affected zone of the previous process, and the distance between the spot center and the edge of the molten zone generated in the previous process is 0.17mm.

[0092] Result: The width of the heat-affected zone decreased to 0.54 mm, while the minimum hardness remained at 240 HV. The power was too low to effectively remelt the previous heat-affected zone.

[0093] Comparative Example 4

[0094] The laser-welded joint obtained after welding in Comparative Example 1 underwent another laser remelting in the heat-affected zone. The remelting laser beam used was a single-mode laser (beam quality M). 2 =1.3), the irradiation spot diameter is 0.05mm, the welding speed is 3.0m / min, the laser power is 600w, the center of the spot is located in the heat-affected zone of the previous process, and the distance between the spot center and the edge of the molten zone generated in the previous process is 0.3mm.

[0095] Result: The minimum hardness of the heat-affected zone was 245HV. The spot offset was too large, and the previous heat-affected zone could not be effectively remelted.

[0096] Comparative Example 5

[0097] The laser-welded joint obtained after welding in Comparative Example 1 underwent another laser remelting in the heat-affected zone. The remelting laser beam used was a single-mode laser (beam quality M). 2 =1.3), the irradiation spot diameter is 0.5mm, the welding speed is 3.0m / min, the laser power is 2.0kw, the center of the spot is located in the heat-affected zone of the previous process, and the distance between the spot center and the edge of the melting zone generated in the previous process is 0.17mm.

[0098] Results: The width of the heat-affected zone was 0.56 mm, and the minimum hardness of the heat-affected zone was 242 HV.

Claims

1. A laser welding method for high-strength metals, characterized in that, The method includes the following steps: 1) Provide a set of high-strength metal workpieces to be assembled into a welding assembly, wherein the welding assembly has a welding line to be welded; 2) Provide a first laser heat source to irradiate the welding line to form a first main laser melting zone and a first heat-affected zone adjacent to the melting zone; 3) Perform at least one progressive laser processing step, each step including: Provide the (k-1)th heat-affected zone formed in the previous process before the kth laser heat source irradiation, where k≥2, and melt the entire region or a part of the adjacent melting zone to form a region with a width B. k The kth thermally affected zone; The parameter control satisfies the following conditions: the heat input of the k-th laser heat source is less than the heat input of the (k-1)-th laser heat source, where the heat input Q = P / v, v is the welding speed, and P is the power of the laser heat source; and the irradiation area of ​​the k-th laser heat source is less than or equal to the irradiation area of ​​the (k-1)-th laser heat source.

2. The laser welding method for high-strength metals according to claim 1, characterized in that, The parameter control satisfies the following conditions: the power of the k-th laser heat source is ≤ the power of the (k-1)-th laser heat source; the welding speed of the k-th laser heat source is ≥ the welding speed of the (k-1)-th laser heat source.

3. The laser welding method for high-strength metals according to claim 1, characterized in that, The final heat-affected zone width Bn of the welded joint formed by performing step 3) is ≤0.5mm and less than 60% of the initial width; the initial width is the width B1 of the first heat-affected zone.

4. The laser welding method for high-strength metals according to claim 1, characterized in that, The equivalent circular diameter of the spot area of ​​the first laser heat source is 0.4-0.5 mm, and the equivalent circular diameter of the spot area of ​​the second laser heat source is no more than 0.3 mm, and even narrower, no more than 0.2 mm.

5. The laser welding method for high-strength metals according to claim 4, characterized in that, The equivalent circle diameter of the spot area of ​​the third laser heat source shall not exceed 0.1 mm, and more narrowly not exceed 0.05 mm.

6. The laser welding method for high-strength metals according to claim 1, characterized in that, The beam quality of the k-th laser heat source performing the progressive laser processing step satisfies M 2 ≤1.3; The first laser heat source is used in welding by any one of laser welding alone, laser filler wire welding, or laser composite welding.

7. The laser welding method for high-strength metals according to claim 1, characterized in that, Two k-th laser heat sources are symmetrically distributed on both sides of the weld formed by the melting of the first laser heat source, and the area of ​​the heat-affected zone formed by the melting of the (k-1)-th laser heat source is more than 50%, and the area of ​​the melted zone formed by the melting of the (k-1)-th laser heat source is less than 50%.

8. The laser welding method for high-strength metals according to claim 1, characterized in that, Parameter control satisfies: 0.2Q k-1 ≤Q k ≤0.7Q k-1 Q k Q k-1 These are the heat inputs of the k-th and (k-1)-th laser heat sources, respectively; 0.2P k-1 ≤P k ≤P k-1 And P2≤0.6P1, P k P k-1 , respectively, are the powers of the k-th and (k-1)-th laser heat sources; 1.4v k-1 ≥v k ≥v k-1 v k v k-1 These are the welding speeds of the k-th and (k-1)-th laser heat sources, respectively; 0.01S k-1 ≤S k ≤S k-1 S k S k-1 , respectively, are the spot areas of the k-th and (k-1)-th laser heat sources; The center of the laser spot of the k-th laser heat source is located in the (k-1)-th heat-affected zone, and the distance between it and the edge of the melting zone generated by the irradiation of the (k-1)-th laser heat source is 0.1B. k-1 ~0.3B k-1 B k-1 denoted as the width of the (k-1)th heat-affected zone.

9. The laser welding method for high-strength metals according to claim 1, characterized in that, The number of times n in the progressive laser processing step is executed satisfies 1 ≤ n ≤ 5.

10. The laser welding method for high-strength metals according to any one of claims 1-9, characterized in that, All laser heat sources act simultaneously on the assembly to be welded at the same welding speed. The irradiation spot of the k-th laser heat source and the (k-1)-th laser heat source maintain a preset distance in the welding travel direction. The preset distance is set to satisfy the following: when the k-th laser heat source irradiates the target area of ​​the (k-1)-th heat-affected zone formed in the previous process, the melting zone formed by the (k-1)-th laser heat source in the target area and adjacent to the target area has solidified into a solid state.

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