A method for pulse - continuous composite spot - ring laser welding of dissimilar metals

Abstract

The present invention discloses a method for pulsed - continuous composite spot - ring laser welding of dissimilar metals. The spot - ring light source formed by the beam combination of pulsed laser and continuous laser can achieve simultaneous output in the time domain but be decoupled in the space domain. When applied to the welding of dissimilar metals, the annular continuous laser can effectively make up for the insufficient average output power of the pulsed laser, break through the size limitation of the weldable plate thickness, and at the same time give full play to a series of advantages of the pulsed laser, such as low average power, high peak power, good energy controllability, and high beam quality. By adjusting parameters such as waveform, pulse width, and frequency, the regulation of the composition and proportion of IMCs in the weld of dissimilar metals can be realized under the condition of not changing the overall heat input. The present invention efficiently combines pulsed spot laser and continuous ring laser and applies them in the field of laser welding, can flexibly adjust the energy ratio of the spot - ring light source, has a wide application range, and is especially suitable for the welding of thin - plate or medium - thick - plate dissimilar metals.

Description

Technical Field

[0001] The invention belongs to the technical field of laser processing, and more specifically, relates to a pulse-continuous composite spot ring laser welding method for dissimilar metals. Background Art

[0002] With the rapid development of industrial manufacturing in my country, the pursuit of lower costs, higher performance and lighter weight is becoming a prominent feature of modern manufacturing. For the same structural parts, the use of a single alloy material usually cannot meet the differentiated service environment and load requirements of various regions. To overcome this pain point, heterogeneous metal composite structures have gradually emerged. By comprehensively utilizing the performance advantages of different materials, they effectively avoid the shortcomings of a single alloy and can fully adapt to the development trend of "functional integration and lightweight structure".

[0003] Due to the differences in the physical and chemical properties of dissimilar metals, the welding of dissimilar metals is more difficult than that of homogeneous metals. For example, during the welding process, the high-melting-point metal shrinks and solidifies prematurely to form huge welding residual stress, which causes large deformation of the structural parts. Secondly, dissimilar metals usually react to form brittle intermetallic compounds (IMCs), which can easily lead to weld cracking. At present, the welding of dissimilar metals mainly includes explosion welding, brazing, stir friction welding, arc welding and laser welding. Among them, laser welding has attracted widespread attention due to its advantages such as precise energy control, small heat-affected zone, small workpiece deformation and high degree of automation. According to the time domain characteristics of laser output, it can be divided into continuous laser welding and pulsed laser welding. The output power range of continuous laser is wide and the stability is good, but the adjustability is insufficient. Relatively speaking, pulsed laser has a series of advantages such as low average power, high peak power, good energy controllability and high beam quality. It can adjust the waveform, pulse width, frequency and other parameters without changing the overall heat input. The control of the composition and proportion of IMCs in the weld is achieved, which is particularly suitable for the connection of dissimilar metals.

[0004] However, the average output power of existing pulsed lasers is relatively low, and the achievable welding penetration depth is shallow, which is only suitable for welding thin plates. To make up for the insufficient average output power of pulsed lasers and break through the dimensional limitation of weldable plate thickness, pulsed lasers and continuous lasers can be combined into pulsed-continuous composite lasers for dissimilar metal welding. The pulsed-continuous composite laser can fully combine the advantages of good adjustability of pulsed lasers and a wide output power range of continuous lasers, and while achieving medium and thick plate welding, it can also regulate the IMCs in the weld seam. The existing methods for realizing the combination of these two types of lasers mainly include: (1) merging pulsed lasers and continuous lasers into the same optical path for simultaneous output through optical path design, and the two beams are overlapped and combined in the time domain and space; (2) separately outputting pulsed lasers and continuous lasers in the same optical path through a clock controller, and only one of the pulsed or continuous lasers is output at a certain moment, and the two beams are spliced in the time domain but overlapped in space. Generally speaking, the existing pulsed-continuous composite lasers will overlap and couple in space, and when performing dissimilar metal welding, there is mutual interference between heat sources, which is not conducive to the regulation of IMCs. Summary of the Invention

[0005] Aiming at the defects and improvement requirements of the prior art, the present invention provides a method for pulsed-continuous composite spot-ring laser welding of dissimilar metals, aiming to solve the technical problems that when welding dissimilar metals by laser, it is difficult to break through the plate thickness limitation using a single pulsed laser, and the ability to adjust IMCs in the weld seam using a single continuous laser is poor.

[0006] In the first aspect, the present invention provides a method for pulsed-continuous composite spot-ring laser welding of dissimilar metals. During the welding process, pulsed lasers and annular continuous lasers are combined into spot-ring lasers and applied to the surface of the workpiece to form a welding molten pool. The welding penetration depth is increased by the external annular continuous laser, and the flow field of the molten pool and the proportion of intermetallic compounds in the weld seam are regulated by the internal pulsed laser; the interaction between pulsed and continuous lasers can increase the laser energy absorption efficiency and improve the quality of dissimilar metal welded joints.

[0007] Further, the type of dissimilar metal welded joint is a butt joint, a lap joint or a T-joint.

[0008] Further, the total output power of the spot-ring laser is 100W - 3000W. The total output power of the spot-ring laser is the sum of the output powers of the pulsed laser and the annular continuous laser, where the output power of the pulsed laser is 0W - 1000W.

[0009] Further, the welding speed is 0.5 - 3m / min.

[0010] Further, when the type of dissimilar metal welded joint is a butt joint or a T-joint, the center of the spot-ring laser is biased towards the side of the low melting point metal, and the offset is 0 - 5mm.

[0011] Furthermore, the pulsed laser includes, but is not limited to, any one of nanosecond laser, picosecond laser, and femtosecond laser, and the annular continuous laser includes, but is not limited to, any one of gas laser, semiconductor laser, disk laser, and fiber laser.

[0012] Furthermore, the two dissimilar metal workpieces to be welded include, but are not limited to, any one of aluminum-steel, aluminum-magnesium, magnesium-steel, steel-titanium, steel-copper, and aluminum-copper.

[0013] In a second aspect, the present invention provides an output structure for implementing the method for pulsed-continuous composite spot-ring laser welding of dissimilar metals as described in the first aspect, including: a plurality of continuous laser transmission optical fibers, a pulsed laser transmission optical fiber, an optical fiber coupler, and a spot-ring laser transmission optical fiber;

[0014] The plurality of continuous laser transmission optical fibers surround the pulsed laser transmission optical fiber;

[0015] The optical fiber coupler is used to couple the plurality of continuous laser transmission optical fibers and the pulsed laser transmission optical fiber into the spot-ring laser transmission optical fiber;

[0016] The spot-ring laser transmission optical fiber has an inner and outer double-clad waveguide structure, where the inner core transmits the pulsed laser, the outer fiber cladding transmits the continuous laser, and the pulsed-continuous composite spot-ring laser is output at the end.

[0017] In a third aspect, the present invention provides an output structure for implementing the method for pulsed-continuous composite spot-ring laser welding of dissimilar metals as described in the first aspect, including: an annular continuous laser transmission optical fiber and a unidirectional total transmission and total reflection mirror;

[0018] The annular continuous laser is incident on the total reflection surface of the unidirectional total transmission and total reflection mirror through the annular continuous laser transmission optical fiber to form a reflected light beam; the pulsed laser is incident on the total transmission surface of the unidirectional total transmission and total reflection mirror to form a transmitted light beam; the reflected light beam and the transmitted light beam are combined to form a pulsed-continuous composite spot-ring laser;

[0019] Wherein, the geometric centers of the pulsed laser and the annular continuous laser coincide.

[0020] In a fourth aspect, the present invention provides an output structure for implementing the method for pulsed-continuous composite spot-ring laser welding of dissimilar metals as described in the first aspect, including: a galvanometer and a unidirectional total transmission and total reflection mirror;

[0021] The dot-shaped continuous laser realizes the output of the annular continuous laser through the galvanometer. The annular continuous laser is incident on the total reflection surface of the unidirectional total transmission and total reflection mirror to form a reflected light beam; the pulsed laser is incident on the total transmission surface of the unidirectional total transmission and total reflection mirror to form a transmitted light beam; the reflected light beam and the transmitted light beam are combined to form a pulsed-continuous composite spot-ring laser;

[0022] Among them, the geometric centers of the pulsed laser and the annular continuous laser coincide.

[0023] Generally speaking, through the above technical solutions conceived by the present invention, the following beneficial effects can be achieved:

[0024] (1) Compared with the existing pulsed - continuous laser compound which is essentially still a point - like laser, the present invention combines and outputs the pulsed laser and the continuous laser through a point - ring mode. The output point - ring laser is composed of an internal pulsed laser and an external annular continuous laser, thereby realizing the continuity of the two types of light sources in the time domain but decoupling in the space domain. While avoiding mutual interference, it makes full use of the good adjustability of the pulsed laser and the wide output power range of the continuous laser, and enhances the mutual synergy performance.

[0025] (2) The present invention uses the external annular continuous laser to assist in melting the metal material to form a molten pool, making it easier for the internal pulsed laser to form a stable keyhole, which can increase the laser energy absorption efficiency, greatly improve the welding penetration depth, and break through the size limit of the weldable plate thickness in single - pulsed laser welding.

[0026] (3) The present invention adjusts the pulsed laser to control the melt flow and melt quality in the molten pool. On the one hand, it can drive the uniform distribution of internal elements and homogenize the IMCs in the weld seam. On the other hand, the high - frequency pulse can enhance the molten pool disturbance, promote the escape of bubbles, reduce the porosity in the weld seam, and improve the mechanical properties of the dissimilar metal welded joint. Description of the Drawings

[0027] Figure 1 It is one of the schematic diagrams of the point - ring laser output structure of pulsed - continuous compound provided by the present invention.

[0028] Figure 2 It is another schematic diagram of the point - ring laser output structure of pulsed - continuous compound provided by the present invention.

[0029] Figure 3 It is the third schematic diagram of the point - ring laser output structure of pulsed - continuous compound provided by the present invention.

[0030] Figure 4 It is the schematic diagram of the point - ring laser welding method for the Fe / Al lap joint provided in the first embodiment of the present invention.

[0031] Figure 5 It is the schematic diagram of the point - ring laser welding method for the Mg / Al butt joint provided in the second embodiment of the present invention.

[0032] In all the accompanying drawings, the reference numerals are respectively represented as follows: 1 - continuous laser transmission optical fiber; 2 - pulsed laser transmission optical fiber; 3 - optical fiber coupler; 4 - dot-ring laser transmission optical fiber; 5 - focusing mirror; 6 - pulsed-continuous composite dot-ring laser; 7 - annular continuous laser transmission optical fiber; 8 - pulsed laser; 9 - unidirectional fully transparent and fully reflecting mirror; 10 - reflecting mirror; 11 - galvanometer; 12 - oscillating lens a; 13 - oscillating lens b; 14 - weld bead; 15 - Fe sheet; 16 - Al sheet; 17 - Mg sheet. Specific Embodiment

[0033] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0034] The implementation process of the present invention is as follows:

[0035] A dot-ring laser beam is generated by a pulsed-continuous composite dot-ring laser output structure and acts on dissimilar metal workpieces. The external annular continuous laser preheats the workpieces during the welding process and assists in forming a welding molten pool. The internal pulsed laser perturbs and impacts the welding molten pool with its high peak power and frequency, accelerating the heat and mass transfer process in the molten pool, promoting the uniform distribution of alloying elements, reducing the formation of IMCs or obtaining IMC components with better performance. The annular continuous laser and the pulsed laser are efficiently combined through the dot-ring mode, realizing simultaneous output in the time domain and decoupling in the space domain, and can flexibly adjust the energy ratio of the dot-ring light source. Without changing the overall heat input, it breaks through the plate thickness limit and realizes the regulation of the composition and proportion of IMCs in dissimilar metal welds. The combined effect of the continuous laser and the pulsed laser acts on the photoinduced plasma, welding molten pool temperature field, welding molten pool flow field and welding stress-strain field during the welding process, and completes the welding process of dissimilar metals under the coupling action of multiple energy fields.

[0036] The method for welding dissimilar metals with a pulsed-continuous composite dot-ring laser according to the present invention organically combines the advantages of pulsed lasers and continuous lasers in metal welding. Among them, the annular continuous laser assists in forming a welding molten pool, preheating the workpieces, which can reduce and homogenize the welding stress, avoid stress concentration in the weld, and at the same time effectively improve the absorption rate of the metal to the pulsed laser, greatly increasing the welding penetration depth. The pulsed laser acts on the welding molten pool through fast and high-frequency laser pulses, enhancing the fluidity and orderliness of the molten flow and molten matter in the welding molten pool, suppressing the porosity and crack defects in the molten pool, and improving the solidification and crystallization behavior in the molten pool, forming finer, more uniform and higher-quality IMCs, and improving the performance of dissimilar metal welded joints.

[0037] The above-mentioned method for pulsed-continuous composite spot-ring laser welding of dissimilar metals includes the following steps:

[0038] (1) Fix two workpieces of dissimilar metals to be welded in accordance with the joint type;

[0039] (2) Set the total output power of the spot-ring laser to be 100W - 3000W. The total output power of the spot-ring laser is the sum of the output powers of the pulsed laser and the continuous laser, where the output power of the pulsed laser is 0W - 1000W;

[0040] (3) Output the spot-ring laser from the laser welding head to the surface of the workpiece to be welded, and then control the laser welding head or the workpiece to be welded to move along the welding trajectory, thereby completing the welding.

[0041] In the present invention, terms such as "first", "second", etc. (if any) in the present invention and the accompanying drawings are used to distinguish similar objects, and do not necessarily need to describe a specific order or sequence.

[0042] In the present invention, in order to obtain a more effective welding effect of dissimilar metals, a spot-ring laser output structure capable of realizing pulsed-continuous compounding is also proposed.

[0043] As Figures 1 to 3 shown, the present invention provides three different spot-ring laser output structures for pulsed-continuous compounding. The spot-ring laser output by this structure is composed of an internal pulsed laser and an external annular continuous laser. Compared with a conventional point light source, it has advantages such as good adjustable performance, high welding efficiency, and good welding stability, and is particularly suitable for welding dissimilar metals of thin plates or medium-thick plates. Specifically:

[0044] Embodiment 1: Compound the pulsed laser and the continuous laser into a two-in-one optical fiber through an optical fiber coupler for combined beam output. As Figure 1 shown, it is a combined beam output structure through an optical fiber coupler, mainly including: a plurality of continuous laser transmission optical fibers 1, at least one pulsed laser transmission optical fiber 2, an optical fiber coupler 3, and a spot-ring laser transmission optical fiber 4. The plurality of continuous laser transmission optical fibers 1 surround the at least one pulsed laser transmission optical fiber 2; the optical fiber coupler 3 is used to couple the plurality of continuous laser transmission optical fibers 1 and at least one pulsed laser transmission optical fiber 2 into the spot-ring laser transmission optical fiber 4; the spot-ring laser transmission optical fiber 4 is an internal and external double-clad waveguide structure, the internal core transmits the pulsed laser, the external optical fiber cladding transmits the continuous laser, and the pulsed-continuous composite spot-ring laser is output at the end.

[0045] It can be understood that this output structure further includes a focusing mirror 5. The pulsed-continuous composite spot-ring laser output from the end of the spot-ring laser transmission optical fiber 4 needs to be focused by the focusing mirror 5 before it can be used for welding dissimilar metals.

[0046] Embodiment 2: The pulsed laser and the ring-shaped continuous laser are directly combined and output in space through optical path design. As Figure 2 Shown is a beam combining output structure through optical path design, mainly including: a ring-shaped continuous laser transmission fiber 7 and a unidirectional all-transmissive and all-reflective mirror 9; the ring-shaped continuous laser is incident on the total reflection surface of the unidirectional all-transmissive and all-reflective mirror 9 through the ring-shaped continuous laser transmission fiber 7 to form a reflected beam; the pulsed laser is incident on the total transmission surface of the unidirectional all-transmissive and all-reflective mirror 9 to form a transmitted beam; the reflected beam and the transmitted beam are combined to form a pulsed-continuous composite point ring laser; wherein, the geometric centers of the pulsed laser and the ring-shaped continuous laser coincide. It should be noted that the unidirectional all-transmissive and all-reflective mirror 9 is placed at an angle of 45° with the horizontal plane.

[0047] It can be understood that the output structure further includes a focusing mirror 5. The pulsed-continuous composite point ring laser emitted from the unidirectional all-transmissive and all-reflective mirror 9 needs to be focused by the focusing mirror 5 before it can be used for dissimilar metal welding.

[0048] In addition, a reflecting mirror 10 can be placed in the optical path between the unidirectional all-transmissive and all-reflective mirror 9 and the focusing mirror 5, so as to change the beam transmission direction and enable the pulsed-continuous composite point ring laser to be vertically output.

[0049] Embodiment 3: The same as Embodiment 2 is that the coupling output of the pulsed laser and the continuous laser in space is realized through optical path design. The difference is that the ring-shaped continuous laser outside the composite point ring laser is realized through a galvanometer. As Figure 3 Shown is a beam combining output structure of the ring-shaped continuous laser and the pulsed laser realized through a galvanometer, mainly including: a galvanometer 11 and a unidirectional all-transmissive and all-reflective mirror 9; the dot-shaped continuous laser realizes the output of the ring-shaped continuous laser through the galvanometer 11, and the ring-shaped continuous laser is incident on the total reflection surface of the unidirectional all-transmissive and all-reflective mirror 9 to form a reflected beam; the pulsed laser is incident on the total transmission surface of the unidirectional all-transmissive and all-reflective mirror 9 to form a transmitted beam; the reflected beam and the transmitted beam are combined to form a pulsed-continuous composite point ring laser; wherein, the geometric centers of the pulsed laser and the ring-shaped continuous laser coincide. It should be noted that the unidirectional all-transmissive and all-reflective mirror 9 is placed at an angle of 45° with the horizontal plane.

[0050] Specifically, the dot-shaped continuous laser realizes the output of the ring-shaped continuous laser through two oscillating lenses in the galvanometer, and then is combined with the pulsed laser on the unidirectional all-transmissive and all-reflective mirror 9 to output a point ring laser.

[0051] It can be understood that the output structure further includes a focusing mirror 5. The pulsed-continuous composite point ring laser emitted from the unidirectional all-transmissive and all-reflective mirror 9 needs to be focused by the focusing mirror 5 before it can be used for dissimilar metal welding.

[0052] In addition, a reflector 10 can be placed in the optical path between the one-way fully transparent and fully reflective mirror 9 and the focusing mirror 5, thereby changing the beam transmission direction and enabling the pulsed-continuous composite spot-ring laser to be vertically output.

[0053] A method for welding dissimilar metals with a pulsed-continuous composite spot-ring laser provided by the present invention, wherein the spot-ring laser used includes but is not limited to the above three embodiments.

[0054] The following combines specific implementation cases to further illustrate the beneficial effects of the pulsed-continuous composite spot-ring laser output structure provided by the present invention for welding dissimilar metals.

[0055] Example 1

[0056] This example illustrates the present invention by taking the butt joint of aluminum-steel dissimilar metals with the largest demand in industrial applications as an example. As Figure 4 shown, an aluminum-steel butt joint is used to carry out the pulsed-continuous composite spot-ring laser welding process test. Since the melting points of Al and Fe differ by 877 °C, the thermal conductivities differ by about 2.1 times, and the linear expansion coefficients differ by about 1 time, it is difficult for the two metals to melt simultaneously during welding, and large thermal stresses are easily formed after welding, with a great tendency for joint cracking. In this example, a nanosecond pulsed laser and a fiber continuous laser are combined through a fiber coupler into a two-in-one fiber and output as a spot-ring laser for welding heat source. The parameters of the nanosecond pulsed spot laser are: laser power 300 W, spot diameter 0.5 mm, pulse frequency 300 kHz, and pulse width 100 ns. The parameters of the ring continuous laser are: laser power 1500 W, ring spot diameter 2 mm. To reduce the melting on the steel side and avoid the formation of excessive IMCs, the center of the pulsed-continuous composite spot-ring laser is biased about 1 mm towards the aluminum side. The moving speed of the laser welding head is 2 m / min, and the protective gas used is argon with a purity of 99.99%, and the protective gas flow rate is 15 L / min. The final obtained weld length is 200 mm, and no cracks are generated on the surface.

[0057] During the pulsed-continuous composite spot-ring laser welding of aluminum-steel dissimilar metals, the ring continuous laser preheats the substrate, making it easier for the molten aluminum alloy melt to spread and wet on the steel side, while reducing the reflectivity of the aluminum alloy to the pulsed laser. The pulsed spot laser is used to achieve a greater welding penetration depth, with a smaller heat affected zone, and due to the stirring effect of the high-frequency pulsed laser on the molten pool, the formation of continuous coarse IMCs can be avoided. The thickest IMC layer detected in the middle of the weld is 0.8 μm, which is much smaller than the layer thickness of IMCs in conventional laser welding, and the maximum tensile strength is greater than 130 MPa. Using the pulsed-continuous composite spot-ring laser welding aluminum-steel butt joint proposed by the present invention can effectively prevent weld cracking, and the improvement effect of the mechanical properties of the weld is remarkable.

[0058] Example 2

[0059] This embodiment takes the welding of two lightest structural materials, aluminum and magnesium, as an example to illustrate the present invention. Figure 5 As shown in the figure, the pulse-continuous composite spot ring laser welding process test was carried out using an aluminum-magnesium lap joint. Since Al and Mg react easily to form brittle IMCs (Al3Mg2 and Al 12 Mg 17 ), which makes the weld cracking tendency extremely high. The current process methods will cause uneven heating and reaction at the interface, making it difficult to achieve effective connection. In this implementation case, the pulsed laser and the continuous laser are combined by optical path design to obtain a point ring laser for welding test. It should be noted that in this experiment, there is a Ti intermediate layer with a thickness of 0.2mm between the aluminum-magnesium substrate. The parameters of the nanosecond pulse point laser are: laser power 500W, point spot diameter 0.5mm, pulse frequency 500kHz, and pulse width 58ns. The parameters of the ring continuous laser are: laser power 1000W, ring spot diameter 2mm, and other process parameters are the same as those in implementation case one. The final aluminum-magnesium lap weld length is 200mm, which can achieve effective connection.

[0060] Different from Example 1, the energy of the pulse-continuous composite point ring laser will mainly act on the upper magnesium alloy. Because the melting point of titanium alloy is much higher than that of aluminum / magnesium alloy, during the welding process, the Ti intermediate layer is basically not melted, while the aluminum / magnesium substrate is melted and combined with the Ti layer. The annular continuous laser preheats the substrate, so that the keyhole formed by the pulse point laser is enlarged, the stability is improved, and more heat is conducted to the lower material. Due to the pinning effect of the pulse laser on the upper magnesium alloy molten pool, the bonding interface of the intermediate layer is serrated, which can achieve effective connection, and the maximum shear resistance is 3.3kN.

[0061] In summary, the present invention combines pulsed laser and continuous laser beams into a point ring light source, which can achieve simultaneous output in the time domain, but decoupled and non-interfering in space. When applied to dissimilar metal welding, the ring-shaped continuous laser can be used to effectively make up for the insufficient average output power of the pulsed laser, break through the size limit of the weldable plate thickness, and give full play to the series of advantages of the pulsed laser such as low average power, high peak power, good energy controllability and high beam quality. By adjusting the waveform, pulse width, frequency and other parameters, the IMCs component and proportion in the dissimilar metal weld can be controlled without changing the overall heat input. The present invention efficiently combines the pulsed point laser with the continuous ring laser and applies it in the field of laser welding. The energy proportion of the point ring light source can be flexibly adjusted, and the application range is wide. It can fully combine the advantages of good adjustability of the pulsed laser and the wide output power range of the continuous laser, and is particularly suitable for the welding of dissimilar metals in thin plates or medium and thick plates.

[0062] Those skilled in the art can easily understand that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A pulse - continuous composite spot - ring laser welding method for dissimilar metals, characterized in that, During the welding process, the pulsed laser and the annular continuous laser are combined into a dot-ring laser and applied to the surface of the workpiece to form a welding molten pool. The welding penetration is increased by the external annular continuous laser, and the flow field of the molten pool and the proportion of intermetallic compounds in the weld are regulated by the internal pulsed laser. The interaction between the pulsed and continuous lasers can increase the laser energy absorption efficiency and improve the quality of dissimilar metal welded joints. The dot-ring laser transmission optical fiber has a double-clad waveguide structure. The internal core transmits the pulsed laser, and the external fiber cladding transmits the continuous laser. The pulsed-continuous composite dot-ring laser is output at the end.

2. The method for pulse - continuous composite spot - ring laser welding of dissimilar metals according to claim 1, wherein The types of dissimilar metal welded joints are butt joints, lap joints or T-joints.

3. The pulse - continuous composite spot - ring laser welding method for dissimilar metals according to claim 1, characterized in that, The total output power of the dot-ring laser is 100W - 3000W. The total output power of the dot-ring laser is the sum of the output powers of the pulsed laser and the annular continuous laser, where the output power of the pulsed laser is 0W - 1000W.

4. The method for pulse - continuous composite spot - ring laser welding of dissimilar metals according to claim 1, characterized in that, The welding speed is 0.5 - 3m / min.

5. The method for pulsed - continuous composite spot - ring laser welding of dissimilar metals according to claim 1, characterized in that, When the type of dissimilar metal welded joint is a butt joint or a T-joint, the center of the dot-ring laser is biased towards the side of the low melting point metal, and the offset is 0 - 5mm.

6. The method for pulse - continuous composite spot - ring laser welding of dissimilar metals according to claim 1, wherein The pulsed laser includes any one of nanosecond laser, picosecond laser and femtosecond laser, and the annular continuous laser includes any one of gas laser, semiconductor laser, disk laser and fiber laser.

7. The pulse - continuous composite spot - ring laser welding method for dissimilar metals according to claim 1, characterized in that, The two dissimilar metal workpieces to be welded include any one of aluminum-steel, aluminum-magnesium, magnesium-steel, steel-titanium, steel-copper, and aluminum-copper.

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