A lap welding method based on laser pre-melting in-situ modification

Abstract

The present invention is applicable to the field of welding technology, and provides a lap welding method based on laser pre-melting in-situ modification, comprising the following steps: preparing a welding base material and a pre-melting material; using a pulsed laser heat source to melt the pre-melting material and the surface of the welding base material to form a laser pre-melting in-situ modified layer; leveling the surface of the laser pre-melting in-situ modified layer, fixing the upper and lower welding base materials in an overlapping form, with the laser pre-melting in-situ modified layer facing the overlapping surface; selecting a suitable welding method to melt or fuse the laser pre-melting in-situ modified layer to form a lap joint. The present invention achieves efficient metallurgical bonding between the welding base material and the pre-melting material by introducing the laser pre-melting in-situ modification technology, which not only reduces the overlapping surface and eliminates the overlapping gap, but also enhances heat conduction, avoiding the occurrence of defects such as incomplete fusion, incomplete penetration and welding cracks. At the same time, the technology promotes the in-situ generation of strengthening phases in the welding base material, refines the weld metal microstructure, and improves the tensile strength of the lap weld.

Description

Technical Field

[0001] The invention belongs to the technical field of welding, and in particular relates to a lap welding method based on laser pre-melting in-situ modification. Background Art

[0002] Lap welding is a key form of welding joint. It is achieved by stacking two pieces of welding base metal, and using the welding heat source (stirring head) to act on the upper surface of the welding base metal, so that the heat penetrates the upper welding base metal, thereby combining the overlapping area into one. This welding technology is widely used in many fields such as petrochemicals, medical equipment and electrical components, and is crucial to the quality of welded joints. Due to the special stacking structure of lap welding, non-filling welding methods such as high-energy beam welding, TIG welding and stir friction welding are usually used. In these methods, the overlapping area is composed of the lower surface of the upper plate and the upper surface of the lower plate. Therefore, the bonding quality of the overlapping area directly determines the tensile strength of the joint.

[0003] In order to improve the bonding quality of the overlap area, researchers have tried to pre-place strengthening powder or foil on the overlap surface, hoping to optimize the weld metal structure of the overlap area and improve the quality of the overlap joint through the welding chemical metallurgical reaction of the fusion zone. However, the pre-placed powder or foil will increase the overlap surface and the overlap gap, resulting in an increase in contact thermal resistance and a decrease in heat conduction, which often leads to problems of incomplete fusion and incomplete penetration. At the same time, insufficient powder fusion will also cause welding cracks, which will eventually lead to cracking of the overlap joint, which in turn reduces the welding quality. In order to solve these problems, improving the form of pre-placed powder or foil so that it can optimize the weld metal structure of the overlap area while maintaining the flatness of the contact area and the constant contact thermal resistance, thereby improving the welding quality, is a technical solution that welding workers are striving to seek to improve. To this end, the present invention proposes a lap welding method based on laser pre-melting in-situ modification. Summary of the invention

[0004] The object of the present invention is to provide a lap welding method based on laser pre-melting in-situ modification, aiming to solve the problems raised in the above background technology.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] A lap welding method based on laser pre-melting in-situ modification comprises the following steps:

[0007] Step 1: Prepare welding base material and pre-melted material;

[0008] Step 2: Select a Nd:YAG pulse laser welding machine and set pre-melting parameters, including peak power, pulse time, pulse waveform, welding speed, defocusing amount and shielding gas flow rate;

[0009] Step 3: Select an area 1 to 20 mm away from the edge of the welding base material for pre-melting, and use a pulsed laser heat source to melt the pre-melted material and the surface of the welding base material to form a laser pre-melted in-situ modified layer;

[0010] Step 4: Smooth the surface of the laser pre-melted in-situ modified layer, and then fix the upper and lower welding base materials in an overlapping manner, with the width of the overlapping area being 1-20 mm, and the laser pre-melted in-situ modified layer facing the overlapping surface;

[0011] Step 5: Select a welding method, set welding parameters, and use a welding heat source to melt or fuse the laser pre-melted in-situ modified layer to form a lap joint.

[0012] Furthermore, the pre-melted material is a pre-melted foil or powder; if powder is selected for pre-melting, the powder is mixed with anhydrous ethanol in a ratio of 1:1 and stirred thoroughly to form a suspension, and then the suspension is evenly sprayed on the surface of the welding base material and dried for later use.

[0013] Furthermore, the composition of the pre-melted material is a mixture of one or more of ceramic materials, carbon nanotubes, carbon fibers and metals, and the ceramic material is one or more of WC, TiB2, TiC, Al2O3 and TiO2.

[0014] Furthermore, the upper and lower welding base materials are the same or different metals, and one side of one welding base material is provided with a laser pre-melted in-situ modified layer or one side of both welding base materials is provided with a laser pre-melted in-situ modified layer.

[0015] Furthermore, in step 2, the pulse peak power is 0.5~2kW, the pulse time is 0~5ms, the pulse waveform is a rectangular wave, the welding speed is 180~600mm / min, the defocus amount is ±3mm, and the shielding gas flow rate is 0~10L / min.

[0016] Furthermore, in step 5, the welding methods are non-filled fusion welding methods and pressure welding methods. The non-filled fusion welding methods include laser welding, electron beam welding and TIG welding, and the pressure welding methods include stir friction welding.

[0017] Furthermore, when the welding method adopts laser welding, a pulse laser welder is selected for lap welding, and the parameters are set: peak power p=3kW, pulse time t=4ms, pulse waveform is rectangular wave, defocus amount is +2mm, shielding gas is argon, and flow rate is 10L / min.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The present invention achieves efficient metallurgical bonding between the welding base material and the pre-melted material by introducing the laser pre-melting in-situ modification technology, which not only reduces the overlap surface and eliminates the overlap gap, but also enhances heat conduction, effectively avoiding the occurrence of defects such as incomplete fusion, incomplete penetration and welding cracks. At the same time, this technology promotes the in-situ generation of strengthening phases in the welding base material, refines the weld metal microstructure, and improves the tensile strength of the overlap weld. Therefore, the present invention successfully solves the problems of incomplete weld melting, incomplete penetration and welding cracks caused by insufficient fusion of the overlap area in the existing pre-set powder or foil technology, and provides an innovative solution for the development of welding technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Flow chart of the method of the present invention.

[0021] Figure 2 Schematic diagram of lap welding based on laser pre-melting in-situ modification.

[0022] Figure 3 This is the microstructure of the magnesium alloy side in Example 1.

[0023] Figure 4 This is the microstructure of the magnesium alloy side in Example 2.

[0024] Figure 5 This is the microstructure of the titanium alloy side in Example 1.

[0025] Figure 6 This is the microstructure of the titanium alloy side in Example 2.

[0026] Figure 7 The AlB in the laser pre-melted layer in Example 2 12 TEM diffraction patterns.

[0027] Figure 8 This is the TEM diffraction pattern of Ti2B5 in the laser pre-melted layer in Example 2.

[0028] Fig. 9 This is the TEM diffraction pattern of Ti3Al in the laser pre-melted layer in Example 2.

[0029] Fig.10 The TiB in the laser pre-melted layer in Example 2 55 TEM diffraction patterns.

[0030] Fig.11 This is the XRD test result of the laser pre-melted layer in Example 2.

[0031] In the figure: 1. Welding heat source; 2. Laser pre-melting in-situ modified layer; 3. Welding base material. DETAILED DESCRIPTION

[0032] In order to have a clearer understanding of the technical features, purposes and beneficial effects of the present invention, the technical solution of the present invention is now described in detail below, but it should not be construed as limiting the applicable scope of the present invention.

[0033] The specific implementation of the present invention is described in detail below in conjunction with specific embodiments.

[0034] An embodiment of the present invention provides a lap welding method based on laser pre-melting in-situ modification, the method comprising the following steps:

[0035] Prepare welding base material 3 and pre-melting material. The pre-melting material can be foil or powder. The powder needs to be mixed with anhydrous ethanol and evenly sprayed on the surface of welding base material 3, and then dried for use; use pulsed laser heat source to melt the pre-melting material and the surface of welding base material 3 to form laser pre-melting in-situ modified layer 2; flatten the surface of laser pre-melting in-situ modified layer 2, fix the upper and lower welding base materials 3 in an overlapping form, and the laser pre-melting in-situ modified layer 2 faces the overlapping surface. Select a suitable welding method to melt or fuse the laser pre-melting in-situ modified layer 2 to form an overlapping joint.

[0036] In the embodiment of the present invention, compared with pre-powder or foil in the overlap area, laser pre-melting can make the pre-melted material metallurgically bonded with the surface of the welding base material 3, reduce the overlap surface, eliminate the overlap gap, enhance heat conduction, and inhibit the occurrence of defects such as incomplete fusion, incomplete penetration and welding cracks in the joint; in addition, the welding base material 3 can generate a strengthening phase in situ, refine the weld metal microstructure, and improve the tensile strength of the overlap weld by means of fine grain strengthening, mismatch strengthening, pinning strengthening, etc.

[0037] like Figure 1 As shown, the specific steps of the method are as follows:

[0038] Step 1, prepare welding base material 3 and pre-melting material, use sandpaper and alcohol to remove oxide film, rust, moisture and oil on the surface of welding base material 3; the pre-melting material is pre-melting foil or powder; if powder is selected for pre-melting, mix the powder with anhydrous ethanol in a ratio of 1:1 and stir well to make a suspension, then spray the suspension evenly on the surface of welding base material 3, and dry for use. The composition of the pre-melting material can be a mixture of one or more of ceramic material, carbon nanotube, carbon fiber and metal, and the ceramic material can be one or more of WC, TiB2, TiC, Al2O3, TiO2.

[0039] Step 2. Select Nd:YAG pulse laser welding machine and set pre-melting parameters: pulse peak power (0.5~2kW), pulse time (0~5ms), pulse waveform is rectangular wave, welding speed (180~600mm / min), defocus (±3mm), shielding gas flow (0~10L / min).

[0040] Step 3, select an area 1 to 20 mm away from the edge of the welding base material 3 for pre-melting, and use a pulsed laser heat source to melt the pre-melted material and the surface of the welding base material 3 to form a laser pre-melted in-situ modified layer 2. The upper and lower welding base materials 3 can be the same or different metals, and one side of one welding base material 3 can be attached with a laser pre-melted in-situ modified layer 2, or one side of two welding base materials 3 can be attached with a laser pre-melted in-situ modified layer 2.

[0041] Step 4, smoothing the surface of the laser pre-melted in-situ modified layer 2, and then fixing the upper and lower welding base materials 3 in an overlapping form, the width of the overlapping area is 1-20 mm, and the laser pre-melted in-situ modified layer 2 faces the overlapping surface;

[0042] Step 5, select a suitable welding method, set welding parameters, and use the welding heat source 1 to melt or fuse the laser pre-melted in-situ modified layer 2 to form a lap joint. The lap joint is formed by lap welding the welding base material 3 with the laser pre-melted in-situ modified layer 2 (one or two of which are accompanied by the laser pre-melted in-situ modified layer 2), and using the high temperature of the welding heat source 1 to fully melt the laser pre-melted in-situ modified layer 2 and the overlapping area of ​​the two welding base materials 3 and fuse them with each other.

[0043] The welding method can be non-filled melting welding and pressure welding methods such as laser welding, electron beam welding, TIG welding and stir friction welding. When laser welding is used, a pulse laser welder is selected for lap welding, and the parameters are set as follows: peak power p=3kW, pulse time t=4ms, pulse waveform is rectangular wave, defocus is +2mm, shielding gas is argon, and flow rate is 10L / min.

[0044] Embodiment 1, conventional pre-set lap welding method;

[0045] The two pieces of welding base materials 3 are AZ31 magnesium alloy and TC4 titanium alloy respectively. The length and width of magnesium alloy base materials and titanium alloy base materials are both 90*60mm, the thickness of magnesium alloy base materials is 0.5mm, and the thickness of titanium alloy base materials is 1mm. Sandpaper and alcohol are used to remove the oxide film, rust, moisture and oil on the surface of welding base materials 3. The magnesium alloy base material is placed on the titanium alloy base material, and the overlap area size is 10mm. A pulse laser welder is selected for overlap welding, and the parameters are set: peak power p=3kW, pulse time t=4ms, pulse waveform is rectangular wave, defocus is +2mm, shielding gas is argon, and the flow rate is 10L / min to form an overlap joint.

[0046] Through welding metallographic treatment, the microstructure of magnesium alloy side is obtained (such as Figure 2 ) and the titanium alloy side microstructure diagram (as shown Figure 4 The mechanical properties of the lap joint were tested by tensile test, and the results showed that its tensile strength was 29Mpa.

[0047] Embodiment 2, lap welding method based on laser pre-melting in-situ modification;

[0048] The two welding base materials 3 are AZ31 magnesium alloy and TC4 titanium alloy respectively. The length and width of the magnesium alloy base material and the titanium alloy base material are both 90*60mm, the thickness of the magnesium alloy base material is 0.5mm, and the thickness of the titanium alloy base material is 1mm. Sandpaper and alcohol are used to remove the oxide film, rust, moisture and oil on the surface of the welding base material 3. Micro / nano (1:1) micron ceramic particles TiB2 are selected as filling powder, which are mixed with anhydrous ethanol in a ratio of 1:1 and fully mixed to form a suspension, and then the suspension is evenly sprayed on the 10mm area of ​​the side end face of the TC4 titanium alloy and dried for use. Nd:YAG pulse laser welding machine is selected for pre-melting, and the pre-melting parameters are set as follows: peak power p=2kW, pulse time t=4ms, pulse waveform is rectangular wave, welding speed is 400mm / min, defocus is +3mm, protective gas is argon, and flow rate is 10L / min; laser pre-melting modified layers of titanium alloy base material and TiB2 are obtained. Through transmission electron microscopy (TEM) ( Figure 7-10 ) and X-ray diffractometer (XRD) ( Fig.11 )The test results show that Ti3Al, Ti2B5, AlB 12 , TiB 55 Metal phases. Smooth the surface of the laser pre-melted modified layer, place the magnesium alloy base material on the titanium alloy base material, and the overlap area size is 10mm; use a pulse laser welder for overlap welding, and set the parameters: peak power p=3kW, pulse time t=4ms, pulse waveform is rectangular wave, defocus is +2mm, shielding gas is argon, and the flow rate is 10L / min. During the overlap welding process, the laser pre-melted in-situ modified layer 2 is melted or fused using the welding heat source 1 to form an overlap joint.

[0049] Through metallographic treatment of the lap joint, the microstructure of the magnesium alloy side was obtained (e.g. Figure 3 ) and the titanium alloy side microstructure diagram (as shown Figure 5 ), Figure 3 and Figure 2 , Figure 5 and Figure 4 By comparison, it can be found that the in-situ phase generated by laser pre-melting can significantly reduce the grain size of magnesium alloy and titanium alloy. The mechanical properties of the lap joint were tested by tensile test, and the results showed that its tensile strength was 50.5Mpa. Compared with Example 1, it can be seen that the lap welding method based on laser pre-melting in-situ modification proposed in the present invention can refine the weld grains and increase the tensile strength by 74.14%.

[0050] The lap welding method based on laser pre-melting in-situ modification proposed by the present invention can select pulse laser pre-melting parameters according to the thickness of the pre-melted powder / foil, and combine with a suitable welding method to finally complete the lap welding. It should be noted that for technicians in the welding field, preparing the pre-melted powder by stirring and proportioning and selecting suitable parameters for laser pre-melting do not constitute implementation difficulties.

[0051] The above are only preferred embodiments of the present invention. It should be pointed out that, for those skilled in the art, several modifications and improvements can be made without departing from the concept of the present invention. These should also be regarded as the protection scope of the present invention. These will not affect the effect of the implementation of the present invention and the practicality of the patent.

Claims

1. A lap welding method based on laser pre-melting in-situ modification, characterized in that: The following steps are involved: Step 1: Prepare welding base material and pre-melted material; Step 2: Select a Nd:YAG pulse laser welding machine and set pre-melting parameters, including peak power, pulse time, pulse waveform, welding speed, defocusing amount and shielding gas flow rate; Step 3: Select an area 1 to 20 mm away from the edge of the welding base material for pre-melting, and use a pulsed laser heat source to melt the pre-melted material and the surface of the welding base material to form a laser pre-melted in-situ modified layer; Step 4: Smooth the surface of the laser pre-melted in-situ modified layer, and then fix the upper and lower welding base materials in an overlapping manner, with the width of the overlapping area being 1-20 mm, and the laser pre-melted in-situ modified layer facing the overlapping surface; Step 5: Select a welding method, set welding parameters, and use a welding heat source to melt or fuse the laser pre-melted in-situ modified layer to form a lap joint; The pre-melting material is a pre-melting foil or powder; if the powder is selected for pre-melting, the powder is mixed with anhydrous ethanol in a ratio of 1:1 and stirred thoroughly to form a suspension, and then the suspension is evenly sprayed on the surface of the welding base material and dried for later use; The pre-melted material is a mixture of one or more of a ceramic material, a carbon nanotube, a carbon fiber and a metal, and the ceramic material is one or more of WC, TiB2, TiC, Al2O3 and TiO2; The upper and lower welding base materials are the same or different metals, and one side of one welding base material is provided with a laser pre-melted in-situ modified layer or one side of both welding base materials is provided with a laser pre-melted in-situ modified layer; In step 2, the pulse peak power is 0.5-2kW, the pulse time is 0-5ms, the pulse waveform is a rectangular wave, the welding speed is 180-600mm / min, the defocusing amount is ±3mm, and the shielding gas flow rate is 0-10L / min; In step 5, the welding method is a non-filling fusion welding method and a pressure welding method, the non-filling fusion welding method includes laser welding, electron beam welding and TIG welding, and the pressure welding method includes stir friction welding; When the welding method adopts laser welding, a pulse laser welder is selected for lap welding, and the parameters are set as follows: peak power p=3kW, pulse time t=4ms, pulse waveform is rectangular wave, defocus amount is +2mm, shielding gas is argon, and flow rate is 10L / min.

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