A laser welding method for aluminum-silicon coated steel

Abstract

This invention discloses a laser welding method for aluminum-silicon coated steel, comprising the following steps: selecting a stainless steel welding wire with a high molybdenum content; taking two aluminum-silicon coated steel plates; performing butt laser welding with a filler wire; and performing hot stamping after welding. This method eliminates the need to remove the coating and enables the joining of aluminum-silicon coated steel using only the filler wire. After hot stamping, the welded joint achieves the same strength and toughness as the parent material, improving product quality and production efficiency.

Description

Technical Field

[0001] The present invention relates to a laser tailor welding method for aluminum-silicon coated steel, which is used for tailor welding aluminum-silicon coated steel and hot stamping after welding, and can obtain a weld joint with the same tensile strength and elongation as the base material, and has good corrosion resistance and wear resistance. Background Art

[0002] With the increasing number of cars, energy shortages, environmental pollution, and the greenhouse effect are becoming increasingly prominent. The advocacy for green environmental protection and energy conservation and emission reduction is growing stronger, placing higher demands on vehicle safety and energy efficiency. Vehicle design must ensure both safety and reliability while also conserving energy and reducing emissions. The most important way to achieve these two goals is to reduce vehicle weight while maintaining rigidity and strength. According to statistics, a 10% reduction in vehicle weight can improve fuel efficiency by 6% to 8% and reduce fuel consumption by 7%. Aluminum-silicon coated steel, with a tensile strength of up to 1500 MPa after hot stamping, has become a leading lightweight material for vehicle bodies and is widely used in the manufacture of structural components such as A-pillars, B-pillars, and crossbeams.

[0003] To prevent oxidation during the hot stamping process, the surface is typically pre-coated. Aluminum-silicon coatings, due to their excellent corrosion resistance and resistance to high-temperature oxidation, are a common coating for coated steel. However, the presence of the aluminum-silicon coating significantly degrades welding performance, making it difficult to guarantee weld quality with traditional welding methods. Laser welding, with its advantages of a small heat-affected zone, excellent joint strength, and high production efficiency, has become the preferred method for welding aluminum-silicon-coated steel. However, there are drawbacks. During laser welding, the coating melts into the weld, producing a high amount of ferrite and reducing the mechanical properties of the welded joint.

[0004] CN 101426612 B discloses a welding method for removing the coating from aluminum-silicon coated steel. This method uses a wire brush or laser to remove the coating, preventing the influence of the aluminum element in the coating on the weld and achieving good weld quality. However, this method is implemented by removing the coating, and post-removal testing is generally required. In actual production, the use of additional equipment for decoating and testing significantly increases production costs and process steps.

[0005] CN 111050980 A discloses a method for welding press-hardened manganese-boron steel using oscillating laser welding with filler wire. This method utilizes an oscillating laser beam to heat and melt the base material and welding wire, producing high-quality tailor-welded blanks. However, this method utilizes the optical lens system of an oscillating welding head to oscillate the laser beam. This oscillating welding head is expensive, and during laser oscillation welding, the interaction between the molten pool and the welding wire is less stable, which can easily generate significant spatter.

[0006] CN 104023899 B discloses a tailor-welded blank and its manufacturing method. During laser welding, a welding wire containing high levels of carbon and manganese promotes austenite transformation, thereby improving the mechanical properties of the welded joint. This method improves weld quality to a certain extent, but the high levels of carbon and manganese increase the weld's cold brittleness and aging sensitivity, and also reduces the weld's corrosion resistance and the service life of the tailor-welded blank.

[0007] CN 111065486 A discloses a method and apparatus for laser welding tailored blanks. During the laser welding process, a layer of graphite particles is coated on the surface of the welding wire and then filled into the molten pool to improve weld quality. However, due to interference from shielding gas, compressed air, and other factors during the welding process, this method makes it difficult for the graphite particles to be evenly filled into the molten pool, which can affect the mechanical properties of the weld to a certain extent. The device for coating the graphite particles requires high precision control, and the welding process is complex.

[0008] CN 106457465 B discloses a method for laser welding pre-coated sheet metal. This method uses a combination of two laser beams to weld the sheet metal. One scattered laser beam melts the coating while simultaneously blowing air to remove the molten metal. The other focused laser beam heats and melts the sheet metal to form a weld joint, improving the mechanical properties of the weld. This method significantly increases production costs and process steps, reduces production efficiency, and overly complicates the welding process due to the use of scattered laser beams to melt the coating and high-pressure gas blowing.

[0009] CN 106488824 B discloses a method for joining two blanks. By filling the blanks with an austenitic stabilizer, the tensile properties of the weld joint are improved. This method, using laser arc hybrid welding, increases the heat input and the likelihood of thermal deformation, hindering the joining of thin sheets. Furthermore, the tensile strength of the welded joint is less than 1500 MPa.

[0010] In response to the problems existing in the prior art, technicians in this field are committed to developing a welding method that can achieve equal strength and toughness of aluminum-silicon coated steel without removing the aluminum-silicon coating. Summary of the Invention

[0011] The purpose of the present invention is to provide a laser tailor welding method for aluminum-silicon coated steel, which does not require removal of the coating before welding. By filling a stainless steel welding wire with a high molybdenum content during the welding process, wherein the weight percentage of Mo is 0.5% to 12%, and the tensile strength of the welding wire is 400 to 1200 MPa, after hot stamping, a weld joint with the same tensile strength and elongation as the base material can be obtained, and has good corrosion resistance and wear resistance.

[0012] In order to achieve the above object, the technical solution of the present invention is as follows:

[0013] A laser welding method for aluminum-silicon coated steel, characterized by: selecting a stainless steel welding wire containing molybdenum as a filler wire; using a laser beam to weld two aluminum-silicon coated steel plates; and performing hot stamping after welding;

[0014] The weight percentage of Mo in the molybdenum-containing stainless steel welding wire is 0.5% to 12%, and the tensile strength of the welding wire is 400 to 1200 MPa.

[0015] Preferably, the weight percentage of Mo in the molybdenum-containing stainless steel welding wire is 1% to 10% by weight, and the tensile strength of the welding wire is 450 to 1000 MPa.

[0016] Preferably, the aluminum silicon coating consists of a metal alloy layer and an intermetallic compound alloy layer, the thickness of the intermetallic compound alloy layer is less than 20 μm, the total thickness of the coating is less than 60 μm, and the thickness of the steel plate is 0.5 to 5 mm.

[0017] Preferably, during the welding process, a laser beam is used to weld the two steel plates together, while a wire feeding nozzle feeds wire into the molten pool.

[0018] Preferably, the diameter of the welding wire is 0.4 to 2 mm, the wire feeding angle is 20 to 70°, the distance between the welding wire and the laser beam is smaller than the diameter of the welding wire, and the dry extension length is 2 to 30 mm.

[0019] Preferably, the width of the maximum gap between the two steel plates is less than 50% of the diameter of the welding wire.

[0020] Preferably, the hot stamping refers to heating the two steel plates after being joined and using a water-cooled mold or water-cooled quenching.

[0021] Preferably, the heating temperature of the hot stamping is 830-1050° C., the holding time is 1-20 min, and the cooling rate is greater than or equal to 27° C. / s.

[0022] Compared with the welding method mentioned in the prior art, the beneficial effects of the present invention are:

[0023] 1) There is no need to remove the aluminum-silicon coating before welding, which can achieve high-efficiency and high-quality welding.

[0024] 2) The tensile strength and elongation of the welded joint after stamping are consistent with those of the base material.

[0025] 3) The weld has excellent corrosion resistance and wear resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present invention may be better understood by the following description given with reference to the accompanying drawings, which are given by way of example only and not limitation. In the drawings:

[0027] Figure 1 A schematic diagram showing a laser filler wire welding method;

[0028] Figure 2 A schematic diagram showing the laser wire welding process;

[0029] Figure 3 The fracture position of the laser welded joint filled with high-molybdenum stainless steel welding wire according to an embodiment of the present invention is shown;

[0030] Figure 4 The fracture position of the laser welded joint filled with high-molybdenum stainless steel welding wire according to an embodiment of the present invention is shown;

[0031] Figure 5 The figure shows the fracture position of the weld joint of the laser autogenous welding of comparative example 1;

[0032] Figure 6 The fracture position of the laser welded joint filled with ER50G welding wire in comparative example 2 is shown; DETAILED DESCRIPTION

[0033] To make the above-mentioned objects, features and advantages of the present invention more clearly understood, the specific implementation of the present invention is described in detail below with reference to the accompanying drawings. First of all, it should be noted that the present invention is not limited to the specific implementations described below. Those skilled in the art should understand the present invention from the spirit embodied in the following implementations, and each technical term should be understood in the broadest sense based on the spirit of the present invention.

[0034] Figure 1 This schematic diagram illustrates a laser welding method with filler wire. Steel plates 1 and 2 are butted together to form a weld area 12. A laser beam 11 is emitted from a weld joint 10 to heat and melt the weld area 12, forming a molten pool 14. Simultaneously, a welding wire 6 is fed into the molten pool 14 via a wire feed nozzle 9. The heat energy from the laser beam 11 and the molten pool 14 causes the welding wire 6 to melt and fill the molten pool 14.

[0035] Figure 2 Schematic diagram of the laser wire welding process is shown. Steel plate 1 and steel plate 2 are butted together to form a welded area 12. In this example, the two steel plates are to be joined, i.e. welded edge to edge.

[0036] Both steel plates 1 and 2 may be steel plates having an aluminum-silicon coating. Aluminum-silicon coating 3 and aluminum-silicon coating 4 are composed of an aluminum-silicon layer 15 and an aluminum alloy layer 16. When steel plates 1 and 2 are welded, welding wire 6 mixes with portions of the coatings on steel plates 1 and 2 under the action of laser beam 11. In these embodiments, arrow 17 indicates the welding direction.

[0037] Laser beam 11 is emitted from welding head 10, with welding wire 6 serving as filler material. Under the action of laser beam 11, the area to be welded 12 formed by steel plates 1 and 2 melts. Welding wire 6 is then fed into molten pool 14 through wire feed nozzle 9. Simultaneously, the molten wire mixes with the molten areas 12 of steel plates 1 and 2. As welding continues, all gaps between steel plates 1 and 2 are filled, and the molten pool cools to form weld seam 5.

[0038] Aluminum in the coating is permitted in the weld zone but does not affect the mechanical properties of the welded joint after hot stamping. A high Mo content in the welding wire refines the weld microstructure, resulting in a martensitic microstructure with excellent mechanical properties after hot stamping.

[0039] The laser beam can be moved in two modes: non-swinging and swinging. The swinging trajectory includes clockwise swinging, counterclockwise swinging, Z-shaped swinging, and infinite shape swinging.

[0040] MAG (metal active gas), MIG (metal inert gas), or TIG (tungsten inert gas) can be used as wire feeding alternatives.

[0041] Welding can be performed directly in the air without protective gas.

[0042] The laser beam can be one or two beams in combination, with a spot diameter of 0.2 to 1.6 mm and a double spot spacing of 0 to 3 mm.

[0043] The wire feed nozzle can be placed in front of or behind the laser beam and welds synchronously with the welding head.

[0044] The above methods can be used to join two steel plates. At least one of the steel plates has a coating composed of aluminum, silicon and other elements. Specifically, an Al-Si coating can be used.

[0045] This method utilizes the high content of Mo in the welding wire to refine the structure of the weld. After hot stamping, a martensitic microstructure with excellent mechanical properties can be obtained.

[0046] It can be seen that in this case, there is no need to remove the coating of the steel substrate before welding, which can reduce the number of processes, improve production efficiency and significantly reduce costs.

[0047] The technical solutions of the present invention will be described in detail and completely below through specific implementation methods. It is obvious that the described embodiments are only part of the present invention, not all of the embodiments. All other embodiments derived by those skilled in the art based on the embodiments of the present invention without inventive effort shall fall within the scope of protection of the present invention.

[0048] Example 1:

[0049] A laser welding method for aluminum-silicon coated steel comprises the following steps:

[0050] S1. Take two 1.4mm thick aluminum-silicon coated steel plates cut by a shearing machine. The microstructure of the steel plates is ferrite and pearlite. Use alcohol to clean the oil stains on both steel plates.

[0051] S2. Fix the two steel plates on the welding table with a clamp and use zero gap splicing.

[0052] S3. Use a fiber laser and set the wire-feeding welding parameters: laser power 5500 W, laser scanning speed 3.6 m / min, laser spot diameter 0.98 mm, no shielding gas during welding, wire feeding speed 4 m / min, wire feeding angle 45°.

[0053] S5: The fiber laser emits laser light at the butt joint of the two pieces of steel, while the wire feed nozzle feeds the welding wire into the molten pool. The molten welding wire mixes with the melted butt joint of the two pieces of steel and solidifies to form a weld.

[0054] S6. Hot stamping is performed after welding.

[0055] By filling the stainless steel wire with a high molybdenum content, the diameter is 1mm, of which the weight percentage of Mo is 2.13%, and the tensile strength of the wire is 543MPa. After hot stamping, the obtained weld joint has a martensite structure with excellent mechanical properties in the fusion zone. The tensile strength is measured to be 1572.85MPa, and the fracture position occurs in the base material. The tensile strength and elongation of the weld joint are consistent with those of the base material. Figure 3 shown.

[0056] Example 2:

[0057] A laser welding method for aluminum-silicon coated steel comprises the following steps:

[0058] S1. Take two 1.4mm thick aluminum-silicon coated steel plates cut by a shearing machine. The microstructure of the steel plates is ferrite and pearlite. Use alcohol to clean the oil stains on both steel plates.

[0059] S2. Fix the two steel plates on the welding table with a clamp and use zero gap splicing.

[0060] S3. Use a fiber laser and set the welding parameters: laser power 5500W, laser scanning speed 4.2m / min, laser spot diameter 0.98mm, no shielding gas during welding. The wire feed speed is 3m / min and the wire feed angle is 45°.

[0061] S5: The fiber laser emits laser light at the butt joint of the two pieces of steel, while the wire feed nozzle feeds the welding wire into the molten pool. The molten welding wire mixes with the melted butt joint of the two pieces of steel and solidifies to form a weld.

[0062] S6. Hot stamping is performed after welding.

[0063] By filling the stainless steel wire with a high molybdenum content, the diameter is 1mm, of which the weight percentage of Mo is 2.13%, and the tensile strength of the wire is 543MPa. After hot stamping, the obtained weld joint has a martensite structure with excellent mechanical properties in the fusion zone. The tensile strength is measured to be 1557.6MPa, and the fracture position occurs in the base material. The tensile strength and elongation of the weld joint are consistent with those of the base material. Figure 4 shown.

[0064] Comparative Example 1:

[0065] As a comparative embodiment, the same sheet material and the same pretreatment method were selected as the target material of the tailor-welded blanks.

[0066] The conventional laser autogenous welding method was selected, with a laser power of 2500W, a laser scanning speed of 6m / min, a spot diameter of 0.5mm, and no protective gas during the welding process. After the same hot stamping process, the fusion zone structure was δ ferrite and lath martensite. The tensile strength was measured to be only 1180.6MPa, and the fracture position was the fusion zone. Figure 5 shown.

[0067] Comparative Example 2:

[0068] As a comparative embodiment, the same sheet material and the same pretreatment method were selected as the target material of the tailor-welded blanks.

[0069] The welding process was conducted with ER50G welding wire of 1mm diameter, 5500W laser power, 4.2m / min laser scanning speed, 0.98mm laser spot diameter, and no shielding gas. The wire feed speed was 3m / min, the wire feed angle was 45°, and no shielding gas was used.

[0070] After welding and undergoing the exact same hot stamping process, the tensile strength of the welded joint is only 1229.73 MPa, and the fracture position is the fusion zone, e.g. Figure 6 shown.

[0071] Comparative Example 3:

[0072] The method disclosed in patent number CN 106488824 B uses laser arc hybrid welding for tailor welding, and the weight percentage of Mo in the stainless steel welding wire is 0% to 0.4%. The plate to be tailor welded is 1.4mm thick Usibor The weight percentage of Mo in the stainless steel welding wire is 0.3%.

[0073] Implementation effect: The tensile strength of the welded joint after stamping by this method is only 1409 MPa, which is lower than the tensile strength of the welded joint welded by uncoated 22MnB5 steel, which is 1527 MPa.

[0074] Experiments have shown that the tailored welding method provided by this invention eliminates the need for pre-welding coating removal. By using stainless steel welding wire with a high molybdenum content (2.13% by weight) and a tensile strength of 543 MPa, hot stamping can produce a welded joint with the same strength and toughness as the parent material. This significantly improves welding quality and production efficiency, while also reducing production costs.

[0075] Although only a few examples are disclosed herein, other alternatives, modifications, uses, and / or their equivalents are possible. In addition, all possible combinations of the described examples are also covered. Therefore, the scope of this disclosure should not be limited by the specific examples, but should be determined only by a proper reading of the appended claims.

Claims

1. A laser welding method for aluminum-silicon coated steel, characterized by: A stainless steel wire containing molybdenum was selected as the filler wire; two steel plates with aluminum-silicon coatings were welded using a laser beam; and hot stamping was performed after welding. The weight percentage of Mo in the molybdenum-containing stainless steel welding wire is 2.13%, the tensile strength of the welding wire is 543 MPa, and the fusion zone of the tailor-welded blank after hot stamping is a martensitic structure with excellent mechanical properties.

2. The laser welding method for aluminum-silicon coated steel according to claim 1, characterized in that: The aluminum silicon coating consists of a metal alloy layer and an intermetallic compound alloy layer. The thickness of the intermetallic compound alloy layer is less than 20 μm, the total thickness of the coating is less than 60 μm, and the thickness of the steel plate is 0.5-5 mm.

3. The laser welding method for aluminum-silicon coated steel according to claim 1, characterized in that: During the welding process, a laser beam is used to weld two steel plates together, while a wire feed nozzle feeds wire into the molten pool.

4. The laser welding method for aluminum-silicon coated steel according to claim 3, characterized in that: The diameter of the welding wire is 0.4-2 mm, the wire feeding angle is 20-70 degrees, the distance between the welding wire and the laser beam is smaller than the diameter of the welding wire, and the dry extension length is 2-30 mm.

5. The laser welding method for aluminum-silicon coated steel according to any one of claims 1 to 3, characterized in that: The width of the maximum gap between the two steel plates is less than 50% of the diameter of the welding wire.

6. The laser welding method for aluminum-silicon coated steel according to claim 1, characterized in that: The hot stamping is to heat the two steel plates after joining and use a water-cooled die or water-cooled quenching.

7. The laser welding method for aluminum-silicon coated steel according to claim 6, characterized in that: The heating temperature of the hot stamping is 830-1050° C., the holding time is 1-20 minutes, and the cooling rate is greater than or equal to 27° C. / s.

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