WO2022016929A1

WO2022016929A1 - Laser tailor welding method of aluminum-silicon coated steel

Info

Publication number: WO2022016929A1
Application number: PCT/CN2021/088888
Authority: WO
Inventors: 许伟; 杨上陆; 陶武
Original assignee: 中国科学院上海光学精密机械研究所
Priority date: 2020-07-22
Filing date: 2021-04-22
Publication date: 2022-01-27
Also published as: WO2022017374A1; CN113967789A

Abstract

A laser tailor welding method of aluminum-silicon coated steel, comprising the following steps: selecting a stainless steel welding wire having a high molybdenum content (6); taking two steel plates (1, 2) having an aluminum-silicon coating (3, 4); implementing laser filler wire tailor welding; and carrying out hot stamping after welding.

Description

A kind of laser tailor welding method of Al-Si coated steel

technical field

The 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, which can obtain welded joints consistent with the tensile strength and elongation of the base metal, and has good corrosion and wear resistance.

Background technique

With the increasing number of automobiles, a series of problems such as energy shortage, environmental pollution and greenhouse effect have become increasingly prominent. The theme of people advocating green environmental protection, energy saving and emission reduction is becoming more and more intense, and it also puts forward higher requirements for the safety and energy consumption of automobiles. Vehicle design must not only ensure the safety and reliability of the vehicle, but also save energy and reduce emissions. The most important way to achieve these two goals is to reduce the weight of the car body on the premise of ensuring the rigidity and strength of the car body. According to statistics, if the weight of the car is reduced by 10%, the fuel efficiency can be increased by 6% to 8%, and the fuel consumption can be reduced by 7%. The tensile strength of aluminum-silicon-coated steel after hot stamping can reach 1500MPa, and it has become the main force of lightweight materials for car bodies.

To avoid oxidation during hot stamping, the surface is usually pre-coated. Al-Si coating has become a commonly used coating for coated steel due to its excellent corrosion resistance and high temperature oxidation resistance. Due to the presence of Al-Si coating, the welding performance is seriously deteriorated. The traditional welding method is difficult to guarantee the welding quality. Laser welding has the advantages of small heat-affected zone, good bonding strength and high production efficiency, and has become the preferred method for welding aluminum-silicon coated steel. However, there are also shortcomings. When using laser welding, the coating will melt into the weld, resulting in more ferrite and reducing the mechanical properties of the welded joint.

In CN 101426612 B, a welding method for removing the coating of aluminum-silicon coated steel is disclosed. The coating is removed by a wire brush or a laser, so as to avoid the influence of the Al element in the coating on the welding seam, and obtain a good welding quality. However, this method is realized by removing the coating, and generally requires the detection after the coating is removed. In actual production, the production cost and process increase significantly due to the use of other equipment for decoating and inspection.

In CN 111050980 A, a welding method for oscillating laser wire filling and pressure-quenching manganese-boron steel is disclosed. The oscillating laser beam is used to heat and melt the base material and the welding wire to obtain high-quality tailor-welded blanks. However, this method uses the optical lens group of the oscillating welding head to realize the oscillation of the laser beam. The price of the oscillating welding head is expensive. During the laser oscillating welding process, the stability of the interaction between the molten pool and the welding wire is reduced, and it is easy to generate large splashes.

In CN 104023899 B, a tailor-welded blank and a manufacturing method thereof are disclosed. During the laser welding process, the transformation of austenite is promoted by filling the welding wire with higher C and Mn elements, so as to improve the mechanical properties of the welded joint. Target. This method improves the quality of welding to a certain extent, but higher elements of C and Mn will increase the cold brittleness and aging sensitivity of the weld, and also reduce the corrosion resistance of the weld and the service life of the tailor-welded blank. .

In CN 111065486 A, a method and device for tailor welded blanks are disclosed. During the laser welding process, a layer of graphite particles is coated on the surface of the welding wire and filled into the molten pool to improve the welding quality. In this method, due to the interference of shielding gas, compressed air and other factors during the welding process, it is difficult for graphite particles to fill the molten pool uniformly, and the mechanical properties of the weld are affected to a certain extent. The device for coating graphite particles requires high precision control, and the welding process is complicated.

In CN 106457465 B, a method of laser welding pre-coated sheet metal is disclosed, and the plate is welded by a combination of two laser beams. A scattered laser beam is used to melt the coating and blow air at the same time to blow away the molten metal; another focused laser beam heats and melts the sheet to form a welded joint, which improves the mechanical properties of the welded joint. In this method, due to the use of scattered laser beams to melt the coating and blowing of high-pressure gas, production costs and procedures are significantly increased, production efficiency is also reduced, and the welding process is too complicated.

A method of joining two blanks is disclosed in CN 106488824 B, which improves the tensile properties of the welded joint by filling with austenite stabilizing fillers. In this method, when the laser arc hybrid welding is used, the heat input increases, which increases the probability of thermal deformation of the plate, which is not conducive to the splicing of the thin plate. And the tensile strength of its welded joint is lower than 1500MPa.

In view of the problems existing in the prior art, those skilled in the art are devoted to developing a tailor-welding method that can realize the equal strength and toughness of the aluminum-silicon coated steel without removing the aluminum-silicon coating.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a laser tailor welding method for aluminum-silicon coated steel, without removing the coating before welding, by filling the stainless steel wire with high molybdenum content during the welding process, wherein the weight percentage of Mo is 0.5% to 12% %, the tensile strength of the welding wire is 400-1200MPa, after hot stamping, a welded joint that is consistent with the tensile strength and elongation of the base metal can be obtained, and has good corrosion resistance and wear resistance.

In order to achieve the above object, the technical scheme of the present invention is as follows:

A laser tailor welding method for aluminum-silicon coated steel, which is characterized in that: a stainless steel wire containing molybdenum is selected as a filler wire; two steel plates with aluminum-silicon coating are used for tailor-welding with a laser beam; and hot stamping is performed after welding;

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

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

Preferably, the aluminum-silicon coating is composed 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.

Preferably, a laser beam is used to tailor-weld the two steel plates during the welding process, and the wire feeding nozzle feeds wire to the molten pool at the same time.

Preferably, the diameter of the welding wire is 0.4-2 mm, the wire feeding angle is 20-70°, the distance between the welding wire and the laser beam is smaller than the diameter of the welding wire, and the dry elongation is 2-30 mm.

Preferably, the width of the largest gap between the two steel plates is less than 50% of the diameter of the welding wire.

Preferably, the hot stamping refers to heating the joined two steel plates and using a water-cooled die or water-cooled quenching.

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

Compared with the welding methods mentioned in the prior art, the beneficial effects of the present invention are:

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

2) The tensile strength and elongation of the welded joint after stamping are consistent with the base metal.

3) The weld has excellent corrosion resistance and wear resistance.

Description of drawings

The present invention may be better understood from the description given below with reference to the accompanying drawings, which description is given by way of example only and not limitation. In the attached image:

Figure 1 shows a schematic diagram of a laser wire filler welding method;

Fig. 2 shows the schematic diagram of the laser wire filling welding process;

FIG. 3 shows the fracture position of the laser welded joint filled with the high molybdenum stainless steel wire according to the embodiment of the present invention;

FIG. 4 shows the fracture position of the laser welded joint filled with the high molybdenum stainless steel wire according to the embodiment of the present invention;

Fig. 5 shows the fracture position of the welded joint of laser self-fusion welding of Comparative Example 1;

Fig. 6 shows the fracture position of the laser welded joint filled with ER50G welding wire of Comparative Example 2;

detailed description

In order to make the above objects, features and advantages of the present invention more clearly understood, the following detailed description of the specific implementation of the present invention will be given in conjunction with the accompanying drawings. First of all, it should be noted that the present invention is not limited to the following specific embodiments. Those skilled in the art should understand the present invention from the spirit embodied in the following embodiments, and each technical term can be optimized based on the spirit of the present invention. broad understanding.

FIG. 1 shows a schematic diagram of a method of laser wire-filling welding, where a steel plate 1 and a steel plate 2 are butted together to form an area to be welded 12 . The welding joint 10 emits a laser beam 11 for heating and melting the area to be welded 12 to form a molten pool 14 . At the same time, the welding wire 6 is fed to the molten pool 14 through the wire feeding nozzle 9 . The welding wire 6 is melted by the combined action of the laser beam 11 and the thermal energy of the molten pool 14, and is filled into the molten pool 14.

FIG. 2 shows a schematic diagram of the laser wire filling welding process. The steel plate 1 and the steel plate 2 are butted together to form the to-be-welded area 12 . In this example, two steel sheets will be joined, ie welded edge to edge.

Both the steel sheet 1 and the steel sheet 2 may be steel sheets with an aluminum-silicon coating. The aluminum-silicon coating 3 and the aluminum-silicon coating 4 are composed of the aluminum-silicon layer 15 and the aluminum alloy layer 16 . When the steel sheet 1 and the steel sheet 2 are welded, the welding wire 6 is mixed with the partial coating of the steel sheet 1 and the steel sheet 2 under the action of the laser beam 11 . In these embodiments, arrow 17 indicates the welding direction.

The laser beam 11 is emitted from the welding head 10, and the welding wire 6 is used as a filler. Under the action of the laser beam 11, the to-be-welded area 12 composed of the steel plate 1 and the steel plate 2 is melted, the welding wire 6 is filled into the molten pool 14 by the wire feeding nozzle 9, and at the same time, the molten welding wire is mixed with the melting area 12 of the steel plate 1 and the steel plate 2. . As the welding continues, all gaps between steel plate 1 and steel plate 2 are filled, and the weld 5 is formed after the molten pool cools.

Aluminum in the coating is allowed to exist in the weld zone, but does not affect the mechanical properties of the welded joint after hot stamping. The higher content of Mo element in the welding wire can refine the microstructure in the weld. After hot stamping, a martensitic microstructure with excellent mechanical properties can be formed.

The walking trajectory that can use the laser beam can be in two modes: non-swinging and swinging. The swinging trajectory includes clockwise swing, counterclockwise swing, Z-shaped swing, and infinite-shaped swing.

MAG (Metal Active Gas), MIG (Metal Inert Gas), TIG (Tungsten Inert Gas) can be used as alternatives for wire feeding.

Welding can be performed directly in air without shielding gas.

The laser beam can use one beam or a combination of two beams, the spot diameter is 0.2-1.6mm, and the double spot spacing is 0-3mm.

The wire feed nozzle can be placed in front of or behind the laser beam for simultaneous welding with the welding head.

The various methods described above can be used to join two steel sheets. At least one of the steel sheets has a coating composed of aluminum and silicon and other elements. Specifically, Al-Si coatings can be used.

The method can refine the microstructure in the weld by using the Mo element with higher content in the welding wire. Martensitic microstructure with excellent mechanical properties after hot stamping.

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.

The technical solutions of the present invention will be described in detail and completely below through specific embodiments. It is obvious that the described embodiments are only some, but not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative efforts shall fall within the protection scope of the present invention.

Example 1:

A laser tailor welding method for aluminum-silicon coated steel, comprising the following steps:

S1. Take a 1.4mm thick steel plate with Al-Si coating cut by two shears, and the microstructure of the steel plate is ferrite and pearlite. Use alcohol to clean the oil stains on the two steel plates for purification.

S2. The two steel plates are spliced and fixed on the welding table through a fixture, and spliced with zero gap.

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

S5. The fiber laser emits laser light on the butt joint of the two steels, and at the same time, the welding wire is fed from the wire feeding nozzle to the molten pool. The molten welding wire mixes with the butt area where the two pieces of steel melt and solidifies to form the weld.

S6, hot stamping after welding.

By filling the stainless steel welding wire with high molybdenum content, the diameter is 1mm, the weight percentage of Mo is 2.13%, and the tensile strength of the welding wire is 543MPa. After hot stamping, the obtained welded joint has excellent mechanical properties. body structure. The measured tensile strength is 1572.85MPa, and the fracture position appears in the base metal. The tensile strength and elongation of the welded joint are consistent with the base metal, as shown in Figure 3.

Embodiment 2:

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

S6, hot stamping after welding.

By filling the stainless steel welding wire with high molybdenum content, the diameter is 1mm, the weight percentage of Mo is 2.13%, and the tensile strength of the welding wire is 543MPa. After hot stamping, the obtained welded joint has excellent mechanical properties. body structure. The tensile strength was measured to be 1557.6MPa, and the fracture position appeared in the base metal. The tensile strength and elongation of the welded joint were consistent with the base metal, as shown in Figure 4.

Comparative example 1:

As a comparative embodiment, the exact same blank and the same pretreatment method are selected as the target material of the tailor welded blank.

The ordinary laser self-fusion welding method is selected, the laser power is 2500W, the laser scanning speed is 6m/min, the spot diameter is 0.5mm, and there is no protective gas during the welding process. After the exact same hot stamping process, the fusion zone structure is δ-ferrite. body and lath martensite. The measured tensile strength is only 1180.6MPa, and the fracture position is the fusion zone, as shown in Figure 5.

Comparative example two:

The welding wire filled with ER50G is selected, the diameter is 1mm, the laser power is 5500W, the laser scanning speed is 4.2m/min, the diameter of the laser spot is 0.98mm, and there is no protective gas during the welding process. The wire feeding speed is 3m/min, the wire feeding angle is 45°, and there is no shielding gas during the welding process.

After the exact same hot stamping process after welding, the tensile strength of the welded joint is only 1229.73MPa, and the fracture position is the fusion zone, as shown in Figure 6.

Comparative example three:

The method disclosed in Patent No. CN 106488824 B uses laser arc hybrid welding for tailor welding, and the weight percentage of Mo in the filled stainless steel wire is 0% to 0.4%. The plate to be welded is 1.4mm thick

plate, the Mo weight percentage in the filled stainless steel wire is 0.3%.

Implementation effect: The tensile strength of the welded joint punched by this method is only 1409 MPa, which is lower than the tensile strength of 1527 MPa of the welded joint welded with uncoated 22MnB5 steel.

It is found through experiments that the tailor welding method provided by the present invention does not need to remove the coating before welding. By filling the stainless steel welding wire with high molybdenum content, the weight percentage of Mo is 2.13%, and the tensile strength of the welding wire is 543MPa. After hot stamping, Welded joints with the same strength and toughness as the base metal can be obtained. The welding quality and production efficiency of the product are significantly improved, and the production cost is also reduced.

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

Claims

A laser tailor welding method for aluminum-silicon-coated steel, which is characterized in that: a stainless steel welding wire containing molybdenum is selected as the filler wire; two steel plates with aluminum-silicon coating are used for tailor-welding with a laser beam; and hot stamping is performed after welding;

The weight percentage of Mo in the molybdenum-containing stainless steel wire is 0.5% to 12%, and the tensile strength of the wire is 400 to 1200MPa.
The laser tailor welding method for aluminum-silicon coated steel according to claim 1, wherein the molybdenum-containing stainless steel wire contains Mo in the weight percentage of 1% to 10% by weight, and the wire tensile strength is 450-10% by weight. 1000MPa.
The laser tailor welding method of aluminum-silicon coated steel according to claim 1, wherein the aluminum-silicon coating is composed of a metal alloy layer and an intermetallic compound alloy layer, and 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.
The laser tailor welding method for aluminum-silicon coated steel according to claim 1, characterized in that: in the welding process, a laser beam is used to tailor-weld two steel plates, and a wire feeding nozzle feeds wire to the molten pool at the same time.
The laser tailor welding method for aluminum-silicon coated steel according to claim 4, wherein the diameter of the welding wire is 0.4-2 mm, the wire feeding angle is 20-70°, and the distance between the welding wire and the laser beam is smaller than that of the welding wire Diameter, dry elongation of 2 ~ 30mm.
The laser tailor welding method for aluminum-silicon coated steel according to any one of claims 1-4, wherein the width of the maximum gap between the two steel plates is less than 50% of the diameter of the welding wire.
The laser tailor welding method of aluminum-silicon coated steel according to claim 1, characterized in that: the hot stamping refers to heating the joined two steel plates, and using a water-cooled die or water-cooled quenching.
The laser tailor welding method for aluminum-silicon coated steel according to claim 7, wherein the heating temperature of the hot stamping is 830-1050°C, the holding time is 1-20min, and the cooling rate is greater than or equal to 27°C/ s.