Laser welding method for inhibiting formation of aluminum-rich phase of welding seam

Abstract

The invention discloses a laser welding method for inhibiting formation of a weld joint aluminum-rich phase, and belongs to the technical field of metal material processing. The method comprises the steps that firstly, welding edges of two steel plates are fixed after being in butt joint, laser wire filling welding is conducted, excess weld metal on the surface of a weld joint is removed, a welded plate is obtained, then the welded plate is placed in a heating furnace at the temperature of 900-960 DEG C, heat preservation is conducted for 3-10 min, the welded plate is taken out and quenched immediately, and martensite structures are formed by the quenched steel plates and the weld joint. According to the method, a welding wire is added into a welding seam in a laser wire filling welding mode, components of welding seam metal are optimized, a welding seam structure without an aluminum-rich phase is obtained, meanwhile, the welding wire enters the welding seam, the size and the weight of the welding seam metal are increased, the mass percentage content of aluminum alloy in the welding seam metal is further reduced, and generation of the welding seam aluminum-rich phase is weakened; the strength of a welded joint of the plated steel plate is larger than that of a base metal, a welding seam is of a complete martensitic structure after the welded joint is thermally formed, and the strength of the welding seam is larger than or equal to 1500 MPa.

Description

Technical Field

[0001] The invention belongs to the technical field of metal material processing, and in particular relates to a laser welding method for inhibiting the formation of aluminum-rich phase in a weld. Background Art

[0002] Aluminum-silicon coated hot-formed steel is widely used in the manufacturing of automotive safety structural parts, such as automobile door rings, anti-collision beams, etc., due to its high strength, high temperature formability and oxidation resistance. An important problem with this steel during laser welding is that the weld strength after laser welding is low and cannot meet the joint strength requirements. The reason is that the aluminum-silicon coating on the surface of the steel plate enters the weld during the laser welding process and forms an aluminum-rich phase structure in the weld. The aluminum-rich phase structure does not undergo phase transformation during the hot forming process of the steel plate and remains in the weld after hot forming, causing the weld strength to decrease and unable to meet the welding requirements.

[0003] In order to improve the problem of low performance of welded joints, invention patent CN108472767B "Method for manufacturing pre-coated metal plates with coating removal by tilted laser beam and corresponding metal plates" realizes laser welding of coated steel plates by partially removing the coating on the surface of the steel plate. Invention patent CN106334875A "A steel welding component with aluminum or aluminum alloy coating and its manufacturing method" realizes the welding of steel plates by completely removing the coating on the surface of the steel plate and processing the coating into a certain angle. However, since the thickness of the coating on the surface of the steel plate is only at the micron level, the coating removal process is relatively complicated and requires professional equipment for precise operation. Therefore, the manufacturing process of the welded parts is complicated, the operation is difficult, and the welding cost is high. Summary of the invention

[0004] In order to solve the technical problem that the aluminum-rich phase in the weld leads to a decrease in weld strength, the purpose of the present invention is to provide a laser welding method for inhibiting the formation of aluminum-rich phase in the weld. The present invention adds welding wire to the weld by laser wire welding. On the one hand, the alloy elements in the welding wire can inhibit the formation of aluminum-rich phase in the weld metal. On the other hand, the welding wire enters the weld, increases the volume of the weld metal, optimizes the composition distribution of the weld metal, reduces the enrichment of harmful element aluminum, has a dilution effect on the homogenization of the alloy elements in the weld and the content of harmful element aluminum in the weld, weakens the enrichment of aluminum in the weld, thereby avoiding the generation of aluminum-rich phase, and realizes that the strength of the joint after the coated steel plate is welded is greater than the strength of the parent material. After the weld joint is hot formed, the weld is a complete martensitic structure.

[0005] The object of the present invention is to achieve the following:

[0006] The present invention provides a laser welding method for suppressing the formation of aluminum-rich phase in a weld, comprising the following steps:

[0007] (1) The welding edges of two steel plates are butted and fixed, and laser wire welding is performed to remove the excess height of the weld surface to obtain a welded plate;

[0008] (2) The welded plate obtained in step (1) is kept in a heating furnace at 900-960° C. for 3-10 min, and the welded plate is taken out and immediately quenched, and after quenching, the steel plate and the weld both form a martensitic structure.

[0009] Based on the above technical solution, further, the steel plate in step (1) comprises aluminum-plated hot-formed steel and aluminum-silicon-plated hot-formed steel, and the single-side coating weight is ≤90g / m 2 .

[0010] Based on the above technical solution, further, the lower surfaces of the two steel plates described in step (1) are located on the same plane.

[0011] Based on the above technical solution, further, the splicing gap between the two steel plates described in step (1) is 0 to 0.4 mm.

[0012] Based on the above technical solution, further, the laser power of the laser wire welding described in step (1) is 1 to 10 kW, the defocus amount is -2 to 2 mm, the welding speed is 0.01 to 0.20 m / s, the welding wire diameter is 0.8 to 1.2 mm, the wire feeding method is front wire feeding, the angle between the welding wire and the steel plate to be welded is 30° to 60°, and the shielding gas is an inert gas.

[0013] Based on the above technical solution, further, the welding wire speed is added ≥ 0.7 * welding speed. The purpose of this design is to ensure that there is enough welding wire entering the weld, and the weld metal composition is adjusted by the alloy elements in the welding wire. The addition of welding wire can increase the weld volume and dilute the mass fraction of unfavorable elements in the weld, thereby realizing the regulation of the weld alloy elements and obtaining high-quality welded joints.

[0014] Based on the above technical solution, further, the composition and weight percentage of the welding wire in step (1) are: C: 0.01% to 0.30%, Si: 0.1% to 2.6%, Mn: 1.0% to 2.0%, Cr: 1.0% to 4.0%, Ni: 0.3% to 7%, Mo≤5.0%, B: 0 to 0.005%, Al≤2.0%, Cu: 0.01% to 2.0%, and the remainder is Fe and unavoidable impurities.

[0015] The design ideas of the metal composition of the welding wire of the present invention are as follows:

[0016] C: It is an important element to improve weld strength, expand the austenite phase area of ​​the weld and increase the hardenability of the weld metal. The higher the C content, the higher the strength of the weld, which is beneficial to improve the weld strength and avoid the appearance of aluminum-rich phase in the weld. However, too high C content will increase the brittleness and cold crack sensitivity of the weld, so the C content in the welding wire is controlled at 0.01% to 0.30%.

[0017] Si, Mn: can improve the strength of the weld and also play a role in deoxidation. The content of Si and Mn elements in the steel plate and the Si and Mn in the welding wire enter the weld. Their main functions are steel plate smelting deoxidation, slag removal and improvement of welding processability of the welding wire. The Si content in the welding wire of the present invention is controlled between 0.1% and 2.6%, and the Mn content is controlled between 1.0% and 2.0%.

[0018] Cr and Mo: are important elements that can increase the hardenability of the weld, improve the weld strength and inhibit the appearance of aluminum-rich phase in the weld. The higher the content of the two elements, the more significant the effect of improving the weld strength and inhibiting the aluminum-rich phase in the weld. However, the two elements mainly enter the weld through the welding wire. The higher the Cr and Mo content in the weld, the more the amount added to the welding wire, which is not conducive to the production and manufacturing of the welding wire and increases the cost of the welding wire. When the Cr content in the welding wire is lower than 2.0%, the effect of inhibiting the aluminum-rich phase in the weld is not significant. Taking all factors into consideration, the Cr content is controlled at Cr: 1.0% ~ 4.0%, Mo ≤ 5.0%.

[0019] Ni: An element that forms and stabilizes austenite, can expand the austenite phase region, and is an important element that inhibits the appearance of aluminum-rich phases in welds. When used in combination with elements such as chromium and molybdenum, it can improve weld plasticity and toughness, and can increase the corrosion resistance of the weld. Comprehensively considering the Ni content of the welding wire of the present invention: 0.3% to 7%.

[0020] B: It is an important element that strongly improves the hardenability of steel and inhibits the formation of aluminum-rich phase in the weld. A trace amount of B in the weld can significantly inhibit the formation of aluminum-rich phase. At the same time, this element has strong hardenability and can promote the transformation of the weld structure to the martensitic zone to form a martensitic structure.

[0021] Al: It is an element that promotes the formation of ferrite. Increasing its content will promote the formation of high-temperature ferrite and reduce the performance of the weld. Therefore, the lower the Al content, the better.

[0022] Cu: It forms compounds with Al and Fe in the welding pool, promotes the dispersion of high aluminum phase and avoids agglomeration. Since the alloy phase of Cu is a brittle phase, too high a content of Cu will increase the brittleness of the weld and affect the performance of the weld.

[0023] Based on the above technical solution, further, the welding wire composition and weight percentage are: C: 0.01%~0.30%, Si: 0.1%~2.6%, Mn: 1.0%~2.0%, Cr: 2.0%~4.0%, Ni: 0.3%~5%, Mo≤1.0%, B: 0~0.005%, Al≤2.0%, Cu: 0.01%~2.0%, and the balance is Fe and unavoidable impurities.

[0024] Based on the above technical solution, further, the method of removing the excess height of the weld surface in step (1) includes removing with a scraper, removing by grinding, and removing by a milling cutter.

[0025] Based on the above technical solution, further, the height of the weld surface after removal is not lower than the surface of the steel plate and is not greater than 0.2 times the thickness of the steel plate.

[0026] Based on the above technical solution, further, the cooling rate of quenching in step (2) is ≥20°C / s.

[0027] Based on the above technical solution, further, the weld strength of the welded plate obtained in step (2) is ≥1500MPa.

[0028] The beneficial effects of the present invention compared with the prior art are as follows:

[0029] 1. The present invention adopts a laser wire-filling welding process, optimizes the weld composition, reduces the mass percentage of unfavorable alloys in the weld, and realizes direct welding of aluminum-silicon coated hot-formed steel without removing the coating, avoiding the formation of aluminum-rich phase structure in the weld that leads to a decrease in weld strength. The excess height of the weld surface is removed by a scraper to ensure the weld structure size. After quenching, the fracture position of the weld joint in the tensile test is on the base material, and the strength is not less than 1500MPa.

[0030] 2. The welding process of the present invention is simple, easy to operate, and suitable for mass production applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention, the drawings related to the embodiments are briefly introduced below.

[0032] Figure 1 It is a schematic diagram of the welding process in the embodiment, wherein 1-welding plate, 2-welding wire, 3-laser, 4-scraper, 5-weld seam. DETAILED DESCRIPTION

[0033] The present invention is described in detail below with reference to the embodiments, but the embodiments of the present invention are not limited thereto. Obviously, the embodiments described below are only partial embodiments of the present invention. For those skilled in the art, other similar embodiments obtained without creative labor all fall within the protection scope of the present invention.

[0034] Example 1

[0035] Aluminum-silicon hot-formed steel with double-sided surface coating was selected as the tailored steel plate. The parameters of aluminum-silicon hot-formed steel are shown in Table 1. The welding edges of the two hot-formed steel plates were butt-jointed and fixed with a clamp to keep the lower surfaces of the two hot-formed steel plates on the same plane. The gap between the steel plates is shown in Table 2. Fiber laser welding was adopted, and Ar gas was used as the protective gas. The defocus amount, laser power, welding speed, wire feeding speed and welding wire diameter are shown in Table 2. The wire feeding method adopted was front wire feeding. The angle between the welding wire and the steel plate to be welded was 45°. The composition of the welding wire is shown in Table 3. The upper and lower surface excess height of the weld (the height of the weld surface above the steel plate surface) was about 0.15 mm. A scraper was arranged 50 mm behind the weld to remove the excess height of the weld surface. The welded plate was placed in a heating furnace for insulation for a period of time. After the time was up, it was taken out and placed in a hot forming mold for quenching. After cooling, the welded plate was taken out. The heating conditions and quenching process parameters are shown in Table 4. A uniform transition was formed between the weld and the steel plate surface to finally form a welded part. The strength and fracture position of the weld area of ​​the welded hot-formed steel were tested and the results are shown in Table 5.

[0036] Table 1 Parameters of aluminum-silicon hot-formed steel

[0037]

[0038] Table 2 Parameters of fiber laser welding

[0039]

[0040]

[0041] Table 3 Chemical composition and weight percentage of welds (wt%)

[0042]

[0043] Table 4 Heating and quenching process parameters

[0044]

[0045] Table 5 Strength and fracture location of the weld area of ​​hot-formed steel

[0046] Serial number Strength of weld area (MPa) Fracture location Example 1 1550 On the parent material Example 2 1532 On the parent material Example 3 1512 On the parent material Example 4 1530 On the parent material Example 5 1540 On the parent material

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A laser welding method for suppressing the formation of aluminum-rich phase in welds, It is characterized in that The steps include: (1) The welding edges of two steel plates are butted and fixed, and laser wire welding is performed to remove the excess height of the weld surface to obtain a welded plate; (2) keeping the welded plate obtained in step (1) in a heating furnace at 900-960° C. for 3-10 min, taking out the welded plate and immediately quenching it, wherein the steel plate and the weld both form a martensitic structure after quenching; The laser power of the laser wire-filling welding described in step (1) is 1-10 kW, the defocusing amount is -2-2 mm, the welding speed is 0.01-0.20 m / s, the welding wire diameter is 0.8-1.2 mm, the wire feeding method is front wire feeding, the angle between the welding wire and the steel plate to be welded is 30°-60°, and the shielding gas is an inert gas; the welding wire adding speed is ≥0.7*welding speed; The welding wire composition and weight percentage in step (1) are: C: 0.01%-0.30%, Si: 0.1%-2.6%, Mn: 1.0%-2.0%, Cr: 1.0%-4.0%, Ni: 0.3%-7%, Mo≤5.0%, B: 0-0.005%, Al≤2.0%, Cu: 0.01%-2.0%, and the balance is Fe and unavoidable impurities.

2. The laser welding method according to claim 1, It is characterized in that The steel plate in step (1) comprises aluminum-plated hot-formed steel and aluminum-silicon-plated hot-formed steel, and the weight of the coating on one side is ≤ 90 g / m 2 .

3. The laser welding method according to claim 1, It is characterized in that The lower surfaces of the two steel plates described in step (1) are located on the same plane.

4. The laser welding method according to claim 1, It is characterized in that The splicing gap between the two steel plates described in step (1) is 0 to 0.4 mm.

5. The laser welding method according to claim 1, It is characterized in that Step (1) The method of removing the excess height on the weld surface includes using a scraper to remove, grinding to remove, or milling with a milling cutter to remove.

6. The laser welding method according to claim 5, It is characterized in that The height of the weld surface after removal shall not be lower than the surface of the steel plate and shall not be greater than 0.2 times the thickness of the steel plate.

7. The laser welding method according to claim 1, It is characterized in that The weld strength of the welded plate obtained in step (2) is ≥1500MPa.

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