A laser welding method for suppressing formation of an aluminum-rich phase in a weld

Abstract

The application discloses a laser welding method for inhibiting formation of aluminum-rich phase in a weld, and belongs to the technical field of metal material processing. Firstly, welding edges of two steel plates are butted and fixed, laser wire filling welding is performed, the excess height on the surface of the weld is removed, and a welded plate is obtained; then the welded plate is kept in a heating furnace at 900-960 DEG C for 3-10 min, and the welded plate is taken out and quenched immediately; after quenching, the steel plate and the weld form martensite structures. The laser wire filling welding method is used to add welding wires into the weld, the composition of the weld metal is optimized, the aluminum-rich phase free weld structure is obtained, the welding wires entering the weld increase the volume and weight of the weld metal, the mass percentage content of the aluminum alloy in the weld metal is further reduced, the generation of the aluminum-rich phase in the weld is weakened, the joint strength after welding of the plated steel plate is greater than the base material strength, after hot forming of the welded joint, the weld is a complete martensite structure, and the weld strength is greater than or equal to 1500 MPa.

Description

TECHNICAL FIELD

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

[0002] Aluminum-silicon plated hot forming steel is widely used in the manufacturing field of automobile safety structural parts, such as automobile door rings, anti-collision beams and the like, due to high strength, high-temperature formability and oxidation resistance. An important problem in the laser tailor-welding process of the steel is that the weld strength is low after laser welding, which cannot meet the joint strength requirement. The reason is that the aluminum-silicon plating layer on the surface of the steel plate enters the weld during laser welding, and an aluminum-rich phase structure is formed in the weld. The aluminum-rich phase structure does not change during the hot forming process of the steel plate, and is still retained in the weld after hot forming, resulting in a decrease in the weld strength and failure to meet the welding requirement.

[0003] In order to improve the low performance of the welded joint, the patent CN108472767B "Method for manufacturing pre-coated metal sheet with removal of coating by inclined laser beam and corresponding metal sheet" realizes laser welding of the plated steel sheet by removing part of the plating layer on the surface of the steel sheet. The patent CN106334875A "Steel welding part with aluminum or aluminum alloy plating layer and manufacturing method thereof" removes the plating layer on the surface of the steel sheet in its entirety, and processes the plating layer into a certain angle, thereby realizing welding of the steel sheet. However, since the thickness of the plating layer on the surface of the steel sheet is only microns, the plating layer removal process is relatively complex and needs to be accurately operated by professional equipment. Therefore, the manufacturing process of the welded part is complex, the operation is difficult, and the welding cost is high. SUMMARY

[0004] In order to solve the technical problem of the decrease in the weld strength caused by the aluminum-rich phase in the weld, the purpose of the present application is to provide a laser welding method for inhibiting formation of aluminum-rich phase in a weld. The present application adds welding wire into the weld through laser wire filling welding, which can inhibit the formation of aluminum-rich phase in the weld metal on the one hand. 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 the harmful element aluminum, dilutes the content of the harmful element aluminum in the weld and weakens the enrichment of the aluminum element in the weld, thereby avoiding the generation of the aluminum-rich phase, realizing that the joint strength after welding of the plated steel sheet is greater than the base material strength, and the weld is completely martensite structure after hot forming of the welded joint.

[0005] The purpose of the present application is achieved in the following way:

[0006] The present application provides a laser welding method for inhibiting formation of aluminum-rich phase in a weld, which comprises the following steps:

[0007] (1) butt joint the welding edges of two steel plates and fix them, laser welding with filler wire, remove the excess height on the surface of the weld, and obtain a welded plate;

[0008] (2) heat the welded plate obtained in step (1) in a heating furnace at 900-960 ℃ for 3-10 min, take out the welded plate and immediately quench it, and martensite structure is formed in the steel plate and the weld after quenching.

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

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

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

[0012] Based on the above technical scheme, further, the laser power of the laser welding with filler wire 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 wire diameter is 0.8-1.2 mm, the wire feeding mode is forward wire feeding, the included angle between the wire and the steel plate to be welded is 30°-60°, and the protective gas is inert gas.

[0013] Based on the above technical scheme, further, the wire feeding speed is ≥0.7*the welding speed, and the purpose of this design is to ensure that sufficient wire enters the weld, to adjust the weld metal composition through the alloy elements in the wire, to increase the weld volume by adding the wire, to dilute the mass fraction of the harmful elements in the weld, and to realize the regulation and control of the weld alloy elements, thereby obtaining a high-quality welded joint.

[0014] Based on the above technical scheme, further, the wire composition and weight percentage in step (1) are as follows: 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 inevitable impurities.

[0015] The design idea of the wire metal composition is as follows:

[0016] C: is an important element to improve the strength of the weld, expand the austenite phase zone of the weld and increase the hardenability of the weld metal, the higher the content of C, the higher the strength of the weld, which is beneficial to improve the strength of the weld and avoid the formation of aluminum-rich phase in the weld; however, too high C content will increase the brittleness and cold cracking sensitivity of the weld, therefore, the content of C in the welding wire is controlled at 0.01% to 0.30%.

[0017] Si, Mn: are elements that can not only improve the strength of the weld but also play a deoxidizing role, the content of Si, Mn in the welding wire enters the weld; the main function is to deoxidize and deslag during steel smelting and improve the welding process of the welding wire, the content of Si in the welding wire of the present application is controlled at 0.1% to 2.6%, and the content of Mn is controlled at 1.0% to 2.0%.

[0018] Cr, Mo: are important elements that can increase the hardenability of the weld, improve the strength of the weld and inhibit the formation of aluminum-rich phase in the weld, the higher the content of the two elements, the more significant the effect of improving the strength of the weld and inhibiting the formation of aluminum-rich phase in the weld, however, the two elements mainly enter the weld through the welding wire, the higher the content of Cr, Mo in the weld, the more the amount of addition in the welding wire, which is not conducive to the production and manufacture of the welding wire, and increases the cost of the welding wire; the content of Cr in the welding wire is less than 2.0%, the effect of inhibiting the formation of aluminum-rich phase in the weld is not significant, and the content of Cr is controlled at Cr: 1.0% to 4.0% and Mo≤5.0% in consideration of the whole.

[0019] Ni: is an element that can form and stabilize austenite, expand the austenite phase zone, inhibit the formation of aluminum-rich phase in the weld and improve the plasticity and toughness of the weld, and can increase the corrosion resistance of the weld; the content of Ni in the welding wire of the present application is 0.3% to 7% in consideration of the whole.

[0020] B: is an important element that can strongly improve the hardenability of steel and inhibit the formation of aluminum-rich phase in the weld, a small amount of B in the weld can significantly inhibit the formation of aluminum-rich phase, and the element has strong hardenability, which can promote the transformation of the weld structure to the martensite zone and form martensite structure.

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

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

[0023] Based on the above technical scheme, further, the welding wire component and the weight percentage are as follows: 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 inevitable impurities.

[0024] Based on the above technical scheme, further, the way of removing the excess height of the weld surface in step (1) includes removing by using a scraper, removing by polishing, and removing by a milling cutter.

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

[0026] Based on the above technical scheme, further, the cooling speed of quenching in step (2) is ≥20℃ / s.

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

[0028] The present application has the following beneficial effects relative to the prior art:

[0029] 1. The present application adopts a laser filler wire welding process, optimizes the weld component, reduces the mass percentage of the adverse alloy in the weld, realizes direct welding of the aluminum-silicon plated hot-formed steel without removing the plating, avoids the formation of aluminum-rich phase organization in the weld, which leads to the decrease of the weld strength, removes the excess height of the weld surface by using a scraper, ensures the weld structure size, and the tensile test of the welded joint after quenching breaks at the base material, and the strength is not less than 1500MPa.

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

[0031] In order to more clearly illustrate the embodiments of the present application, the drawings involved in the embodiments will be briefly introduced below.

[0032] Figure 1 The figure is a schematic diagram of the welding process in the embodiments, wherein 1 is a welded plate, 2 is a welding wire, 3 is a laser, 4 is a scraper, and 5 is a weld. DETAILED DESCRIPTION

[0033] The application will be described in detail below with reference to the embodiments, but the embodiments of the application are not limited thereto. It is obvious that the embodiments described below are only some of the embodiments of the application, and other similar embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the application.

[0034] Example 1

[0035] The surface double-sided aluminized silicon hot forming steel was selected as the tailor-welded steel plate, and the aluminized silicon hot forming steel parameters are shown in Table 1. The welding edges of two hot forming steel plates were butted and fixed by a fixture, the lower surfaces of the two hot forming steel plates were kept on a plane, the steel plate splicing gap is shown in Table 2, and the fiber laser was used for welding, Ar gas was used as the protective gas, the defocusing amount, laser power, welding speed, wire feeding speed and wire diameter are shown in Table 2, the wire feeding mode was front wire feeding, the included angle between the wire and the steel plate to be welded was 45°, the composition of the wire is shown in Table 3, the weld upper and lower surface excess height (the height of the weld surface above the steel plate surface) was about 0.15 mm, and a scraper was arranged at 50 mm behind the weld to remove the weld surface excess height; the welded plate was placed in a heating furnace for a certain period of time, and then taken out and placed in a hot forming die for quenching, after cooling, the welded plate was taken out, the heating conditions and quenching process parameters are shown in Table 4; a uniform excess was formed on the weld and the steel plate surface, and finally a welded part was formed. The strength and fracture position of the weld region of the welded hot forming steel were tested, and the results are shown in Table 5.

[0036] Table 1 Aluminized silicon hot forming steel parameters

[0037]

[0038] Table 2 Parameters of fiber laser welding

[0039]

[0040]

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

[0042]

[0043] Table 4 Heating and quenching process parameters

[0044]

[0045] Table 5 Strength and fracture position of the weld region of the hot forming steel

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

[0047] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application; although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions recorded in the above embodiments can be modified, or some or all of the technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A laser welding method for suppressing formation of an aluminum-rich phase in a weld, characterized by, The method comprises the following steps: (1) abutting and fixing the welding edges of two steel plates, laser welding with filler wire, removing the excess height on the surface of the weld, and obtaining a welded plate; (2) keeping the welded plate obtained in step (1) in a heating furnace at 900-960 ℃ for 3-10 min, taking out the welded plate and immediately quenching, and forming martensite structure in the steel plate and the weld after quenching; In step (1), the laser power of the laser welding with filler wire is 1-10 kW, the defocusing amount is -2-2 mm, the welding speed is 0.01-0.20 m / s, the diameter of the welding wire is 0.8-1.2 mm, the wire feeding mode is forward wire feeding, the included angle between the welding wire and the steel plate to be welded is 30-60°, and the protective gas is inert gas; and the addition wire feeding speed is greater than or equal to 0.7 times the welding speed; In step (1), the composition of the welding wire is as follows in terms of percentage by weight: 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 being Fe and inevitable impurities; In step (1), the gap between the two steel plates is 0-0.4 mm. The method for removing the excess height on the surface of the weld in step (1) comprises removing by using a scraper, removing by grinding, and removing by milling.

2. The laser welding method according to claim 1, characterized in that, The steel sheet of step (1) includes an aluminum plated hot forming steel and an aluminum-silicon plated hot forming steel, and the single-sided plated layer weight is ≤ 90 g / m 2 .

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

4. The laser welding method according to claim 1, characterized by, The height of the surface of the weld after removal is not less than the surface of the steel plate and not greater than 0.2 times the thickness of the steel plate.

5. The laser welding method according to claim 1, characterized by, The weld strength of the welded plate obtained in step (2) is greater than or equal to 1500 MPa.

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