Solder, and laser welded joint and manufacturing method therefor

Abstract

A solder, and a laser welded joint and a manufacturing method therefor capable of ensuring excellent joint strength and toughness after butt welding and hot-stamping quenching of a steel sheet having an aluminum coating. During formation of the laser welded joint, when two steel sheet base metals are butt-welded by laser welding, a laser welding solder is added to a weld pool to form an initial weld seam, and the initial weld seam is quenched to form the laser welded joint. At least one of the steel sheets is a steel sheet having an aluminum coating or an aluminum alloy coating. The internal lath martensite volume fraction of the laser welded joint is not less than 90%, the average mass fraction of Ni element is not less than 1.6%, the average mass fraction of Al element is not higher than 1.6%, and the average mass fraction of C element is lower than the C content of the steel sheet base metal. A final weld seam positive reinforcement h1 and a final weld seam negative reinforcement h2 formed by the laser welded joint do not exceed 0.4 mm.

Description

A solder, laser welded joint and method of manufacturing the same TECHNICAL FIELD

[0001] The present invention relates to the manufacture of high strength steel plated parts, in particular to a solder, laser welded joint and method of manufacturing the same. BACKGROUND

[0002] In certain fields, particularly in the manufacture of parts for automobiles and aerospace, there is a requirement for high corrosion resistance in the materials used, so more and more materials with a surface coating are being used. Steel with a surface coating of aluminium or aluminium alloy manufactured by cold rolling or hot rolling not only has good corrosion resistance, but also has high high-temperature resistance, which is beneficial to the manufacture of certain parts using hot working methods, so steel plates with a surface coating of aluminium alloy are particularly used in the manufacture of automobile bodies, in parts of the automobile structure, such as door reinforcements, B-pillar structures, roof reinforcements and the like, particularly in the application of hot-stamped parts with ultra-high strength, in order to achieve high corrosion resistance, reduce the weight of the automobile body and improve the energy absorption in a collision.

[0003] At the same time, in the automobile manufacturing industry, in order to reduce the weight of the vehicle and achieve the goal of lightweighting, more and more materials of the same thickness, different thicknesses, the same material and different materials are first welded and then hot-stamped to manufacture the welded parts, so as to achieve better weight reduction and cost reduction. The laser welding method is the preferred method for this approach, with higher quality, higher efficiency and better flexibility, known as "laser tailor-welded blank". Often, the flat workpiece is first laser butt-welded and then hot-stamped and quenched to obtain a high-strength martensitic steel structure. When hot-stamping, the weld structure is first heated to above the AC3 temperature of the steel workpiece to complete austenitization, and due to the high temperature, surface oxidation and decarburization of the bare plate are inevitable, resulting in a decrease in the final structure performance; therefore, a coating layer is also required on the surface, and an aluminium or aluminium alloy coating layer is widely used in this process; the document represented by patent CN101583486B describes such materials in detail.

[0004] However, there are great difficulties in manufacturing laser tailor-welded blanks with aluminum or aluminum alloy coated on the surface. When welding the material with aluminum or aluminum alloy coated on the surface, the coating layer on the original surface will enter the molten zone, especially the molten zone of the weld, which will cause the formation of ferrite structure at high temperature during cooling, even if the cooling is through high temperature austenitization, the ferrite will remain in the final weld to cause the joint performance to decrease. Under the action of subsequent mechanical load, these large amounts of ferrite will become the initial position of failure cracks, which will seriously weaken the load-carrying capacity of the welded joint and directly break in the weld under load. Therefore, it is necessary to inhibit the decrease of joint performance caused by the aluminum entering the weld.

[0005] Patents CN101426612B, 106334875A and the like remove the coating layer on the surface by mechanical method, laser method or other methods in advance to prevent it from entering the weld. However, this method has problems of high cost and complex process.

[0006] Patent CN106392328B discloses a method for welding aluminum-silicon coated hot-formed steel under the condition of protective gas. The patent uses an oxidizing gas to combine with aluminum elements in the coating layer to produce aluminum oxide during welding, which does not affect the toughness of the weld. However, in the welding process, the time for the metal to melt to form a molten pool and then solidify into a weld is very short, and the reaction time of the oxidizing gas with the aluminum elements is limited. Once the aluminum elements that have not reacted with the oxidizing gas enter the molten pool, aluminum accumulation will be generated in the molten pool, which will reduce the toughness and strength of the weld, and there is a risk of cracking of the hot stamping part.

[0007] Patent CN106488824B discloses a method for joining two blanks by filling welding wire, the welding wire is made of stainless steel alloy including the following components by weight percentage: 0%-0.3% of carbon, 0%-1.3% of silicon, 0.5%-7% of manganese, 5%-22% of chromium, 6%-20% of nickel, 0%-0.4% of molybdenum, 0%-0.7% of niobium and the balance of iron and inevitable impurities. In this method, when laser and arc welding are used, the heat input increases, which increases the probability of thermal deformation of the plate and is not conducive to the splicing of thin plates. Moreover, the welding speed of laser and arc welding is limited, which reduces the production efficiency. At the same time, the types of alloy elements added are more, which makes the process control more difficult and the manufacturing cost higher.

[0008] In CN 111432975 A, a welding wire is filled with the following components by weight percentage: 0.03% carbon, 0.5% silicon, 1.8% manganese, 20.5% chromium, 25% nickel, 4.7% molybdenum, less than 0.05% sulfur, less than 0.05% phosphorus, and 1.6% copper. When using this welding wire as a filler material, Cr acts as an austenite stabilizing element, and a high content of Cr can cause the formation of ferrite in the weld zone of the tailor-welded blank after hot stamping, resulting in a decrease in the mechanical properties of the welded joint, which cannot guarantee the quality of the product, and there is a high risk of failure of the welded joint. At the same time, a large number of alloying elements are added, which are complex and have high costs. In CN 112368105 A, a laser welding method is disclosed for laser welding coated steel blanks using a filler wire. The welding wire contains nickel, chromium, and carbon elements, with weight percentages of 1.68-10.48%, 0-2.70%, and 0.91-2.00%, respectively. The high content of carbon in the welding wire can lead to an excessively high carbon content in the tailor-welded zone, reducing plasticity and impact performance, and an excessively high carbon content can cause the weld to be prone to cracking, and can also reduce the corrosion resistance of the weld and the service life of the tailor-welded blank. Moreover, the welding wire has a high content of C element, which makes it difficult to produce and draw during the welding wire production process, and it is prone to work hardening and breakage.

[0009] In CN 108025400 A, a laser welding method is disclosed for a quenchable steel semi-finished plate with an aluminum-based or aluminum-silicon-based coating layer. In this method, the sum of the weight percentages of Cr and Mo is 0.5 to 2.0, and the weight percentage of Ni is 1 to 4. The addition of Mo and Cr can cause the precipitation of carbides in the weld and increase the brittleness of the joint, making the performance unstable.

[0010] In CN 104994989 A, a welding wire is filled with the following components by weight percentage: 0.05-0.15% carbon, 0.5-2.0% silicon, 1.0-2.5% manganese, 0.5-2.0% chromium and molybdenum, 1.0-4.0% nickel, and the balance of iron and unavoidable impurities. The welding wire contains lower chromium and molybdenum elements, and the use of this welding wire as a filler wire results in a welded joint with poor hardenability and corrosion resistance, and cannot completely suppress the influence of ferrite during high-temperature heat treatment, increasing the risk of failure of the welded joint in the weld and heat-affected zone.

[0011] CN104023899B discloses a laser welding method using a filler wire containing carbon or manganese elements to prevent the formation of ferrite structures in the weld at 900-950°C. High content of carbon or manganese can easily cause brittleness, and manganese elements can easily segregate to make the joint performance worse.

[0012] A welding wire for laser welding, a preparation method and a tailor-welded blank process are disclosed in CN 112548395 A. The method fills a welding wire with a higher carbon content, and the carbon content in the welding wire is about 2.5-10 times that of the base material, resulting in an excessively high carbon content in the tailor-welded blank area, reducing plasticity and impact performance, and an excessively high carbon content can cause the weld to crack, also reducing the corrosion resistance of the weld and the service life of the tailor-welded blank.

[0013] A welding method for coated steel sheets is disclosed in US20210008665 A1. The carbon content of the welding wire is 0.80-2.28 times that of the base material, which is too high and can cause the weld to crack and become brittle, also reducing the corrosion resistance of the weld and the service life of the tailor-welded blank, resulting in poor mechanical properties of the welded joint and reducing product quality, which is not suitable for mass production.

[0014] Currently, the welding wire for laser welding of coated steel blanks usually needs to be matched with special laser processes or equipment to improve the quality of steel plate welding. In addition, the added welding wire is mainly composed of multiple alloy elements, including C, Cr, Ni, Mo, Mn, Si, etc. This type of welding wire is difficult to fully guarantee the stable and excellent mechanical properties and corrosion performance of the welded part after welding, and at the same time, due to the addition of multiple alloy elements, work hardening is easy to occur during the drawing forming stage of the welding wire, resulting in low yield of the welding wire and high manufacturing difficulty. At the same time, the complex ratio of multiple alloy elements is difficult to effectively control in the process, which can easily cause the final weld performance to be unqualified. The more expensive Mo element also makes the manufacturing cost higher. Moreover, high content of Mo and Cr elements can easily form coarse carbides inside the weld, causing the weld to become brittle, especially in impact performance. Due to the addition of multiple alloy elements, galvanic corrosion occurs in the weld, and its corrosion performance also deteriorates, so a better method is needed to achieve high-efficiency laser welding of surface-coated sheets and laser welding joints with high strength, high toughness, and high corrosion resistance. SUMMARY

[0015] The present application provides a solder, a high-performance laser welding joint and a manufacturing method. In the present application, a solder composed of Fe-Ni is added to the molten pool during welding to obtain a high-performance laser welding joint without removing the surface aluminum plating. The welding joint obtained after quenching has a volume fraction of lath martensite of not less than 90%, an average mass fraction of Ni of not less than 1.6%, an average mass fraction of Al of not higher than 1.6%, and an average mass fraction of C lower than the C content of the steel plate base material. The front face excess height h1 and the back face excess height h2 of the final weld seam are not more than 0.4 mm, which greatly improves the mechanical properties and stability of the welded part. The present method can greatly reduce the addition of other alloying elements by adding a solder mainly composed of Fe and Ni to the molten pool during welding. In the manufacture of the solder, Fe and Ni can be infinitely solid-solved, which ensures that the solder has excellent plasticity.

[0016] In addition, the saving of other alloying elements also reduces the complexity of the solder ratio and the difficulty of process control in the manufacturing process. The present application mainly adds Fe and Ni elements without additional large amounts of alloying elements, which can reduce the formation of coarse carbides in the final weld seam and thus improve the mechanical properties. At the same time, the addition of high-Ni content solder can ensure the removal of ferrite in the final weld seam and retain more than 90% of the weld seam structure of martensite to ensure the performance of the weld seam. However, in actual welding process, there is often an uncertain assembly gap. When adding a solder with multiple alloying elements, it is often difficult to completely match the solder, and the solder adaptability is poor. At the same time, in the previous method, austenite-forming elements such as Cr and Mo are also added to the welding wire to achieve precipitation strengthening through the formation of carbides. Therefore, the wire feed amount needs to be increased during welding, which on the one hand requires a reduction in welding speed or an increase in wire feed speed, resulting in a higher demand for welding materials and low welding manufacturing efficiency, which increases the overall manufacturing cost. The solder and method of the present application can ensure the formation of a high-reliability and stable weld seam under different assembly gaps, with excellent fracture strength and elongation.

[0017] The following solutions are specifically provided:

[0018] In a first aspect, the present application provides a laser welding joint, wherein when two steel base materials are butted and laser welded, a laser welding filler is added to the molten pool to form an initial weld, and the initial weld is quenched to form the laser welding joint, wherein at least one of the steel plates is an aluminum-coated or aluminum alloy-coated steel plate, the volume fraction of the internal plate strip martensite of the laser welding joint is not less than 90%, the average mass fraction of Ni element is not less than 1.6%, the average mass fraction of Al element is not higher than 1.6%, and the average mass fraction of C element is lower than the C content of the steel base material, and the front face excess height h1 of the final weld formed by the laser welding joint and the back face excess height h2 of the final weld are not more than 0.4 mm,

[0019] The filler is a welding wire, and the welding speed S1 and the wire feeding speed S0 of the welding wire during welding satisfy the following relationship:

[0020] Wherein d is the diameter of the welding wire, d is in the range of 0.6-1.6 mm and more than 2 times the assembly gap width B, B is in the range of 0-0.5 mm, S1 is not less than 3 m / min, B1 is the average width of the upper and lower surfaces of the formed weld, S0 is in the range of 0.5-4.0 m / min, and t is the average thickness of the two steel plates;

[0021] The composition of the filler is as follows: Ni≥10%, the total amount of Fe and Ni≥98%, trace alloying elements 0-0.36%, and the rest is unavoidable impurities; wherein the trace alloying elements are at least one of Nb, V, and Ti elements, and the content of Nb, V, and Ti elements is not more than 0.12%.

[0022] Further, the specific steps of the quenching are as follows: the initial weld is kept at 880-980℃ for 90-500s, and then rapidly cooled by a mold with rapid cooling or a liquid medium, and the cooling speed is≥25℃ / s.

[0023] Further, the rapid cooling mode is flat die stamping cooling, and the front face excess height h1 of the final weld formed by the laser welding joint and the back face excess height h2 of the final weld satisfy Wherein t1 is the thickness of the first steel plate, and t2 is the thickness of the second steel plate.

[0024] Further, the rapid cooling mode is water quenching, and the front face excess height h10 of the initial weld and the back face excess height h11 of the initial weld satisfy Wherein t1 is the thickness of the first steel plate, t2 is the thickness of the second steel plate, B10 is the upper surface width of the initial weld, and B11 is the lower surface width of the initial weld.

[0025] In a second aspect, the present application provides a laser welding filler for forming the laser welding joint as described above, the filler comprising the following components in the following weight percentages: Ni≥10%, the total amount of Fe and Ni≥98%, trace alloying elements 0-0.36%, and the remainder being unavoidable impurities; wherein the trace alloying elements are at least one of Nb, V, and Ti, and the content of each of Nb, V, and Ti is not more than 0.12%.

[0026] Preferably, the total amount of Fe and Ni in the filler is≥99%, and Ni≥20%.

[0027] In a third aspect, the present application provides a method for manufacturing a laser welding joint, the method comprising the following steps:

[0028] Step one: providing two steel plate base materials, at least one of which is a steel plate with an aluminum or aluminum alloy plating layer, and butt joining the two steel plates;

[0029] Step two: laser welding the butt joined combination of the steel plates, wherein a filler as described in the second aspect is added to the molten pool during the welding process to form an initial weld seam;

[0030] Step three: quenching the initial weld seam to obtain the laser welding joint as described in the first aspect;

[0031] During the laser welding process of step two, the molten volume of the two steel plates is V1, and the volume of the filler in the molten pool is V2, V1 and V2 satisfy

[0032] In a fourth aspect, the present application provides a high-strength steel workpiece, which is composed of two steel plate base materials and a laser welding joint between the base materials; when the high-strength steel workpiece is subjected to a tensile test, the fracture failure is in the base material region.

[0033] In a fifth aspect, the present application provides a component comprising the laser welding joint as described above, for use in structural components or safety components of mechanized land motor vehicles. BRIEF DESCRIPTION OF DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor based on these drawings.

[0035] Figure 1 shows a schematic diagram of a typical laser welding joint cross-section of the present application;

[0036] Figure 2 shows a cross-sectional view of the steel plate base material involved in the present application;

[0037] Figure 3 shows a schematic view of the main steps of the laser welding joint manufacturing process involved in the present application;

[0038] Figure 4 shows a schematic view of the steel plates involved in the present application when they are butted;

[0039] Figure 5 shows a schematic view of the laser welding process involved in the present application;

[0040] Figure 6 shows a schematic view from above of the laser welding process involved in the present application;

[0041] Figure 7 shows a cross-sectional view of the initial weld obtained involved in the present application;

[0042] Figure 8 shows another cross-sectional view of the initial weld obtained involved in the present application;

[0043] Figure 9 shows another cross-sectional view of the initial weld obtained involved in the present application;

[0044] Figure 10 shows another cross-sectional view of the initial weld obtained involved in the present application;

[0045] Figure 11 shows a metallographic cross-section of the final weld obtained in one of the embodiments involved in the present application;

[0046] Figure 12 shows the state of the welded joint obtained in the embodiment of Figure 11 after tensile failure;

[0047] Figure 13 shows a metallographic cross-section of the final weld obtained in one of the embodiments involved in the present application;

[0048] Figure 14 shows the state of the welded joint obtained in the embodiment of Figure 13 after tensile failure;

[0049] Figure 15 shows a metallographic cross-section of the final weld obtained in one of the embodiments involved in the present application;

[0050] Figure 16 shows the state of the welded joint obtained in the embodiment of Figure 15 after tensile failure;

[0051] Figure 17 shows a metallographic cross-section of the final weld obtained in one of the embodiments involved in the present application;

[0052] Figure 18 shows the state of the welded joint obtained in the embodiment of Figure 17 after tensile failure. DETAILED DESCRIPTION

[0053] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the present application will be further described below with specific examples. It should be understood that the examples are only used to illustrate the present application but not to limit the scope of the present application. In addition, the drawings are schematic drawings, thus the present application devices and equipment are not limited by the size or proportion of the schematic drawings.

[0054] It should be noted that, in the claims and specification of the present patent, the relationship terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between the entities or operations. Moreover, the terms "include", "contain" or any other variants thereof are intended to cover non-exclusive inclusion, so that the process, method, article or equipment including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such process, method, article or equipment. Without more limitation, the element defined by the statement "including one" does not exclude the presence of another identical element in the process, method, article or equipment including the element. In the present application, the final weld refers to a laser welded joint.

[0055] The present application provides a solder for laser welding of steel plates with aluminum or aluminum alloy plating, the solder having the following components by weight percentage: Ni≥10%, the total amount of Fe and Ni≥98%, and the rest being inevitable impurities. The solder can also contain trace amounts of Nb, V or Ti alloying elements, each of which is generally not more than 0.12%. In a preferred example, the total mass fraction of Fe+Ni is not less than 99%, and the mass fraction of Ni is not less than 20%. In addition to Fe and Ni, other elements are not necessarily present. A higher total content of Fe and Ni can ensure the simplicity of the welding wire manufacturing process, while ensuring the minimum ferrite content of the welded joint to ensure joint performance. The solder can be in various forms such as wire, powder or sheet; for example, solid welding wire or flux-cored welding wire, which is in the form of welding wire with a diameter of 0.8-2.0 mm, preferably 1.0-1.2 mm. Since Fe and Ni can be infinitely solid-solved, the difficulty in wire drawing manufacturing can be reduced, ensuring excellent plasticity, and the welding material with other alloying elements is easier to wire than the welding material with other alloying elements.

[0056] Referring to FIG. 1, a laser welded joint 2 is formed by butt jointing two steel plates (a first steel plate 11 and a second steel plate 12) and laser welding. At least one of the first steel plate 11 and the second steel plate 12 has an aluminum plating layer on one surface. The joint has the following characteristics when viewed along the cross section of the weld: the joint 2 is composed of lath martensite 21 with a volume fraction of not less than 90%, and the included austenite structure 22 is not more than 10%; preferably, the lath martensite is more than 92%; in a preferred example, the martensite content in the weld is not less than 93%, and more extremely, the joint is composed of all lath martensite. In addition, there can be trace amounts of carbides and alloy compounds in the final weld in addition to the lath martensite and austenite. The residual austenite in the weld can have various forms and sizes, and the presence of trace amounts of austenite in the weld can ensure that TRIP effect occurs during the load bearing of the weld to transform the austenite into martensite structure, provide additional plasticity for the weld, and ensure sufficient strength. The average mass fraction of Ni in the joint 2 is not less than 1.6%. The Ni element mainly exists in the form of solid solution in the weld, and can also be in the form of compound with the element Al. The performance of the weld is strengthened by the solid solution and compound of Ni in the weld. The average mass fraction of Al is not more than 1.6%, and the average mass fraction of C is lower than the C content of the steel plate. The weld can also contain elements such as Mn, Si, Cr, and Mo from the steel plate, wherein the average mass fraction of Mn is 0.3-3.0%, preferably 0.5-2.0%, and the average mass fraction of Si is 0.2-1.0%. It is worth mentioning that the weld can also contain trace amounts of Nb, V, and Ti alloy elements for precipitation strengthening and fine-grain strengthening, each of which is generally less than 0.12%, and can be from the steel plate or the welding material, further improving the tensile properties of the joint.

[0057] The steel sheet generally has at least one surface coating layer, such as the first steel sheet 11 shown in FIG. 2 having a first surface coating layer 111 and a second surface coating layer 112. The coating layer is generally composed of aluminum and silicon, wherein the aluminum content is not less than 85%, and preferably the aluminum content is more than 90%. The total thickness of the coating layer is generally 10-50 μm. The coating layer of the steel sheet generally consists of a metal alloy layer and an intermetallic compound alloy layer. The steel sheet base material is generally composed of ferrite and pearlite, wherein the carbon content is not less than 0.1%, and has a boron element content of about 0.002-0.006 to satisfy the hardenability of the subsequent quenching process, so that a full martensite structure is formed after quenching, and has a higher strength, and the typical boron steel tensile strength is not less than 500 MPa. The typical steel sheet base material is 22MnB5, and the elements contained therein have a mass percentage of: 0.15%≤C≤0.45%; 0.5%≤Mn≤2.5%; 0.08%≤Si≤0.4%; Al≤0.45%; 0.01%≤Cr≤0.5%; Ti≤0.1%; Nb≤0.1%; V≤0.1%; S≤0.05%; P≤0.05%; 0.002%≤B≤0.006%; and the rest is Fe and unavoidable impurities. The steel sheet base material involved in the present application is various steel grades of hot stamping forming steel, boron steel, martensitic steel, etc. known in the art, which have different carbon contents or alloy elements, but it is the raw material before quenching (stamping forming), and the thickness is generally 1.0-3.0 mm, which is well known in the art and will not be described here. In addition, the welding joint can be laser welded from the first steel sheet 11 and the second steel sheet 12 with different thicknesses or different coating states, including the strength level which can also have differences, i.e. the combination of different thicknesses or different strengths, such as the tensile strength of the steel sheet base material after hot stamping forming can be more than 2000 MPa.

[0058] The manufacturing method of the laser welding joint 2 mainly includes three steps: steel sheet butt joint, laser welding and quenching treatment, as shown in FIG. 3.

[0059] In step 1, a set of first steel sheets 11 and second steel sheets 12 with aluminum coating layers to be welded are first provided, and then the first steel sheets 11 and the second steel sheets 12 are butt jointed for welding, and the first steel sheets 11 and the second steel sheets 12 can have a gap or no gap. As shown in FIG. 4, the assembly gap width B is generally between 0-0.5 mm.

[0060] In step 2, laser welding is performed on the assembled steel sheets, as shown in FIG. 5. A laser beam 3 and a welding material 4 are provided and delivered to the butt joint position to travel along the welding path at a certain welding speed, and the first steel sheet 11, the second steel sheet 12 and the welding material are melted by the laser beam to form an initial weld 6 on the travel path. During the laser welding process in step 2, the melted volume of the two steel sheets is V1, and the volume of the welding material in the molten pool is V2, and V1 and V2 satisfy The solder 4 is the laser welding solder of the present application. The relative position between the solder and the laser beam can include various types, including coaxial delivery or off-axis delivery, which is well known in the art. Among them, during the execution of the laser welding process, the laser beam is generally emitted by a laser, which can include various types, such as solid-state laser beam or gas laser beam, which can specifically include fiber laser, disc laser, semiconductor diode laser and Nd:YAG type solid-state laser, or CO2 gas laser. Of course, other types can also be included, as long as they can generate a laser beam and generate a keyhole and a molten weld pool. Figure 6 shows a top view schematic diagram during the welding process, the first steel plate 11, the second steel plate 12 and the solder 4 form a molten pool 5 under the action of the laser beam, and the initial weld 6 formed after cooling and solidification. Among them, the laser beam during the welding process can also be composed of one or more light spots, and the beam energy distribution can be in the form of Gaussian distribution, average distribution or point ring distribution, etc. While the laser beam travels along the welding direction during the welding process, it can also be fixed or synchronized with high-speed motion in the form of swing, etc. At this time, the swing shape can include various shapes such as circle, broken line, 8 shape, ∞ shape, etc., the swing frequency is generally 50-500HZ, and the swing amplitude is between 0.2-1.5mm. Various single or mixed protective gases can also be added during the welding process, such as Ar gas, He gas, etc. or under the condition of no protective gas.

[0061] The solder can be added in various forms during the welding process, including powder or wire delivery. When delivered by wire, it is a laser wire filling welding, which is well known in the art, and the wire feeding device can be, for example, MAG (metal active gas), MIG (metal inert gas), TIG (tungsten inert gas) as a substitute for the device for feeding. The welding wire can be solid wire or flux-cored wire. The solder can also be added by combining two different devices, such as by two filler devices, which deliver different solders, one delivers a solder containing a certain composition, and the other delivers another solder containing a certain composition, and the combination of the two solders is used to achieve the desired composition of the solder delivered into the molten pool. In addition, the solder 4 can be added by multiple steps or multiple components; for example, the solder 4 is composed of two independent wires, and the average mass composition of the two solder combinations meets the requirements of the present application; and the two solders can be one with Fe as the main element and the other with Ni as the main element. In addition, the solder can be added in multiple steps, such as front and back, left and right, etc., so that the microstructure of the final welded joint is more than 90% martensite. The combination of multiple wires will be more conducive to the production of welding wires and reduce the difficulty of wire production.

[0062] In the present invention, the control of the different melting amount is realized by matching the laser welding speed and the welding wire feeding speed and controlling the composition of the welding wire. In the present invention, the welding speed and the feeding speed of the welding material are controlled so that the initial weld front face excess height h10 and the initial weld back face excess height h11 are not less than the final weld front face excess height h1 and the final weld back face excess height h2, which can be estimated according to the diameter of the welding material, the welding speed and the feeding speed. Generally, the welding speed S1 is not less than 3 m / min, and when the welding material is a welding wire, the diameter of the welding wire is d, generally 0.8-1.6 mm, more commonly 1.0-1.2 mm, which is generally more than 2 times the assembly gap width B. In the present invention, assuming that the average width of the upper and lower surfaces of the formed weld is B1, the wire feeding speed of the welding wire is S0, and the average thickness of the two steel plates is t, the following conditions need to be met Generally, S0 is 0.5-4.0 m / min; so as to ensure that the initial weld front face excess height h10 and the initial weld back face excess height h11 after welding are not more than 0.4 mm. Generally, the excess height on both sides of the obtained initial weld cross section is a whole dome-shaped morphology with a higher steel plate base surface. The volume of the melted welding material in the whole process is V2, which includes the case of gap or no gap; and the total volume of the melted steel plate base material is V1; 0.02≤V2 / V1≤0.8, more narrowly 0.03≤V2 / V1≤0.5, the whole weld volume is composed of V1 and V2. B1 is generally between 0.5 mm and 4.0 mm, B10 is the initial weld upper surface width, and B11 is the initial weld lower surface width. As shown in FIG. 7, it is a schematic diagram of the cross section of the initial weld obtained after laser welding. The cross section morphology of the formed initial weld can include various types; as shown in FIG. 7, it is a whole X-shaped morphology; it can also be a Y-shaped or U-shaped morphology; as shown in FIGS. 8 and 9, they are schematic diagrams of Y-shaped and U-shaped welds respectively, and the specific morphology can be adjusted by matching the process parameters of the laser welding process. As shown in FIG. 10, it is a schematic diagram when the first steel plate thickness t1 and the second steel plate thickness t2 are different. Generally, the internal organization of the obtained initial weld is mainly martensite and residual austenite, and the martensite content accounts for the majority. Since the addition of the welding material containing Ni into the weld, the complete austenitizing temperature of the initial weld will inevitably be different from that of the base material, so the austenitizing temperature Ac31 of the obtained initial weld joint (weld) is offset from the base material austenitizing temperature Ac30 value by not more than 100°; and the martensite transformation start temperature Ms1 is offset from the base material martensite transformation start temperature Ms0 value by not more than 100°. The Ni content in the weld after hot stamping and quenching is not less than 1.6%, preferably 2.0-15%, and the volume fraction of the residual austenite in the weld is not more than 10%, more narrowly not more than 5%.

[0063] In order to ensure that the initial weld can be fully austenitized at the heating temperature and holding time, the temperature is generally 880-980°C, and the holding time is 90-500s. After holding, rapid cooling is performed, which can be achieved by a die with rapid cooling or a liquid medium, and the cooling speed is generally not less than 25°C / s. When stamping cooling is performed using a die, various shaped parts including a flat plate and parts with a part shape can be formed, i.e., a flat plate die or a shaped die is used. When stamping cooling is performed using a flat plate die, the initial weld surface excess height morphology is flattened under the action of pressure, and the final weld front surface excess height h1 and the final weld back surface excess height h2 are smaller than the initial weld front surface excess height h10 and the initial weld back surface excess height h11. When the surface excess height is approximately equivalent to a rectangular cross section, the following mathematical formula is satisfied: 0.03≤(h1+h2) / (t1+t2)≤0.2. When water quenching is used, the initial weld surface excess height and the final weld excess height do not change much in shape, and the following mathematical formula is also satisfied: The method, solder, and welded joint can be used to manufacture components including hot stamping steel applications, such as various vehicles, for example, various complex rocker panels, door ring parts, and monolithic door rings.

[0064] The technical solutions of the present application will be described in detail below through specific embodiments.

[0065] Example 1

[0066] As shown in FIG. 11, a cross-sectional view of a final weld obtained using the method of the present application is shown. The original material welded is hot formed steel 22MnB5 with a plated layer of aluminum-silicon about 30 μm thick on both the upper and lower surfaces, with a tensile strength of more than 1500 MPa after quenching, and an original C content of 0.23% and a thickness of 1.5 mm. The final weld is generally X-shaped, with a lath martensite content of 97% in the weld, an average mass fraction of Ni of 6.4% in the weld, an average mass fraction of Al of 1.4% in the weld, and a C content in the weld lower than the original C content. The final weld has a width of about 2.0 mm and 2.5 mm on both sides, which is obtained by stamping using a flat plate die during quenching. The final weld front surface excess height h1 and the final weld back surface excess height h2 are about 0.06 mm and 0.12 mm, respectively. The solder added during welding is composed of 35% by mass of Ni, 64% by mass of Fe, and unavoidable impurities, with a total content of Fe and Ni of 99%. The diameter of the welding wire used is 1.2 mm, and the laser wire filling welding method is used to manufacture the tailor-welded blank, with an assembly gap width B of 0 mm, a welding speed S1 of 5.0 m / min, a wire feeding speed S0 of 2 m / min, and an average molten volume V1 of the two steel plates per minute of about 16875 mm 3, the volume V2 of the filler metal melted in the molten pool per minute is about 2262mm 3 , satisfies After welding, the initial weld is placed in a heating furnace, the heating temperature is 930℃, and the holding time is about 300s. Then, the hot stamping is performed under a flat die at a cooling rate of 40℃ / s, and the laser welded joint is obtained.

[0067] Figure 12 shows the mechanical property test results of the obtained laser welded joint after standard tensile specimen preparation. As can be seen from the results: all three samples are broken in the base material area, and the elongation is more than 7%.

[0068] Example 2

[0069] As shown in Figure 13, it is a cross-sectional view of a final weld obtained using the method of the present application. The original material welded is hot-formed steel 22MnB5 with plated layer of about 30μm thickness on the upper and lower surfaces, the strength after quenching is more than 1500Mpa, the original C content is 0.23%, and the thickness is 1.4mm. The final weld is generally Y-shaped, the lath martensite content in the weld is 95.5%, the average mass fraction of Ni element in the weld is 6.0%, the average mass fraction of Al element is 1.3%, and the C element content in the weld is lower than the original C content; the bilateral width of the final weld is about 1.6mm and 1.5mm respectively, which is obtained by stamping with a flat die during quenching; the front face excess height h1 and the back face excess height h2 of the final weld are about 0.1mm and 0.05mm respectively; the filler metal added during welding is composed of 15% mass fraction of Ni element, 83% mass fraction of Fe element, and unavoidable impurities, and the total content of Fe and Ni is 98%. The wire diameter used is 1.2mm, the laser wire filling welding method is used to manufacture the tailor-welded blank, the assembly gap width B is about 0.15mm, the welding speed S1 is 5.0m / min, the wire feeding speed S0 is 3m / min, and the average melting volume V1 of the two steel plates per minute is about 10850mm 3 , the volume V2 of the filler metal melted in the molten pool per minute is about 3393mm 3 , satisfies After welding, the initial weld is placed in a heating furnace, the heating temperature is 930℃, and the holding time is about 300s. Then, the hot stamping is performed under a flat die at a cooling rate of 40℃ / s, and the laser welded joint is obtained.

[0070] Figure 14 shows the mechanical property test results of the obtained laser welded joint. As can be seen from the results: all five samples are broken in the base material area, and the elongation is more than 7%.

[0071] Example 3

[0072] A cross-section of a final weld joint obtained using the method of the present application is shown in Figure 15. The original materials welded are unequal strength hot-formed steel 22MnB5 with plating layers of aluminium-silicon plating on both upper and lower surfaces, with thicknesses of about 30 μm, and strengths after quenching of about 1500 MPa and 2000 MPa respectively, and thicknesses of 1.4 mm. The final weld joint is generally X-shaped, with a lath martensite content of 96% in the weld joint, an average mass fraction of Ni of 5.4% in the weld joint, an average mass fraction of Al of 1.5% in the weld joint, and a C content in the weld joint lower than the original C content. The final weld joint has a width of about 1.8 mm and 1.6 mm on both sides, and is obtained by stamping using a flat die during quenching. The front face excess height h1 and the back face excess height h2 of the final weld joint are about 0.1 mm and 0.08 mm respectively. The filler material used during welding is composed of 15% by mass of Ni, 83% by mass of Fe and unavoidable impurities, with a total content of Fe and Ni of 98%. The welding wire used has a diameter of 1.2 mm, and the welding method used is laser welding with filler wire, with an assembly gap width B of 0.2 mm, a welding speed S1 of 5.0 m / min, a wire feed speed S0 of 2.5 m / min, and an average molten volume V1 of the two steel plates per minute of about 11900 mm 3 , 3 , satisfies After welding, the initial weld joint is placed in a heating furnace at a heating temperature of 930 °C for about 300 s. Subsequently, the laser welded joint is hot-stamped at a cooling rate of 40 °C / s using a flat die and cooled to form a final product.

[0073] The results of the mechanical property test of the laser welded joint after preparation of a standard tensile specimen are shown in Figure 16. As can be seen from the results, all three specimens failed in the lower strength base material region, with an elongation of over 7%.

[0074] Example 4

[0075] A cross-section of a final weld joint obtained by using the method of the present application is shown in Fig. 17. The original materials welded are both equal strength hot formed steel 22MnB5 with plated layer of Al-Si about 20 μm in thickness on both upper and lower surfaces, and quenched strength about 1500 MPa, with original C content of 0.23%, and thickness of 1.4 mm and 1.6 mm respectively. The final weld joint is in a shape of X, and the lath martensite content in the weld joint reaches 94%, the mass fraction of Ni in the weld joint reaches 6.8%, the average mass fraction of Al in the weld joint is 1.5%, and the C content in the weld joint is lower than the original C content. The initial weld joint upper surface width B10 and initial weld joint lower surface width B11 are about 1.4 mm and 1.7 mm respectively, which are obtained by water quenching during quenching; the initial weld joint front face excess height h10 and initial weld joint back face excess height h11 are about 0.2 mm and 0.3 mm respectively; the final weld joint front face excess height h1 and final weld joint back face excess height h2 are about 0.2 mm and 0.3 mm respectively; the filler metal added during welding is composed of 20% mass fraction of Ni element, 78% mass fraction of Fe element, and unavoidable impurities, and the total content of Fe and Ni reaches 98%. The welding wire diameter used is 1.2 mm, and the laser welding method is used to manufacture the tailor-welded blank, the assembly gap width B is 0 mm, the welding speed S1 is 5 m / min, the welding wire feeding speed S0 is 2.8 m / min, and the average melting volume V1 of the two steel plates per minute is about 11625 mm 3 , and the average melting volume V2 of the filler metal in the molten pool per minute is about 3167 mm 3 , meets After welding, the initial weld joint is placed in a heating furnace, the heating temperature is 930 °C, and the holding time is about 300 s. Then the cooling rate is performed at a speed of about 40 °C / s to obtain the laser welded joint by water cooling.

[0076] The mechanical property test results of the laser welded joint obtained are shown in Fig. 18 after standard tensile specimen preparation. It can be seen from the results that all three specimens are broken in the base material region, and the elongation exceeds 7%.

[0077] Example 5

[0078] The welding raw material is hot forming steel 22MnB5 with plated layer of aluminum-silicon with thickness of about 30 μm on the upper and lower surfaces, and the tensile strength after quenching is more than 1500 MPa. The original C content of the steel is 0.23%, and the thickness is 1.5 mm. The final weld is in the shape of X, the content of lath martensite in the weld is 94%, the average content of Ni in the weld is 1.6%, the average content of Al in the weld is 0.9%, and the content of C in the weld is lower than the original C content. The width of the final weld on both sides is about 2.4 mm and 2.5 mm respectively, and the final weld is obtained by stamping with a flat die during quenching. The front face excess height h1 of the final weld and the back face excess height h2 of the final weld are about 0.05 mm and 0.08 mm respectively. The welding material added during welding is composed of 10% of Ni by mass fraction, 88% of Fe by mass fraction and inevitable impurities, and the total content of Fe and Ni is 98%. The diameter of the welding wire used is 1.2 mm, and the laser welding method is used to manufacture the tailor-welded blank. The assembly gap width B is 0 mm, the welding speed S1 is 4.2 m / min, the wire feeding speed S0 is 2 m / min, the average melting volume V1 of the two steel plates per minute is about 15435 mm 3 , and the average melting volume V2 of the welding material in the molten pool per minute is about 2262 mm 3 , meets After welding, the initial weld is placed in a heating furnace, the heating temperature is 930℃, and the holding time is about 300 s. Then the laser welded joint is obtained by hot stamping and cooling forming under a flat die at a cooling rate of 40℃ / s. According to the tensile test results of the joint, all three samples are broken in the base material region, and the elongation is more than 7%.

[0079] Example 6

[0080] The welding raw material is hot forming steel 22MnB5 with plated layer of aluminum-silicon with thickness of about 30 μm on the upper and lower surfaces, and the tensile strength after quenching is more than 1500 MPa. The original C content of the steel is 0.23%, and the thickness is 1.5 mm. The final weld is in the shape of X, the content of lath martensite in the weld is 94%, the average content of Ni in the weld is about 1.8%, the average content of Al in the weld is 0.9%, and the content of C in the weld is lower than the original C content. The width of the final weld on both sides is about 2.4 mm and 2.5 mm, respectively, and the final weld is obtained by stamping using a flat die during quenching. The front face excess height h1 of the final weld and the back face excess height h2 of the final weld are about 0.06 mm and 0.08 mm, respectively. The welding material added during welding is composed of 10% of Ni by mass fraction, 88% of Fe by mass fraction and inevitable impurities, and the total content of Fe and Ni is 98%. The diameter of the welding wire used is 1.2 mm, and the laser welding method is used to manufacture the tailor-welded blank. The assembly gap width B is 0 mm, the welding speed S1 is 4.2 m / min, the wire feeding speed S0 is 2.2 m / min, the average melting volume V1 of the two steel plates per minute is about 15435 mm 3 , and the average melting volume V2 of the welding material in the molten pool per minute is about 2488 mm 3 , meets After welding, the initial weld is placed in a heating furnace, the heating temperature is 930℃, and the holding time is about 300 s. Then, the laser welded joint is obtained by hot stamping and cooling forming under a flat die at a cooling rate of 40℃ / s. According to the tensile test results of the joint, all three samples are broken in the base material region, and the elongation is more than 7%.

[0081] Example 7

[0082] The welding raw material is hot formed steel 22MnB5 with plated layer of aluminum silicon with thickness of about 30 μm on the upper and lower surfaces, and the tensile strength after quenching is more than 1500 MPa, and the original C content is 0.23%, and the thickness is 1.5 mm. The final weld is in the shape of X, the content of lath martensite in the weld is 93%, the average mass fraction of Ni in the weld is about 1.8%, the average mass fraction of Al in the weld is about 1.6%, and the content of C in the weld is lower than the original C content; the final weld has a width of about 1.8 mm and 2.4 mm on both sides, and is obtained by stamping with a flat die during quenching; the front face excess height h1 and the back face excess height h2 of the final weld are about 0.06 mm and 0.08 mm respectively; the welding material added during welding is composed of 15% of Ni element, 83% of Fe element and inevitable impurities, and the total content of Fe and Ni is 98%. The diameter of the welding wire used is 1.2 mm, the laser welding method is used to manufacture the tailor-welded blank, the assembly gap width B is 0 mm, the welding speed S1 is 4.2 m / min, the wire feeding speed S0 is 2.2 m / min, the average melting volume V1 of the two steel plates per minute is about 13230 mm 3 , and the average melting volume V2 of the welding material in the molten pool per minute is about 2262 mm 3 , meet After welding, the initial weld is placed in a heating furnace, the heating temperature is 930℃, and the holding time is about 300 s. Then the laser welded joint is obtained by hot stamping and cooling forming under a flat die at a cooling rate of 40℃ / s. The tensile test results of the joint show that all the three samples are broken in the base material region, and the elongation is more than 7%.

[0083] The welding joint performance and related result data obtained in the above embodiments are listed in Table 1.

[0084] Table 1: Result data of different embodiments

[0085] All the samples of the laser welded joints of Examples 1-7 are broken in the base material region, the breaking strength is greater than 1560 MPa, the elongation is greater than 7.0, and the mechanical properties are very high, which can meet the production and manufacturing of related parts.

[0086] Comparative example

[0087] The welding raw material of the comparative example is the same as that of Example 1, and the welding is performed without filling the wire, and the surface is treated differently. The welding joint of the comparative example is broken in the weld position, and the related mechanical properties are as follows:

[0088] Table 2

Claims

A laser-welded joint, wherein during laser welding of two steel plates, laser welding filler is added to the molten pool to form an initial weld, and the initial weld is quenched to form the laser-welded joint, wherein at least one of the steel plates is a steel plate with an aluminum coating or an aluminum alloy coating, characterized in that... The laser-welded joint has an internal lath martensite volume fraction of not less than 90%, an average Ni element mass fraction of not less than 1.6%, an average Al element mass fraction of not more than 1.6%, and an average C element mass fraction lower than the C content of the steel base material. The final weld reinforcement height h1 on the front side and h2 on the back side of the laser-welded joint do not exceed 0.4 mm. The welding material is welding wire. During the welding process, the welding speed S1 and the wire feeding speed S0 satisfy the following relationship: Where d is the diameter of the welding wire, the value of d ranges from 0.6 to 1.6 mm and exceeds twice the assembly gap width B, the value of B ranges from 0 to 0.5 mm, S1 is not less than 3 m / min, B1 is the average width of the upper and lower surfaces of the formed weld, S0 ranges from 0.5 to 4.0 m / min, and t is the average thickness of the two steel plates; the composition weight percentage of the welding material is: Ni ≥ 10%, the total amount of Fe and Ni ≥ 98%, trace alloying elements 0 to 0.36%, and the remainder are unavoidable impurities; wherein, the trace alloying elements are at least one of Nb, V, and Ti, and the content of Nb, V, and Ti elements does not exceed 0.12%; The specific steps of the quenching are as follows: the initial weld is held at 880-980℃ for 90-500s, and then rapidly cooled by a mold or liquid medium with rapid cooling, with a cooling rate ≥25℃ / s. The rapid cooling method is flat die stamping cooling, and the final weld reinforcement height h1 on the front side and h2 on the back side of the laser welded joint meet the following requirements. Where t1 is the thickness of the first steel plate and t2 is the thickness of the second steel plate; Alternatively, the rapid cooling method may be water quenching, and the initial weld reinforcement height h10 on the front side and h11 on the back side satisfy the following conditions: Where t1 is the thickness of the first steel plate, t2 is the thickness of the second steel plate, B10 is the width of the initial weld upper surface, and B11 is the width of the initial weld lower surface. The laser welding joint as described in claim 1 is characterized in that, The volume fraction of martensite in the lath is not less than 93%. The laser welding joint as described in claim 1 is characterized in that, The laser-welded joint has an average Mn element mass fraction of 0.3-3.0% and an average Si element mass fraction of 0.2-1.0%, and the Mn and Si elements are derived from the steel plate base material. The laser welding joint as described in claim 3 is characterized in that, The average mass fraction of the Mn element is 0.5-2.0%. The laser welding joint as described in claim 1 is characterized in that, The steel plate with aluminum coating or aluminum alloy coating has a coating on at least one side, the coating being composed of aluminum and silicon, wherein the aluminum content is not less than 85%. A laser welding solder for forming a laser welded joint as described in any one of claims 1 to 5, characterized in that, The solder contains ≥99% Fe and ≥20% Ni. The laser welding solder according to claim 6 is characterized in that, The solder is either solid welding wire or flux-cored welding wire. The laser welding solder according to claim 6 is characterized in that, The diameter of the welding wire is 1.0-1.2 mm. A method for manufacturing a laser-welded joint, characterized in that, The method includes the following steps: Step 1: Provide two steel plates as base materials, at least one of which is a steel plate with an aluminum coating or an aluminum alloy coating, and then join the two steel plates together. Step 2: Perform laser welding on the butt joint of the steel plates, during which flux is gradually added into the molten pool to form the initial weld. Step 3: Quenching and cooling the initial weld seam to obtain the laser welded joint as described in any one of claims 1 to 5; In step two, during laser welding, the molten volume of the two steel plates is V1, and the volume of the weld in the molten pool is V2. V1 and V2 satisfy... The solder composition by weight percentage is as follows: Ni ≥ 10%, total Fe and Ni ≥ 98%, trace alloying elements 0-0.36%, and the remainder being unavoidable impurities; wherein the trace alloying elements are at least one of Nb, V, and Ti, and the content of each of Nb, V, and Ti elements does not exceed 0.12%. A high-strength steel workpiece, characterized in that, The high-strength steel workpiece consists of two steel plate base materials and a laser-welded joint as described in any one of claims 1-5 for connecting the base materials; when the high-strength steel workpiece is subjected to tensile testing, the fracture failure occurs in the base material region and the fracture elongation is not less than 5%.

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