Laser welding method and heat treatment method for hot-formed steel with aluminum-silicon coating on the surface

Abstract

The present invention discloses a laser welding method and a heat treatment method for hot-formed steel with an aluminum-silicon coating on its surface. The specific steps are as follows: a first step, preparing at least two plates to be welded with the aluminum-silicon coating on their surfaces, selecting a solder containing Ni, wherein the minimum weight percentage of Ni contained in the solder is determined by the ratio N of the sum of the thickness of the aluminum-silicon coating on the upper and lower surfaces of the plates to be welded to the thickness of the plates; a second step, butting the edges to be welded of plates A and B; a third step, performing laser welding at the butt joint of plates A and B, filling solder during the laser welding process so that the right edge of plate A, the left edge of plate B and the solder are melted together to form a weld joint; a fourth step, heat treating the welded plates at a heat treatment temperature of 890-960°C to fully austenitize them, and the required heat treatment time TKH is at least 114.5+125.5*(TA+TB)*0.5-903*P(Ni)-S≥163.475 seconds.

Description

Technical Field

[0001] The present invention belongs to the field of welding technology, and in particular relates to a laser welding method and a heat treatment method for hot-formed steel with an aluminum-silicon coating on the surface. Background Art

[0002] With the increasing demand for energy conservation and emission reduction, lightweighting vehicles is an effective means of reducing energy consumption. Against this backdrop, upgraded collision regulations are placing higher demands on the design and use of automotive structural safety components, such as bumpers, anti-collision beams, and B-pillars. Driven by both carbon reduction and safety, the development of ultra-high-strength steel for automotive applications, as the most widely used and highest-strength material in automotive structural safety components, presents new challenges. Hot forming technology leverages the material's excellent hot working properties at high temperatures, employing a forming-first-then-hardening approach to address the trade-off between strength and formability. Currently, hot-formed steels, such as 22MnB5, are the most widely used, boasting tensile strengths exceeding 1500 MPa and elongations of 5% to 7%. As collision regulations become increasingly stringent, parts with a single strength or thickness cannot meet the needs of lightweight and safety. In practical applications, plates of different strengths or thicknesses need to be laser welded together and then hot stamped. In order to protect the plate substrate during the hot stamping process to prevent oxidation or decarburization, a layer of protective material needs to be coated on the upper and lower surfaces of the plate. Aluminum-silicon coating is usually used to protect the plate. Aluminum-silicon coating has a good protective effect on the substrate and does not affect the subsequent coating process. It is the most widely used hot forming protective coating. However, during the laser welding process, the aluminum-silicon coating on its surface dissolves or melts, thereby forming a continuous iron-aluminum phase structure in the weld area of ​​the weld joint. A large amount of brittle phase is generated during the subsequent hot working process, which seriously reduces the strength and plasticity of the weld joint.

[0003] Invention patent: A solder paste and process for improving the plasticity of welded joints of hot-formed steel tailor-welded blanks with aluminum-silicon coatings, patent number CN 111975242 A. The invention involves applying a rare earth solder paste to the welded areas of aluminum-silicon coated plates before welding. However, the amount of solder paste applied is difficult to control, the stability of the welding process is difficult to ensure, and the low application efficiency is not conducive to mass production applications.

[0004] Invention patent: A laser welding method for hot-formed steel with ALSi coating, patent number CN106392328A. The invention involves laser welding of aluminum-silicon coated plates, using protective gas to increase the oxygen partial pressure in the welding area, converting the aluminum in the aluminum-silicon coating into aluminum oxide, and improving the weld strength. However, this method cannot completely convert the aluminum in the aluminum-silicon coating into aluminum oxide, and a large amount of aluminum-silicon coating still melts into the weld joint, making the weld joint strength impossible to guarantee.

[0005] Invention patent: Method for producing pre-coated steel plates and related plates, patent number CN111246962B. The invention content is to laser cut the edge of the aluminum-silicon coated plate, form a corrosion improvement zone on the cut edge by laser cutting, and then weld. The corrosion improvement zone cannot reduce the melting of the aluminum-silicon coating into the weld joint, and the strength of the weld joint cannot be guaranteed.

[0006] In response to the problems existing in the prior art, the low-cost technical solution provided by the present invention is committed to ensuring the mechanical properties of the weld, and can also obtain good weld formation and consistency, thereby realizing the large-scale production of aluminum-silicon coated steel components. Summary of the Invention

[0007] The melting of aluminum in the aluminum-silicon coating will lead to a decrease in the strength of the weld joint, which does not meet production requirements. The only thing that really affects the amount of aluminum melting is the thickness of the aluminum-silicon coating within the coverage area of ​​the weld joint. The inventors found that the coverage area of ​​the weld joint is proportional to the thickness of the welded plate, that is, the thicker the plate, the larger the coverage area of ​​the weld joint. After research, it was found that the width of the single-sided plate covered by the weld joint is approximately 0.5 times the thickness of the single-sided welded plate; so if you want to effectively control the content and distribution of aluminum elements in the weld joint, you need to first confirm the ratio of the aluminum-silicon coating thickness within 0.5 times the plate thickness of the edge of the plate to be welded to the thickness of the plate to be welded, and calculate the aluminum content in the weld joint after welding through this ratio, and select the welding wire with the minimum Ni content required for welding based on the aluminum content.

[0008] During the laser welding process of aluminum-silicon coated plates, the addition of Ni element can effectively inhibit the generation of brittle phases in the weld joint, making the weld joint easier to austenitize during the heat treatment process, thereby improving the strength of the weld joint. However, Ni is an expensive metal, and excessive addition will lead to an increase in production costs. Therefore, the method of the present invention can accurately control the Ni content in the solder, while ensuring the welding strength, reducing the production cost to the greatest extent. At the same time, the addition of Ni element can shorten the austenitization process, thereby reducing the heat treatment time, and then reducing energy consumption, which can further reduce production costs.

[0009] Aluminum has no significant effect on the shape of the isothermal transformation curve of steel. At normal content, it has little effect on the time required for transformation, so the effect of aluminum melting into the weld joint on the austenitization process is not considered. Nickel can accelerate the austenitization process, so the influence of nickel is considered during heat treatment.

[0010] The present invention provides a laser welding method and a heat treatment method for hot-formed steel with an aluminum-silicon coating on the surface. According to the thickness of the coating on the edge of the plate to be welded, a solder containing elements such as Ni is selected to be filled during the welding process. A weld joint with the same tensile strength as the parent material can be obtained. The weld has excellent formation and consistency, and has good corrosion resistance and wear resistance. It can also realize the production of large quantities of structural parts to meet actual production needs.

[0011] The technical solution adopted by the present invention is as follows:

[0012] The laser welding method and heat treatment method of hot-formed steel with an aluminum-silicon coating on the surface of the present invention specifically include the following steps:

[0013] The first step is to prepare at least two plates to be welded, namely plate A and plate B, with aluminum-silicon coatings on their surfaces. A solder containing Ni is selected, wherein the minimum weight percentage of Ni in the solder is determined by the ratio N of the sum of the thickness of the aluminum-silicon coatings on the upper and lower surfaces of the plate to be welded within a range of 0 to 0.5 times the plate thickness to the plate thickness, where N = (T1+T2+T3+T4)*0.5 / (TA+TB)*0.5.

[0014] Where:

[0015] T1 is the thickness of the aluminum-silicon coating on the upper surface of the plate A to be welded within the range of 0 to 0.5 times the plate thickness.

[0016] T2 is the thickness of the aluminum-silicon coating on the lower surface of the plate A to be welded within the range of 0 to 0.5 times the plate thickness.

[0017] T3 is the thickness of the aluminum-silicon coating on the upper surface of the plate B to be welded within the range of 0 to 0.5 times the plate thickness.

[0018] T4 is the thickness of the aluminum-silicon coating on the lower surface of plate B within the range of 0 to 0.5 times the plate thickness.

[0019] TA is the thickness of plate A,

[0020] TB is the thickness of plate B;

[0021] When N≤2%, the minimum weight percentage of Ni in the selected solder is MinNi=2*0.85*N / 2.9;

[0022] When 2<N≤4%, the minimum weight percentage of Ni in the selected solder is MinNi=1.17%+(2*0.85*N / 2.9-1.17%)*2,

[0023] When 2<N≤4% or N>4%, the thickness of the aluminum-silicon coating on at least one surface of the edges to be welded of the sheet A and the sheet B within the range of 0 to 0.5 times the thickness of the sheet is reduced to make N≤2%. The minimum weight percentage of Ni in the selected solder is MinNi=2*0.85*N / 2.9.

[0024] Preferably, the maximum width of the aluminum silicon coating thinning is 0.5*plate thickness+0.15mm, and the minimum width of the aluminum silicon coating thinning is 0.5*plate thickness-0.15mm.

[0025] More preferably, the maximum width of the aluminum-silicon coating thinned is 0.5*plate thickness+0.07mm, and the minimum width of the aluminum-silicon coating thinned is 0.5*plate thickness-0.07mm;

[0026] The second step is to butt joint the edges of the plate A and the plate B to be welded;

[0027] The third step is to perform laser welding on the joint of the sheet A and the sheet B. During the laser welding process, solder is filled so that the right edge of the sheet A and the left edge of the sheet B and the solder are melted together to form a welded joint.

[0028] The fourth step is to heat treat the welded plate to make it completely austenitized, then perform hot stamping and cooling. The heat treatment temperature is 890-960℃, and the required heat treatment time TKH is at least 114.5+125.5*(TA+TB)*0.5-903*P(Ni)-S≥163.475 seconds.

[0029] Among them: P(Ni)-S=P(Ni)-W*P(W / T)+P(Ni)-A*(TA / (TA+TB))*(1-P(W / T))+P(Ni)-B*(TB / (TA+TB))*(1-P(W / T))

[0030] Where:

[0031] P(Ni)-S is the weight percentage of Ni element in the weld joint,

[0032] P(Ni)-W is the weight percentage of Ni element in the solder,

[0033] P(Ni)-A is the weight percentage of Ni element in plate A,

[0034] P(Ni)-B is the weight percentage of Ni element in plate B,

[0035] P(W / T) is the ratio of the weight Q(W) of the solder melted per unit length to the total weight Q(M)+Q(W) of the base material and solder melted per unit length, that is, P(W / T)=Q(W) / (Q(M)+Q(W)).

[0036] After the plate is completely austenitized, it is placed in a mold with cooling water circulation for compaction and then cooled at a rate of 30°C / s or more.

[0037] Preferably, during the welding process, the minimum ratio of the weight Q(W) of the solder melted per unit length to form the weld joint and the weight Q(M) of the base material melted per unit length to form the weld joint is 5:95, and the maximum ratio is 1:1.

[0038] More preferably, during the welding process, the minimum ratio of the weight Q(W) of the solder melted per unit length to form the weld joint and the weight Q(M) of the base material melted per unit length to form the weld joint is 1:9, and the maximum ratio is 2:3.

[0039] Preferably, the thickness of the aluminum-silicon coating is in the range of 6 to 60 microns, and the main components of the aluminum-silicon coating are aluminum, silicon and a small amount of iron, wherein the aluminum content is greater than 80%.

[0040] More preferably, the thickness of the aluminum-silicon coating is in the range of 8 to 45 microns, and the main components of the aluminum-silicon coating are aluminum, silicon and a small amount of iron, wherein the aluminum content is greater than 82%.

[0041] Preferably, the plate has a thickness of 0.75-5 mm.

[0042] More preferably, the plate has a thickness of 1.0-3.5 mm.

[0043] Preferably, the main components of the solder are Ni, C, Mn, Si, Mo, Cr, Fe elements, and other inevitable impurities.

[0044] Preferably, the main components of the solder are Ni, Co, C, Mn, Si, Mo, Cr, Fe elements, and other inevitable impurities.

[0045] Preferably, the weight percentage of Ni in the solder P(Ni)-W ranges from 0.1% to 10%, the weight percentage of Cr in the solder P(Cr)-W ranges from 0.01% to 1.5%, the weight percentages of Mn and Si elements in the solder are respectively greater than or equal to the weight percentages of Mn and Si elements in at least one of the plates to be welded, and the weight percentage of Co in the solder P(Co)-W ranges from 0.001% to 5%.

[0046] More preferably, the weight percentage of Ni in the solder P(Ni)-W ranges from 0.5% to 7.4%, the weight percentage of Cr in the solder P(Cr)-W ranges from 0.02% to 0.49%, the weight percentages of Mn and Si elements in the solder are respectively greater than or equal to the weight percentage of Mn element in at least one of the plates to be welded + 0.1% and the weight percentage of Si element + 0.1%, and the weight percentage of Co in the solder P(Co)-W ranges from 0.001% to 3.5%.

[0047] Preferably, when the solder is a solid welding wire, the tensile strength of the welding wire in the cold stretched state is greater than or equal to 700 MPa; when the solder is a flux-cored welding wire, the elements other than Fe are processed into powder, the iron sheet wraps the powder, and the powder forms a flux core in the middle of the welding wire, and the tensile strength of the flux-cored welding wire in the cold stretched state is greater than or equal to 180 MPa.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] 1. The laser welding method and heat treatment method of a hot-formed steel with an aluminum-silicon coating on the surface of the present invention can prevent the embrittlement of the weld joint and achieve better residual strain at the weld.

[0050] 2. The present invention provides a laser welding method and a heat treatment method for hot-formed steel with an aluminum-silicon coating on the surface. When the ratio N of the sum of the average thickness of the upper and lower surfaces of the plate edges within the range of 0 to 0.5 times the plate thickness to the average thickness of the two plates is less than or equal to 4%, there is no need to pretreat the surface of the aluminum-silicon coating and wire welding can be performed directly, which reduces the manufacturing links, facilitates welding for workers, improves work efficiency, reduces processing difficulty, and reduces welding manufacturing costs.

[0051] 3. The laser welding method and heat treatment method of the present invention for hot-formed steel with an aluminum-silicon coating on the surface have been tested and found that the tensile strength of the welded blank after welding according to the method of the present invention and hot stamping quenching is not lower than the tensile strength of the base material. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0053] Figure 1 This is a schematic diagram of the butt joint of the edges of the plates to be welded having an aluminum-silicon coating on their surfaces according to the present invention.

[0054] Figure 2 This is a schematic diagram of the butt joint of the welding edges of the plates to be welded after the aluminum-silicon coating is thinned according to the present invention.

[0055] Figure 3 It is a schematic cross-sectional view of a welded joint of a plate having an aluminum-silicon coating on its surface according to the present invention.

[0056] Figure 4 This is a schematic diagram of the laser wire-filling welding process of the present invention.

[0057] Figure 5 The present invention is a flowchart of a laser welding method and a heat treatment method for hot-formed steel with an aluminum-silicon coating on the surface.

[0058] Among them, A-plate A, B-plate B, C-aluminum-silicon coating on the upper surface of plate A, D-aluminum-silicon coating on the lower surface of plate A, E-aluminum-silicon coating on the upper surface of plate B, F-aluminum-silicon coating on the lower surface of plate B, G-welding joint, H-welding wire, L-laser, TA-thickness of plate A, TB-thickness of plate B, T1-average thickness of the upper surface coating of plate A within the range of 0~0.5 times the plate thickness of the edge to be welded, T2-average thickness of the lower surface coating of plate A within the range of 0~0.5 times the plate thickness of the edge to be welded, T3-average thickness of the upper surface coating of plate B within the range of 0~0.5 times the plate thickness of the edge to be welded, T4-average thickness of the lower surface coating of plate B within the range of 0~0.5 times the plate thickness of the edge to be welded. Implementation Method

[0059] In order to further understand the present invention, preferred embodiments of the present invention are described below. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0060] The laser welding method and heat treatment method of hot-formed steel with an aluminum-silicon coating on the surface of the present invention specifically include the following steps:

[0061] The first step is to prepare at least two plates to be welded, namely plate A and plate B, with aluminum-silicon coatings on their surfaces. A solder containing Ni is selected, wherein the minimum weight percentage of Ni in the solder is determined by the ratio N of the sum of the thickness of the aluminum-silicon coatings on the upper and lower surfaces of the plate to be welded within a range of 0 to 0.5 times the plate thickness to the plate thickness, where N = (T1+T2+T3+T4)*0.5 / (TA+TB)*0.5.

[0062] Where:

[0063] T1 is the thickness of the aluminum-silicon coating on the upper surface of the plate A to be welded within the range of 0 to 0.5 times the plate thickness.

[0064] T2 is the thickness of the aluminum-silicon coating on the lower surface of the plate A to be welded within the range of 0 to 0.5 times the plate thickness.

[0065] T3 is the thickness of the aluminum-silicon coating on the upper surface of the plate B to be welded within the range of 0 to 0.5 times the plate thickness.

[0066] T4 is the thickness of the aluminum-silicon coating on the lower surface of plate B within the range of 0 to 0.5 times the plate thickness.

[0067] TA is the thickness of plate A,

[0068] TB is the thickness of plate B;

[0069] When N≤2%, the minimum weight percentage of Ni in the selected solder is MinNi=2*0.85*N / 2.9;

[0070] When 2<N≤4%, the minimum weight percentage of Ni in the selected solder is MinNi=1.17%+(2*0.85*N / 2.9-1.17%)*2,

[0071] When 2<N≤4% or N>4%, the thickness of the aluminum-silicon coating on at least one surface of the edges to be welded of the sheet A and the sheet B within the range of 0 to 0.5 times the thickness of the sheet is reduced to make N≤2%. The minimum weight percentage of Ni in the selected solder is MinNi=2*0.85*N / 2.9.

[0072] In the above technical solution, preferably, the maximum width of the aluminum-silicon coating thinned is 0.5*plate thickness+0.15mm, and the minimum width of the aluminum-silicon coating thinned is 0.5*plate thickness-0.15mm.

[0073] More preferably, the maximum width of the aluminum-silicon coating thinned is 0.5*plate thickness+0.07mm, and the minimum width of the aluminum-silicon coating thinned is 0.5*plate thickness-0.07mm;

[0074] In the above technical solution, when N ≤ 2%, in order to reduce the weight percentage of Ni in the solder, the thickness of at least one surface aluminum-silicon coating within the range of 0 to 0.5 times the thickness of the plate to be welded of plate A and plate B can be reduced to make N less than or equal to 2%. The minimum weight percentage of Ni in the selected solder is MinNi = 2*0.85*N / 2.9;

[0075] In the above technical solution, preferably, the maximum width of the aluminum-silicon coating thinned is 0.5*plate thickness+0.15mm, and the minimum width of the aluminum-silicon coating thinned is 0.5*plate thickness-0.15mm.

[0076] More preferably, the maximum width of the aluminum-silicon coating thinned is 0.5*plate thickness+0.07mm, and the minimum width of the aluminum-silicon coating thinned is 0.5*plate thickness-0.07mm;

[0077] In the above technical solution, the method of thinning the aluminum silicon coating includes but is not limited to chemical reaction replacement, laser shock cleaning, milling cutter grinding, grinding wheel grinding, and scraping;

[0078] In the above technical solution, the thickness of the aluminum-silicon coating is measured by metallographic method or X-ray spectroscopy;

[0079] The second step is to butt joint the edges of the plate A and the plate B to be welded;

[0080] The third step is to perform laser welding on the joint of the sheet A and the sheet B. During the laser welding process, solder is filled so that the right edge of the sheet A and the left edge of the sheet B and the solder are melted together to form a welded joint.

[0081] The fourth step is to heat treat the welded plate to make it completely austenitized, then perform hot stamping and cooling. The heat treatment temperature is 890-960℃, and the required heat treatment time TKH is at least 114.5+125.5*(TA+TB)*0.5-903*P(Ni)-S≥163.475 seconds.

[0082] Among them: P(Ni)-S=P(Ni)-W*P(W / T)+P(Ni)-A*(TA / (TA+TB))*(1-P(W / T))+P(Ni)-B*(TB / (TA+TB))*(1-P(W / T))

[0083] Where:

[0084] P(Ni)-S is the weight percentage of Ni element in the weld joint,

[0085] P(Ni)-W is the weight percentage of Ni element in the solder,

[0086] P(Ni)-A is the weight percentage of Ni element in plate A,

[0087] P(Ni)-B is the weight percentage of Ni element in plate B,

[0088] P(W / T) is the ratio of the weight Q(W) of the solder melted per unit length to the total weight Q(M)+Q(W) of the base material and solder melted per unit length, that is, P(W / T)=Q(W) / (Q(M)+Q(W)).

[0089] After the plate is completely austenitized, it is placed in a mold with cooling water circulation for compaction and then cooled at a rate of 30°C / s or more.

[0090] In the above technical solution, it is preferred that during the welding process, the minimum ratio of the weight Q(W) of the solder melted per unit length to form the weld joint and the weight Q(M) of the base material melted per unit length to form the weld joint is 5:95, and the maximum ratio is 1:1.

[0091] More preferably, during the welding process, the minimum ratio of the weight Q(W) of the solder melted per unit length to form the weld joint and the weight Q(M) of the base material melted per unit length to form the weld joint is 1:9, and the maximum ratio is 2:3.

[0092] In the above technical solution, preferably, the thickness of the aluminum-silicon coating ranges from 6 to 60 microns, and the main components of the aluminum-silicon coating are aluminum, silicon and a small amount of iron, wherein the aluminum content is greater than 80%.

[0093] In the above technical solution, it is more preferred that the thickness of the aluminum-silicon coating ranges from 8 to 45 microns, and the main components of the aluminum-silicon coating are aluminum, silicon and a small amount of iron, wherein the aluminum content is greater than 82%.

[0094] In the above technical solution, preferably, the thickness of the plate is 0.75~5mm.

[0095] In the above technical solution, it is more preferred that the thickness of the plate is 1.0~3.5mm.

[0096] In the above technical solution, the main components of the solder are Ni, C, Mn, Si, Mo, Cr, Fe elements, and other inevitable impurities.

[0097] In the above technical solution, the main components of the solder are Ni, Co, C, Mn, Si, Mo, Cr, Fe elements, and other inevitable impurities.

[0098] In the above technical solution, preferably, the weight percentage of Ni in the solder P(Ni)-W ranges from 0.1% to 10%, the weight percentage of Cr in the solder P(Cr)-W ranges from 0.01% to 1.5%, the weight percentages of Mn and Si elements in the solder are respectively greater than or equal to the weight percentages of Mn and Si elements in at least one of the plates to be welded, and the weight percentage of Co in the solder P(Co)-W ranges from 0.001% to 5%.

[0099] In the above technical solution, it is more preferred that the weight percentage of Ni in the solder P(Ni)-W ranges from 0.5% to 7.4%, the weight percentage of Cr in the solder P(Cr)-W ranges from 0.02% to 0.49%, the weight percentages of Mn and Si elements in the solder are respectively greater than or equal to the weight percentage of Mn element in at least one of the plates to be welded + 0.1% and the weight percentage of Si element + 0.1%, and the weight percentage of Co in the solder P(Co)-W ranges from 0.001% to 3.5%.

[0100] In the above technical solution, when the solder is a solid welding wire, the tensile strength of the welding wire in the cold stretched state is greater than or equal to 700 MPa; when the solder is a flux-cored welding wire, the elements other than Fe are processed into powder, the iron sheet wraps the powder, and the powder forms a flux core in the middle of the welding wire. The tensile strength of the flux-cored welding wire in the cold stretched state is greater than or equal to 180 MPa.

[0101] The terms used in the present invention generally have the meanings commonly understood by those skilled in the art, unless otherwise specified. In order to enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to the embodiments.

[0102] In the following examples, various processes and methods not described in detail are conventional methods known in the art. Unless otherwise specified, the materials, devices, instruments, equipment, etc. used in the following examples can be obtained from commercial channels.

[0103] The present invention is further described below with reference to the examples.

[0104] Example 1

[0105] A laser welding method and heat treatment method for hot-formed steel with an aluminum-silicon coating on the surface:

[0106] Select the hot-formed plates A and B to be welded with aluminum-silicon coating on the surface. The size of plate A is 300mm long × 300mm wide × 1.6mm thick, and the size of plate B is 300mm long × 300mm wide × 1.6mm thick. The base material of plates A and B is 22MnB5. The average thickness of the aluminum-silicon coating on the upper and lower surfaces of the edge to be welded within the range of 0 to 0.5 times the plate thickness is 27um and 27um respectively. The average thickness of the aluminum-silicon coating on the upper and lower surfaces of the edge to be welded within the range of 0 to 0.5 times the plate thickness is 26.8um and 26.8um respectively. The edges to be welded of plates A and B are The ratio of the sum of the average thickness of the upper and lower surfaces aluminum-silicon coatings in the range of 0~0.5 times the plate thickness to the average thickness of the two plates is N=(T1+T2+T3+T4)*0.5 / (TA+TB)*0.5=(27+27+26.8+26.8)*0.5 / (1600+1600)*0.5=3.3625%. Because the N value is in the range of 2%~4%, the minimum weight percentage formula of Ni element MinNi=1.17%+(2*0.85*N / 2.9-1.17%)*2 is used to calculate: the minimum weight percentage of Ni element in the required solder is 2.7722%.

[0107] The edges to be welded of plates A and B are butt-jointed, and laser wire welding is performed with a welding power of 5950 W and a welding speed of 5 m / min. The selected solder is a solid welding wire. Calculated by weight percentage, the weight percentage of Ni element in the welding wire is 2.91%, and the weight percentages of other elements are C: 0.1%, Mn: 1.81%, Si: 4.9%, Mo: 0.55%, Cr: 0.24%. The rest are iron and unavoidable impurities. The welding wire diameter is 1.0 mm and the wire feeding speed is 3.8 m / min.

[0108] According to the above welding parameters, the required holding time TKH is calculated as 114.5+125.5*(TA+TB)*0.5-903*P(Ni)-S, which means the minimum heat treatment time is 311.23s. In the above formula, P(Ni)-S=P(Ni)-W*P(W / T)+P(Ni)-A*(TA / (TA+TB))*(1-P(W / T))+P(Ni)-B*(TB / (TA+TB))*(1-P(W / T))=2.91%*15.5%=0.45105%.

[0109] The welded plates were heat treated at 950 degrees Celsius for 312 seconds, and then transferred to a mold with cooling water circulating inside for compaction within 8 seconds (holding and cooling for 15 seconds, with a nominal force of 1000 kN), and cooled at a rate of more than 30 degrees Celsius per second.

[0110] Example 2

[0111] A laser welding method and heat treatment method for hot-formed steel with an aluminum-silicon coating on the surface:

[0112] Select hot-formed plates A and B to be welded with aluminum-silicon coating on their surfaces. The dimensions of plate A are 300 mm long × 300 mm wide × 1.3 mm thick, and the dimensions of plate B are 300 mm long × 300 mm wide × 1.3 mm thick. The base material of plates A and B is 22MnB5. The average thickness of the aluminum-silicon coating on the upper and lower surfaces of plate A within the range of 0 to 0.5 times the plate thickness to be welded are 27 μm and 27 μm respectively. The average thickness of the aluminum-silicon coating on the upper and lower surfaces of plate B within the range of 0 to 0.5 times the plate thickness to be welded are 27 μm and 27 μm respectively. The ratio of the sum of the average thickness of the aluminum-silicon coating on the upper and lower surfaces of plates A and B within the range of 0 to 0.5 times the plate thickness to be welded to the average thickness of the two plates is N= (T1+T2+T3+T4)*0.5 / (TA+TB)*0.5=(27+27+27+27)*0.5 / (1300+1300)*0.5=4.138%. First, the aluminum-silicon coating on the upper and lower surfaces of the edges to be welded of plates A and B within the range of 0~0.5 times the thickness of the plate is thinned by scraping to 12um and 12.2um. The aluminum-silicon coating on the edge to be welded of plate A has a thinning width of 0.5*1.3mm=0.65mm, and the aluminum-silicon coating on the edge to be welded of plate B has a thinning width of 0.5*1.3mm=0.65mm. According to the formula N= It is calculated by (T1+T2+T3+T4)*0.5 / (TA+TB)*0.5 that after thinning the aluminum-silicon coating, N=(12+12.2) / 1300=1.86%. Because the N value after thinning is less than 2%, according to the minimum weight percentage formula of Ni element MinNi=2*0.85*N / 2.9, it is calculated that the minimum weight percentage of Ni element in the required solder is 1.09%.

[0113] The edges to be welded of plates A and B are butt-jointed, and laser wire welding is performed with a welding power of 5950 W and a welding speed of 5 m / min. The selected solder is a solid welding wire. Calculated by weight percentage, the weight percentage of Ni element in the welding wire is 1.2%, and the weight percentages of other elements are C: 0.1%, Mn: 1.81%, Si: 4.9%, Mo: 0.55%, Cr: 0.24%. The rest are iron and unavoidable impurities. The welding wire diameter is 1.0 mm and the wire feeding speed is 3.2 m / min.

[0114] Based on the above welding parameters, the required holding time TKH is calculated as 114.5 + 125.5 * (TA + TB) * 0.5 - 903 * P (Ni) - S = 114.5 + 125.5 * 1.3 - 903 * 0.2748% = 275.17s, that is, the minimum required heat treatment time is 275.17s; in the above formula: P (Ni) - S = P (Ni) - W * P (W / T) + P (Ni) - A * (TA / (TA + TB)) * (1 - P (W / T)) + P (Ni) - B * (TB / (TA + TB)) * (1 - P (W / T)) = 1.2% * 22.9% = 0.2748%.

[0115] The welded plates were heat treated at 950 degrees Celsius for 277 seconds, and then transferred to a mold with cooling water circulating inside for compaction within 8 seconds (holding and cooling for 15 seconds, with a nominal force of 1000 kN), and cooled at a rate of more than 30 degrees Celsius per second.

[0116] Example 3

[0117] A laser welding method and heat treatment method for hot-formed steel with an aluminum-silicon coating on the surface:

[0118] Select hot-formed plates A and B to be welded with aluminum-silicon coating on the surface. The size of plate A is 300mm long × 300mm wide × 1.6mm thick, and the size of plate B is 300mm long × 300mm wide × 1.6mm thick. The base material of plates A and B is 22MnB5. The surface coating of plates A and B is aluminum-silicon coating. The average thickness of the aluminum-silicon coating on the upper and lower surfaces of plate A within the range of 0 to 0.5 times the plate thickness to be welded are 27um and 27um respectively. The average thickness of the aluminum-silicon coating on the upper and lower surfaces of plate B within the range of 0 to 0.5 times the plate thickness to be welded are 26.8um and 26.8um respectively. The ratio of the sum of the average thickness of the aluminum-silicon coating on the upper and lower surfaces of plates A and B within the range of 0 to 0.5 times the plate thickness to be welded to the average thickness of the two plates is N= (T1+T2+T3+T4)*0.5 / (TA+TB)*0.5=(27+27+26.8+26.8)*0.5 / (1600+1600)*0.5=3.3625%. First, the aluminum-silicon coating on the upper and lower surfaces of the welded edges of plates A and B within the range of 0~0.5 times the plate thickness is thinned by scraping. After thinning, the upper and lower aluminum-silicon coatings on the welded edges of plate A within the range of 0~0.5 times the plate thickness are thinned. The average thickness of the aluminum-silicon coating on the surface is 13um and 13um respectively. The average thickness of the aluminum-silicon coating on the upper and lower surfaces of the plate B to be welded within the range of 0 to 0.5 times the plate thickness is 13.1um and 13.1um respectively. The aluminum-silicon coating thinning width of the edge to be welded of plate A is 0.5*1.6mm=0.8mm, and the aluminum-silicon coating thinning width of the edge to be welded of plate B is 0.5*1.6mm=0.8mm. According to the formula N= It is calculated by (T1+T2+T3+T4)*0.5 / (TA+TB)*0.5 that after thinning the aluminum-silicon coating, N=(13+13+13.1+13.1)*0.5 / 1600=1.63125%. Because the N value after thinning is less than 2%, according to the minimum weight percentage formula of Ni element MinNi=2*0.85*N / 2.9, it is calculated that the minimum weight percentage of Ni element in the required solder is 0.95625%.

[0119] The edges to be welded of plates A and B are butt-jointed, and laser wire welding is performed with a welding power of 5950 W and a welding speed of 5 m / min. The selected solder is a solid welding wire. Calculated by weight percentage, the weight percentage of Ni element in the welding wire is 1.2%, and the weight percentages of other elements are C: 0.1%, Mn: 1.81%, Si: 4.9%, Mo: 0.55%, Cr: 0.24%. The rest are iron and unavoidable impurities. The welding wire diameter is 1.0 mm and the wire feeding speed is 3.8 m / min.

[0120] According to the above welding parameters, the required holding time TKH is calculated as 114.5+125.5*(TA+TB)*0.5-903*P(Ni)-S, which means TKH=114.5+125.5*1.6-903*0.186%=313.62, that is, the minimum heat treatment time required is 313.62S; in the above formula: P(Ni)-S=P(Ni)-W*P(W / T)+P(Ni)-A*(TA / (TA+TB))*(1-P(W / T))+P(Ni)-B*(TB / (TA+TB))*(1-P(W / T))=1.2%*15.5%=0.186%.

[0121] The welded plates are heat treated at 950 degrees Celsius for 315 seconds, and then transferred to a mold with cooling water circulating inside for compaction within 8 seconds (holding and cooling for 15 seconds, the nominal force of the press is 1000KN), and cooled at a rate greater than 30°C / s.

[0122] Comparative Example 1

[0123] Select hot-formed plates A and B to be welded with aluminum-silicon coating on the surface. The dimensions of the plates are 300 mm long × 300 mm wide × 1.6 mm thick, and the dimensions of plate B are 300 mm long × 300 mm wide × 1.6 mm thick. The base material of plates A and B is 22MnB5. The coating on the surface of plates A and B is aluminum-silicon coating. The average thickness of the aluminum-silicon coating on the upper and lower surfaces of plate A within the range of 0 to 0.5 times the plate thickness to be welded are 27 μm and 27 μm respectively. The average thickness of the aluminum-silicon coating on the upper and lower surfaces of plate B within the range of 0 to 0.5 times the plate thickness to be welded are 26.8 μm and 26.8 μm respectively. The ratio of the sum of the average thickness of the aluminum-silicon coating on the upper and lower surfaces of plates A and B within the range of 0 to 0.5 times the plate thickness to be welded to the average thickness of the two plates is N= (T1+T2+T3+T4)*0.5 / (TA+TB)*0.5=(27+26.8) / (1600+1600)*0.5=3.3625%. According to the formula for the minimum weight percentage of Ni element, MinNi=1.17%+(2*0.85*N / 2.9-1.17%)*2, it is calculated that the minimum weight percentage of Ni element in the required solder is 2.7722%.

[0124] The edges to be welded of plates A and B are butt-jointed, and laser wire welding is performed with a welding power of 5950 W and a welding speed of 5 m / min. The selected solder is a solid welding wire. Calculated by weight percentage, the weight percentage of Ni element in the welding wire is 1.2%, and the weight percentages of other elements are C: 0.1%, Mn: 1.81%, Si: 4.9%, Mo: 0.55%, Cr: 0.24%. The rest are iron and unavoidable impurities. The welding wire diameter is 1.0 mm and the wire feeding speed is 3.8 m / min.

[0125] According to the above welding parameters, the required holding time TKH is calculated as 114.5+125.5*(TA+TB)*0.5-903*P(Ni)-S, which means the minimum heat treatment time is 313.62s. In the above formula, P(Ni)-S=P(Ni)-W*P(W / T)+P(Ni)-A*(TA / (TA+TB))*(1-P(W / T))+P(Ni)-B*(TB / (TA+TB))*(1-P(W / T))=1.2%*15.5%=0.186%.

[0126] The welded plates are heat treated at 950 degrees Celsius for 315 seconds, and then transferred to a mold with cooling water circulating inside for compaction within 8 seconds (holding and cooling for 15 seconds, the nominal force of the press is 1000KN), and cooled at a rate greater than 30°C / s.

[0127] Comparative Example 2

[0128] Select the hot-formed plates A and B to be welded with aluminum-silicon coating on the surface. The size of plate A is 300mm long × 300mm wide × 1.6mm thick, and the size of plate B is 300mm long × 300mm wide × 1.6mm thick. The base material of plates A and B is 22MnB5. The average thickness of the aluminum-silicon coating on the upper and lower surfaces of the edge to be welded within the range of 0~0.5 times the plate thickness of plate A is 27um and 27um respectively. The average thickness of the aluminum-silicon coating on the upper and lower surfaces of the edge to be welded within the range of 0~0.5 times the plate thickness of plate B is 26.8um and 26.8um respectively. The average thickness of the aluminum-silicon coating on the upper and lower surfaces of the edge to be welded within the range of 0~0.5 times the plate thickness of plate A and plate B is 0~0.5 times the plate thickness. The ratio of the sum of the average thickness of the upper and lower surfaces of the aluminum-silicon coating within the thickness range to the average thickness of the two plates is N=(T1+T2+T3+T4)*0.5 / (TA+TB)*0.5=(27+27+26.8+26.8)*0.5 / (1600+1600)*0.5=3.3625%. Because the N value is in the range of 2%~4%, the minimum weight percentage of Ni element formula MinPercent-wire-Ni=1.17%+(2*0.85*N / 2.9-1.17%)*2 is used to calculate: the minimum weight percentage of Ni element in the required solder is 2.7722%.

[0129] The edges to be welded of plates A and B are butt-jointed, and laser wire welding is performed with a welding power of 5950 W and a welding speed of 5 m / min. The selected solder is a solid welding wire. Calculated by weight percentage, the weight percentage of Ni element in the welding wire is 2.91%, and the weight percentages of other elements are C: 0.1%, Mn: 1.81%, Si: 4.9%, Mo: 0.55%, Cr: 0.24%. The rest are iron and unavoidable impurities. The welding wire diameter is 1.0 mm and the wire feeding speed is 3.8 m / min.

[0130] According to the above welding parameters, the required holding time TKH is calculated as 114.5+125.5*(TA+TB)*0.5-903*P(Ni)-S, which means the minimum heat treatment time is 311.22s. In the above formula, P(Ni)-S=P(Ni)-W*P(W / T)+P(Ni)-A*(TA / (TA+TB))*(1-P(W / T))+P(Ni)-B*(TB / (TA+TB))*(1-P(W / T))=2.91%*15.5%=0.45105%.

[0131] The welded plates are heat treated at 950 degrees Celsius for 240 seconds, and then transferred to a mold with cooling water circulating inside for compaction within 8 seconds (holding and cooling for 15 seconds, the nominal force of the press is 1000KN), and cooled at a rate greater than 30°C / s.

[0132] The performance of the welded joints of Examples 1-3 and Comparative Examples 1-2 was tested. The testing method is as follows: A50 standard dumbbell-shaped specimens were cut according to GB / T228 "Room Temperature Tensile Test Method for Metallic Materials", and the specimens were subjected to tensile testing using a universal tensile machine with a maximum test force of 200kN. First, the mechanical properties of the thermoformed sheet were measured. The tensile strength of the thermoformed sheet was found to be higher than 1400Mpa, and the elongation was greater than or equal to 4%. The mechanical properties of the welded joint were then measured. The welded joint was located in the middle of the specimen being tested, and the direction of the weld was perpendicular to the direction of the tensile force applied in the test. The mechanical test results are shown in Table 1.

[0133] Table 1 Welding tensile test results of the welded parts of Examples 1-3 and Comparative Examples 1-2

[0134] Tensile strength (Mpa) Elongation (%) Fracture location Metallographic structure of welded joint Ratio of coating thickness to substrate thickness (%) Ratio of coating thickness after thinning to substrate thickness (%) Ni weight percentage in welding wire (%) Test results Example 1 ＞1400 ≥4 parent material Martensite 3.3625 — 2.91 qualified Example 2 ＞1400 ≥4 parent material Martensite 4.138 1.86 1.2 qualified Example 3 ＞1400 ≥4 parent material Martensite 3.3625 1.63125 1.2 qualified Comparative Example 1 <1400 ＜4 weld Ferrite, martensite and bainite 3.3625 — 1.2 Unqualified Comparative Example 2 <1400 ＜4 weld Martensite and bainite 3.3625 — 2.91 Unqualified

[0135] As can be seen from Table 1, the tensile strength of the welded joints obtained by the welding methods of Examples 1-3 is higher than 1400 MPa, and the elongation is greater than or equal to 4%, which meets the requirements; the tensile strength of the welded joints obtained by the welding methods of Comparative Examples 1-2 is lower than 1400 MPa, and the elongation is less than 4%, which does not meet the requirements;

[0136] Cause analysis: The welding and heat treatment methods of Examples 1-3 were carried out in full accordance with the methods of the present invention, and the experimental results were qualified; the Ni weight percentage in the welding wire used in Comparative Example 1 was not set according to the minimum Ni content of the present invention, and the heat treatment time in Comparative Example 2 was not set according to the minimum time of the present invention, and the experimental results were unqualified.

[0137] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the embodiments. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all embodiments here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A laser welding method for hot-formed steel with an aluminum-silicon coating on the surface, characterized in that: The specific steps are as follows: The first step is to prepare at least two plates to be welded, namely plate A and plate B, with aluminum-silicon coatings on their surfaces. A Ni-containing solder is selected. The main components of the solder have two combinations: one is Ni, C, Mn, Si, Mo, Cr, Fe, and other inevitable impurities; the other is Ni, Co, C, Mn, Si, Mo, Cr, Fe, and other inevitable impurities. The minimum weight percentage of Ni contained in the solder is determined by the ratio N of the sum of the thickness of the aluminum-silicon coatings on the upper and lower surfaces of the plate to be welded within a range of 0 to 0.5 times the plate thickness to the plate thickness, N = (T1 + T2 + T3 + T4) * 0.5 / (TA + TB) * 0.5, Where: T1 is the thickness of the aluminum-silicon coating on the upper surface of the plate A to be welded within the range of 0 to 0.5 times the plate thickness. T2 is the thickness of the aluminum-silicon coating on the lower surface of the plate A to be welded within the range of 0 to 0.5 times the plate thickness. T3 is the thickness of the aluminum-silicon coating on the upper surface of the plate B to be welded within the range of 0 to 0.5 times the plate thickness. T4 is the thickness of the aluminum-silicon coating on the lower surface of plate B within the range of 0 to 0.5 times the plate thickness. TA is the thickness of plate A, TB is the thickness of plate B; When N≤2%, the minimum weight percentage of Ni in the selected solder is MinNi=2*0.85*N / 2.9; When 2<N≤4%, the minimum weight percentage of Ni in the selected solder is MinNi=1.17%+(2*0.85*N / 2.9-1.17%)*2, When 2<N≤4% or N>4%, the thickness of the aluminum-silicon coating on at least one surface of the edges to be welded of the plates A and B within the range of 0 to 0.5 times the plate thickness is thinned to make N≤2%, the minimum weight percentage of Ni in the selected solder is MinNi=2*0.85*N / 2.9, the maximum width of the aluminum-silicon coating thinned is 0.5*plate thickness+0.15mm, and the minimum width of the aluminum-silicon coating thinned is 0.5*plate thickness-0.15mm; The second step is to butt joint the edges of the plate A and the plate B to be welded; The third step is to perform laser welding on the joint of the sheet A and the sheet B. During the laser welding process, solder is filled so that the right edge of the sheet A and the left edge of the sheet B and the solder are melted together to form a welded joint. The fourth step is to heat treat the welded plate to make it completely austenitized, then perform hot stamping and cooling. The heat treatment temperature is 890-960℃, and the required heat treatment time TKH is at least 114.5+125.5*(TA+TB)*0.5-903*P(Ni)-S≥163.475 seconds. Among them: P(Ni)-S=P(Ni)-W*P(W / T)+P(Ni)-A*(TA / (TA+TB))*(1-P(W / T))+P(Ni)-B*(TB / (TA+TB))*(1-P(W / T)) Where: P(Ni)-S is the weight percentage of Ni element in the weld joint, P(Ni)-W is the weight percentage of Ni element in the solder, P(Ni)-A is the weight percentage of Ni element in plate A, P(Ni)-B is the weight percentage of Ni element in plate B, P(W / T) is the ratio of the weight Q(W) of the solder melted to form the welded joint per unit length to the total weight Q(M)+Q(W) of the base material and solder melted to form the welded joint per unit length, that is, P(W / T)=Q(W) / (Q(M)+Q(W)).

2. The laser welding method for hot-formed steel with an aluminum-silicon coating on the surface according to claim 1, characterized in that: During the welding process, the minimum ratio of the weight Q(W) of the solder melted per unit length to form the weld joint and the weight Q(M) of the base material melted per unit length to form the weld joint is 5:95, and the maximum ratio is 1:

1.

3. The laser welding method for hot-formed steel with an aluminum-silicon coating on the surface according to claim 1, characterized in that: The thickness of the aluminum-silicon coating ranges from 6 to 60 microns. The main components of the aluminum-silicon coating are aluminum, silicon and a small amount of iron, wherein the aluminum content is greater than 80%.

4. The laser welding method for hot-formed steel with an aluminum-silicon coating on the surface according to claim 1, characterized in that: The thickness of the plate is 0.75-5 mm.

5. The laser welding method for hot-formed steel with an aluminum-silicon coating on the surface according to claim 1, characterized in that: The weight percentage of Ni in the solder (P(Ni)-W) is in the range of 0.1% to 10%, the weight percentage of Cr in the solder (P(Cr)-W) is in the range of 0.01% to 1.5%, the weight percentages of Mn and Si elements in the solder are respectively greater than or equal to the weight percentages of Mn and Si elements in at least one of the plates to be welded, and the weight percentage of Co in the solder (P(Co)-W) is in the range of 0.001% to 5%.

6. The laser welding method for hot-formed steel with aluminum-silicon coating on the surface according to claim 1, characterized in that: When the solder is a solid welding wire, the tensile strength of the welding wire in the cold stretched state is greater than or equal to 700 MPa; when the solder is a flux-cored welding wire, the elements other than Fe are processed into powder, the iron sheet wraps the powder, and the powder forms a flux core in the middle of the welding wire. The tensile strength of the flux-cored welding wire in the cold stretched state is greater than or equal to 180 MPa.

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