CN115255715B - Alloy welding wire for laser welding and method for improving weld strength of aluminum-boron-plated steel - Google Patents

Abstract

The invention belongs to the field of laser welding processing, and particularly discloses an alloy welding wire for laser welding and a method for improving the weld strength of aluminum-boron-plated steel; the alloy welding wire for laser welding comprises the following components in percentage by mass: c:0.205 to 0.219 weight percent of Cr:1.26 to 1.34 weight percent of Ni:5.25 to 5.60 weight percent of Mn:3.05 to 3.15 weight percent of Nb:0.10 to 0.12 weight percent of Si:0.10 to 0.15 weight percent, and the balance of Fe; the invention also discloses a method for improving the weld strength of the laser welding aluminum-boron plated steel by utilizing the alloy welding wire, which can eliminate the pain point of the decrease of the weld strength under the condition that an aluminum plating layer is not required to be removed or the thickness of the aluminum plating layer is reduced, and incidentally, the welding defects of pits, undercut and the like caused by the clamping gap error of the steel plate during butt welding are also overcome; the welding seam strength is guaranteed in two aspects, meanwhile, the alloy welding wire can be directly coupled to a laser welding process, the welding process is not increased, the production flow is not changed, the production cost is effectively controlled, and the welding wire is low in cost and easy to process and manufacture.

Description

Alloy welding wire for laser welding and method for improving weld strength of aluminum-boron-plated steel

Technical Field

The invention belongs to the field of laser welding processing, and particularly discloses an alloy welding wire for laser welding and a method for improving the weld strength of aluminum-boron-plated steel.

Background

With the vigorous development of automobile industry in China, the fuel economy and driving safety of automobiles are more and more paid attention to, and for automobile bodies, the improvement of the strength of steel plates is a mainstream design direction of automobile lightweight technology while the thickness of the steel plates is reduced, so that the ultra-high strength boron steel plates with the strength of 1.5GPa are more and more commonly used on front and rear anti-collision beams and A, B, C columns of automobiles.

Laser welding steel sheets has numerous advantages: the thermal deformation is small, the welding seam is attractive in appearance, the welding efficiency is high, the lap welding is not needed, the steel plate consumption is saved, and the lightweight design is facilitated. On the other hand, in order to protect the surface of boron steel from oxidation and decarburization during hot stamping, aluminum (silicon) plating is often used to protect the boron steel. The technological process of the technology is as follows: aluminizing boron steel, laser welding, heating and preserving heat for about 5 minutes in a 930-degree resistance furnace, hot stamping and forming, and air cooling, as shown in figure 1. However, when the mechanical properties of the finished product were tested, it was found that the location of the tensile fracture was at the weld and that the average hardness in this region was much lower than in the heat affected zone and the substrate. Further observation of this region found that: 1) This region has an unevenly distributed aluminum element (Al: 0.1 to 1.5wt% of aluminum plating thickness of about 20 μm); 2) The decarburization is serious; 3) The ferrite phase is more as shown in fig. 2 and 6. It was also found that the regions with severe decarburization and regions with a large ferrite phase have a high content of aluminum elements and exhibit high coincidence, and that boron steel is free of aluminum elements, so that these aluminum elements are necessarily caused by the mixing of the aluminum elements of the coating into the weld joint during welding.

Some attempts have been made to replace the aluminum plate with galvanized sheet, but the melting point of zinc is only 419.5 degrees, and most of the coating is gasified off during laser welding and 930 degrees heating and heat preservation, which does not protect the steel plate. Nickel plating, chromium plating, and copper plating have also been proposed to replace aluminum plating but are not known due to problems such as cost and post-weld segregation.

With the intensive research, it is widely recognized that aluminum plating and aluminum segregation are major contradictions leading to low weld strength, so solutions have been mainly focused on two aspects of < A > removal or reduction of the thickness of the aluminum plating; for example, chinese patent application No. 201911122011.6 discloses a double beam tailor welding method of a hot formed steel sheet with an Al-Si coating. The patent achieves the aim of reducing aluminum segregation by using a double-beam method, and specifically comprises the steps of converting an aluminized layer into an Fe-Al intermetallic compound by using a front beam and then performing splice welding by using a rear beam. The applicant has also carried out similar tests with this method, the main problem being concentrated in two aspects: (1) If the effective scanning width of the front beam is larger than that of the rear beam, part of the area of the substrate is not effectively protected during the subsequent thermoforming treatment, and oxidation and decarburization are easy; if the effective scanning width of the front beam is equal to or less than that of the rear beam, segregation still exists after the rear light speed splice welding, because the segregation position is mainly concentrated near the fusion line; (2) The aluminized steel plate is double-sided aluminized, after the front surface is scanned and welded in a splicing way, the back surface is required to be scanned and welded in a splicing way, and the welding is equivalent to the welding of the back surface for two times, so that efficiency is not high, welding defects such as undercut and pits are aggravated, even if the front surface and the back surface of the steel plate are scanned first, then the welding is performed once, and the instability of product quality is caused by low efficiency and clamping errors caused by clamping of the two steel plates. < B > aluminum segregation in the weld is reduced by the equipment means without removing the aluminized layer. For example, the chinese patent application No. 201910949005.1 discloses a pulse tailor welding method for a hot formed steel sheet with an al—si coating. The patent melts the molten pool by peak power and trough power generated by the pulse laser, thereby eliminating segregation of aluminum element. The peak power of the pulse laser can instantly melt steel but the trough power cannot melt, so that the following molten metal cannot be supplemented with the molten metal, and the defects of air holes, slag inclusion and the like of a welding line can be caused due to the fact that the molten metal is melted and solidified too fast, in addition, the segregation degree of aluminum elements is directly related to the welding speed, the cooling speed is also increased when the welding speed is too fast, the volume of the welding line can be reduced, the aluminum elements mixed into the welding line have no time and space to diffuse, the concentration of the aluminum elements is increased, and the segregation is increased. Pulsed lasers are not generally used in the field of automotive welding, and industrial factories require stable and reliable product quality, and the requirement for lasers is that energy output must have continuous stability, and laser power cannot swing greatly.

In summary, the solutions provided by the prior art mainly focus on how to replace or control aluminum, and these methods cannot completely replace or remove aluminum element in the weld joint, and cannot prevent the decrease of the strength of the weld joint. Because: firstly, the 'aluminum replacement' scheme has the problem of industrial application, and secondly, the aluminized layer and the base material have undergone chemical reaction, and the aluminized layer and the base material are integrated; secondly, the cooling speed of laser welding is too high, aluminum element does not have time to be fully diffused and dissolved, and heat treatment within a few minutes cannot be solved; third, any solution does not completely block the presence of aluminum elements within the weld.

Disclosure of Invention

In order to solve the problems, the invention discloses an alloy welding wire for laser welding and a method for improving the weld strength of aluminum-boron-plated steel.

The technical scheme of the invention is as follows:

an alloy welding wire for laser welding comprises the following components in percentage by mass:

c:0.205 to 0.219 weight percent of Cr:1.26 to 1.34 weight percent of Ni:5.25 to 5.60 weight percent of Mn:3.05 to 3.15 weight percent of Nb:0.10 to 0.12 weight percent of Si:0.10 to 0.15wt percent and the balance of Fe.

Further, the alloy welding wire for laser welding is applied to the field of laser welding processing in the automobile industry.

Further, in the above application, the alloy welding wire is used for improving the weld strength of aluminum-boron-plated steel during laser welding.

Further, in the above application, the type of the aluminized boron steel is 20MnTiB.

Further, in the above-mentioned application, the aluminized layer thickness of the aluminized boron steel is 20 to 25 μm.

Further, a method for improving the weld strength of aluminum-boron-plated steel by using a laser welding wire, which uses the laser welding alloy welding wire, comprises the following steps:

1) Selecting a 20MnTiB series aluminum-boron-plated steel plate with the workpiece thickness of 1.0-1.4mm and the plating layer thickness of 20-25 mu m;

2) Fixing the steel plate on a clamp, and butt-jointing and clamping the steel plate;

3) YAG or fiber laser with the diameter of the light spot of 0.6-0.7mm, the power of 3000-3500W, the welding speed of 1.0-1.7m/min, the flow rate of argon protection of 15-20L/min, and the inclination angle of the laser of 5 degrees;

4) Selecting an alloy welding wire with the diameter of 0.5-0.6mm, the wire feeding speed of 0.7-1.2m/min, the wire feeding angle of 35-40 ℃ and the optical wire distance of 0mm;

5) And (3) planning a welding path, welding, directly placing the steel plate into a resistance furnace at 930+/-10 ℃ after welding, heating for 5-7 minutes, and hot stamping in air after discharging.

The chinese patent application No. 201380001259.1 discloses a tailor welded blank, a method of manufacturing the same, and a hot stamped component using the same. From the information provided in this patent, it is known that: 1) The content provided by the patent uses a laser filler wire welding technology to solve the problem that aluminum elements in a welding line of aluminum-boron-plated steel are increased in the welding process; 2) The design idea of the alloy welding wire provided by the patent is to reduce ferrite stabilizing elements in the welding line through austenite stabilizing elements; 3) The content of carbon and manganese elements in the welding wire is higher than that in the base material.

The filler wire component provided by the patent content and the alloy wire component provided by the invention have essential differences in element selection, design thought and microstructure: first, elemental carbon and elemental manganese are inherent elements that must be present for all steels and iron-based welding materials. Secondly, the carbon component and the manganese element of the alloy welding wire are respectively higher than the corresponding elements of the base material by 0.1 to 0.8 weight percent and 1.5 to 7.0 weight percent, and the elements provided by the invention not only comprise carbon and manganese elements but also comprise nickel, chromium, niobium and silicon elements. The components provided in this patent are mainly for suppressing the formation of ferrite elements, and the present invention is to add ferrite elements such as chromium, niobium, silicon, etc., and the content of carbon elements provided in the present invention is not within the range of the patent. Again, the invention has been specifically described as "a component system that does not generate a ferrite structure in a temperature range from 800 ℃ to 950 ℃; the filler wire has a greater number of austenite stabilizing elements "this design concept is the same as the prior art approach of" aluminum control "using laser equipment or process methods, because aluminum is a ferrite stabilizing element. The design concept of the invention is to improve the toughness of the lifting weld by carbon fixation and proper ferrite phase introduction. The alloy system provided by the invention is composed of an austenite forming element, ferrite forming element and carbide forming element ternary alloy system. This is one of the most fundamental distinguishing features from this patent. Finally, the alloy component provided by the invention cannot solve the problem of the decrease of the welding seam strength of the boron steel, and the reason is:

1) As described above, the carbon element and manganese element contents provided by the invention are very high, which can lower the martensite transformation temperature to cause the existence of a large amount of residual austenite phase, the hardness of the austenite phase is lower, which can directly cause the decrease of the strength of the welding seam, and the CCT curve simulation is carried out according to the embodiment provided by the invention, so that the hardness in the welding seam is only 317Hv, and the residual austenite content is as high as 72.6v%, as shown in figure 8. Therefore, this patent aims to suppress ferrite phase instead of solving the actual engineering problem, and the design concept of the alloy is seriously against the basic principle of material transformation, resulting in deterioration of the weld structure, because if the martensite transformation temperature is too low, the transformation reaction between the retained austenite phase and the martensite phase occurs directly in the room temperature environment, which causes rebound phenomenon of the hot stamping formed automobile parts, and more seriously, the unsafe factor for engineering materials increases, which is absolutely strictly prohibited by any industry.

2) In general, boron steels used in the automotive industry have aluminum plating thicknesses of between 20 and 30 μm, and applicant found in experiments that if the plating thickness is not less than 27 μm and the welding speed is higher than 3m/min, the aluminum segregation in the weld joint increases exponentially up to 5.1wt%, even when the welding wire composition of 0.8wt% carbon+7.0 wt% manganese provided by the patent is used in combination and heat treatment is performed at 950 degrees or less, the weld joint still has the formation of a large amount of ferrite phase (about 47v% or less), which is contrary to the original design of alloy composition provided by the patent, and the formation of a large amount of brittle phase further deteriorates the microstructure of the weld joint, as shown in fig. 9. No limitation is disclosed in the content provided by this patent, which means that the information provided by this patent document is not generic and violates the basic requirement of the patent laws that "implementation" be "by one of ordinary skill in the art.

3) In the automobile industry, medium-low carbon hypoeutectoid steel with carbon content below 0.45wt% is generally selected for preventing the alloy structural steel material from cracking in the welding or heat treatment process. The carbon content disclosed in the patent is up to 0.8wt%, which belongs to the field of hypereutectoid steel, and the cracking phenomenon is easy to occur in actual welding, so that the brittleness of a welding seam is very high in automobile body application, and safety accidents are easy to occur. This is in contrast to the "component system that does not generate a ferrite structure upon heat treatment" in the content provided by the present invention; and have a much larger number of austenite stabilizing elements "design considerations". Only the design thought of carbon fixation can balance the contradiction between high strength and no cracking. This is also one of the biggest distinguishing features between the technology provided by this patent and the prior art.

In summary, the solutions provided by the prior art mainly focus on how to replace or control aluminum, and these methods cannot completely replace or remove aluminum element in the weld joint, and cannot prevent the decrease of the strength of the weld joint. Because: firstly, the 'aluminum replacement' scheme has the problem of industrial application, and secondly, the aluminized layer and the base material have undergone chemical reaction, and the aluminized layer and the base material are integrated; secondly, the cooling speed of laser welding is too high, aluminum element does not have time to be fully diffused and dissolved, and heat treatment within a few minutes cannot be solved; third, any solution does not completely block the presence of aluminum elements within the weld. The invention is different from the prior art, the focus of solving the problem is focused on alloying, in particular to focusing on how to construct an alloy system to form solid solution of more carbon elements, and then the high strengthening effect of the carbon elements is utilized to promote the generation of proper high-hardness strengthening tissues in the welding seam, so that the strength of the welding seam can be improved only.

The invention has the following beneficial effects:

1. the method for improving the weld strength of the laser welding aluminum-boron-plated steel by using the alloy welding wire can eliminate the pain point of the decrease of the weld strength under the condition that an aluminum plating layer is not required to be removed or the thickness of the aluminum plating layer is reduced. Incidentally, the welding defects of pits, undercuts and the like caused by the clamping gap errors of the steel plates during butt welding are overcome. The weld strength is ensured in two aspects. Compared with the technologies of zinc plating, chromium plating, nickel plating and copper plating, the method has the beneficial effect of saving cost.

2. According to the method for improving the weld strength of the laser welding aluminum-boron steel by using the alloy welding wire, the alloy welding wire can be directly coupled to the laser welding process, the welding process is not increased, the production flow is not changed, and the production cost is effectively controlled. And the welding wire has low cost and is easy to process and manufacture.

Drawings

FIG. 1 is a schematic illustration of a laser filler wire welding and hot stamping process;

FIG. 2 is a binary phase diagram of a weld according to the composition of the weld when the aluminum element segregation is 1.5wt% and no filler wire is present, using the prior art;

FIG. 3 is a binary phase diagram according to the composition of a weld joint when the segregation amount of aluminum element is 1.5wt% and the dilution ratio of the welding wire is 0% by using the method provided by the invention;

FIG. 4 is a binary phase diagram according to the composition of a weld joint when the segregation amount of aluminum element is 1.5wt% and the dilution ratio of the welding wire is 50% by using the method provided by the invention;

FIG. 5 is a CCT curve made according to the composition of a weld joint when the amount of segregation of aluminum element is 1.5wt% and the dilution rate of a welding wire is 50% using the method provided by the present invention;

FIG. 6 is a graphical representation of microhardness profiles and representative values of a cross section of a welded joint measured using the prior art;

FIG. 7 is a graphical representation of measured hardness profiles of cross sections of welded joints and representative values using the method provided by the present invention;

FIG. 8 is a graph of CCT made according to an example provided by patent application number 201380001259.1;

fig. 9 is a binary phase diagram made in accordance with the example provided by patent application No. 201380001259.1.

Detailed Description

The following description of the embodiments of the present invention will be made clearly and completely, and it is apparent that the described embodiments are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

The reagents or instruments used in the examples of the present invention were not manufacturer-identified and were conventional reagent products commercially available.

In the present invention, the element selection and the element content selection of the alloy wire for laser welding are shown in the following table 1.

Table 1 principle of selecting element and element content

In order to improve the strength of the welding seam and reduce the aluminum segregation amount in the welding seam and the dilution rate of the welding wire to the maximum extent, the following steps are defined: the thickness of the aluminized layer is 20-25 mu m, the welding speed is 1.0-1.7m/min, and the laser power is 3000-3500W. Wherein, the boron steel grade selected by the invention is 20MnTiB alloy structural steel commonly used, and the chemical components and mechanical properties measured are shown in Table 2. At this time, the relationship among the dilution ratio of the welding wire in the weld, the aluminum segregation amount range, and the material properties was determined from the phase transition simulation calculations shown in fig. 2 to 5 and the metallographic and mechanical property indexes actually measured in fig. 6 to 7, as shown in table 3.

TABLE 2 chemical composition and mechanical Property Table

TABLE 3 relationship between dilution ratio of welding wire in weld, aluminum segregation range, and material properties

Example 1

A method for improving weld strength of aluminized boron steel by using a laser welding wire comprises the following components in percentage by weight:

C：0.205wt％；

Cr：1.26wt％；

Ni：5.25wt％；

Mn：3.05wt％；

Nb：0.10wt％；

Si：0.10wt％；

fe is the balance.

The preparation method of the welding wire can use the existing mature method, which comprises the steps of electric furnace smelting, cogging, continuous casting and continuous rolling into a coil element, drawing, copper plating and winding to form the welding wire for laser welding, and the specific reference is made to the 'welding wire selection guideline'; chemical industry Press 2011.5.

A method for improving the weld strength of aluminized boron steel by using a laser welding wire comprises the following steps:

1) Selecting a 20MnTiB series aluminum-boron-plated steel plate with the workpiece thickness of 1.0mm and the plating layer thickness of 20 mu m;

2) Fixing the steel plate on a clamp, and butt-jointing and clamping the steel plate;

3) YAG or fiber laser with the light spot diameter of 0.6mm, the power of 3500 watts, the welding speed of 1.0m/min, the flow rate of argon protection of 15L/min, and the inclination angle of the laser of 5 degrees;

4) Selecting an alloy welding wire with the diameter of 0.5mm, the wire feeding speed of 0.7m/min, the wire feeding angle of 35 degrees and the optical wire distance of 0mm;

5) And (3) planning a welding path, welding, directly placing the steel plate into a resistance furnace at 930+/-10 ℃ after welding, heating for 5 minutes, and hot stamping in air after discharging.

Example 2

A method for improving weld strength of aluminized boron steel by using a laser welding wire comprises the following components in percentage by weight:

C：0.219wt％；

Cr：1.34wt％；

Ni：5.60wt％；

Mn：3.15wt％；

Nb：0.12wt％；

Si：0.15wt％；

fe is the balance.

The preparation method of the welding wire can use the existing mature method, which comprises the steps of electric furnace smelting, cogging, continuous casting and continuous rolling into a coil element, drawing, copper plating and winding to form the welding wire for laser welding, and the specific reference is made to the 'welding wire selection guideline'; chemical industry Press 2011.5.

A method for improving the weld strength of aluminized boron steel by using a laser welding wire comprises the following steps:

1) The 20MnTiB series aluminum boron steel plate with the workpiece thickness of 1.4mm and the plating layer thickness of 25 μm is selected.

2) Fixing the steel plate on a clamp, and butt-jointing and clamping the steel plate;

3) YAG or fiber laser with 0.7mm of spot diameter, 3500 watts of power, 1.7m/min of welding speed, 20L/min of argon protection flow rate and 5 degrees of inclination angle of the laser;

4) Selecting an alloy welding wire with the diameter of 0.6mm, the wire feeding speed of 1.2m/min, the wire feeding angle of 40 degrees and the optical wire distance of 0mm;

5) And (3) planning a welding path, welding, directly placing the steel plate into a resistance furnace at 930+/-10 ℃ after welding, heating for 7 minutes, and hot stamping in air after discharging.

Example 3

A method for improving weld strength of aluminized boron steel by using a laser welding wire comprises the following components in percentage by weight:

C：0.212wt％；

Cr：1.30wt％；

Ni：5.42wt％；

Mn：3.10wt％；

Nb：0.11wt％；

Si：0.12wt％；

fe is the balance.

The preparation method of the welding wire can use the existing mature method, which comprises the steps of electric furnace smelting, cogging, continuous casting and continuous rolling into a coil element, drawing, copper plating and winding to form the welding wire for laser welding, and the specific reference is made to the 'welding wire selection guideline'; chemical industry Press 2011.5.

A method for improving the weld strength of aluminized boron steel by using a laser welding wire comprises the following steps:

1) A20 MnTiB series aluminized boron steel plate with the workpiece thickness of 1.2mm and the plating layer thickness of 22 mu m is selected.

2) Fixing the steel plate on a clamp, and butt-jointing and clamping the steel plate;

3) YAG or fiber laser with 0.7mm light spot diameter, 3200W power, welding speed of 1.4m/min, argon protection flow rate of 17L/min, and inclination angle of the laser of 5 degrees;

4) Selecting an alloy welding wire with the diameter of 0.6mm, the wire feeding speed of 0.9m/min, the wire feeding angle of 37 degrees and the optical wire distance of 0mm;

5) And (3) planning a welding path, welding, directly placing the steel plate into a resistance furnace at 930+/-10 ℃ after welding, heating for 6 minutes, and hot stamping in air after discharging.

Summarizing:

the invention is based on the principle of material alloying design, the purpose of improving the strength of a welding line is achieved by a method of filling a welding line with laser, and the background technology of the invention is that three alloys of a base material, a welding line and an aluminized layer coexist in the welding line respectively, and the problem of the dilution rate after welding exists for the welding line; the aluminum plating layer has a segregation problem caused by uneven distribution of aluminum element. Therefore, in order to solve the problem of the decrease of the welding strength by using the alloy welding wire, the first step is to find out the dilution rate and the segregation range value under a certain precondition. In other words, if the dilution ratio of the welding wire is above 60%, and the maximum segregation amount of aluminum element in the welding seam after heat treatment is above 5.1wt%, the alloy welding wire provided by the invention cannot solve the technical problems of the invention. For specific information, refer to table 3.

The applicant found on the basis of experiments that: when the laser power is 3000-3500W, the welding speed is 1.0-1.7m/min, the thickness of the aluminum layer is 20-25 mu m, and the heat treatment method is according to the heat treatment system (described in the background technology) commonly used in the automobile industry. The dilution ratio of the welding wire within the weld is in the range of 0 to 50%, wherein the dilution ratio near the center line of the weld is the smallest, and the dilution ratio of the fusion zone and the heat affected zone is the largest. On the other hand, the range of the aluminum segregation amount after heat treatment is within 1.5 weight percent, and the distribution rule of the aluminum segregation is more consistent with the dilution distribution rule of the welding wire. From the experimentally measured data (shown in table 3), the weld strength was unlikely to decrease.

The applicant needs to explain the main characteristic differences of dilution and segregation in the material science, wherein the dilution is a phenomenon that the content of each element in an alloy system is wholly reduced according to a certain ratio, and the dilution is an unavoidable phenomenon when dissimilar metals are welded. The segregation is that the content of one element in the alloy is too high in a certain area, the content of other elements is too low, and each element has no proportional relation. In order to prevent segregation of the components of the welding wire, a large amount of chromium, manganese and nickel elements similar to the physicochemical properties of iron elements are used, and the three elements also have the functions of solid solution carbon and decarburization prevention, namely, a so-called carbon element homogenization technology, which is shown in a hardness distribution diagram of a welding seam, as shown in fig. 7.

Unlike the prior art, the following are: the core design concept of the invention is to preferentially construct a ternary alloying system capable of dissolving more carbon elements, and then utilize the high strengthening effect of the carbon elements to promote the generation of a proper amount of high-hardness strengthening tissue in the welding line so as to improve the strength of the welding line. The essential cause of the decrease in weld strength is the decrease in hardness due to the microstructure transformation. Many people have made the mixing of aluminum as an essential cause of the decrease in weld strength, so the solution has focused on how to reduce the thickness of the aluminized layer or control the aluminum content. This view is clearly limited. First, the thickness of the aluminized layer at the upper and lower ends of the heat affected zone is much thinner than the thickness of the aluminized layer at the upper and lower ends of the substrate, as shown in fig. 6 and 7. The aluminum plating layer is firstly removed by the shock wave of laser during laser welding, and then the purpose of stirring a molten pool and welding is achieved by utilizing the Key Hole effect of the laser. This welding method has achieved the so-called reduction of the thickness of the aluminized layer or control of the content of aluminum elements in the prior art, which is a complete multi-pass behaviour. Second, even without an aluminized layer, the weld strength is lower than the substrate. This is due to weld defects such as undercut and pit caused by decarburization behavior of the weld and clamping gap errors during heat treatment. Finally, no matter any method is used, aluminum element in the welding line exists more or less, so the problem of strength reduction of the welding line cannot be fundamentally solved in the prior art, and the generation of a low-hardness microstructure can be effectively restrained by a welding wire alloying method, so that the uniformity of the hardness of the welding line and the stability of the tensile strength are ensured, and the problem of strength reduction can be fundamentally solved only.

The above examples represent only a limited number of preferred embodiments of the invention, which are described in more detail and are not to be construed as limiting the scope of the invention. It should be noted that it will be apparent to those skilled in the art that several variations and modifications can be made without departing from the spirit of the invention, which are all within the scope of the invention.

Claims (1)

1. A method for improving the weld strength of aluminum-boron plated steel by using a laser welding wire is characterized in that the alloy welding wire for laser welding consists of the following components in percentage by mass:

c:0.212wt%, cr:1.30wt%, ni:5.42wt%, mn:3.10wt%, nb:0.11wt%, si:0.12wt% of Fe with the balance;

the method comprises the following steps:

1) Selecting a 20MnTiB series aluminum-boron-plated steel plate with the workpiece thickness of 1.2mm and the plating layer thickness of 22 mu m;

2) Fixing the steel plate on a clamp, and butt-jointing and clamping the steel plate;

3) YAG or fiber laser with 0.7mm light spot diameter, 3200W power, welding speed of 1.4m/min, argon protection flow rate of 17L/min, and inclination angle of the laser of 5 degrees;

4) Selecting an alloy welding wire with the diameter of 0.6mm, the wire feeding speed of 0.9m/min, the wire feeding angle of 37 degrees and the optical wire distance of 0mm;

5) And (3) planning a welding path, welding, directly placing the steel plate into a resistance furnace at 930+/-10 ℃ after welding, heating for 6 minutes, and hot stamping in air after discharging.