Carbon filament wire for laser welding of a steel sheet having an aluminum-based plating layer, a method for laser welding of a steel sheet having an aluminum-based plating layer using the same, and a welded product manufactured thereby

Abstract

Provided are a carbon filament wire for laser welding of a steel plate having an aluminum-based plating layer, the carbon filament wire including a resin matrix and two or more carbon filaments provided inside the resin matrix, a method for laser welding a steel plate having an aluminum-based plating layer using the same, and a welded product manufactured thereby. [Solution] A carbon filament wire for laser welding of steel plates having an aluminum-based plating layer, characterized in that it includes a resin matrix and two or more carbon filaments provided inside the resin matrix, and the carbon filament wire has a diameter of 0.1 to 5 mm and a shape ratio (length / diameter) of the carbon filaments is 10,000 or more.

Description

Technical Field

[0001] The present invention relates to a carbon filament wire for laser welding of a steel sheet having an aluminum-based plating layer, a laser welding method for a steel sheet having an aluminum-based plating layer using the same, and a welded product manufactured thereby.

Background Art

[0002] In order to reduce exhaust gas or improve fuel efficiency while ensuring the safety of automobiles, the materials used for the vehicle body are required to have higher strength. However, when the strength of the material increases, not only is it difficult to perform forming such as pressing, but also problems occur in welding for component assembly. This is because elements such as C, Si, Cr, and Mn added to increase the strength of the material increase the weld hardening ability, thereby increasing the brittleness of the welded part.

[0003] Hot stamping is a process of manufacturing a product by heating a material to a temperature above the A3 transformation temperature and then performing cooling simultaneously with forming by pressing. At this time, the austenite in the material transforms into martensite due to rapid cooling by the press die, increasing the strength of the material. The above technology is increasingly applied to components such as B-pillars that require excellent collision performance in automobiles. Furthermore, in order to reduce weight while increasing strength, the tendency is increasing to manufacture components using TWB panels manufactured by laser welding materials having different thicknesses or steel grades for each position.

[0004] On the one hand, when press-forming a hot-heated sheet metal, problems such as oxidation and decarburization occurring on the surface of the sheet metal and the sheet metal sticking to the mold may occur. Thus, conventionally, in the case of galvanized steel sheets mainly used as automotive materials, since the evaporation temperature of zinc (about 906°C) is low, there is a drawback that it is difficult to use. To solve such problems, the use of aluminum or aluminum-silicon plated steel sheets is increasing. However, since aluminum and silicon are elements that promote the formation of ferrite, this causes a problem of reducing the strength of the welded part of hot-formed parts. That is, when welding an aluminum or aluminum-silicon plated steel sheet, the aluminum or silicon component of the plating layer mixes into the welded part and promotes the formation of ferrite. As a result, the formation of martensite in the welded part of the hot-formed part is hindered and the strength decreases.

[0005] As a technique for solving such problems, there is Patent Document 1. Patent Document 1 proposes a method of laser welding after removing the plating layer in the region where the welded part is formed with a brush or a laser. However, this method has a problem that since an additional process is required, the process becomes complicated and the cost is increased.

[0006] As another technique, there is Patent Document 2. Patent Document 2 proposes a method of promoting the formation of austenite in the welded part using a filler wire. However, this method has a problem that there are restrictions on the addition amount of the austenite formation promoting element, and since excessive weld beads are formed, an additional processing step is required and the manufacturing cost of the parts increases.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] An object of the present invention is to provide a carbon filament wire for laser welding of a steel sheet having an aluminum-based plating layer, a laser welding method for a steel sheet having an aluminum-based plating layer using the same, and a welded product manufactured thereby.

Means for Solving the Problems

[0009] The present invention provides a carbon filament wire for laser welding of a steel sheet having an aluminum-based plating layer, including a resin matrix and two or more carbon filaments provided inside the resin matrix.

[0010] Further, the present invention provides a welding method for laser welding two or more aluminum-based plated steel sheets, characterized in that, during the laser welding, a carbon filament wire including a resin matrix and two or more carbon filaments provided inside the resin matrix is fed.

[0011] Furthermore, the present invention provides a welded product manufactured by the above manufacturing method.

Effects of the Invention

[0012] According to the present invention, it is possible to provide a carbon filament wire for laser welding of a steel sheet having an aluminum-based plating layer, a laser welding method for a steel sheet having an aluminum-based plating layer using the same, and a welded product manufactured thereby, thereby solving the problem that an additional process is required during component manufacturing by hot press forming and the strength of the welded part is reduced compared to the base material.

Brief Description of the Drawings

[0013]

Figure 1

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Figure 6

Mode for Carrying Out the Invention

[0014] Hereinafter, a carbon filament wire for laser welding of a steel sheet having an aluminum-based plating layer of the present invention will be described.

[0015] FIG. 1 is a cross-sectional view of a carbon filament wire for laser welding of a steel sheet having an aluminum-based plating layer of the present invention.

[0016] As shown in FIG. 1, the carbon filament wire 10 of the present invention includes a resin matrix 2 and two or more carbon filaments 2 provided inside the above resin matrix. 1 and contains.

[0017] The above resin matrix imparts strength and rigidity to the carbon filaments with very small diameters so that they can be joined to each other and fed to the welding part. A part of the carbon generated by being decomposed by the laser beam serves to contribute to suppressing the formation of ferrite by being mixed into the welding part. In the present invention, the type of the above resin matrix is not particularly limited, and thermoplastic resins, thermosetting resins, etc. can be used. For example, polyamide, polyvinyl chloride, polyacetal, polyethylene, polypropylene, polystyrene, polyvinyl acetate, polyacrylate, methacrylic resin, polyvinylidene chloride, fluororesin, polycarbonate, phenol resin, furan resin, urea resin, melamine resin, epoxy resin, unsaturated ester resin, alkyd resin, polyurethane, epoxy Fat, Po resulfide, silicon, nitrile rubber, etc. can be used.

[0018] The above carbon filaments are decomposed by the laser beam during welding and play a role in suppressing the formation of ferrite by being mixed into the welding part. More specifically, in the conventional welding wire, carbon at a level similar to the base material component of the plated steel sheet (1% or less) is added, whereas the carbon filaments of the present invention can contain a higher level of carbon, so that even if Al in the plating layer is mixed into the welding part, the formation of ferrite can be suppressed. On the other hand, when there are two or more of the above carbon filaments, the feedability of the carbon filament wire can be improved. This is because the above carbon filaments have a very small diameter and are excessively flexible, which is disadvantageous for feeding. When a plurality of strands of carbon filaments are impregnated with resin, the rigidity increases.

[0019] The diameter of the above carbon filament wire may be 0.1 to 5 mm. When the diameter of the above carbon filament wire is less than 0.1 mm, it may be difficult to feed the above carbon filament wire during welding. When it exceeds 5 mm, not only does the amount of carbon mixed into the welding part become excessive, but it may also be difficult to sufficiently melt the above carbon filament wire with the laser beam during welding.

[0020] The aspect ratio (length / diameter) of the carbon filament may be 10,000 or more. When the aspect ratio of the carbon filament is less than 10,000, sufficient ductility cannot be ensured, and smooth and continuous feeding of the carbon filament wire may become impossible during welding. The larger the aspect ratio (length / diameter) of the carbon filament, the more advantageous it is for continuous operation. Therefore, in the present invention, the upper limit thereof is not particularly limited.

[0021] The diameter of the carbon filament may be 1 to 1000 μm. When the diameter of the carbon filament is less than 1 μm, it is not only likely to break during the manufacturing process, but also the carbon content in the carbon filament wire may decrease. When it exceeds 1000 μm, the flexibility of the carbon filament wire decreases, and it may be difficult to sufficiently melt the carbon filament wire with a laser beam during welding.

[0022] Based on the cross-section of the carbon filament wire, the fraction occupied by the carbon filaments in the carbon filament wire may be 50 to 90 area%. The resin matrix easily burns and cannot significantly contribute to carbon mixing into the welded part. Instead, it may contaminate the welded part or the surroundings. Therefore, when the area ratio of the carbon filament is less than 50%, there is a possibility of contaminating the welded part or the surrounding environment. On the contrary, when the area ratio of the carbon filament exceeds 90%, the bonding force between the carbon filaments becomes weak, and the feedability may decrease.

[0023] On the other hand, at least one of the carbon filaments can be replaced with a solid wire. The solid wire is composed of components similar to those of the base material of the plated steel sheet, and can play a role in complementing the underfill (insufficient filling) that may occur due to gaps or spatter in the welded part, or increasing the overlap (overlap) of the welded part to strengthen the welded part. In addition, since the solid wire has relatively high rigidity, the strength and rigidity of the carbon filament wire can be improved.

[0024] The above solid wire can be one commonly used in the relevant technical field. For example, in terms of weight percentage, it contains C: 0.001 - 1.0%, Mn: 0.01 - 25%, Si: 0.01 - 5.0%, with the balance being Fe and inevitable impurities.

[0025] The above solid wire may have a diameter of 0.01 - 0.05 mm. When the diameter of the above solid wire is less than 0.01 mm, the effects such as the increase in the volume of the welded part and the reinforcement of rigidity may be reduced. When it exceeds 0.05 mm, the effect of increasing the carbon content of the welded part may be reduced.

[0026] On the other hand, in the present invention, the manufacturing method of the above carbon filament wire is not particularly limited. However, for example, the above carbon filament wire can be manufactured by passing the carbon filament through a container provided with a resin in a liquid or plastic state, passing it through a nozzle with a desired diameter, and then cooling it naturally, or performing a curing treatment as necessary. At this time, the above carbon filament can exist in a twisted form (twisted with each other) for easy feeding into the container provided with the resin.

[0027] Hereinafter, the laser welding method of the steel plate having an aluminum-based plating layer of the present invention will be described.

[0028] The laser welding method of the steel plate having an aluminum-based plating layer of the present invention is a welding method for laser welding an aluminum-based plated steel plate, characterized in that during the above laser welding, a carbon filament wire containing a resin matrix and two or more carbon filaments provided inside the resin matrix is fed.

[0029] In the present invention, the laser welding method is not particularly limited, and all methods commonly used in the technical field can be used. Regarding the plated steel sheet, as long as an aluminum-based plating layer is formed, all types of steel sheets used in the technical field can be used. Furthermore, the plated steel sheets to be welded can have different thicknesses and strengths from each other. On the other hand, the aluminum-based plating layer may be an Al-based plating layer or an Al-Si-based plating layer.

[0030] During the above laser welding, the heat input amount for welding may be 10 to 200 J / mm. When the heat input amount for welding is less than 10 J / mm, it may be difficult to sufficiently melt the material to be welded or the carbon filament wire. When it exceeds 200 J / mm, there is a possibility that the molten material of the material to be welded and the carbon filament is lost due to dripping. On the other hand, the heat input amount Q for welding can be obtained by Q = P L / V, where P L is the laser output (watt (W)), and V means the welding speed (mm / s).

[0031] The feeding speed of the above carbon filament wire may be 2 to 200 mm / s. When the feeding speed of the carbon filament wire is less than 2 mm / s, the dilution amount of carbon in the welded part is small, and it may be difficult to suppress the formation of the ferrite phase. When it exceeds 200 mm / s, not only is it difficult to sufficiently melt the carbon filament wire with the laser beam, but also the amount of carbon added to the welded part becomes excessive, and the welded part may become fragile. The feeding speed s can be obtained by s = t·v / d, where t is the thickness (mm) of the material to be welded, v is the welding speed, and d is the diameter (mm) of the carbon filament wire. On the other hand, when the thicknesses of the materials to be welded, that is, the plated steel sheets, are different from each other, the feeding speed can be obtained by considering the average thickness.

[0032] Hereinafter, a welded product according to an embodiment of the present invention will be described.

[0033] The present invention provides a welded product manufactured by a laser welding method of a steel sheet having an aluminum-based plating layer using the carbon filament wire described above.

[0034] In the present invention, since the plating layer in the region where the welded portion is formed is not removed, Al in the plating layer of the plated steel sheet is mixed into the welded portion in the above-described welded product. Further, since welding is performed using a carbon filament wire, the carbon content of the welded portion also increases. As a result, the welded product of the present invention has a higher content of Al and C than the base material. Thereby, a martensite structure is easily formed in the welded portion, and the strength and rigidity are improved.

[0035] On the other hand, the above-described welded product may be a welded steel sheet, or may be a formed part obtained by hot press forming the above-described welded steel sheet. The formed part may have the same thickness and strength for two or more steel sheets, or may be a TWB (Tailor Welded Blank) having different thicknesses or strengths. Further, the formed part can be applied to an A-pillar, B-pillar, bumper beam, door beam, cross member, etc. of an automobile.

[0036] Hereinafter, the present invention will be described in more detail with reference to examples. However, the following examples are illustrative for explaining the present invention in more detail, and do not limit the scope of rights of the present invention.

[0037] (Example) After producing a carbon filament wire having the conditions shown in Table 1 below, after butting together steel sheets of a tensile strength of 1.5 GPa class having an Al-Si based plating layer, while feeding the above carbon filament wire, laser welding was performed under the conditions shown in Table 1 below. At this time, an epoxy resin was used as the resin matrix. After hot press forming the welded product thus manufactured, the microstructure, tensile strength and hardness of the welded portion were measured, and the results are shown in Table 2 below. On the other hand, Comparative Example 1 is a self-welded product without feeding a welding wire.

[0038] The microstructure was observed under an optical microscope after the test piece containing the welded part was molded, polished, corroded with a 2% nital corrosion solution, and then observed under an optical microscope.

[0039] The tensile strength was measured by processing the test piece according to KS B 0801 No. 13B standard, performing a tensile test according to KS B 0802, and measuring the maximum load.

[0040] The hardness was measured by a Vickers hardness test according to KS B 0811 with a load of 500 gf.

[0041]

Table 1

[0042]

Table 2

[0043] As can be seen from Tables 1 and 2 above, in Invention Example 1, martensite is formed and the tensile strength and hardness are at a high level. In contrast, in Comparative Example 1, some ferrite is formed and the tensile strength and hardness are at a low level.

[0044] Figure 2 is a photograph of the welded parts of Invention Example 1 and Comparative Example 1 observed under an optical microscope, and Figure 3 is a photograph of the welded parts of Invention Example 1 and Comparative Example 1 observed under a scanning electron microscope. As can be seen from Figures 2 and 3, in the case of Invention Example 1, martensite is formed, while in the case of Comparative Example 1, ferrite is formed in addition to martensite.

[0045] Figure 4 is a photograph of the concentrations of Al and C in the welded parts of Invention Example 1 and Comparative Example 1 observed by EPMA (Electron Probe Micro Analysis). As can be seen from Figure 4, Invention Example 1 and Comparative Example 1 have similar Al contents. However, in the case of Comparative Example 1, the carbon contents of the welded part and the base metal are at a similar level, while in the case of Invention Example 1, it can be seen that the C content of the welded part is higher than that of the base metal.

[0046] Figure 5 is a graph showing the hardness distribution of the welded joints of Invention Example 1 and Comparative Example 1. As can be seen from Figure 5, in the case of Invention Example 1, the hardness of the welded joint is at a higher level compared to the base material, while in the case of Comparative Example 1, it can be seen that the hardness of the welded joint is at a lower level compared to the base material.

[0047] Figure 6 is a photograph obtained by observing the fracture surface after the tensile test of Invention Example 1 and Comparative Example 1 with a scanning electron microscope. As can be seen from Figure 6, in the case of Invention Example 1, it shows a form of fine intragranular fracture, while in the case of Comparative Example 1, it can be seen that wall-opening fracture occurred.

Explanation of Reference Signs

[0048] 1: Carbon filament 2: Resin matrix 10: Carbon filament wire

Claims

Claim 1: A carbon filament wire for laser welding, comprising: a resin matrix; two or more carbon filaments provided inside the resin matrix; and the diameter of the carbon filament wire is 0.1 to 5 mm; the aspect ratio (length / diameter) of the carbon filament is 10,000 or more; the diameter of the carbon filament is 1 to 1000 μm; A carbon filament wire for laser welding of a steel sheet having an aluminum-based plating layer, characterized in that, based on the cross-section of the carbon filament wire, the fraction occupied by the carbon filaments in the carbon filament wire is 50 to 90 area%. Claim 2 At least one of the carbon filaments is replaced by a solid wire, The carbon filament wire for laser welding of a steel sheet having an aluminum-based plating layer according to claim 1, wherein the solid wire has a diameter of 0.01 to 0.05 mm. Claim 3 The carbon filament wire for laser welding of a steel sheet having an aluminum-based plating layer according to claim 2, wherein the solid wire contains, by weight%, C: 0.001 to 1.0%, Mn: 0.01 to 25%, Si: 0.01 to 5.0%, and the balance consists of Fe and unavoidable impurities. Claim 4 A welding method for laser welding two or more aluminum-based plated steel sheets, comprising: feeding a carbon filament wire containing a resin matrix and two or more carbon filaments provided inside the resin matrix during the laser welding; the diameter of the carbon filament wire is 0.1 to 5 mm; the aspect ratio (length / diameter) of the carbon filament is 10,000 or more; the diameter of the carbon filament is 1 to 1000 μm; A laser welding method for a steel sheet having an aluminum-based plating layer, characterized in that, based on the cross-section of the carbon filament wire, the fraction occupied by the carbon filaments in the carbon filament wire is 50 to 90 area%. Claim 5 The laser welding method for a steel sheet having an aluminum-based plating layer according to claim 4, wherein the aluminum-based plating layer is an Al-based plating layer or an Al-Si-based plating layer. Claim 6 The laser welding method for a steel sheet having an aluminum-based plating layer according to claim 4, wherein the heat input during the laser welding is 10 to 200 J / mm. Claim 7 The laser welding method of a steel sheet having an aluminum-based plating layer according to claim 4, characterized in that the feeding speed of the carbon filament wire is 2 to 200 mm / s.

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