Aluminum coated blank and manufacturing method thereof

Abstract

To provide an aluminum coated blank that may minimize a reduction in hardness and physical properties of a joint portion of a blank.SOLUTION: There is provided a manufacturing method of an aluminum coated blank including the steps of: arranging edges of a first coated steel sheet and a second coated steel sheet to face each other; and providing a filler wire at a boundary between the first coated steel sheet and the second coated steel sheet and irradiating the first coated steel sheet and the second coated steel sheet with a laser beam from a laser head to melt the first coated steel sheet, the second coated steel sheet and the filler wire, thereby forming a joint portion. Therein each of the first coated steel sheet and the second coated steel sheet includes a base iron and a coated layer that is formed with an adhesion amount of 20 to 100 g / m2 on at least one surface of the base iron and includes aluminum.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an aluminum-based plating blank and a method for manufacturing the same.

Background Art

[0002] Parts with various strengths are used in vehicles. For example, when a vehicle collides or overturns, parts that must absorb energy require relatively low strength, and parts that need to maintain their shape to ensure the survival space of passengers require high strength.

[0003] If the strength of the parts that must absorb energy during a collision is excessively high, the impact energy cannot be appropriately absorbed and is directly transmitted to other parts, which rather causes a problem of transmitting excessive impact to passengers and other parts of the vehicle.

[0004] Vehicles are constantly required to be lightweight and cost-reduced, which makes it necessary for one part to have partially different heterogeneous strengths.

[0005] A partial section of a part requires high strength for passenger protection, while a partial section requires relatively low strength for impact energy absorption.

[0006] Typical examples of such parts include the B-pillar of a passenger car. The lower part of the B-pillar requires relatively low tensile strength, and the upper part requires high tensile strength. The reason for the difference in strength is that during a vehicle collision, parts that maintain their shape at high strength (the upper part that must support the roof during overturning) and parts that absorb impact while collapsing (the lower part that is highly likely to collide with other vehicles on the side) are both required.

[0007] In addition, in order to ensure a stable space that can prevent passengers from being injured, the upper part of the B-pillar must maintain its shape, so high strength is required. If the upper strength of the B-pillar is not ensured, when the vehicle overturns, the roof will be crushed, posing a great threat to the safety of passengers. However, the lower part of the B-pillar must absorb impact energy while being deformed, so relatively low strength is required. If the lower part of the B-pillar also has high strength, the impact energy during a side collision will not be absorbed, and the impact will be transmitted to other structural materials.

[0008] The specific required strength varies depending on the type and form of the vehicle. In the case of the upper part of the B-pillar, a tensile strength of approximately 1500 MPa is required, while in the case of the lower part of the B-pillar, a tensile strength of approximately 500 - 1000 MPa is required.

[0009] Conventionally, a method of forming parts with low-strength materials and then attaching separate reinforcing materials to the parts that require high strength has been used. However, when one part requires different strengths in sections, for the upper part, a material with high hardenability (or thick material) is used, and for the lower part, a material with low strength and low hardenability (or thin material) is used. The two materials are joined by laser to make a blank, and the final product is produced through a hot stamping process.

[0010] On the other hand, tailor welded blank (TWB) is a part manufactured by joining two or more steel sheet materials, one or more of which are different from each other in terms of material and thickness. As such a steel sheet material for TWB, an Al-Si plating layer is used on the surface.

[0011] However, if the plated steel sheet materials are joined by laser, the components of the plating layer will be dissolved into the molten pool at the joint (weld), so the joint will have physical properties different from those of the base material. When the plating layer is aluminum-silicon (Al-Si) or zinc (Zn)-based, the plating components will be mixed into the joint during laser welding, causing a decrease in mechanical physical properties.

[0012] Therefore, although the strength reduction phenomenon of the joint can be solved or minimized by the composition of the filler wire, problems such as the plating layer component (Al) mixed due to the material (material with a large amount of plating adhesion) and the joining condition (high joining speed) not being uniformly diluted with the base material and segregation occurring, and only the effect of the filler wire component is insufficient.

[0013] The background art related to the present invention is disclosed in Korean Registered Patent Publication No. 10-1637084 (published on July 6, 2016, title of the invention: Filler Wire and Method for Manufacturing Customized Welded Blanks Using the Same).

Summary of the Invention

Problems to be Solved by the Invention

[0014] According to the problem to be solved by the present invention, it is to provide an aluminum-based plated blank capable of minimizing the decrease in hardness and physical properties of the blank joint part.

[0015] According to an embodiment of the present invention, it is to provide an aluminum-based plated blank capable of preventing defects such as segregation generation in the blank joint part.

[0016] According to an embodiment of the present invention, it is to provide an aluminum-based plated blank capable of minimizing the decrease in physical properties of the blank joint part after the hot stamping process.

[0017] According to an embodiment of the present invention, it is to provide a method for manufacturing the aluminum-based plated blank.

Means for Solving the Problems

[0018] One embodiment of the present invention includes a first plated steel sheet; a second plated steel sheet connected to the first plated steel sheet; and a joint portion connecting the first plated steel sheet and the second plated steel sheet at the boundary between the first plated steel sheet and the second plated steel sheet. The first plated steel sheet and the second plated steel sheet each include a base iron and a plating layer formed on at least one surface of the base iron with an adhesion amount of 20 to 100 g / m 2 and including a plating layer containing aluminum. The base iron contains 0.01 to 0.5 wt% carbon (C), 0.01 to 1.0 wt% silicon (Si), 0.5 to 3.0 wt% manganese (Mn), more than 0 and up to 0.05 wt% phosphorus (P), more than 0 and up to 0.01 wt% sulfur (S), more than 0 and up to 0.1 wt% aluminum (Al), more than 0 and up to 0.001 wt% nitrogen (N), and the balance of iron (Fe) and other inevitable impurities. The joint portion contains 0.2 wt% or more and 2.0 wt% or less aluminum (Al), 0.8 wt% or more and 2.5 wt% or less manganese (Mn), and 0.1 wt% or more and 0.4 wt% or less carbon (C). Disclosed is an aluminum-based plating blank in which ferrite is not formed at a temperature equal to or higher than the highest Ac3 temperature among the first plated steel sheet and the second plated steel sheet.

[0019] In this embodiment, when the aluminum-based plating blank is heated to a temperature equal to or higher than Ac3 and press-formed, and then cooled at a cooling rate of 10 °C / s to 500 °C / s to 300 °C or lower for hot stamping forming, the average hardness of the joint portion is equal to or higher than the average hardness of the base iron.

[0020] In this embodiment, after the hot stamping forming, the joint portion contains 90 area% or more of martensite.

[0021] In this embodiment, the base iron further contains one or more components among niobium (Nb), titanium (Ti), chromium (Cr), molybdenum (Mo), and boron (B).

[0022] In this embodiment, the plating layer includes a surface layer formed on the surface of the base iron and containing 80% by weight or more of aluminum (Al); and an alloying layer formed between the surface layer and the base iron; the alloying layer includes aluminum-iron (Al-Fe) and aluminum-iron-silicon (Al-Fe-Si) intermetallic compounds and contains 20 to 70% by weight of iron (Fe).

[0023] Another embodiment of the present invention includes the steps of arranging the edges of the first plated steel sheet and the second plated steel sheet to face each other; and a joining step of providing a filler wire at the boundary between the first plated steel sheet and the second plated steel sheet and irradiating a laser beam to form a joint portion connecting the first plated steel sheet and the second plated steel sheet; the joint portion is formed by melting the first plated steel sheet, the second plated steel sheet, and the filler wire together by irradiation with the laser beam, and the first plated steel sheet and the second plated steel sheet each include base iron and a plating layer formed on at least one surface of the base iron with an adhesion amount of 20 to 100 g / m 2 and containing aluminum, and the joint portion contains 0.2% by weight or more and 2.0% by weight or less of aluminum (Al), 0.8% by weight or more and 2.5% by weight or less of manganese (Mn), and 0.1% by weight or more and 0.4% by weight or less of carbon (C), but discloses a manufacturing method of an aluminum-based plated blank in which ferrite is not formed at a temperature equal to or higher than the highest Ac3 temperature among the first plated steel sheet and the second plated steel sheet.

[0024] In this embodiment, the laser beam is irradiated so as to reciprocate across the boundary, the laser beam has a frequency of 100 to 1500 Hz and a power of 1 to 20 kW, and the forming speed of the joint portion is also 15 to 170 mm / sec.

[0025] In this embodiment, the forming speed of the joint portion is 15 to 120 mm / sec, and the frequency of the laser beam, the radius of the laser beam, and the forming speed of the joint portion satisfy the relationship of the following formula 1.

Equation

[0026] (In the formula 1, α is 0.7, f is the frequency (Hz) of the laser beam, r is the radius (mm) of the laser beam measured on the surface of the aluminum-plated steel sheet, and v is the forming speed (mm / sec) of the joint part).

[0027] In this example, the base iron contains 0.01 to 0.5 wt% of carbon (C), 0.01 to 1.0 wt% of silicon (Si), 0.5 to 3.0 wt% of manganese (Mn), more than 0 and 0.05 wt% or less of phosphorus (P), more than 0 and 0.01 wt% or less of sulfur (S), more than 0 and 0.1 wt% or less of aluminum (Al), more than 0 and 0.001 wt% or less of nitrogen (N), and the balance of iron (Fe) and other inevitable impurities. The plating layer includes a surface layer formed on the surface of the base iron and containing 80 wt% or more of aluminum (Al), and an alloying layer formed between the surface layer and the base iron. The alloying layer includes aluminum-iron (Al-Fe) and aluminum-iron-silicon (Al-Fe-Si) intermetallic compounds and contains 20 to 70 wt% of iron (Fe).

[0028] In this example, when the aluminum-plated blank is heated above Ac3 and press-formed, and then cooled at a cooling rate of 10 °C / s to 500 °C / s to 300 °C or lower for hot stamping forming, the average hardness of the joint part is equal to or higher than the average hardness of the base iron, and after the hot stamping forming, the joint part can be formed to have a microstructure containing 90 area% or more of martensite.

[0029] In this example, the filler wire contains 1.5 wt% or more and 4.5 wt% or less of manganese (Mn) and 0.4 wt% or more and 0.9 wt% or less of carbon (C), and the difference between the product of the first strength and the first thickness of the first plated steel sheet and the product of the second strength and the second thickness of the second plated steel sheet is also more than 500 MPA×mm and 1000 MPA×mm or less.

[0030] In this embodiment, the filler wire contains 2.5 wt% or more and 4.0 wt% or less of manganese (Mn) and 0.5 wt% or more and 0.9 wt% or less of carbon (C), and the difference between the product of the first strength and the first thickness of the first plated steel sheet and the product of the second strength and the second thickness of the second plated steel sheet is also 500 MPA×mm or less.

[0031] In this embodiment, during the irradiation of the laser beam, one or more of the first plated steel sheet, the second plated steel sheet, and the laser head for irradiating the laser beam can move.

Advantages of the Invention

[0032] The aluminum-based plated blank of the present invention is manufactured by joining two or more aluminum-based plated steel sheets, one or more of which differ from each other in terms of strength and thickness, thereby minimizing the decrease in hardness and physical properties of the blank joint portion, preventing the occurrence of defects such as segregation in the blank joint portion, and minimizing the joint breakage caused by the phase change of the segregation into Al-Fe intermetallic compounds during the hot stamping process.

Brief Description of the Drawings

[0033]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Mode for Carrying Out the Invention

[0034] The present invention can be variously transformed and can have various embodiments. Specific embodiments are illustrated in the drawings and will be described in detail in the detailed description. The effects and features of the present invention and the methods for achieving them will become clear by referring to the embodiments described in detail later together with the drawings. However, the present invention is not limited to the embodiments disclosed below and can also be embodied in various forms.

[0035] In the following embodiments, terms such as first, second, etc. are not used in a limiting sense but are used for the purpose of distinguishing one component from another component.

[0036] In the following embodiments, singular expressions include plural expressions unless the context clearly indicates otherwise.

[0037] In the following embodiments, terms such as "comprising" or "having" mean that the features or components described in the specification exist and do not preclude the possibility of adding one or more different features or components in advance.

[0038] In the following embodiments, when a part such as a film, region, component, etc. is on or above another part, it includes not only the case where it is directly above the other part but also the case where other films, regions, components, etc. are interposed in between.

[0039] In the drawings, for the sake of convenience of explanation, the components may have their sizes exaggerated or reduced. For example, the sizes and thicknesses of the respective components shown in the drawings are arbitrarily shown for the convenience of explanation and the present invention is not necessarily limited to the places shown in the drawings.

[0040] When a certain embodiment can be embodied differently, the specific process order can be carried out differently from the order described. For example, two processes described continuously can be carried out substantially simultaneously and can be advanced in the reverse order from the order described.

[0041] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. When explaining with reference to the drawings, the same or corresponding components are given the same drawing reference numerals.

[0042] FIG. 1 is a cross-sectional view schematically showing an aluminum-based plating blank according to an embodiment of the present invention, FIGS. 2 and 3 are perspective views schematically showing the manufacturing process of an aluminum-based plating blank according to an embodiment of the present invention, respectively, and FIG. 4 is a plan view schematically showing the process of joining an aluminum-based plated steel sheet by irradiating a laser beam.

[0043] First, referring to FIG. 1, an aluminum-based plating blank 100 according to an embodiment of the present invention includes a first plated steel sheet 10, a second plated steel sheet 20 connected to the first plated steel sheet 10, and a joint portion 30 that connects the first plated steel sheet 10 and the second plated steel sheet 20 at the boundary between the first plated steel sheet 10 and the second plated steel sheet 20.

[0044] The first plated steel sheet 10 includes a first base iron 12 and a first plating layer 14 formed on at least one surface of the first base iron 12. The second plated steel sheet 20 includes a second base iron 22 and a second plating layer 24 formed on at least one surface of the second base iron 22. The first base iron 12 and the second base iron 22 contain the same components, and the first plating layer 14 and the second plating layer 24 contain the same components. Hereinafter, for convenience of explanation, the first base iron 12 and the first plating layer 14 will be described, but this can be similarly applied to the second base iron 22 and the second plating layer 24 respectively.

[0045] The first base iron 12 contains 0.01 to 0.5 wt% of carbon (C), 0.01 to 1.0 wt% of silicon (Si), 0.5 to 3.0 wt% of manganese (Mn), more than 0 and 0.05 wt% or less of phosphorus (P), more than 0 and 0.01 wt% or less of sulfur (S), more than 0 and 0.1 wt% or less of aluminum (Al), more than 0 and 0.001 wt% or less of nitrogen (N), and the balance of iron (Fe) and other inevitable impurities.

[0046] Carbon (C) is a main element that determines the strength and hardness of steel and is added for the purpose of ensuring the tensile strength of the steel material after the hot stamping (or hot pressing) process. It is also added for the purpose of ensuring hardenability characteristics. In one specific example, the carbon is contained in an amount of 0.01 to 0.5 wt% based on the total weight of the first base iron 12. When the carbon is contained in an amount less than 0.01 wt%, it is difficult to achieve the mechanical strength of the present invention. When it exceeds 0.5 wt%, problems such as a decrease in the toughness of the steel material or problems in controlling the brittleness of the steel will occur.

[0047] Silicon (Si) acts as a ferrite stabilizing element in the first base iron 12. It can perform the functions of improving ductility by cleaning the ferrite and improving the carbon concentration in austenite by suppressing carbide formation in the low-temperature range. Furthermore, it is a core element for hot rolling, cold rolling, hot stamping structure homogenization (pearlite, manganese segregation band control), and fine dispersion of ferrite. In a specific example, the silicon is contained in an amount of 0.01 to 1.0% by weight based on the total weight of the first base iron 12. When the silicon is contained in an amount less than 0.01% by weight, the above-described functions cannot be fully exerted. When it exceeds 1.0% by weight, the hot rolling and cold rolling loads increase, the hot rolling red scale becomes excessive, and the joinability deteriorates.

[0048] Manganese (Mn) is added for the purpose of hardenability and strength increase during heat treatment. In a specific example, the manganese is contained in an amount of 0.5 to 3.0% by weight based on the total weight of the first base iron 12. When the manganese is contained in an amount less than 0.5% by weight, there is a high possibility of insufficient material (insufficient hard phase fraction) after hot stamping due to insufficient hardenability. When it exceeds 3.0% by weight, the ductility and toughness decrease due to manganese segregation or pearlite band, which causes a decrease in bending performance and the occurrence of inhomogeneous fine structures.

[0049] Phosphorus (P) is an element that easily segregates and inhibits the toughness of steel. In a specific example, the phosphorus (P) is contained in an amount exceeding 0 and not exceeding 0.05% by weight based on the total weight of the first base iron 12. When contained within the above range, a decrease in toughness can be prevented. When the phosphorus is contained in an amount exceeding 0.05% by weight, cracks are induced during the process, and iron phosphide compounds are formed, resulting in a decrease in toughness.

[0050] Sulfur (S) is an element that inhibits workability and physical properties. In a specific example, the sulfur is contained in an amount exceeding 0 and not exceeding 0.01% by weight based on the total weight of the first base iron 12. When the sulfur is contained in an amount exceeding 0.01% by weight, the hot workability deteriorates, and surface defects such as cracks due to the formation of large inclusions occur.

[0051] Aluminum (Al) serves as a deoxidizer for removing oxygen in the first base iron 12. In a specific example, the aluminum is contained in an amount exceeding 0 and not exceeding 0.1% by weight based on the total weight of the first base iron 12. If the content of the aluminum exceeds 0.1% by weight, it will cause nozzle blockage during steelmaking, and during casting, hot brittleness will occur due to aluminum oxide or the like, resulting in cracks or a decrease in ductility.

[0052] Nitrogen (N), when added in a large amount, increases the amount of dissolved nitrogen, reduces the impact properties and elongation of the first base iron 12, and greatly reduces the toughness of the joint part. In a specific example, the nitrogen is contained in an amount exceeding 0 and not exceeding 0.001% by weight based on the total weight of the first base iron 12. When the nitrogen is contained in an amount exceeding 0.001% by weight, the impact properties and elongation of the first base iron 12 decrease, and the toughness of the joint part decreases.

[0053] In a specific example, the first base iron 12 further contains one or more components among niobium (Nb), titanium (Ti), chromium (Cr), molybdenum (Mo), and boron (B).

[0054] Niobium (Nb) is added for the purpose of increasing strength and toughness by reducing the martensite packet size. In a specific example, the niobium is contained in an amount of 0.005 to 0.1% by weight based on the total weight of the first base iron 12. When contained within this range, it has an excellent effect of refining the crystal grains of the steel material in the hot rolling and cold rolling processes, preventing the occurrence of slab cracks and brittle fracture of the product during steelmaking / continuous casting, and minimizing the generation of coarse precipitates in steelmaking.

[0055] Titanium (Ti) can be added for the purpose of hardenability strengthening and material improvement by precipitate formation after hot stamping heat treatment. Also, it forms precipitate phases such as Ti(C,N) at high temperatures and effectively contributes to the refinement of austenite crystal grains. In one specific example, the titanium is contained in an amount of 0.005 to 0.1% by weight based on the total weight of the first base iron 12. When contained within the said content range, it is possible to prevent continuous casting defects and coarsening of precipitates, easily ensure the physical properties of the steel material, and prevent defects such as crack generation on the surface of the steel material.

[0056] The chromium (Cr) is added for the purpose of improving the hardenability and strength of the first aluminum-based plated steel sheet 10. In one specific example, the chromium is contained in an amount of 0.01 to 0.5% by weight based on the total weight of the first base iron 12. When contained within the said range, it is possible to improve the hardenability and strength of the first aluminum-based plated steel sheet 10 and prevent an increase in production cost and a decrease in the toughness of the steel material.

[0057] Molybdenum (Mo) can contribute to strength improvement by suppressing coarsening of precipitates and increasing hardenability during hot rolling and hot stamping. Molybdenum (Mo) is contained in an amount of 0.001 to 0.008% by weight based on the total weight of the first base iron 12. When contained within the said range, during hot rolling and hot stamping, the effect of suppressing coarsening of precipitates and increasing hardenability is excellent.

[0058] Boron (B) is added for the purpose of ensuring the hardenability and strength of the steel material by ensuring a martensite structure, and has a crystal grain refinement effect due to an increase in the austenite crystal grain growth temperature. In one specific example, the boron is contained in an amount of 0.001 to 0.008% by weight based on the total weight of the first base iron 12. When contained within the said range, it is possible to prevent the occurrence of hard phase grain boundary brittleness and ensure high toughness and bendability.

[0059] In one specific example, the first plated steel sheet 10 is produced by reheating a steel slab containing 0.01 to 0.5 wt% carbon (C), 0.01 to 1.0 wt% silicon (Si), 0.5 to 3.0 wt% manganese (Mn), more than 0 wt% and 0.05 wt% or less phosphorus (P), more than 0 wt% and 0.01 wt% or less sulfur (S), more than 0 wt% and 0.1 wt% or less aluminum (Al), more than 0 wt% and 0.001 wt% or less nitrogen (N), and the balance of iron (Fe) and other inevitable impurities, finish rolling the reheated slab, winding up the hot-rolled steel sheet, cold rolling the wound-up steel sheet, annealing the cold-rolled sheet, and forming a first plating layer 14 on the surface of the annealed sheet.

[0060] The first plating layer 14 formed on at least one surface of the first base iron 12 can be formed with an adhesion amount of 20 to 100 g / m² on a single-sided basis. 2 Also, the first plating layer 14 contains aluminum (Al). In one specific example, the first plating layer 14 can be formed by including a step of immersing the first base iron 12 in a plating bath containing one or more of molten aluminum and aluminum alloys at 600 to 800°C and then cooling it at an average cooling rate of 1 to 50°C / s.

[0061] In one specific example, after immersing the first base iron 12 in the plating bath, one or more of air and gas are sprayed onto the surface of the first base iron 12 to wipe the molten plating layer, and by adjusting the spraying pressure, the plating adhesion amount of the first plating layer 14 can be adjusted.

[0062] The plating adhesion amount can be formed at 20 to 150 g / m² on at least one surface of the first base iron 12. 2 Desirably, it is formed at 20 to 100 g / m² on at least one surface of the first base iron 12. 2 When the plating adhesion amount is formed to be less than 20 g / m², the corrosion resistance decreases, and when it is more than 100 g / m², 2 the corrosion resistance decreases. 2When it exceeds, when joining the first aluminum-based plated steel sheet 10 and the second aluminum-based plated steel sheet 20, the amount of aluminum (Al) mixed into the joint portion 30 increases, and after hot stamping, the strength of the joint portion 30 may decrease.

[0063] In one specific example, the first plating layer 14 is formed on the surface of the first base iron 12, and includes a surface layer containing 80 wt% or more of aluminum (Al) and an alloying layer formed between the surface layer and the first base iron 12, the alloying layer containing aluminum-iron (Al-Fe) and aluminum-iron-silicon (Al-Fe-Si) intermetallic compounds and containing 20 to 70 wt% of iron (Fe).

[0064] In one specific example, the surface layer contains 80 to 100 wt% of aluminum, and the average thickness is 10 to 40 μm. When the average thickness of the surface layer is less than 10 μm, the corrosion resistance of the first aluminum-based plated blank 10 decreases. When the average thickness of the surface layer exceeds 40 μm, when joining the first aluminum-based plated blank 10 and the second aluminum-based plated blank 20, the amount of aluminum (Al) mixed into the joint portion 30 increases, and after hot stamping, the mechanical properties of the joint portion 30 decrease. For example, the average thickness of the surface layer is also 10 to 30 μm.

[0065] In one specific example, the alloying layer contains 20 to 70 wt% of iron (Fe). Under the above conditions, the alloying layer has a high melting point and can prevent the occurrence of the liquid metal embrittlement phenomenon where the surface layer is melted in the hot stamping heating furnace and penetrates into the structure of the first base iron 12. For example, the alloying layer contains 20 to 60 wt% of iron (Fe).

[0066] The joint part 30 is formed by aligning the side surfaces of the first plated steel sheet 10 and the second plated steel sheet 20 to face each other, then supplying a filler wire 200 to the boundary between the first plated steel sheet 10 and the second plated steel sheet 20, and irradiating with a laser to melt the first plated steel sheet 10, the second plated steel sheet 20, and the filler wire 200. The formed joint part 30 is composed of a component system in which ferrite is not formed at a temperature equal to or higher than the higher Ac3 temperature among the Ac3 temperature of the first plated steel sheet 10 and the Ac3 temperature of the second plated steel sheet 20. Desirably, the joint part 30 can be composed of a component system in which ferrite is not formed at 850 °C or higher. Specifically, the joint part 30 after the hot stamping process, that is, after heating the aluminum-based plated blank 100 to 850 to 1000 °C, performing press forming, and rapidly cooling at an average cooling rate of 10 to 500 °C / s, can be composed of a component system having a microstructure containing martensite with an area fraction of 90% or more. For example, at the hot stamping heating temperature, the joint part 30 exists as a full austenite structure, and thereafter, during cooling, it can be transformed into a martensite structure with an area fraction of 90% or more, desirably, a full martensite structure.

[0067] The joint part 30 contains 0.2 to 2.0% by weight of aluminum (Al). The content of the aluminum is also the sum of the aluminum (Al) mixed from the melted first plated steel sheet 10, the second plated steel sheet 20, and the filler wire 200. If the aluminum (Al) content of the joint part 30 is less than 0.2% by weight, when joining the first plated steel sheet 10 and the second plated steel sheet 20, the first and second plating layers 14, 24 must be removed to adjust the amount of aluminum (Al) mixed in, so the efficiency of the manufacturing process decreases. On the other hand, if the aluminum (Al) content of the joint part 30 exceeds 2.0% by weight, after hot stamping, the martensite fraction of the joint part decreases and the mechanical properties of the plated blank 100 deteriorate. On the other hand, if the joint part 30 contains more than 1.0% by weight of aluminum, there is a risk of forming an oxide film on the surface of the joint part 30. To prevent this, the joint part 30 can contain 0.2 to 1.0% by weight of aluminum.

[0068] Further, the joint part 30 contains more austenite stabilizing elements than the first and second base steels 12 and 22. For example, the joint part 30 contains 0.1 wt% or more and 0.4 wt% or less of carbon (C) and 0.8 wt% or more and 2.5 wt% or less of manganese (Mn).

[0069] The content of carbon (C) contained in the joint part 30 is also the sum of carbon (C) mixed from the melted first plated steel sheet 10, second plated steel sheet 20, and filler wire 200. If the content of carbon (C) in the joint part 30 is less than 0.1 wt%, the hardness of the joint part 30 is smaller than the hardness of the first plated steel sheet 10 and the second plated steel sheet 20, and fracture occurs in the joint part 30. On the other hand, if the content of carbon (C) exceeds 0.4 wt%, the hardness of the joint part 30 rises excessively, and brittle fracture may occur in the joint part 30 due to an external impact or the like.

[0070] The content of manganese (M) contained in the joint part 30 is also the sum of manganese (M) mixed from the melted first plated steel sheet 10, second plated steel sheet 20, and filler wire 200. If the content of manganese (M) in the joint part 30 is less than 0.8 wt%, a ferrite structure coexists in the joint part 30 during hot stamping. If the content of manganese (M) exceeds 2.5 wt%, the viscosity drops during melting of the joint part 30, and during transformation to a solid phase, the quality of the shape of the joint part 30 deteriorates due to an increase in the expansion coefficient, and cracks or the like occur in the joint part 30.

[0071] On the other hand, the average hardness of the first plated steel sheet 10 and the average hardness of the second plated steel sheet 20 are also different from each other. Further, the average hardness of the joint part 30 is also greater than the average hardness of the first plated steel sheet 10 and the average hardness of the second plated steel sheet 20. As an example, the minimum hardness value of the joint part 30 is greater than the maximum hardness value of the first plated steel sheet 10 and the second plated steel sheet 20.

[0072] Further, when the aluminum-based plating blank 100 is heated to a temperature above Ac3, press-formed, and then cooled at a cooling rate of 10 to 500 °C / s to 300 °C or lower to perform hot stamping forming, the average hardness of the joint part 30 is greater than the average hardness values of the first base iron 12 and the second base iron 22.

[0073] Among the strength and thickness, one or more of the first plated steel sheet 10 and the second plated steel sheet 20 are different from each other. In that case, when the first plated steel sheet 10 and the second plated steel sheet 20 are joined, the amount of components dissolved from the first plating layer 14 and the second plating layer 24 into the joint part 30 also differs depending on the strength and thickness of the first plated steel sheet 10 and the second plated steel sheet 20. On the other hand, in order to prevent ferrite from being formed in the joint part 30 at a temperature above the Ac3 temperature, when the first plated steel sheet 10 and the second plated steel sheet 20 are joined, the filler wire 200 takes into account the components dissolved from the first plating layer 14 and the second plating layer 24, and varies the content of those components. As a result, the content of austenite stabilizing elements contained in the joint part 30 is different.

[0074] For example, when the first plated steel sheet 10 has a first thickness T1 and a first strength, and the second plated steel sheet 20 has a second thickness T2 and a second strength, if the difference between the product of the first strength and the first thickness T1 and the product of the second strength and the second thickness T2 is 500 MPa·mm or less, the joint part 30 contains 0.25 wt% or more and 0.4 wt% or less of carbon (C) and 1.5 wt% or more and 2.5 wt% or less of manganese (Mn).

[0075] Further, when the difference between the product of the first strength and the first thickness T1 and the product of the second strength and the second thickness T2 is greater than 500 MPa·mm and 1000 MPa·mm or less, the joint part 30 contains 0.2 wt% or more and 0.3 wt% or less of carbon (C) and 1.0 wt% or more and 2.0 wt% or less of manganese (Mn).

[0076] When the difference between the product of the first strength and the first thickness T1 and the product of the second strength and the second thickness T2 is greater than 1000 MPa·mm, the joint part 30 contains carbon (C) of 0.1 wt% or more and 0.25 wt% or less, and manganese (Mn) of 0.8 wt% or more and 1.5 wt% or less.

[0077] That is, as the difference between the product of the first strength and the first thickness T1 and the product of the second strength and the second thickness T2 increases, the contents of carbon (C) and manganese (Mn) contained in the joint part 30 decrease. When the above range is satisfied, at the hot stamping heating temperature, the joint part 30 exists as a full austenite structure, and thereafter, during cooling, it can be transformed into a martensite structure with an area fraction of 90% or more, preferably a full martensite structure.

[0078] On the other hand, after heating the aluminum-based plated blank 100 as described above to a temperature above Ac3, press forming is performed, and then it is cooled at an average cooling rate of 10 to 500 °C / s to a temperature of 300 °C or lower to form a hot stamping member. Among the formed hot stamping members, the portions corresponding to the first and second plated steel sheets 10, 20 and the joint part 30 of the blank 100 have a higher tensile strength than the first and second plated steel sheets 10, 20 and the joint part 30 of the blank 100. In particular, the joint part 30 of the blank 100 can have a fine structure containing martensite with an area fraction of 90% or more.

[0079] Hereinafter, with reference to FIGS. 2 and 3, a method for manufacturing an aluminum-based plated blank will be described.

[0080] The method for manufacturing the aluminum-based plated blank 100 according to an embodiment of the present invention includes a step of arranging the edges of the first plated steel sheet 10 and the second plated steel sheet 20 to face each other, and a joining step of providing a filler wire 200 at the boundary between the first plated steel sheet 10 and the second plated steel sheet 20 and irradiating a laser beam 310 to form a joint part 30 that connects the first plated steel sheet 10 and the second plated steel sheet 20.

[0081] The side surface of the first plated steel sheet 10 and the side surface of the second plated steel sheet 20 are arranged to face each other. At this time, the side surface of the first plated steel sheet 10 and the side surface of the second plated steel sheet 20 can be in contact with each other.

[0082] At the boundary between the first plated steel sheet 10 and the second plated steel sheet 20, a filler wire 200 is provided, and a laser beam 310 is irradiated from a laser head 300 to form a joint part 30 that connects the first plated steel sheet 10 and the second plated steel sheet 20 at the boundary between the first plated steel sheet 10 and the second plated steel sheet 20.

[0083] The joint part 30 is formed by melting the first plated steel sheet 10, the second plated steel sheet 20, and the filler wire 200 by the laser beam 310. During this process, the components of the first plating layer 14 of the first plated steel sheet 10 and the second plating layer 24 of the second plated steel sheet 20 are dissolved into the joint part 30. Therefore, the composition of the filler wire 200 must be determined in consideration of the dissolution of the components of the first plating layer 14 and the second plating layer 24 during laser welding.

[0084] In a specific example, the filler wire 200 contains an austenite stabilizing element. For example, the austenite stabilizing element contains one or more of carbon (C) and manganese (Mn). Such a filler wire 200 can be dissolved into the joint part 30 to adjust the component system of the joint part 30.

[0085] Specifically, even if aluminum (Al) in the first plating layer 14 and the second plating layer 24 is mixed into the molten pool of the joint part 30, the microstructure of the joint part 30 has a martensite structure with an area fraction of 90% or more, preferably a full martensite structure, after hot stamping due to the austenite stabilizing element added to the filler wire 200. That is, according to the present invention, without removing the first plating layer 14 and the second plating layer 24, even if the components of the first plating layer 14 and the second plating layer 24 are mixed into the joint part 30, it is possible to prevent a decrease in the hardness and strength of the joint part 30 and prevent a fracture phenomenon of the joint part 30.

[0086] On the one hand, at least one of the strength and thickness of the first plated steel sheet 10 and the second plated steel sheet 20 may be different from each other. In that case, when the first plated steel sheet 10 and the second plated steel sheet 20 are joined, the amount of components dissolved from the first plating layer 14 and the second plating layer 24 into the joint portion 30 may also be different from each other depending on the strength and thickness of the first plated steel sheet 10 and the second plated steel sheet 20. In such a case, the contents of carbon (C) and manganese (Mn) contained in the filler wire 200 may also be different from each other depending on the strength and thickness of the first plated steel sheet 10 and the second plated steel sheet 20.

[0087] For example, when the first plated steel sheet 10 has a first thickness T1 and a first strength, and the second plated steel sheet 20 has a second thickness T2 and a second strength, if the difference between the product of the first strength and the first thickness T1 and the product of the second strength and the second thickness T2 is 500 MPa·mm or less, the filler wire 200 contains 0.5 wt% or more and 0.9 wt% or less of carbon (C) and 2.5 wt% or more and 4.5 wt% or less of manganese (Mn).

[0088] Also, when the difference between the product of the first strength and the first thickness T1 and the product of the second strength and the second thickness T2 is greater than 500 MPa·mm and 1000 MPa·mm or less, the filler wire 200 contains 0.4 wt% or more and 0.9 wt% or less of carbon (C) and 1.5 wt% or more and 4.5 wt% or less of manganese (Mn).

[0089] Also, when the difference between the product of the first strength and the first thickness T1 and the product of the second strength and the second thickness T2 is greater than 1000 MPa·mm, the filler wire 200 contains 0.3 wt% or more and 0.9 wt% or less of carbon (C) and 0.3 wt% or more and 4.5 wt% or less of manganese (Mn).

[0090] In this way, due to the difference in the product of the strength and thickness between the first plated steel sheet 10 and the second plated steel sheet 20, the contents of carbon (C) and manganese (M) contained in the filler wire 200 are contained differently as described above. As a result, the contents of carbon (C) and manganese (M) contained in the joint portion 30 are adjusted. As a result, at the hot stamping heating temperature, the joint portion 30 exists as a full austenite structure, and thereafter, it can be transformed into a martensite structure with an area fraction of 90% or more during cooling, desirably, a full martensite structure.

[0091] On the other hand, even if the components dissolved in the first and second plating layers 14 and 24 are diluted by the filler wire 200, the components of the filler wire 200 and the first and second plating layers 14 and 24 cannot be uniformly distributed in the first and second base iron 12 and 14 components depending on the joining conditions. In order to prevent this, when joining the first and second plated steel sheets 10 and 20, the laser beam 310 can be irradiated so as to form a pattern at a predetermined angle with respect to the forming direction of the joint portion 30.

[0092] In one specific example, in the pattern, when the laser beam 310 is irradiated, one or more of the first and second plated steel sheets 10 and 20 and the laser head 300 move.

[0093] For example, the laser beam 310 moves in a pattern at a predetermined angle with respect to the direction in which the joint portion 30 is formed, and the filler wire 200 and the first and second plated steel sheets 10 and 20 can be melted to form the joint portion 30.

[0094] In addition, the joint portion 30 is irradiated while the laser beam 310 moves in a pattern, and one or more of the first and second plated steel sheets 10 and 20 and the laser head 300 move. In this specification, the "relative movement" means that one or more of the first and second plated steel sheets 10 and 20 and the laser 300 head move. Desirably, the first and second plated steel sheets 10 and 20 can be stopped and the laser head 300 can move to form the joint portion 30.

[0095] As an example, FIG. 2 is a drawing schematically showing a process in which the first and second plated steel plates 10 and 20 perform a pattern movement to form a joint portion 30. Referring to FIG. 2, the laser head 300 is fixed, and the filler wire 200 is supplied toward the opposing portions of the first and second plated steel plates 10 and 20, and the laser beam 310 can be irradiated. On the other hand, the first and second plated steel plates 10 and 20 move parallel to the opposite direction D1 with respect to the direction Y2 in which the joint portion 30 is formed, and perform a pattern movement so that the movement path Y1 of the laser beam 310 forms a predetermined angle with the forming direction Y2 of the joint portion 30, and the laser beam 310 is irradiated to form the joint portion 30.

[0096] As another example, FIG. 3 is a drawing schematically showing a process in which the laser head 300 moves to form the joint portion 30. Referring to FIG. 3, the first and second plated steel plates 10 and 20 are fixed, and the filler wire 200 is supplied toward the opposing portions of the aluminum-based plated steel plates 10 and 20, and the laser head 300 moves and the laser beam 310 can be irradiated. At this time, the laser head 300 moves parallel to the same direction D2 as the forming direction Y2 of the joint portion 30, and performs a pattern movement so that the movement path Y1 of the laser beam 310 forms a predetermined angle with the forming direction Y2 of the joint portion 30, and the laser beam 310 is irradiated to form the joint portion 30. The laser beam 310 can perform a pattern movement at 45° or more and less than 90° with respect to the joint portion forming direction Y2.

[0097] In FIG. 3, the laser beam 310 can move in a direction different from the movement direction D2 of the laser head 300. Desirably, the movement direction of the laser beam 310 can form a certain angle with the movement direction D2 of the laser head 300.

[0098] As an example, the moving direction of the laser beam 310 is also a direction perpendicular to the moving direction D2 of the laser head 300. In an alternative embodiment, the laser beam 310 can be pattern-moved at an angle of 45° or more and less than 90° with respect to the moving direction D2 of the laser head 300.

[0099] As a result, the laser beam 310 can be irradiated while pattern-moving at a predetermined angle with the forming direction Y2 of the joint portion. Therefore, not only is the moving length of the laser beam 310 on the surfaces of the first and second plated steel sheets 10 and 20 longer than when the laser beam 310 is irradiated in the same direction as the joint portion forming direction Y2, and the area for transmitting the energy of the laser beam 310 to the first and second plated steel sheets 10 and 20 becomes wider, but also where the region where energy is transmitted by the moving path Y1 of the laser beam 310 and the radius size of the laser beam 310 can be overlapped, the components of the first and second plating layers 14 and 24 and the component of the filler wire 200 can be sufficiently diluted with the components of the first and second base irons 12 and 14 to form the joint portion 30.

[0100] In one specific example, the laser beam 310 also has a frequency of 100 to 1500 Hz and a power of 1 to 20 kW. In one specific example, the power of the laser beam 310 can mean the output value of the laser oscillation unit, and the frequency of the laser beam 310 can mean the frequency of the pattern movement of the laser beam 310.

[0101] In a specific example, when manufacturing the aluminum-based plating blank 100, the forming speed of the joint part 30 should be 1 m / min or more, the laser frequency should be 1500 Hz or less, and the laser beam 310 power should be 20 kW or less in order to ensure the minimum productivity and business viability. The higher the laser frequency and the laser beam 310 power, the better. However, to achieve frequencies exceeding 1500 Hz and powers exceeding 20 kW, high-performance equipment is required, which leads to problems such as an increase in equipment size and equipment cost. Also, to ensure the minimum productivity, it is necessary to maintain the forming speed of the joint part 30 at 1 m / min or more. The forming speed of the joint part 30 means the displacement per unit time when the laser head 300 moves relative to the joint part forming direction Y2 in parallel.

[0102] In a specific example, the forming speed of the joint part 30 is also 1 to 10 m / min. When the forming speed of the joint part 30 exceeds 10 m / min, even if the laser beam 310 is irradiated under the conditions of a frequency of 100 to 1500 Hz, a power of 1 to 20 kW, and a beam radius of 0.1 to 1.0 mm, the angle between the moving path Y1 of the laser beam 310 and the direction Y2 in which the joint part 30 is formed increases. When the first and second plating layers 14, 24 and the first and second base irons 12, 22 are melted by the laser beam 310, there may be a portion where the components of the first and second plating layers 14, 24 cannot be sufficiently diluted into the components of the first and second base irons 12, 22.

[0103] In a specific example, the forming speed of the joint part 30 is 15 to 170 mm / sec. Desirably, it is also 1 to 7 m / min. Desirably, the forming speed of the joint part 30 is also 15 to 120 mm / sec.

[0104] In one specific example, the radius of the laser beam 310 is also 0.1 to 1.0 mm. In order for the radius of the laser beam 310 to exceed 1.0 mm, the distances between the filler wire 200, the first and second plating steel plates 10, 20, and the laser head 300 must be close. However, in such a case, when the space where the filler wire 200 is supplied or when the filler wire 200 is consumed, the space for replacing it is not sufficient, and the manufacturing process efficiency will decrease. On the other hand, when the radius of the laser beam 310 is less than 0.1 mm, as shown in FIG. 4, there may be a region (S) where the laser beam 310 is not irradiated. Referring to FIG. 4, when the radius of the laser beam is less than 0.1 mm, even if the laser beam is irradiated under the conditions of a frequency of 100 to 1500 Hz and a power of 1 to 20 kW, due to the small radius of the laser beam, there may be a region (S) where the laser beam 310 is not irradiated.

[0105] On the other hand, if the frequency of the laser beam 310 is less than 100 Hz, the interval between the spots of the laser beam 310 increases. Therefore, even when satisfying the conditions of a laser beam power of 1 to 20 kW, a radius of the laser beam 310 of 0.1 to 1.0 mm, and a joint part 30 forming speed of 1 to 7 m / min, when irradiating the laser beam 310, there may be a portion where the components of the first and second plating layers 14, 24 cannot be sufficiently diluted into the components of the first and second base irons 12, 22.

[0106] Also, when the power of the laser beam 310 is less than 1 kW, even when satisfying the conditions of a frequency of the laser beam 310 of 100 to 1500 Hz, a radius of the laser beam 310 of 0.1 to 1.0 mm, and a forming speed of the joint part 30 of 1 to 7 m / min, even if irradiating the laser beam 310 due to insufficient energy transmitted to the first and second plating steel plates 10, 20, there may be a portion where the components of the first and second plating layers 14, 24 cannot be sufficiently diluted into the components of the first and second base irons 12, 22.

[0107] As a selective embodiment, when irradiating the laser beam 310, the first laser beam and the second laser beam separated from each other can be irradiated. For example, the first laser beam melts the filler wire 200, the first and second plating layers 14, 24, and the first and second base steels 12, 22, and the second laser beam maintains the melted state, and uniform stirring of the melted part is performed to prevent the occurrence of segregation in the joint part 30, and it is also excellent in quality and mechanical physical properties. On the other hand, when using the first laser beam and the second laser beam, the sum of the powers of the first laser beam and the second laser beam is also 1 to 20 kW.

[0108] On the other hand, when the aluminum-based plating blank 100 is joined within the above-described laser beam power, radius, frequency, and the forming speed range of the joint part 30, and then heat treatment of heating at a high temperature and quenching is performed, the average hardness of the joint part 30 is also equal to or higher than the average hardness of the first and second plating steel sheets 10, 20. Desirably, the minimum hardness of the joint part 30 is also equal to or higher than the average hardness of the first and second plating steel sheets 10, 20. When the average hardness of the joint part 30 is less than the average hardness of the first and second plating steel sheets 10, 20, when a tensile force is applied to the heat-treated blank 100, there is a possibility of breakage occurring in the joint part 30. In a specific example, when the aluminum-based plating blank 100 is heated to Ac3 or higher and press-formed, and cooled at a cooling rate of 10 to 500 °C / s to 300 °C or lower for hot stamping forming, the average hardness of the joint part 30 is equal to or higher than the average hardness of the first and second plating steel sheets 10, 20.

[0109] In a specific example, the forming speed of the joint part 30 is 15 to 120 mm / sec. At this time, the frequency of the laser beam 310, the radius of the laser beam 310, and the forming speed of the joint part 30 satisfy the relationship of the following formula 1:

Equation

[0110] (In the above formula 1, α is 0.7, f is the frequency (Hz) of the laser beam, r is the radius (mm) of the laser beam measured on the surface of the aluminum-based plated steel sheet, and v is the forming speed (mm / sec) of the joint part).

[0111] Even if the frequency, power, radius of the laser beam 310 of the above formula 1 and the forming speed of the joint part 310 are controlled, in order to ensure sufficient tensile strength of the joint part 30, the segregation area fraction of aluminum (Al) must be reduced. For this purpose, not only the frequency, power, radius of the laser beam 310 and the forming speed of the joint part 30, but also the energy loss generated while the laser beam 310 is irradiated from the laser head 300 and transmitted to the first and second plated steel sheets 10, 20, the thermal reflectivity of the first and second plating layers 14, 24, the thermal conductivity of the first and second plated steel sheets 10, 20, the thicknesses of the first and second base irons 12, 22, and the thicknesses of the first and second plating layers 14, 24, etc. must be considered.

[0112] Also, when controlling the radius of the laser beam 310, the energy density on the surfaces of the first and second plated steel sheets 10, 20 must be considered, and the movement path of the laser beam 310 on the surfaces of the first and second plated steel sheets 10, 20 determined by the frequency of the laser beam 310 and the forming speed of the joint part 300 must also be considered to uniformly transmit energy to the joint part 30.

[0113] Therefore, the inventor has derived the conditions under which sufficient tensile strength of the joint part 30 can be ensured only by using the correction coefficient (α) considering the above-mentioned various situations through excessive repeated experiments, with the frequency and radius of the laser beam 310 and the forming speed of the joint part 30.

[0114] When the conditions according to Formula 1 are satisfied, the aluminum (Al) segregation fraction can be reduced to 5% or less. However, at this time, the forming speed of the joint portion 30 is desirably 1 to 7 m / min, and more desirably, it is also 15 to 120 mm / sec. When the forming speed of the joint portion 30 is high, there is a problem that the time for uniformly transmitting energy to the joint portion 30 is insufficient. For example, under the forming speed condition of the joint portion 30 of 120 to 170 mm / s, even if Formula 1 is satisfied, excessive Al segregation in the joint portion may occur.

[0115] On the other hand, even if the aluminum (Al) segregation area fraction of the joint portion 30 satisfies 5% or less, when aluminum (Al) segregation occurs at the interface between the joint portion 30 and the first and second base steels 12 and 22, there is a high possibility of breakage occurring at the interface of the joint portion 30, specifically, at the interface of the joint portion 30 and the first and second plated steel sheets 10 and 20.

[0116] In a specific example, when the pattern angle of the laser beam 310 is implemented at 45° or more and less than 90°, the occurrence of aluminum (Al) segregation at the interface between the joint portion 30 and the first and second plated steel sheets 10 and 20 can be prevented. The pattern angle means the angle formed by the forming direction Y2 of the joint portion 30 and the moving path Y1 of the laser beam on the surfaces of the first and second plated steel sheets 10 and 20 when the joint portion 30 is formed.

[0117] FIG. 5 is a cross-sectional view schematically showing an aluminum-based blank manufacturing apparatus according to an embodiment of the present invention.

[0118] Referring to FIG. 5, an aluminum-based plating blank manufacturing apparatus 1000 includes a laser oscillation unit 500 that generates a laser light source, a steel plate loading unit 400 where two or more aluminum-based plated steel plates are arranged such that the edges of one plated steel plate face the edges of another plated steel plate, a wire supply unit 210 that supplies a filler wire 200 for forming a joint portion of the plated steel plates, and a laser head 300 that irradiates laser beams to the opposing portions of the aluminum-based plated steel plates and the supplied filler wire using the laser light source supplied from the laser oscillation unit 500.

[0119] In one specific example, the laser head 300 is fastened to a robot arm 320 and can move in a direction opposite to the direction in which the joint portion is formed.

[0120] In one specific example, the aluminum-based plated steel plates can be moved in the same direction as the direction in which the joint portion is formed using the steel plate loading unit 400.

[0121] When joining the steel plates, the laser beams are irradiated and joined so as to form a pattern at a predetermined angle with respect to the formation direction of the joint portion. The laser beams have a frequency of 100 to 1500 Hz and a power of 1 to 20 kW. The formation speed of the joint portion is 1 to 10 m / min, preferably 15 to 170 mm / sec.

[0122] The aluminum-based plated steel plates are also the aforementioned first and second plated steel plates (10 and 20 in FIG. 1).

[0123] In one specific example, the pattern is formed by one or more of the plated steel plates and the laser beams in the steel plate loading unit moving in a pattern.

[0124] Hereinafter, the configuration and operation of the present invention will be described in more detail through desirable embodiments of the present invention. However, this is presented as a desirable exemplification of the present invention and should not be construed as limiting the present invention in any way.

Example

[0125] Examples and Comparative Examples Example 1 Base iron containing 0.01 to 0.5 wt% carbon (C), 0.01 to 1.0 wt% silicon (Si), 0.5 to 3.0 wt% manganese (Mn), more than 0 and 0.05 wt% or less phosphorus (P), more than 0 and 0.01 wt% or less sulfur (S), more than 0 and 0.1 wt% or less aluminum (Al), more than 0 and 0.001 wt% or less nitrogen (N), and the balance iron (Fe) and other inevitable impurities; and a plating layer containing aluminum (Al) formed on at least one surface of the base iron in an adhesion amount of 20 to 100 g / m 2 Two or more aluminum-based plated steel sheets having different strengths and thicknesses from each other were prepared. The plating layers of the aluminum-based plated steel sheets were each formed on the surface of the base iron, and included a surface layer containing 80 wt% or more aluminum (Al); and an alloying layer formed between the surface layer and the base iron, containing aluminum-iron (Al-Fe) and aluminum-iron-silicon (Al-Fe-Si) intermetallic compounds and containing 20 to 70 wt% iron (Fe).

[0126] Then, at the steel sheet loading part of the manufacturing apparatus of the aluminum-based plated blank as shown in FIG. 5, the edges of one plated steel sheet and the edges of another plated steel sheet among the two or more aluminum-based plated steel sheets were arranged to face each other. Then, a filler wire was provided from a wire supply part to the parts where the aluminum-based plated steel sheets faced each other, and a laser beam was irradiated to melt the parts where the aluminum-based plated steel sheets faced each other and the filler wire to form a joint part, thereby manufacturing an aluminum-based plated blank.

[0127] When joining the steel plates, laser beams were irradiated and joined so as to form a pattern at a predetermined angle with respect to the forming direction of the joint part. Specifically, while the laser head moved parallel in the same direction as the joint part forming direction, the laser beam was irradiated while performing a pattern movement at 60° with respect to the joint part forming direction. Further, the laser beam was irradiated at a frequency of 100 Hz, a beam power of 1 kW, and a beam radius of 0.1 mm, and the joint part was formed at a forming speed of 1 m / min.

[0128] Table 1 below shows the difference in the product of the strength and thickness of two plated steel plates connected by a joint part, and the judgment result of the joint part during the tensile test of an aluminum-based plated blank based on the contents of carbon (C) and manganese (M) contained in the filler wire.

Table 1

[0129] When the products of the strength and thickness of two plated steel plates connected by a joint part are different from each other, a difference occurs in the amount of components dissolved in the joint part during laser irradiation. Therefore, in order for the joint part to exist as a full austenite structure at the hot stamping heating temperature and then transform into a martensite structure with an area fraction of 90% or more, preferably a full martensite structure during cooling, the contents of carbon (C) and manganese (M) contained in the filler wire can be adjusted differently depending on the difference in the product of the strength and thickness of the two plated steel plates.

[0130] As can be seen from Table 1 above, when the difference in the product of the strength and thickness of the two plated steel sheets is 500 MPa·mm or less, the filler wire contains 0.5 wt% to 0.9 wt% carbon (C) and less than 2.5 wt% to 4.5 wt% manganese (Mn). When the difference in the product of the strength and thickness of the two plated steel sheets is greater than 500 MPa·mm and 1000 MPa·mm or less, the filler wire contains 0.4 wt% to 0.9 wt% carbon (C) and 1.5 wt% to 4.5 wt% manganese (Mn). When the difference in the product of the strength and thickness of the two plated steel sheets is greater than 1000 MPa·mm, the filler wire 200 contains 0.3 wt% to 0.9 wt% carbon (C) and 0.3 wt% to 4.5 wt% manganese (Mn), and the occurrence of fracture in the joint part can be prevented.

[0131] This is because, depending on the difference in the product of the strength and thickness of the two plated steel sheets, when the filler wire contains carbon (C) and manganese (M) within the above ranges, the joint part formed also has different contents of carbon (C) and manganese (M) depending on the difference in the product of the strength and thickness of the two plated steel sheets. At this time, even if the components of the first plating layer and the second plating layer are mixed into the joint part due to the contents of carbon (C) and manganese (M) contained in the joint part, it is possible to prevent a decrease in the hardness and strength of the joint part, and the fracture phenomenon of the joint part is prevented.

[0132] That is, when the difference in the product of the strength and thickness of the two plated steel sheets to be joined is 500 MPa·mm or less, the joint part contains 0.25 wt% to 0.4 wt% carbon (C) and 1.5 wt% to 2.5 wt% manganese (Mn). When the difference in the product of the strength and thickness of the two plated steel sheets is greater than 500 MPa·mm and 1000 MPa·mm or less, the joint part contains 0.2 wt% to 0.3 wt% carbon (C) and 1.0 wt% to 2.0 wt% manganese (Mn). When the difference in the product of the strength and thickness of the two plated steel sheets is greater than 1000 MPa·mm, the joint part contains 0.1 wt% to 0.25 wt% carbon (C) and 0.8 wt% to 1.5 wt% manganese (Mn). At the hot stamping heating temperature, the joint part exists as a full austenite structure, and thereafter, during cooling, it can be transformed into a martensite structure with an area fraction of 90% or more, preferably a full martensite structure.

[0133] Examples 2 to 16 and Comparative Examples 1 to 12 An aluminum-plated blank was produced in the same manner as in Example 1, except that an aluminum-plated steel sheet was joined by applying the laser beam power, beam radius, frequency, and joint formation speed conditions shown in Table 2 below.

[0134] Experimental Example (1) Hardness Test: After producing three specimens of the aluminum-plated blanks of Examples 1 to 16 and Comparative Examples 1 to 12 respectively, each specimen was heated to a temperature above the austenite single-phase region temperature (Ac3 or higher) and cooled at a cooling rate of 10 to 500 °C / s to 300 °C or lower. Then, the average hardness values of the joint parts of the aluminum-plated blanks and the aluminum-plated steel sheets were measured. Here, the hardness was measured by the Vickers hardness test method for metallic materials (load: 300 g). When the minimum hardness of the joint part was equal to or higher than the average hardness of the base iron, it was judged as Pass; when it was lower than the average hardness, it was judged as Fail. The results are shown in Table 2 below. Also, the minimum hardness of the joint part was the minimum value among the hardness values of the joint part measured at five points spaced at regular intervals, and the average hardness of the base iron was the average value of the hardness values of the base iron measured at five points spaced at regular intervals.

Table 2

[0135] Hereinafter, in the present invention, "energy density" is assumed to be "the value obtained by dividing the beam power P (kW) of the laser oscillator by the laser beam area on the steel sheet surface JPEG2025093977000007.jpg4132 (where r is the radius of the laser beam)".

[0136] From the results in Table 2 above, it was found that in the case of Examples 1 to 16 that satisfy the irradiation of the laser beam and the joint formation speed of the present invention, the minimum hardness of the joint part is equal to or higher than the average hardness of the base iron.

[0137] On the one hand, in the cases of Comparative Examples 1, 2, 7, and 8, although the energy density is sufficient, even if the joint formation speed is minimized, due to the small radius of the laser beam, when the plating layer of the aluminum-plated steel sheet and the base iron are melted by the laser beam, there are portions where the components of the plating layer cannot be sufficiently diluted into the base iron components, and the minimum hardness of the joint was formed to be less than the average hardness of the base iron.

[0138] In the cases of Comparative Examples 3, 4, 9, and 10, even when the laser beam radius value was maximized (1.0 mm) and the joint formation speed was minimized (1 m / min), due to the low frequency, the interval of the laser beam movement path became large. When the plating layer of the aluminum-plated steel sheet and the base iron were melted by the laser beam, there were portions where the components of the plating layer could not be sufficiently diluted into the base iron components, and the minimum hardness of the joint was formed to be less than the average hardness of the base iron.

[0139] Also, in the cases of Comparative Examples 5, 6, 11, and 12, although the energy density was sufficient and the beam radius was also maximized, the speed was very fast, the interval of the laser beam movement path became large. When the plating layer of the aluminum-plated steel sheet and the base iron were melted by the laser beam, there were portions where the components of the plating layer could not be sufficiently diluted into the base iron components, and the minimum hardness of the joint was formed to be less than the average hardness of the base iron.

[0140] Examples 17 to 68 and Comparative Examples 13 to 52 An aluminum-based plated steel sheet was joined by applying the laser beam power, beam radius, frequency, joint formation speed according to Tables 3 to 6 below and the conditions according to Equation 1 below. The aluminum-based plating blank was manufactured in the same manner as in Example 1, except that the laser head moved parallel in the same direction as the joint formation direction, and the laser beam was irradiated while performing a 45° pattern movement with respect to the joint formation direction.

Number

[0141] (In the formula (1), α is 0.7, f is the frequency (Hz) of the laser beam, r is the radius (mm) of the laser beam measured on the surface of the aluminum-based plated steel sheet, and v is the forming speed (mm / sec) of the joint portion).

[0142] Experimental Example (2) Aluminum (Al) segregation fraction (%) and tensile test of the joint portion: After manufacturing three blank specimens each of the Examples 17 to 68 and Comparative Examples 13 to 52, each specimen was heated to a temperature above the austenite single-phase region temperature (Ac3 or higher) and cooled at a cooling rate of 10 to 500 °C / s to 300 °C or lower. Next, the aluminum segregation area fraction and tensile test of the joint portion of each specimen were carried out, and the results are shown in Tables 3 to 6 below. Specifically, the measurement of the area fraction of aluminum (Al) segregation in the joint portion is shown as the average value of the Al segregation area fractions of three specimens, and the tensile test results are indicated as Pass when none of the three specimens break at the joint portion after applying a tensile force to the specimen, and Fail when breakage occurs one or more times from the joint portion. [Table 3]

[0143] [Table 4]

[0144] [Table 5]

[0145] [Table 6]

[0146] Referring to the results in Tables 3 to 6, in the case of Examples 17 to 68 of the present invention, the conditions of Formula 1 were satisfied, the aluminum segregation area fraction of the joint part satisfied 5% or less, and no fracture occurred at the joint part in the tensile test result (PASS). However, in the case of Comparative Examples 13 to 52 that deviated from the conditions of the present invention, when the conditions of Formula 1 of the present invention were not satisfied, the aluminum segregation area fraction of the joint part exceeded 5%, and fracture occurred at the joint part during the tensile test. Further, even when Formula 1 was satisfied, when the joint part forming speed exceeded 7 m / min, the joint part forming speed was high, the laser beam could not sufficiently stir the inside of the base steel, excessive aluminum segregation occurred, and fracture occurred at the joint part during the tensile test.

[0147] Examples 69 to 98 and Comparative Examples 53 to 72 Aluminum-plated steel sheets were joined by applying the laser beam power, joint part forming speed, beam radius, and frequency according to Tables 7 and 8 below. The laser head was moved parallel to the joint part forming direction, and the laser beam was irradiated at the pattern angles of the conditions in Tables 7 and 8 below with respect to the joint part forming direction. An aluminum-plated blank was manufactured in the same manner as in Example 1 except for this. At this time, the pattern angle means the angle formed by the joint part forming direction and the moving path of the laser beam on the surface of the plated steel sheet when the joint part is formed.

[0148] Experimental Example (3) Confirmation of aluminum (Al) segregation fraction (%) of joint part, aluminum segregation at joint part interface, and presence or absence of fracture of joint part: After manufacturing three blank specimens each of Examples 69 to 98 and Comparative Examples 53 to 72, each specimen was heated to a temperature above the austenite single-phase region temperature (above Ac3) and cooled at a cooling rate of 10 to 500 °C / s to 300 °C or lower. Next, the aluminum segregation area fraction of the joint part of each specimen, the presence or absence of aluminum segregation at the joint part interface, and the tensile test results are shown in Tables 7 and 8 below. Specifically, the measurement of the area fraction of aluminum (Al) segregation of the joint part is shown as the average value of the Al segregation area fractions of three specimens, and the tensile test result is determined as × when no fracture occurs at the joint part in all three specimens after applying a tensile force to the specimen, and as ○ when fracture occurs at the joint part one or more times.

Table 7

[0149]

Table 8

[0150] On the one hand, even if the area fraction of aluminum segregation in the joint part satisfies 5% or less, when aluminum (Al) segregation occurs at the interface between the joint part and the base steel, the possibility of fracture at the interface between the joint part, specifically, the joint part and the steel plate is high. Referring to the results in Table 7 and Table 8, in the case of the examples where the pattern angle is applied at 45° or more and less than 90°, it is found that the aluminum segregation in the joint part is formed with an area fraction of 5% or less, the occurrence of aluminum (Al) segregation at the interface between the joint part and the base steel is prevented, and the fracture of the joint part during the tensile test is prevented. On the other hand, in the case of Comparative Examples 53 to 72 where the pattern angle is less than 45°, aluminum segregation occurs at the joint interface and fracture of the joint part occurs.

[0151] FIG. 6 shows a cross-section of an aluminum-based blank manufactured by a conventional method that joins with a laser beam but does not apply a laser beam at a predetermined pattern angle, and FIG. 7 is an optical micrograph showing a cross-section of the aluminum-based blank of Example 1. Referring to FIGS. 6 and 7, when applying a conventional method that does not apply a laser beam at a predetermined pattern angle, the components of the plating layer are not sufficiently diluted into the components of the base steel, and the area fraction of aluminum segregation in the joint part increases. However, in the case of Example 1, the components of the plating layer are sufficiently diluted into the components of the base steel, and the occurrence of aluminum segregation in the joint part can be minimized.

[0152] FIG. 8 is a graph showing the hardness change by part after hot stamping forming of the aluminum-based blank of Example 7, and FIG. 9 is a graph showing the hardness change by part of the aluminum-based blank of Comparative Example 5. Referring to FIGS. 8 and 9, in Example 7, after hot stamping forming, the minimum hardness of the joint part 30 was equal to or higher than the average hardness of the base iron. However, in the case of Comparative Example 5 which deviated from the conditions of the present invention, after hot stamping forming, the minimum hardness of the joint part 30 was less than the average hardness of the base iron.

[0153] FIG. 10 shows a cross section of the aluminum-based blank of Example 34, and FIG. 11 is an optical micrograph showing a cross section of the aluminum-based blank of Comparative Example 28.

[0154] Referring to FIGS. 10 and 11, the aluminum-based blank of Example 34 minimized the aluminum segregation in the joint part. However, in the case of Comparative Example 28 which deviated from the conditions of Formula 1 of the present invention, the occurrence of aluminum segregation in the joint part increased compared to Example 34.

[0155] Thus, although the present invention has been described based on one illustrated embodiment, this is merely exemplary, and those having ordinary knowledge in the art will understand that various modifications and variations of the embodiments are possible therefrom. Therefore, the true technical protection scope of the present invention must be determined by the technical idea of the claims.

Claims

1. disposing an edge portion of the first plated steel sheet and an edge portion of the second plated steel sheet so as to face each other; providing a filler wire at a boundary between the first plated steel sheet and the second plated steel sheet, and irradiating a laser beam from a laser head to melt the first plated steel sheet, the second plated steel sheet, and the filler wire to form a joint, The first plated steel sheet and the second plated steel sheet are plated on at least one surface of the base iron and the base iron, respectively, in a range of 20 to 100 g / m ２ and a plating layer containing aluminum, The base iron contains 0.01 to 0.5 wt% carbon (C), 0.01 to 1.0 wt% silicon (Si), 0.5 to 3.0 wt% manganese (Mn), more than 0 and not more than 0.05 wt% phosphorus (P), more than 0 and not more than 0.01 wt% sulfur (S), more than 0 and not more than 0.1 wt% aluminum (Al), more than 0 and not more than 0.001 wt% nitrogen (N), with the balance being iron (Fe) and other unavoidable impurities, The steel sheets are joined by irradiating a laser beam such that a pattern angle is formed between a direction in which the joint portion is formed and a moving path of the laser beam on each surface of the plated steel sheet; The pattern angle is equal to or greater than 45° and less than 90°, The laser beam has a frequency of 100 to 1500 Hz and a power of 1 to 20 kW, and the forming speed of the joint portion is 15 to 170 mm / sec. The radius of the laser beam is greater than 0.5 mm and less than 1 mm; A method for manufacturing an aluminum-based plated blank, wherein the frequency of the laser beam, the radius of the laser beam, and the joint forming speed satisfy the relationship of the following formula 1: [0010] (In the above formula 1, α is 0.7, f is the frequency (Hz) of the laser beam, r is the radius (mm) of the laser beam measured on the surface of the aluminum-based plated steel sheet, and v is the forming speed (mm / sec) of the joint portion).

2. The method for producing an aluminum-based plated blank according to claim 1 , wherein the filler wire comprises carbon (C) and manganese (Mn).

3. The method for producing an aluminum-based plated blank according to claim 1 , wherein the pattern is formed by moving one or more of the plated steel sheet and the laser head during irradiation of the laser beam.

4. 2. The method for producing an aluminum-based plated blank according to claim 1, wherein the plating layer includes: a surface layer formed on a surface of the base iron and containing 80% by weight or more of aluminum (Al); and an alloying layer formed between the surface layer and the base iron.

5. 5. The method for producing an aluminum-based plated blank according to claim 4, wherein the alloyed layer comprises aluminum-iron (Al-Fe) and aluminum-iron-silicon (Al-Fe-Si) intermetallic compounds, and the iron (Fe) is present in an amount of 20 to 70% by weight.

6. When the aluminum-based plated blank is heated to Ac3 or higher, which is the highest temperature among the first plated steel sheet and the second plated steel sheet, press-formed, and then cooled to 300° C. or lower at a cooling rate of 10 to 500° C. / s to perform hot stamping, The method for manufacturing an aluminum-based plated blank according to claim 1, characterized in that the average hardness of the joint portion is equal to or greater than the average hardness of the base steel.

7. The method for producing an aluminum-based plated blank according to claim 6, wherein after the hot stamping, the joint portion has a microstructure containing martensite in an area ratio of 90% or more.

Images