Aluminum-plated blanks

Abstract

One embodiment of the present invention discloses an aluminum-based plated blank including: 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 a boundary between the first plated steel sheet and the second plated steel sheet.

Description

[Technical Field]

[0001] The present invention relates to an aluminum-based plated blank. [Background technology]

[0002] Vehicles use parts with various strengths. For example, parts that must absorb energy in the event of a vehicle collision or rollover require relatively low strength, while parts that must maintain their shape to ensure the survival space of passengers require high strength.

[0003] If the strength of the part that must absorb energy during a collision is too high, the impact energy cannot be properly absorbed and is instead transferred to other parts, causing problems such as excessive impact being transferred to passengers and other parts of the vehicle.

[0004] Vehicles are constantly being required to be lighter and have lower costs, which has led to the need for parts of the same vehicle to have different strengths.

[0005] Some sections of the component require high strength to protect passengers, while other sections require relatively low strength to absorb impact energy.

[0006] A typical example of such a part is the B-pillar of a passenger car. The lower part of the B-pillar requires a relatively low tensile strength, while the upper part requires a high tensile strength. The reason for the difference in strength is that the B-pillar must simultaneously have a part that must be strong enough to maintain its shape during a vehicle collision (the upper part, which must support the roof in the event of a rollover), and a part that must crush and absorb the impact (the lower part, which is more likely to be hit by a side collision with another vehicle).

[0007] Additionally, the upper part of the B-pillar must maintain its shape to ensure a stable space that prevents passenger injury, so it requires high strength. If the upper part of the B-pillar does not have sufficient strength, the roof will be crushed if the vehicle rolls over, posing a major threat to passenger safety. However, the lower part of the B-pillar must absorb impact energy while deforming, so it requires relatively low strength. If the lower part of the B-pillar also had high strength, the impact energy would not be absorbed in the event of a side collision, and would instead be transferred to other structural materials.

[0008] The specific strength requirements vary depending on the type and configuration of the vehicle, but for the upper B-pillar, a tensile strength of approximately 1,350 MPa or more is required, while for the lower B-pillar, a tensile strength of approximately 450 MPa or more but less than approximately 1,350 MPa is required.

[0009] Previously, a part was formed using a low-strength material, and then a separate reinforcing material was attached to the parts that required high strength. However, when different strengths were required in different sections of a part, a material with excellent hardening ability (or a thick material) was used for the upper part, and a material with low strength and low hardening ability (or a thin material) was used for the lower part. The materials were then joined with a laser to create a blank, which was then subjected to a hot stamping process to create the final product.

[0010] On the other hand, a tailored welded blank (TWB) is a component manufactured by joining two or more steel sheets that differ in at least one of material quality and thickness. The steel sheets for such TWBs have an Al-Si plating layer on the surface.

[0011] However, when plated steel sheets are joined with a laser, the components of the plating layer dissolve into the molten pool at the joint, resulting in a joint with different physical properties from the base material.If the plating layer is aluminum-silicon (Al-Si) or zinc (Zn), the plating components are mixed into the joint during laser joining, causing a decrease in mechanical properties.

[0012] Therefore, although the decrease in strength of the joint can be solved or minimized depending on the composition of the filler wire, problems such as segregation can occur when the mixed plating layer component (Al) is not uniformly diluted with the base material depending on the material (e.g., material with a high plating coverage) and joining conditions (e.g., high joining speed), and the effect of the filler wire composition alone is insufficient.

[0013] The background art related to the present invention is disclosed in Korean Patent Publication No. 10-1637084 (published on July 6, 2016, title of invention: Filler wire and method for manufacturing tailored welded blanks using the same). Summary of the Invention [Problem to be solved by the invention]

[0014] The problem to be solved by the present invention is to provide an aluminum-based plated blank that minimizes deterioration in hardness and physical properties of a blank joint.

[0015] Another problem to be solved by the present invention is to provide an aluminum-based plated blank that can prevent defects such as segregation from occurring in the joint portion of the blank.

[0016] Another object of the present invention is to provide an aluminum-based plated blank that can minimize deterioration in physical properties of a blank joint after a hot stamping process.

[0017] Another problem to be solved by the present invention is to provide a method for producing the aluminum-based plated blank. [Means for solving the problem]

[0018] One embodiment of the present invention is an aluminum-based plated blank, comprising: a first plated steel sheet; a second plated steel sheet connected to the first plated steel sheet; and a joint portion located between the first plated steel sheet and the second plated steel sheet and connecting the first plated steel sheet and the second plated steel sheet; wherein each of the first plated steel sheet and the second plated steel sheet has a thickness of 20 to 100 g / m 2 and the joint portion contains aluminum (Al), and the average content of aluminum (Al) in the joint portion is 0 wt % or more and less than 0.5 wt %.

[0019] In this embodiment, the standard deviation of the aluminum (Al) content of the joint portion is equal to or greater than 0 and equal to or less than 0.45.

[0020] In this embodiment, the joint portion may include a first side portion adjacent to the first plated steel sheet, a second side portion adjacent to the second plated steel sheet, and a center portion between the first side portion and the second side portion.

[0021] In this embodiment, the standard deviation of the aluminum (Al) content of the first side portion is 0 or more and 0.4 or less.

[0022] In this embodiment, the base iron may contain carbon (C) of 0.01% to 0.5% by weight, silicon (Si) of 0.01% to 1.0% by weight, manganese (Mn) of 0.3% to 2.0% by weight, phosphorus (P) of more than 0 to 0.1% by weight, sulfur (S) of more than 0 to 0.1% by weight, the balance being iron (Fe) and other unavoidable impurities.

[0023] In this embodiment, the first plated steel sheet and the second plated steel sheet may have the same strength.

[0024] In this embodiment, the first plated steel sheet and the second plated steel sheet have different thicknesses. [Effects of the Invention]

[0025] The present invention minimizes the deterioration of hardness and physical properties of the blank joint, prevents defects such as segregation in the blank joint, and minimizes joint fractures caused by the phase transformation of segregation into Al-Fe compounds during the hot stamping process. [Brief explanation of the drawings]

[0026] [Figure 1] 1 is a cross-sectional view schematically illustrating an aluminum-based plated blank according to one embodiment of the present invention. [Figure 2] 1 is a cross-sectional view schematically illustrating an aluminum-based plated blank according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0027] The present invention can be embodied in various forms and in various modifications, and specific embodiments are illustrated in the drawings and described in detail in the detailed description. The advantages and features of the present invention, as well as methods for achieving them, will become more apparent from the following detailed description of the embodiments, taken in conjunction with the drawings. However, the present invention is not limited to the embodiments disclosed below, and may be embodied in various forms.

[0028] In the following examples, terms such as first and second are used not in a limiting sense but to distinguish one component from another.

[0029] In the following examples, the singular expression includes the plural expression unless the context clearly indicates otherwise.

[0030] In the following examples, terms such as "comprise" or "have" mean the presence of a feature or component described in the specification, and do not preclude the possibility of adding one or more other features or components.

[0031] In the following examples, when a film, region, component, or other part is said to be on or above another part, this includes not only the case where it is directly on top of the other part, but also the case where another film, region, component, or the like is interposed between them.

[0032] In the drawings, the size of elements may be exaggerated or reduced for the sake of clarity. For example, the size and thickness of each element shown in the drawings are arbitrarily shown for the sake of clarity, and the present invention is not necessarily limited to the illustrated examples.

[0033] Certain steps may be performed in a different order than that described, as different embodiments may be implemented differently. For example, two steps described in succession may be performed substantially simultaneously, or may be performed in the reverse order of that described.

[0034] 1 and 2 are cross-sectional views that schematically show an aluminum-based plated blank according to one embodiment of the present invention.

[0035] First, referring to FIG. 1 , an aluminum-based plated blank 100 according to one embodiment of the present invention may include 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 located between the first plated steel sheet 10 and the second plated steel sheet 20 to connect the first plated steel sheet 10 and the second plated steel sheet 20.

[0036] In one embodiment, the first plated steel sheet 10 may include a first base iron 12 and a first plating layer 14 formed on at least one surface of the first base iron 12, and the second plated steel sheet 20 may include a second base iron 22 and a second plating layer 24 formed on at least one surface of the second base iron 22.

[0037] In one embodiment, the first base steel 12 and the second base steel 22 may have the same composition (or alloy composition, component), and the first coating layer 14 and the second coating layer 24 may have the same composition. Alternatively, the first base steel 12 and the second base steel 22 may have different compositions, and the first coating layer 14 and the second coating layer 24 may have the same composition.

[0038] For the sake of convenience, the following description will be made on the first base iron 12, but this can also be applied to the second base iron 22 in the same manner.

[0039] In one embodiment, the first base iron 12 and the second base iron 22 may have a first alloy composition, which may include 0.01% to 0.50% by weight of carbon (C), 0.01% to 1.00% by weight of silicon (Si), 0.3% to 2.0% by weight of manganese (Mn), more than 0 and less than 0.1% by weight of phosphorus (P), more than 0 and less than 0.1% by weight of sulfur (S), and the balance being iron (Fe) and other unavoidable impurities.

[0040] The first alloy composition may further include one or more of boron (B), titanium (Ti), niobium (Nb), chromium (Cr), molybdenum (Mo), and nickel (Ni). Specifically, the first alloy composition may further include one or more of 0.0001 wt% to 0.0050 wt% of boron (B), 0.01 wt% to 0.10 wt% of titanium (Ti), 0.01 wt% to 0.10 wt% of niobium (Nb), 0.01 wt% to 0.50 wt% of chromium (Cr), 0.01 wt% to 0.50 wt% of molybdenum (Mo), and 0.01 wt% to 1.00 wt% of nickel (Ni). For example, the first plated steel sheet 10 may be understood to include the first alloy composition when it includes the first base iron 12.

[0041] The aluminum-based plated blank 100 includes a first plated steel sheet 10 and a second plated steel sheet 20 having a first alloy composition and different thicknesses, and after hot stamping the aluminum-based plated blank 100, impact energy can be absorbed in a portion of the blank. For example, the aluminum-based plated blank 100 includes a first plated steel sheet 10 and a second plated steel sheet 20 having the same composition and the same or similar strength after hot stamping but different thicknesses, and impact energy can be absorbed by the steel sheet having a smaller product of the tensile strength (MPa) and thickness (mm) of the first plated steel sheet 10 or the second plated steel sheet 20. However, the present invention is not limited thereto.

[0042] The aluminum-based plated blank 100 includes a first plated steel sheet 10 and a second plated steel sheet 20 that have a first alloy composition but different compositions and the same or different thicknesses, and after hot stamping the aluminum-based plated blank 100, impact energy can be absorbed in a portion of the blank. For example, the aluminum-based plated blank 100 may include a first plated steel sheet 10 and a second plated steel sheet 20 that have different compositions, different strengths (e.g., tensile strengths) after hot stamping, and the same thickness, or may include a first plated steel sheet 10 and a second plated steel sheet 20 that have different compositions, different strengths after hot stamping, and different thicknesses, and impact energy can be absorbed by the steel sheet that has a smaller product of the tensile strength (MPa) and thickness (mm) of the first plated steel sheet 10 or the second plated steel sheet 20. However, the present invention is not limited thereto.

[0043] Carbon (C) is a major element that determines the strength and hardness of steel and may be added to ensure the tensile strength of the steel after the hot stamping (or hot pressing) process. Carbon may also be added to ensure the hardenability of the steel. In one embodiment, carbon may be included in an amount of 0.01 wt% to 0.50 wt% of the total weight of the first base iron 12. If the carbon content of the first base iron 12 is less than 0.01 wt%, it may be difficult to achieve the mechanical strength of the present invention. On the other hand, if the carbon content of the first base iron 12 is more than 0.50 wt%, it may cause problems such as a decrease in the toughness of the steel or problems in controlling the brittleness of the steel.

[0044] Silicon (Si) may act as a ferrite stabilizer in the first base iron 12. Silicon (Si) improves softness by purifying ferrite and suppresses the formation of low-temperature carbides, thereby improving carbon enrichment in austenite. Silicon (Si) is also a key element for homogenizing the structure during hot rolling, cold rolling, and hot stamping (controlling pearlite and manganese segregation zones) and finely dispersing ferrite. In one embodiment, silicon may be included in the first base iron 12 in an amount of 0.01 wt% to 1.00 wt% based on the total weight. If the silicon content of the first base iron 12 is less than 0.01 wt%, the above-mentioned functions may not be fully achieved. On the other hand, if the silicon content of the first base iron 12 is more than 1.00 wt%, the hot rolling and cold rolling loads may increase, resulting in excessive hot-rolled red scale and reduced bondability.

[0045] Manganese (Mn) may be added to increase hardenability and strength during heat treatment. In one embodiment, manganese may be included in an amount of 0.3 wt % to 2.0 wt % of the total weight of the first base steel 12. If the manganese content of the first base steel 12 is less than 0.3 wt %, the hardenability may be insufficient, resulting in insufficient material properties (e.g., insufficient hard phase fraction) after hot stamping. On the other hand, if the manganese content of the first base steel 12 is more than 2.0 wt % of the total weight, manganese segregation or pearlite bands may result in reduced softness and toughness, which may lead to reduced bending performance and the formation of a heterogeneous microstructure.

[0046] Phosphorus (P) is an element that is prone to segregation and can also impair the toughness of steel. In one embodiment, phosphorus (P) may be contained in an amount of more than 0 to 0.1 wt% based on the total weight of the first base iron 12. When the phosphorus content of the first base iron 12 is within the above range based on the total weight, a decrease in the toughness of the steel can be prevented. On the other hand, when the phosphorus content of the first base iron 12 is more than 0.1 wt% based on the total weight, cracks can be generated during processing, and iron phosphide compounds can be formed, which can reduce the toughness of the steel.

[0047] Sulfur (S) is an element that impairs workability and physical properties. In one embodiment, sulfur may be contained in an amount of more than 0 to 0.1 wt % based on the total weight of the first base iron 12. If sulfur is contained in an amount of more than 0.1 wt % based on the total weight of the first base iron 12, hot workability may be reduced and surface defects such as cracks may occur due to the formation of large inclusions.

[0048] Boron (B) is added to ensure the hardenability and strength of the steel by ensuring a martensite structure, and may have a grain refinement effect by increasing the austenite grain growth temperature. In one embodiment, boron may be included in the first base steel 12 in an amount of 0.0001 wt % to 0.0050 wt % based on the total weight of the first base steel 12. When boron is included in the above range based on the total weight of the first base steel 12, it is possible to prevent the occurrence of hard phase grain boundary embrittlement and ensure high toughness and bendability.

[0049] Titanium (Ti) may be added to improve hardenability and material properties by forming precipitates after hot stamping heat treatment. Titanium also forms precipitate phases such as Ti(C,N) at high temperatures, which can effectively contribute to austenite grain refinement. In one embodiment, titanium may be included in the first base steel 12 in an amount of 0.01 wt.% to 0.10 wt.% based on the total weight of the first base steel 12. When titanium is included in the above range based on the total weight of the first base steel 12, continuous casting defects and coarsening of precipitates are prevented, the physical properties of the steel are easily maintained, and cracks on the steel surface are prevented or minimized.

[0050] Niobium (Nb) may be added to increase strength and toughness by reducing martensite packet size. In one embodiment, niobium may be included in an amount of 0.01 wt % to 0.1 wt % based on the total weight of the first base steel 12. When niobium is included in the above range based on the total weight of the first base steel 12, it has an excellent effect of refining the grains of the steel during hot rolling and cold rolling processes, preventing cracks in slabs and brittle fractures in products during steelmaking / continuous casting, and minimizing the formation of coarse precipitates that are harmful to steelmaking.

[0051] Chromium (Cr) may be added to improve the hardenability and strength of the steel. In one embodiment, chromium may be included in an amount of 0.01 wt % to 0.5 wt % based on the total weight of the first base steel 12. When chromium is included in the above range based on the total weight of the first base steel 12, the hardenability and strength of the steel may be improved, and an increase in production costs and a decrease in the toughness of the steel may be prevented.

[0052] Molybdenum (Mo) can contribute to improving strength by suppressing coarsening of precipitates and increasing hardenability during hot rolling and hot stamping. Molybdenum (Mo) can be included in an amount of 0.01 wt % to 0.5 wt % based on the total weight of the first base steel 12. When the molybdenum content of the first base steel 12 is within the above range based on the total weight, excellent effects of suppressing coarsening of precipitates and increasing hardenability during hot rolling and hot stamping are achieved.

[0053] Nickel (Ni) may be added to improve hardenability and strength. Nickel is also an austenite-stabilizing element, and can contribute to improving elongation by controlling austenite transformation. In one embodiment, nickel may be included in an amount of 0.01 wt % to 1.0 wt % of the total weight of the first base iron 12. If the nickel content of the first base iron 12 is less than 0.01 wt %, the above-mentioned effects may not be fully realized. If the nickel content of the first base iron 12 is more than 1.0 wt %, the toughness and cold workability may be reduced, and the manufacturing costs of the product may increase.

[0054] In one embodiment, the first and second base irons 12 and 22 may include the same composition. For example, the first and second base irons 12 and 22 may include a second alloy composition including less than 0.20 wt. % carbon.

[0055] In one embodiment, the first base iron 12 and the second base iron 22 may include a second alloy composition, which may include carbon (C) of 0.01% or more and less than 0.20% by weight, silicon (Si) of 0.01% or more and 0.8% or less by weight, manganese (Mn) of 0.8% or more and 2.0% or less by weight, phosphorus (P) of more than 0 and 0.05% by weight, sulfur (S) of more than 0 and 0.01% by weight, and the balance being iron (Fe) and other unavoidable impurities.

[0056] The second alloy composition may further include one or more of boron (B), titanium (Ti), niobium (Nb), chromium (Cr), and aluminum (Al). Specifically, the second alloy composition may selectively further include one or more of 0.0001 wt% to 0.003 wt% boron (B), 0.01 wt% to 0.1 wt% titanium (Ti), 0.01 wt% to 0.1 wt% niobium (Nb), 0.01 wt% to 0.5 wt% chromium (Cr), and 0.001 wt% to 0.1 wt% aluminum (Al). For example, when the first plated steel sheet 10 includes the first base iron 12, it can be understood that the first plated steel sheet 10 includes the second alloy composition.

[0057] In one embodiment, carbon may be contained in an amount of 0.01 wt % or more but less than 0.20 wt % based on the total weight of the first base iron 12. If the carbon content is less than 0.01 wt % based on the total weight of the first base iron 12, it may be difficult to achieve the mechanical strength of the present invention. On the other hand, if the carbon content is 0.20 wt % or more based on the total weight of the first base iron 12, problems may arise such as a decrease in the toughness of the steel or problems with controlling the brittleness of the steel.

[0058] In one embodiment, silicon may be contained in an amount of 0.01 wt % to 0.8 wt % based on the total weight of the first base iron 12. If the silicon content of the first base iron 12 is less than 0.01 wt %, it may be insufficient to perform the above-mentioned functions. On the other hand, if the silicon content of the first base iron 12 is more than 0.8 wt %, the hot rolling and cold rolling loads may increase, resulting in excessive hot-rolled red scale and reduced bondability.

[0059] In one embodiment, manganese may be included in an amount of 0.8 wt % to 2.0 wt % based on the total weight of the first base iron 12. If the manganese content is less than 0.8 wt % based on the total weight of the first base iron 12, the hardenability may be insufficient, resulting in an insufficient material quality after hot stamping (e.g., an insufficient hard phase fraction). On the other hand, if the manganese content is more than 2.0 wt % based on the total weight of the first base iron 12, manganese segregation or pearlite bands may result in reduced softness and toughness, which may cause reduced bending performance and may result in an inhomogeneous microstructure.

[0060] In one embodiment, phosphorus may be contained in an amount of more than 0 to 0.05 wt% based on the total weight of the first base iron 12. When the phosphorus content is within the above range based on the total weight of the first base iron 12, a decrease in the toughness of the steel may be prevented. On the other hand, when the phosphorus content is more than 0.05 wt% based on the total weight of the first base iron 12, cracks may be generated during processing, and iron phosphide compounds may be formed, which may decrease the toughness of the steel.

[0061] In one embodiment, sulfur may be contained in an amount of more than 0 to 0.01 wt % based on the total weight of the first base iron 12. If sulfur is contained in an amount of more than 0.01 wt % based on the total weight of the first base iron 12, hot workability may be reduced and surface defects such as cracks may occur due to the formation of large inclusions.

[0062] In one embodiment, the first base iron 12 and the second base iron 22 may include a third alloy composition including at least 0.20 wt. % carbon.

[0063] In one embodiment, the first base iron 12 and the second base iron 22 may include a third alloy composition, which may include 0.20 wt.% to 0.5 wt.% carbon (C), 0.1 wt.% to 0.8 wt.% silicon (Si), 0.3 wt.% to 2.0 wt.% manganese (Mn), more than 0 wt.% to 0.05 wt.% phosphorus (P), more than 0 wt.% to 0.01 wt.% sulfur (S), with the balance being iron (Fe) and other unavoidable impurities.

[0064] The third alloy composition may further include one or more of boron (B), titanium (Ti), niobium (Nb), chromium (Cr), molybdenum (Mo), and nickel (Ni). Specifically, the third alloy composition may selectively further include one or more of 0.001 to 0.005 wt% of boron (B), 0.01 to 0.1 wt% of titanium (Ti), 0.01 to 0.1 wt% of niobium (Nb), 0.01 to 0.5 wt% of chromium (Cr), 0.01 to 0.5 wt% of molybdenum (Mo), and 0.01 to 1.0 wt% of nickel (Ni).

[0065] In one embodiment, carbon may be contained in an amount of 0.20 wt % to 0.5 wt % based on the total weight of the first base iron 12. If the carbon content of the first base iron 12 is less than 0.20 wt %, it may be difficult to achieve the mechanical strength of the present invention. On the other hand, if the carbon content of the first base iron 12 is more than 0.5 wt %, it may cause problems such as a decrease in the toughness of the steel or problems in controlling the brittleness of the steel.

[0066] In one embodiment, silicon may be contained in an amount of 0.1 wt % to 0.8 wt % based on the total weight of the first base iron 12. If the silicon content of the first base iron 12 is less than 0.1 wt % based on the total weight of the first base iron 12, it may be insufficient to perform the above-mentioned functions. On the other hand, if the silicon content of the first base iron 12 is more than 0.8 wt % based on the total weight of the first base iron 12, the hot rolling and cold rolling loads may increase, resulting in excessive hot-rolled red scale and reduced bondability.

[0067] In one embodiment, manganese may be included in an amount of 0.3 wt % to 2.0 wt % based on the total weight of the first base iron 12. If the manganese content is less than 0.3 wt % based on the total weight of the first base iron 12, the hardenability may be insufficient, resulting in an insufficient material quality after hot stamping (e.g., an insufficient hard phase fraction). On the other hand, if the manganese content is more than 2.0 wt % based on the total weight of the first base iron 12, manganese segregation or pearlite bands may result in reduced softness and toughness, which may cause reduced bending performance and may result in an inhomogeneous microstructure.

[0068] In one embodiment, phosphorus may be contained in an amount of more than 0 to 0.05 wt% based on the total weight of the first base iron 12. When the phosphorus content is within the above range based on the total weight of the first base iron 12, a decrease in the toughness of the steel may be prevented. On the other hand, when the phosphorus content is more than 0.05 wt% based on the total weight of the first base iron 12, cracks may be generated during processing, and iron phosphide compounds may be formed, which may decrease the toughness of the steel.

[0069] In one embodiment, sulfur may be contained in an amount of more than 0 to 0.01 wt % based on the total weight of the first base iron 12. If sulfur is contained in an amount of more than 0.01 wt % based on the total weight of the first base iron 12, hot workability may be reduced and surface defects such as cracks may occur due to the formation of large inclusions.

[0070] In one embodiment, when the first plated steel sheet 10 and / or the second plated steel sheet 20 containing the second alloy composition are hot stamped, the first plated steel sheet 10 and / or the second plated steel sheet 20 after hot stamping may have a tensile strength of 450 MPa or more, preferably 450 MPa or more and less than 1350 MPa.

[0071] In one embodiment, when the first plated steel sheet 10 and / or the second plated steel sheet 20 containing the third alloy composition are hot stamped, the first plated steel sheet 10 and / or the second plated steel sheet 20 after hot stamping may have a tensile strength of 1350 MPa or more and less than 2300 MPa, desirably 1350 MPa or more and less than 1680 MPa. Alternatively, the first plated steel sheet 10 and / or the second plated steel sheet 20 after hot stamping may have a tensile strength of 1680 MPa or more, desirably 1680 MPa or more and less than 2300 MPa.

[0072] In one embodiment, the first plated steel sheet 10 and the second plated steel sheet 20 may have different thicknesses, but the present invention is not limited thereto.

[0073] In one embodiment, the first base iron 12 and the second base iron 22 may have different compositions. In one embodiment, the first base iron 12 may have a second alloy composition containing less than 0.20 wt% carbon, and the second base iron 22 may have a third alloy composition containing 0.20 wt% or more carbon. In this case, the second alloy composition and the third alloy composition may each have the composition described above.

[0074] In one embodiment, when the first plated steel sheet 10 including the second alloy composition is hot stamped, the first plated steel sheet 10 after hot stamping may have a tensile strength of 450 MPa or more, preferably 450 MPa or more and less than 1350 MPa.

[0075] In one embodiment, when the second plated steel sheet 20 containing the third alloy composition is hot stamped, the second plated steel sheet 20 after hot stamping may have a tensile strength of 1350 MPa or more and less than 2300 MPa, preferably 1350 MPa or more and less than 1680 MPa. Alternatively, the second plated steel sheet 20 after hot stamping may have a tensile strength of 1680 MPa or more, preferably 1680 MPa or more and less than 2300 MPa. In other words, the first plated steel sheet 10 and the second plated steel sheet 20 after hot stamping may have different tensile strengths.

[0076] In one embodiment, the first plated steel sheet 10 and the second plated steel sheet 20 may have the same thickness, but the present invention is not limited thereto.

[0077] In one embodiment, the aluminum-based plated blank 100 includes a first plated steel sheet 10 and a second plated steel sheet 20 that have different compositions and the same or different thicknesses, but contain a second alloy composition containing less than 0.20 wt % carbon, so that impact energy can be absorbed in a portion of the blank after hot stamping the aluminum-based plated blank 100. For example, the aluminum-based plated blank 100 includes a first plated steel sheet 10 and a second plated steel sheet 20 that have different compositions, different strengths (e.g., tensile strengths) after hot stamping, and the same thicknesses, or the aluminum-based plated blank 100 includes a first plated steel sheet 10 and a second plated steel sheet 20 that have different compositions, different strengths after hot stamping, and different thicknesses, so that impact energy can be absorbed by the plated steel sheet with the smaller product of the tensile strength (MPa) and thickness (mm) of the plated steel sheet, between the first plated steel sheet 10 and the second plated steel sheet 20.

[0078] In one embodiment, the aluminum-based plated blank 100 includes a first plated steel sheet 10 and a second plated steel sheet 20 that have different compositions and the same or different thicknesses, but contain a third alloy composition containing 0.20 wt % or more of carbon, so that impact energy can be absorbed in a portion of the blank after hot stamping the aluminum-based plated blank 100. For example, the aluminum-based plated blank 100 may include a first plated steel sheet 10 and a second plated steel sheet 20 that have different compositions, different strengths after hot stamping, and the same thicknesses, or the aluminum-based plated blank 100 may include a first plated steel sheet 10 and a second plated steel sheet 20 that have different compositions, different strengths after hot stamping, and different thicknesses, so that impact energy can be absorbed by the plated steel sheet with the smaller product of the tensile strength (MPa) and thickness (mm) of the first plated steel sheet 10 or the second plated steel sheet 20.

[0079] In one embodiment, the first plated steel sheet 10 may be manufactured by the steps of reheating a steel slab having a first alloy composition, a second alloy composition, or a third alloy composition, finish rolling the reheated slab, coiling the hot-rolled steel sheet, cold-rolling the coiled steel sheet, annealing the cold-rolled sheet, and forming the first plating layer 14 on the surface of the annealed sheet.

[0080] In one embodiment, the second plated steel sheet 20 may be manufactured by the steps of reheating a steel slab having the first alloy composition, the second alloy composition, or the third alloy composition, finish rolling the reheated slab, coiling the hot-rolled steel sheet, cold-rolling the coiled steel sheet, annealing the cold-rolled sheet, and forming the second plating layer 24 on the surface of the annealed sheet.

[0081] In one embodiment, the first plating layer 14 and the second plating layer 24 may contain the same components. For convenience of explanation, the first plating layer 14 will be described below, but this may also be applied to the second plating layer 24.

[0082] In one embodiment, the first coating layer 14 may be formed by immersing the first base iron 12 in a coating bath containing one or more of molten aluminum and an aluminum alloy at 600 to 800°C, and then cooling the bath at an average cooling rate of 1 to 50°C / s.

[0083] A first coating layer 14 may be formed on at least one surface of the first base steel 12. The first coating layer 14 may include a diffusion layer and a surface layer sequentially stacked on the first base steel 12. The surface layer contains 80% or more by weight of aluminum (Al) and may prevent oxidation of the first base steel 12. The diffusion layer is formed by interdiffusion of iron (Fe) of the first base steel 12 and aluminum (Al) of the first coating layer 14, and may include aluminum-iron (Al-Fe) and aluminum-iron-silicon (Al-Fe-Si) compounds. The diffusion layer may contain 20% to 60% by weight of iron (Fe), 30% to 80% by weight of aluminum (Al), and 0.1% to 40% by weight of silicon (Si).

[0084] In one embodiment, the diffusion layer may have a higher melting point than the surface layer. By providing a diffusion layer having a higher melting point than the surface layer between the first base iron 12 and the surface layer, it is possible to prevent or minimize the occurrence of liquid metal embrittlement, in which the surface layer melts during the hot pressing process and aluminum (Al) from the surface layer penetrates into the structure of the first base iron 12.

[0085] In one embodiment, after the first base steel 12 is immersed in a coating bath, one or more of air and gas are sprayed onto the surface of the first base steel 12 to wipe the hot-dip coating layer, and the spray pressure is adjusted to control the coating weight of the first coating layer 14.

[0086] In one embodiment, the coating weight of the first base steel 12 is 20 to 150 g / m 2 Preferably, the coating weight is 20 to 100 g / m on at least one surface of the first base steel 12. 2 The plating weight is 20g / m 2 If the plating coating weight is less than 100 g / m, the corrosion resistance of the contact area between the first plating layer 14 and the joint 30 after hot stamping may be reduced. 2 If the content exceeds this range, when the first plated steel sheet 10 and the second plated steel sheet 20 are joined, the amount of aluminum (Al) mixed into the joint 30, particularly the amount of aluminum (Al) mixed into the joint 30 in the plating layer adjacent to the joint 30, increases, which may cause aluminum (Al) segregation.

[0087] In one embodiment, the area fraction of the surface layer, which is the ratio of the cross-sectional area of ​​the surface layer to the cross-sectional area of ​​the plating layer (cross-sectional area of ​​the surface layer / cross-sectional area of ​​the first plating layer), is 97% or less. Preferably, the area fraction of the surface layer, which is the ratio of the cross-sectional area of ​​the surface layer to the cross-sectional area of ​​the plating layer (cross-sectional area of ​​the surface layer / cross-sectional area of ​​the first plating layer), is 65% or more and 97% or less.

[0088] In one embodiment, the surface layer contains 80 wt% to 100 wt% aluminum (Al) and has an average thickness of 10 μm to 40 μm. The surface layer is a layer with a high aluminum (Al) content. If the area fraction of the surface layer exceeds 97 wt% or the average thickness of the surface layer exceeds 40 μm, the amount of aluminum (Al) mixed into the joint 30 increases, which may cause aluminum (Al) segregation. Furthermore, since the thickness of the diffusion layer is thin, the aluminum (Al) in the surface layer may melt during hot stamping, and the molten aluminum (Al) may penetrate into the structure of the first base steel 12 or penetrate through the structure of the first base steel 12 to the interface between the joint 30 and the first base steel 12. Furthermore, if the area fraction of the surface layer is less than 65% or the average thickness of the surface layer is less than 10 μm, the thickness of the diffusion layer becomes thick, which may reduce the productivity of hot stamped parts.

[0089] In one embodiment, the joint 30 may be formed by aligning the side of the first plated steel sheet 10 and the side of the second plated steel sheet 20 so that they face each other, and then irradiating a laser at the boundary between the first plated steel sheet 10 and the second plated steel sheet 20 to melt the first plated steel sheet 10 and the second plated steel sheet 20. The joint 30 may contain 0% by weight or more but less than 0.5% by weight of aluminum (Al), with the remainder being components mixed in the first plated steel sheet 10 and the second plated steel sheet 20.

[0090] In one embodiment, the joint 30 may be formed by aligning the side surfaces of the first plated steel sheet 10 and the second plated steel sheet 20 so that they face each other, supplying a filler wire to the boundary between the first plated steel sheet 10 and the second plated steel sheet 20, and irradiating a laser to melt the first plated steel sheet 10, the second plated steel sheet 20, and the filler wire. The joint 30 may contain 0% by weight or more but less than 0.5% by weight of aluminum (Al), with the remainder being the first plated steel sheet 10, the second plated steel sheet 20, and components mixed in as the filler wire.

[0091] In one embodiment, the joint 30 may include 0.01% to less than 1.5% by weight of carbon (C), 0.05% to less than 1.0% by weight of silicon (Si), 1.0% to less than 3.0% by weight of manganese (Mn), 0 to less than 0.3% by weight of phosphorus (P), 0 to less than 0.3% by weight of sulfur (S), 0.01% to less than 0.5% by weight of titanium (Ti), 0.0005% to less than 0.01% by weight of boron (B), 0 to less than 0.5% by weight of aluminum (Al), with the balance being iron (Fe) and other unavoidable impurities. The joint 30 may also include one or more of 0.01% to less than 1.5% by weight of niobium (Nb) and 0.05% to less than 2.0% by weight of chromium (Cr).

[0092] In one embodiment, when the carbon content of the first plated steel sheet 10 and / or the second plated steel sheet 20 is 0.2 wt % or more, the joint 30 may be made of a chemical composition in which ferrite is not formed at or above the Ac3 temperature of the first plated steel sheet 10 and / or the second plated steel sheet 20. Desirably, the joint 30 may be made of a chemical composition in which ferrite is not formed at or above 840°C. Specifically, the joint 30 after undergoing a hot stamping process, i.e., after undergoing a hot stamping process in which an aluminum-based plated blank 100 is heated to 850 to 1000°C, press-formed, and quenched at an average cooling rate of 10 to 500°C / s, may be made of a chemical composition having a microstructure containing 90% or more martensite by area fraction. For example, the joint 30 exists as a full austenite structure at the hot stamping heating temperature, and can be transformed into a martensite structure with an area fraction of 90% or more, preferably a full martensite structure, during subsequent cooling.

[0093] In one embodiment, the joint 30 may contain aluminum (Al) in an amount of 0 wt % or more and less than 0.5 wt %. The aluminum content in the joint 30 is the sum of the aluminum mixed in from the molten first plated steel sheet 10 and the second plated steel sheet 20. Alternatively, the aluminum content in the joint 30 is the sum of the aluminum mixed in from the molten first plated steel sheet 10, the second plated steel sheet 20, and the filler wire.

[0094] The joint 30 may contain carbon (C) in an amount of 0.01 wt % or more and less than 1.5 wt %. If the carbon content of the joint 30 is less than 0.01 wt %, the joint 30 may be softened, and the hardness of the joint 30 may be less than the hardness of the first plated steel sheet 10 and the second plated steel sheet 20, which may cause fracture of the joint 30. On the other hand, if the carbon content is 1.5 wt % or more, the hardness of the joint 30 may increase excessively, which may cause brittle fracture of the joint 30 due to external impact, etc.

[0095] The joint 30 may contain silicon (Si) in an amount of 0.05 wt% or more and less than 1.0 wt%. If the silicon content of the joint 30 is less than 0.05 wt%, brittle fracture may occur in the joint 30. On the other hand, if the silicon content of the joint 30 is 1.0 wt% or more, slag may occur on the bead surface.

[0096] The joint 30 may contain 1.0 wt % or more but less than 3.0 wt % manganese (Mn). If the manganese (Mn) content of the joint 30 is less than 1.0 wt %, the joint 30 may soften during hot stamping, resulting in a lower hardness of the joint 30 than the hardness of the first plated steel sheet 10 and / or the second plated steel sheet 20, which may cause fracture of the joint 30. On the other hand, if the manganese content is 3.0 wt % or more, the hardness of the joint 30 may increase excessively, causing brittle fracture of the joint 30 due to external impact, and the viscosity of the joint 30 may decrease when melted and the expansion coefficient may increase when the joint 30 transforms to a solid phase, which may cause deterioration in the shape of the joint 30 and cracks in the joint 30.

[0097] The joint 30 may contain more than 0 and less than 0.3 wt % of phosphorus (P). If the phosphorus content of the joint 30 is 0.3 wt % or more, brittle fracture due to segregation may occur in the joint 30.

[0098] The joint 30 may contain more than 0 and less than 0.3 wt% sulfur (S). If the sulfur (S) content of the joint 30 is 0.3 wt% or more, cracks may occur in the joint 30 due to the formation of inclusions.

[0099] The joint 30 may contain titanium (Ti) in an amount of 0.01 wt% or more and less than 0.5 wt%. If the titanium content of the joint 30 is less than 0.01 wt%, the joint 30 may soften during hot stamping, resulting in a lower hardness of the joint 30 than the hardness of the first plated steel sheet 10 and / or the second plated steel sheet 20, which may cause fracture of the joint 30. On the other hand, if the titanium content of the joint 30 is 0.5 wt% or more, brittle fracture may occur in the joint 30.

[0100] The joint 30 may contain 0.0005 wt% or more and less than 0.01 wt% boron (B). If the boron content of the joint 30 is less than 0.0005 wt%, the joint 30 may soften during hot stamping, and the hardness of the joint 30 may become lower than the hardness of the first plated steel sheet 10 and / or the second plated steel sheet 20, which may cause fracture of the joint 30. On the other hand, if the boron content of the joint 30 is 0.01 wt% or more, brittle fracture may occur in the joint 30.

[0101] 2 , in one embodiment, the joint part 30 may include a first side part 31, a second side part 33, and a center part 35. The first side part 31 is a part of the joint part 30 adjacent to the first plated steel sheet 10, the second side part 33 is a part of the joint part 30 adjacent to the second plated steel sheet 20, and the center part 35 is a part located between the first side part 31 and the second side part 33. In other words, the center part 35 of the joint part 30 is also a central (or middle) part of the joint part 30.

[0102] In one embodiment, the first side portion 31, the second side portion 33, and the center portion 35 of the joint portion 30 may have the same width. For example, the width of the first side portion 31 is 1 / 3 of the overall width of the joint portion 30, the width of the second side portion 33 is 1 / 3 of the overall width of the joint portion 30, and the width of the center portion 35 is also 1 / 3 of the overall width of the joint portion 30. However, the present invention is not limited thereto. In this case, the overall width of the joint portion 30 may refer to the width between the boundary between the joint portion 30 and the first plated steel sheet 10 and the boundary between the joint portion 30 and the second plated steel sheet 20.

[0103] In one embodiment, the first side portion 31 may include a first portion 31 a, a second portion 31 b, and a third portion 31 c. The first portion 31 a, the second portion 31 b, and the third portion 31 c of the first side portion 31 may be sequentially arranged in a direction intersecting the width direction of the joint portion 30.

[0104] In one embodiment, the second side portion 33 may include a fourth portion 33 a, a fifth portion 33 b, and a sixth portion 33 c. The fourth portion 33 a, the fifth portion 33 b, and the sixth portion 33 c of the second side portion 33 may be arranged sequentially in a direction intersecting the width direction of the joint portion 30.

[0105] In one embodiment, the central portion 35 may include a seventh portion 35a, an eighth portion 35b, and a ninth portion 35c. The seventh portion 35a, the eighth portion 35b, and the ninth portion 35c of the central portion 35 may be arranged sequentially in a direction intersecting the width direction of the joint portion 30.

[0106] In one embodiment, the average aluminum (Al) content of the joint portion 30, including the first side portion 31, the second side portion 33, and the center portion 35, is 0% by weight or more and less than 0.5% by weight. Specifically, the average aluminum (Al) content measured in the first portion 31a to the ninth portion 35c of the joint portion 30 is 0% by weight or more and less than 0.5% by weight.

[0107] In one embodiment, the standard deviation of the aluminum (Al) content of the joint 30 including the first side portion 31, the second side portion 33, and the center portion 35 is 0.45 or less, for example, 0 or more and 0.45 or less. Specifically, the standard deviation of the aluminum (Al) content measured in the first portion 31a to the ninth portion 35c of the joint 30 is 0 or more and 0.45 or less.

[0108] In one embodiment, the standard deviation of the aluminum (Al) content of the first side portion 31 is greater than or equal to 0.4. Specifically, the standard deviation of the aluminum (Al) content measured in the first portion 31a, the second portion 31b, and the third portion 31c of the first side portion 31 is greater than or equal to 0.4. If the standard deviation of the aluminum (Al) content of the first side portion 31 exceeds 0.4, this may indicate that aluminum (Al) is unevenly distributed within the first side portion 31. In other words, if the standard deviation of the aluminum (Al) content of the first side portion 31 exceeds 0.4, aluminum (Al) is unevenly distributed within the first side portion 31, and therefore, local aluminum (Al) segregation may occur in the first side portion 31 of the joint portion 30 after hot stamping. Therefore, when the standard deviation of the aluminum (Al) content of the first side portion 31 is greater than or equal to 0 and less than 0.4, aluminum (Al) is uniformly distributed within the first side portion 31, which prevents local aluminum (Al) segregation from occurring in the first side portion 31 of the joint portion 30 after hot stamping, makes the microstructure of the first side portion 31 uniform after hot stamping, and prevents fractures from occurring in the joint portion 30.

[0109] In one embodiment, the standard deviation of the aluminum (Al) content of the second side portion 33 is greater than or equal to 0.4. Specifically, the standard deviation of the aluminum (Al) content measured at the fourth portion 33a, the fifth portion 33b, and the sixth portion 33c of the second side portion 33 is greater than or equal to 0.4. If the standard deviation of the aluminum (Al) content of the second side portion 33 exceeds 0.4, this may indicate that aluminum (Al) is unevenly distributed within the second side portion 33. In other words, if the standard deviation of the aluminum (Al) content of the second side portion 33 exceeds 0.4, aluminum (Al) is unevenly distributed within the second side portion 33, and local aluminum (Al) segregation may occur in the second side portion 33 of the joint portion 30 after hot stamping. Therefore, when the standard deviation of the aluminum (Al) content of the second side portion 33 is greater than or equal to 0 and less than 0.4, aluminum (Al) is uniformly distributed within the second side portion 33, which prevents local aluminum (Al) segregation from occurring in the second side portion 33 of the joint portion 30 after hot stamping, makes the microstructure of the second side portion 33 uniform after hot stamping, and prevents fractures from occurring in the joint portion 30.

[0110] If aluminum (Al) segregation occurs in the area where the first plated steel sheet 10 and the joint portion 30 are adjacent (e.g., the first side portion 31) and the area where the second plated steel sheet 20 and the joint portion 30 are adjacent (e.g., the second side portion 33), there is a high possibility of fracture occurring between the first plated steel sheet 10 and the joint portion 30 and between the second plated steel sheet 20 and the joint portion 30.

[0111] In one embodiment, the standard deviation of the aluminum (Al) content in the portion where the first plated steel sheet 10 and the joint portion 30 are adjacent (e.g., the first side portion 31) and the portion where the second plated steel sheet 20 and the joint portion 30 are adjacent (e.g., the second side portion 33) is set to be greater than or equal to 0.4, thereby uniformly distributing aluminum (Al) in the first side portion 31 and the second side portion 33, thereby preventing or minimizing fractures between the first plated steel sheet 10 and the joint portion 30 and between the second plated steel sheet 20 and the joint portion 30.

[0112] In one embodiment, the standard deviation of the aluminum (Al) content of the first side portion 31 or the second side portion 33, which is adjacent to a plated steel sheet having a large product of tensile strength (MPa) and thickness (mm) after hot stamping, is equal to or less than the standard deviation of the aluminum (Al) content of the side adjacent to a plated steel sheet having a small product of tensile strength (MPa) and thickness (mm) after hot stamping. The aluminum (Al) is more uniformly distributed on the side adjacent to a steel sheet having a large product of tensile strength (MPa) and thickness (mm), which has a relatively low impact energy absorption capacity after hot stamping, thereby preventing fractures from occurring at the joint 30.

[0113] In one embodiment, when the first plated steel sheet 10 and the second plated steel sheet 20 after hot stamping have different tensile strengths, the average silicon (Si) content of the joint 30 including the first side portion 31, the second side portion 33, and the center portion 35 is 0.3 wt % or more and 0.8 wt % or less. Specifically, the average silicon (Si) content measured in the first portion 31a to the ninth portion 35c of the joint 30 is 0.3 wt % or more and 0.8 wt % or less.

[0114] In one embodiment, the standard deviation of the silicon (Si) content of the joint portion 30, including the first side portion 31, the second side portion 33, and the center portion 35, is greater than or equal to 0 and less than or equal to 0.2. Specifically, the standard deviation of the silicon (Si) content measured in the first portion 31a to the ninth portion 35c of the joint portion 30 is greater than or equal to 0 and less than or equal to 0.2.

[0115] Silicon (Si) is a ferrite stabilizing element and can promote ferrite transformation. If the average silicon (Si) content of the joint 30 is less than 0.3 wt%, brittle fracture may occur in the joint 30. On the other hand, if the average silicon (Si) content of the joint 30 is more than 0.8 wt%, a large amount of ferrite is formed, and fracture may occur in the joint 30 when tension is applied.

[0116] In addition, if the standard deviation of the silicon (Si) content of the joint 30 exceeds 0.2, silicon (Si) may be partially concentrated in the joint 30, causing soft phases such as ferrite to accumulate, which may cause fracture of the joint 30 when subjected to tension.

[0117] In one embodiment, even if the average aluminum (Al) content and standard deviation of the joint 30 satisfy the above-described conditions, if the silicon (Si) content in the joint 30 is excessive, causing a large amount of ferrite to be generated, or if silicon (Si) is partially concentrated and soft phases such as ferrite accumulate, the joint 30 may fracture when subjected to tension. Specifically, even if the average aluminum (Al) content of the joint 30 is greater than or equal to 0 wt% and less than 0.5 wt%, the standard deviation of the aluminum (Al) content of the joint 30 is greater than or equal to 0.45, and the standard deviation of the aluminum (Al) content of the first side portion 31 and the second side portion 33 is greater than or equal to 0.4, if the average silicon (Si) content of the joint 30 exceeds 0.8 wt% or the standard deviation of the silicon (Si) content of the joint 30 exceeds 0.2, a large amount of ferrite may be generated due to the excessive silicon (Si) content in the joint 30, or silicon (Si) may be partially concentrated, causing soft phases such as ferrite to accumulate, which may cause fracture of the joint 30 when subjected to tension. Therefore, when the average silicon (Si) content of the joint 30 is 0.3 wt % or more and 0.8 wt % or less, and the standard deviation of the silicon (Si) content of the joint 30 is 0 wt % or more and 0.2 wt % or less, the formation of a large amount of ferrite in the joint 30 is prevented, and the silicon (Si) is partially concentrated in the joint 30, which causes the accumulation of soft phases such as ferrite, and therefore the occurrence of fracture in the joint 30 when tensioned can be prevented.

[0118] In one embodiment, the average hardness of the joint portion 30 is equal to or greater than the average hardness of the first plated steel sheet 10 and the average hardness of the second plated steel sheet 20. That is, the average hardness of the joint portion 30 is equal to or greater than the average hardness of the first base steel 12 and the average hardness of the second base steel 22.

[0119] Specifically, when the aluminum-based plated blank 100 is heated to Ac3 or higher, 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 average hardness of the joint 30 is equal to or greater than the average hardness of the first plated steel sheet 10 and the average hardness of the second plated steel sheet 20. When the aluminum-based plated blank 100 is combined with steel sheets of the same composition (for example, when the first plated steel sheet 10 and the second plated steel sheet 20 contain a first alloy composition, when the first plated steel sheet 10 and the second plated steel sheet 20 contain a second alloy composition, or when the first plated steel sheet 10 and the second plated steel sheet 20 contain a third alloy composition and the first plated steel sheet 10 and the second plated steel sheet 20 have the same composition), the average hardness of the joint 30 after hot stamping is equal to or greater than the average hardness of the first plated steel sheet 10 and the average hardness of the second plated steel sheet 20 after hot stamping.

[0120] That is, when the aluminum-based plated blank 100 is heated to Ac3 or higher, 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 average hardness of the joint 30 is equal to or greater than the average hardness of the first base steel 12 and the average hardness of the second base steel 22. When the aluminum-based plated blank 100 is combined with steel sheets of the same composition (for example, when the first plated steel sheet 10 and the second plated steel sheet 20 contain a first alloy composition, or when the first plated steel sheet 10 and the second plated steel sheet 20 contain a second alloy composition, or when the first plated steel sheet 10 and the second plated steel sheet 20 contain a third alloy composition and the first plated steel sheet 10 and the second plated steel sheet 20 have the same composition), the average hardness of the joint 30 after hot stamping is equal to or greater than the average hardness of the first base steel 12 and the second base steel 22 after hot stamping.

[0121] In one embodiment, the minimum hardness of the joint 30 after hot stamping is equal to or greater than the minimum hardness of the first plated steel sheet 10 and the second plated steel sheet 20 after hot stamping. Specifically, when the aluminum-based plated blank 100 is combined with steel sheets of the same composition (e.g., when the first plated steel sheet 10 and the second plated steel sheet 20 contain a first alloy composition, when the first plated steel sheet 10 and the second plated steel sheet 20 contain a second alloy composition, or when the first plated steel sheet 10 and the second plated steel sheet 20 contain a third alloy composition and the first plated steel sheet 10 and the second plated steel sheet 20 have the same composition), the minimum hardness of the joint 30 after hot stamping is equal to or greater than the minimum hardness of the first plated steel sheet 10 and the second plated steel sheet 20 after hot stamping.

[0122] That is, after hot stamping, the minimum hardness of the joint portion 30 is equal to or greater than the minimum hardness of the first base steel 12 and the second base steel 22 after hot stamping. Specifically, when the aluminum-based plated blank 100 is combined with steel sheets of the same composition (for example, when the first plated steel sheet 10 and the second plated steel sheet 20 contain a first alloy composition, when the first plated steel sheet 10 and the second plated steel sheet 20 contain a second alloy composition, or when the first plated steel sheet 10 and the second plated steel sheet 20 contain a third alloy composition and the first plated steel sheet 10 and the second plated steel sheet 20 have the same composition), the minimum hardness of the joint portion 30 after hot stamping is equal to or greater than the minimum hardness of the first base steel 12 and the second base steel 22 after hot stamping.

[0123] After hot stamping, the minimum hardness of the joint portion 30 is set to be equal to or greater than the minimum hardness of the first plated steel sheet 10 and the second plated steel sheet 20 after hot stamping, thereby preventing or minimizing fractures in the joint portion 30.

[0124] In other words, by making the minimum hardness of the joint portion 30 after hot stamping equal to or greater than the minimum hardness of the first base iron 12 and the second base iron 22 after hot stamping, fracture of the joint portion 30 can be prevented or minimized.

[0125] In one embodiment, the value obtained by multiplying the thickness of the joint portion 30 by the tensile strength of the joint portion 30 after hot stamping is equal to or greater than the value obtained by multiplying the thickness of the first plated steel sheet 10 by the tensile strength of the first plated steel sheet 10 after hot stamping and the value obtained by multiplying the thickness of the second plated steel sheet 20 by the tensile strength of the second plated steel sheet 20 after hot stamping.

[0126] Specifically, when the aluminum-based plated blank 100 is combined with steel sheets of the same composition (for example, when the first plated steel sheet 10 and the second plated steel sheet 20 contain a first alloy composition, when the first plated steel sheet 10 and the second plated steel sheet 20 contain a second alloy composition, or when the first plated steel sheet 10 and the second plated steel sheet 20 contain a third alloy composition and the first plated steel sheet 10 and the second plated steel sheet 20 have the same composition), the value obtained by multiplying the maximum thickness of the joint portion 30 by the tensile strength of the joint portion 30 after hot stamping is greater than the value obtained by multiplying the thickness of the thinner plated steel sheet between the first plated steel sheet 10 and the second plated steel sheet 20 by the tensile strength of the plated steel sheet after hot stamping.

[0127] In other words, when the aluminum-based plated blank 100 is combined with steel sheets of the same composition (for example, when the first plated steel sheet 10 and the second plated steel sheet 20 contain a first alloy composition, when the first plated steel sheet 10 and the second plated steel sheet 20 contain a second alloy composition, or when the first plated steel sheet 10 and the second plated steel sheet 20 contain a third alloy composition and the first plated steel sheet 10 and the second plated steel sheet 20 have the same composition), the value obtained by multiplying the maximum thickness of the joint portion 30 by the tensile strength of the joint portion 30 after hot stamping is also greater than the value obtained by multiplying the thickness of the thinner base iron between the first base iron 12 and the second base iron 22 by the tensile strength of the base iron after hot stamping.

[0128] In one embodiment, when the aluminum-based plated blank 100 is combined using steel sheets of the same composition (e.g., when the first plated steel sheet 10 and the second plated steel sheet 20 contain a first alloy composition, when the first plated steel sheet 10 and the second plated steel sheet 20 contain a second alloy composition, or when the first plated steel sheet 10 and the second plated steel sheet 20 contain a third alloy composition and the first plated steel sheet 10 and the second plated steel sheet 20 have the same composition), the joint 30 may be made of a composition system in which ferrite is not formed at or above the Ac3 temperature of the first plated steel sheet 10 and the second plated steel sheet 20. Desirably, the joint 30 may be made of a composition system in which ferrite is not formed at or above 840°C. Specifically, the aluminum-based plated blank 100 is heated to 850 to 1000°C, press-formed, and then quenched at an average cooling rate of 10 to 500°C / s through a hot stamping process, resulting in a joint 30 having a microstructure containing 90% or more martensite by area fraction and the remainder being other unavoidable structures. For example, the joint 30 exists as a full austenite structure at the hot stamping heating temperature, and can then be transformed into a martensite structure, preferably a full martensite structure, by area fraction of 90% or more upon cooling.

[0129] In one embodiment, the average hardness of the first plated steel sheet 10 and the average hardness of the second plated steel sheet 20 may be different from each other. In addition, the average hardness of the joint portion 30 may be greater than at least one of the average hardness of the first plated steel sheet 10 and the average hardness of the second plated steel sheet 20. That is, the average hardness of the joint portion 30 may be greater than at least one of the average hardness of the first base steel 12 and the average hardness of the second base steel 22.

[0130] Specifically, when the aluminum-based plated blank 100 is heated to 850°C or higher, 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 average hardness of the joint 30 is greater than at least one of the average hardness of the first plated steel sheet 10 and the average hardness of the second plated steel sheet 20. That is, the average hardness of the joint 30 is greater than at least one of the average hardness of the first base steel 12 and the average hardness of the second base steel 22.

[0131] When the aluminum-based plated blank 100 is combined with steel sheets of different compositions (for example, the first plated steel sheet 10 and the second plated steel sheet 20 contain the second alloy composition and the third alloy composition, respectively, or the first plated steel sheet 10 and the second plated steel sheet 20 contain the first alloy composition, or the first plated steel sheet 10 and the second plated steel sheet 20 contain the second alloy composition, or the first plated steel sheet 10 and the second plated steel sheet 20 contain the third alloy composition and the first plated steel sheet 10 and the second plated steel sheet 20 have different compositions), the average hardness of the joint portion 30 after hot stamping is also greater than the minimum hardness of the plated steel sheet with the lower tensile strength, between the first plated steel sheet 10 and the second plated steel sheet 20 after hot stamping. In this case, even when both the first plated steel sheet 10 and the second plated steel sheet 20 contain the first alloy composition, the compositions of the first plated steel sheet 10 and the second plated steel sheet 20 are different from each other, and the tensile strengths of the first plated steel sheet 10 and the second plated steel sheet 20 are different from each other. Even when both the first plated steel sheet 10 and the second plated steel sheet 20 contain the second alloy composition, the compositions of the first plated steel sheet 10 and the second plated steel sheet 20 are different from each other, and the tensile strengths of the first plated steel sheet 10 and the second plated steel sheet 20 are different from each other. Even when both the first plated steel sheet 10 and the second plated steel sheet 20 contain the third alloy composition, the compositions of the first plated steel sheet 10 and the second plated steel sheet 20 are different from each other, and the tensile strengths of the first plated steel sheet 10 and the second plated steel sheet 20 are different from each other.

[0132] In other words, when the aluminum-based plated blank 100 is combined with steel sheets of different compositions, the average hardness of the joint portion 30 after hot stamping is greater than the minimum hardness of the base steel having the lower tensile strength, between the first base steel 12 and the second base steel 22 after hot stamping.

[0133] In one embodiment, the minimum hardness of the joint portion 30 after hot stamping is also greater than the minimum hardness of the first plated steel sheet 10 and the second plated steel sheet 20 after hot stamping. That is, the minimum hardness of the joint portion 30 after hot stamping is also greater than the minimum hardness of the first base steel 12 and the second base steel 22 after hot stamping.

[0134] When the aluminum-based plated blank 100 is combined with steel sheets of different compositions, the minimum hardness of the joint portion 30 after hot stamping is greater than the minimum hardness of the plated steel sheet with the lower tensile strength, between the first plated steel sheet 10 and the second plated steel sheet 20 after hot stamping.

[0135] In other words, when the aluminum-based plated blank 100 is combined with steel sheets of different compositions, the minimum hardness of the joint portion 30 after hot stamping is greater than the minimum hardness of the base steel having the lower tensile strength, between the first base steel 12 and the second base steel 22 after hot stamping.

[0136] Since the minimum hardness of the joint portion 30 after hot stamping is greater than the minimum hardness of the first plated steel sheet 10 and the second plated steel sheet 20 after hot stamping, fracture of the joint portion 30 can be prevented or minimized.

[0137] In other words, since the minimum hardness of the joint portion 30 after hot stamping is greater than the minimum hardness of the first base iron 12 and the second base iron 22 after hot stamping, fracture of the joint portion 30 can be prevented or minimized.

[0138] In one embodiment, the value obtained by multiplying the thickness of the joint portion 30 by the tensile strength of the joint portion 30 after hot stamping is greater than at least one of the values ​​obtained by multiplying the thickness of the first plated steel sheet 10 by the tensile strength of the first plated steel sheet 10 after hot stamping and the value obtained by multiplying the thickness of the second plated steel sheet 20 by the tensile strength of the second plated steel sheet 20 after hot stamping.

[0139] Specifically, when the aluminum-based plated blank 100 is combined with steel sheets having different compositions (for example, when the first plated steel sheet 10 and the second plated steel sheet 20 contain the second alloy composition and the third alloy composition, respectively, or when the first plated steel sheet 10 and the second plated steel sheet 20 contain the first alloy composition but have different compositions), the value obtained by multiplying the maximum thickness of the joint portion 30 by the tensile strength of the joint portion 30 after hot stamping is greater than at least one of the value obtained by multiplying the thickness of the first plated steel sheet 10 by the tensile strength of the first plated steel sheet 10 after hot stamping and the value obtained by multiplying the thickness of the second plated steel sheet 20 by the tensile strength of the second plated steel sheet 20 after hot stamping.

[0140] A method for manufacturing the aluminum-based plated blank 100 will now be described.

[0141] A manufacturing method of an aluminum-based plated blank 100 according to one embodiment may include the steps of arranging the edges of a first plated steel sheet 10 and a second plated steel sheet 20 so that they face each other, and irradiating a laser beam to form a joint portion 30 that connects the first plated steel sheet 10 and the second plated steel sheet 20.

[0142] In one embodiment, the side of the first plated steel sheet 10 and the side of the second plated steel sheet 20 may be disposed to face each other. In this case, the side of the first plated steel sheet 10 and the side of the second plated steel sheet 20 may abut against each other.

[0143] In one embodiment, before the side surfaces of the first plated steel sheet 10 and the second plated steel sheet 20 are arranged to face each other, a step of removing at least a portion of the first plated layer 14 of the first plated steel sheet 10 and at least a portion of the second plated layer 24 of the second plated steel sheet 20 may be performed first. That is, before the first plated steel sheet 10 and the second plated steel sheet 20 are laser welded together, the plated layers of the first plated steel sheet 10 and the second plated steel sheet 20 may be removed in advance from the portions to be welded. However, the present invention is not limited thereto. The step of removing at least a portion of the first plated layer 14 of the first plated steel sheet 10 and at least a portion of the second plated layer 24 of the second plated steel sheet 20 may be omitted.

[0144] In one embodiment, at least a portion of the first plating layer 14 of the first plated steel sheet 10 may be removed. Specifically, at least a portion of the first plating layer 14 of the first plated steel sheet 10 may be removed from a portion to be welded.

[0145] In this case, the first plating layer 14 may be removed by a method including melting and vaporization. Specifically, the first plating layer 14 may be removed by a laser beam. For example, removal of the first plating layer 14 may be performed by a laser beam. When a high-power, high-energy-density laser beam is irradiated onto the surface of the first plating layer 14 to remove the first plating layer 14, the surface of the first plating layer 14 may be liquefied and vaporized. Furthermore, the first plating layer 14 liquefied by plasma pressure may be expelled to the surrounding area. The laser beam may be adjusted to remove only a portion of the first plating layer 14 in the thickness direction, or the entire first plating layer 14.

[0146] As described above, the first plating layer 14 may include a diffusion layer and a surface layer. In one embodiment, when at least a portion of the first plating layer 14 of the first plated steel sheet 10 is removed, both the diffusion layer and the surface layer of the first plating layer 14 may be removed.

[0147] Furthermore, the first coating layer 14 may be disposed on both one side and the other side of the first base steel 12 in the thickness direction of the first plated steel sheet 10. In one embodiment, only at least a portion of the first coating layer 14 disposed on one side of the first base steel 12 may be removed, and the first coating layer 14 disposed on the other side of the first base steel 12 may not be removed.

[0148] In one embodiment, at least a portion of the second plating layer 24 of the second plated steel sheet 20 may be removed. Specifically, at least a portion of the second plating layer 24 may be removed from the portion of the second plated steel sheet 20 that is to be welded. In this case, the second plating layer 24 may be removed by a method including melting and evaporation.

[0149] As described above, the second plating layer 24 may include a diffusion layer and a surface layer. In one embodiment, when at least a portion of the second plating layer 24 of the second plated steel sheet 20 is removed, both the diffusion layer and the surface layer of the second plating layer 24 may be removed.

[0150] In addition, the second plating layer 24 may be disposed on both one side and the other side of the second base steel 22 in the thickness direction of the second plated steel sheet 20. In one embodiment, only at least a portion of the second plating layer 24 disposed on one side of the second base steel 22 may be removed, and the second plating layer 24 disposed on the other side of the second base steel 22 may not be removed.

[0151] In one embodiment, at least a portion of the first plating layer 14 of the first plated steel sheet 10 and at least a portion of the second plating layer 24 of the second plated steel sheet 20 may be removed simultaneously. In this case, at least a portion of the first plating layer 14 of the first plated steel sheet 10 and at least a portion of the second plating layer 24 of the second plated steel sheet 20 may be removed using a laser beam. Specifically, the first plated steel sheet 10 and the second plated steel sheet 20 may be arranged to be spaced apart from each other by a predetermined distance, and then a laser beam may be irradiated to simultaneously remove at least a portion of the first plating layer 14 of the first plated steel sheet 10 and at least a portion of the second plating layer 24 of the second plated steel sheet 20. For example, the first plated steel sheet 10 and the second plated steel sheet 20 may be arranged to be spaced apart from each other by a predetermined distance, and then at least a portion of the first plating layer 14 and at least a portion of the second plating layer 24 may be removed using a laser.

[0152] In one embodiment, at least a portion of the first coating layer 14 disposed on one side of the first base steel 12 and at least a portion of the first coating layer 14 disposed on the other side of the first base steel 12 may be removed. Specifically, of the first coating layers 14 disposed on one and the other sides of the first base steel 12, both the diffusion layer and the surface layer of the first coating layer 14 in the portions to be welded may be removed.

[0153] In one embodiment, at least a portion of the second coating layer 24 disposed on one side of the second base steel 22 and at least a portion of the second coating layer 24 disposed on the other side of the second base steel 22 may be removed. Specifically, of the second coating layers 24 disposed on one and the other sides of the second base steel 22, both the diffusion layer and the surface layer of the second coating layer 24 in the portions to be welded may be removed.

[0154] In one embodiment, when at least a portion of the first coating layer 14 of the first plated steel sheet 10 is removed, only a portion of the first coating layer 14 may be removed in the thickness direction of the first plated steel sheet 10. For example, only the surface layer of the surface layer and diffusion layer of the first coating layer 14 may be removed from the portion of the first plated steel sheet 10 to be welded. In this case, in the case of the first coating layer 14 disposed on one side of the first base steel 12, only the surface layer of the surface layer and diffusion layer may be removed, and the first coating layer 14 disposed on the other side of the first base steel 12 may not be removed, or only the surface layer of the surface layer and diffusion layer of the first coating layer 14 may be removed, or both the surface layer and diffusion layer of the first coating layer 14 may be removed. However, the opposite is also possible.

[0155] In one embodiment, when at least a portion of the second plating layer 24 of the second plated steel sheet 20 is removed, only a portion of the second plating layer 24 may be removed in the thickness direction of the second plated steel sheet 20. For example, only the surface layer of the surface layer and diffusion layer of the second plating layer 24 may be removed from the portion of the second plated steel sheet 20 to be welded. In this case, in the case of the second plating layer 24 disposed on one side of the second base steel 22, only the surface layer of the surface layer and diffusion layer may be removed, and the second plating layer 24 disposed on the other side of the second base steel 22 may not be removed, or only the surface layer of the surface layer and diffusion layer of the second plating layer 24 may be removed, or both the surface layer and diffusion layer of the second plating layer 24 may be removed. However, the reverse is also possible.

[0156] In addition, when the surface layers of the first plating layer 14 and the second plating layer 24 are removed, at least a portion of the diffusion layer may also be removed.

[0157] In one embodiment, the plating amount is 50 g / m on one side of the first base steel 12. 2 If the thickness is less than 50 g / m, the first coating layer 14 disposed on the first base steel 12 will not be removed. 2 If the thickness is less than 100 μm, the first coating layer 14 disposed on each of the one surface and the other surface of the first base steel 12 will not be removed.

[0158] In one embodiment, the plating amount is 50 g / m2 based on one side of the second base steel 22. 2 If the thickness is less than 50 g / m, the second coating layer 24 disposed on the second base steel 22 will not be removed. 2 If the thickness is less than 100 μm, the second plating layer 24 disposed on each of the one surface and the other surface of the second base steel 22 will not be removed.

[0159] In one embodiment, a laser beam may be irradiated from a laser head to the boundary between the first plated steel sheet 10 and the second plated steel sheet 20 to form a joint portion 30 connecting 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.

[0160] The joint 30 is formed by melting the first plated steel sheet 10 and the second plated steel sheet 20 with a laser beam, and through 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 may be melted into the joint 30. However, because at least a portion of the first plating layer 14 and / or the second plating layer 24 of the first plated steel sheet 10 and the second plated steel sheet 20 is pre-removed from the portions to be welded in the first plated steel sheet 10 and the second plated steel sheet 20 before laser welding is performed on the first plated steel sheet 10 and the second plated steel sheet 20, the aluminum (Al) content in the joint 30 may be very low.

[0161] In one embodiment, a filler wire may be used in the process of laser welding the first plated steel sheet 10 and the second plated steel sheet 20. In this case, the filler wire may be used for the purpose of gap bridging and element compensation to enhance the hardenability of the joint 30.

[0162] First, when the edges of the first plated steel sheet 10 and the second plated steel sheet 20 are arranged facing each other, a gap may occur at the interface between the first plated steel sheet 10 and the second plated steel sheet 20. In this case, if a filler wire is used, the gap occurring at the interface between the first plated steel sheet 10 and the second plated steel sheet 20 can be filled.

[0163] In one embodiment, a filler wire may be provided at the interface between the first plated steel sheet 10 and the second plated steel sheet 20 in a joining step of irradiating a laser beam to form a joint 30 connecting the first plated steel sheet 10 and the second plated steel sheet 20. That is, after arranging the edges of the first plated steel sheet 10 and the second plated steel sheet 20 so that they face each other, a joining step of providing a filler wire at the interface between the first plated steel sheet 10 and the second plated steel sheet 20 and irradiating a laser beam to form the joint 30 connecting the first plated steel sheet 10 and the second plated steel sheet 20 may be performed. However, a filler wire is not provided at the interface between the first plated steel sheet 10 and the second plated steel sheet 20.

[0164] In one embodiment, a filler wire is provided at the boundary between the first plated steel sheet 10 and the second plated steel sheet 20, and a laser beam is irradiated from a laser head to form a joint portion 30 connecting 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.

[0165] The joint 30 is formed by melting the first plated steel sheet 10, the second plated steel sheet 20, and the filler wire with a laser beam, and through this process, the components of the first plated layer 14 of the first plated steel sheet 10 and the second plated layer 24 of the second plated steel sheet 20 can be infused into the joint 30. Therefore, the composition of the filler wire must be determined in consideration of the infusion of the components of the first plated layer 14 and the second plated layer 24 during laser welding.

[0166] In one embodiment, the filler wire may include an austenite stabilizing element. For example, the filler wire may include one or more of carbon (C) and manganese (Mn), with the remainder being iron (Fe) and unavoidable impurities. In this case, the carbon (C) content of the filler wire is 0.01% to 1.5% by weight, the silicon (Si) content is 0.1% to 2.0% by weight, and the manganese (Mn) content is 0.01% to 20.0% by weight. Such a filler wire is melt-inserted into the joint 30 to adjust the composition of the joint 30.

[0167] In one embodiment, the filler wire may include carbon (C) of 0.01 to 1.5% by weight, silicon (Si) of 0.1 to 2.0% by weight, manganese (Mn) of 0.01 to 20.0% by weight, phosphorus (P) of greater than 0 to 0.1% by weight, sulfur (S) of greater than 0 to 0.1% by weight, the balance being iron (Fe) and other unavoidable impurities.

[0168] The filler wire may contain carbon (C) in an amount of 0.01 wt% or more and 1.5 wt% or less. If the carbon (C) content of the filler wire is less than 0.01 wt%, the joint 30 may be softened and its hardness may be lower than that of the first plated steel sheet 10 and the second plated steel sheet 20, which may cause fracture of the joint 30. On the other hand, if the carbon (C) content of the filler wire is more than 1.5 wt%, brittle fracture may occur in the joint 30.

[0169] The filler wire may contain silicon (Si) in an amount of 0.1 to 2.0 wt %. If the silicon (Si) content of the filler wire is less than 0.1 wt %, brittle fracture may occur at the joint 30. On the other hand, if the silicon (Si) content of the filler wire is more than 2.0 wt %, slag may form on the bead surface.

[0170] The filler wire may contain manganese (Mn) in an amount of 0.01 wt% or more and 20.0 wt% or less. If the manganese (Mn) content of the filler wire is less than 0.01 wt%, the joint 30 may be softened and its hardness may be lower than that of the first plated steel sheet 10 and the second plated steel sheet 20, which may cause fracture of the joint 30. On the other hand, if the manganese (Mn) content of the filler wire is more than 20.0 wt%, brittle fracture may occur in the joint 30.

[0171] The filler wire may contain more than 0 to 0.1 wt% of phosphorus (P). If the content of phosphorus (P) contained in the filler wire exceeds 0.1 wt%, brittle fracture due to segregation may occur.

[0172] The filler wire may contain sulfur (S) in an amount of more than 0 to 0.1 wt %. If the sulfur (S) content in the filler wire exceeds 0.1 wt %, cracks may occur due to the formation of inclusions.

[0173] Specifically, even if aluminum (Al) from the first coating layer 14 and the second coating layer 24 is mixed into the molten pool of the joint 30, the austenite stabilizing element added to the filler wire allows the microstructure of the joint 30 to have a martensite structure, preferably a full martensite structure, with an area fraction of 90% or more after hot stamping. That is, according to the present invention, even if the components of the first coating layer 14 and the second coating layer 24 are mixed into the joint 30 without removing the first coating layer 14 and the second coating layer 24, it is possible to prevent a decrease in the hardness and strength of the joint 30 and prevent fracture of the joint 30.

[0174] Furthermore, when the first plated steel sheet 10 and the second plated steel sheet 20 have different compositions, even if aluminum (Al) from the first plated layer 14 and the second plated layer 24 is mixed into the molten pool at the joint 30, the austenite stabilizing element added to the filler wire 200 prevents the microstructure of the joint 30 from containing excessive ferrite after hot stamping, thereby preventing fracture at the joint 30.

[0175] In one embodiment, the radius of the filler wire is equal to or less than the radius of the laser beam (described later). Specifically, the radius of the filler wire is equal to or less than 0.9 times the radius of the laser beam. That is, if the radius of the laser beam is BR, the radius of the filler wire is equal to or less than BR*0.9.

[0176] In one embodiment, the filler wire injection rate is 0.6 to 1.3 times the formation rate of the joint 30, which will be described later. If the filler wire injection rate is less than 0.6 times the formation rate of the joint 30, the gap bridging effect is weak, making it difficult to achieve the goal of improving the hardenability of the joint 30. On the other hand, if the filler wire injection rate is more than 1.3 times the formation rate of the joint 30, the thickness of the joint 30 increases. Therefore, if the filler wire injection rate is 0.6 to 1.3 times the formation rate of the joint 30, gaps that occur at the interface between the first plated steel sheet 10 and the second plated steel sheet 20 are filled, the hardenability of the joint 30 is improved, and an increase in the thickness of the joint 30 can be prevented.

[0177] In one embodiment, the angle between the filler wire and the laser beam is 30° or greater. Preferably, the angle between the filler wire and the laser beam is 45° or greater. Specifically, the injection angle of the filler wire relative to the direction of irradiation of the laser beam is 30° or greater. Preferably, the injection angle of the filler wire relative to the direction of irradiation of the laser beam is 45° or greater.

[0178] Meanwhile, depending on the joining conditions, the components of the first coating layer 14, the second coating layer 24, and the filler wire may be unevenly distributed among the components of the first base steel 12 and the second base steel 22 at the joint. To prevent this, the wavelength of the laser beam irradiated when joining the first plated steel sheet 10 and the second plated steel sheet 20 may be controlled.

[0179] In one embodiment, the wavelength of the laser beam is 0.1 μm or more and 10 μm or less. If the wavelength of the laser beam is less than 0.1 μm, the laser beam wavelength is too short, and the power of the laser beam must be increased to melt the joint 30, which may reduce productivity and business viability. If the wavelength of the laser beam exceeds 10 μm, the laser absorption rate of the plated steel sheets 10, 20 decreases, making it difficult to uniformly distribute aluminum (Al) mixed into the welded joint (or joint 30) from the plating layer 14, 24. In other words, aluminum (Al) segregation may occur in the welded joint (or joint 30). Therefore, when the wavelength of the laser beam satisfies the range of 0.1 μm to 10 μm, the laser is well absorbed by the plated steel sheets 10, 20, and can sufficiently melt the portions to be welded in the plated steel sheets 10, 20, and aluminum (Al) can be uniformly distributed in the welded portion (or joint 30). That is, aluminum (Al) segregation can be prevented from occurring in the welded portion (or joint 30).

[0180] In one embodiment, the power of the laser beam is 0.5 kW to 20 kW. In one example, the power of the laser beam may refer to the output value of the laser oscillation unit.

[0181] In one embodiment, when manufacturing the aluminum-based plated blank 100, minimum productivity and business viability can be ensured if the forming speed of the joint 30 is 1 m / min or more and the laser beam power is 20 kW or less. While higher laser beam power is preferable, achieving power exceeding 20 kW requires high-performance equipment, which increases the equipment size and costs. In addition, to ensure minimum productivity, the forming speed of the joint 30 must be maintained at 1 m / min or more. The forming speed of the joint 30 refers to the displacement per unit time of the relative movement of the laser head parallel to the direction of forming the joint.

[0182] In one embodiment, the forming speed of the joint 30 is 1 to 15 m / min. If the forming speed of the joint 30 exceeds 15 m / min, it is difficult to sufficiently melt the first plated steel sheet 10 and the second plated steel sheet 20 even when a laser beam having a wavelength of 0.1 to 10 μm, a power of 0.5 to 20 kW, and a beam radius of 0.1 to 2.0 mm is irradiated.

[0183] In one embodiment, the radius of the laser beam is 0.1 to 2.0 mm. For the radius of the laser beam to exceed 2.0 mm, the distance between the filler wire, the first and second plated steel sheets 10 and 20, and the laser head must be close. In such a case, however, there may be insufficient space for supplying the filler wire or for replacing the filler wire when it is consumed, which may reduce the efficiency of the manufacturing process. On the other hand, if the radius of the laser beam is less than 0.1 mm, the laser beam radius is small and the width of the joint 30 is excessively small.

[0184] In one embodiment, a first laser beam and a second laser beam spaced apart from each other may be irradiated during laser beam irradiation. For example, the first laser beam melts the first coating layer 14, the second coating layer 24, the first base steel 12, and the second base steel 22, and the second laser beam maintains the molten state, uniformly stirring the molten portion and preventing segregation at the joint 30, resulting in excellent quality and mechanical properties. Meanwhile, when the first laser beam and the second laser beam are used, the sum of the powers of the first laser beam and the second laser beam is 0.5 to 20 kW.

[0185] Meanwhile, when the aluminum-based plated blank 100 is joined within the above-mentioned ranges of the laser beam wavelength, laser beam power, laser beam radius, and forming speed of the joint 30, and then subjected to a heat treatment of high temperature heating and rapid cooling, the average hardness of the joint 30 is equal to or greater than the average hardness of the first plated steel sheet 10 and the second plated steel sheet 20, and preferably equal to or greater than the minimum hardness of the first plated steel sheet 10 and the second plated steel sheet 20.

[0186] That is, when the aluminum-based plated blank 100 is joined within the above-mentioned ranges of the laser beam wavelength, laser beam power, laser beam radius, and forming speed of the joint portion 30, and then subjected to a heat treatment of high temperature heating and rapid cooling, the average hardness of the joint portion 30 is equal to or greater than the average hardness of the first base iron 12 and the second base iron 22, and preferably the minimum hardness of the joint portion 30 is equal to or greater than the minimum hardness of the first base iron 12 and the second base iron 22.

[0187] Specifically, when the aluminum-based plated blank 100 is combined with steel sheets of the same composition (for example, when the first plated steel sheet 10 and the second plated steel sheet 20 contain a first alloy composition, when the first plated steel sheet 10 and the second plated steel sheet 20 contain a second alloy composition, or when the first plated steel sheet 10 and the second plated steel sheet 20 contain a third alloy composition and the compositions of the first plated steel sheet 10 and the second plated steel sheet 20 are the same), the minimum hardness of the joint portion 30 after hot stamping is equal to or greater than the minimum hardness of the first plated steel sheet 10 and the second plated steel sheet 20 after hot stamping.

[0188] Meanwhile, when the aluminum-based plated blank 100 is joined within the above-mentioned ranges of the laser beam wavelength, laser beam power, laser beam radius, and forming speed of the joint 30, and then subjected to a heat treatment of high temperature heating and rapid cooling, the average hardness of the joint 30 is greater than at least one of the average hardnesses of the first plated steel sheet 10 and the second plated steel sheet 20, and preferably the minimum hardness of the joint 30 is greater than the minimum hardness of the first plated steel sheet 10 and the second plated steel sheet 20.

[0189] That is, when the aluminum-based plated blank 100 is joined within the above-mentioned ranges of the laser beam wavelength, laser beam power, laser beam radius, and forming speed of the joint 30, and then subjected to a heat treatment of high temperature heating and rapid cooling, the average hardness of the joint 30 is greater than at least one of the average hardnesses of the first base iron 12 and the second base iron 22, and preferably the minimum hardness of the joint 30 is greater than the minimum hardness of the first base iron 12 and the second base iron 22.

[0190] Specifically, when the aluminum-based plated blank 100 is combined with steel sheets of different compositions, the average hardness of the joint portion 30 after hot stamping is greater than the minimum hardness of the steel sheet with the lower tensile strength among the first plated steel sheet 10 and the second plated steel sheet 20 after hot stamping.

[0191] In other words, when the aluminum-based plated blank 100 is combined with steel sheets of different compositions, the average hardness of the joint portion 30 after hot stamping is greater than the minimum hardness of the base iron having the lower tensile strength, either the first base iron 12 or the second base iron 22 after hot stamping.

[0192] In one embodiment, the forming speed of the joint 30 is 1 to 15 m / min, and the laser beam power, wavelength, and radius are 0.5 to 20 kW, 0.1 to 10 μm, and 0.1 to 2.0 mm, respectively.

[0193] When the laser beam power, wavelength, and radius satisfy the above-mentioned conditions, aluminum (Al) segregation can be suppressed, and fracture of the joint during tension can be prevented. However, in this case, the forming speed of the joint 30 is 1 to 15 m / min. If the forming speed of the joint 30 exceeds 15 m / min, there is insufficient time for energy to be uniformly transmitted to the joint 30. For example, when the forming speed of the joint 30 is 15 to 30 m / min, excessive aluminum (Al) segregation can occur in the joint 30 even if the laser beam power, wavelength, and radius satisfy the above-mentioned conditions.

[0194] The constitution and operation of the present invention will be explained in more detail through preferred experimental examples below, which are presented as preferred examples of the present invention and should not be construed as limiting the present invention in any way.

[0195] Experimental Example 1 A steel slab containing 0.22 wt% carbon (C), 0.3 wt% silicon (Si), 1.5 wt% manganese (Mn), 0.02 wt% phosphorus (P), 0.015 wt% sulfur (S), 0.25 wt% chromium (Cr), 0.0025 wt% boron (B), 0.05 wt% titanium (Ti), the balance being iron (Fe) and other unavoidable impurities was reheated and finish-rolled, and the hot-rolled steel sheet was coiled. The coiled steel sheet was cold-rolled, and the cold-rolled steel sheet was annealed. The annealed steel sheet was then immersed in a coating bath containing 8.5 wt% silicon (Si), the balance being aluminum (Al) and other unavoidable impurities, and cooled, thereby forming a coating layer on at least one surface of the base steel, and a first coated steel sheet and a second coated steel sheet were prepared, which had the same strength but different thicknesses of 1.2 mm and 1.6 mm, respectively.

[0196] Thereafter, portions of the coating layers formed on both sides of the base steel at the portions to be welded in the first plated steel sheet and the second plated steel sheet were removed using a laser beam. For example, portions of the coating layers disposed on one side and the other side of the base steel at the portions to be welded were removed using a laser beam.

[0197] Then, the edges of the first plated steel sheet and the second plated steel sheet were arranged so as to face each other, and then a laser beam was irradiated to melt the facing portions of the aluminum-based plated steel sheets to form a joint, thereby producing aluminum-based plated blanks of Examples 1 to 3 and Comparative Examples 1 to 4.

[0198] In Examples 1 to 3 and Comparative Examples 1 to 3, 70 g / m2 was applied to both sides of the base steel. 2 In Comparative Example 4, the plating was applied to both sides of the base steel with a coating weight of 100 g / m 2 The plating was formed with a coating weight of When joining the steel plates, the laser beam was irradiated with a power of 4 kW and a radius of 1.0 mm, and the joint was formed at a forming speed of 5 m / min.

[0199] In this case, Example 1 was irradiated with a laser beam having a wavelength of 5 μm, Example 2 was irradiated with a laser beam having a wavelength of 2 μm, Example 3 was irradiated with a laser beam having a wavelength of 10 μm, Comparative Examples 1 to 3 were irradiated with a laser beam having a wavelength of 11 μm, and Comparative Example 4 was irradiated with a laser beam having a wavelength of 9 μm.

[0200] That is, the power of the laser beam irradiated to Examples 1 to 3 and Comparative Examples 1 to 4, the radius of the laser beam, and the speed at which the joint is formed are the same, but the wavelength of the laser beam is different from each other.

[0201] Table 1 below shows the location of fractures during tensile testing after hot stamping according to the average aluminum content of the joint and the standard deviation of the aluminum content.

[0202] [Table 1]

[0203] As described above, the average aluminum (Al) content of the joint portion 30 is equal to or greater than 0 wt % and less than 0.5 wt %. The joint portion 30 includes a first side portion 31, a second side portion 33, and a center portion 35. The standard deviation of the aluminum (Al) content of the joint portion 30 is equal to or greater than 0 and 0.45, and the standard deviation of the aluminum (Al) content of the first side portion 31 and the second side portion 33 is equal to or greater than 0 and 0.4.

[0204] Referring to Table 1, when the average aluminum (Al) content of the joint portion 30, the standard deviation of the aluminum (Al) content of the joint portion 30, the standard deviation of the aluminum (Al) content of the first side portion 31, and the standard deviation of the aluminum (Al) content of the second side portion 33 satisfy the above-mentioned conditions, it can be confirmed that after hot stamping the aluminum-based plated blank 100, fracture occurs in the plated steel sheet (e.g., the first plated steel sheet 10 and / or the second plated steel sheet 20) during a tensile test.

[0205] In Comparative Example 1, the standard deviation of the aluminum content of the joint 30 exceeds 0.45. Although the average aluminum content of the joint 30 is less than 0.50 wt % and the standard deviation of the aluminum content of the first and second sides is 0.4 or less, it was confirmed that fracture occurred in the joint 30 during a tensile test after hot stamping the aluminum-based plated blank 100. In Comparative Example 1, the wavelength of the laser beam exceeds 10 μm. Although the aluminum content of the joint satisfies the requirement of less than 0.50 wt %, the wavelength of the laser beam is too long, reducing the laser absorptivity of the plated steel sheets 10, 20, and the aluminum mixed into the joint 30 from the plating layers 14, 24 is not uniformly distributed in the joint 30. For example, although the aluminum content of the joint 30 is less than 0.50 wt %, which satisfies the aluminum content requirement of the joint 30, the wavelength of the laser beam is too long, so the aluminum is not well mixed in the joint 30 and is not uniformly distributed in the joint 30.

[0206] In Comparative Example 2, the standard deviation of the aluminum content at the second side exceeds 0.4, and although the average aluminum content at the joint is less than 0.50 wt %, the standard deviation of the aluminum content at the joint is 0.45 or less, and the standard deviation of the aluminum content at the first side is 0.4 or less, it was confirmed that fracture occurred at the joint 30 during a tensile test after hot stamping the aluminum-based plated blank 100. In Comparative Example 2, the wavelength of the laser beam exceeds 10 μm, and although the aluminum content at the joint 30 satisfies the requirement of less than 0.50 wt %, the wavelength of the laser beam is excessively long, reducing the laser absorptivity of the plated steel sheets 10, 20, and therefore aluminum mixed into the joint 30 from the plating layers 14, 24 is not uniformly distributed in the joint 30. For example, although the aluminum content of the joint 30 is less than 0.50 wt %, which satisfies the aluminum content requirement of the joint 30, the wavelength of the laser beam is too long, so the aluminum is not well mixed in the joint 30 and is not uniformly distributed in the joint 30.

[0207] In Comparative Example 3, the standard deviation of the aluminum content in the first side exceeded 0.4, and the average aluminum content was less than 0.50 wt %, the standard deviation of the aluminum content in the joint was 0.45 or less, and the standard deviation of the aluminum content in the second side was 0.4 or less. However, after hot stamping the aluminum-based plated blank 100, fracture occurred in the joint 30 during a tensile test. In Comparative Example 3, the wavelength of the laser beam exceeded 10 μm, and the aluminum content in the joint 30 satisfied the requirement of less than 0.50 wt %, but the wavelength of the laser beam was too long, reducing the laser absorptivity of the plated steel sheets 10, 20, and causing the aluminum mixed into the joint 30 from the plating layers 14, 24 to be distributed unevenly in the joint 30. For example, although the aluminum content of the joint 30 is less than 0.50 wt %, which satisfies the aluminum content requirement of the joint 30, the wavelength of the laser beam is too long, so the aluminum is not well mixed in the joint 30 and is not uniformly distributed in the joint 30.

[0208] In Comparative Example 4, the average aluminum content was 0.50 wt% or more, the standard deviation of the aluminum content at the joint was more than 0.45, and the standard deviation of the aluminum content at the second side was more than 0.4. Although the standard deviation of the aluminum content at the first side was 0.4 or less, it was confirmed that fracture occurred at the joint 30 during a tensile test after hot stamping the aluminum-based plated blank 100. In Comparative Example 4, the laser beam wavelength was 10 μm or less, which satisfied the welding conditions, but the aluminum content at the joint 30 was too high, so the aluminum at the joint 30 was not well mixed and was not uniformly distributed at the joint 30.

[0209] Therefore, when the average aluminum (Al) content of the joint portion 30 is 0 wt % or more and less than 0.5 wt %, and the standard deviation of the aluminum (Al) content of the joint portion 30 is 0 wt % or more and 0.45 wt % or less, fractures in the joint portion 30 can be prevented or minimized during a tensile test after hot stamping the aluminum-based plated blank 100. In particular, when the standard deviation of the aluminum (Al) content of the portion where the first plated steel sheet 10 and the joint portion 30 are adjacent (e.g., the first side portion 31) and the portion where the second plated steel sheet 20 and the joint portion 30 are adjacent (e.g., the second side portion 33) is 0 wt % or more and 0.4 wt % or less, aluminum (Al) is uniformly distributed in the first side portion 31 and the second side portion 33, and fractures between the first plated steel sheet 10 and the joint portion 30 and between the second plated steel sheet 20 and the joint portion 30 can be prevented or minimized.

[0210] Experimental Example 2 A first plated steel sheet was prepared by finish-rolling a reheated steel slab containing 0.06 wt% carbon (C), 0.45 wt% silicon (Si), 1.75 wt% manganese (Mn), 0.015 wt% phosphorus (P), 0.003 wt% sulfur (S), 0.002 wt% boron (B), 0.015 wt% titanium (Ti), the balance being iron (Fe) and other unavoidable impurities, coiling the hot-rolled steel sheet, cold-rolling the coiled steel sheet, annealing the cold-rolled steel sheet, and immersing the annealed steel sheet in a coating bath containing 8.5 wt% silicon (Si), the balance being aluminum (Al) and other unavoidable impurities, followed by cooling. The first plated steel sheet had a thickness of 1.4 mm.

[0211] A second plated steel sheet was prepared by finish-rolling a reheated steel slab containing 0.29 wt% carbon (C), 0.2 wt% silicon (Si), 1.5 wt% manganese (Mn), 0.02 wt% phosphorus (P), 0.01 wt% sulfur (S), 0.2 wt% chromium (Cr), 0.0025 wt% boron (B), 0.035 wt% titanium (Ti), the balance being iron (Fe) and other unavoidable impurities, coiling the hot-rolled steel sheet, cold-rolling the coiled steel sheet, annealing the cold-rolled steel sheet, and immersing the annealed steel sheet in a coating bath containing 8.5 wt% silicon (Si), the balance being aluminum (Al) and other unavoidable impurities, followed by cooling. The thickness of the second plated steel sheet was 1.4 mm.

[0212] Thereafter, portions of the coating layers formed on both sides of the base steel at the portions to be welded in the first plated steel sheet and the second plated steel sheet were removed using a laser beam. For example, portions of the coating layers disposed on one side and the other side of the base steel at the portions to be welded were removed using a laser beam.

[0213] Then, the edges of the first plated steel sheet and the second plated steel sheet were arranged so that they faced each other, and then a laser beam was irradiated to melt the facing portions of the aluminum-based plated steel sheets to form joints, thereby producing aluminum-based plated blanks of Examples 4 to 6 and Comparative Examples 5 to 8.

[0214] In Examples 4 to 6 and Comparative Examples 5 to 7, 70 g / m2 was applied to both sides of the base steel. 2 In Comparative Example 8, the plating was applied to both sides of the base steel with a coating weight of 100 g / m 2 The plating was formed with a coating weight of .

[0215] When joining the steel plates, the laser beam was irradiated with a power of 4 kW and a radius of 1.0 mm, and the joint was formed at a forming speed of 5 m / min.

[0216] In this case, Example 4 was irradiated with a laser beam having a wavelength of 5 μm, Example 5 was irradiated with a laser beam having a wavelength of 2 μm, Example 6 was irradiated with a laser beam having a wavelength of 10 μm, Comparative Examples 5 to 7 were irradiated with a laser beam having a wavelength of 11 μm, and Comparative Example 8 was irradiated with a laser beam having a wavelength of 9 μm.

[0217] That is, the power of the laser beam irradiated to Examples 4 to 6 and Comparative Examples 5 to 8, the radius of the laser beam, and the speed at which the joint is formed are the same, but the wavelength of the laser beam is different from each other.

[0218] Table 2 below shows the location of fractures during tensile testing after hot stamping according to the average aluminum content of the joint and the standard deviation of the aluminum content.

[0219] [Table 2]

[0220] As described above, the average aluminum content of the joint is 0% by weight or more and less than 0.5% by weight. The joint includes a first side portion, a second side portion, and a center portion, and the standard deviation of the aluminum content of the joint is 0% by weight or more and 0.45% by weight or less, and the standard deviation of the aluminum content of the first side portion and the second side portion is 0% by weight or more and 0.4% by weight or less.

[0221] Referring to Table 2, when the average aluminum content of the joint portion, the standard deviation of the aluminum content of the joint portion, the standard deviation of the aluminum content of the first side portion, and the standard deviation of the aluminum content of the second side portion satisfy the above-mentioned conditions, it can be confirmed that after hot stamping an aluminum-based plated blank, fracture occurs in the plated steel sheet (e.g., the first plated steel sheet and / or the second plated steel sheet) during a tensile test.

[0222] In Comparative Example 5, the standard deviation of the aluminum content of the joint exceeded 0.45. The average aluminum content of the joint was less than 0.50 wt. %. The standard deviation of the aluminum content of the first and second sides was 0.4 or less. However, after hot stamping the aluminum-based plated blank, fractures occurred at the joint during a tensile test. Comparative Example 5 also occurred when the laser beam wavelength exceeded 10 μm. While the aluminum content of the joint met the requirement of less than 0.50 wt. %, the excessively long laser beam wavelength reduced the laser absorption rate of the plated steel sheet, resulting in an inconsistent distribution of aluminum from the plating layer at the joint. For example, the aluminum content of the joint was less than 0.50 wt. %, satisfying the required aluminum content of the joint. However, the excessively long laser beam wavelength prevented aluminum from being mixed into the joint, resulting in an inconsistent distribution of aluminum at the joint.

[0223] In Comparative Example 6, the standard deviation of the aluminum content at the second side exceeded 0.4, and the average aluminum content at the joint was less than 0.50 wt.%, the standard deviation of the aluminum content at the joint was 0.45 or less, and the standard deviation of the aluminum content at the first side was 0.4 or less. However, after hot stamping the aluminum-based plated blank, fractures were observed at the joint during a tensile test. In Comparative Example 6, the laser beam wavelength exceeded 10 μm, and the aluminum content at the joint was less than 0.50 wt.%, but the laser beam wavelength was too long, reducing the laser absorption rate of the plated steel sheet and resulting in an inconsistent distribution of aluminum mixed into the joint from the plating layer. For example, the aluminum content at the joint was less than 0.50 wt.%, satisfying the required aluminum content at the joint, but the laser beam wavelength was too long, resulting in an inconsistent distribution of aluminum at the joint.

[0224] In Comparative Example 7, the standard deviation of the aluminum content in the first side exceeded 0.4, the average aluminum content was less than 0.50 wt%, the standard deviation of the aluminum content in the joint was 0.45 or less, and the standard deviation of the aluminum content in the second side was 0.4 or less. However, after hot stamping the aluminum-based plated blank, fractures were observed at the joint during a tensile test. In Comparative Example 7, the laser beam wavelength exceeded 10 μm, and the aluminum content in the joint satisfied the requirement of less than 0.50 wt%, but the laser beam wavelength was too long, reducing the laser absorption rate of the plated steel sheet and resulting in an inconsistent distribution of aluminum mixed into the joint from the plating layer. For example, the aluminum content in the joint was less than 0.50 wt%, satisfying the required aluminum content of the joint, but the laser beam wavelength was too long, resulting in an inconsistent distribution of aluminum in the joint.

[0225] In Comparative Example 8, the average aluminum content was 0.50 wt% or more, the standard deviation of the aluminum content at the joint was more than 0.45, and the standard deviation of the aluminum content at the second side was more than 0.4. Although the standard deviation of the aluminum content at the first side was 0.4 or less, it was confirmed that fractures occurred at the joint during a tensile test after hot stamping the aluminum-based plated blank. In Comparative Example 8, the laser beam wavelength was 10 μm or less, which met the welding conditions, but the aluminum content at the joint was too high, and the aluminum at the joint was not well mixed and uniformly distributed at the joint.

[0226] Therefore, when the average aluminum content of the joint is 0 wt.% or more and less than 0.5 wt.%, and the standard deviation of the aluminum content of the joint is 0 wt.% or more and 0.45 wt.% or less, fractures at the joint can be prevented or minimized during a tensile test after hot stamping an aluminum-based plated blank. In particular, when the standard deviation of the aluminum content of the portion adjacent to the first plated steel sheet and the joint (e.g., the first side) and the portion adjacent to the second plated steel sheet and the joint (e.g., the second side) is 0 wt.% or more and 0.4 wt.%, aluminum is uniformly distributed at the first side and the second side, and fractures between the first plated steel sheet and the joint and between the second plated steel sheet and the joint can be prevented or minimized.

[0227] Experimental Example 3 Examples 7 to 9 and Comparative Examples 9 to 11 are aluminum-based plated blanks manufactured under the same conditions as Examples 4 to 6 and Comparative Examples 5 to 7 of Experimental Example 2. In this case, Example 7 was irradiated with a laser beam having a wavelength of 2 μm, Example 8 was irradiated with a laser beam having a wavelength of 5 μm, Example 9 was irradiated with a laser beam having a wavelength of 10 μm, and Comparative Examples 9 to 11 were irradiated with a laser beam having a wavelength of 11 μm.

[0228] Table 3 below shows the location of fractures during tensile testing after hot stamping depending on the average silicon content and / or standard deviation of the silicon content of the joint.

[0229] [Table 3]

[0230] As described above, the average silicon content of the joint is 0.3% by weight or more and 0.8% by weight or less, and the standard deviation of the silicon content of the joint is 0% by weight or more and 0.2% by weight or less.

[0231] Referring to Table 3, it can be confirmed that when the average silicon content of the joint and the standard deviation of the silicon content of the joint satisfy the above-mentioned conditions, fracture occurs in the plated steel sheets (e.g., the first plated steel sheet and / or the second plated steel sheet) during a tensile test after hot stamping an aluminum-based plated blank.

[0232] In Comparative Examples 9 to 11, even when the average silicon content of the joint satisfied the requirement of 0.3 wt.% to 0.8 wt.%, if the laser beam wavelength exceeded 10 μm, the silicon content of the joint satisfied the requirement of 0.80 wt.% or less, but the excessively long wavelength of the laser beam reduced the laser absorption rate of the plated steel sheet, resulting in the silicon being mixed into the joint from the plating layer not being uniformly distributed in the joint. For example, although the silicon content of the joint was 0.80 wt.% or less and satisfied the required silicon content of the joint, the excessively long wavelength of the laser beam prevented the silicon from being mixed well in the joint, resulting in the silicon not being uniformly distributed in the joint.

[0233] As mentioned above, the present invention has been described based on one embodiment shown in the drawings, but this is merely an example, and those skilled in the art will understand that various modifications and variations of the embodiment are possible. Therefore, the true technical scope of protection of the present invention should be determined by the technical spirit of the claims.

Claims

1. An aluminum-based plated blank, a first plated steel sheet; a second plated steel plate connected to the first plated steel plate; a joint portion located between the first plated steel sheet and the second plated steel sheet, the joint portion connecting the first plated steel sheet and the second plated steel sheet, The first plated steel sheet and the second plated steel sheet each have a thickness of 20 to 100 g / m on at least one surface of the base iron. ２ and a plating layer containing aluminum (Al), The joint portion contains aluminum (Al), and the average content of aluminum (Al) in the joint portion is equal to or greater than 0 wt % and less than 0.5 wt %.

2. 2. The aluminum-based plated blank according to claim 1, wherein the standard deviation of the aluminum (Al) content of the joint portion is 0 or more and 0.45 or less.

3. 2. The aluminum-based plated blank according to claim 1, wherein the joint portion includes a first side portion adjacent to the first plated steel sheet, a second side portion adjacent to the second plated steel sheet, and a center portion between the first side portion and the second side portion.

4. The aluminum-based plated blank according to claim 3 , wherein the standard deviation of the aluminum (Al) content of the first side is equal to or greater than 0 and equal to or less than 0.

4.

5. 2. The aluminum-based plated blank according to claim 1, wherein the base steel contains carbon (C) of 0.01% by weight or more and 0.5% by weight or less, silicon (Si) of 0.01% by weight or more and 1.0% by weight or less, manganese (Mn) of 0.3% by weight or more and 2.0% by weight or less, phosphorus (P) of more than 0.1% by weight or less, sulfur (S) of more than 0.1% by weight or more, the balance being iron (Fe) and other unavoidable impurities.

6. The aluminum-based plated blank according to claim 1 , wherein the first plated steel sheet and the second plated steel sheet have the same strength.

7. The aluminum-based plated blank according to claim 1 , wherein the first plated steel sheet and the second plated steel sheet have different thicknesses.

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