KR102709439B1 - Aluminum coated blank - Google Patents

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 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

ALUMINUM COATED BLANK

The present invention relates to an aluminum-based plating blank.

Vehicles use parts with different strengths. For example, parts that must absorb energy when the vehicle collides or rolls over require relatively low strength, while parts that must maintain their shape to ensure survival space for passengers require high strength.

This is because if the part that is supposed to absorb energy during a collision has too much strength, it will not be able to properly absorb the impact energy and will instead transfer it to other parts, which can cause excessive impact to be transferred to passengers and other parts of the vehicle.

Vehicles are continuously required to be lightweight and cost-effective, which has led to the need for a single part to have different strengths in different parts.

Some sections of the part require high strength to protect the occupants, while other sections require relatively low strength to absorb impact energy.

A representative example of such parts is the B-pillar of a passenger car. The B-pillar requires relatively low tensile strength at the bottom, and high tensile strength at the top. The reason for the difference in strength is that the part that must maintain its shape with high strength in the event of a vehicle collision (the upper part that must support the roof when overturned) and the part that must absorb impact while being crushed (the lower part that is highly likely to collide with other vehicles from the side) are both required.

In addition, in order to secure a stable space that can prevent injury to passengers, the upper part of the B-pillar must maintain its shape, so high strength is required. If the upper strength of the B-pillar is not secured, the roof will sink when the vehicle overturns, posing a great threat to the safety of passengers. However, the lower part of the B-pillar must absorb impact energy while deforming, so relatively low strength is required. If the lower part of the B-pillar also has high strength, the impact energy will not be absorbed in the event of a side collision, and the impact will be transmitted to other structural materials.

The specific required strength will vary depending on the type and shape of the vehicle, but the upper part of the B-pillar requires a tensile strength of approximately 1350 MPa or more, while the lower part of the B-pillar requires a tensile strength of approximately 450 MPa or more and less than 1350 MPa.

In the past, a method was used to form a part with a low-strength material and then attach a separate reinforcing material to the part where high strength was required, but when a single part required different strengths in different sections, a material with high hardenability (or a thick material) was used for the upper part, and a material with low strength and low hardenability (or a thin material) was used for the lower part, and the two materials were joined with a laser to create a blank, which was then used to manufacture the final product through a hot stamping process.

Meanwhile, a tailor welded blank (TWB) is a component manufactured by joining two or more steel plate materials with at least one different material and thickness. The steel plate material for such TWB uses an Al-Si plating layer on the surface.

However, when plated steel sheet materials are joined with a laser, the plating layer components are dissolved into the molten pool of the joint (seam), so the joint has different properties from the parent material. If the plating layer is aluminum-silicon (Al-Si) or zinc (Zn), the plating components are mixed into the joint during laser joining, resulting in a deterioration in mechanical properties.

Accordingly, the phenomenon of reduced strength of the joint can be resolved or minimized by the filler wire component, but depending on the material (material with a large amount of plating adhesion) and the joining conditions (high joining speed), the mixed plating layer component (Al) may not be evenly diluted with the base material, causing problems such as segregation, and thus the effect of the filler wire component alone may be insufficient.

Background technology related to the present invention is disclosed in Korean Patent Publication No. 10-1637084 (published on July 6, 2016, title of the invention: Filler wire and method for manufacturing a custom welding blank using the same).

No. 10-1637084

According to one embodiment of the present invention, an aluminum-based plated blank is provided which can minimize deterioration in hardness and physical properties of a blank joint.

According to one embodiment of the present invention, an aluminum-plated blank is provided that can prevent the occurrence of defects such as segregation at a blank joint.

According to one embodiment of the present invention, an aluminum-based plated blank is provided which can minimize deterioration of physical properties of a blank joint after a hot stamping process.

According to one embodiment of the present invention, a method for manufacturing the aluminum-based plating blank is provided.

According to one embodiment of the present invention, an aluminum-based plating blank is provided, comprising: a first plated steel sheet; a second plated steel sheet connected to the first plated steel sheet; and a joint 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, wherein each of the first plated steel sheet and the second plated steel sheet includes a plating layer formed on at least one surface of the base steel with a bonding amount of 20 to 100 g/ ^m2 and including aluminum (Al), and the joint includes aluminum (Al) and silicon (Si), and an average content of aluminum (Al) in the joint is 0 wt% or more and less than 0.5 wt%, and an average content of silicon (Si) in the joint is 0.3 wt% or more and 0.8 wt% or less.

In the present embodiment, the standard deviation of the aluminum (Al) content of the joint may be 0 or more and 0.45 or less.

In the present embodiment, the joint may include a first side adjacent to the first plated steel plate, a second side adjacent to the second plated steel plate, and a central portion between the first side and the second side.

In the present embodiment, the standard deviation of the aluminum (Al) content of the first side may be 0 or more and 0.4 or less.

In the present embodiment, the standard deviation of the silicon (Si) content of the joint may be 0 or more and 0.2 or less.

In the present embodiment, the first plated steel sheet and the second plated steel sheet each include a first base iron and a second base iron, and the first base iron and the second base iron may each include carbon (C) of 0.01 wt% or more and 0.5 wt% or less, silicon (Si) of 0.01 wt% or more and 1.0 wt% or less, manganese (Mn) of 0.3 wt% or more and 2.0 wt% or less, phosphorus (P) of 0 to 0.1 wt% or less, sulfur (S) of 0 to 0.1 wt% or less, the remainder iron (Fe), and other unavoidable impurities.

In the present embodiment, the first plated steel sheet and the second plated steel sheet may have different tensile strengths.

In the present embodiment, the first plated steel sheet and the second plated steel sheet each include a first base iron and a second base iron, and the first base iron includes carbon (C) of 0.01 wt% or more and less than 0.20 wt%, silicon (Si) of 0.01 wt% or more and 0.8 wt% or less, manganese (Mn) of 0.8 wt% or more and 2.0 wt% or less, phosphorus (P) of more than 0 and 0.05 wt% or less, sulfur (S) of more than 0 and 0.01 wt% or less, and the remainder iron (Fe) and other unavoidable impurities, and the second base iron includes carbon (C) of 0.20 wt% or more and 0.5 wt% or less, silicon (Si) of 0.1 wt% or more and 0.8 wt% or less, manganese (Mn) of 0.3 wt% or more and 2.0 wt% or less, phosphorus (P) of more than 0 and 0.05 wt% or less, sulfur (S) of more than 0 and 0.01 wt% or less, It may contain residual iron (Fe) and other unavoidable impurities.

In the present embodiment, the first plated steel sheet and the second plated steel sheet each include a first base iron and a second base iron, and the first base iron and the second base iron may each include carbon (C) of 0.01 wt% or more and less than 0.20 wt%, silicon (Si) of 0.01 wt% or more and 0.8 wt% or less, manganese (Mn) of 0.8 wt% or more and 2.0 wt% or less, phosphorus (P) of more than 0 and 0.05 wt% or less, sulfur (S) of more than 0 and 0.01 wt% or less, iron (Fe) as a remainder, and other unavoidable impurities.

In the present embodiment, the first plated steel sheet and the second plated steel sheet may have different tensile strengths.

In the present embodiment, the first plated steel sheet and the second plated steel sheet each include a first base iron and a second base iron, and the first base iron and the second base iron may each include carbon (C) of 0.20 wt% or more and 0.5 wt% or less, silicon (Si) of 0.1 wt% or more and 0.8 wt% or less, manganese (Mn) of 0.3 wt% or more and 2.0 wt% or less, phosphorus (P) of more than 0 and 0.05 wt% or less, sulfur (S) of more than 0 and 0.01 wt% or less, iron (Fe) as a remainder, and other unavoidable impurities.

In the present embodiment, the first plated steel sheet and the second plated steel sheet may have different tensile strengths.

In this embodiment, the first plated steel sheet and the second plated steel sheet may have different thicknesses.

In this embodiment, the first plated steel sheet and the second plated steel sheet may have the same thickness.

The present invention can minimize the deterioration of hardness and physical properties of a blank joint, prevent the occurrence of defects such as segregation in the blank joint, and minimize joint breakage caused by phase change of segregation into an Al-Fe compound by a hot stamping process.

FIGS. 1 and 2 are cross-sectional views schematically illustrating an aluminum-based plating blank according to one embodiment of the present invention.

The present invention can be modified in various ways and has various embodiments, and specific embodiments are illustrated in the drawings and described in detail in the detailed description. The effects and features of the present invention and the methods for achieving them will become clear with reference to the embodiments described in detail below together with the drawings. However, the present invention is not limited to the embodiments disclosed below, and can be implemented in various forms.

In the examples below, the terms first, second, etc. are not used in a limiting sense but are used for the purpose of distinguishing one component from another.

In the examples below, singular expressions include plural expressions unless the context clearly indicates otherwise.

In the examples below, terms such as “include” or “have” mean that a feature or component described in the specification is present, and do not exclude in advance the possibility that one or more other features or components may be added.

In the following examples, when a part such as a film, region, component, etc. is said to be on or above another part, it includes not only the case where it is directly on top of the other part, but also the case where another film, region, component, etc. is interposed in between.

In the drawings, the sizes of components may be exaggerated or reduced for convenience of explanation. For example, the sizes and thicknesses of each component shown in the drawings are arbitrarily shown for convenience of explanation, and therefore the present invention is not necessarily limited to what is shown.

In some embodiments, where the embodiments are otherwise feasible, a particular process sequence may be performed in a different order than the order described. For example, two processes described in succession may be performed substantially simultaneously, or in a reverse order from the order described.

FIGS. 1 and 2 are cross-sectional views schematically illustrating an aluminum-based plating blank according to one embodiment of the present invention.

First, referring to FIG. 1, an aluminum-based plating 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 (30) positioned between the first plated steel sheet (10) and the second plated steel sheet (20) and connecting the first plated steel sheet (10) and the second plated steel sheet (20).

In one embodiment, the first plated steel sheet (10) may include a first base steel (12) and a first plating layer (14) formed on at least one surface of the first base steel (12), and the second plated steel sheet (20) may include a second base steel (22) and a second plating layer (24) formed on at least one surface of the second base steel (22). The first base steel (12) and the second base steel (22) may include different components, and the first plating layer (14) and the second plating layer (24) may include the same components. However, the present invention is not limited thereto. The first base steel (12) and the second base steel (22) may include the same components.

In the following, for convenience of explanation, the first small iron (12) will be described, but the same can be applied to the second small iron (22).

In one embodiment, the first base material (12) may include a first alloy composition. The first alloy composition may include carbon (C) of 0.01 wt% or more and 0.5 wt% or less, silicon (Si) of 0.01 wt% or more and 1.0 wt% or less, manganese (Mn) of 0.3 wt% or more and 2.0 wt% or less, phosphorus (P) of more than 0 wt% and 0.1 wt% or less, sulfur (S) of more than 0 wt% and 0.1 wt% or less, iron (Fe) as a remainder, and other unavoidable impurities.

In addition, the first alloy composition may further include one or more components from among boron (B), titanium (Ti), niobium (Nb), chromium (Cr), molybdenum (Mo), and nickel (Ni). Specifically, the first alloy composition may further include one or more components from among 0.0001 wt% or more and 0.005 wt% or less of boron (B), 0.01 wt% or more and 0.1 wt% or less of titanium (Ti), 0.01 wt% or more and 0.1 wt% or less of niobium (Nb), 0.01 wt% or more and 0.5 wt% or less of chromium (Cr), 0.01 wt% or more and 0.5 wt% or less of molybdenum (Mo), and 0.01 wt% or more and 1.0 wt% or less of nickel (Ni). For example, since the first galvanized steel sheet (10) includes the first base steel (12), it can be understood that the first galvanized steel sheet (10) includes the first alloy composition.

An aluminum-based plating blank (100) can be hot stamped to absorb impact energy in a portion of the blank, including a first plated steel sheet (10) and a second plated steel sheet (20) that have different components and the same or different thicknesses, but include a first alloy composition. For example, the aluminum-based plating blank (100) can include a first plated steel sheet (10) and a second plated steel sheet (20) that have different components and different strengths (e.g., tensile strengths) after hot stamping and the same thicknesses, or can include a first plated steel sheet (10) and a second plated steel sheet (20) that have different components and different strengths after hot stamping and different thicknesses, and among the first plated steel sheet (10) and the second plated steel sheet (20), the steel sheet having a smaller product of the tensile strength (MPa) and the thickness (mm) of the steel sheet can absorb impact energy. However, the present invention is not limited thereto.

Carbon (C) is a major element that determines the strength and hardness of steel, and can be added for the purpose of securing the tensile strength of steel after the hot stamping (or hot pressing) process. In addition, carbon can be added for the purpose of securing the hardenability characteristics of steel. In one embodiment, carbon may be included in an amount of 0.01 wt% or more and 0.5 wt% or less with respect to the total weight of the first base steel (12). If carbon is included in an amount of less than 0.01 wt% with respect to the total weight of the first base steel (12), it may be difficult to achieve the mechanical strength of the present invention. On the other hand, if carbon is included in an amount exceeding 0.5 wt% with respect to the total weight of the first base steel (12), a problem of deterioration in the toughness of the steel or a problem of controlling the brittleness of the steel may occur.

Silicon (Si) can act as a ferrite stabilizing element in the first base steel (12). Silicon (Si) can improve ductility by purifying ferrite, and can improve carbon concentration in austenite by suppressing the formation of low-temperature carbides. Furthermore, silicon (Si) can be a key element for hot-rolling, cold-rolling, and hot stamping tissue homogenization (control of pearlite and manganese segregation zones) and ferrite microdispersion. In one embodiment, silicon can be included in an amount of 0.01 wt% or more and 1.0 wt% or less with respect to the total weight of the first base steel (12). When silicon is included in an amount of less than 0.01 wt% with respect to the total weight of the first base steel (12), the aforementioned function may not be sufficiently exhibited. On the other hand, when silicon is included in an amount exceeding 1.0 wt% with respect to the total weight of the first base steel (12), hot-rolling and cold-rolling loads increase, hot-rolling red-type scale may be excessive, and bondability may deteriorate.

Manganese (Mn) may be added during heat treatment for the purpose of increasing hardenability and strength. In one embodiment, manganese may be included in an amount of 0.3 wt% or more and 2.0 wt% or less based on the total weight of the first base steel (12). If manganese is included in an amount of less than 0.3 wt% based on the total weight of the first base steel (12), there is a high possibility that the material after hot stamping will be insufficient (insufficient hard phase fraction) due to insufficient hardenability. On the other hand, if manganese is included in an amount of more than 2.0 wt% based on the total weight of the first base steel (12), ductility and toughness may be deteriorated due to manganese segregation or pearlite bands, which may cause deterioration in bending performance and may cause inhomogeneous microstructures.

Phosphorus (P) is an element that is easily segregated and may be an element that lowers the toughness of steel. In one embodiment, phosphorus (P) may be included in an amount greater than 0 and less than 0.1 wt% based on the total weight of the first base steel (12). When phosphorus is included in the above-described range based on the total weight of the first base steel (12), the toughness of steel may be prevented from deteriorating. On the other hand, when phosphorus is included in an amount greater than 0.1 wt% based on the total weight of the first base steel (12), cracks may be induced during the process and phosphide compounds may be formed, which may lower the toughness of steel.

Sulfur (S) may be an element that inhibits processability and physical properties. In one embodiment, sulfur may be included in an amount greater than 0 and less than 0.1 wt% based on the total weight of the first base steel (12). When sulfur is included in an amount greater than 0.1 wt% based on the total weight of the first base steel (12), hot processability may be deteriorated, and surface defects such as cracks may occur due to the generation of large inclusions.

Boron (B) is added to secure the hardenability and strength of steel by securing a martensite structure, and can have a grain refinement effect by increasing the austenite grain growth temperature. In one embodiment, boron may be included in an amount of 0.0001 wt% or more and 0.005 wt% or less with respect to the total weight of the first base steel (12). When boron is included in the above-mentioned range with respect to the total weight of the first base steel (12), occurrence of hard phase grain boundary embrittlement can be prevented, and high toughness and bendability can be secured.

Titanium (Ti) can be added for the purpose of strengthening the hardenability and improving the material quality by forming precipitates after hot stamping heat treatment. In addition, titanium can effectively contribute to the refinement of austenite grains by forming precipitate phases such as Ti(C,N) at high temperatures. In one embodiment, titanium can be included in an amount of 0.01 wt% or more and 0.1 wt% or less based on the total weight of the first base steel (12). When titanium is included in the above-mentioned range based on the total weight of the first base steel (12), poor performance can be prevented, coarsening of precipitates can be prevented, the physical properties of the steel can be easily secured, and cracks on the surface of the steel can be prevented or minimized.

Niobium (Nb) may be added for the purpose of increasing strength and toughness by reducing the martensite packet size. In one embodiment, niobium may be included in an amount of 0.01 wt% or more and 0.1 wt% or less based on the total weight of the first base steel (12). When niobium is included in the above-mentioned range based on the total weight of the first base steel (12), the grain refinement effect of the steel material is excellent in the hot rolling and cold rolling processes, cracks in the slab and brittle fracture of the product are prevented during steelmaking/rolling, and the formation of coarse precipitates in the steelmaking process can be minimized.

Chromium (Cr) may be added for the purpose of improving the hardenability and strength of the steel. In one embodiment, chromium may be included in an amount of 0.01 wt% or more and 0.5 wt% or less based on the total weight of the first base steel (12). When chromium is included in the above-mentioned 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 cost and a decrease in the toughness of the steel may be prevented.

Molybdenum (Mo) can contribute to the improvement of strength by suppressing the coarsening of precipitates during hot rolling and hot stamping and increasing the hardenability. Molybdenum (Mo) can be included in an amount of 0.01 wt% or more and 0.5 wt% or less based on the total weight of the first base steel (12). When molybdenum is included in the above-mentioned range based on the total weight of the first base steel (12), the effect of suppressing the coarsening of precipitates during hot rolling and hot stamping and increasing the hardenability can be excellent.

Nickel (Ni) may be added for the purpose of securing hardenability and strength. In addition, nickel is 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% or more and 1.0 wt% or less with respect to the total weight of the first base steel (12). If nickel is included in an amount of less than 0.01 wt% with respect to the total weight of the first base steel (12), it may be difficult to properly implement the above-described effect. If nickel is included in an amount of more than 1.0 wt% with respect to the total weight of the first base steel (12), toughness may be deteriorated, cold workability may be deteriorated, and the manufacturing cost of the product may increase.

In one embodiment, the first alloy (12) and the second alloy (22) may include different components. In one embodiment, the first alloy (12) may include a second alloy composition including less than 0.20 wt % carbon, and the second alloy (22) may include a third alloy composition including greater than 0.20 wt % carbon.

In one embodiment, the first alloy composition (12) may include a second alloy composition. The second alloy composition may include carbon (C) of 0.01 wt% or more and less than 0.20 wt%, silicon (Si) of 0.01 wt% or more and less than 0.8 wt%, manganese (Mn) of 0.8 wt% or more and less than 2.0 wt%, phosphorus (P) of more than 0 and less than 0.05 wt%, sulfur (S) of more than 0 and less than 0.01 wt%, iron (Fe) as a remainder, and other unavoidable impurities.

In addition, the second alloy composition may further include one or more components from among boron (B), titanium (Ti), niobium (Nb), chromium (Cr), and aluminum (Al). Specifically, the second alloy composition may further optionally include one or more components from among 0.0001 wt% or more and 0.003 wt% or less of boron (B), 0.01 wt% or more and 0.1 wt% or less of titanium (Ti), 0.01 wt% or more and 0.1 wt% or less of niobium (Nb), 0.01 wt% or more and 0.5 wt% or less of chromium (Cr), and 0.001 wt% or more and 0.1 wt% or less of aluminum (Al). For example, since 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.

In one embodiment, carbon may be included in an amount of 0.01 wt% or more and less than 0.20 wt% based on the total weight of the first base steel (12). If carbon is included in an amount of less than 0.01 wt% based on the total weight of the first base steel (12), it may be difficult to achieve the mechanical strength of the present invention. On the other hand, if carbon is included in an amount of 0.20 wt% or more based on the total weight of the first base steel (12), a problem of reduced toughness of the steel or a problem of controlling brittleness of the steel may occur.

In one embodiment, silicon may be included in an amount of 0.01 wt% or more and 0.8 wt% or less relative to the total weight of the first base steel (12). If silicon is included in an amount of less than 0.01 wt% relative to the total weight of the first base steel (12), the aforementioned function may not be sufficiently exhibited. On the other hand, if silicon is included in an amount of more than 0.8 wt% relative to the total weight of the first base steel (12), hot-rolling and cold-rolling loads may increase, hot-rolling red-type scale may become excessive, and bondability may deteriorate.

In one embodiment, manganese may be included in an amount of 0.8 wt% or more and 2.0 wt% or less based on the total weight of the first base steel (12). If manganese is included in an amount of less than 0.8 wt% based on the total weight of the first base steel (12), there is a high possibility that the material after hot stamping will be insufficient (insufficient hard phase fraction) due to insufficient hardenability. On the other hand, if manganese is included in an amount of more than 2.0 wt% based on the total weight of the first base steel (12), ductility and toughness may be deteriorated due to manganese segregation or pearlite bands, which may cause deterioration in bending performance and may cause inhomogeneous microstructures.

In one embodiment, phosphorus may be included in an amount of more than 0 wt% and less than or equal to 0.05 wt% based on the total weight of the first base steel (12). When phosphorus is included in the above-described range based on the total weight of the first base steel (12), the toughness of the steel may be prevented from deteriorating. On the other hand, when phosphorus is included in an amount of more than 0.05 wt% based on the total weight of the first base steel (12), cracks may be induced during the process, and phosphorus compounds may be formed, thereby deteriorating the toughness of the steel.

In one embodiment, sulfur may be included in an amount greater than 0 wt% and less than or equal to 0.01 wt% based on the total weight of the first base steel (12). If sulfur is included in an amount greater than 0.01 wt% based on the total weight of the first base steel (12), hot workability may be deteriorated, and surface defects such as cracks may occur due to the generation of large inclusions.

In one embodiment, the second alloy composition (22) may include a third alloy composition. The third alloy composition may include carbon (C) of 0.20 wt% or more and 0.5 wt% or less, silicon (Si) of 0.1 wt% or more and 0.8 wt% or less, manganese (Mn) of 0.3 wt% or more and 2.0 wt% or less, phosphorus (P) of more than 0 wt% and 0.05 wt% or less, sulfur (S) of more than 0 wt% and 0.01 wt% or less, iron (Fe) as a remainder, and other unavoidable impurities.

In addition, the third alloy composition may further include one or more components from among boron (B), titanium (Ti), niobium (Nb), chromium (Cr), molybdenum (Mo), and nickel (Ni). Specifically, the third alloy composition may further optionally include one or more components from among 0.001 wt% or more and 0.005 wt% or less of boron (B), 0.01 wt% or more and 0.1 wt% or less of titanium (Ti), 0.01 wt% or more and 0.1 wt% or less of niobium (Nb), 0.01 wt% or more and 0.5 wt% or less of chromium (Cr), 0.01 wt% or more and 0.5 wt% or less of molybdenum (Mo), and 0.01 wt% or more and 1.0 wt% or less of nickel (Ni). For example, since the second plated steel sheet (20) includes the second base steel (22), it can be understood that the second plated steel sheet (20) includes the third alloy composition.

In one embodiment, carbon may be included in an amount of 0.20 wt% or more and 0.5 wt% or less relative to the total weight of the second base steel (22). If carbon is included in an amount of less than 0.20 wt% relative to the total weight of the second base steel (22), it may be difficult to achieve the mechanical strength of the present invention. On the other hand, if carbon is included in an amount of more than 0.5 wt% relative to the total weight of the second base steel (22), a problem of reduced toughness of the steel or a problem of controlling brittleness of the steel may occur.

In one embodiment, silicon may be included in an amount of 0.1 wt% or more and 0.8 wt% or less relative to the total weight of the second base steel (22). If silicon is included in an amount of less than 0.1 wt% relative to the total weight of the second base steel (22), the aforementioned function may not be sufficiently exhibited. On the other hand, if silicon is included in an amount of more than 0.8 wt% relative to the total weight of the second base steel (22), hot-rolling and cold-rolling loads may increase, hot-rolling red-type scale may become excessive, and bondability may deteriorate.

In one embodiment, manganese may be included in an amount of 0.3 wt% or more and 2.0 wt% or less relative to the total weight of the second base steel (22). If manganese is included in an amount of less than 0.3 wt% relative to the total weight of the second base steel (22), there is a high possibility that the material after hot stamping will be insufficient (insufficient hard phase fraction) due to insufficient hardenability. On the other hand, if manganese is included in an amount of more than 2.0 wt% relative to the total weight of the second base steel (22), ductility and toughness may be deteriorated due to manganese segregation or pearlite bands, which may cause deterioration in bending performance and may cause inhomogeneous microstructures.

In one embodiment, phosphorus may be included in an amount of more than 0 wt% and less than or equal to 0.05 wt% based on the total weight of the second base steel (22). When phosphorus is included in the above-described range based on the total weight of the second base steel (22), the deterioration of the toughness of the steel may be prevented. On the other hand, when phosphorus is included in an amount exceeding 0.05 wt% based on the total weight of the second base steel (22), cracks may be induced during the process, and phosphorus compounds may be formed, which may deteriorate the toughness of the steel.

In one embodiment, sulfur may be included in an amount greater than 0 wt% and less than or equal to 0.01 wt% based on the total weight of the second base steel (22). If sulfur is included in an amount greater than 0.01 wt% based on the total weight of the second base steel (22), hot workability may be deteriorated and surface defects such as cracks may occur due to the generation of large inclusions.

In one embodiment, when hot stamping a first plated steel sheet (10) including a second alloy composition, the first plated steel sheet (10) after hot stamping may have a tensile strength of about 450 MPa or more, preferably about 450 MPa or more and less than about 1350 MPa. In one embodiment, when hot stamping a second plated steel sheet (20) including a third alloy composition, the second plated steel sheet (20) after hot stamping may have a tensile strength of about 1350 MPa or more and less than about 2300 MPa, preferably about 1350 MPa or more and less than about 1680 MPa. Alternatively, the second plated steel sheet (20) after hot stamping may have a tensile strength of about 1680 MPa or more, preferably about 1680 MPa or more and less than about 2300 MPa. That is, after hot stamping, the first plated steel sheet (10) and the second plated steel sheet (20) may have different tensile strengths.

In one embodiment, the thicknesses of the first plated steel sheet (10) and the second plated steel sheet (20) may be provided to be the same. However, the present invention is not limited thereto. For example, the thicknesses of the first plated steel sheet (10) and the second plated steel sheet (20) may be provided to be different from each other.

In one embodiment, an aluminum-based plating blank (100) comprises a second alloy composition containing less than 0.20 wt% carbon, but comprising first and second plating steel sheets (10) and (20) having different compositions and the same or different thicknesses, so that the aluminum-based plating blank (100) can be hot stamped to absorb impact energy in a portion of the blank. For example, the aluminum-based plating blank (100) may include a first plated steel sheet (10) and a second plated steel sheet (20) that have different components and thus have different strengths (e.g., tensile strengths) after hot stamping and the same thickness, or the aluminum-based plating blank (100) may include a first plated steel sheet (10) and a second plated steel sheet (20) that have different components and thus have different strengths after hot stamping and different thicknesses, and among the first plated steel sheet (10) and the second plated steel sheet (20), the plated steel sheet having a smaller product of the tensile strength (MPa) and the thickness (mm) of the plated steel sheet may absorb impact energy.

In one embodiment, an aluminum-based plating blank (100) may be hot stamped to include a third alloy composition containing carbon in an amount of 0.20 wt% or more, but including first and second plating steel sheets (10) and (20) having different compositions and the same or different thicknesses, so as to absorb impact energy in a portion of the blank. For example, the aluminum-based plating blank (100) may include a first plated steel sheet (10) and a second plated steel sheet (20) that have different components, different strengths after hot stamping, and the same thickness, or the aluminum-based plating blank (100) may include a first plated steel sheet (10) and a second plated steel sheet (20) that have different components, different strengths after hot stamping, and different thicknesses, and among the first plated steel sheet (10) and the second plated steel sheet (20), the plated steel sheet having a smaller product of the tensile strength (MPa) of the plated steel sheet and the thickness (mm) thereof can absorb impact energy.

In one embodiment, the first galvanized steel sheet (10) can be manufactured by including 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 steel sheet, and forming a first galvanized layer (14) on the surface of the annealed steel sheet.

In one embodiment, the second galvanized steel sheet (20) can be manufactured by including 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 steel sheet, and forming a second galvanized layer (24) on the surface of the annealed steel sheet.

In one embodiment, the first plating layer (14) and the second plating layer (24) may contain the same components. Hereinafter, for convenience of explanation, the first plating layer (14) will be described, but this can be equally applied to the second plating layer (24).

의 용융 알루미늄 및 알루미늄 합금 중 하나 이상을 포함하는 도금욕에 제1 소지철(12)을 침지한 다음 평균 1~50℃/s의 냉각 속도로 냉각시키는 단계를 포함하여 형성될 수 있다.In one embodiment, the first plating layer (14) is 600 to 800

It can be formed by including a step of immersing the first base iron (12) in a plating bath containing at least one of molten aluminum and aluminum alloys and then cooling it at an average cooling rate of 1 to 50°C/s.

A first plating layer (14) may be formed on at least one surface of the first base iron (12). The first plating layer (14) may include a diffusion layer and a surface layer sequentially laminated on the first base iron (12). The surface layer is a layer containing 80 wt% or more of aluminum (Al) and may prevent oxidation of the first base iron (12), etc. The diffusion layer is formed by mutual diffusion of iron (Fe) of the first base iron (12) and aluminum (Al) of the first plating layer (14), and may include aluminum-iron (Al-Fe) and aluminum-iron-silicon (Al-Fe-Si) compounds. The diffusion layer may include 20 wt% to 60 wt% of iron (Fe), 30 wt% to 80 wt% of aluminum (Al), and 0.1 wt% to 40 wt% of silicon (Si).

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 steel (12) and the surface layer, the liquid metal embrittlement phenomenon in which the surface layer melts during a hot press process and aluminum (Al) of the surface layer penetrates into the structure of the first base steel (12) can be prevented or minimized.

In one embodiment, after immersing the first base material (12) in a plating bath, the molten plating layer is wiped by spraying at least one of air and gas onto the surface of the first base material (12) to control the spray pressure, thereby controlling the plating adhesion amount of the first plating layer (14).

In one embodiment, the plating adhesion amount may be formed at 20 to 150 g/m ² on at least one surface of the first base steel (12). Preferably, the plating adhesion amount may be formed at 20 to 100 g/m ² on at least one surface of the first base steel (12). When the plating adhesion amount is less than 20 g/m ² , the corrosion resistance of the portion where the first plating layer (14) and the joint (30) come into contact after hot stamping may be deteriorated. On the other hand, when the plating adhesion amount exceeds 100 g/m ² , the amount of aluminum (Al) mixed into the joint (30) when the first plated steel sheet (10) and the second plated steel sheet (20) are joined may increase, causing aluminum (Al) segregation to occur.

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), may be 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), may be 65% or more and 97% or less.

In one embodiment, the surface layer may contain 80 wt% to 100 wt% of aluminum (Al), and the average thickness of the surface layer may be 10 μm to 40 μm. The surface layer is a layer having a high aluminum (Al) content. When 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. In addition, since the thickness of the diffusion layer becomes thin, the aluminum (Al) of 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 into the interface between the joint (30) and the first base steel (12) through the structure of the first base steel (12). In addition, if the area fraction of the surface layer is less than 65% or the average thickness of the surface layer is less than 10 ㎛, the thickness of the diffusion layer becomes thick, which may reduce the productivity of the hot stamping part.

In one embodiment, the joint (30) may be formed by aligning the side surface of the first plated steel sheet (10) and the side surface of the second plated steel sheet (20) so as to face each other, and then irradiating a laser to 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 include 0 wt% or more and less than 0.5 wt% of aluminum (Al), with the remainder being components mixed in the first plated steel sheet (10) and the second plated steel sheet (20).

In one embodiment, the joint (30) may be formed by aligning the side surface of the first plated steel sheet (10) and the side surface of the second plated steel sheet (20) so as to 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 include 0 wt% or more and less than 0.5 wt% of aluminum (Al), and the remainder being components mixed in the first plated steel sheet (10), the second plated steel sheet (20), and the filler wire.

In one embodiment, the joint (30) may include carbon (C) of 0.01 wt% or more and less than 1.5 wt%, silicon (Si) of 0.05 wt% or more and less than 1.0 wt%, manganese (Mn) of 1.0 wt% or more and less than 3.0 wt%, phosphorus (P) of 0 wt% or more and less than 0.3 wt%, sulfur (S) of 0 wt% or more and less than 0.3 wt%, titanium (Ti) of 0.01 wt% or more and less than 0.5 wt%, boron (B) of 0.0005 wt% or more and less than 0.01 wt%, aluminum (Al) of 0 wt% or more and less than 0.5 wt%, iron (Fe) as a remainder, and other unavoidable impurities. Additionally, the joint (30) may further include one or more components of niobium (Nb) of 0.01 wt% or more and less than 1.5 wt% and chromium (Cr) of 0.05 wt% or more and less than 2.0 wt%.

In one embodiment, when the carbon content of the first plated steel sheet (10) and the second plated steel sheet (20) is 0.2 wt% or more, the joint (30) may be formed of a component system in which ferrite is not formed at a temperature higher than Ac3 of the first plated steel sheet (10) and the second plated steel sheet (20). Preferably, the joint (30) may be formed of a component system in which ferrite is not formed at a temperature higher than 840°C. Specifically, the joint (30) after the hot stamping process, that is, the joint (30) after the hot stamping process in which the aluminum-based plated blank (100) is heated to 850 to 1000°C, press-formed, and then rapidly cooled at an average cooling rate of 10 to 500°C/s, may be formed of a component system that may have a microstructure including martensite having an area fraction of 90% or more. For example, at the hot stamping heating temperature, the joint (30) exists as a full austenite structure, and upon subsequent cooling, it can be transformed into a martensite structure having an area fraction of 90% or more, preferably a full martensite structure.

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

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 become soft and the hardness of the joint (30) may be smaller than the hardness of the first plated steel plate (10) and the second plated steel plate (20), and thus a fracture may occur in the joint (30). On the other hand, if the carbon content is 1.5 wt% or more, the hardness of the joint (30) may excessively increase, and thus a brittle fracture may occur in the joint (30) due to external impact, etc.

The joint (30) may contain 0.3 wt% or more and 0.8 wt% or less of silicon (Si). If the content of silicon contained in the joint (30) is less than 0.3 wt%, brittle fracture may occur in the joint (30). On the other hand, if the content of silicon contained in the joint (30) exceeds 0.8 wt%, slag may occur on the surface of the bead.

The joint (30) may contain manganese (Mn) in an amount of 1.0 wt% or more and less than 3.0 wt%. If the manganese (Mn) content of the joint (30) is less than 1.0 wt%, the joint (30) may soften during hot stamping, and the hardness of the joint (30) may be smaller than the hardness of the first plated steel sheet (10) and the second plated steel sheet (20), which may cause a fracture in the joint (30). On the other hand, if the manganese content is 3.0 wt% or more, the hardness of the joint (30) may excessively increase, which may cause brittle fracture in the joint (30) due to external impact, etc., and the quality of the shape of the joint (30) may deteriorate and cracks may occur in the joint (30) due to a decrease in viscosity when the joint (30) is melted and an increase in the coefficient of expansion when the joint is transformed into a solid phase.

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

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

The joint (30) may contain 0.01 wt% or more and less than 0.5 wt% of titanium (Ti). If the content of titanium in the joint (30) is less than 0.01 wt%, the joint (30) may soften during hot stamping, and the hardness of the joint (30) may be lower than the hardness of the first plated steel sheet (10) and the second plated steel sheet (20), so that a fracture may occur in the joint (30). On the other hand, if the content of titanium in the joint (30) is 0.5 wt% or more, a brittle fracture may occur in the joint (30).

The joint (30) may contain boron (B) in an amount of 0.0005 wt% or more and less than 0.01 wt%. If the content of boron in 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 be lower than the hardness of the first plated steel sheet (10) and the second plated steel sheet (20), which may cause a fracture in the joint (30). On the other hand, if the content of boron in the joint (30) is 0.01 wt% or more, a brittle fracture may occur in the joint (30).

Referring to FIG. 2, in one embodiment, the joint (30) may include a first side (31), a second side (33), and a center (35). The first side (31) may be a portion of the joint (30) adjacent to the first plated steel plate (10), the second side (33) may be a portion of the joint (30) adjacent to the second plated steel plate (20), and the center (35) may be a portion located between the first side (31) and the second side (33). That is, the center (35) of the joint (30) may be a central (or middle) portion of the joint (30).

In one embodiment, the first side (31), the second side (33), and the center (35) of the joint (30) may be provided with the same width. For example, the width of the first side (31) may be 1/3 of the overall width of the joint (30), the width of the second side (33) may be 1/3 of the overall width of the joint (30), and the width of the center (35) may be 1/3 of the overall width of the joint (30). However, the present invention is not limited thereto. In this case, the overall width of the joint (30) may mean the width between the boundary between the joint (30) and the first plated steel plate (10) and the boundary between the joint (30) and the second plated steel plate (20).

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

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

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 sequentially arranged in a direction intersecting the width direction of the joint (30).

In one embodiment, the average content of aluminum (Al) in the joint (30) including the first side (31), the second side (33), and the center (35) may be 0 wt% or more and less than 0.5 wt%. Specifically, the average value of the content of aluminum (Al) measured in the first portion (31a) to the ninth portion (35c) of the joint (30) may be 0 wt% or more and less than 0.5 wt%.

In one embodiment, the standard deviation of the aluminum (Al) content of the joint (30) including the first side (31), the second side (33), and the center (35) may be 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) may be 0 or more and 0.45 or less.

In one embodiment, the standard deviation of the aluminum (Al) content of the first side (31) may be 0 or more and 0.4 or less. Specifically, the standard deviation of the aluminum (Al) content measured in the first part (31a), the second part (31b), and the third part (31c) of the first side (31) may be 0 or more and 0.4 or less. When the standard deviation of the aluminum (Al) content of the first side (31) exceeds 0.4, it may mean that aluminum (Al) is unevenly distributed within the first side (31). That is, when the standard deviation of the aluminum (Al) content of the first side (31) exceeds 0.4, since aluminum (Al) is unevenly distributed and exists within the first side (31), local aluminum (Al) segregation may occur in the first side (31) of the joint (30) after hot stamping. Accordingly, when the standard deviation of the aluminum (Al) content of the first side (31) is 0 or more and 0.4 or less, aluminum (Al) is evenly distributed and present within the first side (31), so that local aluminum (Al) segregation can be prevented from occurring in the first side (31) of the joint (30) after hot stamping, the microstructure of the first side (31) can be made uniform after hot stamping, and at the same time, fracture can be prevented from occurring in the joint (30).

In one embodiment, the standard deviation of the aluminum (Al) content of the second side (33) may be 0 or more and 0.4 or less. Specifically, the standard deviation of the aluminum (Al) content measured in the fourth portion (33a), the fifth portion (33b), and the sixth portion (33c) of the second side (33) may be 0 or more and 0.4 or less. When the standard deviation of the aluminum (Al) content of the second side (33) exceeds 0.4, it may mean that aluminum (Al) is unevenly distributed within the second side (33). That is, when the standard deviation of the aluminum (Al) content of the second side (33) exceeds 0.4, since aluminum (Al) is unevenly distributed and exists within the second side (33), local aluminum (Al) segregation may occur in the second side (33) of the joint (30) after hot stamping. Accordingly, when the standard deviation of the aluminum (Al) content of the second side (33) is 0 or more and 0.4 or less, aluminum (Al) is evenly distributed and present within the second side (33), so that local aluminum (Al) segregation can be prevented from occurring in the second side (33) of the joint (30) after hot stamping, the microstructure of the second side (33) can be made uniform after hot stamping, and at the same time, fracture can be prevented from occurring in the joint (30).

When aluminum (Al) segregation occurs in the portion where the first plated steel plate (10) and the joint (30) are adjacent (e.g., the first side (31)) and the portion where the second plated steel plate (20) and the joint (30) are adjacent (e.g., the second side (33)), there is a high possibility that fracture will occur between the first plated steel plate (10) and the joint (30) and between the second plated steel plate (20) and the joint (30).

In one embodiment, the standard deviation of the aluminum (Al) content of a portion (e.g., a first side portion (31)) where the first plated steel plate (10) and the joint (30) are adjacent and a portion (e.g., a second side portion (33)) where the second plated steel plate (20) and the joint (30) are adjacent is 0 or more and 0.4 or less, so that aluminum (Al) is evenly distributed in the first side portion (31) and the second side portion (33), thereby preventing or minimizing occurrence of fracture between the first plated steel plate (10) and the joint portion (30) and between the second plated steel plate (20) and the joint portion (30).

In one embodiment, the standard deviation of the aluminum (Al) content of the side adjacent to the steel plate having a large product of tensile strength (MPa) and thickness (mm) after hot stamping among the first side (31) and the second side (33) may be less than or equal to the standard deviation of the aluminum (Al) content of the side adjacent to the steel plate having a small product of tensile strength (MPa) and thickness (mm) after hot stamping. By more uniformly distributing the aluminum (Al) of the side adjacent to the steel plate having a large product of tensile strength (MPa) and thickness (mm) with relatively low impact energy absorption performance after hot stamping, it is possible to prevent a fracture from occurring at the joint (30).

In one embodiment, the average content of silicon (Si) in the joint (30) including the first side (31), the second side (33), and the center (35) may be 0.3 wt% or more and 0.8 wt% or less. Specifically, the average value of the content of silicon (Si) measured in the first portion (31a) to the ninth portion (35c) of the joint (30) may be 0.3 wt% or more and 0.8 wt% or less.

In one embodiment, the standard deviation of the silicon (Si) content of the joint (30) including the first side (31), the second side (33), and the center (35) may be 0 or more and 0.2 or less. Specifically, the standard deviation of the silicon (Si) content measured in the first portion (31a) to the ninth portion (35c) of the joint (30) may be 0 or more and 0.2 or less.

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

In addition, if the standard deviation of the silicon (Si) content of the joint (30) exceeds 0.2, silicon (Si) is partially densely packed within the joint (30), causing a soft phase such as ferrite to accumulate, which may cause a fracture in the joint (30) during tension.

In one embodiment, even if the average content and standard deviation of aluminum (Al) in the joint (30) satisfy the conditions described above, if the content of silicon (Si) in the joint (30) is excessive, a large amount of ferrite is generated, or if silicon (Si) is partially densely packed and a soft phase such as ferrite is accumulated, a fracture may occur in the joint (30) during tension. Specifically, even when the average content of aluminum (Al) of the joint (30) satisfies 0 wt% or more and less than 0.5 wt%, the standard deviation of the aluminum (Al) content of the joint (30) satisfies 0 wt% or more and 0.45 or less, and the standard deviation of the aluminum (Al) content of the first side (31) and the second side (33) satisfies 0 wt% or more and 0.4 or less, if the average content of silicon (Si) of the joint (30) exceeds 0.8 wt% or the standard deviation of the silicon (Si) content of the joint (30) exceeds 0.2, the content of silicon (Si) in the joint (30) may be excessive, causing a large amount of ferrite to be generated, or silicon (Si) may be partially densely packed, causing a soft phase such as ferrite to accumulate, which may cause a fracture of the joint (30) during tension.

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 (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). In other words, the average hardness of the joint (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).

Specifically, when an aluminum-based plating blank (100) is heated to 850°C or higher, press-formed, and cooled to 300°C or lower at a cooling rate of 10 to 500°C/s to hot stamp, the average hardness of the joint (30) may be greater than at least one of the average hardness of the first plating steel sheet (10) and the average hardness of the second plating steel sheet (20). In other words, the average hardness of the joint (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).

When the aluminum-based plating blank (100) is combined with different composition steel sheets (for example, when the first plating steel sheet (10) and the second plating steel sheet (20) each include a second alloy composition and a third alloy composition, or when the first plating steel sheet (10) and the second plating steel sheet (20) include a first alloy composition, or when the first plating steel sheet (10) and the second plating steel sheet (20) include a second alloy composition, or when the first plating steel sheet (10) and the second plating steel sheet (20) include a third alloy composition so that the compositions of the first plating steel sheet (10) and the second plating steel sheet (20) are different), the average hardness of the joint (30) after hot stamping may be greater than the minimum hardness of the plating steel sheet having a lower tensile strength among the first plating steel sheet (10) and the second plating steel sheet (20) after hot stamping. At this time, even if both the first plated steel sheet (10) and the second plated steel sheet (20) contain the first alloy composition, the component contents of the first plated steel sheet (10) and the second plated steel sheet (20) may be different from each other, so that the tensile strengths of the first plated steel sheet (10) and the second plated steel sheet (20) may be different from each other. Even if both the first plated steel sheet (10) and the second plated steel sheet (20) contain the second alloy composition, the component contents of the first plated steel sheet (10) and the second plated steel sheet (20) may be different from each other, so that the tensile strengths of the first plated steel sheet (10) and the second plated steel sheet (20) may be different from each other. Even when both the first plated steel sheet (10) and the second plated steel sheet (20) contain a third alloy composition, the component contents of the first plated steel sheet (10) and the second plated steel sheet (20) may be different from each other, so that the tensile strengths of the first plated steel sheet (10) and the second plated steel sheet (20) may be different from each other.

In other words, when the aluminum-plated blank (100) is combined with a dissimilar steel plate, the average hardness of the joint (30) after hot stamping may be greater than the minimum hardness of the base steel having a lower tensile strength among the first base steel (12) and the second base steel (22) after hot stamping.

In one embodiment, the minimum hardness of the joint (30) after hot stamping may be greater than the minimum hardness of the first plated steel sheet (10) and the second plated steel sheet (20) after hot stamping. In other words, the minimum hardness of the joint (30) after hot stamping may be greater than the minimum hardness of the first base steel (12) and the second base steel (22) after hot stamping.

When the aluminum-based plating blank (100) is combined with dissimilar component steel plates, the minimum hardness of the joint (30) after hot stamping may be greater than the minimum hardness of the plating steel plate with a lower tensile strength among the first plating steel plate (10) and the second plating steel plate (20) after hot stamping.

In other words, when the aluminum-plated blank (100) is combined with a dissimilar steel plate, the minimum hardness of the joint (30) after hot stamping may be greater than the minimum hardness of the base steel having a lower tensile strength among the first base steel (12) and the second base steel (22) after hot stamping.

Since the minimum hardness of the joint (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, the occurrence of breakage in the joint (30) can be prevented or minimized.

In other words, since the minimum hardness of the joint (30) after hot stamping is greater than the minimum hardness of the first base steel (12) and the second base steel (22) after hot stamping, the occurrence of breakage in the joint (30) can be prevented or minimized.

In one embodiment, the product of the thickness of the joint (30) and the tensile strength of the joint (30) after hot stamping may be greater than at least one of the product of the thickness of the first plated steel sheet (10) and the tensile strength of the first plated steel sheet (10) after hot stamping and the product of the thickness of the second plated steel sheet (20) and the tensile strength of the second plated steel sheet (20) after hot stamping.

Specifically, when the aluminum-based plating blank (100) is combined with steel plates having different components (for example, when the first plating steel plate (10) and the second plating steel plate (20) each include a second alloy composition and a third alloy composition, or when the first plating steel plate (10) and the second plating steel plate (20) include a first alloy composition so that the components of the first plating steel plate (10) and the second plating steel plate (20) are different), a value obtained by multiplying the maximum thickness of the joint (30) by the tensile strength of the joint (30) after hot stamping may be greater than at least one of a value obtained by multiplying the thickness of the first plating steel plate (10) by the tensile strength of the first plating steel plate (10) after hot stamping and a value obtained by multiplying the thickness of the second plating steel plate (20) by the tensile strength of the second plating steel plate (20) after hot stamping.

Below, a method for manufacturing an aluminum-based plating blank (100) is described.

A method for manufacturing an aluminum-based plating blank (100) according to one embodiment may include a step of arranging edges of a first plated steel sheet (10) and a second plated steel sheet (20) so that they face each other, and a step of forming a joint (30) connecting the first plated steel sheet (10) and the second plated steel sheet (20) by irradiating a laser beam.

In one embodiment, the side surface of the first plated steel plate (10) and the side surface of the second plated steel plate (20) may be arranged to face each other. At this time, the side surface of the first plated steel plate (10) and the side surface of the second plated steel plate (20) may be in contact with each other.

In one embodiment, before the step of arranging the side surfaces of the first plated steel sheet (10) and the side surfaces of the second plated steel sheet (20) to face each other, a step of removing 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 performed first. That is, before laser welding the first plated steel sheet (10) and the second plated steel sheet (20), the plating layers of the portions to be welded in the first plated steel sheet (10) and the second plated steel sheet (20) may be removed in advance. However, the present invention is not limited thereto. The step of removing 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 omitted.

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 portion to be welded in the first plated steel sheet (10) may be removed.

At this time, the first plating layer (14) can be removed by a method including melting and evaporation. Specifically, the first plating layer (14) can be removed by a laser beam. For example, the removal of the first plating layer (14) can be performed by a laser beam. When a high-power and high-energy density laser beam is irradiated on the surface of the first plating layer (14) to remove the first plating layer (14), the surface of the first plating layer (14) can be liquefied and evaporated. In addition, the liquefied first plating layer (14) due to the plasma pressure can be discharged to the surroundings. By controlling the laser beam, only a part of the first plating layer (14) in the thickness direction or the entire first plating layer (14) can be removed.

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.

In addition, the first plating 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 plating layer (14) disposed on one side of the first base steel (12) may be removed, and the first plating layer (14) disposed on the other side of the first base steel (12) may not be removed.

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) of the welded portion of the second plated steel sheet (20) may be removed. At this time, the second plating layer (24) may be removed by a method including melting and evaporation.

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.

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 plate (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.

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) can be removed simultaneously. At this time, 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) can be removed by a laser beam. Specifically, after the first plated steel sheet (10) and the second plated steel sheet (20) are positioned to be spaced apart from each other by a predetermined interval, a laser beam is 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, after the edges of the first plated steel sheet (10) and the second plated steel sheet (20) are arranged so that they are spaced apart by a predetermined distance, at least a portion of the first plated layer (14) and at least a portion of the second plated layer (24) can be removed using a laser.

In one embodiment, at least a portion of the first plating layer (14) disposed on one surface of the first base steel (12) and at least a portion of the first plating layer (14) disposed on the other surface of the first base steel (12) can be removed. Specifically, both the diffusion layer and the surface layer of the first plating layer (14) of the welded portion among the first plating layers (14) disposed on the one surface and the other surface of the first base steel (12) can be removed.

In one embodiment, at least a portion of the second plating layer (24) disposed on one surface of the second base steel (22) and at least a portion of the second plating layer (24) disposed on the other surface of the second base steel (22) can be removed. Specifically, both the diffusion layer and the surface layer of the second plating layer (24) of the welded portion among the second plating layers (24) disposed on the one surface and the other surface of the second base steel (22) can be removed.

In one embodiment, when at least a portion of the first plating layer (14) of the first plated steel sheet (10) is removed, only at least a portion of the first plating layer (14) in the thickness direction of the first plated steel sheet (10) may be removed. For example, only the surface layer among the surface layer and the diffusion layer of the first plating layer (14) of the portion to be welded in the first plated steel sheet (10) may be removed. At this time, in the case of the first plating layer (14) disposed on one surface of the first base steel (12), only the surface layer among the surface layer and the diffusion layer may be removed, and in the case of the first plating layer (14) disposed on the other surface of the first base steel (12), only the surface layer among the surface layer and the diffusion layer of the first plating layer (14) may be removed, or both the surface layer and the diffusion layer of the first plating layer (14) may be removed. However, the opposite case is also possible.

In one embodiment, when at least a portion of the second plating layer (24) of the second plated steel sheet (20) is removed, only at least 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 among the surface layer and the diffusion layer of the second plating layer (24) of the welded portion of the second plated steel sheet (20) may be removed. At this time, in the case of the second plating layer (24) disposed on one surface of the second base steel (22), only the surface layer among the surface layer and the diffusion layer may be removed, and in the case of the second plating layer (24) disposed on the other surface of the second base steel (22), only the surface layer among the surface layer and the diffusion layer of the second plating layer (24) may be removed, or both the surface layer and the diffusion layer of the second plating layer (24) may be removed. However, the opposite case is also possible.

Additionally, in the first plating layer (14) and the second plating layer (24), at least a portion of the diffusion layer may also be removed when the surface layer is removed.

In one embodiment, when the plating amount on one side of the first base iron (12) is less than 50 g/m ² , the first plating layer (14) disposed on the first base iron (12) may not be removed. Specifically, further, when the plating amount on each of one side and the other side of the first base iron (12) is less than 50 g/m ² , the first plating layer (14) disposed on each of the one side and the other side of the first base iron (12) may not be removed.

In one embodiment, when the plating amount on one side of the second base iron (22) is less than 50 g/m ² , the second plating layer (24) disposed on the second base iron (22) may not be removed. Specifically, further, when the plating amount on each of one side and the other side of the second base iron (22) is less than 50 g/m ² , the second plating layer (24) disposed on each of the one side and the other side of the second base iron (22) may not be removed.

In one embodiment, a laser beam is irradiated from a laser head to the boundary between the first plated steel sheet (10) and the second plated steel sheet (20), so that a joint (30) connecting the first plated steel sheet (10) and the second plated steel sheet (20) can be formed at the boundary between the first plated steel sheet (10) and the second plated steel sheet (20).

The joint (30) is formed by melting the first plated steel sheet (10) and the second plated steel sheet (20) by 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 dissolved into the joint (30). However, prior to performing laser welding on the first plated steel sheet (10) and the second plated steel sheet (20), at least a portion of the first plated layer (14) and/or the second plated layer (24) of the portion to be welded in the first plated steel sheet (10) and the second plated steel sheet (20) is removed in advance, and therefore the aluminum (Al) content included in the joint (30) can have a very low value.

In one embodiment, a filler wire may be used in the process of laser welding the first galvanized steel sheet (10) and the second galvanized steel sheet (20). At this time, the filler wire may be used for the purpose of component compensation for gap bridging and strengthening the quenchability of the joint (30).

First, when the edges of the first plated steel sheet (10) and the second plated steel sheet (20) are arranged so that they face each other, a gap may occur at the boundary between the first plated steel sheet (10) and the second plated steel sheet (20). At this time, when a filler wire is used, the gap that occurs at the boundary between the first plated steel sheet (10) and the second plated steel sheet (20) can be filled.

In one embodiment, in a joining step of forming a joint (30) connecting a first plated steel sheet (10) and a second plated steel sheet (20) by irradiating a laser beam, a filler wire may be provided at the boundary between the first plated steel sheet (10) and the second plated steel sheet (20). That is, after a step of arranging the edges of the first plated steel sheet (10) and the second plated steel sheet (20) to face each other, a joining step of providing a filler wire at the boundary between the first plated steel sheet (10) and the second plated steel sheet (20) and forming a joint (30) connecting the first plated steel sheet (10) and the second plated steel sheet (20) by irradiating a laser beam may be performed. However, a filler wire may not be provided at the boundary between the first plated steel sheet (10) and the second plated steel sheet (20).

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 (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).

The joint (30) is formed by melting the first plated steel plate (10), the second plated steel plate (20), and the filler wire by a laser beam, and through this process, the components of the first plated layer (14) of the first plated steel plate (10) and the second plated layer (24) of the second plated steel plate (20) can be dissolved into the joint (30). Therefore, the composition of the filler wire should be determined by considering the penetration of the components of the first plated layer (14) and the second plated layer (24) during laser welding.

In one embodiment, the filler wire may include an austenite stabilizing element. For example, the filler wire may include at least one austenite stabilizing element among carbon (C) and manganese (Mn), and the remainder iron (Fe) and inevitable impurities. At this time, the content of carbon (C) in the filler wire may be 0.01 wt% or more and 1.5 wt% or less, the content of silicon (Si) may be 0.1 wt% or more and 2.0 wt% or less, and the content of manganese (Mn) may be 0.01 wt% or more and 20.0 wt% or less. Such a filler wire is melted into the joint (30) and may control the component system of the joint (30).

In one embodiment, the filler wire may include carbon (C) of 0.01 wt% or more and 1.5 wt% or less, silicon (Si) of 0.1 wt% or more and 2.0 wt% or less, manganese (Mn) of 0.01 wt% or more and 20.0 wt% or less, phosphorus (P) of 0 wt% or more and 0.1 wt% or less, sulfur (S) of 0 wt% or more, iron (Fe) as a remainder, and other unavoidable impurities.

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

The filler wire may contain 0.1 wt% or more and 2.0 wt% or less of silicon (Si). If the content of silicon (Si) contained in the filler wire is less than 0.1 wt%, brittle fracture may occur at the joint (30). On the other hand, if the content of silicon (Si) contained in the filler wire exceeds 2.0 wt%, slag may occur on the surface of the bead.

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

The filler wire may contain phosphorus (P) in an amount greater than 0 and less than or equal to 0.1 wt%. If the content of phosphorus (P) in the filler wire exceeds 0.1 wt%, brittle fracture due to segregation may occur.

The filler wire may contain sulfur (S) in an amount greater than 0 and less than or equal to 0.1 wt%. If the content of sulfur (S) in the filler wire exceeds 0.1 wt%, cracks may occur due to the formation of inclusions.

Specifically, even if aluminum (Al) of the first plating layer (14) and the second plating layer (24) is mixed into the molten pool of the joint (30), the microstructure of the joint (30) can have a martensite structure of 90% or more in area fraction, preferably a full martensite structure, after hot stamping due to the austenite stabilizing element added to the filler wire. That is, according to the present invention, even if the components of the first plating layer (14) and the second plating layer (24) are mixed into the joint (30) without removing the first plating layer (14) and the second plating layer (24), the hardness and strength of the joint (30) can be prevented from being reduced, thereby preventing the fracture phenomenon of the joint (30).

In addition, when the components of the first plated steel sheet (10) and the second plated steel sheet (20) are different, even if aluminum (Al) of the first plated layer (14) and the second plated layer (24) is mixed into the molten pool of the joint (30), the microstructure of the joint (30) after hot stamping is prevented from excessively including ferrite by the austenite stabilizing element added to the filler wire (200), thereby preventing breakage at the joint (30).

In one embodiment, the radius of the filler wire may be less than or equal to the radius of the laser beam as described below. Specifically, the radius of the filler wire may be less than or equal to 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 may be less than or equal to BR * 0.9.

In one embodiment, the injection speed of the filler wire may be 0.6 to 1.3 times the formation speed of the joint (30) described below. When the injection speed of the filler wire is less than 0.6 times the formation speed of the joint (30), the gap bridging effect may be weak and it may be difficult to achieve the purpose of strengthening the hardenability of the joint (30). On the other hand, when the injection speed of the filler wire is more than 1.3 times the formation speed of the joint (30), the thickness of the joint (30) may become thicker. Therefore, when the injection speed of the filler wire satisfies 0.6 to 1.3 times the formation speed of the joint (30), the gap occurring at the boundary between the first plated steel sheet (10) and the second plated steel sheet (20) can be filled, the hardenability of the joint (30) can be strengthened, and the thickness of the joint (30) can be prevented from becoming thicker.

In one embodiment, the angle between the filler wire and the laser beam may be 30 degrees or greater. Preferably, the angle between the filler wire and the laser beam may be 45 degrees or greater. Specifically, the injection angle of the filler wire with respect to the direction in which the laser beam is irradiated may be 30 degrees or greater. Preferably, the injection angle of the filler wire with respect to the direction in which the laser beam is irradiated may be 45 degrees or greater.

Meanwhile, even if the penetration components of the first plating layer (14) and the second plating layer (24) are diluted by the filler wire (200), the components of the filler wire (200) and the first plating layer (14) and the second plating layer (24) may not be evenly distributed in the components of the first base steel (12) and the second base steel (22) depending on the bonding conditions. To prevent this, the wavelength of the laser beam irradiated during bonding of the first plated steel sheet (10) and the second plated steel sheet (20) may be controlled.

In one embodiment, the wavelength of the laser beam may be 0.1 ㎛ or more and 10 ㎛ or less. When the wavelength of the laser beam is less than 0.1 ㎛, the wavelength of the laser beam is too short, so that the power of the laser beam must be increased to melt the joint (30), which may reduce productivity and business feasibility. When the wavelength of the laser beam exceeds 10 ㎛, the laser absorption rate of the plated steel sheet (10, 20) is reduced, so that it may be difficult to uniformly distribute aluminum (Al) mixed into the weld (or joint (30)) from the plating layer (14, 24) in the weld (or joint (30)). In other words, aluminum (Al) segregation may occur in the weld (or joint (30)). Therefore, when the wavelength of the laser beam satisfies a range of 0.1 ㎛ or more and 10 ㎛ or less, the laser is well absorbed by the plated steel plate (10, 20) and can sufficiently melt the portion of the plated steel plate (10, 20) to be welded, so that aluminum (Al) can be uniformly distributed in the welded portion (or joint portion (30)). In other words, aluminum (Al) segregation can be prevented from occurring in the welded portion (or joint portion (30)).

In one embodiment, the power of the laser beam may be from 0.5 kW to 20 kW. In one embodiment, the power of the laser beam may mean the output value of the laser oscillation unit.

In one embodiment, when manufacturing an aluminum-based plating blank (100), the formation speed of the joint (30) must be 1 m/min or more and the power of the laser beam must be 20 kW or less to ensure minimum productivity and business feasibility. The higher the power of the laser beam, the better. However, in order to implement power exceeding 20 kW, high-performance equipment is required, which increases the size of the equipment and increases the price of the equipment. In addition, in order to secure minimum productivity, the formation speed of the joint (30) must be maintained at 1 m/min or more. The formation speed of the joint (30) means the displacement per unit time in which the laser head moves relative to the direction of forming the joint.

In one embodiment, the formation speed of the joint (30) may be 1 to 15 m/min. If the formation speed of the joint (30) exceeds 15 m/min, even if a laser beam having a wavelength of 0.1 to 10 ㎛, a power of 0.5 to 20 kW, and a beam radius of 0.1 to 2.0 mm is irradiated, the first plated steel sheet (10) and the second plated steel sheet (20) may not be sufficiently melted.

In one embodiment, the radius of the laser beam may be 0.1 to 2.0 mm. In order for the radius of the laser beam to exceed 2.0 mm, the distance between the filler wire and the first and second plated steel plates (10, 20) and the laser head must be close. In this case, the space for supplying the filler wire or the space for replacing the filler wire when consumed may not be sufficient, which may lower the efficiency of the manufacturing process. On the other hand, when the radius of the laser beam is less than 0.1 mm, the width of the joint (30) may be too small because the radius of the laser beam is small.

In one embodiment, when irradiating the laser beam, a first laser beam and a second laser beam spaced apart from each other can be irradiated. For example, the first laser beam melts the first plating layer (14), the second plating layer (24), the first base iron (12), and the second base iron (22), and the second laser beam maintains the molten state, thereby uniformly stirring the molten portion, thereby preventing segregation of the joint (30), and improving the quality and mechanical properties. Meanwhile, when using the first laser beam and the second laser beam, the sum of the powers of the first laser beam and the second laser beam can be 0.5 to 20 kW.

Meanwhile, when the aluminum-based plating blank (100) is subjected to heat treatment by heating to a high temperature and then rapidly cooling after joining within the above-described ranges of the wavelength of the laser beam, the power of the laser beam, the radius of the laser beam, and the speed of forming the joint (30), the average hardness of the joint (30) may be 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) may be greater than the minimum hardnesses of the first plated steel sheet (10) and the second plated steel sheet (20).

In other words, when the aluminum-based plating blank (100) is subjected to heat treatment by heating to a high temperature and then rapidly cooling after joining within the above-described ranges of the wavelength of the laser beam, the power of the laser beam, the radius of the laser beam, and the speed of forming the joint (30), the average hardness of the joint (30) may be greater than at least one of the average hardnesses of the first base steel (12) and the second base steel (22), and preferably, the minimum hardness of the joint (30) may be greater than the minimum hardnesses of the first base steel (12) and the second base steel (22).

Specifically, when the aluminum-based plating blank (100) is combined with dissimilar component steel plates, the average hardness of the joint (30) after hot stamping may be greater than the minimum hardness of the steel plate with a lower tensile strength among the first plating steel plate (10) and the second plating steel plate (20) after hot stamping.

In other words, when the aluminum-plated blank (100) is combined with a dissimilar steel plate (the average hardness of the joint (30) after hot stamping may be greater than the minimum hardness of the base steel having a lower tensile strength among the first base steel (12) and the second base steel (22) after hot stamping.

In one embodiment, the formation speed of the joint (30) is 1 to 15 m/min, and at this time, the power of the laser beam, the wavelength of the laser beam, and the radius of the laser beam may be 0.5 to 20 kW, 0.1 to 10 μm, and 0.1 to 2.0 mm, respectively.

When the power of the laser beam, the wavelength of the laser beam, and the radius of the laser beam satisfy the conditions described above, aluminum (Al) segregation can be suppressed, thereby preventing the fracture of the joint during tension. However, at this time, the speed of forming the joint (30) may be 1 to 15 m/min. When the speed of forming the joint (30) exceeds 15 m/min, there may be insufficient time for energy to be evenly transmitted to the joint (30). For example, under the condition of a speed of forming the joint (30) of 15 to 30 m/min, aluminum (Al) segregation may occur excessively at the joint (30) even when the power of the laser beam, the wavelength of the laser beam, and the radius of the laser beam satisfy the conditions described above.

Hereinafter, the configuration and operation of the present invention will be described in more detail through preferred embodiments of the present invention. However, these are presented as preferred examples of the present invention and cannot be interpreted as limiting the present invention in any way.

Experimental Example 1

A first plated steel sheet comprising a steel slab containing 0.06 wt% of carbon (C), 0.45 wt% of silicon (Si), 1.75 wt% of manganese (Mn), 0.015 wt% or less of phosphorus (P), 0.003 wt% or less of sulfur (S), 0.002 wt% or less of boron (B), 0.015 wt% or less of titanium (Ti), the remainder being iron (Fe) and other unavoidable impurities, is subjected to finish rolling of the reheated slab, the hot-rolled steel sheet is coiled, the coiled steel sheet is cold rolled, the cold-rolled steel sheet is annealed, and the annealed steel sheet is immersed in a plating bath containing 8.5 wt% of silicon (Si), the remainder being aluminum (Al) and other unavoidable impurities, and cooled to form a first plating layer on at least one surface of a first base steel sheet. At this time, the thickness of the first plated steel sheet is 1.4 mm.

In addition, a second plated steel sheet containing a steel slab containing 0.29 wt% of carbon (C), 0.2 wt% of silicon (Si), 1.5 wt% of manganese (Mn), 0.02 wt% or less of phosphorus (P), 0.015 wt% or less of sulfur (S), 0.2 wt% or less of chromium (Cr), 0.0025 wt% or less of boron (B), 0.035 wt% or less of titanium (Ti), the remainder iron (Fe) and other unavoidable impurities, was prepared by finish-rolling the reheated slab, 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 plating bath containing 8.5 wt% of silicon (Si), the remainder aluminum (Al) and other unavoidable impurities, and cooling the same to form a second plating layer on at least one surface of a second base steel. At this time, the thickness of the second galvanized steel plate is 1.4 mm.

Thereafter, a portion of the plating layer formed on both sides of the base steel at the welded portion was removed using a laser beam in the first and second plating steel sheets. For example, a portion of the plating layer disposed on one side and the other side of the base steel at the welded portion was removed using a laser beam.

Then, the edges of the first galvanized steel sheet and the edges of the second galvanized steel sheet were arranged to face each other, and a laser beam was irradiated to melt the facing portions of the aluminum-based galvanized steel sheets to form a joint, thereby manufacturing aluminum-based galvanized blanks of Examples 1 to 3 and Comparative Examples 1 to 4.

Examples 1 to 3 and Comparative Examples 1 to 3 were formed with a plating amount of 70 g/m ² on both sides of the base steel, and Comparative Example 4 was formed with a plating amount of 100 g/m ² on both sides of the base steel.

In addition, 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 formation speed of 5 m/min.

At this time, a laser beam with a wavelength of 5 μm was irradiated in Example 1, a laser beam with a wavelength of 2 μm was irradiated in Example 2, a laser beam with a wavelength of 10 μm was irradiated in Example 3, a laser beam with a wavelength of 11 μm was irradiated in Comparative Examples 1 to 3, and a laser beam with a wavelength of 9 μm was irradiated in Comparative Example 4.

That is, the power of the laser beam, the radius of the laser beam, and the joint formation speed irradiated in Examples 1 to 3 and Comparative Examples 1 to 4 are the same, but the wavelengths of the laser beams may be different from each other.

Table 1 below shows the fracture locations in the tensile test after hot stamping according to the average aluminum content and standard deviation of the aluminum content in the joint.

division At the joint
Average aluminum content
(weight%) Standard deviation of aluminum content of joints Standard deviation of aluminum content in the first side Standard deviation of aluminum content in the second side After hot stamping
During tensile testing
Fracture site Example 1 0.12 0.03 0.03 0.04 Galvanized steel sheet Example 2 0.40 0.07 0.05 0.06 Galvanized steel sheet Example 3 0.49 0.45 0.38 0.38 Galvanized steel sheet Comparative Example 1 0.47 0.46 0.39 0.39 Joint Comparative Example 2 0.48 0.43 0.37 0.41 Joint Comparative Example 3 0.48 0.45 0.41 0.39 Joint Comparative Example 4 0.53 0.46 0.38 0.43 Joint

As described above, the average aluminum content of the joint can be 0 wt% or more and less than 0.5 wt%. In addition, the joint can include a first side portion, a second side portion, and a center portion, and a standard deviation of the aluminum content of the joint can be 0 or more and 0.45 or less, and a standard deviation of the aluminum contents of the first side portion and the second side portion can be 0 or more and 0.4 or less.

Referring to Table 1, when the average aluminum content of the joint, the standard deviation of the aluminum content of the joint, the standard deviation of the aluminum content of the first side, and the standard deviation of the aluminum content of the second side satisfy the conditions described above, it can be confirmed that a 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 after hot stamping the aluminum-based plated blank.

Comparative Example 1 is a case where the standard deviation of the aluminum content of the joint exceeds 0.45, and although the average aluminum content of the joint is less than 0.50 wt% and the standard deviation of the aluminum contents of the first side and the second side is 0.4 or less, it can be confirmed that a fracture occurs at the joint during a tensile test after hot stamping the aluminum-plated blank. Comparative Example 1 is a case where the wavelength of the laser beam exceeds 10 ㎛, and although the aluminum content of the joint satisfies the condition of less than 0.50 wt%, the wavelength of the laser beam is too long, so that the laser absorption rate of the plated steel sheet is reduced, and thus the aluminum mixed into the joint from the plating layer is not uniformly distributed at the joint. For example, although the aluminum content of the joint is less than 0.50 wt%, and thus the aluminum content of the joint satisfies the required condition, the wavelength of the laser beam is too long, so that the aluminum is not well mixed at the joint, and thus the aluminum is not uniformly distributed at the joint.

Comparative Example 2 is a case where 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 satisfies 0.4 or less, it can be confirmed that a fracture occurs at the joint during a tensile test after hot stamping the aluminum-plated blank. Comparative Example 2 is a case where the wavelength of the laser beam exceeds 10 ㎛, and although the aluminum content at the joint satisfies less than 0.50 wt%, the wavelength of the laser beam is too long, so that the laser absorption rate of the plated steel sheet is reduced, and thus the aluminum mixed into the joint from the plating layer is not uniformly distributed at the joint. For example, although the aluminum content at the joint is less than 0.50 wt%, and the aluminum content at the joint satisfies the required condition, the wavelength of the laser beam is too long, so that the aluminum is not mixed well at the joint, and thus the aluminum is not uniformly distributed at the joint.

Comparative Example 3 is a case where the standard deviation of the aluminum content on the first side exceeds 0.4, the average aluminum content 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 second side satisfies 0.4 or less, but it can be confirmed that a fracture occurs at the joint during a tensile test after hot stamping the aluminum-plated blank. Comparative Example 3 is a case where the wavelength of the laser beam exceeds 10 ㎛, and the aluminum content at the joint satisfies less than 0.50 wt%, but the wavelength of the laser beam is too long, so that the laser absorption rate of the plated steel sheet is reduced, and the aluminum mixed into the joint from the plating layer is not uniformly distributed at the joint. For example, when the aluminum content at the joint is less than 0.50 wt%, the aluminum content at the joint satisfies the required condition, but the wavelength of the laser beam is too long, so that the aluminum is not mixed well at the joint, and so the aluminum is not uniformly distributed at the joint.

Comparative Example 4 is a case where the average aluminum content is 0.50 wt% or more, the standard deviation of the aluminum content of the joint is more than 0.45, and the standard deviation of the aluminum content of the second side is more than 0.4, and even though the standard deviation of the aluminum content of the first side is 0.4 or less, it can be confirmed that a fracture occurs at the joint during a tensile test after hot stamping the aluminum-plated blank. In Comparative Example 4, the welding conditions are satisfied because the wavelength of the laser beam is 10 ㎛ or less, but the aluminum content of the joint is too much, so the aluminum at the joint is not mixed well and the aluminum is not uniformly distributed at the joint.

Therefore, when the average aluminum content of the joint is provided as 0 wt% or more and less than 0.5 wt%, and the standard deviation of the aluminum content of the joint is provided as 0 or more and 0.45 or less, the occurrence of a fracture at the joint during a tensile test after hot stamping the aluminum-plated blank can be prevented or minimized. 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 provided as 0 or more and 0.4 or less, aluminum is evenly distributed at the first side and the second side, so that the occurrence of a fracture between the first plated steel sheet and the joint and between the second plated steel sheet and the joint can be prevented or minimized.

Experimental example 2

Examples 4 to 6 and Comparative Examples 5 to 7 are aluminum-based plating blanks manufactured under the same conditions as Examples 1 to 3 and Comparative Examples 1 to 3 of Experimental Example 1, respectively. At this time, Example 4 was irradiated with a laser beam having a wavelength of 2 μm, Example 5 was irradiated with a laser beam having a wavelength of 5 μm, Example 6 was irradiated with a laser beam having a wavelength of 10 μm, and Comparative Examples 5 to 7 were irradiated with a laser beam having a wavelength of 11 μm.

Table 2 below shows the fracture locations in a tensile test after hot stamping according to the average silicone content and/or standard deviation of the silicone content in the joint.

division At the joint
Average content of silicon
(weight%) Standard deviation of silicone content of joints After hot stamping
During tensile testing
Fracture site Example 4 0.3 0.06 Galvanized steel sheet Example 5 0.5 0.13 Galvanized steel sheet Example 6 0.8 0.20 Galvanized steel sheet Comparative Example 5 0.7 0.21 Joint Comparative Example 6 0.8 0.22 Joint Comparative Example 7 0.8 0.21 Joint

As described above, the average silicone content of the joint may be 0.3 wt% or more and 0.8 wt% or less. In addition, the standard deviation of the silicone content of the joint may be 0 or more and 0.2 or less.

Referring to Table 2, when the average silicon content of the joint and the standard deviation of the silicon content of the joint satisfy the conditions described above, it can be confirmed that a 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 after hot stamping the aluminum-based plated blank.

Referring to Comparative Examples 5 to 7, even when the average content of silicon in the joint satisfies 0.3 wt% or more and 0.8 wt% or less, when the wavelength of the laser beam exceeds 10 ㎛, the silicon content in the joint satisfies 0.80 wt% or less, but the wavelength of the laser beam is too long, so the laser absorption rate of the plated steel sheet is reduced, so that the silicon mixed into the joint from the plating layer is not uniformly distributed in the joint. For example, when the silicon content in the joint is 0.80 wt% or less, the silicon content in the joint satisfies the required condition, but the wavelength of the laser beam is too long, so that the silicon is not mixed well in the joint, so that the silicon is not uniformly distributed in the joint.

Although the present invention has been described with reference to one embodiment shown in the drawings, this is merely exemplary, and those skilled in the art will understand that various modifications and variations of embodiments are possible from this. Accordingly, the true technical protection scope of the present invention should be determined by the technical idea of the appended patent claims.

Claims (14)

As an aluminum-based plating blank,
1st galvanized steel plate;
A second plated steel sheet connected to the first plated steel sheet; and
Including a joint connecting the first plated steel sheet and the second plated steel sheet at the boundary between the first plated steel sheet and the second plated steel sheet;
Each of the first plated steel sheet and the second plated steel sheet includes a base steel and a plated layer formed on at least one surface of the base steel and containing aluminum (Al),
The above joint comprises aluminum (Al) and silicon (Si),
The average content of aluminum (Al) in the above joint is 0 wt% or more and less than 0.5 wt%,
The average content of silicon (Si) in the above joint is 0.3 wt% or more and 0.8 wt% or less,
An aluminum-based plating blank, wherein the standard deviation of the silicon (Si) content of the above joint is 0 or more and 0.2 or less. In the first paragraph,
An aluminum-plated blank, wherein the standard deviation of the aluminum (Al) content of the above joint is 0 or more and 0.45 or less. In the first paragraph,
An aluminum-based plated blank, wherein the joint comprises a first side adjacent to the first plated steel sheet, a second side adjacent to the second plated steel sheet, and a center portion between the first side and the second side. In the third paragraph,
An aluminum-based plating blank, wherein the standard deviation of the aluminum (Al) content of the first side is 0 or more and 0.4 or less. delete In the first paragraph,
The above first galvanized steel sheet and the above second galvanized steel sheet each include a first base steel and a second base steel,
An aluminum-based plating blank, wherein the first and second base irons each contain 0.01 wt% or more of carbon (C) and 0.5 wt% or less, 0.01 wt% or more to 1.0 wt% or less of silicon (Si), 0.3 wt% or more to 2.0 wt% or less of manganese (Mn), more than 0 wt% or more of phosphorus (P), more than 0 wt% or less of sulfur (S), and the remainder iron (Fe) and other unavoidable impurities. In Article 6,
An aluminum-based plating blank, wherein the first plating steel sheet and the second plating steel sheet have different tensile strengths. In the first paragraph,
The above first galvanized steel sheet and the above second galvanized steel sheet each include a first base steel and a second base steel,
The above first base iron contains carbon (C) of 0.01 wt% or more and less than 0.20 wt%, silicon (Si) of 0.01 wt% or more and less than 0.8 wt%, manganese (Mn) of 0.8 wt% or more and less than 2.0 wt%, phosphorus (P) of more than 0 and less than 0.05 wt%, sulfur (S) of more than 0 and less than 0.01 wt%, and the remainder iron (Fe) and other unavoidable impurities.
An aluminum-based plating blank, wherein the second base material comprises carbon (C) of 0.20 wt% or more and 0.5 wt% or less, silicon (Si) of 0.1 wt% or more and 0.8 wt% or less, manganese (Mn) of 0.3 wt% or more and 2.0 wt% or less, phosphorus (P) of more than 0 and 0.05 wt% or less, sulfur (S) of more than 0 and 0.01 wt% or less, the remainder iron (Fe) and other unavoidable impurities. In the first paragraph,
The above first galvanized steel sheet and the above second galvanized steel sheet each include a first base steel and a second base steel,
An aluminum-based plating blank, wherein the first and second base irons each contain carbon (C) of 0.01 wt% or more and less than 0.20 wt%, silicon (Si) of 0.01 wt% or more and less than 0.8 wt%, manganese (Mn) of 0.8 wt% or more and less than 2.0 wt%, phosphorus (P) of more than 0 and less than 0.05 wt%, sulfur (S) of more than 0 and less than 0.01 wt%, the remainder iron (Fe) and other unavoidable impurities. In Article 9,
An aluminum-based plating blank, wherein the first plating steel sheet and the second plating steel sheet have different tensile strengths. In the first paragraph,
The above first galvanized steel sheet and the above second galvanized steel sheet each include a first base steel and a second base steel,
An aluminum-based plating blank, wherein the first and second base irons each contain carbon (C) of 0.20 wt% or more and 0.5 wt% or less, silicon (Si) of 0.1 wt% or more and 0.8 wt% or less, manganese (Mn) of 0.3 wt% or more and 2.0 wt% or less, phosphorus (P) of more than 0 and 0.05 wt% or less, sulfur (S) of more than 0 and 0.01 wt% or less, the remainder iron (Fe) and other unavoidable impurities. In Article 11,
An aluminum-based plating blank, wherein the first plating steel sheet and the second plating steel sheet have different tensile strengths. In the first paragraph,
An aluminum-based plating blank, wherein the first plating steel sheet and the second plating steel sheet have different thicknesses. In the first paragraph,
An aluminum-based plating blank, wherein the first plating steel sheet and the second plating steel sheet have the same thickness.

Images