TWI788080B - Hot forming steel sheet with hardened aluminum-based plating and method for producing the same - Google Patents

Abstract

The present invention relates to a hot forming steel sheet with a hardened aluminum-based plating and a method for producing the same. The method for producing the hot forming steel sheet with the hardened aluminum-based plating forms a plating with a specific structure by using a plating liquid with a specific composition, during a hot-stamped forming, the plating can undergo a rapid an alloyed reaction to transform a Fe-Al layer and an antioxidant layer. An outer area of the Fe-Al layer has a specific composition to prevent the plating from sticking a hearth roll and enhance a welding capability of the hot forming steel sheet with the hardened aluminum-based plating. The antioxidant layer can resist a high temperature to prevent the steel sheet from poor welding caused by an oxidation.

Description

Thermoformed hardened aluminum-based coated steel sheet and method of manufacturing the same

The present invention relates to a thermoformed hardened aluminum-based coated steel sheet and its manufacturing method, and in particular to a thermoformed hardened aluminum-based coated steel sheet with a coating of a specific structure and its manufacturing method.

Nowadays, the automobile manufacturing industry is focusing on reducing the weight of the vehicle body in order to cope with the increasingly stringent regulations on carbon dioxide emissions. The technical means of reducing the thickness of the steel plate by increasing the strength of the steel plate has become a development strategy for automobile lightweight. However, increasing the strength of the steel plate will reduce the formability of the steel plate, so the automobile manufacturing industry adopts a hot stamping forming process to improve the formability of the steel plate.

In detail, the hot stamping forming process includes heat treatment of the steel material to be ironized (that is, heating the steel), stamping and rapid cooling of the steel material that has been ironed, so as to obtain the heat of the Matian loose iron phase. Stamped and formed steel sheet. Although the auto parts formed by this hot stamping steel sheet have a strength higher than 1000 MPa, in the heating forming step of the hot stamping process, the steel is severely oxidized and decarburized at high temperature, thereby reducing the strength of the hot stamping steel sheet and subsequent The characteristics of welding, and shorten the service life of the mold. Therefore, in the heating forming step of the hot stamping process, a nitrogen atmosphere must be used to protect the heat-treated steel to slow down oxidation and decarburization. In addition, after the hot stamping process, it is necessary to remove the iron oxide film formed on the surface of the steel plate by means of surface blasting.

Although the hot-dip galvanized coating has excellent cathodic anti-corrosion effect and is applied to the anti-corrosion coating of automobile steel sheets, the zinc coating does not have high-temperature oxidation resistance. During hot stamping, the surface of the zinc coating will still be severely oxidized, and a zinc oxide film with a thickness of 5 μm to 10 μm will be formed, which will reduce the welding characteristics of the hot-formed steel sheet (for example: severe flying explosion during welding, occurrence of weld nugget surface burrs and weld nugget surface pole head sticking).

In order to improve the aforementioned shortcomings of oxidation, the hot-dip galvanized coating is modified into a hot-dip aluminum-silicon coating. However, because the alloying reaction rate of the aluminum-silicon coating is too slow, the aluminum-silicon coating will exist in a liquid state during the heating step of the hot stamping process. Furnace roll nodules, thus reducing the quality of parts made from hot-formed steel sheets. In addition, furnace roll nodules will increase the replacement frequency of furnace rolls, thus reducing productivity and increasing production costs.

In view of this, there is an urgent need to develop a new method for manufacturing hot-formed hardened aluminum-based plated steel sheets to improve the above-mentioned shortcomings of conventional methods for manufacturing hot-formed steel sheets.

In view of the above problems, an aspect of the present invention is to provide a method for manufacturing a hot-formed hardened aluminum-based plated steel sheet. This method uses a specific composition of immersion plating solution to form a coating with a specific structure. This coating can undergo rapid alloying reaction during hot stamping to prevent the coating from sticking to the furnace roll and improve the welding of hot-formed hardened aluminum-based coated steel sheets. ability.

Another aspect of the present invention is to provide a thermoformed hardened aluminum base plated steel sheet. The hot-formed hardened aluminum-based coated steel sheet is produced by the above-mentioned manufacturing method of the hot-formed hardened aluminum-based coated steel sheet.

According to an aspect of the present invention, a method of manufacturing a hot-formed hardened aluminum-based plated steel sheet is proposed. In this manufacturing method, a base steel plate is provided, and then the base steel plate is annealed to obtain an annealed steel plate. Next, the annealed steel sheet is subjected to a hot-dip aluminum plating treatment to obtain an aluminum-based plated steel sheet. The hot-dip aluminizing treatment includes forming a coating on the surface of annealed steel sheet with a dipping solution at a temperature of 640°C to 700°C, wherein the concentration of silicon in the dipping solution is not less than 8% by weight, and the amount of coating on one side of the coating is 25g /m ² to 90 g/m ² . Then, the aluminum-based coated steel sheet is subjected to a hot stamping forming process to obtain a hot-formed hardened aluminum-based coated steel sheet. The hot stamping process includes a heating forming step and a cooling step including cooling the aluminum-based coated steel sheet. The aforementioned thermoforming step includes heating the aluminum-based coated steel sheet to 850°C to 950°C to carry out an alloying reaction on the coating, and to make the coating into an iron-aluminum layer and an anti-oxidation layer, and the alloying time of the alloying reaction is 60 seconds to 120 seconds.

According to an embodiment of the present invention, the coating includes Al-Si coating and Fe-Al-Si metal coating, and the thickness of the Fe-Al-Si metal coating is 2 μm to 6 μm.

According to another embodiment of the present invention, the average iron content is 0.5% by weight to 2.0% by weight in the outer region of the FeAlSi metal coating.

According to yet another embodiment of the present invention, the average silicon content in the outer region of the Fe-Al-Si intermetallic coating is 8% by weight to 25% by weight.

Another aspect of the present invention is to provide a thermoformed hardened aluminum base plated steel sheet. The hot-formed hardened aluminum-based coated steel sheet is produced by the above-mentioned manufacturing method of the hot-formed hardened aluminum-based coated steel sheet. The hot-formed hardened aluminum-based plated steel sheet does not include an aluminum-silicon coating, but includes a base steel plate, an iron-aluminum layer and an anti-oxidation layer, wherein the iron-aluminum layer is arranged between the base steel plate and the anti-oxidation layer. The thickness of the anti-oxidation layer is 0.15 μm to 0.5 μm.

According to an embodiment of the present invention, the thickness of the Fe-Al layer is 15 μm to 30 μm.

According to another embodiment of the present invention, the average iron content in the outer region of the Fe-Al layer is 35% by weight to 50% by weight.

According to yet another embodiment of the present invention, the average silicon content in the outer region of the Fe-Al layer is 1.0% by weight to 5.0% by weight.

According to yet another embodiment of the present invention, the average aluminum content in the outer region of the Fe-Al layer is greater than 60% by weight.

According to another embodiment of the present invention, the Fe-Al layer is an Fe-Al (Fe ₂ Al ₅ ) alloy phase, and the Fe-Al layer includes an inner region, an outer region and a middle region. The inner region contains doped silicon and is located on the side of the Fe-Al layer adjacent to the base steel plate. The outer region contains bulk silicon and is located on the other side of the Fe-Al layer away from the base steel plate. The middle area is located between the inner area and the outer area.

The method of manufacturing hot-formed hardened aluminum-based plated steel sheet according to the present invention, in which a coating layer with a specific structure is formed by using a dipping solution of a specific composition, and the coating layer can undergo rapid alloying reaction in hot stamping forming to become an iron-aluminum layer and anti-oxidation layer. The outer region of this Fe-Al layer has a specific composition to prevent the coating from sticking to the furnace rolls and to improve the weldability of the thermoformed hardened Al-based coated steel sheet. In addition, the anti-oxidation layer can resist high temperature to avoid poor welding of steel plates caused by oxidation.

The making and using of embodiments of the invention are discussed in detail below. It should be appreciated, however, that the embodiments provide many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are illustrative only and do not limit the scope of the invention.

The manufacturing method of the hot-formed hardened aluminum-based plated steel sheet of the present invention is to use a immersion plating solution with a specific composition (silicon with a concentration of not less than 8 weight percent (wt.%)) to form a specific structure (including aluminum-silicon coating and iron-aluminum coating) Silicon intermetallic coating) coating, this coating can undergo alloying reaction quickly (60 seconds to 120 seconds) in the hot stamping process to become an iron-aluminum layer and an anti-oxidation layer. The outer region of the iron-aluminum layer (the side of the iron-aluminum layer away from the base steel plate) has a specific composition (an average iron content of 35% by weight to 50% by weight, an average silicon content of 1.0% by weight to 5.0% by weight, and an average aluminum content of The content is greater than 60% by weight), so that the melting point of the outer region of the iron-aluminum layer is greater than 1160°C (greater than the Wostian ironization temperature of the hot stamping process), so in the heating step of the hot stamping process, the iron-aluminum layer The outer areas of the layer can remain solid, thus preventing the coating from sticking to the furnace rolls. Furthermore, the specific composition of the outer region of the iron-aluminum layer can also improve the weldability of the thermoformed hardened aluminum-based coated steel sheet (hereinafter referred to as the thermoformed aluminum-based coated steel sheet). In addition, the aforementioned anti-oxidation layer can resist oxidation at high temperature (such as high temperature during welding of steel plates), so as to avoid poor welding of steel plates caused by oxidation.

Referring to FIG. 1 , in the manufacturing method 100 of hot-forming hardened aluminum-based plated steel sheet, a base steel sheet is firstly provided, as shown in operation 110 . The base steel plate may be a hot-rolled steel plate or a cold-rolled steel plate. In some embodiments, the composition of the base steel plate may include 0.1 to 0.5 weight percent of carbon, 0.5 to 3.0 weight percent of manganese, 0.01 to 1.2 weight percent of chromium, 0.1 to 1.2 weight percent of Silicon, 0.0005% to 0.01% by weight of boron, less than 0.22% by weight of titanium, less than 0.12% by weight of aluminum, less than 0.12% by weight of phosphorus, less than 0.06% by weight of sulfur, the balance of iron and unavoidable impurities. When the composition of the base steel plate includes 0.1% to 0.5% by weight of carbon, 0.5% to 3.0% by weight of manganese, 0.1% to 1.2% by weight of silicon and less than 0.12% by weight of phosphorus, the base steel plate has a suitable thermal The mechanical properties of stamping processing (such as: elongation higher than 20% and tensile strength higher than 1000MPa) are conducive to hot stamping and provide good welding characteristics.

After operation 110 , the base steel sheet is annealed to obtain an annealed steel sheet, as shown in operation 120 . The annealing treatment is to restore the metallographic structure deformed by the rolling of the base steel plate in the hot rolling or cold rolling process to the normal shape through recrystallization. In some embodiments, the annealing treatment includes heating from the dew point temperature to 750°C to 850°C in a reducing atmosphere, and maintaining the temperature for 60 seconds to 120 seconds, then cooling to 660°C to 740°C, and maintaining the temperature for 30 seconds to 60 seconds .

The reducing atmosphere can prevent the base steel plate from being oxidized at high temperature, and produce oxides on the surface of the base steel plate (this oxide may lead to uneven and weak dipping), so the reducing atmosphere can be beneficial to the formation of the coating in the subsequent hot-dip aluminum plating treatment on the surface of the steel plate. A specific example of the reducing atmosphere may include but not limited to 10 volume percent hydrogen and 90 volume percent nitrogen. Furthermore, a specific example of the dew point temperature may be -30°C to -60°C. When the dew point temperature is within the aforementioned range, defects (such as holes) are less likely to exist in the subsequent hot-dip aluminum-coating coating, so the oxidation resistance and welding properties of the hot-formed aluminum-based coated steel sheet are improved.

After operation 120 , the annealed steel sheet is subjected to a hot-dip aluminizing treatment to obtain an aluminum-based coated steel sheet, as shown in operation 130 . The hot-dip aluminum plating treatment is to form a coating on the surface of the annealed steel plate with a dipping solution. The dipping temperature for hot-dip aluminizing treatment is 640°C to 700°C. If the immersion plating temperature is lower than 640°C or higher than 700°C, the composition of the immersion plating solution is unstable, and it is easy to delaminate or solidify and precipitate, resulting in uneven dipping of the coating or the formation of a defective coating. Preferably, the immersion plating temperature may be 670°C to 690°C.

The immersion plating time of the hot-dip aluminizing treatment of the present invention is not particularly limited, but the purpose is to achieve the amount of subsequent single-side plating. In some embodiments, the immersion plating time may be 1 second to 10 seconds, and preferably may be 2 seconds to 5 seconds.

The composition of the bath may include silicon, aluminum, and a balance of iron. Based on 100% by weight of the immersion plating solution, the silicon concentration of the immersion plating solution is not less than 8% by weight, and preferably 9% to 12% by weight. If the silicon concentration is less than 8% by weight, the silicon content of the formed coating is reduced, and the coating cannot be alloyed quickly (within 60 seconds to 120 seconds), so that the coating sticks to the furnace roll. In addition, this coating will reduce the thickness of the anti-oxidation layer of the hot-formed aluminum-based coated steel sheet, thus reducing the weldability of the hot-formed aluminum-based coated steel sheet. When the silicon concentration is 9% by weight to 12% by weight, the uniformity of the coating can be improved to improve the welding characteristics of the hot-formed aluminum-based coated steel sheet and prevent the coating from sticking to the furnace roll.

In some embodiments, the aluminum concentration of the immersion plating solution may be 85% by weight to 91% by weight. When the aluminum concentration of the immersion plating solution is in the aforementioned range, it is beneficial to form a dense anti-oxidation layer to improve the welding properties of the hot-formed aluminum-based plated steel sheet. In some specific examples, the aluminum concentration of the immersion plating solution may be the concentration after deducting the silicon concentration and the iron concentration from the total concentration (ie 100 weight percent), ie, the concentration of the balance amount.

In some embodiments, one or more of magnesium, manganese and zinc may be excluded from the immersion bath of the present invention. When the immersion plating solution excludes the above-mentioned components, it can be more conducive to the uniform formation of the coating on the surface of the base steel plate, to improve the oxidation resistance and welding ability of the hot-formed aluminum-based plated steel plate, and to increase the melting point of the formed iron-aluminum layer, and It can reduce its sticking to the conveying furnace roller.

The single-side coating amount of the hot-dip plating treatment is 25g/m ² to 90g/m ² , and preferably 32g/m ² to 76g/m ² . The double-side coating amount of the coating is twice that of the single-side coating amount. If the amount of coating on one side is less than 25g/m ² , the anti-oxidation layer and/or the iron-aluminum layer will be excessively thinned, thus deteriorating the welding properties of the hot-formed aluminum-based coated steel sheet and/or increasing the adhesion of the coating to the furnace roll. If the amount of coating on one side is greater than 90g/m ² , the time for alloying reaction will be increased, and the adhesion of the coating to the furnace roll will be increased.

The coating includes aluminum-silicon coating and iron-aluminum-silicon metal coating, and the aluminum-silicon coating is located in the outer area of the coating, and the iron-aluminum-silicon metal coating is located in the inner area of the coating, wherein the iron-aluminum-silicon intermetallic coating is close to the surface of the annealed steel plate, and the aluminum The silicon coating is kept away from the surface of the annealed steel sheet. The "aluminum-silicon coating" referred to in the present invention refers to a coating containing aluminum and silicon elements. The "iron-aluminum-silicon intermetallic coating" referred to in the present invention refers to a coating containing an intermetallic compound composed of iron, aluminum and silicon elements. In addition, in some embodiments, the thickness of the Al-Si coating is 5 μm to 24 μm, and preferably 8 μm to 22 μm. When the thickness of the aluminum-silicon coating is in the aforementioned range, the alloying reaction time can be shortened, thereby reducing the degree of adhesion of the coating to the furnace roll.

The thickness of the iron-aluminum-silicon intermetallic coating is 2 μm to 6 μm. When the thickness of the iron-aluminum-silicon intermetallic coating is within the aforementioned range, it is beneficial for the alloying reaction to occur in the hot stamping process described later, so as to shorten the alloying reaction time, thereby reducing the adhesion of the coating to the furnace roll. Preferably, the thickness of the iron-aluminum-silicon intermetallic coating can be 2 μm to 4 μm, so as to shorten the alloying reaction time and prevent the coating from sticking to the furnace roller.

Further, in the outer area of the Fe-Al-Si intermetallic coating, the average iron content is 0.5 wt% to 2.0 wt%, and the average silicon content is 8 wt% to 25 wt%. When the average iron content and average silicon content are in the aforementioned ranges, it is beneficial to the alloying reaction described later to reduce the adhesion of the coating to the furnace roll, and the formed iron-aluminum layer can improve the strength of the hot-formed aluminum-based coated steel sheet. Welding ability. Preferably, the average iron content can be 0.6% by weight to 1.7% by weight, and the average silicon content can be 10.7% by weight to 19.3% by weight, so as to prevent the coating from sticking to the furnace roll and further improve the strength of the hot-formed aluminum-based coated steel sheet. Welding ability.

In some embodiments, the average aluminum content may be greater than 60% by weight in the outer region of the FeAlSi metallization layer. When the average aluminum content is within the aforementioned range, an anti-oxidation layer can be formed after hot stamping of the aluminum-based coated steel sheet to improve the oxidation resistance of the hot-formed aluminum-based coated steel sheet, thereby improving its welding ability .

After operation 130 , the aluminum-based coated steel sheet is subjected to a hot stamping process to obtain a hot-formed hardened aluminum-based coated steel sheet, as shown in operation 140 . The hot stamping process includes a heating forming step and a cooling step. In the heating forming step, the aluminum-based plated steel sheet is heated to 850°C to 950°C, which is the temperature of the ferrite of the Al-base plated steel sheet, which is beneficial to the subsequent use of the mold. Steel sheets are hot stamped.

When the aluminum-based coated steel sheet is heated to the aforementioned temperature, the coating will undergo an alloying reaction to become an iron-aluminum layer and an anti-oxidation layer. In detail, in the alloying reaction, the iron element in the base steel plate diffuses to the coating, and the aluminum and silicon elements in the coating diffuse to the base steel plate, and with the diffusion of these elements, the aluminum-silicon coating gradually disappears, and the original iron The aluminum-silicon intermetallic coating becomes thicker and becomes an iron-aluminum layer. At the same time, a new anti-oxidation layer is formed on the side of the iron-aluminum layer away from the base steel plate, that is, the iron-aluminum layer is between the base steel plate and the anti-oxidation layer. In some embodiments, the base steel plate is an annealed steel plate.

In general, the base of the Fe-Al layer is Fe-Al (Fe ₂ Al ₅ ) alloy phase. Further, the diffusion of the aforementioned elements can produce an inner region (the side adjacent to the base steel plate), an outer region (the other side away from the base steel plate), and an intermediate region between the inner region and the outer region in the iron-aluminum layer, wherein The inner region is a continuous silicon-doped iron-aluminum (Fe ₂ Al ₅ ) alloy phase (continuous phase for short), and the outer region is a discontinuous iron-aluminum (Fe ₂ Al ₅ ) alloy phase embedded in bulk silicon (abbreviated as discontinuous phase), and the middle region is an iron-aluminum (Fe ₂ Al ₅ ) alloy phase (that is, a pure iron-aluminum alloy phase) that is not doped with silicon and does not embed bulk silicon.

Furthermore, according to the binary phase diagram of Fe-Al and Al-Si, the melting point of the Fe ₂ Al ₅ phase is greater than 1160°C, and the melting point of the Al-Si coating is about 580°C. Since the high temperature of the heating step in the hot stamping process is 850° C. to 950° C., the aluminum-silicon coating exists in a liquid state at this high temperature. As the aluminum-silicon coating in the coating exists for a longer period of time, the adhesion to the furnace rollers that convey the steel plate is more serious. On the contrary, the melting point of the outer region of the iron-aluminum layer is higher than the ferrochemical temperature of Vostian, so the outer region of the iron-aluminum layer can be kept in a solid state under the high temperature of the heating and forming step, thereby reducing the adhesion of the coating to the furnace roll. Accordingly, the disappearance time of the Al-Si coating (equivalent to the alloying time of the alloying reaction) will affect the adhesion.

The alloying time of the aforementioned alloying reaction is 60 seconds to 120 seconds. If the alloying time is shorter than 60 seconds, the diffusion of aluminum and silicon elements is not completed, which lowers the melting point of the outer area of the iron-aluminum layer, and aggravates the adhesion of the coating to the furnace roll. If the alloying time is longer than 120 seconds, the aluminum-silicon coating disappears too slowly, and the low-melting-point aluminum-silicon coating remains in a liquid state for too long, which aggravates the adhesion of the coating to the furnace roller. In some preferred embodiments, the alloying time may be 75 seconds to 90 seconds, and the generated discontinuous phase may further improve the weldability of the produced hot-formed aluminum-based plated steel sheet.

In some embodiments, in a heating furnace, the aluminum-based coated steel sheet is heated at a rate of 6°C/sec to 10°C/sec, from room temperature to 850°C to 950°C, and kept at a constant temperature for 2 minutes to 6 minutes. Then, within 3 seconds to 12 seconds, the aluminum-based plated steel plate is removed from the heating furnace to the mold, and then hot stamping is performed in the mold. During this constant temperature, the aforementioned alloying reaction can occur.

After the thermoforming step, the aluminum-based coated steel sheet is cooled to fix the shape of the thermoformed hardened aluminum-based coated steel sheet. In some embodiments, the aluminum-based coated steel sheet is quenched to room temperature through a die at a cooling rate of 30°C/sec to 70°C/sec. The aforementioned cooling rate can quickly cool the iron-aluminum layer and the anti-oxidation layer, and the two are still closely attached after cooling, and will not fall off from the base steel plate.

Please refer to FIG. 2 , the hot-formed hardened aluminum-based coated steel sheet 200 is produced by the aforementioned manufacturing method of the hot-formed hardened aluminum-based coated steel sheet. The hot-formed hardened aluminum-based coated steel plate 200 includes a base steel plate 210 , an iron-aluminum layer 220 and an anti-oxidation layer 230 , wherein the iron-aluminum layer 220 is disposed between the base steel plate 210 and the anti-oxidation layer 230 . The thickness of the Fe-Al layer 220 is 15 μm to 30 μm. If the thickness of the iron-aluminum layer 220 is less than 15 μm, the alloying reaction of the coating may not be completed, and the aluminum-silicon coating has not completely disappeared, and the aluminum content and/or silicon content in the composition of the iron-aluminum layer 220 may be insufficient, thus reducing the temperature of hot forming. Welding characteristics of hardened aluminum base plated steel plate 200. If the thickness of the iron-aluminum layer 220 is greater than 30 μm, the structure of the iron-aluminum layer 220 may be too loose and not dense enough, thus degrading the weldability of the thermoformed hardened aluminum-based plated steel sheet 200 . Preferably, the thickness of the Fe-Al layer 220 may be 15 μm to 22.5 μm.

The thickness of the anti-oxidation layer 230 is 0.15 μm to 0.5 μm. If the thickness of the anti-oxidation layer 230 is less than 0.15 μm, the anti-oxidation ability of the over-thin anti-oxidation layer 230 is low, so the oxygen resistance ability of the thermoformed hardened aluminum-based plated steel sheet 200 is reduced, thereby reducing its weldability. If the thickness of the anti-oxidation layer 230 is greater than 0.5 μm, the excessively thick anti-oxidation layer 230 will lead to too high resistance between the pole head and the thermoformed hardened aluminum-based plated steel plate 200 during resistance spot welding, thus reducing its welding performance. Preferably, the anti-oxidation layer 230 may have a thickness of 0.22 μm to 0.32 μm. In some embodiments, the anti-oxidation layer 230 may be an aluminum oxide film.

As mentioned above, due to the alloying reaction, the Fe-Al layer 220 includes an inner region 220A, a middle region 220B and an outer region 220C. The inner region 220A is a silicon-doped FeAl alloy phase (ie, the aforementioned continuous phase) and is located on the side (referred to as the inner side) 221 of the Fe-Al layer 220 adjacent to the base steel plate 210 . The outer region 220C is a FeAl alloy phase embedded in bulk silicon (ie, the aforementioned discontinuous phase) and is located on the other side (referred to as the outer side) 222 of the Fe-Al layer 220 away from the base steel plate 210 . The middle region 220B is a Fe ₂ Al ₅ alloy phase that is not doped with silicon and does not embed bulk silicon, and the middle region 220B is located between the inner region 220A and the outer region 220C. In some embodiments, the inner region 220A may have a thickness of 2 μm to 7 μm, and the outer region 220C may have a thickness of 3 μm to 8 μm.

The average iron content of the outer region 220C of the Fe-Al layer 220 is 35% by weight to 50% by weight. When the average iron content is within the aforementioned range, the weldability of the produced thermoformed hardened aluminum-based plated steel sheet 200 can be further improved. Preferably, the average iron content may be 36% by weight to 42% by weight. Secondly, the average silicon content of the outer region 220C of the Fe-Al layer 220 is 1.0 wt % to 5.0 wt %. When the average silicon content is in the aforementioned range, the weldability of the thermoformed hardened aluminum-based coated steel sheet 200 can be further improved. Preferably, the average silicon content may range from 1.8% by weight to 3.2% by weight.

Furthermore, the average aluminum content of the outer region 220C of the Fe-Al layer 220 is greater than 60% by weight. When the average aluminum content is within the aforementioned range, the oxidation resistance of the produced thermoformed hardened aluminum-based coated steel sheet 200 can be further improved, thereby improving its welding ability.

The following examples are used to illustrate the application of the present invention, but they are not intended to limit the present invention. Anyone skilled in this art can make various changes and modifications without departing from the spirit and scope of the present invention.

Preparation of Hot-Formed Hardened Aluminum-Based Coated Steel Sheets

Example 1

The preparation of the hot-formed hardened aluminum-based plated steel sheet in Example 1 is to prepare the base steel sheet (its composition includes 0.1% by weight to 0.5% by weight of carbon, 0.5% by weight to 3.0% by weight of manganese, 0.01% by weight to 1.2% by weight of Chromium, 0.1 to 1.2 weight percent silicon, 0.0005 to 0.01 weight percent boron, less than 0.22 weight percent titanium, less than 0.12 weight percent aluminum, less than 0.12 weight percent phosphorus, less than 0.06 weight percent sulfur, The rest of the iron and unavoidable impurities) in nitrogen containing 10 volume percent hydrogen, from -30 ℃ (dew point temperature) to 800 ℃, and keep the temperature for 60 seconds, then cool to 700 ℃, and keep the temperature for 60 seconds, to Perform annealing treatment. Then, at 680° C., a plating layer was plated on the surface of the base steel plate with an immersion plating solution to obtain the aluminum-based plated steel plate of Example 1. The coating structure includes an outer aluminum-silicon coating and an inner iron-aluminum-silicon intermetallic coating. Then, in the heating furnace, heat the aluminum-based coated steel sheet at a rate of 8°C/sec, from room temperature to 930°C, and keep the temperature constant for 4 minutes, then remove the aluminum-based plated steel sheet from the heating furnace within 5 seconds to 8 seconds. Clad steel plate to mould. The aluminum-based coated steel sheet is hot-stamped in a mold, and then quenched through the mold to room temperature at a cooling rate of 50° C./second to obtain the thermoformed hardened aluminum-based coated steel sheet of Example 1. The thickness of the inner region is 2-7 μm, and the thickness of the outer region is 3-8 μm. Then, the hot-formed hardened aluminum-based plated steel sheet was tested in the following evaluation manner.

Examples 2 to 10 and Comparative Examples 1 to 2

In Examples 2 to 10 and Comparative Examples 1 to 2, the same method as in Example 1 was used to prepare thermoformed hardened aluminum-based plated steel sheets. The difference is that Examples 2 to 10 and Comparative Examples 1 to 2 use different immersion plating temperatures and immersion plating solutions. Comparative Example 2 uses a zinc-containing immersion plating solution, which contains 0.12 weight percent aluminum and a balance of zinc, and an induction heater is used to heat the zinc-based plated steel sheet to 520° C. for 20 seconds to carry out alloying reaction. The hot-formed hardened zinc-based coated steel sheet is obtained, and the metallographic phase of the formed coating is α-phase Fe (expressed as α-Fe(Zn)) containing zinc, and does not contain aluminum-silicon coating and iron-aluminum-silicon intermetallic coating. The specific conditions and evaluation results of the aforementioned Examples 1 to 10 and Comparative Examples 1 to 2 are shown in Tables 1 and 2.

Evaluation method

1. Coating test

The test of the coating is to use an electron microscope to observe the coating of the aluminum-based coated steel sheet (or zinc-based coated steel sheet) and its structure and thickness changes after hot stamping, and to analyze the chemical composition of the coating with an X-ray energy dispersive analyzer Composition, to obtain the silicon content, iron content or aluminum content in the coating, and then analyze the changes in the coating due to hot stamping, and its influence on the adhesion to the furnace roll, welding ability and oxidation resistance.

2. Coating adhesion test

Coating adhesion characteristics test uses X-ray energy dispersive analyzer to analyze the disappearance time of the aluminum-silicon coating in the coating after hot stamping forming, which is used as the alloying time of the alloying reaction, and is used to evaluate the adhesion of the coating to the furnace roll. Condition. When the alloying time is 60 seconds to 120 seconds, the coating does not stick to the furnace roll.

3. Resistance spot welding characteristic test

表示程度中等；

表示程度嚴重。 The resistance spot welding characteristic test uses a welding current of 4kA to 7kA and a head pressure of 7kN to carry out resistance spot welding on the plated steel plate, and uses the degree of flying explosion during the welding process, the degree of burr on the surface of the weld nugget and the head of the weld nugget surface The degree of sticking evaluates the resistance spot welding characteristics of the coating on the plated steel plate, and its specific evaluation criteria are as follows: ◎ indicates a slight degree;

Expressed moderately;

Indicates seriousness.

Table 1

Table 2

Please refer to Table 2. After the aluminum-based plated steel sheets of each embodiment are hot-stamped, the coating is only slightly oxidized, so a relatively thin aluminum oxide film is formed on the surface of the coating. This thin aluminum oxide film makes the resistance between the pole head and the plated steel plate not too high during resistance spot welding, and reduces the degree of flying explosion, burrs on the surface of the weld nugget and sticking of the pole head on the surface of the weld nugget. This shows the advantages of each embodiment. The aluminum oxide film of thermoformed hardened aluminum-based plated steel is resistant to oxidation and has good welding characteristics.

Furthermore, the plating layer of each embodiment undergoes an alloying reaction during the hot stamping process, and the plating layer becomes an iron-aluminum layer and an aluminum oxide film. In the inner region of the iron-aluminum layer is the FeAl alloy phase doped with silicon, in the outer region of the iron-aluminum layer is the FeAl alloy phase embedded in bulk silicon, and in the middle region of the iron-aluminum layer is pure iron-aluminum (Fe ₂ Al ₅ ) Alloy phase.

Secondly, after the hot stamping process, the iron-aluminum-silicon intermetallic coating becomes a thicker iron-aluminum layer. Furthermore, the element content of the Fe-Al layer also changes with the aforementioned alloying reaction, wherein the average Fe content increases and the average Si content decreases. In addition, the average aluminum content in the outer area of the iron-aluminum layer is still higher than 60wt.%, so an aluminum oxide film can be formed on the surface of the iron-aluminum layer.

In the heat forming step of the hot stamping process, the aluminum-silicon coating of each embodiment can completely disappear within 75 seconds to 90 seconds, so compared with the aluminum-based coated steel sheet of Comparative Example 1 (the aluminum-silicon coating takes a long time can disappear) can reduce coating sticking furnace roller.

After the iron-zinc coating of Comparative Example 2 was processed by hot stamping, an excessively thick zinc oxide film was formed. During resistance spot welding, the over-thick zinc oxide film causes the resistance between the electrode head and the plated steel plate to be too high, resulting in serious flying explosions, burrs on the surface of the weld nugget, and adhesion of the electrode head on the surface of the weld nugget. This shows that thermoforming Hardened zinc-based coated steel sheets have poor weldability.

To sum up, the manufacturing method of the hot-formed hardened aluminum-based plated steel sheet of the present invention utilizes a dipping solution of a specific composition to form a coating layer with a specific structure, and the coating layer can undergo rapid alloying reaction in hot stamping forming to become iron Aluminum layer and anti-oxidation layer. The outer region of this Fe-Al layer has a specific composition to prevent the coating from sticking to the furnace rolls and to improve the weldability of the thermoformed hardened Al-based coated steel sheet. In addition, the anti-oxidation layer can resist high temperature to avoid poor welding of steel plates caused by oxidation.

Although the present invention has been disclosed above in terms of implementation, it is not intended to limit the present invention. Anyone with ordinary knowledge in the technical field of the present invention can make various modifications and changes without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be defined by the scope of the appended patent application.

100: method

110, 120, 130, 140: operation

200: hot formed hardened aluminum base plated steel plate

210: base steel plate

220: iron aluminum layer

220A: Medial area

220B: middle area

220C: Outer area

221: inside

222: outside

230: anti-oxidation layer

In order to have a more complete understanding of the embodiments of the present invention and their advantages, please refer to the following descriptions together with the corresponding drawings. It must be emphasized that the various features are not drawn to scale and are for illustration purposes only. The contents of relevant diagrams are explained as follows: FIG. 1 is a flowchart illustrating a method for manufacturing a hot-formed hardened aluminum-based plated steel sheet according to an embodiment of the present invention. FIG. 2 is a schematic diagram illustrating a thermoformed hardened aluminum-based plated steel sheet according to an embodiment of the present invention.

100: method

110, 120, 130, 140: operation

Claims (10)

A method for manufacturing a hot-formed hardened aluminum-based coated steel plate, comprising: providing a base steel plate; performing an annealing treatment on the base steel plate to obtain an annealed steel plate; performing a hot-dip aluminizing treatment on the annealed steel plate to obtain a Aluminum-based coated steel sheet, wherein the hot-dip aluminizing treatment includes forming a coating layer on a surface of the annealed steel sheet with a dipping solution at a temperature of 640°C to 700°C, and the silicon concentration of the dipping solution is not less than 8% by weight, the one-sided coating weight of the coating is 25g/m ² to 90g/m ² , and the coating includes an aluminum-silicon coating and an iron-aluminum-silicon intermetallic coating; and the aluminum-based coated steel sheet is A hot stamping process to obtain the thermoformed hardened aluminum-based coated steel sheet, wherein the hot stamped forming process comprises: a heating forming step, wherein the heating forming step comprises heating the aluminum-based coated steel sheet to 850°C to 950°C , to carry out an alloying reaction to the coating, and make the coating become an iron-aluminum layer and an anti-oxidation layer, and an alloying time of the alloying reaction is 60 seconds to 120 seconds; and a cooling step, wherein the The cooling step includes cooling the aluminum-based coated steel sheet. The method for manufacturing a hot-formed hardened aluminum-based plated steel sheet as described in claim 1, wherein the thickness of the iron-aluminum-silicon intermetallic coating is 2 μm to 6 μm. The manufacturing method of hot-formed hardened aluminum-based plated steel sheet as described in claim 2, wherein in an outer region of the Fe-Al-Si intermetallic layer, an average iron content is 0.5% by weight to 2.0% by weight. The manufacturing method of hot-formed hardened aluminum-based plated steel sheet as described in claim 2, wherein an average silicon content is 8% by weight to 25% by weight in an outer region of the Fe-Al-Si intermetallic layer. A thermoformed hardened aluminum-based coated steel sheet, obtained by the method for manufacturing a thermoformed hardened aluminum-based coated steel sheet according to any one of claims 1 to 4, wherein the thermoformed hardened aluminum-based coated steel sheet does not contain An aluminum-silicon coating, but comprising: a base steel plate; an iron-aluminum layer; and an anti-oxidation layer, wherein a thickness of the anti-oxidation layer is 0.15 μm to 0.5 μm, and the iron-aluminum layer is arranged on the base steel plate and the between the antioxidant layers. The hot-formed hardened aluminum-based coated steel sheet as claimed in claim 5, wherein a thickness of the iron-aluminum layer is 15 μm to 30 μm. The hot-formed hardened aluminum-based coated steel sheet as claimed in claim 5, wherein an average iron content in an outer region of the iron-aluminum layer is 35% by weight to 50% by weight. The hot-formed hardened aluminum-based plated steel sheet as claimed in claim 5, wherein an average silicon content in an outer region of the iron-aluminum layer is 1.0 wt. % to 5.0 wt. %. The hot-formed hardened aluminum-based coated steel sheet as claimed in claim 5, wherein an average aluminum content in an outer region of the iron-aluminum layer is greater than 60 weight percent. The hot-formed hardened aluminum-based coated steel sheet as claimed in claim 5, wherein the iron-aluminum layer is an iron-aluminum (Fe ₂ Al ₅ ) alloy phase, and the iron-aluminum layer comprises: an inner region comprising doped silicon and located on the side of the iron-aluminum layer adjacent to the base steel plate; an outer region, containing massive silicon and located on the other side of the iron-aluminum layer away from the base steel plate; and a middle region, located in the inner region and the outer region between.

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