KR20200076072A - Manufacturing method of aluminum plated member - Google Patents

Abstract

The present invention relates to a manufacturing method of an aluminum plated member. In manufacturing a member having an intended shape by molding aluminum-plated steel, an object of the present invention is to provide a method which can manufacture a member having high strength in which a plated layer is kept soundly during cold forming and problems such as volatilization of the plated layer during heat treatment after molding are solved. The manufacturing method of the aluminum plated member includes the following steps of: preparing the aluminum-plated steel; alloying the aluminum-plated steel; cold forming the alloyed aluminum-plated steel; and heat-treating the cold-formed aluminum-plated steel.

Description

Manufacturing method of aluminum plating member {MANUFACTURING METHOD OF ALUMINUM PLATED MEMBER}

The present invention relates to a method of manufacturing an aluminum plating member.

Recently, the application of high-strength steel has been increasing due to the demand for weight reduction of automobile parts.

However, when cold forming is applied to manufacture high-strength steel as an automobile part, the number of rolls increases during roll forming due to an increase in the radius of curvature of parts or an increase in the forming step due to the limitation of securing formability due to low formability of high-strength steel. There is.

In addition, in order to solve the increased springback phenomenon of high-strength steel, the forming step increases, and accordingly, the number of rolls increases when forming a mold or roll. In addition, there are problems such as increase in load during forming and roll forming due to high strength of the material and high price of molds or rolls and increased wear to secure structural safety.

As an alternative to solve the above problems, a technique of cold forming a high-strength steel and performing post-heat treatment has been proposed. Specifically, in the cold forming step, while having low strength, since it has high strength through post-heat treatment, it is possible to partially solve various problems occurring during cold forming of high strength steel.

However, in the case of performing post-heat treatment after cold forming a high-strength steel, in the case where the high-strength steel is a plating material, the plating layer is damaged in the cold forming step or rapidly heated to shorten the processing time in the post-heat treatment process. To do this, the plating layer may volatilize or alloying may not be sufficient.

However, in the case of a heat treatment process after roll forming performed in a continuous process, rapid heating is essential in order to match the process time.

Therefore, in the case of rapid heating for post-heat treatment after molding of the plating material, development of a technology capable of achieving high strength while securing the quality of the plating layer is required.

Republic of Korea Patent Publication No. 10-2010-0132371

In one aspect of the present invention, in manufacturing a member having an intended shape by molding an aluminum plated steel, a method capable of manufacturing a member having high strength while solving problems such as volatilization of a plating layer during heat treatment after molding Is to provide.

The subject of this invention is not limited to the above-mentioned content. Anyone having ordinary knowledge in the technical field to which the present invention pertains will have no difficulty in understanding additional problems of the present invention from the contents throughout the present specification.

One aspect of the present invention, preparing an aluminum plated steel; Alloying the aluminum plated steel; Cold forming the alloyed aluminum plated steel; And heat-treating the cold-formed aluminum plated steel,

The alloyed aluminum plated steel provides a method of manufacturing an aluminum plated member having a Fe content in the plated layer of 60% by weight or more.

According to the present invention, it is possible to provide a method capable of obtaining a member having a significantly improved strength while ensuring a good plating layer even when molding and rapid heating of an aluminum plated steel material.

1 shows a series of process diagrams for manufacturing parts (members) using a conventional steel material.
Figure 2 shows a cross-sectional photograph of a plated layer of aluminum plated steel.
Fig. 3 shows a cross-sectional shape (A) of a molded product after molding an aluminum plated steel in a conventional manner and a cross-sectional photograph (B) of the plating layer inside the curvature (arrow).
Figure 4 shows a cross-sectional photograph of the plating layer after heating the aluminum plated steel in a conventional manner.
Figure 5 shows a cross-sectional photo of the plating layer of the alloyed heat-treated aluminum plated steel according to an aspect of the present invention.
Figure 6 shows a cross-sectional photograph of a plating layer after cold forming an alloyed heat-treated aluminum plated steel according to an aspect of the present invention.

Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings. However, the spirit of the present invention is not limited to the embodiments presented, and a person skilled in the art who understands the spirit of the present invention may add another component within the scope of the same spirit, change, delete, etc. Other embodiments included within the scope of the invention idea can be easily proposed, but this will also be included within the scope of the invention.

In general, the process of heat treatment after cold forming a steel material undergoes a series of processes as shown in FIG. 1, and the member manufactured therefrom may have high strength.

Meanwhile, when the steel material is a plating material, when cold forming is performed on the plating material, an aluminum plating steel material having a plating layer as shown in FIG. 2 may be used. The aluminum-plated steel has a problem in that the aluminum-based plating layer is damaged by friction and bending with a mold during cold forming. For example, as shown in FIG. 3(B), there is a problem in that the plating layer is pushed and thinned or cracks are generated due to the movement of the mold.

In addition, there is a problem that the aluminum-based plating layer is melted when rapidly heated to increase the strength of the aluminum plated steel material cold-formed according to the above.

Accordingly, the present inventors use aluminum-plated steel as its raw material to manufacture automotive parts (members), etc., and minimize the damage to the plating layer during rapid heating to improve strength after cold-forming the aluminum-plated steel. Thus, while securing a good plating quality, a deep study has been conducted to provide a method for obtaining a member having a target level of high strength, thereby leading to providing the present invention.

Hereinafter, the present invention will be described in detail.

A method of manufacturing an aluminum plating member according to an aspect of the present invention comprises preparing an aluminum plated steel and alloying it; Cold forming and heat treatment may be included.

First, the aluminum-plated steel material is a steel material capable of cold forming as mentioned, and any material produced by methods such as ordinary hot-dip plating, alloyed hot-dip plating, and electroplating may be used, and is not particularly limited.

However, in the case of the aluminum-plated steel, in addition to having a plating layer made of aluminum (Al) on at least one surface of the steel sheet, plating with a plating layer containing a small amount or a small amount of silicon (Si), iron (Fe), etc. in addition to aluminum It can be steel. At this time, the Si and Fe may be included in 6% to 12% and 1% to 4% by weight, respectively.

The present invention may be subjected to a process of alloying the aluminum plated steel material prior to cold forming the aforementioned aluminum plated steel material.

That is, the present invention proposes a new method in manufacturing a final member using the aluminum plated steel, as it is confirmed that there are several problems when forming and rapidly heating the aluminum plated steel in a series of processes as shown in FIG. 1. The technical significance of the ship.

Specifically, the present invention can alloy the plated layer of the aluminum plated steel by alloying the aluminum plated steel, wherein the alloying treatment has a Fe content in the plated layer of 60% by weight or more, more advantageously 70% by weight or more. It is desirable to do so.

The alloying treatment is not particularly limited, as long as it is a means capable of sufficiently diffusing Fe in the plated steel sheet of the aluminum plated steel to the plated layer.

As one embodiment, it may be performed by a method of alloying by maintaining a constant time at a temperature of 750°C or lower, preferably 500 to 750°C. When the temperature exceeds 750°C during the alloying treatment, oxides are excessively formed on the surface layer, whereas when the temperature is less than 500°C, alloying cannot be sufficiently performed.

Here, the holding time can be performed for a time when the Fe content in the plating layer becomes 60% or more, and is not particularly limited.

As already mentioned, it has been confirmed that the general aluminum plated steel has a problem in that the plating layer is damaged by friction and bending with a mold during cold forming (see FIG. 3). This may be described in detail with reference to FIG. 4 below.

Figure 4 shows the state of the plated layer after heating the aluminum plated steel containing a certain amount of Si in the plated layer by a conventional method, the Fe content in the plated layer as a whole has a level of 50%, the plating layer is brittle with such alloying level There is a problem with.

Here, heating by a conventional method means a process of heating to a high temperature, for example, it may be a case of heating above the Ac3 temperature.

However, in the case of the present invention, the plating layer is softened (soft) as the Fe content in the plating layer is secured to 60% by weight or more by alloying the plating layer through a process of alloying prior to molding and heat treatment of the aluminum plating steel. ).

The aluminum-plated steel material can obtain a member having a desired strength while securing a good foam-like plating layer even through subsequent cold forming and heat treatment processes, and also has excellent cold formability.

The aluminum plated steel alloyed according to the above can be cold formed.

The cold forming is not particularly limited as long as it is a means capable of forming the aluminum plated steel in cold form. However, a cold stamping process or a roll forming process may be used as the cold forming process.

Through the cold forming process described above, a member having a specific shape of the aluminum plated steel can be manufactured. Here, the specific shape may be a shape that can be suitably applied to automobile parts and the like, and is not limited thereto.

The cold-formed aluminum plated steel can be heat treated according to the above.

The heat treatment after cold forming is a process for increasing the strength of the molded aluminum plated steel material, and may include a process of heating and then cooling the molded aluminum plated steel material.

Specifically, the heat treatment process generates austenite transformation in the holding steel sheet through heating of the molded aluminum plated steel, and ensures a sufficient martensite structure in a subsequent cooling process, thereby having a tensile strength of 1000 to 2000 MPa after heat treatment. It is preferred.

More preferably, the process of heating the molded aluminum plated steel is performed to A3 or more to ensure sufficient austenite transformation, and may be maintained at a heated temperature for a certain period of time. The strength and uniformity of the aluminum plated steel finally heat-treated from the heating and holding process may be secured, and the holding time at this time is not particularly limited, and may be performed for a time period sufficient to obtain the above-described effects.

After the heating process or the heating and holding process according to the above, cooling may be performed at a rate equal to or higher than a critical cooling rate of the aluminum plated steel. When the cooling is performed at a rate slower than the critical cooling rate of the plated steel, there is a fear that transformation into a tissue capable of obtaining a tensile strength of 1000 MPa or more in the cooling process may not be sufficiently achieved.

The speed above the critical cooling rate of the aluminum plated steel is a cooling rate at which transformation occurs in the martensite phase without causing phase transformation such as ferrite or bainite when cooling, and for example, may be performed at a cooling rate of 30 to 50°C/s. .

In the present invention, in the heat treatment, that is, heating and cooling of the molded aluminum plated steel, various methods other than the above-described methods can be applied.

For example, when the molded aluminum plated steel is heated, the plated steel is divided into two or more regions, and at least one region of the region is heated to a temperature of A3 or higher, and the remaining regions are heated to a temperature of A1 or lower, followed by cooling. The entire region can be performed at a speed equal to or higher than the critical cooling rate.

As another example, when the molded aluminum plated steel is heated, the plated steel is divided into two or more regions, heated to A3 or more with respect to the entire region, and then, when cooled, at least one of the regions is subjected to critical cooling. Speed above the speed, the rest of the zone can be done at a speed below the critical cooling rate.

In the present invention, two or more regions of the plated steel are not particularly limited, but can be divided into a high strength region and a low strength region. The high-strength region may be a region having a tensile strength of 1000 to 2000 MPa by forming a hard phase (eg, a martensitic phase) in the final member, whereas the low-strength region is a soft phase (eg, a soft phase) in the final member. Ferrite phase, etc.) may be formed may be a region having a tensile strength of 500 ~ 800MPa.

As described above, in the production of a series of processes proposed in the present invention, specifically, forming and heat-treating an aluminum-plated steel material as a member having a desired shape, when the aluminum-plated steel material is alloyed prior to the molding, molding And even through a heat treatment process, it may have a good quality plating layer.

This means that by using an aluminum plated steel material in which the plating layer is sufficiently alloyed by the alloying treatment of the present invention, not only does it have a targeted strength after molding and heat treatment, but also a problem such as melting of the plating layer has not occurred. do.

Hereinafter, the present invention will be described in more detail through examples. However, it should be noted that the following examples are only intended to illustrate the present invention in more detail and are not intended to limit the scope of the present invention. This is because the scope of the present invention is determined by the items described in the claims and the items reasonably inferred therefrom.

( Example )

An aluminum plated steel material having a plating layer containing 9% Si, 2.5% Fe, balance Al and unavoidable impurities by weight% was prepared.

Thereafter, cold forming (roll forming process) was performed on one aluminum plated steel, and the plating layer (inside the curvature portion (arrow)) was observed (comparative example).

For another aluminum plated steel, after alloying treatment at 500 to 750°C so that the Fe content in the plated layer was 70% by weight, cold forming (roll forming process) was performed, and then the plated layer (inside the curvature portion) was observed (invention example). ).

In order to observe each of the plating layers, after cutting in the thickness direction, the plating layers were observed with an optical microscope.

Figure 3 shows the plating layer of the comparative example, it can be seen that the damage to the plating layer is severe during cold forming.

On the other hand, Figure 6 shows the plating layer of the invention example, it can be confirmed that there is no defect such as cracks in the surface or inside of the plating layer, and it shows a uniform layer even after the molding process.

Claims (9)

Preparing an aluminum plated steel material;
Alloying the aluminum plated steel;
Cold forming the alloyed aluminum plated steel; And
And heat-treating the cold-formed aluminum plated steel,
The alloyed aluminum plated steel is a method of manufacturing an aluminum plating member having a Fe content in the plating layer of 60% by weight or more.
According to claim 1,
The alloying treatment is a method of manufacturing an aluminum plating member that is heated and maintained at a temperature of 750°C or less.
According to claim 1,
The heat treatment step includes a heating and cooling step,
The heating is performed at A3 or higher, and the cooling is performed at a speed equal to or higher than a critical cooling rate of the plated steel.
According to claim 1,
A method of manufacturing an aluminum plating member having a tensile strength of 1000 to 2000 MPa after the heat treatment.
According to claim 3,
The heating is divided into two or more regions of the plated steel, and at least one region is heated to a temperature of A3 or more, and the other regions are Al or less,
The method of manufacturing an aluminum plating member, wherein the cooling is performed at a rate equal to or higher than a critical cooling rate for the entire area.
According to claim 3,
The heating is divided into two or more areas of the plated steel and heated to A3 or more for the entire area,
The cooling method of at least one region is at least a critical cooling rate, and the rest of the region is performed at a rate below the critical cooling rate.
The method of claim 5 or 6,
At least one of the two or more regions is a high-strength region having a tensile strength of 1000 to 2000MPa, and the remaining region is a low-strength region having a tensile strength of 500 to 800MPa.
According to claim 1,
The cold forming step is a method of manufacturing an aluminum plating member that is performed by a cold stamping or roll forming process.
According to claim 1,
The aluminum plated steel material includes a plated steel plate and an aluminum plated layer on at least one surface of the plated steel plate,
The aluminum plating layer is 6% to 12% by weight of silicon (Si), 1 to 4% of iron (Fe), the remaining aluminum (Al) and other inevitable impurities manufacturing method of the aluminum plating member.

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