Zinc alloy plated steel material with excellent corrosion resistance and surface quality, and its manufacturing method.

Abstract

This invention relates to zinc alloy plated steel materials used in automobiles, building materials, home appliances, and more specifically, to zinc alloy plated steel materials with excellent corrosion resistance and surface quality. [Solution] The zinc alloy plated steel material, which has excellent corrosion resistance and surface quality, comprises a base iron and a zinc alloy plating layer formed on the base iron. The zinc alloy plating layer contains, by weight, Al: 8-25%, Mg: 4-12%, with the remainder being Zn and unavoidable impurities. The area fraction occupied by the polygonal solidification phase observed on the surface of the zinc alloy plating layer is 20-90%.

Description

[Technical Field]

[0001] This invention relates to zinc alloy plated steel materials used in automobiles, building materials, home appliances, and the like. It is a material, and more specifically, zinc alloy plated steel with excellent corrosion resistance and surface quality, and this This relates to a method for manufacturing [the product]. [Background technology]

[0002] Iron is the most widely used material in industry and possesses excellent physical and mechanical properties. However, iron has the disadvantage of being easily oxidized and susceptible to corrosion. For this reason, iron As a method to prevent oxidation, a metal that is more reactive with oxygen than iron is used as a protective film on the surface of the material. Methods have been developed to coat surfaces and delay corrosion. Zinc is a typical example. Alternatively, there are galvanized steel materials with a zinc-based coating.

[0003] In the above-mentioned galvanized steel, the zinc, which has an even higher oxidation potential, dissolves before the base iron, thus sacrificing safety. Due to the chemical action and the corrosion inhibitory effect of the dense zinc corrosion products which delay corrosion, corrosion is slowed down. It protects iron from the elements.

[0004] However, recently, corrosive environments are deteriorating day by day, and from the perspective of resource conservation and energy saving, high corrosion resistance is required. We are making great efforts to improve. As part of these efforts, we have developed zinc with excellent corrosion resistance. -Aluminum alloy plating is also being considered, but aluminum is more alkaline than zinc. Because it dissolves easily, it has the disadvantage of being insufficient in terms of long-term durability.

[0005] Recently, we have achieved significant improvements in corrosion resistance by utilizing magnesium (Mg). In Patent Document 1, Mg: 0.05-10.0% by weight, Al: 0.1-10.0% by weight. It has a Zn-Mg-Al alloy plating layer composed of the remainder being Zn and unavoidable impurities. It is characterized by the formation of a coarse plating structure, or by the concentrated formation of a specific structure. First, there is the problem of corrosion occurring.

[0006] On the other hand, as an achievement in controlling the structure of the plating layer to improve corrosion resistance, Patent Document 2 states that Z It has an n-Al-Mg-Si plating layer, and these plating layers are made of Al / Zn / Zn2Mg. A metallic microstructure in which Mg2Si phase, Zn2Mg phase, Al phase, and Zn phase are mixed together in the original eutectic structure. It is characterized by having the following: However, it is limited to high-strength steel containing Si, and in the plating structure Because it always contains silicon components, the cost of manufacturing plating ingots increases, making work management difficult. There is a problem in that other elements are added to the Zn-Al-Mg main component to improve corrosion resistance. Patent document 3, which describes a technology to improve performance, describes adding chromium (Cr) to the plating layer to achieve A The l-Fe-Si alloy layer is characterized by containing Cr, but by adding the Cr component... However, this method has the disadvantage of causing excessive dross formation, which is detrimental to controlling the composition of the plating bath.

[0007] Therefore, while ensuring excellent corrosion resistance, the surface is protected from dross and other contaminants, resulting in a superior surface finish. The demand for high-quality plated steel materials continues. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Published Patent No. 1999-158656 [Patent Document 2] Japanese Patent Application Laid-Open No. 2001-295018 [Patent Document 3] Korean Patent Application Laid-Open No. 10-2011-0088573 [Summary of the Invention] [Problems to be Solved by the Invention]

[0009] One aspect of the present invention is to optimize the composition and microstructure of the plating layer to ensure excellent corrosion resistance and to provide a zinc alloy plated steel sheet having excellent surface characteristics and a method for manufacturing the same. [[ID=十七]]

[0010] The problems of the present invention are not limited to the above matters. Further problems of the present invention are described in the entire contents of the specification, and those skilled in the art to which the present invention pertains will have no difficulty in understanding further problems of the present invention from the contents described in the specification of the present invention. [Means for Solving the Problems]

[0011] One embodiment of the present invention includes a base iron and a zinc alloy plated layer formed on the base iron, wherein the zinc alloy plated layer contains, by weight, Al: 8 to 25%, Mg: 4 to 12%, and the balance is Zn and inevitable impurities, and the area fraction occupied by polygonal solidification phases observed on the surface of the zinc alloy plated layer is 20 to 9 0%, and provides a zinc alloy plated steel sheet having excellent corrosion resistance and surface quality.

[0012] Another embodiment of the present invention includes the steps of preparing a base iron; immersing the prepared base iron in a plating bath containing, by weight, Al: 8 to 25%, Mg: 4 to 12%, and the balance is Zn and inevitable impurities for plating; wiping the plated base iron; and ​The corrosion-resistant step includes forming a polygonal solidified phase on the surface of the hot-dip galvanized layer after the wiping described above. The present invention provides a method for manufacturing zinc alloy plated steel materials with excellent properties and surface quality. [Effects of the Invention]

[0013] According to the present invention, a Zn-Al-Mg-based zinc alloy having excellent corrosion resistance and surface properties is available. We can provide steel materials and methods for manufacturing them. In particular, excellent corrosion resistance and surface properties. Because it possesses these properties, it can be expanded to new fields where conventional plated steel materials were not applicable. This has the advantage of being able to do so. [Brief explanation of the drawing]

[0014] [Figure 1] This is a photograph showing the surface of the plating layer in Invention Example 1, one of the embodiments of the present invention. [Figure 2] This is a photograph showing the surface of the plating layer of Comparative Example 1, one of the embodiments of the present invention. [Modes for carrying out the invention]

[0015] The present invention will be described in detail below.

[0016] The zinc alloy plated steel material of the present invention comprises a base iron and a zinc alloy plated layer formed on the base iron. Includes.

[0017] The type of base iron mentioned above is not particularly limited, and can be applied in the technical field to which the present invention belongs. Local steel is sufficient. Examples include hot-rolled steel sheets, cold-rolled steel sheets, wire rods, and steel wires.

[0018] The above zinc alloy plating layer is based on zinc (Zn), magnesium (Mg), and a Contains luminium (Al). The above zinc alloy plating layer has an Al content of 8-25% by weight, and M g: Preferably 4-12%, with the remainder consisting of Zn and unavoidable impurities. Also, Be, Ca Furthermore, one or more of Ce, Li, Sc, Sr, V, and Y are added in amounts of 0.0005 to 0.009%. It can be included in the following. The compositional range of each component will be explained in detail below.

[0019] Aluminum (Al): 8-25% by weight (hereinafter, %) The above-mentioned Al stabilizes the Mg component during the production of molten metal and suppresses initial corrosion in corrosive environments. It acts as a food barrier, and the Al content can vary depending on the Mg content. If the above Al content is less than 8%, the Mg cannot be stabilized during the production of the molten metal. Mg oxides form on the surface of the molten metal, making it difficult to use. On the other hand, if it exceeds 25%, Because the plating temperature rises and the various equipment installed in the plating bath corrodes excessively, It's not good.

[0020] Magnesium (Mg): 4-12% The above Mg is the main component that forms the structure that exhibits corrosion resistance, and the above Mg is less than 4%. If present, corrosion resistance is not sufficiently achieved, and if it exceeds 12%, a large amount of Mg oxide is formed. This presents a problem that could secondarily lead to various other issues such as material degradation and increased costs. Therefore, it is preferable that the above Mg contains 4-12%. More preferably, the above Mg contains 5 It can contain more than %.

[0021] On the other hand, it is preferable that the above Al and Mg satisfy the following relational expression 1. [Relationship 1] Mg ≤ -0.0186 × Al 2 +1.0093 × Al + 4.5

[0022] Here, Al and Mg represent the content (weight %) of each component. In this invention, plating In order to stabilize the molten metal and suppress oxide formation to the greatest extent possible, the above Al and Mg content is It is preferable that the conditions of relational expression 1 are met.

[0023] On the other hand, in addition to the above Al and Mg, beryllium (B) is used to further stabilize the Mg component. e) Calcium (Ca), Cerium (Ce), Lithium (Li), Scandium (Sc) ), further containing strontium (Sr), vanadium (V), yttrium (Y), etc. It is possible, and preferably contains 0.0005 to 0.009%. Less than 0.0005% Therefore, it is difficult to expect any substantial Mg stabilization effect, and if it exceeds 0.009%, In the final stages, solidification can occur, leading to corrosion and impairing corrosion resistance, which can result in increased costs. Therefore, it is undesirable.

[0024] The remainder of the alloy composition other than the above includes zinc (Zn) and unavoidable impurities. This does not mean that the addition of certain ingredients is excluded.

[0025] The surface of the zinc alloy plating layer contains a polygonal solidification phase, and polygonal solidification is observed on the surface. The area fraction occupied by the phase is preferably between 20% and 90%.

[0026] The surface of the above zinc alloy plating layer is examined using a scanning electron microscope. When observing with a microscope (SEM) or optical microscope, polygons and circles become visible. A variety of tissue forms are observed, including polygonal, elliptical, and sand-like shapes. In this invention, the polygonal solidified phase is described above. This is one of the tissues observed on the surface, exposed in the superficial layer, and is surrounded by other coagulated tissues. It is clearly distinguished by its color and shape. That is, as shown in Figure 1, it is different from the surrounding tissue. The boundary between them is distinguished by an almost linear line, and the above lines intersect to form a constant angle. At that time, the angle can be constructed in various ways, so it is not particularly limited. Also, the above polygon The solidified phase can be formed in multiple layers and can have several angles. The interior of the angular coagulation tissue may not all have the same color or shape. Because the weave can overlap and deform, and may look different, there are two or more corners as described above. In that case, it is included in the polygonal solidification phase.

[0027] The polygonal solidification phase described above showed the presence of 2-3 components from among Zn, Al, and Mg, and was a single intermetallic compound. Alternatively, it is an alloy phase in which the intermetallic compound contains Zn, Al, and additional elements for stabilization. This is possible. Here, the intermetallic compounds are MgZn2, Mg2Zn 11 These are some examples. .

[0028] The area occupied by the polygonal solidified phase described above is preferably 20-90% in terms of surface fraction. i. If the area of ​​the polygonal solidified phase is less than 20%, corrosion resistance and processability will be insufficient. If it exceeds 90%, a problem arises in that corrosion resistance actually decreases. More preferably, area The fraction is 30-70%. The polygonal solidification phase is observed on the surface, and therefore accounts for a portion of the surface area. This indicates the area.

[0029] The average ratio (b / a) of the major axis (b) to the minor axis (a) of the polygonal solidification phase described above is 1 to 3. It is preferable that the polygonal solidified phase has a short axis (a) and a long axis ( b) It may be as defined in b), where some of the solidified phases overlap and are difficult to separate, or This includes all modified forms and can be expressed as a b / a ratio. The above b / a ratio is 1 or less While it offers excellent processability, if the b / a ratio becomes excessively large and the solidification phase becomes excessively long, This has a negative effect on the process. Therefore, if the above b / a ratio exceeds 3, the processability actually becomes unfavorable. Therefore, it is preferable that the above b / a is 1 to 3.

[0030] The zinc alloy plating layer of the present invention may contain various phases. For example, MgZn2, Mg2Zn 11 Al solid solution phase, Zn solid solution phase, Al / Zn / Mg eutectic phase, etc. Among these, the microstructure of the zinc alloy plating layer is MgZn2 and Mg2 Zn 11 It is preferable that one or more of these types constitute 20-45% of the area fraction. It is preferable that it be the surface fraction of the layer's surface area.

[0031] In the present invention, the phase formed on the zinc alloy plating layer is substantially non It may also be produced in equilibrium. For example, in the case of MgZn2, the atomic percentage is Mg / The Zn ratio should ideally be 0.33, but in reality it's between 0.19 and 0.24. This was calculated. Furthermore, although other components may be detected in the above phase generated in a non-equilibrium state, These will be determined after a comprehensive review of component analysis, shape analysis, and other factors.

[0032] The above-mentioned MgZn2 and Mg2Zn 11 If one or more of these are present in less than 20%, the water cycle is always In border and saltwater environments, corrosion resistance is insufficient, and when it exceeds 45%, corrosion resistance increases, The above MgZn2 alloy phase and Mg2Zn 11 Because the alloy phase is hard, cracks appear in the plating layer. The likelihood of this occurring increases. More preferably, it is 20-40%.

[0033] The remainder includes Zn solid solution phase, Al solid solution phase, Al / Zn / Mg eutectic phase, and non-stoichiometric composition. It is possible.

[0034] The following describes in detail one embodiment of the manufacturing method for the zinc alloy plated steel material of the present invention.

[0035] This invention proposes a method for forming a zinc alloy plating layer with excellent corrosion resistance and surface appearance. do.

[0036] The solidification process of the plating layer proceeds through nucleation and growth, but when cooled, solidification nuclei are formed. Therefore, solidification nuclei are formed where the thermodynamically lowest Gibbs free energy is. The difference in Bus free energies is such that when heterogeneous nucleation is more favorable to solidification than homogeneous nucleation. The larger the area of ​​heterogeneous nucleation sites, the more favorable nucleation becomes, and the more nucleation occurs. This occurs. At this time, the heterogeneous nucleation site is where the liquid phase and solid phase of the molten metal come into contact, and steel The surface of a plate is a typical example. Another heterogeneous nucleation site is when the liquid phase of molten metal comes into contact with the air. This is the surface of the molten metal. Here, the inventors of the present invention have multi To form a rectangular solidification phase, we derive a method for controlling the solidification of steel materials after they leave the plating bath. It started to happen.

[0037] The present invention provides a method for producing zinc alloy plated steel, which involves preparing a base iron and using the prepared base iron. After immersion in the plating bath and plating, the thickness of the plating layer is adjusted by wiping, and then hot-dip zinc plating is applied. This process includes the formation of a polygonal solidified phase on the surface of the solidified layer. Each process will be described in detail below. ru.

[0038] First, prepare the base iron. As mentioned above, the type of base iron is not restricted, and this is the first step. If it can be applied in the technical field to which Akira belongs, then there is no problem. The above base iron is A process to remove oxides, impurities, etc. present on the surface before immersion in the bath, and heat for reduction. This may include processing steps, etc.

[0039] The above base iron is immersed in a plating bath to form a zinc alloy plating layer on the surface of the base iron. The bath composition, in weight percent, is Al: 8-25%, Mg: 4-12%, with the remainder being Zn and other unavoidable elements. It is preferable to include pure substances, and additionally Be, Ca, Ce, Li, Sc, Sr, V and Y It can contain 0.0005 to 0.009% of one or more species selected from the following groups. The above Al and Mg content can satisfy the following relational expression 1. The gold composition range is the same as that described above for the alloy composition range of the zinc alloy plating layer. do not have. [Relationship 1] Mg ≤ -0.0186 × Al 2 +1.0093 × Al + 4.5

[0040] The temperature of the plating bath varies depending on its melting point, and the melting point depends on the composition of the plating bath. These are physicochemical properties. The factors determining the temperature of the plating bath are ease of operation and heating costs. Furthermore, the plating quality and other factors vary. Considering all these points together, the temperature of the plating bath is The temperature should be higher than the melting point, preferably 20 to 100°C higher than the melting point.

[0041] On the other hand, the base iron deposited in the plating bath is set considering factors such as ease of operation and heat balance. The plating bath temperature is preferably set to -10 to +10°C above.

[0042] Regarding the zinc alloy plated steel material drawn out of the above plating bath, the air vent at the top of the plating bath The thickness of the plating layer is adjusted by a wiping nozzle called an air knife. The wiping process is performed by spraying air or an inert gas onto the surface. Adjust the thickness of the layer.

[0043] After the wiping process described above, a polygonal solidified phase is formed on the surface of the plating layer. Therefore, the primary A gas containing 78-99% nitrogen by volume is injected (primary gas injection), and secondarily Gases with dew points ranging from -5 to 50°C are injected sequentially (secondary gas injection).

[0044] During the primary gas injection described above, the gas other than nitrogen is not particularly limited, but may be air, oxygen, or nitrogen. It can include inert gases such as argon and mixtures thereof. On the other hand, the above secondary gas The dew point in a gas injection is a specific value that defines the amount of water contained in the gas, and at this time, the secondary gas The type of gas used during injection is not particularly limited. For example, a gas containing 89-99% nitrogen. The body can be used.

[0045] During the primary gas injection described above, if the nitrogen concentration is less than 78%, surface defects are more likely to occur, and 99 If the percentage exceeds a certain level, the formation of the polygonal solidified phase will be insufficient. Also, the dew point will rise during secondary gas injection. While the shape of polygonal solidification nuclei increases, it is not sufficient below -5°C, and the dew point exceeds 50°C. This results in the problem of a large number of surface defects occurring.

[0046] On the other hand, in order to provide an environment favorable for the formation of a polygonal solidification phase after the secondary gas injection, Furthermore, vibrations from 100Hz to 5MHz can be added. If the above vibration is less than 100Hz In such cases, the formation of the polygonal solidification phase on the surface of the plating layer may be insufficient, exceeding 5 MHz. This can sometimes result in surface defects. [Examples]

[0047] The following describes in detail embodiments of the present invention. The following embodiments are for understanding the present invention. This is not intended to limit the scope of the rights of the present invention. The scope of the rights of the present invention is Determined by the matters described in the claims and matters that can be reasonably inferred therefrom. This is because it is such a thing.

[0048] (Examples) The base material is a cold-rolled steel sheet with a thickness of 0.8 mm, and has a composition of 0.03%C-0.2%S by weight. i-0.15 weight %Mn-0.01 weight %P-0.01 weight %S (the remainder is Fe and unavoidable To prepare cold-rolled steel sheets containing pure materials, and to remove impurities such as oil adhering to the surface of the steel sheets After the degreasing process, a reducing atmosphere of 10 vol.% hydrogen and 90 vol.% nitrogen is applied as follows. After undergoing a heat treatment process at 800°C in an air-filled environment, the material is immersed in a molten zinc alloy plating bath and then... (See Table 1 below) A plated steel sheet was manufactured having the following plating layer composition. At this time, the hot-dip zinc plating bath The temperature of the immersion chamber was set to 493°C, and the temperature of the steel plate being drawn in was also set to 493°C. The air wiped after immersion as described above The thickness of the plating layer was adjusted to approximately 8-10 μm via a g. After this, the primary and secondary gs shown in Table 1 were used. The steel sheet was plated by performing a special treatment.

[0049] The manufactured zinc alloy plated steel material was analyzed for phase identification via EDS analysis, and XR MgZn2 and Mg2Zn 11 The phase fraction was measured. On the other hand, The area fraction of the polygonal solidification phase is determined using an image analyzer. The ratio of the major axis (b) to the minor axis (a) (b / a) is calculated by measuring the lengths of each axis. I calculated it.

[0050] The surface quality and corrosion resistance of the above zinc alloy plated steel material were evaluated, and the results are shown in Table 1 as well.

[0051] The above corrosion resistance was evaluated by conducting a salt spray test, measuring the red rust generation time, and comparing it with a comparative sample. At this time, the comparative sample used a zinc alloy plated steel material with a plating layer composition of 94 wt% Zn - 3 wt% Al - 3 wt% Mg. The above salt spray test was carried out at a salinity of 5%, a temperature of 35°C, a pH of 6.8, and a salt spray amount of 2 ml / 80 cm ·1 Hr. 2 ·1 Hr.

[0052] The evaluation result was that when the red rust generation time was 1.5 times or more compared to the comparative sample, it was evaluated as good ( ○), and when it was less than 1.5 times, it was evaluated as bad (×).

[0053] On the other hand, for the surface quality, the appearance of the manufactured sample was observed to evaluate the presence or absence of surface defects such as dross. The results are as follows. Good (○): No occurrence of surface defects such as dross and dots Bad (×): Presence of surface defects such as dross and dots Bad (×): Presence of surface defects such as dross and dots

[0054]

Table 1

[0055] As shown in Table 1 above, it can be seen that all the invention examples satisfying the conditions of the present invention have excellent surface quality and corrosion resistance.

[0056] In particular, FIG. 1 is a photograph observing the surface of the above invention example 1. Referring to FIG. 1, it can be seen that polygonal solidification phases intersecting straight lines to form a certain angle are formed at an appropriate fraction. In contrast, Figure 2 is a photograph of the surface of Comparative Example 1, and when compared to Figure 1, the surface It is clear that observing the polygonal solidification phase from a surface is difficult.

[0057] Comparative Examples 1 and 2 differ in their Al and Mg content, which are essential components of the presented plating layer, from the present invention. In cases outside the range presented, Comparative Example 1 has a very low content of Al and Mg. Furthermore, because the polygonal solidified phase observed on the surface is insufficient, corrosion resistance cannot be ensured, and Comparative Example 2 shows that the Al and Mg content of the plating layer is excessive, resulting in a large amount of polygonal solidification phase on the surface. It is clear that the surface quality and corrosion resistance have all deteriorated.

[0058] Comparative Example 3 shows the case where the Be added for supplementary effects is excessively present in the plating layer. As a result, it can be seen that the surface quality and corrosion resistance have deteriorated. Comparative Examples 4 and 5 are presented in the present invention. The gas injection conditions were not met, resulting in deterioration of the surface corrosion resistance and surface properties of the plating layer. This can be confirmed.

Claims

1. The base iron and the zinc alloy plating layer formed on the base iron are included. The aforementioned zinc alloy plating layer consists of, by weight, Al: 8-25%, Mg: 4-12%, and the remainder being Z n and unavoidable impurities are included. The area fraction occupied by the polygonal solidification phase observed on the surface of the zinc alloy plating layer is 20 to 9 A zinc alloy plated steel material with 0% zinc content, excellent corrosion resistance, and superior surface quality.

2. The ratio (b / a) of the major axis (b) to the minor axis (a) of the polygonal solidified phase is 1 to 3. A zinc alloy plated steel material with excellent corrosion resistance and surface quality as described in claim 1.

3. The microstructure of the zinc alloy plating layer is MgZn ２ and Mg ２ Zn １１ one or more of the following A zinc alloy with excellent corrosion resistance and surface quality as described in claim 1, wherein the area fraction is 20 to 45%. Plated steel.

4. The Al and Mg satisfy the following relational formula 1, and the corrosion resistance and surface quality described in claim 1. Excellent zinc alloy plated steel material. [Relationship 1] Mg≦-0.0186×Al ２ +1.0093×Al+4.5 (However, the Al and Mg mentioned above refer to the content (by weight) of each component.)

5. The zinc alloy plating layer consists of the group comprising Be, Ca, Ce, Li, Sc, Sr, V, and Y. The resistance according to claim 1, further comprising 0.0005 to 0.009% of one or more selected from Zinc alloy plated steel with excellent corrosion resistance and surface quality.

6. The stage of preparing the raw iron; The prepared base iron, in weight percent, consists of Al: 8-25%, Mg: 4-12%, and the remainder is Zn. and the step of immersing in a plating bath containing unavoidable impurities and plating it; The step of wiping the plated base iron; and After the wiping, a step to form a polygonal solidified phase on the surface of the hot-dip galvanized layer; A method for manufacturing zinc alloy plated steel materials that have excellent corrosion resistance and surface quality, including [the specified element].

7. The formation of the aforementioned polygonal solidification phase is A gas containing 78-99% nitrogen by volume is sprayed onto the surface of the hot-dip galvanized layer (primary gas injection). Claim 6 A method for manufacturing zinc alloy plated steel materials with excellent corrosion resistance and surface quality as described above.

8. The method further includes adding vibrations of 100 Hz to 5 MHz after injecting the aforementioned gas. A method for manufacturing zinc alloy plated steel materials with excellent corrosion resistance and surface quality as described in item 7.

9. The Al and Mg satisfy the following relational formula 1, and the corrosion resistance and surface quality described in claim 6. A superior method for manufacturing zinc alloy plated steel. [Relationship 1] Mg≦-0.0186×Al ２ +1.0093×Al+4.5 (However, the Al and Mg mentioned above refer to the content (by weight) of each component.)

10. The plating bath is selected from the group consisting of Be, Ca, Ce, Li, Sc, Sr, V, and Y. The corrosion-resistant and A method for manufacturing zinc alloy plated steel materials with excellent surface quality.

Images