Alloy coated steel sheet

Abstract

The present invention relates to an alloy-coated steel sheet comprising: a steel sheet, and AlMgSiZn alloy layer positioned on the steel sheet, wherein the AlMgSiZn alloy layer comprises a MgZn alloy phase, and wherein the MgZn alloy phase comprises MgZn.sub.2 and Mg.sub.2Zn.sub.11, and the MgZn alloy phase further comprises at least one of MgZn, Mg.sub.21Zn.sub.25, Mg.sub.51Zn.sub.20 and Mg.sub.2Zn.sub.3.

Claims

1. An alloy-coated steel sheet comprising: a steel sheet; and AlMgSiZn alloy layer positioned on the steel sheet, wherein the AlMgSiZn alloy layer comprises a MgZn alloy phase, the MgZn alloy phase comprises MgZn.sub.2 and Mg.sub.2Zn.sub.11, the MgZn alloy phase further comprises at least one of Mg.sub.1Zn.sub.1, Mg.sub.21Zn.sub.25, Mg.sub.51Zn.sub.20 and Mg.sub.2Zn.sub.3, and the AlMgSiZn alloy layer comprises 1 to 20 wt % of Zn based on 100 wt % of total.

2. The steel sheet of claim 1, wherein the AlMgSiZn alloy layer comprises 5 to 30 wt % of Mg based on 100 wt % of total.

3. The steel sheet of claim 1, wherein the AlMgSiZn alloy layer further comprises AlMg alloy phase.

4. The steel sheet of claim 3, wherein the AlMg alloy phase comprises at least one of Al.sub.3Mg.sub.2 and Al.sub.12Mg.sub.17.

5. The steel sheet of claim 1, further comprising AlFeSi alloy layer positioned between the steel sheet and the AlMgSiZn alloy layer.

6. The steel sheet of claim 1, wherein the AlMgSiZn alloy layer further comprises MgSi alloy phase.

7. The steel sheet of claim 6, wherein the MgSi alloy phase comprises Mg.sub.2Si.

8. The steel sheet of claim 1, wherein the AlMgSiZn alloy layer further comprises AlMg alloy phase and MgSi alloy phase.

9. The steel sheet of claim 1, wherein the AlMgSiZn alloy layer comprises Mg.sub.2Si and Al.sub.3Mg.sub.2.

10. The steel sheet of claim 6, wherein the AlMgSiZn alloy layer comprises Mg.sub.2Si and Al.sub.12Mg.sub.17.

11. The steel sheet of claim 6, wherein the AlMgSiZn alloy layer comprises Mg.sub.2Si, Al.sub.3Mg.sub.2 and Al.sub.12Mg.sub.17.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic view of a continuous coating device which may be used for manufacturing an alloy-coated steel sheet.

(2) FIG. 2 is a schematic view of an alloy coated steel sheet according to an exemplary embodiment of the present invention.

(3) FIG. 3 is a glow discharge spectroscopic analysis result of an alloy-coated steel sheet according to an exemplary embodiment of the present invention. FIG. 3(a) is a glow discharge spectroscopic analysis result of 1.2 wt % of a Zn content, FIG. 3(b) is a 2.6 wt % of a Zn content, and FIG. 3(c) is a 7.9 wt % of a Zn content.

(4) FIG. 4 is an X-ray diffraction analysis result of the alloy-coated steel sheet according to an exemplary embodiment of the present invention.

(5) FIG. 5 is a salt spray test result of the alloy-coated steel sheet of Example 1 and Comparative Example 1 of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(6) The terms first, second, third and the like are used to describe various parts, components, areas, layers and/or sections, but are not limited thereto. These terms are only used to distinguish one part, component, area, layer or section from another. Accordingly, a first part, component, region, layer, or section stated below may be referred to as a second part, component, region, layer or section without departing from the scope of the present disclosure.

(7) The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. As used herein, the singular forms are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms comprising and including when used in this specification, specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, and/or components.

(8) When a part is referred to as being on or on another part, it may be directly on or on the other part, or the other part may be involved in between. In contrast, when a part refers to being directly above another part, the other part is not interposed therebetween.

(9) Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art.

(10) It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

(11) Hereinafter, embodiments of the present invention will be described in detail so that those of ordinary skill in the art to which the present invention pertains may easily implement them. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

(12) Recently, in order to solve the problems of the hot-dip aluminum plated steel sheet described in the background art, studies have been conducted to improve sacrificial corrosion prevention together with corrosion resistance by adding magnesium to the hot-dip aluminum plated steel sheet containing silicon.

(13) For example, studies have been conducted to manufacture a coated steel sheet having excellent corrosion resistance by manufacturing an AlMgSi plated steel sheet by hot-dip plating. However, in the case of manufacturing the steel sheet by hot-dip plating, there is a problem in that there is a limit to a control of an Mg content and in the case of a thin plating of 20 g/m.sup.2 or less, there is a disadvantage in that the corrosion resistance is rapidly deteriorated. Further, an Mg.sub.2Si alloy phase is known to improve the corrosion resistance, but in this case, there is a problem in that characteristics are improved only in a small range of abound 6% of Mg.

(14) The AlMgSi plated steel sheet is known to have excellent corrosion resistance because the Mg.sub.2Si phase is formed on the plated layer. The Mg Si phase has been reported to improve the corrosion resistance of the AlMgSi plated steel sheet when an area ratio in the plated layer is 0.5 or more and 30% or less and a long diameter of the Mg.sub.2Si phase is 10 um or less. However, since the AlMgSi plated steel sheet manufactured by the hot-dip plating method has a limitation to the control of the Mg content due to the manufacturing process, it is not easy to manufacture the AlMgSi plated steel sheet having a predetermined content or more of Mg content (about 15% or more). Due to the Mg content limitation of the AlMgSi plated steel sheet and a high processing temperature, it is difficult to form an Al.sub.3Mg.sub.2 phase or an Al.sub.12Mg.sub.17 phase in the AlMgSi alloy layer in addition to the Mg.sub.2Si phase as an intermetallic compound.

(15) As another example, there are studies on a method of forming an AlMg alloy layer by depositing Mg while a substrate coated with aluminum is heated at 350 C. or more and 500 C. or less in vacuum and a method of coating and then heat-treating Mg on the hot-dip aluminum plated steel sheet by physical vapor deposition. However, in these methods, since Mg is deposited on the substrate heated at a high temperature in vacuum, the loss of steam may occur and characteristic change data in accordance with the generation of an intermetallic compound or the intermetallic compound are not presented with respect to an AlMgSi layer.

(16) In order to solve the problems of the aforementioned hot-dip aluminum plated steel sheet and the problems of the AlMg alloy steel sheet described in the present invention, an AlMgSi coated steel sheet with improved sacrificial corrosion prevention characteristic by coating Mg on hot-dip aluminum steel sheets using physical vapor deposition and diffusion heat treatment to increase Mg content and form intermetallic compounds in the plated layer was developed. According to the present invention, since Mg is coated on the hot-dip aluminum plated steel sheet by a physical vapor deposition method, there is no limitation to the Mg content control of the AlMgSi coated layer and it is possible to manufacture a structure of various coated layers.

(17) To provide an alloy-coated steel sheet that provides sacrificial corrosion resistance by depositing Mg on a molten aluminum-coated steel sheet containing silicon and forming an alloy film through heat treatment, and simultaneously, has a high corrosion resistance characteristic even at a thin thickness.

(18) The prevent invention provides high corrosion resistant steel sheet with improved corrosion resistance by adding Zn to an AlMgSi coated steel sheet and a method for manufacturing thereof. Specifically, the intermetallic compound and dissolved Mg and Zn are present in the plated layer by coating Mg and Zn by physical vapor deposition on an aluminum plated steel sheet comprising a plating layer containing Al and Si, and performing diffusion heat treatment, so that the corrosion resistant and sacrificial corrosion prevention characteristics of the coated steel sheet can be improved.

(19) Alloy-Coated Steel Sheet Manufacturing Method

(20) A method of manufacturing an alloy-coated steel sheet according to the present invention comprises a preparation step of preparing a plated steel sheet formed a plated layer containing Al and Si, a first coating step of forming an Mg coated layer containing Mg on the plated layer, a second coating step of forming a Zn coated layer containing Zn on the Mg coated layer, and a heat treatment step of heat-treating the plated steel sheet on which the Mg coated layer and the Zn coated layer are formed to diffuse the Mg and Zn into the plated layer.

(21) In the preparation step, a plated steel sheet formed a plated layer containing Al and Si is prepared

(22) The plated steel sheet may be a hot-dip aluminum plated steel sheet. Specifically, the aluminum plated steel sheet may comprise 88 to 90 wt % of Al, 8 to 10 wt % of Si, and 5 wt % or less of Fe based on 100 wt % of the total.

(23) The plated layer may comprise an AlFeSi alloy layer formed on the steel sheet and an AlSi layer formed on the AlFeSi alloy layer. The AlFeSi alloy layer may be formed by diffusion of Fe of the plated steel sheet into the plated layer when the plated steel sheet is manufactured.

(24) Next, in the first coating step, an Mg coated layer containing Mg is formed on the plated layer. In this case, the coating of Mg may be performed by physical vapor deposition (PVD). Specifically, it may be performed by electromagnetic levitation physical vapor deposition (EML-PVD). However, the present invention is not limited thereto, and various methods may be employed to coat Mg if it is possible to deposit Mg by a physical method such as an electron beam evaporation device, a thermal evaporation device, a sputtering source, or a cathode arc source.

(25) Next, in the second coating step, a Zn coated layer containing Zn is formed on the Mg coated layer. In this case, the coating of Zn may be performed by physical vapor deposition (PVD). Specifically, it may be performed by electromagnetic levitation physical vapor deposition (EML-PVD). However, the present invention is not limited thereto, and various methods may be employed to coat Zn if it is possible to deposit Zn by a physical method such as an electron beam evaporation device, a thermal evaporation device, a sputtering source, or a cathode arc source.

(26) Next, in the heat treatment step, the plated steel sheet on which the Mg coated layer and the Zn coated layer is heat-treated so that Mg and Zn are diffused into the plated layer. It may be heat-treated using an induction heating device. However, the present invention is not limited thereto, and other suitable heat treatment means may be employed.

(27) Specifically, the plated steel sheet may be heat-treated at a temperature of 300 to 450 C., and heat-treated for 5 to 600 seconds.

(28) The AlMgSiZn alloy layer is formed after the heat treatment because Mg and Zn are diffused into the plated layer by the heat treatment. The AlMgSiZn alloy layer may comprise an MgZn alloy phase, and may further comprise at least one of an AlMg alloy phase and an MgSi alloy phase.

(29) MgZn alloy phase may comprise MgZn.sub.2 and Mg.sub.2Zn.sub.11, and the MgZn alloy phase may further comprise at least one of MgZn, Mg.sub.21Zn.sub.25, Mg.sub.51Zn.sub.20 and Mg.sub.2Zn.sub.3.

(30) MgZn.sub.2 and Mg.sub.2Zn.sub.11 in stable forms among the MgZn alloy phase, as well as MgZn, Mg.sub.21Zn.sub.25, Mg.sub.51Zn.sub.20 and Mg.sub.2Zn.sub.3, which are relatively unstable phases, may be further comprised, because it is manufactured by depositing an Mg coated layer and a Zn coated layer on the plated steel sheet and then heat-treating it, rather than dipping the steel sheet in a plating bath containing Al, Mg, Si and Zn to perform hot-dip plating.

(31) In addition, the AlMg alloy phase may comprise at least one of Al.sub.3Mg.sub.2 and Al.sub.12Mg.sub.17, and the MgSi alloy phase may comprise Mg.sub.2Si.

(32) FIG. 1 is a schematic view of a continuous coating device which may be used for manufacturing an alloy-coated steel sheet. However, this is only an example according to an exemplary embodiment of the present invention and is not limited thereto.

(33) The apparatus disclosed in FIG. 1 is configured by a steel sheet supplying device 11 for supplying a hot-dip aluminum plated steel sheet 17 in an atmosphere, an inverse magnetron sputtering source 12 capable of pre-treating the steel sheet in vacuum, a physical vapor deposition (PVD) device 13 for coating Mg after pre-treatment, an inductive heating device 14 capable of heat-treating the steel sheet discharged to the atmosphere, and a steel sheet discharging device 15 for rewinding the heat-treated coated steel sheet again.

(34) The PVD device 13 may be an electromagnetic levitation (EML) source. The inverse magnetron sputtering source 12 and the PVD device 13 may be installed and operated in a vacuum container 16.

(35) First, the hot-dip aluminum plated steel sheet 17 is prepared and alkaline degreasing may be performed to remove residual oils such as anti-rust oil smeared on the surface of the steel sheet.

(36) Thereafter, the steel sheet is supplied to the vacuum container 16 while being transferred by the steel sheet supplying device 11. Next, the surface cleaning of the steel sheet may be performed by applying power to the inverse magnetron sputtering source 12 installed in the vacuum container 16.

(37) After the cleaning is completed, while the steel sheet is continuously transferred, Mg may be vacuum coated on the Al plated layer by the EML source 13 installed in the vacuum container 16. The Mg and Zn coatings can be formed by two-layer form and simultaneous coating.

(38) After the coating is completed, the steel sheet is continuously transferred to be discharged to the atmosphere, and then the steel sheet may be heat-treated at a predetermined temperature for a predetermined time using the inductive heating device 14 in the atmosphere. After the heat treatment is completed, the steel sheet is continuously transferred to obtain the manufactured alloy-coated steel sheet.

(39) Alloy-Coated Steel Sheet

(40) When referring to FIG. 2, An alloy-coated steel sheet according to an exemplary embodiment of the present invention comprises the a steel sheet, and AlMgSiZn alloy layer positioned on the steel sheet, wherein the AlMgSiZn alloy layer comprises a MgZn alloy phase, and wherein the MgZn alloy phase comprises MgZn.sub.2 and Mg.sub.2Zn.sub.11, and the MgZn alloy phase further comprises at least one of MgZn, Mg.sub.21Zn.sub.25, Mg.sub.51Zn.sub.20 and Mg.sub.2Zn.sub.3.

(41) MgZn.sub.2 and Mg.sub.2Zn.sub.11 in stable forms among the MgZn alloy phase, as well as MgZn, Mg.sub.21Zn.sub.25, Mg.sub.51Zn.sub.20 and Mg.sub.2Zn.sub.3, which are relatively unstable phases, may be further comprised. This may be due to a method of manufacturing an alloy-coated steel sheet by depositing an Mg coated layer and a Zn coated layer on the plated steel sheet and then performing heat treatment. According to the presence of such MgZn alloy phase, the corrosion resistant and sacrificial corrosion prevention characteristics of the coated steel sheet may be improved.

(42) In addition, the AlMgSiZn alloy layer may further comprise at least one of an AlMg alloy phase and an MgSi alloy phase. The AlMg alloy phase may comprise at least one of Al.sub.3Mg.sub.2 and Al.sub.12Mg.sub.17, and the MgSi alloy phase may comprise Mg.sub.2Si.

(43) The AlMgSiZn alloy layer may comprise 40 to 80 wt % Al, 15 to 30 wt % Mg, 1 to 10 wt % Si, and 1 to 20 wt % Zn, based on 100 wt % of the total. When Zn exceeds 45 wt %, the amount of ZnMg intermetallic compound increases due to excessive Zn, and problems such as surface blackening and reduced corrosion resistance may occur.

(44) As the Mg coated layer and the Zn coated layer are formed on the plated steel sheet on which the plated layer containing Al and Si may be formed, and then heat treatment is performed, Fe of the plated steel sheet is partially diffused into the plated layer so that An AlFeSi alloy layer may be positioned between the steel sheet and the AlMgSiZn alloy layer.

(45) In addition, the description of the alloy-coated steel sheet will be replaced with the description of the above-described alloy-coated steel sheet manufacturing method.

(46) Hereinafter, specific exemplary embodiments of the present invention may be described. However, this is only an example according to an exemplary embodiment of the present invention and is not limited to exemplary embodiments below.

EXAMPLES

(47) (1) Manufacturing Alloy-Coated Steel Sheet

(48) [Example 1] A Mg coated layer and a Zn coated layer were formed using physical vapor deposition (PVD) on a hot-dip aluminum-coated steel sheet on which a plated layer containing Al and Si was formed, and then heat treatment was performed for 300 seconds based on a heat treatment temperature of 400 C. Zn was 1.2 wt % based on the AlMgSiZn alloy layer produced after heat treatment.

(49) [Example 2] It was prepared under the same conditions as in Example 1, except that Zn was 2.6 wt %.

(50) [Example 3] It was prepared under the same conditions as in Example 1, except that Zn was 5.0 wt %. [Example 4] It was prepared under the same conditions as in Example 1, except that Zn was 8.0 wt %.

(51) [Example 5] It was prepared under the same conditions as in Example 1, except that Zn was 10.0 wt %.

(52) [Example 6] It was prepared under the same conditions as in Example 1, except that Zn was 15.0 wt %.

(53) [Example 7] It was prepared under the same conditions as in Example 1, except that Zn was 42.6 wt %.

(54) [Comparative Example 1] It was prepared under the same conditions as in Example 1, except that heat treatment was performed without forming a Zn coating layer.

(55) (2) Observation of Microstructure Change of Alloy-Coated Steel Sheet

(56) FIG. 3 is a glow discharge spectroscopic analysis result of an alloy-coated steel sheet according to an exemplary embodiment of the present invention. FIG. 3(a) is a glow discharge spectroscopic analysis result of 1.2 wt % of Zn content, FIG. 3(b) is a 2.6 wt % of Zn content, and FIG. 3(c) is a 7.9 wt % of Zn content. As shown in FIG. 3, when the heat treatment time was carried out at 400 C. for 300 seconds, diffusion of Mg and Zn occurs and diffused into the aluminum plating layer. The diffusion depth of Mg and Zn was about 3 m.

(57) On the other hand, FIG. 4 shows the X-ray diffraction analysis results according to the Zn wt %, showing that AlMg, MgSi alloy phases were formed regardless of the Zn content. MgZn alloy phase was observed in the form of MgZn, MgZn.sub.2, Mg.sub.21Zn.sub.25, and other things below 30. As the Zn content is lower, it may be seen from the X-ray diffraction analysis that the strength of the MgZn alloy phase is smaller than that of the AlMg alloy phase and the MgSi alloy phase.

(58) (3) Evaluation of Corrosion Resistance of Alloy-Coated Steel Sheet

(59) FIG. 5 is a salt spray test result of an AlMgSi alloy-coated steel sheet containing no Zn (Example 1) and an AlMgSiZn alloy-coated steel sheet containing 1.2 wt % of Zn (Comparative Example 1). The salt spray test was conducted according to ASTM B-117.

(60) As shown in FIG. 5 and Table 1, in the coated steel sheet containing no Zn, it may be seen that the red rust is spread throughout the specimen after 2700 hours. In the coated steel sheet containing 1.2 wt % of Zn, it may be seen that the red rust did not spread to the entire area of the specimen even after 2700 hours. It may be seen that Examples 3, 5, and 6 have a smaller red rust area than Example 1 even after 4500 hours. Example 7 showed the lowest corrosion resistance among Examples with a Zn content of 42.6 wt %. As described above, as the Zn content increases, the amount of intermetallic compounds increase, which is considered to be due to the phenomenon of blackening and deterioration of corrosion resistance.

(61) TABLE-US-00001 TABLE 1 Plated Zn Heat treatment Heat treatment Plated amount Coating content temperature time Division material (g/m.sup.2) material (wt %) ( C.) (senconds) Example 1 AlSi 15 Mg/Zn 1.2 400 300 Example 2 AlSi 15 Mg/Zn 2.6 400 300 Example 3 AlSi 15 Mg/Zn 5.0 400 300 Example 4 AlSi 15 Mg/Zn 8.0 400 300 Example 5 AlSi 15 Mg/Zn 10.0 400 300 Example 6 AlSi 15 Mg/Zn 15.0 400 300 Example 7 AlSi 15 Mg/Zn 42.6 400 300 Comparative AlSi 15 Mg/Zn 0 400 300 Example 1

(62) The present invention is not limited to the implementation exemplary embodiments and/or examples, but may be manufactured in various forms and those skilled in the art will understand that the present invention may be implemented in another specific form without changing the technical spirit or an essential feature thereof. Therefore, it should be appreciated that the aforementioned implementation exemplary embodiments and/or examples are illustrative in all aspects and are not restricted.

(63) While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.