TW201200630A - Corrosion protection with Al/Zn-based coatings - Google Patents

Abstract

Red rust staining of Al/Zn coated steel strip in ''acid rain'' or ''polluted'' environments can be minimised by forming the coating as an Al-Zn-Si-Mg alloy coating with an OT: SDAS ratio greater than a value of 0.5: 1, where OT is the overlay thickness on a surface of the strip and SDAS is the measure of the secondary dendrite arm spacing for the Al-rich alpha phase dendrites in the coating. Red rust staining in ''acid rain'' or ''polluted'' environments and corrosion at cut edges in marine environments can be minimised in Al-Zn-Si-Mg alloy coatings on steel strip by selection of the composition (principally Mg and Si) and solidification control (principally by cooling rate) and forming Mg2Si phase particles of a particular morphology in interdendritic channels.

Description

201200630 VI. INSTRUCTIONS: [Yun Yi Ming belongs to the _ I 1 彳 mark] FIELD OF THE INVENTION The present invention generally relates to the production of a product having an alloy coating containing aluminum and zinc as main components of the alloy. (hereinafter referred to as A/Zn-based alloy coated product). The term "Al/Zn-based alloy coated product, which is understood to include ribbon, tubular As an example, products in the form of articles and structural segments having a coating of an A1/Zn based alloy on at least a portion of the surface of the products. Although not exclusively exclusive, the present invention is more particularly directed to Al/Zn based on at least the surface of the alloy in the form of a metal, such as steel, ribbon, and having an alloy coating. Alloy coated products, as well as products made from ribbons coated with Al/Zn based alloys. The metal ribbon coated with the A1/Zn-based alloy may be a ribbon coated with inorganic and/or organic compounds for protection, aesthetics or other reasons. Although not exclusively excluded, the present invention more particularly relates to a steel strip coated with an Al/Zn-based alloy, which has a coating other than _Ζη which is not only a trace amount but not only - an element, such as called & Although not exclusive, the present invention is more particularly related to the main hall of the hall: steel strip, which has a coating containing fine enamel, the main alloy of which has a pure V, up to 5% &;, up to 1%% and the remaining Zn and a small amount of other elements, for each other element (4) coffee, all percentages are weight percentage meaning 3 201200630 Yes, unless otherwise explicitly mentioned, all elements discussed Percentages are in this specification and weight percentages. ί: Prior Art 3 Background of the Invention Thin (i.e., 2-100 μπ thick) Al/Zn-based alloy coatings are typically formed on several surfaces of a steel strip to provide protection against corrosion. The Al/Zn-based alloy coating is generally, but not exclusive, the alloy elements A1 and Zn and Mg, Si, Fe, Mn, Ni, Sn and a small amount such as V, Sr. a coating of one or more of the other elements of Ca, Sb. The Al/Zn based alloy coating is generally, but not exclusive, formed on the steel strip by hot dip coating the ribbon through a bath of molten alloy. The steel strip is typically, but not necessarily excluded, heated prior to soaking to promote alloy bonding to the ribbon. The alloy then cures to the ribbon and forms a cured alloy coating as the ribbon emerges from the molten bath. The Al/Zn based alloy coating typically has a microstructure consisting essentially of a mixture of alpha-rich alpha phases in the form of dendrites and Zn-rich eutectic phases in the region between the dendrimers. When the rate of solidification of the molten coating is suitably controlled (for example, as incorporated herein by reference in U.S. Patent No. 3,782,909), the alpha-rich alpha phase solidifies into a sufficiently finely dendritic body. Let it define a continuous channel network in the inter-branched region, and the Zn-rich eutectic phase mixture solidifies in the inter-branched zone. The performance of these coatings depends on the following combinations: (a) Steel Base # 8 201200630 The protection of 'Essence of Zn-rich eutectic mixture, and (b) barrier protection' is supported by the rich A1ia vines. The Zn-rich inter-branched interphase mixture is preferentially corroded to provide sacrificial protection against the steel substrate, and in some environments 'once the Zn-rich inter-branched phase mixture has been depleted' Will continue to provide proper level of sacrificial protection and barrier protection for the steel substrate. However, there are many cases where the barrier protection and sacrificial protection levels imparted by the alpha-rich vines are not sufficient, and the properties of the coated steel ribbon may be impaired. Three such areas are as follows. 1. In “acid rain” or “contaminated” environments containing high concentrations of nitrogen oxides and sulfur oxides. 2. Under the paint film in the marine environment. 3. At areas where the cutting edge or other metallic coating has been damaged to expose the steel substrate to the marine environment. As an example, Applicants have discovered that Al/Zn based alloy coatings on steel strips are particularly thin (i.e., coatings have a total coating mass of coated per square meter). Less than 2 grams, typically less than 15 grams; it is equal to less than 1 gram per square meter of coating on each surface of the steel strip when there is an equal coating thickness on both surfaces Typically less than 75 grams), the microstructure is typically at 11 in the coating. (: / 8 to 1 〇〇. (: / 8 standard cooling rate is formed, tends to be more columnar or bamboo structure extending from the steel strip to the surface of the coating. This microstructure contains (a a rich Zn-rich eutectic mixture formed by a series of octagonal vines and (8) formed as a series of separate columnar channels extending directly from the steel strip to the surface of the coating. 5 201200630 Applicants have also discovered that Such steel ribbons with thin Al/Zn-based alloy coatings with columnar microstructures are exposed to low pH environments commonly described as "acid rain" environments, or exposed to what is commonly described as "contaminated "In the environment of a concentration of sulfur dioxide and nitrogen oxides in the south, the Zn-rich inter-dark phase mixture is rapidly invaded, and the mixture is directly extended from the steel strip to the surface of the coating. The columnar channel acts as a direct path to the steel strip. Where such a direct corrosion path from the surface of the coating to the steel strip is present, the strip may be corroded and corroded ( Iron oxide) will migrate freely to the coating The surface of the object develops a profile known as "red rust." The red rust collapses the aesthetic appearance of the coated steel product and reduces product performance. For example, red rust can reduce the use of roofing materials. Thermal efficiency of coated steel products. Applicants have also discovered that thin Al/Zn based coatings are scratched, cracked or otherwise damaged to reveal steel strips and exposed to "acid rain" environments or The place where the pollution ί ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' A protective steel strip. An "acid rain" environment is understood herein as rain and/or an agglomerate formed on a coated steel strip having an environment having a pH of less than 5, 6. As an example "Contaminated environment" will be typical, but never exclusive, defined as the P2 or P3 category in IS09223. Also as an example, after the rich eighty-one [phased vines are regularly considered to be steel-based In a marine environment that provides good sacrificial protection, this The ability is impaired by the change in the microenvironment under the paint film applied to the metallic coated steel strips. The above description is not to be considered as a general general knowledge of recognition in Australia or elsewhere. SUMMARY OF THE INVENTION Applicants have discovered that red rust collapse in an "acid rain" or "contaminated" environment of a steel strip coated with an Al/Zn based alloy can be formed into an Al by coating -Zn-Si-Mg alloy coating and ensuring that the OT:SDAS ratio of the coating is prevented or minimized by a value greater than 0.5:1, where OT is the coating thickness on the surface of the ribbon and SDAS is coated The measure of the secondary branching arm spacing of the A1 a-branched vines in the covering. The term "coverage thickness" is understood herein to mean a strip-on-coat coating that is subtracted from the thickness of the coating-intermetallic alloy layer. The total thickness of the intermetallic alloy layer is the Al-Fe-Si-Zn formed adjacent to the steel substrate by the reaction between the molten coating and the steel substrate when the coating is applied to the ribbon. Quaternary metal phase layer. According to the present invention, there is provided a corrosion-resistant Al-Zn-Si-Mg alloy for forming an "acid rain" or "contaminated" environment suitable for use as an exemplary metal strip of steel. A method of coating comprising: (a) passing a metal ribbon through a molten bath of an Al-Zn-Si-Mg alloy and forming an alloy coating on one or both surfaces of the ribbon (b) curing the coating on the ribbon to form a cured coating having a microstructure comprising 7 201200630 dendrites having an alpha phase rich in A1 and having a rich An inter-branched channel of Zn eutectic phase mixture extending from the metal ribbon and having Mgji phase particles in the inter-branched inter-body channels, and the method comprising controlling steps (4) and (b) and forming 〇T: The SDAS ratio is greater than 0.5:1 cured coating, where 〇τ is the cover thickness and sdas is the secondary dendrite arm spacing of the A1-rich alpha vines of the coating. The "rich Zn-rich co-soluble phase mixture" is understood herein to mean a mixture of eutectic reaction products, and the mixture contains a 211-rich phase 3 and a Mg:Zn compound phase, for example, MgZn2. According to the present invention, there is also provided a metal ribbon having Al-Zn-Si-Mg alloy on one or both surfaces of which is suitable for use as an exemplary "acid rain" or "contaminated" environment. a coating comprising a microstructure comprising a dendritic body having an alpha phase rich in A1 and an intervening channel having a mixture of zn rich eutectic phases extending from the metal ribbon and having Mg2Si The phase particles are in the inter-branched inter-body channels, and the coating has a 〇T:SDAS ratio greater than 0.5:1 'where the OT system is the cover thickness, and the SDAS system is the A1-rich alpha-phase vine body of the coating. The secondary branches are separated by arms. It is to be noted that 'where the coating is on both surfaces of the ribbon, the thickness of the cover on each surface may be different or the same depending on the requirements of the coated ribbon. In any event, the present invention requires that the OT:SDAS ratio of the coating on each of the two surfaces is greater than 0.5:1. The OT:SDAS ratio can be greater than 1:1. The OT:SDAS ratio can be greater than 2:1. The coating can be a thin coating. In this context, a "thin" coating 201200630 on a metal, such as steel, ribbon is understood herein to mean having a total coating mass on both surfaces of the ribbon that is coated per square meter. A coating having a coating of less than 200 grams is equal to less than 1 gram per square meter of coating on one surface of the steel ribbon, although instances may not always be the case. The coating may have a cover thickness of more than 3 μηι 〇 and the coating may have a cover thickness of less than 20 μm. The coating may have a cover thickness of less than 3 〇μηι. The coating may have a cover thickness of 5-20 μm. The Al-Zn-Si-Mg alloy may contain 20-95% of Si, up to 5% Si, up to 10% of Mg, and the remaining Zn and a small amount of other elements, typically less than 0.5% for each of the other elements. . The Al-Zn-Si-Mg alloy may contain 40-65% of A1. The Al-Zn-Si-Mg alloy may contain 45-60% of A. The Al-Zn-Si-Mg alloy may contain 35-50% of Zn. The Al-Zn-Si-Mg alloy may contain 39-48% of Zn. The Al-Zn-Si-Mg alloy may contain 1-3% Si. The Al-Zn-Si-Mg alloy may contain 1.3 to 2.5% of Si. The Al-Zn-Si-Mg alloy may contain less than 5% of Mg. The Al-Zn-Si-Mg alloy may contain less than 3% of Mg. The Al-Zn-Si-Mg alloy may contain not only 1% of Mg. The Al-Zn-Si-Mg alloy may contain 1.2 to 2.8% of Mg. The Al-Zn-Si-Mg alloy may contain 1.5 to 2.5% of Mg. The Al-Zn-Si-Mg alloy may contain 1.7 to 2.3% of Mg. The metal strip can be a steel strip. 201200630 In addition or in the above event that the 〇T:SDAS ratio cannot be maintained and the coating has an OT:SDAS ratio of less than 0.5:1, the applicant has also discovered red rust in the “acid rain” or “contaminated” environment. And also the rot at the cutting edge in the marine environment can be thinned on the steel strip by the choice of coating alloy composition (primarily PCT and si) and the control of the coating microstructure The -Zn-Si-Mg alloy coating is prevented or minimized. The above composition selection and microstructure control system are particularly useful for thin coatings and/or coatings having an OT:SDAS ratio of less than 〇5:1, but are not limited to these coatings' and are also suitable for Thick coatings and/or coatings with a T:SDAS ratio greater than 〇5:1 Applicants have also discovered corrosion and “acid rain” or “jing” at the edge of the coated steel strip in the marine environment. Contamination, red rust in the environment can be eliminated or minimized in sensitive Al/Zn-based coatings by: 1. Blocking rot along the Zn-rich inter-branched channel to the steel strip I, and/or 2. to make the rich phase 1 1 active in these environments so that it can be sacrificed to protect the steel strip. Generally speaking, in both cases, according to the invention, a metal strip is provided. a coating of Al-Zn-Si-Mg alloy on one or both of the strips suitable for use as an exemplary "acid rain" or "contaminated" environment, the coating comprising a micro Structure 'The microstructure comprises a dendritic body having an alpha phase rich in A1 and an inter-body channel extending from a mixture of eutectic phases rich in Zn extending from the metal strip And the Mg2Si phase particles are in the inter-branched inter-body channels. The term "particles" as used herein in the context of the Mg2Si phase is understood to mean the physical form of the phase precipitates in the microstructure of 201200630. It is understood that ''particles' are formed from the solution via precipitation during solidification of the coating and are not specifically added to the composition. 1. Blocking According to the present invention, there is provided an anti-corrosion Al-Zn for forming an acid rain, or a "contaminated, environmentally friendly" type on a ribbon of a metal, typically a steel. a method of coating a Si-Mg alloy, comprising: (a) passing a metal ribbon through a smelting bath of an Al-Zn-Si-Mg alloy and on one or both surfaces of the ribbon Forming an alloyed coating thereon, (b) curing the coating on the ribbon to form a cured coating. The cured coating has a microstructure comprising a dendritic body having an Alia-rich phase And an inter-branched channel having a Zn-rich eutectic phase mixture extending from the metal ribbon and having a Mg2Si phase in the inter-branched channel, and the method comprises selecting a Mg and Si concentration and controlling the step (b) The cooling rate in the formation of Mg2Si phase particles that block corrosion along the inter-branched channels in the inter-branched channels in the cured coating. As an explanation, in the Al/Zn-based coating with a dendritic structure, Si is present in the form of flaky particles, and although it is not corroded, it is not filled with inter-plant channels. And blocking the inter-branched inter-body channel from the inter-corrosion of the branches of the steel strip. Applicants have discovered that Mg added to the Al/Zn-based coating containing Si can be combined with Si to form the appropriate size and morphology in the inter-branched inter-channel between the A-rich a-branched arms. The Mg2Si phase particles, which may otherwise be the direct septic route to the steel strip, are blocked and help to isolate the underlying steel substrate cathode. Appropriate size and morphology The particles of S- 11 201200630 are formed by controlling the curing of the coating and the cooling rate. In particular, the applicant has found that the cooling rate during the curing of the coating «should be maintained less than 17 〇 - 4_5 CT, where the CR system is. c/sec represents the Δ rate, and or is the strip thickness of the strip of S. The morphology of properly sized Mg2Si phase particles can be described as "Chinese character pattern" when viewed as a planar image, while ## can be described as a petal form when viewed in a 3D image. The morphology as an example is shown in Figures _ and 13 and is discussed further below.

The petals of the MgsSi particles may have a thickness of less than 8 μm.

The flap of the MgaSi phase particles can have a thickness of less than 5 μηι.

The lobes of the MgzSi phase particles may have a thickness in the range of 〇 5_2 5 μηη. The degree of Mg can be selected to be greater than 0.5%. Below this concentration, the Mg2Si phase coarse will not be sufficient to fill and block the inter-plant channel.

The Mg concentration can be selected to be less than 3%. Above this concentration, large Mg2Si particles having a square shape which is ineffective in resisting corrosion between lychee and vines are formed. In particular, the Al-Zn-Si-Mg alloy may contain not only 1% of Mg. In the case of a coating having a Si concentration of from 0.5 to 2%, the volume fraction of the Mg2Si phase between the other Si-containing phases may be greater than 50%. The volume fraction of the Mg2Si phase between the branches can be greater than 80% compared to other Si-containing phases. The proportion of the Mg2Si phase between the branches of the coating in the lower two thirds of the thickness of the coating can be greater than 70% of the total integral of the Mg2Si phase in the coating in order to provide a good barrier to the inter-body passage. The proportion of inter-plant channels that are "blocked" by the Mg2Si phase may be greater than 60% of the total number of channels 8 12 201200630, typically greater than 70%. Applicants for the vine structure have also found that the possible improved protection span of the present invention ranges from 〇T:SDAS ratio of 0.5:1 to OT: SD AS ratio of 6:1. Branch body structure. Corrosion along these pathways is generally retarded, especially in "acid rain," or "red rust through these pathways in a foul environment." In Al/Zn alloy coatings, corrosion along the inter-branched channels is also limited by reducing the size of the channels. The reduction in channel size is the result of the cooling rate during the curing to reduce the SDAS of the coating, as described in US Patent 3,782,909. Said in the middle. However, although this can slow the surface corrosion of the coating (as often measured by mass loss testing), it limits the availability of zinc-rich phase compounds to provide sacrificial protection to steel substrates. Thus, corrosion of the steel substrate is more likely to occur. 2. Activation of the alpha phase In accordance with the present invention, there is provided an anti-corrosive Al-Zn for forming an "acid rain" or "contaminated" environment suitable for use as an exemplary metal strip on steel. a method of coating a coating of Si-Mg alloy, which comprises: (a) passing a metal ribbon through a dazzling bath of an Al-Zn-Si-Mg alloy and on one or both surfaces of the ribbon Forming an alloyed coating thereon, (b) curing the coating on the ribbon to form a cured coating having a microstructure comprising a Α1 < alpha phase An inter-plant channel extending from a mixture of eutectic phases rich in Ζη, extending from the metal ribbon, and having a Mg2Si phase in the inter-plant channel, and the method includes selecting Mg and Si concentration and controlling Cooling fan 13 201200630 in step (b) to form Mg2Si phase particles having a size range, morphology and spatial distribution that activates the alpha phase rich in A1 to provide sacrificial protection in the interbranched channels in the cured coating. . In particular, Applicants have discovered that the Mg2Si phase itself is reactive and susceptible to corrosion. However, Applicants have also discovered conditions for purifying the Mg2Si phase, promoting channel blockage, and promoting and enhancing the activation of the alpha-rich alpha phase in the sacrificial protection of the steel ribbon. In particular, Applicants have discovered that the addition of a suitable Mg and Si concentration to an Al/Zn based alloy coating composition and the selection of a cooling rate to cure the coating with an alloy composition on the steel strip results in The formation of the illusion & phase has a proper dispersion and position in the inter-plant channel to activate the Α12α phase to provide sacrificial protection for certain oceans and “acid rain,” and “contaminated” environments. The activation of the phase contributes to the application of the finer vine structure without the loss of sacrificial protection at the cutting edge or other areas where the steel substrate has been exposed.

The choice of Mg and Si concentration and cooling rate is consistent with the "blocking," description of these parameters under the heading.

In particular, in terms of cooling rate, Applicants have discovered that the cooling rate CR during curing of the coating should be maintained at less than 17 〇 _ 45 CT, where CR is a cooling rate in c/second, but Micron indicates the thickness of the coating on the surface of the ribbon. As far as the composition is concerned, as an example, in the "acid rain," or "contaminated" % and "acidic" micro-grief, the Mg concentration can be greater than 0.5% for formation.

Mg2Si. 8 14 201200630

The Mg concentration can be greater than 1% to ensure efficient activation of the alpha phase.

The Mg concentration can be less than 3%. At higher concentrations, a coarse, widely dispersed primary Mg2Si phase will form, but will not provide a uniformly activated alpha-rich alpha phase. In particular, the Al-Zn-Si-Mg alloy may contain not only 1% of Mg. Applicants have also discovered that the application of the possible improved sacrificial protection of the present invention spans a range of microstructures ranging from OT:SDAS ratio of 0.5:1 dendritic structure to 〇T:SDAS ratio of 6:1 branches Body structure. Applicants have also discovered that ribbons coated with Al-Zn-Si-Mg alloys made in accordance with the present invention and subsequently painted exhibit a narrower and more uniform corrosion front as an A1-rich alpha phase activation and ocean The result of a marginal overcut in the environment. Samples made in accordance with the present invention exhibited a reduced rate "edge creep" or "overcut" from the cut edge as compared to conventional Al/Zn coatings in the experimental work performed by the Applicant. The improved properties have been shown to be suitable for a range of coating structures and a range of paint films. BRIEF DESCRIPTION OF THE DRAWINGS The invention is further described with reference to the accompanying drawings in which: FIG. 1 is an example of an Al-Zn-Si-Mg alloy coating according to the present invention on a test sample in a marine environment. a graph of edge overcutting and Mg concentration; Figures 2 to 4 are test plate photographs and corrosion front image, which verify the example of the Al-Zn-Si-Mg alloy coating according to the present invention in the marine environment Improved performance in the middle; Figure 5 is an experimentally accelerated test plate photograph showing improved surface weathering and improved sacrificial protection according to the metallic rubber coated steel strip of July 201200630; Figures 6 to 11 are photographs of the test panels, which verify that the Al-Zn-Si-Mg alloy coating according to the present invention is in a solid acid rain on a steel strip, or in a "contaminated" environment. Figure 12 is a plan view of a scanning electron microscope image of an Al-Zn-Si-Mg alloy coating according to the present invention, which is an example of the morphology of MgsSi phase particles in the microstructures revealed in the image. And Fig. 13 is the Mg2Si in the A1Zn Si Mg alloy coating of Fig. 12. A 3D image of a network of phase particles. t embodiment; j improved corrosion performance of an example of a steel strip coated with an A1_Zn_Si_Mg alloy according to the present invention has been verified by the applicant for exposure to a range of actual "acid rain", "contaminated" and marine environmental sites On the test sample. Test samples such as 5 hai include test panels developed by the applicant to provide coating corrosion information. Figures 1 to 5 and Tables 1 and 2 verify the improved performance of an example of an Al-Zn-Si-Mg alloy coating produced on a steel strip produced in accordance with the present invention in a marine environment. Performance in the marine environment is assessed by an outdoor exposure test at the address of the IS/NZS 1580.457.1.1996 Appendix B for the IS Ο rating of C 2 to C 5 and by a laboratory cyclic corrosion test (CCT). The data presented in Table 1 shows an example of an Al-Zn-Si-Mg coated steel test panel for a range of metallic coating qualities in accordance with the present invention. 8 16 201200630 Impact exposure in harsh marine environments Improved performance (unit: mm) on the overcut level of the painted edge. The table also includes comparative data for traditional Al/Zn based alloy coated test panels. Oversize of the coating mass edge _ traditional Al / Zn coating edge overcut - the present invention Al / Zn coating 150g / m2 12 5 100g / m2 20 8 75g / m2 21 9 50g / m2 66 10 Obviously In Table 1, the Al-Zn-Si-Mg coated steel test panels according to the present invention have significantly less edge overcuts than conventional Al/Zn based alloy coated test panels. Further information presented in Table 2 reveals an example of an Al-Zn-Si-Mg coated painted steel test panel for a range of paint types in accordance with the present invention for exposure to overcutting in harsh marine environments. Improved performance at the level (unit: mm). The table also includes comparative data for traditional Al/Zn-based alloy coated test panels. Paint type coating quality edge overcutting - traditional Al/Zn coating edge overcutting - Al/Zn coating polyester 150g/m2 of the invention 15 3.5 polyester 100g/m2 15 5 water mainly 150g/m2 8 3.2 Water-based 100g/m2 22 4.5 “Cr-free” 150g/m2 22 6 Obviously from Table 2, the coated steel test plate coated with Al-Zn-Si-Mg according to the present invention is more The £17 201200630 painted test panels coated with conventional A1/Ζη based alloys have significantly less edge overcuts. The test plate photographs and the front image of the burnt edge in Figures 2 to 4 are incorporated into a well. The improved performance of the example of the Al-Zn-Si-Mg coating according to the present invention in marine production. Figure 2 shows the fluorocarbon coated Thai brother according to the present invention.

The Al-Zn-Si-Mg coating is a non-impact exposed corrosion resistance in a harsh marine environment. Figure 3 is an example of a traditional A1/Zn coating with a large money front under Sea Two. Figure 4 is based on this ^^

Al-Zn-Si-Mg coatings have examples of narrower and more aggressive fronts under paint in marine environments. The sentence of the test panel in Fig. 5 verifies the improved ageing ability of the example of the WZnlMg coating according to the present invention under accelerated test conditions. In particular, Figure 5 shows that compared to the conventional Al/Zn coating, the A1_Zn_Si_Mg coating according to the present (4) has a modified surface weathering and improved type in the salt spray cycle rot and test. Sacrifice protection. Figures 6 through 11 verify that the Aim-Mg coated steel test panels were modified in an "acid rain" or "contaminated" environment when produced in accordance with the present invention. The photographs appear in the traditional AI heart. The main alloy coated steel test panel was red-crushed, while the π Si Mg coated steel test panel made according to the present invention did not have red smash. The comparison between Figure 9 and Figure 7 shows The interest system was retained over time. In particular, Figure 6 shows the violent road in the harshness of the rain, 'the environment is up to 6 months of the traditional eight-hearted, covered steel tau (total coating material The amount of coating per square meter of coating is rusted. Figure 7 shows the quality of the coating of A1_Zn_si_Mg coating (10) according to the invention exposed to severe "acid rain, environment up to June. There is no red rust on the 18 201200630 coating system per square meter. Figure 8 shows a conventional A1/Zn-coated steel strip exposed to a harsh "acid rain" environment for 18 months (total coating mass per square meter of coating system i 0 0 There is a red rust on the gram. Figure 9 shows the Al-Zn-Si-Mg coating according to the invention exposed to severe "acid rain, environment for 18 months (the total coating mass is 1 per square meter of coating system) There is no red rust on the gram. The first 显现 diagram shows a traditional A1/Zn coated steel strip with a columnar structure exposed to a harsh “acid rain” environment for 4 months (total coating) The coating quality is 50 grams per square meter of coating system) with red rust. Figure u shows a columnar structure exposed to a severe "acid rain" ring for 4 months according to the invention. There is no red rust on the A1_Zn Si_Mg coating (the total coating mass is 5 gram per square meter of coating system). After that, the applicant has a micro-example of the Al_Zn_Si_Mg coating according to the present invention. In the structural analysis, it was found that the microstructure includes a special morphology of the Mg2Sl phase particles in the inter-body channel with a Zn-rich eutectic phase mixture between the branches of the phase. It is important to improve the corrosion resistance of the coating, as discussed above. Applicants have found that the Mg2Sl phase particles are large. And distribution is also an important factor in promoting the improved corrosion performance of the Al-Zn-Si-Mg coating according to the present invention. Applicants have also discovered that by selecting the coating composition and controlling the cooling rate during curing of the coating The satisfactory morphology, size and distribution of MgzSi phase particles are possible. Figures 12 and 13 show an example of the morphology of the Mg2Si phase particles discussed above. 19 201200630 In the planar image of Fig. 12, the darker The region is rich in gossip. The 1 bright body is the inter-bulk channel with a mixture of Zn-rich eutectic phases and the "Chinese-grain" Mg2Si phase particles filled with these channels. In the 3D image of Fig. 13, the Mg2si "valve, which is shown in red color" and the other phases include: Si (green), MgZn2 (blue), and alpha phase (a dark matrix) rich in A1. Many modifications may be made to the invention described above without departing from the spirit and scope of the invention. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a graph showing the reduction of the impact of exposure to a marginal overcut level in a severe marine environment in accordance with the coated metallic coated steel strip of the present invention. Figure 2 is a modified septic performance of a fluorocarbon coated metallic coated steel strip in accordance with the present invention for impact exposure in severe marine environments. Figure 3 is an example of a conventional Al/Zn coating having a broad set of corrosion contact fronts in a marine environment. Figure 4 is an illustration of a narrow and uniform corrosion front of a metallic coated steel strip in accordance with the present invention in a marine environment. Figure 5 shows an Al/Zn coating with a very fine dendritic structure with improved surface weathering in the salt spray test compared to the conventional structure (B vs A) but with reduced levels of protection. The metal coated steel strip according to the present invention has improved surface weathering and improvement in the salt spray test compared to the Al/Zn coating (C and D vs A and B) having coarse or fine structure. Type of protection. Figure 6 is a conventional Al/Zn-coated steel strip exposed to a harsh "acid rain" environment for 6 months (total coating mass per square meter coated 8 20 201200630 covering system 100 There is a red rust on the gram. Figure 7 of the present invention is an Al/Zn metallic coated steel strip exposed to severe "acid rain, environment for 6 months (total coating quality is 100 grams per square foot of coating system) There is no red rust on the top. Figure 8 is a traditional thin Al/Zn-coated steel strip exposed to a harsh "acid rain" environment for 18 months (the total coating quality is coated per square meter). 100 grams of the system has red rust stains. Figure 9 is an Al/Zn metallic coated steel strip according to the invention exposed to severe "acid rain, environment for 18 months (total coating quality) There is no red rust on the coating system per square meter of 100 grams). Figure 10 is a steel strip that is exposed to severe "acid rain, a typical columnar structure with an environment of 4 months, with A1 / Ζ η as the main coating (the total coating quality is coated per square meter). 50 grams of the system has a red rust. Figure 11 is an Al/Zn metallic coated steel ribbon according to the present invention exposed to a harsh "acid rain" environment having a columnar structure for 4 months. (The total coating quality is 5 gram per square meter of coating) There is no red rust on the rust. Figure 12 is a SEM plan view. Figure 13 is a network 3D form of Mg2Si particles (in red) successively patterned by EPMA. [Main component symbol description] (none) 21

Claims (1)

201200630 VII. Patent application scope: L A coating for forming an anti-corrosion Al-Zn-Si-Mg alloy suitable for use in a metal strip, typically steel, suitable for use in environments such as rain or pollution. A method of coating comprising: (a) passing a metal strip through a molten bath of an A1_Zn_Si_Mg alloy and forming an alloy coating on one or both surfaces of the strip, (b) curing the strip a coating on the article to form a cured coating. The cured coating has a microstructure comprising a dendritic body having an ot phase rich in A1 and a dendritic body having a mixture of Zn-rich eutectic phases The channel 'extends from the metal ribbon and has Mg2Si phase particles in the inter-branched inter-body channels, and the method comprises the control steps (8) and (b) and forms a cured 〇T: SDAS ratio greater than 〇5:1 The coating 'where the tether is the cover thickness, and the S〇AS is the secondary dendritic arm spacing of the A1 alpha-branched body of the coating. [2] The method of claim 1, wherein the OT: SDAS ratio is greater than 1:1 0 of a metal ribbon having an A1-Zn suitable for use in an "acid rain" or "contaminated" environment. a coating of -Si-Mg alloy on one or both surfaces of the ribbon, the coating comprising a microstructure comprising a dendritic body having an A1 rich phase and a eutectic phase rich in Zn The inter-branched channel of the mixture extends from the metal ribbon and there are MgaSi phase particles in the inter-branched channel 'and the coating has an OT: SDAS ratio greater than 〇5:1, wherein the OT system is the cover thickness' The SDAS system is a coating of 8 22 201200630 with a secondary branching arm of A1 alpha vines. 4. A coated metal strip as claimed in claim 3, wherein the OT:SDAS ratio is greater than 1:1 〇5. The coated metal strip of claim 3 or 4 Where the coating has a total coating mass on both surfaces of the ribbon of less than 2 gram per square meter of coating, which is equal to when the ribbon is coated only When the surface and the thickness of the coating are the same on both surfaces, the coating on one surface of the steel strip has less than 1 gram per square meter of coating. The coated metal strip of any one of claims 3-5, wherein the coating has a cover thickness greater than 3 μm. 7. The coated metal strip of any one of claims 3-5, wherein the SDAS of the alpha-rich vines in the coating is greater than 3 μιη, but less than 2 μηηι . 8. The coated metal strip of any one of claims 3-7, wherein the Al-Zn-Si-Mg alloy contains 20-95% of the 5% Si, up to 1% of Mg and the remaining Zn and a small amount of other elements are typically less than 0.5% for each of the other elements. 9. The coated metal strip of any one of claims 3-8, wherein the metal strip is a steel strip. 10. A method for forming a coating of a corrosion-resistant Al-Zn-Si-Mg alloy suitable for use in an environment such as an "acid rain" or "contaminated" environment on a strip of metal, typically steel. , comprising: 0) passing a metal strip through a molten bath of an A1_Zn_Si_Mg alloy and forming an alloy coating on one or both surfaces of the strip, 23 201200630 (b) curing the strip The coating forms a cured coating having a microstructure comprising a dendritic body having an alpha phase rich in A1 and an intervening channel extending from a mixture of Zn-rich eutectic phases extending from a metal ribbon having a Mg2Si phase in the inter-branched channel of the cured coating, and the method comprising selecting a concentration of Mg and Si and controlling a cooling rate in step (b) to effect the branches Mg2Si phase particles are formed in the interbody passage. 11. The method of claim 1, wherein the method comprises selecting a Mg concentration of greater than 0.5%. 12_ The method of claim 10 or n, which comprises selecting Mg to be greater than 1%. 13. The method of any one of claims 10 to 12, which comprises selecting a Mg concentration of less than 3%. 14. The method of any one of claims 1 to 13, wherein the steps of selecting the concentration of Mg and Si and the cooling rate in the controlling step (b) are formed to have an appropriate size in the inter-branched channels And morphology to block Mg2Si phase particles that are corroded along the channels of the branches. 15. The method of claim 14, wherein the morphology of the Mgji phase particles in the inter-branched channel is in the form of a "Chinese character" when viewed in a planar image, and in the form of a 3-dimensional image The time is in the form of a petal. 16. The method of claim 15, wherein the petals have a thickness of less than 5 μιη. 17. The method of claim 15, wherein the lobes have a thickness in the range of 〇·5-2·5 μηη. The method of any one of claims ι〇-14, wherein the concentration of Mg and Si is selected and the cooling rate in step (b) is controlled to form MgsSi phase particles in the inter-branched channels. The step is to form Mg2Syg particles having a size range and spatial distribution that activates the Α12α-rich phase to provide sacrificial protection in the interbranched channels in the cured coating. 19. The method of any one of claims 1 to 18, wherein the cooling rate CR during curing of the coating is less than 170 - 4.5 CT, wherein CR is . C/sec represents the cooling rate, while CT is the thickness of the coating on the surface of the ribbon expressed in microns. 20. A metal ribbon having a coating of Al-Zn-Si-Mg alloy suitable for use in an "acid rain," or "contaminated" environment on one or both surfaces of the ribbon The coating comprises a microstructure comprising a dendritic body having an alpha phase rich in A1 and an intermetallic channel extending from a mixture of Zn-rich eutectic phases extending from the metal ribbon and having Mg2Si phase particles In the inter-branched channel. 21. The coated metal ribbon of claim 20, wherein the Al-Zn-Si-Mg alloy contains 20-95% of A1 and up to 5%. Si, up to 10% of Mg and the remaining Zn and a small amount of other elements are typically less than 0.5% for each of the other elements. 22. The coated metal ribbon of claim 21, wherein Mg The concentration is greater than 0.5% 23. The coated metal ribbon of claim 21, wherein the Mg concentration is greater than 1%. 24. The coated metal ribbon according to claim 21 of the patent application, Wherein 25 201200630 Mg concentration is less than 3%. 25. The coated metal strip as claimed in any one of claims 21-24 Among them, in the case of a coating having a Si concentration of 0.5 to 2%, the volume fraction of the Mg2Si phase between the branches is greater than 50% compared to the other Si-containing phases. The coated metal ribbon of any of the 25 items, wherein the volume fraction of the Mg2Si phase between the branches is greater than 80% compared to the other Si-containing phases. 27. See Patent Application No. 21-26 A coated metal ribbon according to any one of the preceding claims, wherein greater than 70% of the total integral ratio of the Mg2Si phase in the coating is within two-thirds of the thickness of the coating cover. The coated metal ribbon of any of clauses 21-27, wherein greater than 60% of the inter-branched inter-body channels are "blocked" by the Mg2Si phase particles. 8 26