201200631 六、發明說明： 【發明所屬之技術領威】 本發明係關具有防蝕性金屬合金被覆物之條帶，典型 為鋼帶。 本發明特別係關一種含有鋁-鋅-矽-鎂作為合金主要元 素，防紐金屬合金被覆物，因此於後文中基於此而稱作 為「Al-Zn-Si-Mg合金」。該合金被覆物可含有存在作為蓄 思合金化元素或作為無法避免之雜質的其它元素。 本發明特別但非排它地係關被覆以前述Al-Zn-Si-Mg 合金之鋼帶。此等被覆物之一大應用為鋼帶表面上的薄層 (亦即厚2至1〇〇微米，典型為3至3〇微米）被覆物來提#_ 保護。本鋼帶可冷軋成形（例如藉軋製成形）為最終使用產 品’諸如舖頂產品。 如後文所述’「A1_Zn_Si_Mg合金」一詞係指包含 鋁、至多5%矽、至多10%鎂，及差額為鋅，帶有小量其— 元素，典型地小於0.5%之其它元素之一種合金。 、 及Sb 其匕元素可包括Fe、Mn、Ni、Sn、Sr、V、 中之任一者或多者。以鐵為例，典型地鐵含量為至多1 57 且係於藉習知熱浸被覆法形成被覆物之情況下作為雜質^ 比 須瞭解除非另行陳述，否則說明書中述及元 皆為重量百分比。 t先前技術:J 典型地’ Al-Zn-Si-Mg合金包含如所陳述範 圍之下 列元 201200631 素作為主要元素： A1 : 40至60%重量比 zn : 40至60%重量比201200631 VI. Description of the Invention: [Technical Leadership of the Invention] The present invention relates to a strip having an anticorrosive metal alloy coating, typically a steel strip. In particular, the present invention relates to an alloy containing aluminum-zinc-niobium-magnesium as a main element of an alloy, and is therefore referred to as "Al-Zn-Si-Mg alloy" hereinafter. The alloy coating may contain other elements present as a mechanized alloying element or as an unavoidable impurity. The invention particularly, but not exclusively, is a steel strip coated with the aforementioned Al-Zn-Si-Mg alloy. One of these coatings is used as a thin layer (i.e., 2 to 1 micron thick, typically 3 to 3 micron thick) on the surface of the steel strip to provide protection. The steel strip can be cold rolled (e.g., by roll forming) into a final use product such as a roofing product. As used hereinafter, the term '"A1_Zn_Si_Mg alloy" means a type of other element comprising aluminum, up to 5% bismuth, up to 10% magnesium, and the balance being zinc, with a small amount of its element, typically less than 0.5%. alloy. And Sb may include any one or more of Fe, Mn, Ni, Sn, Sr, V, and the like. Taking iron as an example, the typical subway content is at most 1 57 and it is considered as an impurity in the case of forming a coating by the hot dip coating method. It is to be understood that unless stated otherwise, the recited elements are all by weight. t prior art: J typically 'Al-Zn-Si-Mg alloy contains as the main element of the element 201200631 as stated below: A1: 40 to 60% by weight zn: 40 to 60% by weight
Si : 0.3至3%重量比Si : 0.3 to 3% by weight
Mg : 0.3至10%重量比 典型地，防蝕性金屬合金被覆物係藉熱浸被覆法而形 成於鋼帶上。 於習知熱浸金屬被覆法中，鋼帶通常係通過一個或多 個熱處理爐及隨後進入及通過盛裝於被覆盆中之熔融金屬 合金洛。該相鄰於被覆盆之熱處理爐具有向下延伸至接近 /谷上表面位置之出口吻部。 金屬合金通常係藉使用加熱電感器而於被覆盆内維持 炼融°鋼帶通常係透過浸沒入浴槽内呈細長形的爐出口斜 槽或吻部形狀的出口端段而送出熱處理爐。於該浴内，鋼 帶環繞一個或多個浸沒輥通過，及向上帶出離開該浴且當 該鋼帶通過該浴時被被覆以金屬合金。 於鋼帶離開被覆浴後，經金屬合金被覆之鋼帶通過被 覆物厚度控制站，諸如氣刀或氣體擦拭站，於該站，經被 覆的表面接受擦栻氣體之喷射而控制被覆物厚度。 然後經金屬合金被覆之鋼帶通過冷卻區段及接受強制 冷卻。 已冷卻之經金屬合金被覆之鋼帶隨後通過表皮通過式 軋製區段（又稱退火軋製區段)及張力均平區段，選擇性地經 調理。已調理之鋼帶係於盤捲站盤捲。 4 201200631 依據終端應用而定，經金屬被覆之鋼帶於該鋼帶之一 表面或二表面上可經塗漆，例如以聚合塗料塗漆。 澳洲及其它地方廣為人使用於建築產品，特別為有輪 廓壁及舖頂瓦片之一種防蝕性金屬被覆組成物為亦含有石夕 之55%鋁-辞被覆組成物。有輪廓之板材通常係藉冷軋成形 已塗漆之經金屬合金被覆之鋼帶製造。典型地，有輪廓之 板材係藉軋製成形已塗漆之鋼帶製造。 於硬化後，55%鋁-鋅合金被覆物通常係由^^鋁相枝晶 及於枝晶間區之/5鋅相所組成。添加矽至被覆物合金組成 物來防止冷熱浸被覆法中鋼基材與熔融被覆物間之過度合 金化。部分石夕參與第四級合金層的形成，但大半石夕於硬化 期間/尤版為針狀純石夕粒子。此等針狀石夕粒子也存在於枝晶 間區。 申請人發現當鎂含括於55% Al-Zn-Si被覆組成物時，鎮 經由改變所形成的腐蝕產物的本質獲得某些產物效能上的 有利效果，諸如改良之切削刃保護。 但申請人也發現鎂與矽反應而形成Mg2Si相，及Mg2Si 相的形成以多種方式有損前述有利效果。特定言之，Mg2Si 相比矽更為寬鬆，脆變，及具有銳利緣之r漢字」形態。 全部此等因素皆可能有害被覆物之延展性等而促成被覆物 於高應變製造之下碎裂。申請人發現對經預塗漆之產品而 言較大碎裂為不合所需，特別當用於「酸雨」或「污染」 墩境時尤為如此，原因在於其抵消鎂給予塗料薄膜下方之 °玄已被覆條γ之防姓效能帶來的有利效果。如此，就延展 201200631 性及如何影響防蝕效能而言，添加鎂至55% Al-Zn-Si被覆組 成物有其缺點。 前文說明並非視為承認本發明為澳洲或其它地方之一 般已知常識。 【發明内容】 本發明提供一種具有Mg2Si相粒子分散於被覆物之 Al-Zn-Si-Mg合金被覆之條帶具有下列特徵中之一者或多 者： (a) S2微米之粒徑，及 (b) 比前述「漢字」粒子更為球體之形狀。 此外，本發明提供一種形成此種具有Mg2Si相粒子分散 於被覆物之Al-Zn-Si-Mg合金被覆之條帶之方法，包含： (a) 加熱處理已硬化之被覆物來協助於該被覆物中之 Mg2Si相粒子形成小球體，及/或 (b) 改變該被覆浴化學而形成金屬間化合物相，其係作 用Mg2Si相粒子之孕核位置，結果當該被覆物硬化時形成小 型Mg2Si粒子。 圖式簡單說明 第1圖為根據本發明之方法用以製造經Al-Zn-Si-Mg合 金被覆之鋼帶之連續製造生產線之示意圖。 I：實施方式3 較佳實施例之詳細說明 根據本發明提供一種形成經金屬被覆之條帶諸如鋼帶 之方法，該方法包含： 201200631 (a) 將該條帶通過含有A1、Zn、Si及Mg及選擇性的其它 元素之熱浸被覆浴及於該條帶上形成熔融Al-Zn-Si-Mg合 金被覆物； (b) 冷卻該已被覆之條帶來硬化於該條帶上之該熔融 Al-Zn-Si-Mg合金及形成已硬化之被覆物，其具有包含〇；鋁 相枝晶、於枝晶間區之富辞相、及於枝晶間區之Mg2Si相粒 子之微結構；及 (c) 於某個溫度及歷經某段時間加熱處理該已被覆之條 帶而自該如所鑄造之〇：鋁相枝晶及富鋅枝晶間相之微結構 形成Al-Zn相固溶體’及協助分散於該被覆物之Mg2si相粒 子的形成小球體；及 (d) 冷卻該經加熱處理之條帶。 加熱處理步驟(c)可於至少3〇〇。〇之溫度。 加熱處理步驟(c)可於至少350X：之溫度。 加熱處理步驟(c)可於至少45〇〇c之溫度。 加熱處理步驟(c)可於低於600°Ci溫度。 加熱處理步驟(c)可歷時至少15分鐘。 加熱處理步驟(c)可歷時15至3〇分鐘。 加熱處理步驟(c)可歷時少於3〇分鐘。 冷卻步驟(b)可包含以夠高且足以至少部分碎裂Mg2Si 相粒子而形成細小粒子或於第一瞬間於該已硬化之被覆物 中形成細小Mgji相粒子之速率來冷卻該條帶。 細小Mgji粒子之尺寸可小於微米。 冷卻步驟(b)可包含以至少15(rc/秒之速率冷卻該條 7 201200631 帶0 冷卻速率可為至少200〇C/秒。 冷卻速率可為至少400t/秒。 冷卻速率可為至少6〇〇t/秒。 冷部步驟(b)可包含以水霧或冷凝氣體來冷卻該條帶。 ,二部纟驟⑷可包含以可減低Mg2Si相纟子之成長及至 '、保有於该加熱處理步驟（c)所形成之小球體狀 MgzSi相粒子之速率來冷㈣已加減理之條帶。 被覆物之厚度可為3至30微米。 覆v驟（a)可包含對該熱浸被覆浴提供以可作為 Mg2Si粒子之孕核位置之元素或化合物。 該另一種元素可為銻。 。亥方法可包含於該已被覆之條帶上形成塗料之被覆 物。 根據本發明也提供一種製成經金屬被覆之條帶諸如鋼 帶之方法，包含： (a) 將該條帶通過含有A1、Zn、Si&Mg、可作為^^幻& 粒子之孕核位置之另一元素或多元素或一化合物或多化合 物，及選擇性地，其它元素之熱浸被覆浴及於該條帶上形 成溶融Al-Zn-Si-Mg合金被覆物， (b) 冷卻該已被覆之條帶來硬化於該條帶上之該熔融 Al-Zn-Si-Mg合金及形成已硬化之被覆物，其具有包含鋁 相枝晶、於枝ββ間區之富辞相、及於枝晶間區之Mg]Si相粒 子之被覆物微結構。 201200631 該另一種元素可為銻。 該等Mg2Si粒子之尺寸可小於$2微米。 該等Mg2Si粒子可為更為球體之形狀及更少有銳利刃 之「漢字」形態。 根據本發明也提供一種條帶，諸如鋼帶，其具有於該 條帶上之Al-Zn-Si-Mg合金被覆物，該被覆物具有包含 Al-Zn相之固溶體及Mg2Si相粒子於該被覆物之分散體，而 該Mg2Si粒子具有： (a) 小於或等於2微米之粒徑，及 (b) 小球體形狀。 該被覆物於該條帶之至少一側上具有5至30微米之厚 度。 藉本發明所製造之經被覆之微結構就改良被覆物延展 性及加強防餘性而言為優異。 鲁改良被覆物延展性。 如前文說明之細小而更為球體形狀之Mg2Si粒子而非 有銳利刃之「漢字」形態，可減輕於高應變製造中的應力 集中，如此減少碎裂起始與傳播的可能。 參加強被覆物防蝕性。 如前文說明之Mg2Si相修改成為細小而更為球體形狀 之粒子而非有銳利刃之「漢字」形態，可減少被覆物碎裂 的可能。Mg2Si相粒子大為分散於被覆物就促進腐蝕通道的 一致「阻斷」與「活化」而言也有利。結果，被覆物具有 增強的防#性。 9 201200631 將參考附圖進一步舉例說明本發明，該圖為根據本發 明之方法用以製造經Al-Zn-Si-Mg合金被覆之鋼帶之連續 製造生產線之示意圖。 參考附圖’於使用中’冷軋鋼帶卷於展開站（圖中未顯 示）展開’及連續展開的鋼帶長度藉硬焊器（圖中未顯示）以 端對端硬焊而形成鋼帶3之連續長度。 然後鋼帶3連續通過堆積器（圖中未顯示）、鋼帶清潔區 段（圖中未顯示）及爐總成4。該爐總成4包括預熱器、預熱還 原爐、及還原爐。 經由小心控制下列製程變數，鋼帶於爐總成4加熱處 理，該等製程變數包括：⑴爐之熱側寫資料，⑴)爐之還原 氣體濃度，（iii)氣體通過爐之流速，及(iv)鋼帶於爐之駐留 時間（亦即鋼帶速度）。 爐總成4之製程變數係經控制使得鐵氧化物殘餘物自 鋼帶表面移除，及殘油及鐵礦砂自鋼帶表面移除。 然後經加熱處理之鋼帶經由該向下延伸入且通過盛裝 於被覆盆5之含Al-Zn-Si-Mg合金之熔融浴的出口吻部通過 且被被覆以Al-Zn-Si-Mg合金。該浴可含有一個或多個元素 或化合物，其係促進金屬間化合物相之形成而可作為]^以^ 粒子之孕核位置，結果當被覆物硬化時形成小型厘以以粒 子。較佳係經由使用加熱電感器（圖中未顯示）來將被覆盆内 之Al-Zn-Si-Mg合金維持熔融。於該浴槽内，鋼帶環繞浸沒 輥通過，且自浴中向上取出。當鋼帶通過浴時，鋼帶之二 表面上被覆以ί呂-鋅-石夕合金。 10 201200631 離開被覆浴5後，鋼帶垂直通過氣體擦拭站6，於該處 其經被覆之表面接受擦拭氣體喷射來控制被覆物厚度。 然後經被覆之鋼帶通過冷卻區段7及接受強制冷卻。較 佳’鋼帶係以夠高且足以至少部分碎裂Mg2 s丨相粒子而形成 #子或於第一瞬間於該已硬化之被覆物中形成細小 MgzSi相粒子之速率來冷卻之。典型地，如此表示以至少如〇 °C/秒之速率冷卻鋼帶。 冷卻後之經被覆鋼帶然後通過軋製區段8，其調理經被 覆鋼帶之表面D ^ 最後，已綱妥讀帶通過減理爐9切雜加熱處 理。肢言之，鋼帶係於32〇U5()(rC範圍之溫度加熱處 理15至30分鐘來協助被覆物中的^^2义相粒子形成小球 體。然後已經加熱處理之鋼帶經冷卻，典型地係經以水冷 卻，來將Mg2Si相粒子_儘可能地接近於加熱處理步驟結 束時的尺寸及形狀。 可未恃離本發明之精趙及範圍對前文說明之本發明做 出多項修改。 【圖式簡單說曰月】 第1圖為根據本發明之方法用以製造經人 金被覆之鋼帶之連續製造生產線之示意圖。 ^ 【主要元件符號說明】 3·..鋼帶 7...冷卻區段 4...爐總ά 8...軋製區段 5‘·.被覆浴 9…熱處理爐 6··*氣體擦拭站Mg: 0.3 to 10% by weight Typically, the corrosion-resistant metal alloy coating is formed on the steel strip by a hot dip coating method. In conventional hot dip metal coating processes, the steel strip is typically passed through one or more heat treatment furnaces and subsequently into and through the molten metal alloy contained in the coating basin. The heat treatment furnace adjacent to the covered basin has an outlet snout extending downward to a position close to the upper surface of the valley. The metal alloy is usually maintained in the covered basin by means of a heating inductor. The steel strip is usually sent out of the heat treatment furnace through an outlet end section which is immersed in the bath in the shape of an elongated furnace outlet chute or a snout. In the bath, the steel strip passes around one or more immersion rolls and is carried up out of the bath and is coated with a metal alloy as the strip passes through the bath. After the steel strip leaves the coating bath, the metal alloy coated steel strip passes through a coating thickness control station, such as an air knife or a gas wiping station, at which the coated surface is subjected to a jet of rubbing gas to control the thickness of the covering. The steel strip coated with the metal alloy then passes through the cooling section and undergoes forced cooling. The cooled metal alloy coated steel strip is then selectively conditioned through a skin pass-through section (also known as an annealed section) and a tension leveling section. The conditioned steel strip is coiled at the coiling station. 4 201200631 Depending on the end application, the metal-coated steel strip may be painted on one or both surfaces of the strip, for example by a polymeric coating. It is widely used in Australia and other places for building products. In particular, an anti-corrosive metal coating consisting of a wall and a tile is also composed of 55% aluminum-splitting composition of Shi Xi. Profiled sheets are usually made by cold-rolled, painted metal-coated steel strips. Typically, contoured sheets are produced by roll forming a painted steel strip. After hardening, the 55% aluminum-zinc alloy coating usually consists of aluminous phase dendrites and a /5 zinc phase in the interdendritic zone. The crucible is added to the coating alloy composition to prevent excessive alloying between the steel substrate and the molten coating in the hot and cold dip coating method. Part of Shi Xi participates in the formation of the fourth-grade alloy layer, but most of the stone is in the hardening period / especially in the needle-shaped pure stone eve particles. These acicular stones are also present in the interdendritic regions. Applicants have discovered that when magnesium is included in a 55% Al-Zn-Si coating composition, the town obtains certain product performance benefits, such as improved cutting edge protection, by altering the nature of the corrosion products formed. However, Applicants have also discovered that the formation of the Mg2Si phase by the reaction of magnesium with lanthanum and the formation of the Mg2Si phase detract from the aforementioned advantageous effects in various ways. In particular, Mg2Si is more relaxed, brittle, and has a sharp-edged r-character. All of these factors may be harmful to the ductility of the coating, etc., which may cause the coating to fracture under high strain manufacturing. Applicants have found that larger cracking is undesirable for pre-painted products, especially when used in “acid rain” or “pollution” conditions, as it counteracts the magnesium below the coating film. It has been coated with the advantageous effect of the anti-surname effect of γ. Thus, the addition of magnesium to a 55% Al-Zn-Si coating composition has its disadvantages in terms of extending the 201200631 property and how it affects the corrosion resistance. The foregoing description is not to be taken as an admission that the invention is a SUMMARY OF THE INVENTION The present invention provides a strip coated with an Al-Zn-Si-Mg alloy in which Mg2Si phase particles are dispersed in a coating having one or more of the following characteristics: (a) a particle size of S2 micrometers, and (b) The shape of the sphere is more spherical than the aforementioned "Chinese character". Further, the present invention provides a method of forming such a strip coated with an Al-Zn-Si-Mg alloy in which Mg2Si phase particles are dispersed in a coating, comprising: (a) heat treating a hardened coating to assist the coating The Mg2Si phase particles form a small sphere, and/or (b) change the coating bath chemistry to form an intermetallic compound phase, which acts on the pronuclear position of the Mg2Si phase particles, and as a result, forms small Mg2Si particles when the coating hardens. . BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic view showing a continuous production line for producing a steel strip coated with an Al-Zn-Si-Mg alloy according to the method of the present invention. I: Embodiment 3 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In accordance with the present invention, there is provided a method of forming a metal-coated strip such as a steel strip, the method comprising: 201200631 (a) passing the strip through A1, Zn, Si and a hot dip coating bath of Mg and other elements, and a molten Al-Zn-Si-Mg alloy coating on the strip; (b) cooling the coated strip to harden the strip a molten Al-Zn-Si-Mg alloy and a hardened coating having a microstructure comprising strontium; an aluminous phase dendritic, a rhyme phase in the interdendritic region, and a Mg2Si phase particle in the interdendritic region And (c) heat-treating the coated strip at a temperature and for a certain period of time from the as-cast bismuth: microstructure of the aluminum phase dendrites and the zinc-rich interdendritic phase to form an Al-Zn phase a solid solution 'and a small sphere that assists in dispersing Mg2si phase particles of the coating; and (d) cooling the heat treated strip. The heat treatment step (c) may be at least 3 Torr. The temperature of 〇. The heat treatment step (c) can be at a temperature of at least 350X:. The heat treatment step (c) can be at a temperature of at least 45 〇〇c. The heat treatment step (c) may be at a temperature lower than 600 ° Ci. The heat treatment step (c) can last for at least 15 minutes. The heat treatment step (c) may last for 15 to 3 minutes. The heat treatment step (c) can last for less than 3 minutes. The cooling step (b) may comprise cooling the strip at a rate high enough and sufficient to at least partially fragment the Mg2Si phase particles to form fine particles or to form fine Mgji phase particles in the hardened coating at a first instant. The size of the fine Mgji particles can be less than micrometers. Cooling step (b) may comprise cooling the strip 7 at a rate of at least 15 (rc/sec. 201200631 with a 0 cooling rate of at least 200 〇C/sec. The cooling rate may be at least 400 t/sec. The cooling rate may be at least 6 〇. 〇t/sec. The cold step (b) may comprise cooling the strip with water mist or condensed gas. The second step (4) may comprise reducing the growth of the Mg2Si phase rafter and maintaining the heat treatment. The rate of the small spherical MgzSi phase particles formed in the step (c) is to cool (4) the strip which has been added and subtracted. The thickness of the coating may be 3 to 30 μm. The covering v (a) may comprise the hot dip coating bath Providing an element or compound that can serve as a pronuclear site of the Mg2Si particle. The other element can be a ruthenium. The method can be included on the coated strip to form a coating of the coating. According to the present invention, a method is also provided. A metal-coated strip such as a steel strip comprising: (a) passing the strip through another element or elements comprising the A1, Zn, Si & Mg, which can serve as the pronuclear position of the ^^ magic & Or a compound or compounds, and optionally, hot dip of other elements Coating the bath and forming a molten Al-Zn-Si-Mg alloy coating on the strip, (b) cooling the coated strip to cause the molten Al-Zn-Si-Mg alloy to be hardened on the strip and Forming a hardened coating having a microstructure of a coating comprising an aluminum phase dendritic, a fictional phase in the inter-ββ region, and a Mg]Si phase particle in the interdendritic region. 201200631 The other element may be The Mg2Si particles may be less than $2 microns in size. The Mg2Si particles may be in the shape of a more spherical shape and have a lesser "Chinese character" shape with sharp edges. According to the present invention, a strip, such as a steel strip, is also provided. An Al-Zn-Si-Mg alloy coating having the strip having a solid solution of an Al-Zn phase and a dispersion of Mg2Si phase particles in the coating, wherein the Mg2Si particles have: a) a particle size less than or equal to 2 microns, and (b) a small sphere shape. The coating has a thickness of 5 to 30 microns on at least one side of the strip. The coated microstructure produced by the present invention It is excellent in improving the ductility of the coating and enhancing the anti-residue. Lu improves the ductility of the coating. The smaller and more spherical Mg2Si particles, as described above, rather than the "Chinese character" shape with sharp edges, can alleviate the stress concentration in high strain manufacturing, thus reducing the possibility of fragmentation initiation and propagation. Corrosion resistance. As explained above, the Mg2Si phase is modified into a finer and more spherical shape than a sharp-edged "Chinese character" form, which reduces the possibility of fragmentation of the coating. The Mg2Si phase particles are greatly dispersed in the coating. The uniform "blocking" and "activation" of the corrosion channels are also advantageous. As a result, the coating has an enhanced anti-sex property. 9 201200631 The invention will be further illustrated by reference to the accompanying drawings which are schematic illustrations of a continuous manufacturing line for the manufacture of steel strips coated with Al-Zn-Si-Mg alloys in accordance with the method of the present invention. Referring to the drawing 'in use', the cold rolled steel strip is unrolled at the unfolding station (not shown) and the continuously unrolled steel strip length is brazed end-to-end by a brazing machine (not shown) to form a steel strip. 3 consecutive lengths. The strip 3 is then passed continuously through a stacker (not shown), a strip cleaning zone (not shown) and a furnace assembly 4. The furnace assembly 4 includes a preheater, a preheating reduction furnace, and a reduction furnace. The steel strip is heat treated in the furnace assembly 4 by carefully controlling the following process variables, including: (1) hot side data of the furnace, (1) the reducing gas concentration of the furnace, (iii) the flow rate of the gas through the furnace, and Iv) residence time of the steel strip in the furnace (ie strip speed). The process variables of furnace assembly 4 are controlled such that iron oxide residues are removed from the surface of the strip and residual oil and iron ore are removed from the surface of the strip. The heat-treated steel strip is then passed through the exit portion of the molten bath containing the Al-Zn-Si-Mg alloy containing the Al-Zn-Si-Mg alloy and is coated with the Al-Zn-Si-Mg alloy. . The bath may contain one or more elements or compounds which promote the formation of the intermetallic compound phase as a pronuclear site of the particles, with the result that small particles are formed as particles when the coating hardens. Preferably, the Al-Zn-Si-Mg alloy in the covered basin is maintained molten by using a heating inductor (not shown). In the bath, the steel strip passes around the immersion roll and is taken up from the bath. When the steel strip passes through the bath, the surface of the steel strip is covered with ίLu-zinc-Shishi alloy. 10 201200631 After leaving the coating bath 5, the steel strip passes vertically through the gas wiping station 6, where the coated surface is subjected to wiping gas jets to control the thickness of the covering. The coated steel strip then passes through the cooling section 7 and is subjected to forced cooling. Preferably, the steel strip is cooled at a rate sufficient to at least partially break up the Mg2s phase particles to form a #子 or to form fine MgzSi phase particles in the hardened coating at a first instant. Typically, this means cooling the steel strip at a rate of at least 〇 ° C / sec. The cooled steel strip is then passed through a rolling section 8 which is conditioned to the surface of the coated steel strip D. Finally, the finished strip is passed through a reduction furnace 9 to heat the treatment. Extremically, the steel strip is heat treated at 32 ° U5 () for 15 to 30 minutes at the temperature of rC to assist the ^ 2 synthetic phase particles in the coating to form small spheres. Then the heated steel strip is cooled, Typically, the water is cooled to bring the Mg2Si phase particles as close as possible to the size and shape at the end of the heat treatment step. Many modifications may be made to the invention as described above without departing from the scope of the invention. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic view showing a continuous manufacturing line for producing a gold-coated steel strip according to the method of the present invention. ^ [Explanation of main component symbols] 3. Steel strip 7. ..Cooling section 4...furnace total ά8...rolling section 5'·.coated bath 9...heat treatment furnace 6··* gas wiping station