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摘要: 從鋅鋁鎂鍍層的熔池界面反應、鍍層組織、表面和切邊腐蝕機理、腐蝕產物類型變化等方面, 對高耐蝕鋅鋁鎂鍍層的研究進展進行了詳細分析. 根據Al成分含量的不同, 將商用及實驗室鋅鋁鎂鍍層分為"低鋁"、"中鋁"和"高鋁"鋅鋁鎂三種類型: 不同類型的鋅鋁鎂鍍層的金屬間化合物層生長動力學存在差異, 為了控制鍍層厚度, 應合理控制浸鍍時間、溫度與熔池成分; 凝固組織也存在差異, "低鋁"與"中鋁"會析出Al或Zn初晶、Zn/MgZn2二元共晶組織、Zn/MgZn2/Al三元共晶組織, "高鋁"會產生富Al枝晶、枝晶間富Zn相、Mg2Si相、MgZn2相, 不產生共晶組織; 發生表面腐蝕時, "低鋁"與"中鋁"中MgZn2相先電離, 并生成堿性鋅鹽、雙層氫氧化物等致密的腐蝕產物, 抑制腐蝕; 發生切邊腐蝕時, 鋅鋁鎂會出現自修復現象, 在切邊鋼基或鍍層破損處形成堿性鋅鹽, 保護基體.Abstract: Zn-Al-Mg alloy coating, the most promising protective steel coating of the 21st century, is widely employed in construction, automotive, and other fields, due to its high surface and edge corrosion. In recent years, with the increasing demand for Zn-Al-Mg coating, a series of basic studies on Zn-Al-Mg coating materials has been carried out by foreign scholars, making significant progress and achievements. Simultaneously, the gap in the galvanizing industry between domestic and international has been expanding year by year. In order to gradually reduce gradually this gap with foreign countries, it is necessary to summarize and review the research achievements of foreign researchers. In this paper, the research progress into high corrosion resistant Zn-Al-Mg hot dip coatings was reviewed from the perspective of interfacial reactions in pots, coating structures, corrosion mechanisms of surface and cut edges, as well as corrosion product types of Zn-Al-Mg coatings. According to the range of Al content, laboratory and commercial Zn-Al-Mg coatings are divided into three types: "low-aluminum, " "medium-aluminum, " and "high-aluminum" coatings. There are differences in these coatings, including growth kinetics in the intermetallic compound layers of the different types of coating. In order to control the thickness of the coating, reasonable immersion time and temperature should be controlled. There are also differences in the solidification structures of the three types. Primary Al or Zn crystal, Zn/MgZn2 binary eutectics, and Zn/MgZn2/Al ternary eutectics would form in "low-aluminum" and "medium-aluminum, " while Al-rich dendrites, an intergranular Zn-rich phase, a Mg2Si phase, and a MgZn2 phase would occur with "high-aluminum" coatings. During surface corrosion in "low-aluminum" or "medium-aluminum, " the MgZn2 phase is ionized first, giving rise to a dense corrosion product to inhibit corrosion, such as basic zinc salt (BZS) or layered double hydroxide (LDH). Meanwhile, in the cut edge, a self-healing phenomenon occurs; the proposed explanation in this paper for this is Mg-containing corrosion product flowing or pH changing. However, there are some disputed aspects that need further study. In the hot dipping process, the intermetallic compound thickness should be controlled by the interfacial reaction at the steel/liquid melts through changing the molten bath temperature and holding time. The influence of Mg2Zn11 phase and MgZn2 on the corrosion resistance of Zn-Al-Mg coating is also controversial, so that the microstructure of Zn-Al-Mg coating needs further investigation for corrosion. Furthermore, a kinetic model of the corrosion process should be established to discover the controlling factors in the corrosion reaction, so that the life of the coating can be extended.
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表 1 鋅鋁鎂金屬間化合物層生長動力學方程
Table 1. Growth kinetic equation of Zn-Al-Mg IMC layer
熔池 實驗溫度/℃ 金屬間化合物生長動力學方程 文獻來源 11Al-3Mg-Zn 510 Δx=3.1766·t0.6715 [4] 11Al-3Mg-0.2Si-Zn 510 Δx=0.1221·t0.5384 [4] 11Al-3Mg-0.2Si-Zn 480~650 $ \Delta x = 0.25 \cdot {{\rm{e}}^{ - \frac{{101}}{{RT}}}} \cdot {t^{0.5}} $ [5] 6Al-xMg-Zn (x=0, 1, 2, 3, 4, 5) 420~540 — [24] 6Al-3Mg-Zn — Δx=1.2716·t0.6035 [23] 11Al-1.5Mg-Zn 510 Δx=1.8699·t0.8109 [25] 11Al-4.5Mg-Zn 510 Δx=3.0554·t0.6709 [25] 表 2 鋅鋁鎂鍍層組織及代表產品牌號
Table 2. Coating structures and representative products
鋅鋁鎂類型 ωAl/% ωMg/% 鍍層組織類型[16] “低鋁” 1~5 1~2 初生Zn、Zn/MgZn2共晶組織、Zn/MgZn2/Al共晶組織 “中鋁” 6~13 3 初生Al、Zn/MgZn2共晶組織、Zn/MgZn2/Al共晶組織 “高鋁” 47~57 2 富Al枝晶、枝晶間富Zn相、Mg2Si相、MgZn2相 名稱 符號 化學式 雙層氫氧化物 LDH M(Ⅱ)xM(Ⅲ)y(A-)m(OH-)n·zH2O M(Ⅱ)=Zn2+, Mg2+; M(Ⅲ)=Al3+ A-=CO32-, Cl-, SO42- 羥基氯化鋅 ZHC Zn5(OH)8Cl2·H2O 羥基硫酸鋅 ZHS Zn4(OH)6SO4·nH2O,n=3~5 堿式碳酸鋅 HZ Zn5(OH)6(CO3)2·H2O 氧化鋅 ZnO ZnO 氫氧化鋅 Zn(OH)2 Zn(OH)2 氫氧化鎂 Mg(OH)2 Mg(OH)2 氫氧化鋁 Al(OH)3 Al(OH)3 259luxu-164 -
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