Effect of Mg on Microstructure and Growth Kinetics of Zn-22.3Al-1.1Si Coating

Abstract

The effects of Mg on the microstructure and growth kinetics of the hot-dip Zn-22.3Al-1.1Si-x Mg (x = 0, 0.2, 0.4, and 0.6) coatings were investigated in detail. Scanning electron microscopy with energy dispersive spectroscopy and X-ray diffraction studies revealed the presence of η-Zn, α-Al, Zn/Al eutectoid, (Si), Al/Si eutectic, and Zn/Al/Mg₂Zn11 ternary eutectic on the top surface of these Mg-containing coatings. Especially, a small amount of MgZn₂ phase appears in top surface of Zn-22.3Al-1.1Si-0.6Mg coating. Five phases are found in the alloy layers, i e, Fe₂Al₅, FeAl₃, τ_5C, τ_5H, and τ₁. The addition of 0.2% Mg can delay the emergence of FeAl₃ phase. When the Mg content is more than 0.2%, the outer layers of coating change from τ_5C to τ_5H phase. The growth of the inhibition layer is diffusion controlled for various Mg content baths. Mg improves the corrosion resistance of the Mg-containing coatings, and the Zn-22.3Al-1.1Si-0.6Mg coating possesses the highest protective properties.

Keywords

Mg / microstructure / growth kinetics / inhibition layer / diffusion

References

[1] Li SW, Gao B, Yin SH, et al. The Effects of RE and Si on the Microstructure and Corrosion Resistance of Zn–6Al–3Mg Hot Dip Coating[ J]. Applied Surface Science, 2015, 357: 2 004-2 012.

[2] Padilla V, Ghods P, Alfantazi A. Effect of De–icing Salts on the Corrosion Performance of Galvanized Steel in Sulphate Contaminated Soil[J]. Construction & Building Materials, 2013, 40: 908-918.

[3] Vagge ST, Raja VS, Narayanan RG. Effect of Deformation on the Electrochemical Behavior of Hot–dip Galvanized Steel Sheets[J]. Applied Surface Science, 2007, 253(20): 8 415-8 421.

[4] Mandal GK, Das SK, Balasubramaniam R, et al. Evolution of Microstructures of Galvanised and Galvannealed Coatings Formed in 0.2 wt% Aluminium–Zinc Bath[J]. Materials Science and Technology, 2011, 27(8): 1 265-1 270.

[5] Dutta M, Halder AK, Singh SB. Morphology and Properties of Hot Dip Zn–Mg and Zn–Mg–Al Alloy Coatings on Steel Sheet[J]. Surface and Coatings Technology, 2010, 205(7): 2 578-2 584.

[6] Li SW, Gao B, Tu GF, et al. Effects of Magnesium on the Microstructure and Corrosion Resistance of Zn–55Al–1.6Si Coating[J]. Construction & Building Materials, 2014, 71: 124-131.

[7] Liu W, Li MC, Luo Q, et al. Influence of Alloyed Magnesium on the Microstructure and Long–term Corrosion Behavior of Hot–dip Al–Zn–Si Coating in NaCl Solution[J]. Corrosion Science, 2016, 104: 217-226.

[8] Prosek T, Nazarov A, Goodwin F, et al. Improving Corrosion Stability of Zn–Al–Mg by Alloying for Protection of Car Bodies[J]. Surface and Coatings Technology, 2016, 36: 439-447.

[9] Oh MS, Kim SH, Kim JS, et al. Surface and Cut–edge Corrosion Behavior of Zn–Mg–Al Alloy–coated Steel Sheets as a Function of the Alloy Coating Microstructure[J]. Metals and Materials International, 2016, 22(1): 26-33.

[10] Jiang L, Volovitch P, Wolpers M, et al. Activation and Inhibition of Zn–Al and Zn–Al–Mg Coatings on Steel by Nitrate in Phosphoric Acid Solution[J]. Corrosion Science, 2012, 60: 256-264.

[11] Commenda C, Pühringer J. Microstructural Characterization and Quantification of Zn–Al–Mg Surface Coatings[J]. Materials Characterization, 2010, 61(10): 943-951.

[12] Yu KC, Li J, Liu X, et al. Microstructure of Hot–dip Galvanized Zn–Al–Mg Alloy Coating[J]. Journal of Shanghai Jiaotong University (Sci.), 2012, 17: 663-667.

[13] Volovitch P, Allely C, Ogle K. Understanding Corrosion via Corrosion Product Characterization: I. Case Study of the Role of Mg Alloying in Zn–Mg Coating on Steel[J]. Corrosion Science, 2009, 51(6): 1 251-1 262.

[14] Lee JY, Yun YS, Kim WT, et al. Twinning and Texture Evolution in Binary Mg–Ca and Mg–Zn Alloys[J]. Metals and Materials International, 2014, 20(5): 885-891.

[15] Cho JH, Kim HW, Lim CY, et al. Microstructure and Mechanical Properties of Al–Si–Mg Alloys Fabricated by Twin Roll Casting and Subsequent Symmetric and Asymmetric Rolling[J]. Metals and Materials International, 2014, 20(4): 647-652.

[16] Mondolfo LF. Aluminum Alloys: Structure and Properties[M], 2013

[17] Yeh MS, Chang JC, Chuang TH. Stress Corrosion Cracking of a Superplastic and Nonsuperplastic Zn–22.3Al Alloy in 3% NaCl Solution[J]. Journal of Materials Engineering and Performance, 1999, 8(2): 219-224.

[18] Ranjan M, Tewari R, Van Ooij WJ, et al. Effect of Ternary Additions on the Structure and Properties of Coatings Produced by a High Aluminum Galvanizing Bath[J]. Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science, 2004, 35(12): 3 707-3 720.

[19] Wei DS, Tu H, Zhou SJ, et al. Effect of Silicon on the Reaction between Solid Iron and Liquid Zn–22.3wt% Al Bath[J]. Surface and Coatings Technology, 2016, 305: 29-35.

[20] Li Q, Zhao YZ, Luo Q, et al. Experimental Study and Phase Diagram Calculation in Al–Zn–Mg–Si Quaternary System[J]. Journal of Alloys and Compounds, 2010, 501(2): 282-290.

[21] Honda K, Yamada W, Ushioda K. Solidification Structure of the Coating Layer on Hot–dip Zn–11%Al–3%Mg–0.2%Si–Coated Steel Sheet[J]. Materials Transactions, 2008, 49(6): 1 395-1 400.

[22] De Bruycker E, Zermout Z, De Cooman BC. Zn–Al–Mg Coatings: Thermodynamic Analysis and Microstructure Related Properties[J]. Materials Science Forum, 2007, 539: 1 276-1 281.

[23] Shahverdi HR, Ghomashchi MR, Shabestari S, et al. Microstructural Analysis of Interfacial Reaction Between Molten Aluminium and Solid Iron[J]. Journal of Materials Processing Technology, 2002, 124(3): 345-352.

[24] Corby RN, Black PJ. The Structure of α–(AlFeSi) by Anomalous–dispersion Methods[J]. Acta Crystallographica, Section B: Structural Crystallography and Crystal Chemistry, 1977, 33(11): 3 468-3 475.

[25] Pontevichi S, Bosselet F, Barbeau F, et al. Solid–liquid Phase Equilibria in the Al–Fe–Si System at 727 °C[J]. Journal of Phase Equilibria and Diffusion, 2004, 25(6): 528-537.

[26] Liu ZK, Chang YA. Thermodynamic Assessment of the Al–Fe–Si System[ J]. Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science, 1999, 30(4): 1 081-1 095.

[27] Raynor GV, Rivlin VG. Phase Equilibria in Iron Ternary Alloys–A Critical Assessment of the Experimental Literature[J]. The Institute of Metals, 1 Carlton House Terrace, 1988 UK: London SW 1 Y 5 DB.

[28] Phelan D, Xu BJ, Dippenaar R. Formation of Intermetallic Phases on 55 wt.% Al–Zn–Si Hot Dip Strip[J]. Materials Science & Engineering, A: Structural Materials: Properties, Microstructure and Processing, 2006, 420(1): 144-149.

[29] Du Y, Schuster JC, Liu ZK, et al. A Thermodynamic Description of the Al–Fe–Si System over the Whole Composition and Temperature Ranges via a Hybrid Approach of CALPHAD and Key Experiments[J]. Intermetallics, 2008, 16(4): 554-570.

[30] Eleno L, Vezely J, Sundman B, et al. Assessment of the Al Corner of the Ternary Al–Fe–Si System[J]. Materials Science Forum, 2010, 649: 523-528.

[31] Tu H, Song YY, Liu Y, et al. Effect of Silicon on Microstructure and Growth Kinetics of Hot–Dip Galvanized ZnAl4 Coatings[J]. Materials Science and Engineering of Powder Metallurgy, 2015, 20(6): 815-821.

[32] Tang NY, Liu YH. Discussion of “Interfacial Layer in Coatings Produced in Molten Zn–Al Eutectoid Alloy Containing Si”[J]. Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science, 2005, 36(9): 2 541-2 544.

[33] Rivlin VG, Raynor GV. 4: Critical Evaluation of Constitution of Aluminium–Iron–Silicon System[J]. International Metals Reviews, 1981, 26(1): 133-152.

[34] Haitani T, Tamura Y, Motegi T, et al. Solubility of Iron in Pure Magnesium and Cast Structure of Mg–Fe Alloy[J]. Materials Science Forum, 2003, 419: 697-702.

[35] Prosek T, Nazarov A, Bexell U, et al. Corrosion Mechanism of Model Zinc–Magnesium Alloys in Atmospheric Conditions[J]. Corrosion Science, 2008, 50(8): 2 216-2 231.

[36] Schürz S, Luckeneder G, Fleischanderl M, et al. Chemistry of Corrosion Products on Zn–Al–Mg Alloy Coated Steel[J]. Corrosion Science, 2010, 52(10): 3 271-3 279.