摘要
Owing to their low density and high specific strength, magnesium (Mg) alloys are promising lightweight materials for various applications, particularly in the automobile and aerospace industries. However, despite their potential, conventional Mg alloys often suffer from limited ductility and strength. In view of this, the Magnesium Research Center (MRC) at Kumamoto University has developed a series of Mg alloys containing the long-period stacking-ordered (LPSO) phase, significantly enhancing their mechanical properties [1-3]. For the widespread applications of these Mg alloys, corrosion resistance is another critical factor besides their mechanical properties. Therefore, in this study, we focus on Mg-2.05 at%Y-0.85 at%Zn-0.1 at%Yb-0.15 at%Al alloys containing LPSO phase fabricated by three different forming processes (as-cast (C), ingot metallurgy (IM) followed by extrusion, and rapidly solidified (RS) powder metallurgy followed by extrusion [4-6]), to investigate their corrosion behavior through electrochemical measurements and microstructure characterizations and the relationship to the alloy microstructure from different processes. Experimental results indicate that the forming processes dictate the alloy microstructure and the resultant corrosion behavior. While localized corrosion occurred in the as-cast (C) sample during short-term corrosion tests in a 3.5 wt% sodium chloride (NaCl) solution, the extruded IM and RS samples were dominated by uniform corrosion, suggesting a difference in the corrosion mechanism. The LPSO phase in these alloys acts as local cathodes, and the improvement in corrosion resistance highly depends on its size and distribution in the alloys. Furthermore, microstructure characterizations were conducted to study the localized corrosion initiation on the C sample and the surface corrosion films formed on different samples after the corrosion tests, revealing their close relationship to the underlying alloy chemistry and the LPSO phase. These findings provide insights into the corrosion behavior and mechanisms of LPSO phase-containing Mg alloys, demonstrating that proper designs of the alloy microstructure can enhance their corrosion resistance. References: [1] M. Yamasaki, T. Anan, S. Yoshimoto, Y. Kawamura, Mechanical Properties of Warm-Extruded Mg–Zn–Gd Alloy with Coherent 14H Long Periodic Stacking Ordered Structure Precipitate, Scripta Materialia 53(7) (2005) 799–803. [2] S. Yoshimoto, M. Yamasaki, Y. Kawamura, Microstructure and Mechanical Properties of Extruded Mg-Zn-Y Alloys with 14H Long Period Ordered Structure, Materials Transactions 47(4) (2006) 959–965. [3] Y. Kawamura, M. Yamasaki, Formation and Mechanical Properties of Mg 97 Zn 1 RE 2 Alloys with Long-Period Stacking Ordered Structure, Materials Transactions 48(11) (2007) 2986–2992. [4] Y. Kawamura, K. Hayashi, A. Inoue, T. Masumoto, Rapidly Solidified Powder Metallurgy Mg 97 Zn 1 Y 2 Alloys with Excellent Tensile Yield Strength above 600 MPa, Materials Transactions 42(7) (2001) 1172–1176. [5] E. Abe, Y. Kawamura, K. Hayashi, A. Inoue, Long-Period Ordered Structure in a High-Strength Nanocrystalline Mg-1 at% Zn-2 at% Y Alloy Studied by Atomic-Resolution Z-Contrast STEM, Acta Materialia 50(15) (2002) 3845–3857. [6] M. Yamasaki, S. Izumi, Y. Kawamura, Development of High Strength and Highly Corrosion-Resistant Bulk Nanocrystalline Mg-Zn-Y Alloys with Long Period Stacking Ordered Phase, ECS Transactions 16(32) (2009) 81. Figure 1