Effects of Sm on microstructure and corrosion resistance of hot-extruded AZ61 magnesium alloys
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In this study, the effects of Sm on the microstructure and corrosion resistance of hot-extruded AZ61 magnesium alloys were investigated by optical microscopy, scanning electron microscopy, and transmission electron microscopy. The results showed that uniformly dispersed Al2Sm particles with size of ;2 lm were discovered in the hot-extruded AZ61 magnesium alloy sample modified with 1.0 wt% Sm, which promoted dynamic recrystallization grain growth during the hot-extruded process, gradually increasing the grain of the alloy as Sm content increased. The morphology of the corroded surface and the corrosion rate of the hot-extruded AZ61 magnesium alloy both were significantly improved after Sm addition. The alloy sample modified with 2.0 wt % Sm after immersion in 3.5 wt% NaCl solution for 12 h showed minimum corrosion rate value, 3.1 mg/cm2 day, which is only 3.7% of the corrosion rate of unmodified alloy (82 mg/cm2 day).
I. INTRODUCTION
Magnesium alloy is often utilized as a structural material in aerospace, electronics, and automotive industries, favored for its ready castability, high specific strength, low density, and excellent electromagnetic shielding performance.1,2 The corrosion resistance of magnesium alloy is rather poor, however, which significantly limits further development or application of the material.3,4 In recent years, the effects of rare earth microalloying on microstructural and mechanical properties of magnesium alloy have been investigated at length, specifically in an effort to improve corrosion resistance. Studies have shown that the microstructures of magnesium alloys improve considerably after the addition of Rare Earth (RE) elements, facilitated by an RE-rich strengthening phase. Examples include, Al2Yb,5 Mg2Yb,6 Al2Sm,7 Al2Y,8 Al11Nd3,9, and Al3Er.10,11 The effects of rare earth element addition on the corrosion resistance of magnesium alloys have also been reported previously.12–14 Liu et al.,15 for example, found that new c phases containing larger amounts of RE and Al were formed in AM60 magnesium alloys after supplementation with La and Ce. The corrosion resistance of the AM60-RE magnesium alloy was improved due to RE-rich compounds that formed in the corrosion product film surface and successfully inhibited further corrosion. A stable, intermetallic Al11RE3 phase formed in an Mg–8Al alloy in a study Contributing Editor: Jörg F. Löffler a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2015.345 J. Mater. Res., Vol. 30, No. 23, Dec 14, 2015
by Jain and Koo,16 who focused on corrosion properties of extruded magnesium alloys containing rare earth. They found the corrosion rate of the alloy decreases with increasing RE content. Microstructures and tensile properties of as-cast Mg–Al series alloys have been shown to significantly improve by adding Sm.17–20 Relatively few studies regarding the effects of Sm addition on microstructures and properties of wrought magnesium alloys have been conducted, however. Though AZ61 alloy is one of the most advantageous wrough
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