Microstructure Evolution and Mechanical Properties of Long Period Stacking Ordered Mg 96 Gd 3 Ni 1 Alloy with Al and Sr
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DUCTION
MAGNESIUM alloys with long-period stacking ordered (LPSO) structure, exhibiting excellent mechanical properties at both ambient and elevated temperatures, are promising candidates for lightweight structural materials and have attracted extensive attention.[1–9] So far, a variety of LPSO structure have been observed in Mg-Al-Gd alloy[10] and Mg-RE-TM (RE = rare earth metals; TM = Zn, Cu, Ni, Co) alloys.[1–9,11] Many attempts have been made to strengthen the LPSO-containing magnesium alloys by means of extrusion,[12] rolling,[13] heat treatment,[14] and alloying.[15–17] Several alloying elements such as Zr,[15] Mn,[16] and V[17] have been introduced to the alloys to optimize the microstructures and enhance the mechanical properties. As a common element in Mg alloys, Al has been added to refine grains of Mg-10Gd alloy[18] and improve the corrosion resistance of the LPSO-containing Mg-Y-Zn alloys.[19,20] Moreover, once Al is added to Mg alloys, Zr fails to refine the grains due to its reaction with Al to form stable intermetallics, although Zr is well known to have obvious grain refining effect on Mg alloys.[21] To our relief, Sr is favorable grain refiner of Mg-Al alloys.[22,23] Meanwhile, Sr has been found to improve the ductility of long-period stacking ordered Mg94Zn2Y4 DANDAN WANG, Postgraduate Researcher, JINSHAN ZHANG, CHUNXIANG XU, and HONGXIA WANG, Professors, KAIBO NIE, Lecturer, and XIAOFENG NIU and ZHIYONG YOU, Associate Professors, are with the College of Materials Science and Engineering, Taiyuan University of Technology, Taiyuan 030024, P.R. China. Contact e-mail: [email protected] WENBO ZHANG, Research Fellow, is with the Weichai Heavy Machinery Co., Ltd., Weifang 261001, P.R. China Manuscript submitted August 11, 2014. Article published online April 2, 2015 2710—VOLUME 46A, JUNE 2015
alloy.[24] However, the effect of Al on the microstructure and mechanical properties of magnesium alloys with LPSO structure has not been reported yet and the investigation concerning the influence of Sr on those alloys is still insufficient. Therefore, in this study, Mg96Gd3Ni1 and Mg95.7 xGd3Ni1Al0.3Srx (at. pct) (x = 0.0, 0.1, 0.2, 0.3) alloys were prepared to make clear the effect of Al and Sr on the microstructure and mechanical properties of the Mg-Gd-Ni alloys with LPSO structure.
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EXPERIMENTAL PROCEDURES
The chemical compositions of five groups Mg-Gd-NiAl-Sr alloys are listed in Table I. The alloys were melted using pure Mg (99.9 wt pct), Gd (99.9 wt pct), Ni (99.9 wt pct), Al (99.9 wt pct), and Sr (99.9 wt pct) in an electric resistance furnace under a mixed protective gas atmosphere of N2 (97.4 vol pct) and CH2FCF3 (2.6 vol pct) at 1033 K (760 °C).[24] Then they were casted into a preheated mold, respectively. Phase constitution analyses were performed with Y-2000 X-ray diffraction (XRD), using monochromatic Cu-Ka radiation. The microstructures of alloys were investigated by scanning electron microscopy (SEM, JSU-6700F) and transmission electron microscopy (TEM, JEOL 2010). The quantitative analysis of the chem
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