A high-strength extruded Mg-Gd-Zn-Zr alloy with superplasticity
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g,a) X.Q. Zeng, D.L. Lin, and W.J. Ding National Engineering Research Center of Light Alloy Net Forming, Shanghai Jiao Tong University, Shanghai 200240, People’s Republic of China; and The State Key Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University, Shanghai 200240, People’s Republic of China
Y.H. Peng School of Mechanical Engineering, Shanghai Jiao Tong University, Shanghai 200240, People’s Republic of China (Received 12 February 2009; accepted 27 July 2009)
This article presents an extruded Mg–Gd–Zn–Zr alloy produced by conventional ingot metallurgy, exhibiting high-strength and excellent ductility at room and elevated temperatures. The superplastic behavior was observed in the Mg–Gd–Zn (–Zr) alloy at elevated temperatures above 573 K. In the alloy, both the X phase in grain boundaries and the lamellae within matrix have the 14H-type long period stacking ordered structure. It indicates that the X phase and the lamellae within matrix play important roles in the excellent mechanical properties. I. INTRODUCTION
In recent studies, some magnesium (Mg) alloys with high strength and heat resistance have been developed in the Mg-RE system (where RE represents rare earth elements), where more attention has gradually been paid on high-strength Mg–RE–Zn (–Zr) alloys, due to a combined strengthening by solid solution, precipitation,1,2 novel long period stacking ordered (LPSO) structures,3–24 as well as grain refinement8,12 in these alloys. Based on our study3–5 and the previous reports,6–23 various types of LPSO structures such as 6H, 10H, 14H, 18R, 24R have been observed in high-strength Mg–RE(RE = Y, Dy, Ho, Er, Gd, Tb, Tm)–Zn (–Zr) alloys. For example, a highstrength Mg97Zn1Y2 (at.%) alloy with LPSO structure was produced by rapidly solidified powder metallurgy (RS/PM) in 2001 and exhibited remarkable mechanical properties with a tensile yield strength of 610 MPa and an elongation of 5% at room temperature.8 The nanocrystalline Mg solid solutions with LPSO structure in RS/PM Mg97Zn1Y2 (at.%) alloy have been recognized as a decisive strengthening factor.8 It has been found that conventional ingot metallurgy (I/M) process can also refine the microstructure with LPSO structures and improve mechanical properties of Mg–RE–Zn (–Zr) alloys.12,18,19,24 Extrusion is applied as an effective process to achieve Mg alloys with excela)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0425
3596
J. Mater. Res., Vol. 24, No. 12, Dec 2009
lent mechanical properties by refining grains with LPSO structure and dispersing the phases with LPSO structure.18,19 At present, the mechanical properties at elevated temperatures of Mg–Gd–Zn (–Zr) alloys with LPSO structure have not been reported.3–5,16–19 In this study, an extruded Mg96.32Gd2.5Zn1Zr0.18 alloy was produced by conventional I/M process, in which both the X phase in grain boundaries and the lamellae within Mg matrix have the 14H-type LPSO structure. The extruded Mg– Gd–Zn–Zr alloy has good tensile mechanical properties wit
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