Improved ductility of aged Mg-9Al-1Zn alloy strip by electropulsing treatment
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Guoyi Tanga) Advanced Materials Institute, Graduate School at Shenzhen, Tsinghua University, Shenzhen 518055, People’s Republic of China
Chanhung Shek Department of Physics and Materials Science, City University of Hong Kong, Kowloon Tong, Hong Kong
Yaohua Zhu Department of Industrial and Systems Engineering, Hong Kong Polytechnic University, Kowloon, Hong Kong
Lei Guan, Shaonan Wang, and Zhuohui Xu Advanced Materials Institute, Graduate School at Shenzhen, Tsinghua University, Shenzhen 518055, People’s Republic of China (Received 12 October 2008; accepted 23 January 2009)
The effect of electropulsing treatment (EPT) on the microstructure and mechanical properties of aged Mg-9Al-1Zn alloy strip was studied. EPT was found to accelerate tremendously the b phase spheroidization in the aged Mg-9Al-1Zn alloy. This improved microstructure exhibits excellent mechanical properties, that is, increasing elongation to failure significantly without loss of tensile strength. The spheroidization of the b phase during EPT was attributed to the reduction of the nucleation thermodynamic barrier and enhancement of atomic diffusion. I. INTRODUCTION
In recent years, Mg-9Al-1Zn alloy (AZ91) has attracted a lot of attention due to its excellent properties, such as low density, high specific strength, and good damping capacity. However, the AZ91 alloy exhibits low strength and low ductility at room temperature compared to other commercial structural materials, such as Al alloys and steel. These considerably inhibit AZ91’s widespread application. Some research focused on grain refinement of AZ91 using severe plastic deformation (SPD) techniques,1–3 including equal channel angular pressing (ECAC)4,5 and accumulative roll bonding (ARB),6–8 which can improve both the strength and ductility. Nevertheless, SPD techniques have difficulty satisfying industrial needs due to their low production efficiency and high manufacturing cost. In the present work, a novel technique of electropulsing treatment (EPT)9,10 is applied to an aged AZ91 strip for improving ductility without any compromise in tensile strength. a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0197
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J. Mater. Res., Vol. 24, No. 5, May 2009
EPT accelerated spheroidization of the strengthening b phase tremendously in the aged AZ91 alloy strip. Finally, the mechanism of the effect is discussed. II. EXPERIMENTAL
A commercial magnesium alloy AZ91 (9.1wt%Al, 0.9wt%Zn, 0.2wt%Mn, balance Mg) was used. The ingot was homogenized at 673 K for 16 h, and subsequently extruded into strip of width 2.90 mm and thickness 1.45 mm. The extruded strip was then electropulsingrolled11 to 1.00 mm thick. The rolled strip was aged for 12 h at 493 K to obtain the as-aged strip consisting of a-Mg and b-Mg17Al12. The as-aged strips were subjected to EPT with various parameters of electropulsing, as listed in Table I. For comparison, the as-aged strips were heated up to 723 K over the course of about 8 s in a furnace, followed by natural cooling
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