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Guoyi Tang,a) Lei Guan, Shaonan Wang, and Zhuohui Xu 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 (Received 16 March 2008; accepted 24 June 2008)

The effect of electropulsing treatment (EPT) on the solution behavior of aged Mg alloy AZ61 strip was investigated using scanning electron microscope (SEM) and x-ray diffraction (XRD). It was found that EPT accelerated tremendously the dissolution of ␤ phase into ␣ matrix in an aged Mg alloy AZ61 strip. The dissolution of ␤ phase took place in less than 4 s at relatively low temperature under EPT, compared with that in conventional heat treatment. A mechanism for rapid solid solution process during EPT was proposed based on the coupling of the thermal and athermal effects. The results in this investigation indicated that EPT played an important role in the nonequilibrium microstructural evolution in the alloy. It is supposed that EPT can provide a highly efficient approach for solid solution treatment of the alloy.

I. INTRODUCTION

Electropulsing treatment (EPT), as an instantaneous high-energy input method, has been applied for improving microstructure and properties of materials. It has been reported that applying an electric current pulse during the solidification process refined grain size.1–5 EPT was also used during annealing of cold-worked copper to obtain fine recrystallized grains and to retard the formation of annealing twins.6–10 Conrad et al.6–9 proposed that the high mobility of dislocations due to the electric current played an important role in such effects. In our previous work, complete recrystallization of a coldworked Mg alloy AZ31 strip was achieved in several seconds at relatively low temperature (483 K) under EPT. In the case of EPT, the recrystallization mechanism could be attributed to the coupled action of thermal and athermal effects.11 Zhang et al.12,13 developed an electropulsing treatment for synthesizing nanostructured maa)

Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2008.0328 J. Mater. Res., Vol. 23, No. 10, Oct 2008

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terials directly from conventional coarse-grained crystalline materials because of the rapid heating/cooling cycle resulting from electropulsing. However, the method of EPT applied to the solid solution treatment of magnesium alloys on-line has not been reported. In the present paper, the influence of EPT on the solid solution behavior of an aged Mg alloy AZ61 strip (AZ61 strip) is reported and the mechanism of the effect is discussed. II. EXPERIMENTAL

The commercial magnesium alloy AZ61 (6.3 wt% Al, 1.1 wt% Zn, 0.2 wt% Mn, balance Mg) was used. The ingot was homogenized at 673 K for 16 h and subsequently extruded int