Effect of Static Electropulsing on Microstructure and Elongation of a Zn-Al Alloy (ZA22)
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INTRODUCTION
ELECTROPULSING treatment (EPT) has proven to be a very effective process for improving the microstructures[1–8] of materials and their properties.[9–16] Previous work by the present authors and co-workers has shown that electropulsing induced phase transformations consisted of two kinds of phase transformations: forward and reverse phase transformations.[6] It was also reported that with adequate dynamic electropulsing, the elongation of the Zn-Al based alloy was increased by 437 pct at ambient temperature under a high strain rate, whereas the instantaneous tensile stress remained unchanged, compared with that of the nonEPT alloy.[16] The fundamental mechanisms by which such significant changes of phase transformations, microstructures, and properties resulted from electropulsing have yet to be fully established. It is of great practical importance and theoretical significance to explore the mechanism of electropulsing. There are two practical types of applying electropulsing: dynamic electropulsing and static electropulsing. The former is a complex thermal process, which combines simultaneously both electropulsing and tensile deformation. In comparison, the latter is relatively simple and combines only a thermal process and electropulsing. YAOHUA ZHU, Senior Research Fellow, and SUET TO, Associate Professor, are with the State Key Laboratory in UltraPrecision Machining Technology, Department of Industrial and Systems Engineering, The Hong Kong Polytechnic University, Hong Kong, People’s Republic of China. Contact e-mail: yoahuazhu@ hotmail.com XIANMING LIU, Associate Professor, is with the Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, People’s Republic of China. GUOLIANG HU, Postgraduate Student and Postdoctoral Candidate, is with the Gradual School at Shenzhen, Tsinghua University, Tsinghua, People’s Republic of China. Manuscript submitted September 1, 2010. Article published online January 20, 2011 METALLURGICAL AND MATERIALS TRANSACTIONS A
As part of a systematic investigation into this newly developed process, the present work was initiated to study the effect of static electropulsing on the plastic elongation of a previously cold-deformed Zn-Al based alloy (ZA22), in relation to the phase transformations and microstructural changes that took place.
II.
EXPERIMENTAL PROCEDURES
An as-received Zn-Al based alloy wire of 1.5-mm diameter was previously extruded and cold drawn and tempered repeatedly. The nominal composition of the alloy was Zn75.3Al22.1Cu2.6 (mass pct). The wire specimen was cut into pieces of 100-mm length for static EPT (without external stress affect) at ambient temperature (28 C). A self-made electropulsing generator was applied to discharge positive direction multiple pulses with various current intensities (10, 15, 20, and 30) for 10 seconds. The frequency of the multiple electropulses was selected as 100 Hz. The duration of each pulse was kept to ~2300 ls. Using an oscilloscope with a Hall effect compone
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