A Revisited Study of the Processing Map and Optimized Workability of AZ61 Magnesium Alloy
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JMEPEG (2017) 26:2423–2429 DOI: 10.1007/s11665-017-2670-2
A Revisited Study of the Processing Map and Optimized Workability of AZ61 Magnesium Alloy X. Zhou, R.R. Liu, H.T. Zhou, and W.X. Jiang (Submitted October 16, 2016; in revised form March 15, 2017; published online April 11, 2017) The hot deformation behavior of AZ61 magnesium alloy was studied by hot compression testing in the temperature range from 250 to 400 °C with strain rates from 1023 to 1 s21. Typical flow stress/true strain curves with the features of dynamic recrystallization (DRX) have been obtained. According to the flow stress curves, the processing maps were constructed via the dynamic material model (DMM). The maps exhibit a domain of DRX at temperatures between 330 and 370 °C and strain rates ranging from 1023 to 1022 s21. The corresponding extrusion deformation was carried out in this DRX region. Gleeble 3500, optical microscopy (OM) and transmission electron microscopy (TEM) were used to characterize the microstructure evolution. The microstructure detection of this DRX region shows that the average grain size decreases with decreasing extrusion temperature. TEM observation further indicated that there are irregularly shaped subgrains with a high dislocation density, a dislocation network, the feature of dislocation pileup and an appearance of twin formation in the alloy hot-extruded using the parameters determined by our constructed processing maps. Keywords
AZ61 alloy, hot deformation, processing mapping, recrystallization
1. Introduction Magnesium alloys, as lightweight structural materials, have attracted scientific attention in various industrial areas because of their merits of low density, good damping characteristics and stable machinability. However, the flaws of magnesium alloys—i.e., poor formability and limited ductility at room temperature due to a hexagonal close-packed (HCP) structure and intrinsic limited slip systems—severely restrict their further applications (Ref 1-5). As a result, one possible way of further enhancing the ductility and formability of magnesium alloy is to activate non-basal slip systems in HCP structures at high temperatures (higher than the recrystallization temperatures), which can be effectively achieved by processing under hot deformation, such as hot forging, hot extruding and hot rolling (Ref 6-12). It is well acknowledged that magnesium alloys could undergo some metallurgical phenomena, such as dynamic recovery (DRV) and DRX (Ref 13, 14), which result in grain refinement and reduction in deformation resistance during hot deformation. Regarding magnesium alloys, DRX predominates X. Zhou, Key Laboratory of Non-ferrous Metal Materials Science and Engineering of Ministry of Education, School of Materials Science and Engineering, Central South University, Changsha 410083, China; and Department of Mining and Materials Engineering, McGill University, Montre´al, QC H3A 0C5, Canada; R.R. Liu, Key Laboratory of Advanced Civil Engineering Materials of Ministry of Education, Functional Materials Research Laborato
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