Materials Science and Engineering A 410–411 (2005) 324–327 Equal channel angular pressing of magnesium alloy AZ31 K. Xia a,∗ , J.T. Wang b , X. Wu a , G. Chen b , M. Gurvan b a Department of Mechanical and Manufacturing Engineering, University of Melbourne, Vic. 3010, Australia b School of Materials Science and Engineering, Nanjing University of Science and Technology, Nanjing, Jiangsu 210094, PR China Received in revised form 26 May 2005 Abstract Equal channel angular pressing (ECAP) was applied to a wrought magnesium alloy AZ31 for up to 8 passes at temperatures as low as 100 ◦ C. The application of a back pressure was critical in deforming Mg alloys at lower temperatures. Room temperature mechanical properties were obtained by tensile and hardness tests. With increasing ECAP strain, the initial coarse grained structure was transformed into a submicrometer- grained microstructure. In general, hardness increased with decreasing grain size although the changes in tensile strength and ductility were more complicated. © 2005 Elsevier B.V. All rights reserved. Keywords: Equal channel angular pressing; Severe plastic deformation; Magnesium alloys; Ultra-fine-grained microstructure; Back pressure 1. Introduction As the lightest structural material of engineering signifi- cance Mg alloys have attracted considerable recent attention [1,2]. However, Mg alloys exhibit poor formability and pos- sess only moderate strength compared to Al alloys. One of the promising methods to increase ductility and strength in Mg is through microstructural refinement. ECAP has been shown to be effective in refining grains in various Mg alloys with improved ductility, strength and superplasticity [3–11]. In most investigations, however, the processing temperature was at or above 200 ◦ C to avoid cracking [8,10]. Processing at such temperatures resulted in not only complete recrys- tallisation [4] but also grain growth [3]. In this investigation, a back pressure was applied to enable an AZ31 alloy to be ECA deformed at as low as 100 ◦ C with significantly refined grains. 2. Experimental material and procedures AZ31 was used with the following nominal composition: Mg–3Al–1Zn–0.3Mn (wt.%). The as-cast billets were extruded at 380–400 ◦ C to rods of 19 mm in diameter which were ∗ Corresponding author. Tel.: +61 3 8344 6664; fax: +61 3 9347 8784. E-mail address: k.xia@unimelb.edu.au (K. Xia). either used directly or machined by milling into specimens of 8 mm × 8 mm in cross-section dimensions for ECAP. ECAP dies with an angle of 90 ◦ were used. The die was preheated to and stabilised at the testing temperature before a lubricated ECAP specimen was inserted into the entrance chan- nel. It was held for 15 min before pressing. For ECAP at 200 ◦ C, the pressing speed used was 240 mm/min. For ECAP at 150 and 100 ◦ C, the pressing speed was 0.2 mm/min and a back pres- sure of 50 MPa was applied through a back plunger in the exit channel. Up to 8 passes were carried out following the B c route [3]. Microstructures in the as-extruded and ECA pressed mate- rials were examined following standard metallography proce- dures. The polished surface was etched using either a solution of 1 vol.% HNO 3 , 24 vol.% C 2 H 6 O 2 and 75 vol.% H 2 O or of 10 ml acetic acid, 4.2 g picric acid, 10 ml H 2 O and 70 ml ethanol. The microstructures were observed by optical microscopy (OM) and scanning electron microscopy (SEM). The average grain size was obtained following procedures given in ASTM standard E112-95. Tensile specimens with a gauge section of 7 mm × 4 mm × 2 mm were cut along the longitudinal direction of the speci- mens ECA pressed at 200 ◦ C. Tensile tests were conducted at room temperature with an initial strain rate of 1 × 10 −3 s −1 . Tests of the Vickers hardness (HV) with an indenter load of 50 g and a loading time of 25 s were carried out on specimens ECA deformed at 150 and 100 ◦ C. 0921-5093/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2005.08.123