Mechanical properties and precipitate behavior of Mg–9Al–1Zn alloy processed by equal-channel angular pressing and aging Y.C. Yuan a , A.B. Ma a,b,⇑ , J.H. Jiang a,b , Y. Sun c , F.M. Lu a , L.Y. Zhang a , D. Song a a College of Mechanics and Materials, Hohai University, Nanjing 210098, China b Jiangsu Collaborative Innovation Center of Advanced Micro/Nano Materials & Equipment, Nanjing University of Science and Technology, Nanjing 210094, China c School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China article info Article history: Received 6 November 2013 Received in revised form 17 January 2014 Accepted 20 January 2014 Available online 26 January 2014 Keywords: Mg alloy ECAP Aging Precipitate Strength abstract Magnesium alloy processed by equal channel angular processing (ECAP) usually had a good ductility, but often inadequate strength. Herein, an approach was developed to simultaneously achieve high strength and good ductility in the Mg–9Al–1Zn alloy. This approach involved pre-solution treatment, ECAP and subsequent aging. The pre-solution accelerated the grain refinement and increased the strain hardening during the ECAP that improved the strength of the alloy. The spherical big precipitates and dispersed nanosized fine precipitates generated separately during the ECAP and the following aging process. As increasing the ECAP passes from 4 to 12, the strain hardening decreased but the fine structure became more equilibrium. Moreover, the aging hardening became more effective that resulted in a good ductility and a high strength in the Mg–9Al–1Zn alloy. Ó 2014 Elsevier B.V. All rights reserved. 1. Introduction Magnesium alloys are considered as promising structure mate- rials for its low density [1,2]. But for their hexagonal close packed crystal structure, magnesium alloys usually have poor ductility and workability. Equal channel angular pressing (ECAP) [3,4], as a common severe plastic deformation (SPD) process [5], has been demonstrated useful to produce ultra-fine-grained (UFG) or nano-structured materials [6–8]. It has been successfully used in Mg alloys to refine the microstructure and achieve good ductility at ambient or low temperature [9–12]. The room temperature duc- tility of AZ31 [9,13] and AZ61 [10] magnesium alloy was improved up to 50%, which was more than twice larger than that of the con- ventionally extruded alloys. ECAP was also expected to increase the yield stress of Mg alloys at room temperature due to the refined grains, but the yield strength in many magnesium alloys processed by ECAP did not increase but decreased [9,10,13]. One of the main reasons was the strong deformation texture generated after ECAP, which had a high Schmidt factors for the basal slip and accordingly lead to the low yield strength [13,14]. Therefore, in contrast with the ductility improvement, ECAP usually had a gentle strengthening effect in Mg alloys. For precipitate hardening alloys, in addition to the grain refine- ment, precipitation hardening is another approach to strengthen the alloys. By a thermo-mechanical processing, fine grained struc- ture involved fine dispensed metastable phase or second phase precipitates could be fabricated, which simultaneously had the fine grains and precipitate strengthening. Moreover, the fine dispersed precipitate particles inside the grains improved the work harden- ing rate which had advantages for both the strength and the duc- tility of the alloy [15]. However, in the other side, aging the sample after severe plastic deformation may lead to the dislocation recover and grain growing. Therefore, in order to increase the strengthening effect, the aging after the deformation (especially the severe plastic deformation) should be conducted carefully in order to preserve the fine structure of the deformed sample. Such post-aging after severe plastic deformation had been successfully adopted in many Al alloys [15–18]. The yield strength of 2024 Al alloy was improved up to 630 MPa by the pre-ECAP solution, ECAP and low-temperature aging procedure, and moreover the ductility was also higher than the ECAP-processed (ECAPed) alone sample[17]. By similar thermal treatment and cryo-rolling, both of the strength and ductility of the 7075 Al [15] and 2024 Al alloy [18] were simultaneously improved. If such a thermo-mechanical procedure is applied in Mg alloys, because the recrystallization tends to take place at a relative lower temperature, it would be more difficult to maintain the fine structure of the alloy. There are still few studies on the precipitate hardening effect in the severe-plastic-deformed magnesium alloy. http://dx.doi.org/10.1016/j.jallcom.2014.01.140 0925-8388/Ó 2014 Elsevier B.V. All rights reserved. ⇑ Corresponding author at: College of Mechanics and Materials, Hohai University, Nanjing 210098, China. E-mail address: aibin-ma@hhu.edu.cn (A.B. Ma). Journal of Alloys and Compounds 594 (2014) 182–188 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jalcom