Materials Science and Engineering A 532 (2012) 573–578 Contents lists available at SciVerse ScienceDirect Materials Science and Engineering A jo ur n al hom epage: www.elsevier.com/locate/msea The effect of extrusion and high-pressure torsion on the properties of Alumix-231 Ismail Ozdemir a , Ceren Gode b,* , Hakan Yilmazer c , Hasan Callioglu d a Department of Metallurgical and Materials Engineering, Bartin University, 74100 Bartin, Turkey b School of Denizli Vocational Technology, Program of Machine, Pamukkale University, 20100 Denizli, Turkey c Department of Materials Science, Graduate School of Engineering, Tohoku University, 980-8577 Sendai, Japan d Department of Mechanical Engineering, Pamukkale University, 20020 Denizli, Turkey a r t i c l e i n f o Article history: Received 23 May 2011 Received in revised form 24 October 2011 Accepted 27 October 2011 Available online 11 November 2011 Keywords: Extrusion High-pressure torsion Al–Si alloy Mechanical properties EBSD a b s t r a c t The mechanical properties and microstructure of commercial Al–15Si–2.5Cu–0.5Mg (Alumix-231 ® ) alloy was subjected to extrusion (EXTR), hot extrusion into rods at 565 ◦ C at an extrusion ratio of 4:1 and high-pressure torsion (HPT) processing, one of the most severe plastic deformation (SPD) techniques, with an anvil rotation speed of 0.5 rpm under a quasi-hydrostatic pressure of 5 GPa. Afterwards, the microstructures of specimens were systematically investigated using XRD, SEM, EBSD, and TEM. Also, tensile properties of Alumix-231 processed by EXTR and HPT were determined at room temperature. The HPT specimen shows refined microstructure (around average 165 nm) having more spherical and homogeneously distributed eutectic silicon second phases in Al metal matrix as compared to EXTR specimen. The hardness values are greater on the surface of the HPT specimen (239.1 Hv) as com- pared to that EXTR specimen (71.2 Hv) and increase with distance from the center of HPT specimen (198.3 Hv). Tensile strength and ductility of HPT specimen increased approximately 2 times than that of EXTR sample, respectively. The results indicate that the morphological changes in eutectic silicon espe- cially after HPT play a critical role in enhancing or limiting the overall properties of the Alumix-231 material. © 2011 Elsevier B.V. All rights reserved. 1. Introduction HPT processing [1–3] is very effective for fabricating extremely small grains with high-angle boundaries, compared with other SPD techniques such as equal-channel angular pressing (ECAP) [4,5] and accumulative roll bonding (ARB) [2]. The equivalent strain (ε eq ), which increases with the distance from the center of the HPT spec- imen, is an important factor to achieve grain refinement in HPT processing [6]. Therefore, grain refinement begins in the periph- ery of the disk specimen in HPT processing and spreads to the center of the disk specimen with increasing ε eq . Although there is disadvantage due to anisotropic imposed ε eq across diameter of the disks specimen, which leads to microstructural variations on the disk specimen [6], HPT processing has been effective to achieve good grain refinement and homogenization in pure Al [7], an Al–Mg–Sc [6], and an aluminum based metal matrix composites (MMCs) [8]. Al–Si eutectic alloys are widely used in many industries, especially the automobile industry because of their good wear * Corresponding author. Tel.: +90 258 2123788x1133; fax: +90 258 2118065. E-mail address: cgode@pau.edu.tr (C. Gode). resistance, high tensile strength at elevated temperatures and good castability. Conversely, these alloys show a low fracture toughness due to the microstructure, which consists of eutec- tic silicon second, phases in aluminum-based matrix. On the other hand it is reported that the size, morphology [9,10] and distribution [10,11] of silicon phases in the Al based metal matrix have strongly effects to mechanical strength [10,11], hard- ness [11], and ductility [10] of Al–Si alloys. Likewise, significant improvements in strength, ductility, and great wear resistance of Al–Si alloys were achieved by HPT processing with the grain refinement and modifying the eutectic silicon second phases [11–13]. Therefore, the effects of extrusion and HPT process- ing on microstructure and mechanical properties of commercial hypoeutectic Alumix-231 alloy have been investigated in this study. 2. Experimental procedures 2.1. Material The chemical composition (in wt%) of hypoeutectic Alumix- 231 powders used in the present study is given in Table 1. The Alumix-231 powders with an average size of about ∼70 m at 0921-5093/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2011.10.123