Equal channel angular pressing–forward extrusion (ECAP–FE) consolidation of Al particles M.H. Paydar a, * , M. Reihanian b , E. Bagherpour a , M. Sharifzadeh a , M. Zarinejad c , T.A. Dean d a Department of Materials Science and Engineering, School of Engineering, Shiraz University, Shiraz, Iran b Department of Materials Science and Engineering, Faculty of Engineering, Shahid Chamran University, Ahvaz, Iran c School of Mechanical and Aerospace Engineering, 50 Nanyang Avenue, 639798, Singapore d Department of Mechanical Engineering, School of Engineering, University of Birmingham, Edgbaston Birmingham B15 2TT, UK article info Article history: Received 26 June 2007 Accepted 3 June 2008 Available online 10 June 2008 Keywords: Particulates and powders (B) Powder metallurgy (C) Extrusion (C) abstract Particles of commercially pure Al are successfully consolidated at 200 °C by a novel method named equal channel angular pressing-forward extrusion (ECAP–FE). Using this method, both ECAP and forward extru- sion processes are carried out subsequently in a single tool. The extrusion process exerts a back pressure for ECAP process which prevents surface cracking and improves microstructure and mechanical proper- ties of the produced material. The improvement is related to the shear deformation induced during ECAP and the increase in self-diffusion coefficient of Al due to the exerted back pressure. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Powder metallurgy is a conventional method to produce the near-net shape products. The main disadvantage of this method is that the final product contains a level of porosity which affects the performance of the component. Thus, achieving a fully dense material is an important task in the powder processing. Sintering at relatively high temperature is conventionally used to reduce the level of porosity. Recently, it has been shown that equal chan- nel angular pressing (ECAP) is an effective method to consolidate the powders at relatively lower temperatures than that used in conventional powder processing [1–8]. The induced shear defor- mation in ECAP effectively reduces the level of porosities and in- creases the density of consolidated sample to the theoretical value. During ECAP, a sample is deformed through a die having two intersecting channels with equal cross section [9]. The effec- tive strain imposed into the sample in every passage through ECAP is obtained by the equation below [10] e eq ¼ 1 ffiffiffi 3 p 2 cot U 2 þ W 2   þ Wcosec U 2 þ W 2     ð1Þ where U is the channel intersection angle and W is the angle of the outer arc of curvature. For a die having an intersecting channel angle of 90° (U = 90°) and a sharp outer curve (W = 0), as in our ECAP–FE die, the imposed strain in each pass through ECAP is calculated as 1. During consolidation of the particles through ECAP, delaminat- ing of the sample should be prevented. Pre-compaction, sintering or capsulations of the powders are usually used to prevent the sur- face cracking and delaminating of the sample. It has been shown that applying a back pressure during ECAP not only prevents dela- minating but also improves the microstructure and properties of the consolidated material [7]. In this work a new method, named equal channel angular press- ing – forward extrusion (ECAP–FE) is introduced for the consolida- tion of Al particles at 200 °C. The most important feature of this method is that two processes, ECAP and FE, are carried out subse- quently in a single tool and the need for additional equipment is eliminated. The extrusion process designed in the second channel of ECAP die has many potential advantages: (i) it creates a back pressure during the consolidation of the particles through ECAP and can thus prevent delaminating and surface cracking; (ii) it en- ables the production of long bars after ECAP, suitable for mechan- ical testing and also perhaps for industrial application, and (iii) it has the potential of producing ECAP samples with different cross-section geometries through the extrusion process designed in the second channel. 2. Method In this present study, air atomized commercially pure alumi- num powder was used as a raw material. Particles were of irregular shape as shown in Fig. 1 and had an average diameter of about 45 lm. For comparison, a commercially pure Al Ingot (referred as Ingot sample) and a bulk sample of Al powder consolidated by con- 0261-3069/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.matdes.2008.06.012 * Corresponding author. Tel.:+98 711 2307293; fax: +98 711 6287294. E-mail address: Paaydar@shirazu.ac.ir (M.H. Paydar). Materials and Design 30 (2009) 429–432 Contents lists available at ScienceDirect Materials and Design journal homepage: www.elsevier.com/locate/matdes