Research Article

Micro-deformation behavior in micro-compression with high-purity aluminum processed by ECAP

¹ Key Laboratory of Micro-systems and Micro-structures Manufacturing of Ministry of Education, Harbin Institute of Technology, Harbin 150080, P.R. China
² Academy of Fundamental and Interdisciplinary Sciences, Harbin Institute of Technology, Harbin 150080, P.R. China
³ Departments of Aerospace & Mechanical Engineering and Materials Science, University of Southern California, Los Angeles, CA 90089-1453, USA
⁴ Materials Research Group, Faculty of Engineering and the Environment, University of Southampton, Southampton SO17 1BJ, UK

^* e-mail: xjhit@hit.edu.cn

Received: 21 January 2015
Accepted: 9 February 2015

Abstract

Ultrafine-grained (UFG) materials have a potential for applications in micro-forming since grain size appears to be the dominant factor which determines the limiting size of the geometrical features. In this research, high-purity Al was processed by equal-channel angular pressing (ECAP) at room temperature through 1–8 passes. Analysis shows that processing by ECAP produces a UFG structure with a grain size of ~1.3 μm and with microhardness and microstructural homogeneity. Micro-compression testing was carried out with different specimen dimensions using the annealed sample and after ECAP processing through 1–8 passes. The results show the flow stress increases significantly after ECAP processing by comparison with the annealed material. The flow stress generally reaches a maximum value after 2 passes which is consistent with the results of microhardness. The flow stress decreases with decreasing specimen diameter from 4 mm to 1 mm which demonstrates that size effects also exist in the ultrafine-grained materials. However, the deformation mechanism in ultrafine-grained pure Al changes from strain strengthening to softening by dynamic recovery by comparison with the annealed material.