Micro-Indentation of Aluminum Processed by Equal Channel Angular Extrusion
- PDF / 684,737 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 17 Downloads / 228 Views
The near-surface deformation of equal-channel angular extruded (ECAE) pure aluminum was investigated using the micro-indentation technique. Compared with fully annealed Al samples, there is a distinguishable difference in the indentation deformation. The unloading slope of the ECAE deformed Al after a short unloading period was found to be less than that of the annealed samples due to plastic recovery. Work hardening was observed, which depended on the history of local deformation. A new relationship between the plastic energy dissipated in the indentation and the applied load was derived, which is supported by the experimental results.
I. INTRODUCTION
Severe plastic deformation by a process such as equalchannel angular extrusion (ECAE) has been used to produce bulk, ultrafine grained materials with high hardening behavior.1–4 The as-processed materials are in a nonequilibrium state with a high dislocation density and display unusual mechanical behavior. The ECAE process has been applied to different materials, such as pure Al,1 pure Cu,5 Al-Mg alloys,6 etc. Despite the recent research interest, most work to date has focused on examinations of the microstructure and the tensile behavior after selected materials were subjected to the ECAE process. The understanding of the fundamental mechanisms controlling the evolution of the microstructure and mechanical deformation is still at its early stage. In the present work, carefully controlled experiments were undertaken to study the nature of the mechanical deformation of pure Al after single ECAE process. In particular, this work focuses on demonstrating the dependence of the mechanical strengths of the ECAE processed Al on the specimen position related to the nonuniform plastic deformation occurring in the ECAE deformed material. The microindentation technique is used to measure the variation of indentation behavior over the cross-section of the ECAE processed material. II. EXPERIMENTAL
The experiments were conducted with pure (99+%) aluminum rods purchased from Alfa Aesar (Ward Hill, a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2004.0161 J. Mater. Res., Vol. 19, No. 4, Apr 2004
http://journals.cambridge.org
Downloaded: 13 Mar 2015
MA). The as-received rod (12 mm in diameter) was machined into a rod shape with diameter of 8 mm and length of 50.8 mm at ambient temperature. Prior to the ECAE process, the Al rod was annealed at 500 °C for 12 h and furnace-cooled to room temperature to relieve the residual stresses from machining. The ECAE die consisted of two split blocks of tool steel, which were held together to form a single internal channel of circular cross-section with two channels meeting in an L-shape configuration of an angle of 90° (Fig. 1). The surface of the internal channel was lubricated by a lubricant (MoS2 + oil) to reduce the friction between the Al rod and the die wall. The sample was then ECAE pressed at ambient temperature only half through the die, as shown in Fig.1. Specimens for indentation tests
Data Loading...
