Spiral extrusion of aluminum/copper composite for future manufacturing of hybrid rods: A study of bond strength and interfacial characteristics
Introduction
There is a growing interest in hybrid materials for many current industrial applications where the properties of one material alone are inadequate to fulfill particular requirements [1]. Hybrid metallic composites (hybrid materials) are composed of two different metals with the aim to take advantage of their unique properties. An example of this is copper clad aluminum wire which is an attractive alternative to copper wire in electrical power transmission and automotive wiring. In this case, the copper outer sleeve provides low resistivity and the aluminum inner core filler material significantly reduces the weight and the cost of the fabricated wire [2]. In recent years, copper clad aluminum wires have been used in electrical power distribution bus bars [3] and vehicle alternator winding applications [4].
Many hybrid metallic composites are fabricated using mechanical welding, which is generally a high temperature process and only offers a limited number of shapes. In particular, a conventional mechanical welding technique is not convenient for long axi-symmetric shapes because of the difficulties in developing radial pressure at the interface of the sample in a continuous fashion. This makes extrusion, an attractive option for fabrication of bimetallic composite rods. Nilson [5] introduced a technique to manufacture Al/Cu composite rods using hydrostatic extrusion process. Kwon et al. [6] investigated the bond strength of the copper clad aluminum interface of fabricated Al/Cu composite rods using an indirect extrusion and drawing process. They found that the optimum extrusion condition for the process was 350 °C with an extrusion ratio of 21.39 [6]. Rhee et al. studied the fabrication of Al/Cu composites at 320 °C using a horizontal hydrostatic extrusion with extrusion ratios of 8.5,19 and 49. A mechanical bonding by such extrusion processes, however, must be performed under a large extrusion ratio which is expensive. A large extrusion ratio also requires high energy and may not produce uniform core diameter.
In recent years, severe plastic deformation (SPD) processes (see for example Segal [7]) have been considered as alternatives to reduce the mechanical bonding temperature by leveraging the synergy between high pressure and shear deformation. For instance, Al/Cu composite rods have been successfully fabricated using the Equal Channel Angular Extrusion (ECAE) process [8], [9], [10]. The bonding mechanism in ECAE is governed by the presence of the shear and high pressure simultaneously at the interface of aluminum and copper.
The ECAE process produces a homogeneous product which needs route changes to produce an equiaxed grain structure and is limited to produce parts in batch mode only. Zebardast and Taheri [10] produced copper–aluminum composite samples by ECAE at “room temperature” following a 250 °C annealing for 1 h to increase the ductility and to relieve the residual stresses. Their sample showed a good bond strength [10]. However, the role and contribution of the high temperature annealing in the bonding is not clear. Eslami and Taheri [9] investigated the bond strength of Al/Cu composite samples which were fabricated using the ECAE process. They varied the temperature from 100 °C to 225 °C in steps of 25 °C and used the holding times of 20, 40, 60, 80 and 100 min for each of the temperatures. Measuring the shear strength of the bonding, they found an optimum shear bonding strength of 34.9 MPa at 200 °C with a holding time of 60–80 min [9]. Thus, in order to obtain strong bond strength, the ECAE process required either a room temperature extrusion followed by an additional post-heating step or an elevated temperature extrusion followed by a long holding time.
In order to reduce these limitations we propose a method, axi-symmetric forward spiral composite extrusion (AFSCE), to fabricate bimetallic rods in a single step. In the current study, the AFSCE technique is applied to a specific case to fabricate Al/Cu composite rods.
The axi-symmetric forward spiral extrusion (AFSE) process [11] is a recently proposed severe plastic deformation technique which was initially proposed to extrude single materials with the aim to achieve refined grain size at room temperature. The small spiral grooves along the axis of the extrusion die allow a unique “near zero shape change” extrusion, which develops a combination of a compressive and shear forces in the material. The die has a small chamfer section at the entrance, which causes the reduction in cross section of the billet material. The spiral grooves facilitate the material to rotate about the longitudinal (extrusion) axis, which in contrast to an ECAE process to eliminate the need for the route change in the material.
The bonding in this process is governed by developing shear and high pressure at the Al/Cu interface at elevated temperature. In this research, basics of the process including kinematic considerations and shear deformation in the hybrid samples are discussed first. The discussion is assumed independent of the materials chosen for hybrid fabrication. This is followed by an experimental case study of the technique by fabrication of hybrid Al/Cu samples using the AFSCE process at 300 °C with an applied backpressure of 200 MPa. Bond strength is determined experimentally by measuring the shear strength at the interface using a dedicated blanking test (DBT). The DBT results show that for conditions of this study AFSCE has successfully produced a hybrid metal bonding between copper and aluminum.
Section snippets
Implementation of the AFSCE
The main aim of the above design was to facilitate diffusion of atoms at elevated temperature and pressures [12]. Details of the AFSE process for extrusion of single solid materials can be found elsewhere (Khoddam et al. [11], [13]). Three-dimensional schematic views of the AFSCE die shown in Fig. 1a is used here to fabricate a hybrid bimetallic sample by extrusion. The joined composite product is composed of core and clad blanks. The assembly configuration shown in Fig. 1b illustrates the
Experimental procedure
Two materials, pure copper C11000 (99.90% copper) and pure cast aluminum, were used in this experiment to make a composite sample. In order to obtain stress–strain behavior of the materials, hot torsion test was performed at 300 °C and the torque-twist data were converted to the stress–strain curve using the technique presented elsewhere [17]. The flow curves were mathematically modeled using the following expression:
Results and discussion
Fig. 5a shows the composite Cu/Al specimen after AFSCE with two distinct zones: zone 1 with groves and a groove free zone 2 corresponding to the extruded and the non-extruded zones, respectively. A 1 mm thick sample normal to the cross section of zone 1 was sliced from the AFSCE specimen by the EDM wire cutting (Fig. 5a). Wire cutting of the DBT slice prevents the introduction of artifacts and change in properties of the bonding layer which can occur by other slicing techniques. It can be seen
Conclusions
An axi-symmetric forward spiral composite extrusion (AFSCE) process has been proposed to fabricate hybrid rods. This process involves extrusion of a composite sample through a die with engraved spiral grooves to create a final product in a single step. The process can be easily performed and has better dimensional control because of the zero shape change effect of this process. In the current study, an analytical frame work was established for the AFSCE process and an experimental case study of
Acknowledgments
The authors acknowledge the use of the facilities and assistance of Dr. Flame Burgmann and Dr. Xi-Ya Fang at the Monash Centre for Electron Microscopy. We thank Ms. Jane Moodie for proof reading of the manuscript.
References (23)
- et al.
Acta Mater.
(2003) - et al.
Scripta Mater.
(2010) Mater. Sci. Eng., A
(1995)- et al.
Mater. Lett.
(2007) - et al.
Mater. Lett.
(2011) - et al.
J. Mater. Process. Technol.
(2011) - et al.
Mater. Sci. Eng. A
(2011) - et al.
Mech. Mater.
(2011) - et al.
Mater. Sci. Eng., A
(2012) - et al.
J. Mater. Process. Technol.
(2004)
Acta Mater.
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