Different processing routes for deformation via simple shear extrusion (SSE)

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Abstract

Simple shear extrusion (SSE) is a newly introduced severe plastic deformation technique to obtain ultrafine-grained materials. Different parameters can affect properties of the materials processed by this method. Among them, rotation of samples between consecutive passes can be considered as a simple procedure to modify the results. This paper aims to study this parameter by introducing four different processing routes of SSE. These routes were investigated in terms of shearing characteristics and variation of shear strain during the process. The latter was also studied by finite element analysis (FEA) of these different processing routes. In addition, an experimental study of different processing routes was performed by measurement of microhardness homogeneity in the cross-section of samples and normal to extrusion direction.

Introduction

Severe plastic deformation (SPD) is considered as an effective procedure to achieve ultrafine-grained (UFG) or bulk nanostructured materials [1], [2], [3]. Equal channel angular pressing (ECAP) is a well-known SPD technique which has been the subject of many studies [2]. As a result, different parameters are proposed to be effective on properties of materials processed by this technique [2]. Rotation of samples between consecutive passes of ECAP is a simple and effective technique which was proposed by Segal in terms of different processing routes of ECAP [4]. Similar procedures have been carried out on other SPD methods by introducing different processing routes [5], [6]. Application of this simple technique in ECAP provides an opportunity to deform the sample via different strain paths by activation of different slip systems. Various theoretical and experimental investigations have been performed to assess the effect of these processing routes on shearing characteristics, mechanical properties, and microstructural evolution during ECAP [7], [8], [9], [10], [11], [12], [13]. In addition, finite element analysis has been applied as a strong tool to investigate deformation and strain uniformity in different processing routes of ECAP [14], [15], [16]. However, no such investigations have been performed on simple shear extrusion (SSE) which is a novel SPD technique recently introduced by present authors [17]. In this technique, final shape and dimensions of processed sample remain unchanged making it possible to repeat the process as many times to obtain high value of accumulated strain. Meanwhile, different processing routes can be introduced by rotating the sample between consecutive passes of SSE. This paper is intended to study and investigate four new processing routes of SSE.

Section snippets

Different processing routes of SSE

Principles of simple shear extrusion (SSE) have been introduced by Pardis and Ebrahimi [17]. In this method, the initially square cross-section of sample undergoes shear deformation which reaches its highest value in the middle of deformation channel corresponding to maximum distortion angle (α) and deforms back to its initial square shape at the channel outlet (Fig. 1). This makes it possible to repeat the process on the same sample through four main processing routes which are introduced in

Experimental procedure

Billets of 10 mm × 10 mm cross-section by 30 mm long were machined out of commercially pure aluminum (AA1050) and then annealed at 600 °C for 2 h and furnace cooled at a rate of 25 °C/h. Teflon tape and silicon spray were used to lubricate the sample–die interface. SSE was carried with a ram speed of 0.2 mm/s at room temperature using a die with maximum distortion angle α = π/4, and a 60 mm length of the deformation zone. The effect of different processing routes on hardness homogeneity was investigated on

Finite element analysis

Finite element analysis of the process was performed by ABAQUS/Explicit for a material with the same geometry and mechanical properties as those of the experiment. Therefore, the true stress–true strain relationship of the material was approximated by fitting the data obtained from compression test to equation σ = n (MPa), in which the parameters were determined empirically as k = 106 MPa and n = 0.347. Further details regarding frictional condition, modeling and meshing procedure are available in

Results and discussion

The authors considered a specified point on the longitudinal axis of the sample and studied its shear strain variation along the deformation zone [17]. Theoretical calculation of the variation of shear strain along deformation zone was performed by γ = tan(α), where (α) is distortion angle which can be calculated at every section along the deformation zone [17]. A similar procedure can be performed to predict the theoretical variation of shear strain for the two processing routes A and B, as the

Conclusion

Four different processing routes (A–D) were introduced for deformation via simple shear extrusion process. These processing routes were analyzed in terms of their shearing characteristics and variation of hardness homogeneity across the sample's cross-section. In addition, the variation of shear strain along the deformation zone was also investigated. It was concluded that the variation of shear strain was the same in routes B and C while, the homogeneity was improved in route C due to 90°

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