There is an increasing interest in the ultrafine-grained materials due to their exceptional properties [1–7]. It is well known that the reduction in grain sizes in metals and metal alloys has an effect on increasing the mechanical strength without decreasing the ductility properties as in the case of work hardening [8–10]. This advantage is of great interest in manufacturing metals and metal alloys with an extremely fine grain size [11–14].

Equal channel angular pressing (ECAP) is a severe plastic deformation technique that produces very fine-grained of bulk metallic materials. This is possible because the channels of the ECAP bend have identical cross-sections and, therefore, the extrusion can be repeated in order to introduce a high rate of deformation and ultimately refine the grain size to the theoretical limit imposed by the characteristics of the metal or metal alloy used.

The ECAP process, developed in the early 1980s by Segal et al. [15], involved extruding a sample through a die with two channels of equal cross-section forming a bend at their intersection. Figure 1 shows a schematic of an ECAP die at a 90° bend. The sample, forced to move from the inlet channel to the outlet channel, undergoes a large deformation by simple shearing at the plane of intersection of the two channels. The considerable interest in the ECAP process is widely reported by Beyerlein and Toth [16]. This interest is mainly due to the ability of ECAP to control the microstructure and properties of crystalline metals.

The equivalent plastic deformation is given by the formula proposed in 1996 by Iwahashi et al. [17]:

\({\epsilon }^{P}\) = \(\frac{1}{\surd 3}\)[2cot(\(\frac{\phi }{2}\)+\(\frac{\varPsi }{2}\))+Ψcosec (\(\frac{\phi }{2}\)+\(\frac{\varPsi }{2}\)) (1)

The deformations accumulate after each pass through the extruder, therefore the equivalent deformation obtained after N cycles is:

\({\epsilon }^{P}\) *total*= *N*𝜀𝑝

More recently, Goforth et al. [18] simplify Eq. (1) to:

\({\epsilon }^{P}\) = \(\frac{1}{\surd 3}\)[2cot(\(\frac{\phi }{2}\)+\(\frac{\varPsi }{2}\))+Ψ] (2)

An investigation was carried out by Aida et al. [19] to compare the equations (1) and (2). They showed that they are quasiequivalent. Indeed, for the extremities of ψ (with φ fixed) the value of 𝜀𝑝, is the same, as for the intermediate values taken by ψ, the variation in deformation does not exceed 5%

In ECAP, the specimen can be re-injected a large number of times into the die and a high strain rate can be achieved [20]. The way in which the ingot is re-introduced into the die is called the deformation route. Although many routes can be theoretically defined for practical purposes, four fundamental routes are exploited by researchers [21] (Fig. 2)

In order to understand the nature of grain refinement to deformation associated with N passes, and in particular the influence of the processing route, it is necessary to study the shear plane processes that develop in each specimen during repeated passes through the die. These patterns take the form of the dominant shear directions, for the classical routes A, B and C[21–23]. In the Bc route, the two shear directions lie on planes that intersect at 120°. In contrast, road A has two shear planes that intersect at 90°. Road C is subjected to shear deformation in the same plane but the direction of shear is reversed after each pass.

In this work, we investigated the extrusion of commercially pure A1100 aluminum, which is widely used in deep drawing. In order to monitor the effect of preliminary strain hardening on grain refinement, we rolled the test specimens at a thickness reduction rate of Ɛ=60% in one pass