Continuous Grain Refinement of Pure Aluminum During Cyclic Contraction/Expansion Extrusion (CCEE) Analyses by Micromechanical-Based FE and Experimental Methods

Severe plastic deformation (SPD) has become an efficient route for producing ultrafine-grained and nanostructured high-strength metallic materials. The present study investigates the feasibility of synthesizing rod-shaped nanostructured pure aluminium samples with the newly presented severe plastic deformation (SPD) method called cyclic contraction/expansion extrusion (CCEE). Also, the deformation characteristics of this process were studied using both micromechanical-based finite element simulations and experimental methods. Tensile test results showed a noticeable increase in yield and ultimate tensile strength values to 155 MPa and 191 MPa from the initial values of 56 MPa and 112 MPa, respectively, after the second pass of CCEE processing. The microhardness measurements showed a significant increase in hardness values to 61 Hv from the initial value of 27 Hv at the end of the first and second passes of CCEE. Results showed that the proposed technique is an efficient SPD method capable of imposing severe stains in the order of 20 after six repeated cycles. The constitutive micro-mechanical approach was implemented to predict microstructure evolution during CCEE processing. The UFG cylindrical aluminium samples with a mean grain size of 480 nm at the end of the first pass and 360 nm at the end of the second pass of CCEE were processed from the initial grain size of ~55 μm. The XRD-obtained grain sizes were consistent with the FEM-predicted values.