Bulk nanostructured processing of aluminum alloy

Severe plastic deformation (SPD) is an efficient approach for the production of bulk ultra-fine grained or nanostructured materials that involves plastic deformation to very high strain. The Equal Channel Angular Extrusion (ECAE) is a deformation process, which realizes the concept of SPD as such that the above-mentioned structures can be obtained. In this paper, the experimental research on multi-pass ECAE process of a widely used aluminum 6061 alloy is conducted and the mechanical properties after ECAE process are investigated. To study the effect of pre-extrusion heat treatment on the mechanical properties, different heat treatment scenarios are conducted to obtain un-aged and aged samples. Sixteen passes of ECAE process at room temperature are done without any rotation of the workpiece and the relationship of mechanical properties with number of extrusion passes was identified. In addition, mechanical properties including yield strength (YS) and the strain hardening exponent after the processing are investigated to determine the effect of the number of ECAE passes on the mechanical properties of the extruded samples. Results of the uniaxial tensile testing reveal that the YS of un-aged samples increased by ∼70% while aged samples exhibit an increase of ∼150% in YS after four passes of ECAE. There is a significant increase in the strain hardening exponent of the samples subjected to the different heat treatment configurations due to severe plastic deformation after multi-pass ECAE. The fracture surface of the tensile bars after uniaxial tensile testing was examined using scanning electron microscope (SEM) and the comparison of the fracture surfaces of the un-aged and aged specimens were presented.