Experimental study on the effects of Cyclic expansion extrusion on the Microstructural and mechanical Properties of al 6063 alloy

Abstract

Cyclic expansion extrusion (CEE) is a recently developed severe plastic deformation method, used in the production of ultrafine grained (UFG)/bulk nano-structured (BNS) metals from coarse grained metals. This is an efficient technique for the generation of UFG / BNS in rods and bars. Inhomogeneity in grain refinement is the main problem seen in the severe plastic deformation (SPD) methods. Imposing the necessary strain without rack/fracture on the sample is another concern. The main factors influencing imposed strain are the processing temperature, die profile and pressing ram speed. In this current research work, CEE processing was used for developing the UFG structure in AA 6063 alloy and the resulting mechanical properties are reported. Grain refinement depends on the imposed strain, which, in turn is dependent on the die profile, temperature and velocity of pressing. Processing temperature is a very important variable which directly controls the grain refinement. So, the CEE experiment was conducted at three different processing temperatures, namely, 260°C, 200°C and 130°C and pressing velocity of 0.5mm/s and semi-die angle (and#945;) of 22.5°. H13 tool steel was used in the fabrication of the CEE split dies. Net dimensions were achieved by the use of CNC lathe machining. The effects of plastic deformation on the microstructural and mechanical properties were examined after every two passes, by determining the hardness and strength properties. Microstructure analyses were done via Electron Back Scattered Diffraction (EBSD) and Transmission Electron Microscopy (TEM). Effects of processing temperatures were correlated with the microstructure and mechanical properties by means of EBSD and TEM images. Processing at 130°C temperature increases the microhardness and UTS values by 1.5 times. newline