Shahin Khoddam

Hybrid metallic composite materials fabricated by sheathed powder compaction

A new process, sheathed powder compaction (SPC), was proposed to fabricate hybrid metallic composite samples at room temperature. The process involves densification of fine powder in an annulus sheath under combined moderate pressure and shear. Hybrid samples of copper annular with aluminum powder were produced to demonstrate the merits of the process. The fabricated samples were characterized and explored using electron microscopy, micro hardness, micro shear punch tests and density ratio measurements. Comparing “shear punch response” of the samples in the Al region with those of commercially pure aluminum and Al 5005-H34 samples showed an excellent shearing strength in the region. The electron backscatter diffraction analyses and scanning electron microscopy observations suggested that the substantially enhanced strength was facilitated by a significant SPC induced grain refinement. Moreover, the annular sheath (copper) also showed significant grain refinement due to the process. These demonstrated promising potentials of the SPC to manufacture hybrid metals with concurrent grain refinement at room temperature under moderate processing conditions.Graphical Abstract

Mechanical and Microstructural Characterization of Aluminum 6061 Processed by Plane Stress Local Torsion

The process of plane stress local torsion (PSLT) has been recently proposed as localized severe plastic deformation to enhance the mechanical properties of the fastener holes. The PSLT process can create large shear strains and, consequently, substantial grain refinement in the vicinity of the hole with a gradient in the radial direction. It is of great interest and importance to investigate the effect of the PSLT process on a range of materials commonly used in the industry. An introductory investigation of mechanical and microstructural properties of Al6061 samples processed by the PSLT is performed in this work. The PSLT is simulated using the finite-element method, and the torque twist curves obtained from finite-element simulations are compared with experimental measurements. Microstructural changes and the extent of grain refinement are investigated by means of optical microscopy. It is shown that the PSLT is responsible for a considerable improvement in the mechanical properties within the deformation zone. The microhardness tests were used to measure the degree of enhancement in ultimate and yield strengths of the material processed by the PSLT.