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In FSW, tool pin profile has a significant contribution on mechanical and microstructural properties of metallic joints. In the present work, various pin profiles such as conical, pedal, cylindrical with thread, triangular, square and pentagonal pins are used to join the AA2024 plates. Mechanical and microstructural characterization is done for welded plates using different pin profile tools. The mechanical properties such as percentage elongation, ultimate tensile strength (UTS), microhardness and impact strength are significantly improved, when plates are joined using square pin profile. The obtained joint efficiency is 78% using square pin profile tool. The percentage elongation, UTS and impact energy of joint made by square pin tool are measured as 15%, 362 MPa and 5.7 Joule, respectively, which are higher than the values obtained using other pin profiles. EBSD analysis was performed to know the microstructural changes, which are a cause of mechanical properties alteration. Analysis reveals that stirred zone exhibits the recrystallized fine grains with equiaxed structure, which is a result of dynamic recrystallization and heating during plastic deformation of the zone. Large fraction of HAGB is also observed in stirred zone, which is a cause of improved mechanical properties of the joint.

The effect of relative density (RD) and shape of the space holder on microstructural characteristics and compressive behavior of open-cell aluminum foams (OAFs) have been studied. OAFs with tailored porous morphologies (50–81%) were successfully prepared through space holder technique using spherical shape carbamide and cubic shape sucrose space holders in various amounts. Al powder and space holders were mixed with 2 wt% of polyvinyl alcohol (PVA) binder solution, compacted at 300 MPa and finally sintered at 650 °C for 3 h. It was observed that the microstructural characteristics of OAFs varied in accordance with the shapes of space holders. The results reveal that the OAFs prepared with carbamide show smooth microstructure, higher plateau stress (~3 times), higher energy absorption (~3 times) and higher Young's modulus, but lower densification strain, compared to the OAFs prepared with sucrose. The Young's modulus, plateau stress, and energy absorption of OAFs, follow the power-law relationship as a function of its RD irrespective of the shape of space holders. The thermal conductivity of Al-carb and Al-suc OAFs are noted to be not much in variation irrespective of the shape of the pores.

The present investigation deals with the development of AA-7075 metal matrix composites reinforced with nano yttria particles (0.1 to 3 vol.%) and micron yttria particles (1 to 15 vol.%) by powder forging. Matrix powders (AA-7075) and reinforcement powders (yttria) were blended, cold compacted, sintered under pure nitrogen, and finally hot forged in a closed floating die. The hot forged samples were artificially age hardened at 121 °C for various time durations to determine the peak aging time. The mechanical properties in the peak-aged condition as well as density and microstructure were determined and correlated with the reinforcement size and content. The nano composites exhibited a well-densified structure as well as better hardness and tensile/compressive strength as compared to micro-scale composites. The mechanical properties in nano-scale composites peaked at 0.5 vol.% yttria addition while for micro-scale composites these properties peaked at 5 vol.% yttria addition.

The present investigation deals with the microstructural evolution attained during hot forging of Al 7075 prealloyed powders at various temperatures and strains. Preforms were fabricated by uniaxial compaction at 350 MPa followed by sintering at 610 °C for 40 min in nitrogen atmosphere. Sintered preforms were subsequently hot forged at various temperatures (0.6, 0.7, 0.8 and 0.9 T m ) and under various strains (0.51, 0.92 and 1.14). The effect of strain at various forging temperatures on the particle morphology, interparticle porosity, prior particle boundary (oxide layer) and hardness has been investigated. It was observed that a temperature of 0.8 T m and a true strain of 0.92 is required for the disruption of oxide layer during hot forging of the powder preforms. The hardness values reveal that the strain of 0.92 is sufficient for optimum deformation and consolidation of the particles even at lower forging temperatures of 0.6 T m .