Niraj Nayan

Processing and Characterization of Al-Cu-Li Alloy AA2195

The objective of the present study was to melt and cast AA2195 alloy in Vacuum Induction Melting (VIM) under dynamic inert atmosphere. These billets were homogenized and subsequently hot forged and rolled to sheets. The products in the form of sheets were subjected to T8 (Solution Treatment +WQ+CW+Aging) temper condition. Mechanical properties were evaluated at room temperature and correlated with microstructure. Highest mechanical properties obtained in T87 temper have been reported.

On the Possibility of Occurrence of Anisotropy in Processing of Cu-CNT Composites by Powder Metallurgical Techniques

Copper - multiwall carbon nanotubes (MWCNT) composite was processed by powder metallurgical processing technique. Pure copper powder and MWCNT were mechanically alloyed by high energy milling to produce Cu-MWCNT composite powder. The composite powder was subsequently consolidated by vacuum hot pressing. Characterization studies were conducted along axial (hot pressing direction) and radial (transverse) directions. Microstructural observations of the processed composite revealed random distribution of MWCNT in axial direction and aligned distribution in radial direction. The structure property correlation was established and it revealed certain degree of anisotropy in mechanical and electrical properties of the composite.

Optimization of Homogenization Parameters of Al-Cu-Li Alloy Cast Ingots Using Calorimetry and Metallographic Techniques

In the present study, thermal treatments for homogenizing cast structures of Al-Cu-Li alloy AA2195 for improved workability are developed chiefly by empirical methods and detailed Differential Scanning Calorimetry (DSC) and microstructural characterization. DSC has been carried out on as-cast samples to establish the homogenization temperatures and avoid incipient melting. Homogenization time has been calculated empirically and microstructural characterization and DSC has been carriedout to after each cycle to validate the empirically established homogenization cycle. Homogenization cycle (435°C/8hrs+495°C/12hrs+525°C/32hrs) has been established for AA2195 alloy having an average grain size of 500μm based on calorimetric studies and microstructural examination.

A study of reaction kinetics in Al – 2% MWCNT composites

A composite obtained from pure aluminum and multiwall carbon nanotubes by mechanical milling in a high-power mill and ultrasonic mixing is studied. The apparent activation energy and the order of the reaction between carbon nanotubes and aluminum are determined using the Kissinger and Crane equations and differential scanning calorimetry under non-isothermal conditions.

Electroless Coating of Silver on Multiwall Carbon Nanotubes

Silver reinforced with carbon nanotubes, instead of graphite, would increase both the electrical conductivity, hardness and wear resistance of the electrical brush materials. The effective utilization of carbon nanotubes in the Ag/CNT composite depends strongly on its uniform distribution and strong interfacial adhesion to the silver matrix and thus demands for its surface modification. In order to carry out the surface modification of carbon nanotubes, electroless coating was given to them after liquid phase oxidation, sensitization and activation process. The room-temperature chemical treatment results in a nominally complete coating over the entire outer surface of multiwall carbon nanotube. The surface morphology of the carbon nanotubes after each step has been studied using TGA, DSC, XRD, FTIR and SEM.

Processing and Characterization of AA2195 Al-Cu-Li Alloy Bars Processed through Vacuum Induction Melting and Caliber Rolling

A novel technique of pure Lithium addition has been adopted for the processing of Al-Cu-Li alloy AA2195 cast ingots (7-8 kg each) in VIM under dynamic inert atmosphere, which gives more than 95% recovery of Lithium. The cast billets were homogenized, forged and converted into 12mm diameter rods by caliber rolling in the temperature range of 250°C, 300°C, 350°C and 400°C. The caliber rolled rods were treated to T8 (Solution Treatment+WQ+CW+Aging) condition. Mechanical properties were evaluated for T8 tempered bars at room temperature and correlated with microstructural observations. Highest mechanical properties in T87 temper have been obtained for rods caliber rolled at 350°C temperature.

Development of Ti – 6Al – 4V Wire Rods for Fastener Applications

Multipass forging in dies is used to obtain thin rods 4 mm in diameter from alloy Ti – 6Al – 4V. The properties exhibited by the alloy in this process are described and the possibilities of making fasteners from it are considered. The high strain produced by warm swaging makes it possible to fabricate high-strength fasteners without the expensive and labor-intensive operations of solution treatment and aging.

Development of ultrafine-grained microstructure in Al-Cu-Mg alloy through equal-channel angular pressing

Al-Cu-Mg alloys are extensively used for riveting applications in aerospace industries due to their relatively high shear strength coupled with high plasticity. The significant advantage of using V65 aluminum alloy ((Al-4Cu-0.2Mg) for rivet application also stems from its significantly slower natural aging kinetics, which gives operational flexibility to carryout riveting operation even after 4 days of solution heat treatment, in contrast to its equivalent alloy AA2024.Rivets are usually made by cold heading of wire rods. In order to form a defect free rivet head, grain size control in wire rods is essential at each and every stage of processing right from casting onwards upto the final wire drawing stage. Wire drawing is carried out at room temperature to reduce diameter as well as impart good surface finish. In the present study, different microstructures in V65 alloy bars were produced by rolling at different temperatures (room temperature to 523K) and subsequently deformed by equal channel angular pressing (ECAP) at 423K upto an equivalent strain of 7. ECAP was carried out to study the effect of initial microstructure on grain refinement and degree of deformation on the evolution of ultrafine grain structure. The refinement of V65 alloy by ECAP is significantly influenced by Initial microstructure but amount of deformation strongly affects the evolution processes as revealed by optical microscopy and transmission electron microscopy.

Fabrication of high-strength Ti – 6% Al – 4% V titanium alloy by multipass warm rolling

A high-strength Ti – 6% Al – 4% V titanium alloy is studied after warm rolling at 650 – 750°C in several passes. Tensile mechanical tests are used to determine the rupture strength, the yield strength, and the elongation. The microstructure of the rolled alloy is investigated. Warm rolling is shown to be effective for forming superfine grains in the Ti – 6% Al – 4% V alloy and raising considerably the strength characteristics without lowering the ductility.

Processing of V65 Aluminium Alloy Wires Processed from Hot and Warm Rolled Rods for Rivet Applications

High shear strength of 25 kg/mm2 combined with a high plasticity makes Russian grade V65 aluminum alloys as potential candidate compared to AA2024 for riveting applications in aerospace industries. The lower content of magnesium over the AA 2024 alloy decreases the aging kinetics of this alloy because of the decreased vacancy concentration in the as-quenched alloy which in turn gives flexibility to carryout riveting operation even after 4 days after solution heat treat¬ment and natural aging at room temperature. This paper presents the processing and characterization of V65 aluminium alloy wires processed from hot and warm rolled rods. Mechanical properties of the wires have been evaluated in T6 and T4 tempers and correlated with microstructures. Detailed microstructural examination using optical microscopy and fractography of the tensile tested samples using scanning electron microscopy were carriedout.