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Semisolid Die Casting of Wrought A6061 Aluminium Alloy

Electronic Theses of Indian Institute of Science

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Title Semisolid Die Casting of Wrought A6061 Aluminium Alloy
 
Creator Kini, Anoop Raghunath
 
Subject Aluminium Alloys
Semisolid Die Casting (SSDC)
Aluminium Alloys - Semisolid Processing
Wrought Aluminium Alloys - Die Casting
Aluminium Alloys - Semisolid Die Casting
Non-dendritic Cast Billets - Casting
Wrought Aluminium Alloys
Semi Solid Processing (SSP)
Semisolid Die Cast
Metallurgy
 
Description The mechanical properties achieved with high performance wrought aluminium alloys are
superior to cast aluminum alloys. To obtain an intricate shaped component, wrought alloys are commonly subjected to forging followed by subsequent machining operation in the automobile industry. As machining of such high strength wrought aluminium alloys adds to cost, productivity gets affected.
Shortening the process by near net shaped casting would tremendously enhance productivity. However, casting of such alloys frequently encounter hot tear defect. Therefore, circumventing hot tear to
successfully die cast near net shaped wrought alloy components is industrially relevant. A recent advanced casting process, namely â€~Semisolid Die casting’, is proposed as a likely solution.
Hot tearing originates due to lack of liquid flow in the inter-dendritic region. To reduce hot tear susceptibility, fine and non-dendritic grain structure is targeted, amenable for processing by semisolid
route. For semisolid processing an adequate freezing range for processing is required. Accordingly A6061 wrought alloy whose composition is tuned with higher silicon and magnesium content within the grade limits, is chosen for the study.
With the objective of obtaining fine and non-dendritic microstructured billets, electromagnetic stirring (EMS) and cooling slope (CS) methods are employed. On conducting a parametric study with
EMS, a finest possible primary α-Al grain size of about 70 μm is obtained at low stirring time at stirring
current levels of 175 A and 350 A, with the addition of grain refiner. CS, on the other hand, rendered a grain of 60 μm at a slope length of 300 mm at a slope angle of 45° with grain refiner addition. Of the two methods, CS billets are chosen for subsequent induction heating. A 3-step induction heating cycle has been devised to attain a temperature of 641°C in the billet on the basis of factors including coherency
point, viscosity of the slurry and solid fraction sensitivity with temperature. The billet microstructure is found to be homogenous throughout after quenching in water. The characterization of phase along
primary α-Al grain boundary and its composition analysis is done by SEM and EPMA respectively, after billet casting as well as induction heating. In addition, the bulk hardness is determined in BHN.
The induction heated billets are semisolid die cast to produce an engine connecting rod used in automobiles. The microstructure is characterized at various locations, and is found to consist of smooth
α-Al grains in a background matrix of fine grains formed due to secondary solidification. The component
hardness is found to be 66 BHN comparable with A6061 alloy under T4 heat treated condition. X-ray radiography does not confirm presence of surface hot tear, which is the normal defect associated with casting of wrought aluminium alloys. No defects are observed along the constant cross-sectional area of the connecting rod, suggesting that the processing could be suitable for semisolid extrusion.Dutta, Pradip2018-04-02T17:13:00Z2018-04-02T17:13:00Z2018-04-022013Thesishttp://etd.iisc.ernet.in/2005/3317http://etd.iisc.ernet.in/abstracts/4181/G25683-Abs.pdfen_USG25683
oai:etd.iisc.ernet.in:2005/33182018-04-02T17:27:46Zhdl_2005_34Study of Droplet Dynamics in Heated EnvironmentPathak, BinitaNano Fluid DropletsDroplet DynamicsDroplets - AgglomerationDroplets - Dissociation KineticsNano Fluid Droplets - Heat and Mass Transport ModelingNano Silica Particles - DropletsCerium Nitrate Droplets - Chemical ReactionsConvectively Heated DropletsNano Fluid Droplets - VaporizationNanoparticlesDroplet Evaporation ModelDroplet VaporizationComputational Fluid Dynamics (CFD)NanotechnologyDroplets as precursor are extensively applied in diverse fields of science and engineering. Various contributions are provided previously towards analysis of single phase and multi-phase droplets of single and multiple components.
This thesis describes modelling of multi-phase (nano fluid) droplet vaporization. The
evaporation of liquid phase along with migration of dispersed particles in two-dimensional plane within droplet is detailed using the governing transport equations
along with the appropriate boundary and interface conditions.
The evaporation model is incorporated with aggregate kinetics to study agglomeration
among nano silica particles in base water. Agglomeration model based on population
balance approach is used to track down the aggregation kinetics of nano particles in
the droplet. With the simulated model it is able to predict different types of final
structure of the aggregates formed as observed in experimental results available in
literature. High spatial resolution in terms of agglomeration dynamics is achieved
using current model. Comparison based study of aggregation dynamics is done by
heating droplet in convective environment as well as with radiations and using
different combination of heating and physical parameters. The effect of internal flow
field is also analysed with comparative study using levitation and without levitation
individually. For levitation, droplet is stabilized in an acoustic standing wave.
It is also attempted to study the transformation of cerium nitrate to ceria in droplets when heated under different environmental conditions. Reaction kinetics based on modified rate equation is modelled along with vaporization in aqueous cerium nitrate droplet. The thermo physical changes within the droplet along with dissociation
reaction is analysed under different modes of heating. The chemical conversion of
cerium nitrate to ceria during the process is predicted using Kramers' reaction velocity
equation in a modified form. The model is able to explain the kinetics behind
formation of ceria within droplet at low temperatures. Transformation of chemical
species is observed to be influenced by temperature and configuration of the system.
Reaction based model along with CFD (computational fluid dynamics) simulation
within the droplet is able to determine the rate of chemical dissociation of species and
predict formation of ceria within the droplet. The prediction shows good agreement
with experimental data which are obtained from literature.Basu, Saptarshi2018-04-02T17:27:46Z2018-04-02T17:27:46Z2018-04-022013Thesishttp://etd.iisc.ernet.in/2005/3318http://etd.iisc.ernet.in/abstracts/4182/G25686-Abs.pdfen_USG25686
oai:etd.iisc.ernet.in:2005/33192018-04-02T17:36:19Zhdl_2005_34Optimal Synthesis of Adjustable Four-Link Planar and Spherical Crank-Rocker Type Mechanisms for Approximate Multi-Path GenerationVilas, Chanekar PrasadAdjustable Planar Four-Bar MechanismsAdjustable Spherical Four-Link MechanismsMultiple Path GenertionKinematicsAdjustable Four-Link Mechanisms - Optimal SynthesisFour-Link Mechanisms - KinematicsMechanisms (Engineering)Four-Link Mechanisms - Path GenerationPlanar Four-Bar MechanismSpherical Four-Link MechanismAdjustable Four-link Crank-rocker Type MechanismsPath GenerationMechanical EngineeringThe well known synthesis problem of obtaining dimensions of a four-link mechanism such that a point on the coupler link traces a desired path has been extensively studied. There are two types of path generation–path specified by a finite number of precision points where the prescribed points must be exactly traced, and continuous path generation where the path is approximately traced by the coupler point. In various application, more than one or multiple paths are required to be traced by the coupler point and in such cases, adjustable four-link mechanisms where one of the dimension or parameters of the mechanism can be changed is a possible solution. This thesis deals with the synthesis of planar and spherical adjustable four-link crank-rocker type mechanisms for multiple continuous path generation. Approximate multiple path generation is typically solved as an optimization problem where the dimensions and parameters of the four-link mechanism are obtained such that the objective functions, typically in terms of an error between the desired and obtained path, is minimized. In this thesis, we present a two-stage optimization to obtain four-link mechanism dimensions such that the adjustable four-link mechanism can approximately trace multiple desired paths. In the first stage, the parameters in the driving side of the four-link mechanism is obtained and in the second stage, the parameters of the driven side are obtained. In case of adjustable planar four-link mechanism, a novel optimization objective function based on circle-fitting is used and for spherical adjustable mechanisms a novel plane-fitting based objective function is used. The use of these objective functions results in a lesser number of variables to be searched and thus the method presented in this work is more efficient than existing optimization based algorithms available in literature. Several examples are presented for synthesis of adjustable planar and spherical four-link mechanism for tracing multiple paths. In particular, a spherical mechanism which can generate an oval and an‘ 8’shaped path by one single adjustment is synthesized. This mechanism has been made using 3D printing and it is shown that the mechanism indeed traces the desired oval and ‘8’ shaped paths. This mechanism is being planned for use in a flapping wing micro air vehicle where the oval shaped path is known to make the vehicle to move forward while the ‘8’ shaped path results in a hovering motion.
 
Contributor Ghosal, Ashitava
 
Date 2018-04-02T17:36:19Z
2018-04-02T17:36:19Z
2018-04-02
2013
 
Type Thesis
 
Identifier http://etd.iisc.ernet.in/2005/3319
http://etd.iisc.ernet.in/abstracts/4183/G25687-Abs.pdf
 
Language en_US
 
Relation G25687