Dissertations/Theses - Department of Materials & Metallurgical Engineering

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Subject: search.filters.subject.Aluminum alloys

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    In situ aluminium based dual matrix hybrid composite through powder metallurgy route for automotive industries
    (Department of Materials and Metallurgical Engineering (MME), 2023-03-22) Tasratur Reaj, Neha; Gulshan, Dr. Fahmida
    In recent times, the focus of researchers worldwide has shifted from monolithic materials to composite materials, primarily due to the need for high performance and affordable materials. Amongst the various types of composite materials, aluminum metal matrix composites (AMMC) are an excellent choice for manufacturing high-specific-strength automotive components, as well as for various mechanical and tribological applications. They are preferred over other materials because of their lighter weight, which is around one-third as much as steel per cubic meter. This property not only ensures more energy-efficient automobiles but also facilitates their production at a lower cost.This study was carried out to attain a deeper understanding of the structural performance of AMMCs. For this purpose, a simple Al-H3BO3-TiO2 system was utilized for AMMC production through ball milling, cold pressing, and sintering. The ball milling process was found to have a considerable impact on particle growth, and the in situ generated reinforcements provide several benefits, including strong bonding and clean particle-metal interface. During the sintering procedure, reinforcement particles were created and uniformly distributed throughout the Aluminium matrix. AMMC's dual matrix structure was observed to perform as a desired characteristic, increasing both ductility and toughness.The percentage of added external aluminum varied from 0% to 25% to 50% to 75% of the total sample. Differential thermal analysis of the green sample was performed up to 800°C, which indicated that the particle development took place after 550°C. Consequently, the sintering temperature was chosen from 600°C to 800°C. Initial microstructural analysis was carried out using optical microscopy, while scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques were utilized to examine the morphological and structural reinforcing effects of AMMCs.The presence of various in situ reinforcements, including γAl2O3, AlB2, B2O3, TiB2, and TiAlin aluminum matrix was confirmed through X-ray diffraction (XRD) analysis.The mechanical properties were evaluated using a diametral compression tester and a Brinell hardness tester. It was observed that hardness increased with higher sintering temperatures. The sample sintered at 800°C with 0%unmilled aluminum exhibited the highest hardness of 169.2 HV. The results showed that the highest toughness, approximately 6.12 J/m-3, was found in the 75% external aluminum dual matrix compositessintered at 800°C.
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    Effect of copper to magnesium ratio on precipitation induced anisotropy during ageing of recrystallized Al-Zn-Mg-Cu alloy
    (Department of Materials and Metallurgical Engineering, 2020-03-11) Uddin, Md. Jasim; Rashed, Dr. H. M. Mamun Al
    High strength Al–Zn–Mg–Cu alloys (7xxx series aluminium alloys) have been widely used in military and aerospace industries due to high strength, easy formability and low density. Other important properties that must be considered for these applications are strength, ductility, modulus, corrosion and damage tolerance (e.g. fracture toughness and fatigue resistance). Most of these properties can be controlled through appropriate alloying, processing or a combination of these. Age-hardenable 7xxx series aluminium alloys for high-performance structural applications are typically processed in the form of plates, extrusions or forgings. For thick plate products, a typical processing schedule involves casting, homogenising, hot rolling, solution treating, quenching and age hardening. In this work, the effects of variation of Mg and Cu contents in some predefined ratios on the microstructures and mechanical properties of a 7xxx alloy both in longitudinal and transverse directions were studied. Initial cast and homogenised microstructure revealed dendritic structure which was lost completely during hot rolling. After hot rolling, solution treatment and ageing responses were observed at different temperature and time combustions. Interestingly, it was found that under same ageing condition, hardness and strength of the alloys were predominantly controlled by magnesium content, attributed to η-phase. Albeit similar behaviour was shown by copper content, the response was not as effective as that obtained with higher amount of magnesium. From microstructural analysis in optical microscopy and scanning electron microscopy, it can be asserted that higher magnesium to copper ratio yielded higher amount of second phase particles, which was validated by thermodynamic modelling of microstructural phases. In both longitudinal & transverse directions, better mechanical properties (ultimate tensile strength and hardness) were found for the alloy having Cu/Mg ratio of 1.32, owing to S-phase. Along longitudinal direction, fracture surfaces were heavily dimpled, and intergranular features were found that yielded better ductility with high UTS value for alloy of 1.32 Cu/Mg ratio. Along transverse direction, microstructure investigation revealed transgranular and cleave features, attributed to stable S-phases.
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    Finite element analysis of modified high strength aluminium alloys using progressive failure algorithm
    (Department of Materials and Metallurgical Engineering, 2020-03-11) Hossain, Md. Faisal; Shorowordi, Dr. Kazi Md
    The primary objective of this thesis was to develop a reliable finite element analysis procedure to model the complete fracture of ductile specimens using the progressive degradation of the material stiffness algorithm under tensile load. The ductile specimens in this study were three different aluminum 7075 alloys. Another objective was to establish the structure and property relationship of these alloys. The progressive failure algorithm used here was based on the assumption that the material behaves like a stable progressively fracturing solid. The stiffness reduction was carried out at the integration gauss points of the finite element mesh depending on the mode of failure. A number of material properties were necessary for such simulation to carry out and experimentation of the alloys were needed to evaluate these properties. The actual tensile tests data were applied to the finite element simulation. A renowned finite element analysis software Abaqus was used in this study. Besides, different tests were carried out to evaluate the structure-property relationship. It was found that the addition of alloying elements changed these alloys to obtain higher strength, hardness, and toughness. Effects of different mesh sizes on the mode of failure were also investigated. As the mesh sizes became smaller the time required for simulation increased but yielded results closer to the actual tensile test failure. Selected simulation results were verified by comparing true stress with von Mises stress in Abaqus. Computed stress triaxialities were also evaluated in various points on the modeled tensile test samples. Highest stress triaxialities was found near the failure zone of these modeled samples. The verified simulation method has a great importance in practical design of structures and materials.
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    Relationship between microstructure and cold deformation behavior of aluminum alloys using thermodynamic modeling method
    (Department of Materials and Metallurgical Engineering (MME), 2013-06) Nazia Nafsin; Mamun Al Rashed, Dr. Hossain Mohammad
    The current work emphasizes establishment of relationship between microstructure and cold deformation behavior of aluminum-copper -magnesium alloys. Aluminum-coppermagnesium alloys with varying Cu% and Mg% were casted and undergone cold deformation after homogenization, and their microstructures were examined using optical microscope. Using CALPHAD method, phases developed for different levels of Cu and Mg were modeled in JMatPro software package. It has been found that the prediction performed in equilibrium condition matches closely to phase fraction simulation. It can predict several extra phases in comparison to the equilibrium simulation. Image analysis by ImageJ also confirms this finding experimentally. Finally, the effects of deformation were studied by measuring the hardness of those alloys. From this study it was possible to predict the weight fractions of phases formed during solidification and homogenization using CALPHAD modeling. EDX results confirmed the formation of Al2Cu phase (white phase) and Al7Cu2M and Mg2Si phases (black phases) as modeled in CALPHAD. With increasing amount of copper and magnesium in the binary aluminum-copper alloy system, fraction of Al2Cu, Al7Cu2M, Al2CuMg and Mg2Si phases increased which increased hardness values. However, those additions lowered liquidus and solidus temperatures of alloys as investigated from DTA and modeling. The phase fractions of different alloys obtained from CALPHAD were verified using image analysis techniques. Image analysis data showed a convincing conformation of phases that formed during solidification and through solid state diffusion. Homogenization and solution treatment had a negative effect on the hardness values of investigated aluminum alloys due to dissolution of Al2Cu and Mg2Si phases in to the aluminum matrix. On the other hand, deformation increased the number of dislocations by interactions of dislocation during deformation and other defects, which caused an enhancement of hardness values. Deformation also causes microstructural changes by destroying the necklace like shape of Al-Cu-Mg phases initially obtained in as-cast and homogenized alloys. For this reason, with larger amount of deformation, the increment of hardness may not be very significant. After comparing the effects of all the processing parameters i.e. homogenization, deformation and alloy addition on hardness, it was revealed using ANOVA modeling, that magnesium addition and amount of deformation affects hardness of Al-Cu-Mg alloys to a large extent compared to addition of copper and homogenization.
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    Effects of copper and nickel on the structure and properties of heat treated AI-6Si-0.5Mg alloy
    (Department of Materials and Metallurgical Engineering (MME), 2014-05) Abul Hossain; Kurny, Dr. ASW
    The purpose of this research was to investigate the influence of copper and nickel on Al-6Si- 0.5Mg alloy. Copper in the range of 0.5 - 4 wt%, individual nickel 2wt% and combined 2wt%Cu and 2wt% Ni have been added to Al-6Si-0.5Mg alloy by melt processing technique. The cast alloys were subjected to homogenization at 500oC for 24 hours. The homogenised alloys were solution treated for 2 hours at 540oC and quenched in ice-salt-water solution. The evolution of microstructure and mechanical properties during heat treatment was studied. The temperature ranges of interest were; solution treatment at 540°C, natural ageing at room temperature, and artificial ageing at 100-400°C. The changes in dendritic composition and eutectic morphology due to solution treatment were quantified by optical and scanning electron microscopic analysis. For the ageing investigations, characterisation of mechanical properties was done by hardness, resistivity and tensile testing. Artificial and isochronal ageing was conducted in an electric furnace. Isochronal ageing was conducted at 100, 150, 175, 200, 225, 250, 300, 350 and 400oC for 1 hour. For all alloys, the hardness increase was remarkable in the temperature range of 200-250oC and maximum hardness was found at ~225oC. The electrical resistivity of the alloys was found to decrease significantly at 225oC. The isothermal ageing was carried out at 150, 200, 225, 250 and 300oC for time ranging from 15 minutes to 360 minutes. For all alloys under investigation, significant improvement of hardness was achieved by ageing for ~60 minutes at 225oC. Optical Microscopes (OM) and Scanning Electron Microscopes (SEM) were used for the microstructural investigation. The morphology of the intermetallic phases were observed in the as-cast and the heat treated samples. The Cu and Mg-rich intermetallics completely dissolved but the Ni-rich intermetallics did not dissolve completely during solutionising. The eutectic Al- Si phases were modified after homogenization and solution treatment. The aged samples were tested for tensile properties. Tensile tests were performed at a constant strain rate of 10-3s-1 for all ageing conditions. In addition, the peakaged samples (1hr at 225oC) were tested at three different strain rates of 10-2s-1, 10-3 s-1 and 10-4s-1. Tensile strength was found to increase with ageing temperature, the maximum being attained at peak aged condition (1 hr at 225oC). The additions of Cu and/or Ni resulted in an increase in tensile strength and maximum strength was found for 2 wt% Cu addition. The strain rates affected the tensile properties