The purpose of this study is to develop a series of response surfaces that define critical outcomes for welding in Al 7075 based on the tool geometry of a convex scrolled shoulder step spiral (CS4) friction stir processing tool. These response surfaces will be used to find critical minimums in forces which will decrease the required power input for the process. A comprehensive parameterization of the tool geometry is defined in this paper. A pilot study was performed to determine the feasibility of varying certain geometric features. Then a screening experiment eliminated those geometric features that were not as significant in determining the response surfaces. A central composite design with the five most important geometric features was used in order to develop response surfaces for nine different response variables. The nine response variables are the longitudinal, lateral and axial forces; the tool temperature, the spindle torque, the amount of flash, the presence of defects, the surface roughness and the ledge size. By using standard regression techniques, response surface equations were developed that will allow the user to optimize tool geometries based on the desired response variables. The five geometric features, the process parameters and several of their interactions were found to be highly significant in the response surfaces.

In this work, the Bauschinger effect is shown to be intimately tied not only to plasticity but to damage as well. The plasticity-damage effect on the Bauschinger effect is demonstrated by employing different definitions (Bauschinger Stress Parameter, Bauschinger Effect Parameter, the Ratio of Forward-to-Reverse Yield, and the Ratio of Kinematic-to-Isotropic Hardening) for two differently processed aluminum alloys (rolled and cast) in which specimens were tested to different prestrain levels under tension and compression. Damage progression from second phase particles and inclusions that were generally equiaxed for the cast A356-T6 aluminum alloy and elongated for the rolled 7075 aluminum alloy was quantified from interrupted experiments. Observations showed that the Bauschinger effect had larger values for compression prestrains when compared to tension. The Bauschinger effect was also found to be a function of damage to particles/inclusions, dislocation/particle interaction, the work hardening rate, and the Bauschinger effect definition.

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Additive Friction Stir Deposition (AFSD) is a solid state, bulk, metal additive manufacturing technology that seeks to replace certain castings and forgings wherever it is economically feasible among other applications. Critical to its deployment is an in depth understanding of how the solid state deposition process effects engineering alloys used in relevant applications. In this work, an aerospace aluminum alloy 7075 is evaluated both in the as deposited and heat treated condition via age hardening studies and tensile testing. It is found that an embrittlement phenomena occurs that is sensitive to processing parameters and quench rate during heat treatment. Through the use of SEM, TEM, and APT the embrittlement phenomena has been linked to excessive grain boundary precipitation caused by a combination of shear induced mixing and shear induced segregation which allow for the formation of phases at grain boundaries that are slow to dissolve, leaving the grain boundary in a non-equilibrium solute rich state. Critical to this process is the role of dispersoid particles, which are modified by shear processes which provide high energy spots for thermally stable precipitate nucleation. Removal of these dispersoid particles by an alloy modification had been shown to eliminate the embrittlement effect after depositing in a condition where embrittlement is expected for the unmodified 7075. Further work demonstrates the different relationships between processing conditions and the degree of embrittlement for three different tool types. Beyond the implications of the particular alloy studied, this work highlights the fundamental concepts involved when a manufacturing process operates at high strain rates and total strains which can be used for the design of alloys meant for AFSD. / Doctor of Philosophy / Additive Friction Stir Deposition (AFSD) is a new 3D printing process for metals where deformation is used to deposit material in an additive fashion. This work involves understanding and solving an embrittlement issue that occurs during heat treating after deposition for a particular aluminum alloy (7075). In this work, the origins of the embrittlement phenomena are uncovered which have to do with the degree and severity of deformation. Several solutions including alloy development and process control are successfully demonstrated.

Aluminum alloys are having more attention due to their high specific stiffness and processing advantages. 7075 aluminum alloy is a wrought composition aluminum alloy in the Al-Zn-Mg-Cu series. Due to the significant addition of these alloying elements, 7075 has higher strength compared to all other aluminum alloys and effective precipitation hardenability characteristic. On the other hand, aluminum alloys have some drawbacks, which hinder the widespread application of them. One of the most commonly encountered defects in aluminum alloys is the hydrogen porosity. Additionally, in case of 7075, another problem is the lack of fluidity. Magnesium addition is thought to be effective in compensating this deficiency. Accordingly, in this study, die cast 7075 aluminum alloy samples with hydrogen porosity and additional magnesium content were investigated. The aim was to determine the relationship between hydrogen content and hydrogen porosity, and the effects of hydrogen porosity, additional magnesium and T6 heat treatment on ultimate tensile and flexural strength properties of pressure die cast 7075 aluminum alloy. 7075 aluminum alloy returns were supplied from a local pressure die casting company. After spectral analysis, pressure die casting was conducted at two stages. In the first stage, 7075 aluminum alloy with an increase in magnesium concentration was melted and secondly 7075 aluminum alloy was cast directly without any alloying addition. While making those castings, hydrogen content was measured continuously before each casting operation. As a final operation T6 heat treatment is carried out for certain samples. Finally, in order to accomplish our aim, mechanical and microstructural examination tests were conducted.

Aluminum forging products has been increasingly used in automotive and aerospace industry due to their lightness and strength. In this study, aluminum forging processes of a particular industrial part for the two different alloys (Al 7075 and Al 6061) have been analyzed. The forging part, forging process and the required dies have been designed according to the aluminum forging design parameters. The proposed process has been simulated by using the Finite Volume Method. In the simulations, analysis of the part during forging process has been performed / and the required forging force, the temperature distribution and the effective stress distribution in the parts have been obtained. The forging dies were produced in the METU-BILTIR Center CAD/CAM Laboratory. The experimental study has been performed in the METU-BILTIR Center Forging Research and Application Laboratory. The parts were produced without any defects as obtained in the finite volume simulations. The results of the experiment and finite volume simulation are compared and it has been observed good agreement.

This thesis deals with relationship between tensile strength and hardness of aluminium alloys. The introduction provides an overview of aluminum aloys and their properties. In the following section there is an analysis of the processing of aluminum alloys. A large part is devoted to the course of precipitation hardening. The second part of the thesis contains a practical part, which describes the methodology of measuring hardness and tensile strength. The measurement process is described below. At the end, the measured data are processed into various graphs and their results are evaluated.

Slitiny hliníku řad 2XXX a 7XXX nejsou shledávány jako svařitelné s použitím tradičních metod svařování. Jsou však široce používány v leteckých a kosmických konstrukcích. Obvyklý způsob jejich spojování je pomocí nýtování. Nově vznikající technologie lineárního svařování třením rotujícím nástrojem (Friction Stir Welding - FSW) již ukázala slibné výsledky při svařování těchto slitin. V této práci jsme prozkoumali aplikace technologie FSW v leteckých konstrukcích zejména jako náhradu nýtování na panelech vyztužených stringery. Sestavili jsme výrobní postup pro daný panel a navrhli další kroky k jeho optimalizaci. Dále jsme sestavili znalostní bázi základních svařovacích parametrů a porovnali jsme nýtování a FSW na jednoduchém modelu využitím metody konečných prvků a s cílem identifikovat rozdíly v charakteru rozložení napětí v těchto vzorcích.

The effects of weld temperature, travel speed, and backing plate thermal diffusivity on themechanical properties of a weld have been studied. A face centered cubic experiment of designwas completed in which the response variables were yield strength, minimum hardness in the HAZ, and charpy impact toughness. Three models were created from the data gathered usinga stepwise regression in order to see the effects of each parameter. For the yield strength andminimum hardness it was found that only travel speed and backing plate thermal diffusivities werestatistically significant to the properties. The charpy impact toughness saw that all three parameterswere statistically significant to its value. In all three models the travel speed had the greatest affecton the material properties.

Friction Stir Welding (FSW) is an emerging joining technology in which basic process understanding is still inadequate. Knowledge of FSW parameter relationships is needed to better understand the process and implement proper machine control. This study utilized a 3-factor, 3-level factorial design of experiments to investigate relationships between key process inputs and measured output parameters. All experiments utilized 7075-T7 aluminum and a threaded pin tool with a 25.4 mm shoulder diameter, 4.76 mm pin length, and 7.9 mm pin diameter. Spindle speed, feed rate, and tool depth were varied throughout 54 welds while X, Y, and Z forces, X torque, three tool temperatures, and motor power were measured. Empirical models were developed to relate outputs to inputs. The relationships between inputs and outputs are nonlinear and require, at a minimum, a quadratic equation to reasonably model them. These models were further analyzed to explore possible control schemes. Tool depth was found to be the most fundamental means of controlling weld forces and tool temperatures. This research describes the input/output relationships enumerated above for FSW as well as a discussion of possible control schemes.