In this study, firstly, in order to achieve fine grains in solid solution strengthened AZ31 magnesium alloy by friction stir processing (FSP), various efforts have been made. It has found that with a newly designed cooling system, the microstructure of commercial AZ31 alloy can be refined dramatically by carefully controlling the FSP parameters. It is of scientific interest that nanometer grains have been observed in the resultant microstructure for the AZ alloy experienced by two-pass FSP. Besides, in order to modify the microstructure and mechanical properties, FSP is also applied to incorporate AZ31 Mg alloy with nano-ZrO2 particles, nano-SiO2 particles and different fractions of Al and Zn elements. The microstructure and mechanical properties of the modified alloy and composite samples are investigated and compared. By one-pass FSP coupled with rapid heat sink from liquid nitrogen cooling approach, the ultrafine grain size in AZ31 Mg alloy is successfully achieved. The grain boundaries are well defined and the mean grain size can be refined to 100~300 nm from the initial 75 £gm of commercial AZ31 Mg alloys sheets. The ultrafine grained structure can drastically increases the microhardness from the initial 50 up to 120 Hv, or an increment factor of 2.4 times. Furthermore, the nanometer grains can be even achieved by two passes FSP coupled with rapid heat sink. The resulting microstructure exhibits equiaxed grains ranging from 40 nm to 200 nm with an average grain size of less than 100 nm. The nanocrystalline grains can be characterized by the TEM observations and the diffraction rings in SAD patterns. The highest hardness point can reach ~150 Hv which is equal to triple of the AZ31 matrix, and the mean hardness also increases up to around 134 Hv. Bulk Mg-AZ31 based composites with 10~20 vol% of nano-ZrO2 particles and 5~10 vol% of nano-SiO2 particles are also successfully fabricated by FSP. The average grain size of the resultant composites could be effectively refined to 2~4 £gm, and it demonstrates much higher hardness values compared to commercial AZ31 billet. Moreover, for the Mg/ZrO2 composite fabricated by one pass and subsequent cooling pass FSP, the recrystallized grain size could be further refined to 0.4 £gm with the hardness value of 135 Hv. As for multi-element Mg base alloys fabricated by FSP, high fractions of Al and Zn elements can result in apparent grain refinement, this can be proved by the broadening of diffraction peaks. Multi-passes FSP can induce the appearance of intermetallic compounds, however, some of them are quasi-crystals with icosahedral point group symmetry. The average hardness of the resultant alloys reachs nearly 350 in Hv scale due to the generation of intermetallic compounds and grain refinement.

Friction Stir Processing (FSP) has the potential for locally enhancing the properties of Al-Si alloy castings, for demanding applications within the automotive industry. In this thesis, the effect of FSP has been examined on three different cast Al-Si alloys:i) A Hypoeutectic Al-8.9wt%Si Alloyii) A Hypereutectic Al-12.1wt%Si Alloyiii) A Hypereutectic Al-12.1wt%Si-2.4wt%Ni AlloyThe influence of different processing parameters has been investigated at a fundamental level. Image analysis of particle size distributions and growth method of tessellation were used to quantify the level of particle refinement and the homogeneity of the second phase spatial distribution. Stop-action experiments were also carried out, to allow the microstructural changes around the tool during FSP to be studied. Two computer models have been explored, in order to predict the temperature distribution and the material flow behaviour. Furthermore, the stability of the microstructure of the friction stir processed material was studied after being heat treated at elevated temperatures. The changes in particle size and grain structure were examined, hardness measurements were taken across the PZ, and tensile testing were carried out at room and elevated temperatures.After FSP, the microstructure of the cast Al-Si alloys was greatly refined. However, differences in microstructure have been observed throughout the PZ, which tended to be better refined and distributed on the advancing side, than the retreating side of the PZ. Changing the processing parameters also influenced the size and spatial distribution of the second phase particles. By studying the changes in microstructure around the tool from the stop-action experiments, and comparing the results to the thermal distribution and material flow behaviour predicted by the computer models, it has been shown that the flow stress, pitch, and temperature of processing, all needed to be considered, when determining the effects that FSP have on the microstructure. FSP caused very little changes to the hardness of the material, while tensile properties were greatly improved, due to the elimination of porosity and refinement of large flawed particles. In terms of the stability of the microstructure after FSP, particle coarsening and abnormal grain growth has been observed during high temperatures heat treatment. Furthermore, the Al2Cu phase was found to dissolve into solid solution at elevated temperatures, so GPZs and solute clustering can then develop within the alloy during natural ageing.

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.

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Yes / In this study, a new double pin tool was utilized for the development of AA6061/316 stainless steel reinforced composite by employing the friction stir processing technique for the first time. The microstructure, hardness, tensile, tribological, and corrosion behaviors of the fabricated composites were investigated and comparative assessments were made with the results obtained from the single-pin tool. The results showed that particle-matrix reaction did not occur in the composites irrespective of the nature of the tool profile. The double-pin tool outstandingly boosted the grain refinement (7.01–5.78 μm), particle fragmentation, and distribution within the Al matrix due to the additional pin-assisted plastic deformation, high straining, dynamic recrystallization, and Zener pinning effects. The double-pin tool improved the microhardness (127–141 HV), tensile strength (162–233 MPa), and corrosion resistance of the composite with respect to the single-pin tool counterparts. The replacement of the single pin tool with a double pin tool diminished the specific wear rate (0.38–0.22 mm3/Nm) of the composite. The double-pin tool has a favourable impact on the structure, mechanical, and corrosion behaviours of the AA6061/316 stainless steel reinforced composite. It is thus recommended for composite development.

Esta tese tem por objetivo determinar a estampabilidade de chapas de alumínio 5083 O processadas pelo processo de fricção e mistura (PFM). Para atingir os objetivos propostos o processo de fricção por mistura foi estudado e uma ferramenta de soldagem PFM construída, a verificação da qualidade da solda foi realizada com metalografia da região processada para verificar a presença de vazios, obtidas as melhores condições a superplasticidade através do processo PFM é estudada com os ensaios de tração a quente e de saltos. Ensaios de tração a frio foram realizados nos corpos de prova com o processamento e sem o processamento com o objetivo de obter a curva tensão versus deformação do material processado e sem processamento. Foi efetuado o ensaio de microdureza da região soldada. A estampabilidade das chapas foi verificada através do ensaio de expansão hidrostática e empregadas na determinação da conformabilidade das chapas processadas e sem processar. Os ensaios de expansão hidrostática foram realizados em software de elementos finitos com o objetivo de comparar os resultados práticos e teóricos. Este estudo simulou pelo método dos elementos finitos a determinação da curva limite de conformação de chapas de alumínio 5083 O processadas através do processo PFM. A simulação de elementos finitos implicou em utilizar o método não linear e os softwares MSC MARC e Abaqus para simulação. Determinou-se neste estudo que a resistência à tração de chapas após processo PFM é 30% maior do que sem processamento, a estampabilidade à frio das chapas manteve-se a mesma. Os testes práticos determinaram que os softwares Abaqus e MSC MARC possuem boa aproximação para o teste de expansão hidrostática à frio. O Software Abaqus apresentou dificuldades para convergir e tempo de processamento muito superior ao MSC MARC nos estudos de expansão hidrostática à frio e na condição superplástica. Através dos ensaios de saltos determinou-se que a condição 328 rpm e 65 mm/min possui coeficiente de sensibilidade à taxa de deformação m muito superior ao do alumínio 5083 O sem PFM, isto resultou em uma melhor distribuição de espessura da chapa após o ensaio de expansão hidrostática superplástico em software. / The aim of this study is to determine the sheet metal formability of 5083 O aluminum sheets after friction stir processing \"FSP\". To achieve the proposed objectives the friction stir processing was be reviewed and modeled in order to enable the design and manufacture of a proper FSP tool. The quality of the process was carried out through metallographic tests of the FSP region looking for the presence of voids. The best conditions for plasticity and superplastic forming after FSP was studied by means of an approach of jump steps in the hot tensile tests, looking for a coefficient of strain rate sensitivity. The micro hardness tests and tensile tests at room temperature were carried out for the specimens with and without FSP processing in order to characterize their material mechanical behavior. The formability of the FSP blanks was evaluated through Bulge tests. The results enable to plot Forming Limit Curves friction stir processed blanks after FSP and without FSP. The numerical simulation of the Free Bulge tests was carried out using a Finite Element Method model in order to compare the numerical theoretical and experimental practical results. The numerical simulation approach allows for the determination the forming limit curve of 5083 O aluminum sheets processed by the FSP process. The Finite Element Method modeling and simulation have employed two nonlinear FEM codes: the MSC MARC and Abaqus were compared as software for the simulations. The Yeld Strength of specimens with FSP increased 30% in comparison with specimens without FSP in cold tensile tests, the formability of shapes with and without FSP was de same. The practical tests showed that Abaqus and MSC MARC results has a good approach, the processing time in Abaqus was much greater than in MSC MARC, Abaqus had convergence problems when contact condition is applied. Through the jump tensile tests the 328 rpm and 65 mm/min condition showed a m factor much higher in comparison with condition without FSP in AA 5083 O, this results led in a better thickness distribution after the superplastic bulge test in software.

Esta tese tem por objetivo determinar a estampabilidade de chapas de alumínio 5083 O processadas pelo processo de fricção e mistura (PFM). Para atingir os objetivos propostos o processo de fricção por mistura foi estudado e uma ferramenta de soldagem PFM construída, a verificação da qualidade da solda foi realizada com metalografia da região processada para verificar a presença de vazios, obtidas as melhores condições a superplasticidade através do processo PFM é estudada com os ensaios de tração a quente e de saltos. Ensaios de tração a frio foram realizados nos corpos de prova com o processamento e sem o processamento com o objetivo de obter a curva tensão versus deformação do material processado e sem processamento. Foi efetuado o ensaio de microdureza da região soldada. A estampabilidade das chapas foi verificada através do ensaio de expansão hidrostática e empregadas na determinação da conformabilidade das chapas processadas e sem processar. Os ensaios de expansão hidrostática foram realizados em software de elementos finitos com o objetivo de comparar os resultados práticos e teóricos. Este estudo simulou pelo método dos elementos finitos a determinação da curva limite de conformação de chapas de alumínio 5083 O processadas através do processo PFM. A simulação de elementos finitos implicou em utilizar o método não linear e os softwares MSC MARC e Abaqus para simulação. Determinou-se neste estudo que a resistência à tração de chapas após processo PFM é 30% maior do que sem processamento, a estampabilidade à frio das chapas manteve-se a mesma. Os testes práticos determinaram que os softwares Abaqus e MSC MARC possuem boa aproximação para o teste de expansão hidrostática à frio. O Software Abaqus apresentou dificuldades para convergir e tempo de processamento muito superior ao MSC MARC nos estudos de expansão hidrostática à frio e na condição superplástica. Através dos ensaios de saltos determinou-se que a condição 328 rpm e 65 mm/min possui coeficiente de sensibilidade à taxa de deformação m muito superior ao do alumínio 5083 O sem PFM, isto resultou em uma melhor distribuição de espessura da chapa após o ensaio de expansão hidrostática superplástico em software. / The aim of this study is to determine the sheet metal formability of 5083 O aluminum sheets after friction stir processing \"FSP\". To achieve the proposed objectives the friction stir processing was be reviewed and modeled in order to enable the design and manufacture of a proper FSP tool. The quality of the process was carried out through metallographic tests of the FSP region looking for the presence of voids. The best conditions for plasticity and superplastic forming after FSP was studied by means of an approach of jump steps in the hot tensile tests, looking for a coefficient of strain rate sensitivity. The micro hardness tests and tensile tests at room temperature were carried out for the specimens with and without FSP processing in order to characterize their material mechanical behavior. The formability of the FSP blanks was evaluated through Bulge tests. The results enable to plot Forming Limit Curves friction stir processed blanks after FSP and without FSP. The numerical simulation of the Free Bulge tests was carried out using a Finite Element Method model in order to compare the numerical theoretical and experimental practical results. The numerical simulation approach allows for the determination the forming limit curve of 5083 O aluminum sheets processed by the FSP process. The Finite Element Method modeling and simulation have employed two nonlinear FEM codes: the MSC MARC and Abaqus were compared as software for the simulations. The Yeld Strength of specimens with FSP increased 30% in comparison with specimens without FSP in cold tensile tests, the formability of shapes with and without FSP was de same. The practical tests showed that Abaqus and MSC MARC results has a good approach, the processing time in Abaqus was much greater than in MSC MARC, Abaqus had convergence problems when contact condition is applied. Through the jump tensile tests the 328 rpm and 65 mm/min condition showed a m factor much higher in comparison with condition without FSP in AA 5083 O, this results led in a better thickness distribution after the superplastic bulge test in software.

This thesis presents results from the application of cryogenic cooling on multiple-pass friction stir processing and the subsequent orthogonal machining on friction stir processed and as-received Mg AZ31B-O disks, and shows their combined effects on microstructure and microhardness values. A simple friction stir tool, a specially designed fixture and liquid nitrogen are used to perform multiple-pass friction stir processing experiments on Mg AZ31B-O alloy. The friction stir processed and as-received sheets are then made into disks for the orthogonal machining experiments. This study analyzes the microhardness, microstructure changes by cryogenic friction stir processing and the effect of machining conditions such as dry, MQL and cryogenic and cutting parameters on the Mg AZ31B-O alloy. Four different speeds and three different feed rates are used for the orthogonal machining experiments. The effects of stirring parameters such as the translational feed, rotational speed, cooling conditions and the machining parameters are studied. The resulting microstructure and microhardness from these processes hold a key to the mechanical properties of the alloy. This analysis would help to understand and evaluate the specific aspects of grain size and microhardness that influence the fatigue life of a component.

Magnesium alloys are a popular research topic for structural applications because they have a lower density than conventional structural materials, including steel, titanium, and aluminum; however, the reliability and safety of their mechanical properties must be further proven. An important mechanical property for this purpose is fracture toughness, which is the measure of the material's resistance to crack propagation. In this study, a model of an experiment to investigate the fracture toughness of a magnesium alloy WE43 before and after friction stir processing (FSP) is developed, and the results are compared to those produced by a digital image correlation (DIC) system during an experiment from another paper. The model results of the material before FSP matched well with the DIC results, but the model of the material after FSP only partially matches the DIC results. In addition, a theoretical approach to calculating the standard fracture toughness value, KIc, from the modeling results is proposed, and is found to be a conservative approach.