الفهرس 
LITERATURE REVIEWOnly 14 pages are availabe for public view
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Abstract
In the present study, Taguchi approach for experiment design was uti-lized, through an orthogonal array of L9 (33), to investigate the effect of Friction Stir Welding (FSW) process parameters, typically tool rotational speed and welding speed each of three levels, as well as, Post Weld Heat Treatment (PWHT), typically T4 and T6 tempers, on the microstructural characteristics and corrosion behavior of AA7020-O Aluminum alloy (AA) welded plates. Microstructural characteristics are investigated through grains size and aspect ratio, and precipitates size and density. Corrosion behavior is investigated by analyzing Scanning Electron Microscope (SEM) micrographs and Energy-Dispersive X-ray spectroscopy (EDX) of corroded surface of statically immersed samples in a 3.5% Sodium Chlo-ride (NaCl) solution, as well as, results of potentiodynamic test in a 3.5% NaCl solution.
The results have revealed that, the Corrosion Rate (CR) of Base Metal (BM)-O is the least upon all heat treated BMs followed by BM-T4 and BM-T6, in an ascending order. Based on SEM micrographs, heat treatment is greatly affecting the corrosion behavior of the BM; T4 temper has de-creased the BM susceptibility to pitting corrosion as compared to O state, while T6 temper has greatly increased it.
Moreover, the results obtained by Analysis of Variance (ANOVA) re-vealed that, the size of α-Aluminum (Al) grains at center of the Nugget Zone (NZ) is directly statistically significant affected by increasing the tool rotational speed and by changing the PWHT state from the As Weld (AW) state to T4 or T6 tempers with a Percentage Contribution (PC) of 48.83%, and 41.11% respectively, also at center of the NZ, the aspect ratio of α-Al grains is directly statistically significant affected by increasing the tool rotational speed, while it is inversely statistically significant affected by
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increasing the welding speed with a PC of 74.85% and 22.87% respectively. The Corrosion Potential (Ecorr) of the NZ is found to be directly statistical-ly significant affected by increasing the tool rotational speed, while it is inversely statistically significant affected by changing the PWHT state from the AW state to T4 or T6 tempers with a PC of 20.92% and 76.94% respectively. Moreover, the CR of the NZ is found to be directly statistical-ly significant affected by changing the PWHT state from the AW state to T4 or T6 tempers, while, it is inversely statistically significant affected by increasing the tool rotational speed with a PC of 58.35% and 34.62% re-spectively.
Nevertheless, As compared to BM samples, and except for the T6 Post Weld Heat (PWH) treated samples, FSW have decreased the samples tendency to corrode. Also for T4 and T6 tempers, FSW has highly de-creased the CR in the NZ, while it is of comparable values in the case of AW state.
Key words:
FSW, Processing Parameters, PWHT, Taguchi, Microstructure, Corrosion Behavior, Potentiodynamic Polarization, Corrosion Rate.
CHAPTER (In the present study, Taguchi approach for experiment design was uti-lized, through an orthogonal array of L9 (33), to investigate the effect of Friction Stir Welding (FSW) process parameters, typically tool rotational speed and welding speed each of three levels, as well as, Post Weld Heat Treatment (PWHT), typically T4 and T6 tempers, on the microstructural characteristics and corrosion behavior of AA7020-O Aluminum alloy (AA) welded plates. Microstructural characteristics are investigated through grains size and aspect ratio, and precipitates size and density. Corrosion behavior is investigated by analyzing Scanning Electron Microscope (SEM) micrographs and Energy-Dispersive X-ray spectroscopy (EDX) of corroded surface of statically immersed samples in a 3.5% Sodium Chlo-ride (NaCl) solution, as well as, results of potentiodynamic test in a 3.5% NaCl solution.
The results have revealed that, the Corrosion Rate (CR) of Base Metal (BM)-O is the least upon all heat treated BMs followed by BM-T4 and BM-T6, in an ascending order. Based on SEM micrographs, heat treatment is greatly affecting the corrosion behavior of the BM; T4 temper has de-creased the BM susceptibility to pitting corrosion as compared to O state, while T6 temper has greatly increased it.
Moreover, the results obtained by Analysis of Variance (ANOVA) re-vealed that, the size of α-Aluminum (Al) grains at center of the Nugget Zone (NZ) is directly statistically significant affected by increasing the tool rotational speed and by changing the PWHT state from the As Weld (AW) state to T4 or T6 tempers with a Percentage Contribution (PC) of 48.83%, and 41.11% respectively, also at center of the NZ, the aspect ratio of α-Al grains is directly statistically significant affected by increasing the tool rotational speed, while it is inversely statistically significant affected by
xiv
increasing the welding speed with a PC of 74.85% and 22.87% respectively. The Corrosion Potential (Ecorr) of the NZ is found to be directly statistical-ly significant affected by increasing the tool rotational speed, while it is inversely statistically significant affected by changing the PWHT state from the AW state to T4 or T6 tempers with a PC of 20.92% and 76.94% respectively. Moreover, the CR of the NZ is found to be directly statistical-ly significant affected by changing the PWHT state from the AW state to T4 or T6 tempers, while, it is inversely statistically significant affected by increasing the tool rotational speed with a PC of 58.35% and 34.62% re-spectively.
Nevertheless, As compared to BM samples, and except for the T6 Post Weld Heat (PWH) treated samples, FSW have decreased the samples tendency to corrode. Also for T4 and T6 tempers, FSW has highly de-creased the CR in the NZ, while it is of comparable values in the case of AW state.
Key words:
FSW, Processing Parameters, PWHT, Taguchi, Microstructure, Corrosion Behavior, Potentiodynamic Polarization, Corrosion Rate.