Analytical, Numerical and Experimental Studies on Superplastic Forming of Fine-Grained Light-Alloy Sheets

نوع: Type: thesis

مقطع: Segment: PHD

عنوان: Title: Analytical, Numerical and Experimental Studies on Superplastic Forming of Fine-Grained Light-Alloy Sheets

ارائه دهنده: Provider: Ali Ahmadi Jebelli

اساتید راهنما: Supervisors: Dr. Faramarz Fereshteh-Saniee

اساتید مشاور: Advisory Professors:

اساتید ممتحن یا داور: Examining professors or referees: Dr. Ali Alavi Nia - Dr. Mohmmad Bakhshi Jouybari - Dr. Heshmatollah Haghighat

زمان و تاریخ ارائه: Time and date of presentation: 2024/01/31 - 9:30

مکان ارائه: Place of presentation: Faculty of Engineering Amphitheater Hall

چکیده: Abstract: This forming method is generally performed at high temperature and low strain rate. Therefore it does not have the desired speed and efficiency in high volume production lines. Considering the effect of materials' average grain size (AGS) on their resistance to plastic flow, it could be concluded that superplastic properties improvement should be observed at lower temperatures and higher strain rates by reducing the average grain size. This is possible by changing the material microstructure using severe plastic deformation (SPD) methods. In the present study, three passes of constrained groove pressing (CGP) were performed at 250 C on aluminum alloy 5083 sheet. While determining the elements of the primary sheet, the microstructure of both groups of primary and CGPed sheets was first examined by optical microscope, and the average grain sizes were calculated. Then, by examining the images of the scanning electron microscope (SEM) and with the help of the X-ray energy diffraction spectroscopy test, the presence of precipitations, the type of intermetallic compounds and their effects were discussed. Then, with the help of supplementary tests of the second step, microhardness, mechanical properties, fractography, one-dimensional and three-dimensional superplastic properties of all four worksheets were studied. In fact, by analyzing the results of hardness tests, warm uniaxial tension and ambient temperature, and processing the images of the fracture surfaces of these samples, the mechanical and superplastic properties of these worksheets, and their relationships by the microstructural and metallurgical factors were investigated. The results of this research showed that the sample produced during the first pass of the CGP process has the lowest average grain size compared to the other samples. The highest values of yield strength, ultimate tensile strength and Vickers hardness obtained in worksheets are 154 MPa, 317 MPa and 105.1 Hv, respectively. Achieving a 56.2% increase in elongation for the worksheet which is produced in the third pass of the CGP process is one of the important achievements of this research. The third pass sheet with the inhomogeneity factor IF=2.9 is the most homogeneous fine-grained sheet in the distribution of mechanical properties, including hardness. The sheet produced in the first pass is preferred over the sheet in the second pass of this process due to greater improvement in mechanical properties, being more homogeneous and on the other hand having a higher production rate in the preparation of raw materials for production lines

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