بررسی بهبود خواص مکانیکی ورق فلزی آلیاژهای سبک ریزدانه‌شده به روش فشار کنگره‌ای مقید

نوع: Type: thesis

مقطع: Segment: PH.D

عنوان: Title: بررسی بهبود خواص مکانیکی ورق فلزی آلیاژهای سبک ریزدانه‌شده به روش فشار کنگره‌ای مقید

ارائه دهنده: Provider: صادق قربانحسینی

اساتید راهنما: Supervisors: Faramarz Fereshteh-Saniee (Ph.D)

اساتید مشاور: Advisory Professors:

اساتید ممتحن یا داور: Examining professors or referees: دکتر مجید واثقی - دکتر سید جمال حسینی‌پور - دکتر رحمن سیفی

زمان و تاریخ ارائه: Time and date of presentation: 31 اردیبهشت 1399- ساعت برگزاری: 9:00 صبح

مکان ارائه: Place of presentation: آمفی تئاتر دانشکده

چکیده: Abstract: Severe plastic deformation is one of the metal forming processes to improve mechanical properties. The constrained groove pressing is one of the sheet severe plastic deformation methods, which has received much attention in recent years. In the present study, the elevated-temperature constrained groove pressing was performed up to three cycles on the 2024 aluminum alloy and AZ91D magnesium alloys. Optical microscopy, scanning electron microscopy and X-ray diffraction, were used to study the various sample microstructure, and discuss the average grain size, development, and morphology of the precipitations and the secondary phases, grain's preferred orientation by texture analysis. Mechanical properties of various samples such as ultimate tensile strength, yield strength, elongation, Vickers hardness, anisotropy coefficients, fracture toughness and fatigue crack growth rate were also measured. The results of this study showed that the samples produced during the first cycle of the constrained groove pressing in both alloys had the lowest average grain size compared to the other samples. Based on this grain refinement, the yield strength, ultimate tensile strength and Vickers hardness of the annealed 2024 Al alloy specimen were increased by 45%, 21% and 65%, respectively. This increase was also observed in the AZ91D magnesium alloy, which resulted in the yield strength, ultimate tensile strength, and Vickers hardness of 1-passed sample to be 166.7 MPa, 1661.1 MPa and 86.3 Hv, respectively. One of this research's achievements is reaching to 41.0% elongation for the sample produced during the third cycle of this process, for 2024 Al alloy and 36.1% elongation for the 1-passed sample of AZ91D Mg alloy. This study showed that the 1-passed sample in both alloys, having low planar anisotropy. This makes the samples that were produced by the first cycle of the elevated-temperature constrained groove pressing process, suitable for use in secondary metal forming processes. The highest fracture toughness in the 2024 Al alloy was observed in the 1-passed sample with 25.07 MPa.m0.5 and in the AZ91D Mg alloy belonged to the 1-passed sample with 20.20 MPa.m0.5. The highest rate of fatigue crack growth in the stable region in both alloys was related to the 1-passed sample. In this study, the process of constrained groove pressing was simulated in the Abacus software. By using simulation's results in the neural network and genetic algorithm, optimum die dimensions were obtained to achieve the highest and most uniform induced strain distribution and the lowest force required to perform the process. Key Words: Constrained groove pressing, Al 2024 alloy, Mg AZ91D, Simulation, Microstructure, Mechanical properties.

فایل: ّFile: Download فایل