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شرایط پیرسازی و هندسی قطعه: رفتار شکست ورق al2024t8 تحت کشش
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نویسنده
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پاکروان کیاندخت ,حسینی منزه عسل
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منبع
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مهندسي مكانيك شريف - 1399 - دوره : 36-3 - شماره : 1 - صفحه:11 -18
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چکیده
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در این پژوهش، تاثیر عملیات حرارتی پیرسازی مصنوعی به همراه نورد سرد (t8) بر رفتار کششی آلیاژ آلومینیوم 2024 در حضور و عدم حضور شیار مورد بررسی قرار گرفته است. برای تعیین سازوکارهای شکست، با استفاده از sem سطوح شکست، نمونه‌های کششی تحت زمان‌های متفاوت پیرسازی مطالعه شد. نتایج رفتار کششی نشان داد که با ایجاد شیار در نمونه‌ها، تنش تسلیم و نهایی افزایش پیدا کرده و ماده نسبت به شیار مستحکم می‌شود؛ اگرچه به دلیل کاهش چشمگیر کرنش شکست در اثر حضور شیار، چقرمگی نمونه‌های شیاردار به شدت کاهش می‌یابد. این کاهش در اوج پیری بیشترین میزان را دارد. همچنین به نظر می‌رسد تغییر شکل زمینه، ذرات ترک‌خورده و جدایش ذره از زمینه، سازوکارهای شکست در تمامی شرایط پیرسازی و در کل نمونه‌ها هستند، اما حضور شیار به شدت کسر ذرات ترک خورده را افزایش داده و همراه با کاهش حجم زمینه، سبب افت چشمگیر در کرنش شکست و چقرمگی می‌شود.
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کلیدواژه
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آلومینیوم 2024، عملیات حرارتی t8، رفتار کششی، سازوکارهای شکست
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آدرس
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دانشگاه شهید بهشتی, دانشکده ی مهندسی مکانیک و انرژی, ایران, دانشگاه شهید بهشتی, دانشکده ی مهندسی مکانیک و انرژی, ایران
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پست الکترونیکی
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a_hosseinimonazzah@sbu.ac.ir
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AGING HEAT TREATMENT AND SPECIMEN'S GEOMETRY: FRACTURE BEHAVIOR OF AL2024T8 SHEET UNDER TENSION
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Authors
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Pakravan K. ,Hosseini Monazzah A.
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Abstract
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The effect of artificial ageing on tensile properties and fracture behavior of 2024 Al alloy in the presence and absence of notch was investigated. The tensile samples having two V notches, as well as, common tensile specimens were prepared according to ASTM E8. T8 heat treatment consisting of solutionizing, cold rolling, and aging was selected to establish precipitation hardening in Al2024 alloy. Considering T8 condition, following solutionizing of Al sheet at 500^{0}C,samples were cold rolled with 30% reduction. Finally artificial aging was applied at 200^{0}C via different times. The results of Brinell test shows that the maximum value of hardness was achieved at 1 hour, which indicated the peak aging condition. Moreover, soaking samples in aging condition at 200^{0}C for 15 minutes and 4 hours were considered as underaging and overaging states, respectively. Similar to hardness results, the superior amount of yield strength and ultimate tensile strength of unnotched specimens were observed at peak aging time, while in notched samples, the role of aging time was not prominent due to the presence of V shaped flaws. By applying notches on specimens, the yield and ultimate stress were found to increase with simultaneously decrease in elongation at fracture. It was found that due to localizing plastic deformation around flaws, the presence of notch increases the strength of 2024 Al alloy, while elastic behavior controls deformability far from notches. The energy which was absorbed till fracture, was indicated as toughness and it was found to be absolutely dominated by the elongation at fracture and significantly decreased in notched specimens. The peakageing condition of notched tensile specimens had the lowest toughness compare to underageing and overageing conditions. Although three fracture mechanisms, such as matrix deformation, particle cracking and matrix/particle debonding observed in all samples, the distribution of these mechanisms were more homogeneous in unnotched specimens. In the other words, one may claim that the presence of flaws enhanced the cracked particles, which accompanied with lowering matrix deformability lessened the elongation and toughness.
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Keywords
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