بررسی اثر تغییر شکل پلاستیک شدید بر ریزساختار، خواص مکانیکی و هدایت الکتریکی آلیاژ آلومینیوم 7075
محورهای موضوعی : فصلنامه علمی - پژوهشی مواد نوینعلیرضا دشتی 1 , محمدحسین شاعری 2 , رضا تقی آبادی 3
1 - دانش آموخته کارشناسی ارشد، بخش مهندسی مواد، دانشکده فنی و مهندسی، دانشگاه بین‌المللی امام خمینی (ره) قزوین
2 - استادیار، بخش مهندسی مواد، دانشکده فنی و مهندسی، دانشگاه بین‌المللی امام خمینی (ره) قزوین
3 - استادیار ، بخش مهندسی مواد، دانشکده فنی و مهندسی، دانشگاه بین‌المللی امام خمینی (ره) قزوین
کلید واژه: هدایت الکتریکی, ریزساختار, خواص مکانیکی, فرآیندهای ECAP و MDF, آلیاژ 7075- Al,
چکیده مقاله :
هدف پژوهش حاضر، بررسی خواص مکانیکی، هدایت الکتریکی و ریزساختار آلیاژ آلومینیوم 7075 پرس شده بهوسیله فرآیندهای پرس در کانالهای همسان زاویهدار (ECAP) و فورج چندجهتی (MDF) میباشد. در این پژوهش آلیاژ 7075 در حالت عملیات حرارتی آنیل تحت 4 پاس فرآیند ECAP و 3 پاس فرآیند MDF در دمای محیط قرار گرفت. خواص مکانیکی نمونهها با استفاده از آزمونهای سختی و پانچ برشی و ریزساختار نمونهها با استفاده از میکروسکوپ الکترونی عبوری (TEM) بررسی شد. در ضمن هدایت الکتریکی نمونهها نیز به روش جریان گردابی اندازهگیری شد. نتایج این پژوهش نشان میدهد، 4 پاس فرآیند ECAP، باعث افزایش قابل ملاحظه خواص مکانیکی (حدود 2 برابر) و ریزدانه شدن تا اندازه دانه کمتر از 400 نانومتر میشود؛ در ضمن اکثر دانهها پس از ECAP هممحور بوده و بخش عمده مرزهای دانه زاویه بزرگ میباشند. از طرف دیگر، تاثیر فرآیند MDF بر ریزدانهسازی و افزایش خواص مکانیکی کمتر از فرآیند ECAP بوده به طوریکه پس از 3 پاس MDF خواص مکانیکی حدود 50 درصد افزایش یافته و اندازه دانه نمونهها به کمتر از 1000 نانومتر کاهش یافته است. در ضمن در فرآیند MDF کسر مرزهای بزرگ زاویه کمتر از فرآیند ECAP میباشد. نتایج بررسی هدایت الکتریکی نشان داد، حین فرآیندهای ECAP و MDF، هدایت الکتریکی آلیاژ 7075 به مقدار بسیار اندکی کاهش مییابد. لذا میتوان عنوان نمود، ریزدانه سازی بهوسیله فرآیندهای ECAP و MDF یکی از روشهایی است که میتوان بهوسیله آن استحکام را بدون کاهش قابل ملاحظه هدایت الکتریکی افزایش داد.
The aim of current research was to examine the microstructure, mechanical properties and electrical conductivity of Al-7075 alloy that develops during Equal Channel Angular Pressing (ECAP) and Multi Directional Forging (MDF). The Annealed Al-7075 alloy was subjected up to 3 and 4 passes of MDF and ECAP deformation at room temperature, respectively. Followed by ECAP, Vickers microhardness and shear punch test were performed and microstructural observations were undertaken using transmission electron microscopy (TEM). The electrical conductivity was also measured by eddy current method. Microstructural investigations show that after 4 passes of ECAP very fine grains with average grain size of about 350 nm appear and most of the grains evolve into arrays of high angle boundaries. On the other hand, 3 passes of MDF leads to higher grain size (950 nm) and lower fraction of high angle boundaries compared with 4 pass of ECAP. Mechanical properties of specimens increase about 100 and 50 percent after 3 passes of MDF and 4 passes of ECAP, respectively. So, it can be concluded that the ECAP process is more effective than the MDF process in grain refinement and improvement of mechanical properties. The electrical conductivity measurement at room temperature showed that there was no significant change in the conductivity of the processed samples compared with the initial specimen. Finally, it can be deduced that grain refinement during ECAP and MDF processes can be considered as a strategy to improve mechanical strength of pure metals without sacrifice of their electrical conductivity.
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