بررسي خواص مكانيكي و ريز ساختار ورق آلومينيوم 5083 نانو ساختار شده به روش نورد تجمعي - پيوندي (ARB

Evaluation of microstructure and mechanical Properties nano-structured 5083 aluminum alloy By ARB process

فرايند نورد تجمعي (ARB) يكي از روش هاي تغيير شكل پلاستيكي شديد است كه براي رسيدن به مواد فلزي با دانه هاي بسيار ريز (ير ميكرون) بدون تغيير ابعاد ورق استفاده مي شود. د رتحقيق حاضر فرايند ARB تا 6 سيكل روي ورق آلومينيوم 5083 با موفيقت انجام شد. تغييرات ريز ساختاري حين فرايند ARB توسط ميكروسكوپ الكتروني عبوري (TEM) مورد بررسي قرار گرفت. بررسي سطح شكست نمونه هاي ARB شده پس از انجام آزمايش كشش با ميكروسكوپ الكتروني روبشي (SEM) انجام گرفت. نتايج نشان داد كه د رسيكل چهارم د راثر قوع تبلور مجدد پيوسته ساختاري متشكل از دانه هايي با اندازه دانه كمتر از 100 نانو متر حاصل شد. با انجام فرايند ARB روي ورق آلومينيوم 5083 تا شش سيكل استحكام و سختي ورق ها حدود 2 و 3 برابر مقدار اوليه افزايش يافت. همچنين با بررسي سطح شكست مشخص شد كه شكست در ورق آلومينيومي ARB شده به صورت داكتيل با مكانيزم تشكيل ديمپل هاي برشي اتفاق افتاده است.

Accumulative roll bonding (ARB) is a severe plastic deformation process for achieving ultra-fine grains in metallic sheets without changing the sample dimensions. In this study, ARB process was carried out on 5083 aluminum alloy sheets up to 6 cycles. In this process, the surfaces of the strips to be joined are roughened and cleaned and then stacked. After stacking, the specimen is roll-bonded by rolling using a 50% reduction. The rolled specimen is cut into two halves, and the above-mentioned procedure is repeated for several times. Microstructural characterizations were analyzed by transmition electron microscopy (TEM). Tension and Vickers hardness tests were performed on produced sheets for evaluating their mechanical properties. In order to clarify the failure mode, fracture surfaces after tensile tests were observed by scanning electron microscopy (SEM). The results indicated that at the early stages of ARB process, grains were subdivided by deformation induced boundaries. After several ARB cycles, lamellar structure elongated in the rolling direction contains lamellar boundaries was formed. With increasing the strain, mean spacing of lamellar boundaries decreased. Finally, continuous recrystallization resulted in a microstructure covered with small recrystallized grains with an average diameter below 100 nm at the end of four cycle. The tensile strength and hardness of the 6 cycle ARB processed 5083 aluminum alloy sheet increased about two and three times of the initial values, respectively. Results indicated conformity between mechanical evolutions and microstructural changes during ARB process. Fracture surfaces observations showed that failure mode in ARB processed aluminum is shear ductile rupture with elongated small dimples.