مهندسی مکانیک مدرس

مهندسی مکانیک مدرس

بررسی تجربی اثر فرآیند شکل‌دهی دو پاسی انبساط و انقباض تناوبی هیدرواستاتیک بر خواص مکانیکی و ریزساختار لوله‌های مسی

نوع مقاله : پژوهشی اصیل

نویسندگان
گروه مهندسی مکانیک، دانشکده مهندسی مکانیک، دانشگاه تهران، تهران، ایران
چکیده
فرآیند انبساط و روزن‌رانی تناوبی شکل‌دهی هیدرواستاتیک لوله روش تغییر شکل پلاستیک شدید جدیدی است که به‌منظور تولید لوله‌های بلند فوق ریزدانه و نانوساختار با خواص مکانیکی بالا ابداع شده است. در پژوهش حاضر این فرآیند طی دو پاس در دمای اتاق روی مس خالص تجاری اعمال شد و سپس سختی، خواص کششی، سطح شکست و ریزساختار نمونه‌ها مورد بررسی قرار گرفت. هدف این پژوهش به دست آوردن ماده‌ای با استحکام بالا و شکل‌پذیری مطلوب بود. وجود سیال تحت فشار بین لوله و قالب در این فرآیند اولاً موجب بهبود مطلوب خواص مکانیکی، تحت تاثیر تنش‌های هیدرواستاتیک فشاری می‌شود ثانیاً، با حذف نمودن اصطکاک بین لوله و قالب باعث کاهش نیروی مورد نیاز شکل‌دهی می‌شود. این امر تولید لوله‌های فوق ریزدانه و نانوساختار با طول‌های نسبتاً بلند را تسهیل می‌کند. پس از انجام دو پاس از فرآیند، ریزساختاری فوق ریزدانه نسبتاً همگن و هم‌محور مشاهده شد. مقدار حد تسلیم و استحکام نهایی به ترتیب از مقادیر ۷۵ و ۲۰۷مگاپاسکال به ۳۱۰ و ۳۸۶مگاپاسکال افزایش یافت ولی درصد ازدیاد طول تا شکست از ۵۵% به ۳۷% کاهش یافت. همچنین سختی لوله به‌صورت قابل ملاحظه‌ای از ۵۹ویکرز به ۱۴۳ویکرز افزایش یافت و توزیع همگنی از سختی در راستای ضخامت لوله به دست آمد. بررسی‌های شکست‌نگاری حاکی از اتفاق‌افتادن، غالباً شکست داکتیل در نمونه‌های آزمون کشش بودند. فرآیند انبساط و روزن‌رانی تناوبی شکل‌دهی هیدرواستاتیک لوله می‌تواند به‌صورت صنعتی و کاربردی در تولید لوله‌های فوق ریزدانه با طول‌های نسبتاً بلند مورد استفاده قرار گیرد.
کلیدواژه‌ها

موضوعات


عنوان مقاله English

Experimental Investigation of the Effects of Two-Pass Hydrostatic Cyclic Expansion Extrusion Process on the Mechanical Properties and Microstructure of Pure Copper Tubes

نویسندگان English

M. Motallebi Savarabadi
Gh. Faraji
M. Eftekhari
Mechanical Engineering Department, Engineering Faculty, University of Tehran, Tehran, Iran
چکیده English

Hydrostatic tube cyclic expansion extrusion process is a newly invented severe plastic deformation technique for producing long ultrafine-grained and nanostructured tubes with higher mechanical properties. In the present research, this process was applied through two passes at room temperature on the commercial purity copper. Then, the hardness, tensile properties, fracture surface and microstructure of the samples were evaluated. The main goal of this research was to achieve a material with a simultaneous high strength and desirable ductility. In this process, the utilization of pressurized fluid between the die and the tube leads to first, the desired improvement of mechanical properties due to the effects of hydrostatic compressive stress. Second, the reduction of a required deforming force to eliminating the friction between the die and the tube leads to the facilitation of producing relatively long ultrafine-grained and nanostructured tubes. After two passes of process, a nearly equiaxed and homogeneous ultrafine-grained (UFG) microstructure was observed. The yield strength and ultimate strength increased from 75 MPa and 207 MPa to 310 MPa and 386 MPa, respectively. However, elongation to failure decreased from 55% to 37%. Also, the hardness value of the tube increased significantly from 59 Hv to 143 Hv, and the uniform distribution of hardness was obtained through the thickness of the tube. The fractography evaluations revealed that the predominantly ductile fracture happened in all samples of tensile testing. The hydrostatic tube cyclic expansion extrusion process can be utilized as a practical industrial method for producing relatively long ultrafine-grained tubes.

کلیدواژه‌ها English

Severe plastic deformation
AZ31 Alloy
Pure copper
Hydrostatic pressure
Tube
Ultra-fine grain
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