بررسی رفتار کارگرم در آلیاژ Mg-7.1Gd-2.8Y-1.3Nd-0.4Zn(wt%) با استفاده از رابطه سینوس هایپربولیک و نقشه‌های فرآیندی

محورهای موضوعی : فصلنامه علمی - پژوهشی مواد نوین

غلامرضا ابراهیمی ¹ (-دانشیار، گروه مهندسی مواد و پلیمر، دانشکده مهندسی، دانشگاه حکیم سبزواری)
احسان رضایی خیبری ² (دانشحویی دکتری)

تاریخ دریافت : 1398/06/01 تاریخ پذیرش : 1399/02/09 تاریخ انتشار : 1399/02/01

کلید واژه: ریزساختار, تغییرشکل گرم, آلیاژ Mg-RE, معادله سینوس هایپربولیک, نقشه‌های فرآیندی,

چکیده مقاله :

افزودن عناصر نادر خاکی به آلیاژهای منیزیم، موجب توسعه آلیاژهای Mg-RE شده که دارای نسبت استحکام به وزن بالایی بوده و در صنایع هوا-فضا و اتومبیل‌سازی کاربرد دارند. از طرفی یکی از محدودیت‌های توسعه و بکارگیری انواع آلیاژهای منیزیم، تغییر شکل مومسان آن‌ها به واسطه ساختار هگزاگونال فشرده (HCP) آن‌هاست. هدف از این تحقیق، بررسی رفتار کار گرم و توسعه مدل‌ بنیادی آلیاژ منیزیم Mg-7.1Gd-2.8Y-1.3Nd-0.4Zn(wt%) است. بدین منظور آزمایش‌های فشارگرم بر روی آلیاژ اکسترود شده در دماهای ºC475-ºC400 و نرخ کرنش‌های s^-11-s^-1001/0 با کرنش حداکثری 6/0 طراحی و انجام شد. تحلیل منحنی‌های فشارگرم بر اساس روابط بنیادی نشان داد که مقدار پارامترهای توان تنش (n) و انرژی محرکه (Q) آلیاژ به ترتیب برابر با 92/4 و  kJ.mol^-142/307 است. با استفاده از رابطه سینوس هایپربولیک تنش سیلان آلیاژ پیش‌بینی شد و نشان داده شد که مدل‌سازی کارگرم آلیاژ به صورت مناسبی قابل انجام است. با استفاده از مدل دینامیکی مواد نقشه‌های فرآیندی آلیاژ رسم شد و با ریزساختارهای بدست آمده تطبیق داده شد. نقشه‌های فرآیندی، دو منطقه امن برای شکل‌‌دهی شامل (1) دمای ºC475 و نرخ کرنش s^-1 001/0 و (2) دماهای ºC460-ºC425 و نرخ کرنش‌های s^-105/0-s^-1005/0 را پیشنهاد داد که با وقوع و توسعه تبلور مجدد دینامیکی (DRX) همراه بوده است. همچنین یک منطقه ناامن نسبتاً وسیع در دماهای زیر ºC425 برای آلیاژ مورد تحقیق شناسایی گردید.

چکیده انگلیسی:

Addition of rare earth (RE) elements to magnesium alloys has developed the Mg-RE alloys having high specific strength to be used in the aerosapace and automobile industries. Deformability of Mg alloys is limited due to hexcagonal closed packed (HCP) structure and the alloys are routinely processed by hot deformation. The aim of this study is investigation of hot deformation behavior and developed a con-stitutive model for Mg-7.1Gd-2.8Y-1.3Nd-0.4Zn (wt%) alloy. Therefore, hot compression tests were performed at temperature interval of 400ºC-475ºC and at strain rates in the range of 0.001s-1-1s-1 with maxiumum strain of 0.6 on as-extruded specimens. The hyperbolic-sine analysis showed that the stress power (n) and the activation energy (Q) of the investigated alloy are 4.92 and 307.42 kJ.mol-1, respectively. The processing maps were drawn based on the dynamic material model (DMM) in the study of the alloy. The maps suggest two stable domains at: (1) 475ºC-0.001s-1 and (2) 425ºC-460ºC at the strain rates of 0.005s-1-0.05s-1, and indicate a wide unstable region below 425ºC.

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