تأثیر سرعت چرخش ابزار در فرایند همزن اصطکاکی نقطه‌ای بر ترکیدگی ذوب‌شدگی آلیاژ AZ91

نویسندگان

1 گروه مهندسی مواد و پلیمر، دانشگاه حکیم سبزواری

2 گروه مهندسی مواد، مجتمع آموزش عالی گناباد

چکیده

آلیاژ منیزیم AZ91 ریختگی یکی از پرکاربردترین آلیاژهای منیزیم است. این آلیاژ به علت دمای یوتکتیک پایین و همچنین حضور ترکیبات بین فلزی در دمای یوتکتیک از جمله آلیاژهای حساس به ذوب‌شدگی در روش‌های جوشکاری ذوبی و جوش همزن اصطکاکی نقطه‌ای است. هدف از این پژوهش، مطالعه رفتار ذوب‌شدگی آلیاژ AZ91 در حین فرایند جوشکاری همزن اصطکاکی نقطه‌ای است. برای این منظور فرایند جوشکاری همزن اصطکاکی نقطه‌ای در دو سرعت چرخشی متفاوت 1000 و 2500 دور بر دقیقه و زمان ماند یک ثانیه بر روی ورق‌هایی از جنس AZ91 و با ضخامت 10 میلی‌متر انجام شد. نتایج نشان داد در سرعت چرخشی پایین پدیده غالب خردایش مکانیکی، توزیع مجدد و انحلال رسوبات 𝛾 است. درحالی که در سرعت چرخشی بالا پدیده غالب ذوب‌شدگی است. انجماد مجدد مذاب تشکیل شده منجر به جایگزینی ساختار یوتکتیک معمولی با ذرات 𝛾 یوتکتیک می‌شود. علاوه بر آن با نزدیک شدن به منطقه همزده شده ذوب‌شدگی تشدید می‌شود. همچنین حضور لایه مذاب در امتداد مرزدانه سبب کاهش استحکام مرز دانه و وقوع ترکیدگی ذوب‌شدگی می‌شود.

کلیدواژه‌ها

عنوان مقاله [English]

EFFECT OF TOOL ROTATION RATE IN FRICTION STIR SPOT WELDING ON LIQUATION CRACKING OF AZ91 ALLOY

نویسندگان [English]

  • F. Harati 1
  • S. M. Mousavizadeh 2
  • M. A. Jabbareh 1
1 Department of Materials and Polymer Engineering, Faculty of Engineering, Hakim Sabzevari University, Sabzevar, Iran
2 Department of Materials Science and Engineering, University of Gonabad, Gonabad, Iran
چکیده [English]

Cast AZ91 alloy is one of the most used magnesium alloys, which is sensitive to liquation in the fusion weld method,s and friction stir spot welding due to low eutectic temperature and the presence of the intermetallic compound in eutectic temperature. In this research, the liquation behavior of AZ91 alloy during friction stir spot welding was investigated. The process was carried out at two rotation speeds of 1000 and 2500 rpm and a dwell time of 1 second on the plate of AZ91 with a 10 mm thickness. Microstructural characterization was carried out using optical and scanning electron microscopes. The results showed that at low rotation speed (1000 rpm), mechanical grinding redistribution and dissolution of 𝛾-Mg17Al12 precipitates occurred. While at high rotation speed (2500 rpm), the predominant phenomenon was liquation. In this condition, the liquation initiated around the 𝛾 phase, and then the liquid re-solidified, leading to the typical eutectic structure instead of initial 𝛾 precipitates. Moreover, the liquation intensified by approaching the stirred zone. Also, the presence of liquid film along grain boundaries resulted in decreased grain boundary strength and liquation cracking.

کلیدواژه‌ها [English]

  • Friction stir spot welding
  • Liquation
  • Re-solidification
  • Liquation cracking

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مواد پیشرفته در مهندسی
دوره 41، شماره 1
خرداد 1401
صفحه 97-111

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