سلوك المواد فائقة اللدونة ذات البنية المجهرية الناعمة لسبيكة المغنيسيوم نوع AZ31B والمشكلة بواسطة التشكيل العالي الانفعال == Superplastic Behavior of Fine Grained AZ31B Magnesium Alloy Processed By Severe Plastic Deformation
Author name:
زياد طارق عبد الوهاب
Supervisor name:
ازل رفعت اسماعيل
General topic:
Production engineering metallurgy and materials
Specific topic:
Production Engineering
Degree:
Master
University:
University of Technology
Language:
English
University location:
Baghdad
First pages:
50T178 - p.pdf
Abstract:
Superplastic properties and microstructure evolution of commercial AZ31B magnesium alloy processed by two different severe plastic deformation methods Equal Channel Angular Pressing (ECAP) and Equal Channel Angular Rolling) ECAR) were studied. Samples were tested in tension at temperature of 623 K and strain rate ranging from 2.4×10 - 4 1×10 - 2 s - 1. ECAP die with 10 ×10 mm cross section channel, oblique angle of ?=90° and ?=13° was designed to refine the alloy microstructure at temperature of 473 K using route BC. Application of ECAP showed a remarkable grain refinement for AZ31B Mg alloy from 14.1 to 2.1?m after three ECAP passes. Maximum superplastic elongation of 261% was achieved at 623 K and strain rate of 2.45×10 - 4 s - 1. The measured strain rate sensitivity was m = 0.33 demonstrating that viscous glide control creep was the dominant deformation mechanism. In most investigation used ECAR process, the die temperature was set to room temperature, in order to avoid cracking intermediate annealing was used for AZ31B Mg alloy which has poor formability at room temperature. This is caused by a lack of active slip systems, especially in the <c+a> direction. However, in this study a special isothermal ECAR die capable of operating without intermediate annealing was used to process AZ31B Mg alloy. The ECAR was carried out at 623 K using a die of ?115 ° channel angle and without rotation. Processing by ECAR showed less effect on the microstructure refinement where the grain size was reduced from 10?m to 4.2?m after six ECAR passes. ECAR increases the yield and ultimate stress and decreases the elongation corresponding to increasing the number of ECAR passes, the as - received material exhibits large amount of superplastic elongation compared to ECAR processed specimens. Therefore superplastic behavior of the AZ31B magnesium alloy was evaluated at temperatures 623 K and strain rate ranging from 7.8×10 - 4 s - 1? 1×10 - 2 s - 1. The test showed that maximum elongation of 367% can be achieved at 623 K and strain rate of 7.8×10 - 4 s - 1. The strain rate sensitivity (m) was evaluated by two different methods, uniaxial tensile test on the basis of the true stress true strain curve and by strain - rate jump test. The results show small differences between the two method) m = 0.42 - 0.45), which demonstrate that the grain boundary sliding (GBS) is the dominant deformation mechanism during superplastic test Keywords : Superplasticity. Severe plastic deformation. AZ31B magnesium alloy.
