Constitutive Modelling of the 6061-T6 Aluminum Alloy under High-temperature Compression Deformation Conditions

국문 초록 (Abstract)

두랄루민은 양호적인 가공 성능, 경량성, 고강도, 용접성, 그리고 내마모성으로 인해 매우 인기가 있다. 6061은 Al-Mg-Si 시리즈에 속하며 대표적인 변형 두랄루민으로 다양한 분야에 널리 적용되고 있다. 본 연구는 6061-T6 두랄루민을 연구 대상으로 진행하기로 한다. Gleeble-3800 열 시뮬레이션 시험기는 다양한 온도(573K~783K), 다양한 변형공률(0.001~1s-1), 그리고 단향적 열압축 시험에 사용된다. 실험 데이터를 사전처리를 진행하여 유동 응력-변형 곡선을 제작하며, 재료는 외부 조건에서의 응력-변형 관계를 연구하였다. 기본 구조 관계는 두랄루민 구조를 분석 및 응용할 때의 가장 기분적은 문제 중 하나이다. 고온 압축 실험에서 얻은 데이터를 통해 6061-T6 두랄루민을 설명할 수 있는 7가지 구성 모델은 설정됩니다. 이는 수정된 Johnson-Cook (MJC) 모델, Arrhenius-Type (A-T) 모델, 수정된 Zerilli-Armstrong (MZA) 모델, Wang-Jiang(W-J) 모델, SK-Paul 모델, Kobayashi-Dodd (K-D) 모델 및 수정된 Fields Backofen（MFB）모델이다.
예측치를 실험 결과와의 비교를 통해 7가지의 모델이 두랄루민에 적용성을 평가하였다. 6061두랄루민에 대해 더 적합한 기본구조 방안을 얻기 위하는 목적을 가지고 있으므로 이 평가는 계산결정계수(R2)와 평균절대상대오차（AARE）를 포함하였다. 비교해 보면 A-T 모델, MZA 모델, MFB 모델 이 세 가자의 모델은 더 좋은 예측 구조를 갖고 있으므로 온도와 변형률 변화의 영향을 상대적으로 적게 받았다. 다음으로 MJC 모델과 SK-Pual 모델이며 이 들은 온도와 변형률 변화에 따라 변한다. W-J 모델과 K-D 모델은 정확도가 가장 낮다. 이 가운데 MAZ는 양호적인 적합성을 드러내고 있으며 R2은 0.99138로 1에 근접하고 AARE치가 최소인 10.66%로 나타나므로 두랄루민 재료인 6061-T6은 고온에서의 유동적 응력에 대한 가장 정확한 예측이다.
마지막으로 A-T 기분구조 방정식에 대한 연구를 기반으로 활성화 에너지 그래프를 구축하여 온도, 변형, 응변율, 두랄루민 내부 미시적 조직 등 요인이 Q 치에 대한 영향을 설명하였다.

다국어 초록 (Multilingual Abstract)

Aluminum alloy is favored for its good processability, lightweight, high strength, weldability, and wear resistance. 6061 belongs to the Al-Mg-Si series and is a typical deformed aluminum alloy, which has been extensively utilized across different domains. In this paper, the 6061-T6 aluminum alloy is used as the research object. Gleeble-3800 thermal simulation testing machine is used for unidirectional thermal compression test at different temperatures (573K~783K), different strain rates (0.001~0.1s-1), and different strains (0.1~0.8, the interval is 0.1). Perform data preprocessing on the experimental data, the flow stress-strain curve is drawn to study the relationship between the stress and the strain when the material is subjected to external loading. The constitutive relation is one of the basic problems in the analysis and application of aluminum alloy structures. The seven constitutive models that can describe the 6061-T6 aluminum alloy are established through the data obtained from the high-temperature compression experiment: modified Johnson-Cook (MJC) model, Arrhenius-Type (A-T) model, modified Zerilli-Armstrong (MZA) model, Wang-Jiang (W-J) model, SK-Paul model, Kobayashi-Dodd (K-D) model, and modified Fields-Backofen (MFB) model.
The suitability of seven models for the alloy was assessed by comparing the predicted values with the experimental results. This evaluation involved calculating the coefficient of determination (R2) and the average absolute relative error (AARE). The aim was to obtain a more fitting constitutive equation for the 6061 alloy.
In comparison, the three models of the A-T model, MZA model, and MFB model have better-predicted structures. They are less affected by changes in temperature and strain rate, followed by the MJC model and SK-Pual model, which will change due to changes in temperature and strain rate. The W-J model and K-D model have the worst accuracy. Among them, MAZ shows a good fitting effect, and its R2 is 0.99138, which is the closest to 1, and the AARE value is the smallest at 10.66%. It is the most accurate prediction of the flow stress of aluminum alloy material 6061-T6 at high-temperatures.
Then, in the research based on the A-T constitutive equation, the activation energy diagram is established, which describes the influence of Q value by temperature, strain, strain rate, internal microstructure of the alloy, and other factors.

목차 (Table of Contents)

• 1 Introduction 1
• 1.1 Introduction of materials 1
• 1.2 Overview of Methods for Evaluating Mechanical Properties of Materials 6
• 1.3 Compression Molding Process Overview 7
• 1.3.1 Low temperature compression and high-temperature compression 7
• 1.3.2 Principles and advantages of high-temperature compression 9
• 1.4 Tissue Mechanical Properties Research 11
• 1.4.1 The Effect of Grain Size on the Strength of Metals and Alloys 11
• 1.4.2 Effect of Grain Size on Plasticity and Toughness of Metals and Alloys 11
• 1.4.3 Effect of Grain Size on Fatigue Properties of Metals and Alloys 12
• 1.5 Flow Stress of Thermal Deformation of Metal Materials 13
• 1.5.1 Flow Stress of Thermal Deformation of Metal Materials 13
• 1.5.2 Softening Mechanism of Thermal Deformation of Metal Materials 14
• 1.6 Constitutive equation 19
• 1.7 The research content and significance of this paper 20
• 2 Experiment 23
• 2.1 Experimental materials 23
• 2.2 Experimental methods and equipment 24
• 2.2.1 High-temperature compression experiment 24
• 2.2.2 Experimental equipment 26
• 2.3 Experimental results 27
• 3 Constitutive Model 31
• 3.1 Modifed Johnson-Cook Model 32
• 3.1.1 Introduction 32
• 3.1.2 Original Johnson-Cook Model 32
• 3.1.3 Modified Johnson-Cook Model 33
• 3.1.4 Result 37
• 3.2 Arrhenius-type Model 38
• 3.2.1 Introduction 38
• 3.2.2 Arrhenius-type Model 38
• 3.2.3 Result 44
• 3.3 Modified Zerilli-Armstrong Model 45
• 3.3.1 Introduction 45
• 3.3.2 Modified Zerilli-Armstrong Model 45
• 3.3.3 Result 49
• 3.4 Wang-Jiang Model 50
• 3.4.1 Introduction 50
• 3.4.2 Wang-Jiang Model 50
• 3.4.3 Result 53
• 3.5 SK-Paul Model 54
• 3.5.1 Introduction 54
• 3.5.2 SK-Pual Model 55
• 3.5.3 Result 58
• 3.6 Kobayashi-Dodd model 59
• 3.6.1 Introduction 59
• 3.6.2 Kobayashi-Dodd Model 59
• 3.6.3 Result 62
• 3.7 Modified FieldsBackofen Model 63
• 3.7.1 Introduction 63
• 3.7.2 Modified FieldsBackofen Model 63
• 3.7.3 Result 66
• 4 Evolution of activation energy 68
• 4.1 Introduction 68
• 4.2 Effect of strain on activation energy 70
• 4.3 Effect of strain rate on activation energy 72
• 4.4 Effect of temperature on activation energy 73
• 5 Result and Discussion 76
• 6 Conclusion 86
• Reference 88
• Publications during the master's degree period 96
• SCI index: 96
• Scopus index: 96