A Study on the Dissimilar Materials Welding of Steel and Aluminum Alloys by Nd-YAG Laser

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Joo, Sung-Min
Issued Date
이종 금속 간 용접은 아크열원등 기존의 통상적인 열원을 이용해서는 곤란한 점이 많아 거의 불가능하다고 인식되어 왔으나, 산업계의 지속적인 수요에 의해 최근 들어 고밀도 열원을 이용한 시도가 점차 증가하고 있는 추세다.
본 논문에서는 연속파 고체 Nd-YAG레이저를 이용하여 냉연강판과 알루미늄합금(A5052, A1100)의 이종 금속 간 용접을 시도하였으며, 용접 후에는 결함발생의 유무와 금속간 화합물 등의 발생량과 분포 등을 살펴보았으며 인장시험을 통해 접합강도를 평가하였다. 또 이재 접합체의 용접 시 내부의 역학적 거동을 고찰하기 위해 유한요소해석을 수행하였다. 이를 위해 이재접합해석용 유한요소해석 솔버를 개발하고 또한 개발 솔버가 상용프로그램과 전후처리가 연동될 뿐 아니라 개발 솔버에서 계산된 최종 용접잔류응력이 상용 솔버의 초기값이 되도록 데이터를 전송하여 잔류응력을 초기값으로 갖는 상태에서 추가 외력 해석이 가능하도록 해석기법과 인터페이스를 개발하였다.
레이저 용접시에는 입열량 변화에 따른 강도변화를 살펴보았으며 결과적으로 접합강도는 입열량 변화에 민감하게 영향을 받는다는 것을 확인할 수 있었다. 다시 최적의 강도를 갖는 입열 조건에서 용접비드를 2개와 3개로 다중용접을 실시하고 이때 비드간 간격을 달리하면서 용접을 실시하였으며, 접합강도는 조건에 따라 매우 향상되어 모재부에서 파단이 일어날 정도의 좋은 결과를 얻을 수 있었다.
또한 유한요소 해석에 의해 이종 재질간 용접시 발생되는 열 이동현상과 이에 따른 응력 등의 발생특성을 명확하게 고찰할 수 있었으며 특히 강과 알루미늄간 용접과 같은 이종재질간 접합체에서 잔류응력, 소성변형율 및 소성일 분포 등을 고찰함으로써 입열에 의한 재료의 역학적 열화정도를 평가할 수 있었다.|Development of dissimilar weldments represents one of the major challenge and remarkable interests in modern manufacturing processes due to great demands for high quality and high performance. So this thesis work has been focused on lap joints of thin sheet materials and on the investigation of the feasibility of laser welding of dissimilar metallic materials by welding steel to aluminum. Materials used are commercial cold rolled steel sheets (SPCC of 1mm thickness) and aluminum alloys (A1100 and A5052 of both 1mm and 2mm thickness) sheets.
One of the major problems in the dissimilar welding is the amount of intermetallic compound layer generated in the fusion zone. The problem not only depends on the relative conductivity of heat and the melting point of the two constituent materials but also in the heat source. Generally, it is known that by using conventional heat source, welding of dissimilar metallic materials is almost impossible due to difficulties to control the amount of heat input, and thus wide fusion zone and intermetallic compounds are generated. To overcome this problem, in this paper, laser beam is used as a welding heat source and this welding offers many advantages over conventional welding processes namely, due to the small spot diameter of laser beams, and high energy densities are reached locally, which finally results in a significant improvement of joining speed and a reduction of the melt pool diameter, and thus small heat input and less intermetallic compounds occurred.
Welding conditions have been fixed according to the variation of heat input, keeping all other parameters constant. The Fe (SPCC) sheet with higher melting temperature is positioned on the top of the Al sheet with an overlap of 20mm. Also, multiple laser bead weldings have been made and the bead-to-bead distance is changed to investigate its influence on joint strength. FEM analysis has also been carried out for this model and the mechanical behaviors during dissimilar welding is clarified. When the heat input is controlled appropriately, sound dissimilar weldments are achieved.
The result shows the potential of using a laser beam as the leading laser technology for welding of dissimilar materials. Therefore, further investigations have to be carried out in order to utilize all the possible advantages in industrial applications.
Alternative Title
레이저에 의한 강과 알루미늄 합금의 이종 금속 간 용접에 관한 연구
Alternative Author(s)
Graduate School of Chosun University
일반대학원 선박해양공학과
Bang, Han-Sur
Awarded Date
Table Of Contents
Abstract = 3
Chapter 1. Introduction = 1
1.1 A Brief review of dissimilar material welding = 1
1.2. Problem statement = 3
1.3. Scope of the current research = 5
Chapter 2. Thermal elastic-plastic FE analysis of dissimilar welded model = 7
2.1 Description of unsteady-state heat transfer analysis = 7
2.2 Nonlinear thermal elastic-plastic analysis = 10
2.3 Data transferring between commercial FE package and In-house solver = 14
2.3.1 Combination by using PCL = 14
2.3.2 Bridging to ANSYS = 17
2.4 Numerical simulation of dissimilar material welded model = 23
2.4.1 Model and material properties details = 23
2.4.2 Simulation results = 23
2.5 Discussion = 24
Chapter 3. Experiment of dissimilar metallic material welding = 25
3.1 Experiment of welding of single bead = 26
3.1.1 Materials used and experimental procedure = 26
3.1.2 Laser weld zone geometry and microstructure = 29
3.1.3 Tensile properties of laser welded joints = 33
3.2 Experiment of welding of multiple bead = 38
3.2.1 Materials used and experimental procedure = 38
3.2.2 Laser weld zone geometry and microstructure = 41
3.2.3 Tensile properties of laser welded joints = 42
3.3 Discussion = 47
4. FEM simulations = 49
4.1 FE-model and material properties = 49
4.2 Single bead laser welding simulation = 50
4.3 Multiple bead laser welding simulation = 59
4.4 External load simulation with initial stress = 66
4.4.1 Single bead case = 67
4.4.2 Multiple bead case = 69
4.5 Discussion = 70
5. Conclusions = 71
6. Reference = 72
Graduate School of Chosun University
Joo, Sung-Min. (2004). A Study on the Dissimilar Materials Welding of Steel and Aluminum Alloys by Nd-YAG Laser.
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General Graduate School > 4. Theses(Ph.D)
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