Probing Heat Transfer, Fluid Flow and Microstructural Evolution during Fusion Welding of Alloys
Open Access
- Author:
- Zhang, Wei
- Graduate Program:
- Materials Science and Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- May 10, 2004
- Committee Members:
- Tarasankar Debroy, Committee Chair/Co-Chair
Long Qing Chen, Committee Member
John W Elmer, Committee Member
Panagiotis Michaleris, Committee Member
Judith Todd Copley, Committee Member - Keywords:
- fusion welding
phase transformation
fluid flow
heat transfer
diffusion
free surface - Abstract:
- <p>Several important physical processes including the heat transfer, fluid flow and microstructural evolution during fusion welding were modeled based on the fundamentals of transport phenomena and phase transformation theory. The heat transfer and fluid flow calculation is focused on the predictions of the liquid metal convection in the weld pool, the solidification parameters, the temperature distribution in the entire weldment, and the shape and size of the fusion zone (FZ) and heat affected zone (HAZ). The modeling of microstructural evolution is focused on the quantitative understanding of phase transformation kinetics during welding of several important alloys under both low and high heating and cooling conditions.</p> <p>Three numerical models were developed in the present thesis work: (1) a three-dimensional heat transfer and free surface flow model for the gas metal arc (GMA) fillet welding considering the complex weld joint geometry, (2) a phase transformation model based on the Johnson-Mehl-Avrami (JMA) theory, and (3) a one-dimensional numerical diffusion model considering multiple moving interfaces.</p> <p>To check the capabilities of the developed models, several cases were investigated, in which the predictions from the models were compared with the experimental results. The cases studied are the follows. For the modeling of heat transfer and fluid flow, the welding processes studied included gas tungsten arc (GTA) linear welding, GTA transient spot welding, and GMA fillet welding. The calculated weldment geometry and thermal cycles was validated against the experimental data under various welding conditions. For the modeling of microstructural evolution, the welded materials investigated included AISI 1005 low-carbon steel, 1045 medium-carbon steel, 2205 duplex stainless steel (DSS) and Ti-6Al-4V alloy. The calculated phase transformation kinetics were compared with the experimental results obtained using an x-ray diffraction technique by Dr. John W. Elmer of Lawrence Livermore National Laboratory.</p> <p>The thesis research work represents a contribution to the growing quantitative knowledge base in welding. Expansion of this knowledge base is necessary, if not essential, to achieve structurally sound and reliable welds during fusion welding of important engineering materials.</p>