Thesis
Friction Stir Welding (FSW) of dissimilar metals and alloys
- Creator
- Rights statement
- Awarding institution
- University of Strathclyde
- Date of award
- 2025
- Thesis identifier
- T17268
- Person Identifier (Local)
- 201853923
- Qualification Level
- Qualification Name
- Department, School or Faculty
- Abstract
- This thesis presents a comprehensive investigation into the Friction Stir Welding (FSW) process of dissimilar materials, specifically aluminium and copper. The research employed a combination of experimental and numerical methods to evaluate the weld quality through metallurgical and mechanical analyses. Finite Element (FE) methods were utilised as an auxiliary tool, supplementing the experimental work to simulate the FSW process and facilitating the prediction of IMCs formation. The study begins with a literature review emphasising the importance of placing copper on the advancing side (AS) to achieve defect-free dissimilar aluminium to copper FSW joints. However, tool offsetting on the retreating side (RS) or AS was found impractical for industrial applications due to varying tool offsets. Alternatively, researchers achieved defect-free joints by placing aluminium on the AS without tool offset. However, limited research has focused on this configuration, despite its benefits for joint mechanical properties. Further investigation is needed to understand the relationship between intermetallic compound microstructure and mechanical properties. To address these gaps, the research focused on dissimilar FSW between AA5083 aluminium and copper, exploring the influence of tool rotational and traverse speeds on joint quality without introducing tool offsetting. The findings revealed successful weld joints between the dissimilar materials using specific parameter combinations, including rotational speed levels of 1000 rpm (at welding speeds of 100 and 120 mm/min), 1200 rpm (at 80 mm/min), and 1400 rpm (at welding speeds of 80 and 120 mm/min). An inhomogeneous microstructure was observed within the weld, with the predominant intermetallic compounds (IMCs) identified as Al2Cu and Al4Cu9. The volume fraction of IMCs increased with higher tool rotational speeds, leading to improved ultimate tensile strength (UTS) and joint efficiency. Additionally, the study employed a novel approach to predict and validate the formation of IMCs during FSW of AA6061 aluminium to copper. The use of a Coupled Eulerian Lagrangian (CEL) model, combined with a modified friction law, provided good agreement with experimental data. The predicted IMCs, including AlCu, Al2Cu, and Al4Cu9, were confirmed through the comparison of temperature distribution, Al-Cu phase diagram, and elemental concentration. The research demonstrated that defect-free joints could be achieved at specific rotational speeds and traverse speed, where the softer material (AA6061) was placed on the AS. Furthermore, the research focused on optimising the FSW parameters for dissimilar joints between AA5083 and copper using the Taguchi design of experiments (DoE) method. By considering tool rotational speed, welding speed, and FSW tool design, the study successfully identified the significant parameters affecting joint mechanical strength. The optimised parameter combinations resulted in enhanced UTS, and flexure stress compared to the initial parameter sets. Linear regression analysis further confirmed the agreement between predicted and actual values of UTS and flexure stress. Finally, the study investigated the influence of different aluminium grades (AA5083 and AA6061) on dissimilar FSW of aluminium to magnesium AZ31B. Placing the softer material (AZ31B) on the AS consistently produced defect-free joints, and the joint mechanical strength improved when AZ31B was joined to the harder aluminium grade (AA6061). The presence of intermetallic compounds, such as Al3Mg2 and Al12Mg17, contributed to higher hardness values in the weld nugget, resulting in improved joint mechanical efficiency. The findings of this research have advanced the understanding of dissimilar materials FSW and provided insights into optimising the FSW process parameters for enhanced joint quality. The conclusions drawn from this study offer valuable guidance for future research and advancements in the field of dissimilar materials FSW process.
- Advisor / supervisor
- Toumpis, Athanasios
- Galloway, Alex
- Resource Type
- DOI
- Date Created
- 2023
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PDF of thesis T17268 | 2025-05-14 | Public | Download |