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.
| Date of Award | 18 Mar 2025 |
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| Original language | English |
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| Awarding Institution | - University Of Strathclyde
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| Sponsors | University of Strathclyde |
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| Supervisor | Alexander Galloway (Supervisor) & Athanasios Toumpis (Supervisor) |
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