DED-Arc Manufacturing of High-Strength Aluminium 7075 Alloy and Weldability Assessment of Aluminium Alloy Parts Produced by Additive Manufacturing
(2026)
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- The increasing demand for lightweight, high-performance structural components in aerospace, defence and energy applications has driven growing interest in aluminium alloys and additive manufacturing technologies. Among aluminium alloy families, high-strength 7075 (Al–Zn–Mg–Cu) alloys offer outstanding strength-to-weight ratios but remain challenging to process due to their susceptibility to hot cracking, hydrogen-induced porosity and limited weldability. These challenges are further amplified in fusion-based additive manufacturing processes, where repeated thermal cycling and complex solidification conditions strongly influence microstructural evolution and defect formation. In addition to manufacturability, the structural integration of additively manufactured aluminium components through welding represents a critical bottleneck, as additive manufacturing routes introduce distinct microstructural states and defect formation that can strongly affect weld pool behaviour, joint integrity and mechanical performance. Addressing both the fabrication and weldability of additively manufactured aluminium alloys is therefore essential for their reliable deployment in high end industrial applications. Beyond performance considerations, industrial sectors are increasingly driven by sustainability objectives, cost reduction pressures and the need for shorter development cycles. Additive manufacturing offers clear advantages in this regard by enabling near-net-shape fabrication, reduced material waste and enhanced design flexibility. However, for aluminium alloys, particularly high-strength grades, the successful exploitation of these advantages remains strongly constrained by metallurgical and process-related challenges that limit reproducibility, scalability and qualification. This thesis addresses the scientific and technological challenges associated with the additive manufacturing and integration of aluminium alloy components, with particular emphasis on DED-Arc and the weldability of additively manufactured aluminium alloys (DED-Arc and PBF-LBF). The work adopts a holistic manufacturing perspective, treating additive manufacturing and welding as a coupled process chain rather than isolated operations. This approach reflects the reality of industrial manufacturing, where additively manufactured components are rarely used as standalone parts but are instead integrated into larger assemblies through welding or hybrid joining techniques. By explicitly considering the interdependence between additive manufacturing and subsequent joining operations, the thesis aims to provide process knowledge that is directly applicable to industrial qualification and deployment scenarios. The first major part of the thesis focuses on the DED-Arc manufacturing of high-strength aluminium alloy components, with particular attention to the ER7075 alloy. While DED-Arc has demonstrated robust performance for more weldable aluminium alloys such as ER5183, its applicability to crack-sensitive high-strength alloys remains uncertain. To address this gap, a structured experimental programme was developed and divided into three sequential phases. Exploratory investigations on ER5183 and ER2219 alloys were first conducted to establish methodological expertise and identify key process parameters. These studies addressed filler metal quality, arc stability, thermal control, deposition path strategy, laser cleaning and post-weld heat treatment. The use of these reference alloys enabled the systematic identification of critical process variables under controlled conditions, thereby reducing experimental uncertainty when welding the significantly more crack-sensitive ER7075 alloy. This staged methodology ensured that observed effects could be reliably attributed to material behaviour rather than experimental artefacts. Building on this foundation, the created knowledge and expertise were subsequently applied to ER7075. The results demonstrate that DED-Arc manufacturing of high-strength aluminium alloys is feasible, but only within a narrow and highly sensitive processing window governed primarily by alloy-specific metallurgical behaviour. The wide solidification interval, strong susceptibility to hot cracking, hydrogen porosity formation and evaporation of volatile alloying elements impose strict requirements on process stability and thermal management. The thesis shows that filler metal quality is a decisive and often underestimated parameter, directly influencing arc stability, droplet transfer behaviour and hydrogen uptake, and must therefore be treated as a primary process variable. Variations in surface condition, chemical homogeneity and hydrogen content of the filler wire were shown to result in pronounced differences in process stability and defect formation. These findings highlight the need for stricter control and qualification of consumables when high-strength aluminium alloys are processed by DED-Arc. Thermal management was identified as a second critical pillar for successful DED-Arc manufacturing. Control of preheating conditions, interpass temperature and heat input significantly affects melt pool stability, microstructural evolution and defect sensitivity across the build height. In addition, the deposition path strategy was shown to strongly influence build quality, with straight bead strategies providing more stable thermal conditions than oscillating or weaving patterns for high-strength aluminium alloys. Complementary measures such as laser cleaning and post-deposition heat treatment further enhanced process robustness, although their effectiveness was found to depend strongly on the initial build quality achieved during deposition. These results emphasise the cumulative nature of thermal effects in DED-Arc manufacturing, where local instabilities compromise the integrity of the entire component. Effective thermal management must therefore be considered at both the local melt pool level and the global component scale. The second major part of the thesis investigates the weldability of additively manufactured aluminium alloy components, considering both wire-based (DED-Arc ER5183) and powder-based (PBF-LB AlSi10Mg) additive manufacturing processes. The weldability of these materials was benchmarked against conventionally manufactured aluminium alloys (EN AW 5083) using and comparing different fusion and solid-state welding processes. Detailed experimental investigations were conducted to assess defect formation, porosity distribution, microstructural anisotropy and mechanical performance of welded joints. This comparative approach enabled the direct evaluation of how additive manufacturing-induced features, such as porosity, grain morphology and chemical segregation, affect weld pool behaviour and joint performance under comparable welding conditions. The results demonstrate that weldability is strongly governed by the additive manufacturing process and the resulting material properties and characteristics, rather than by the welding process alone. DED-Arc-manufactured aluminium alloys exhibited weldability comparable to conventionally manufactured materials when low defect content and stable microstructures were achieved during additive manufacturing. In contrast, PBF-LB components showed increased sensitivity to fusion welding due to inherent porosity and gas entrapment, leading to pore belt formation and reduced mechanical performance. Solid-state welding processes, particularly Friction Stir Welding, were identified as a robust solution and independent of the base metal condition for joining additively manufactured aluminium components. These findings demonstrate that solid-state joining technologies offer significant advantages for the integration of additively manufactured aluminium parts, particularly in cases where fusion welding is limited by porosity-related defects. An advanced welding optimisation further demonstrated that joint quality can be significantly improved through the proper selection of filler metals, shielding gas compositions and surface preparation strategies, including laser cleaning. These findings reinforce the conclusion that welding optimisation must be considered an extension of the additive manufacturing process rather than a standalone operation. In this context, knowledge of the additive manufacturing history of the component, such as build orientation, thermal exposure and defect distribution, was shown to be essential for defining effective welding strategies. Overall, this study demonstrates that the reliable industrial application of additively manufactured aluminium alloy components depends on a manufacturing strategy that explicitly accounts for material behaviour throughout the entire process chain, from filler metal selection to final joining. DED-Arc is shown to be a viable and scalable additive manufacturing route for high-strength aluminium alloys when combined with rigorous control of filler metal quality, thermal management and deposition strategy. Furthermore, the interaction between additive manufacturing route and weldability is clarified, providing practical guidance for selecting suitable joining processes and supporting the qualification of hybrid additively manufactured structures. By linking process parameters, material characteristics and structural performance, this thesis contributes to the development of more robust qualification strategies for additively manufactured aluminium components intended for demanding industrial applications. The insights and best-practice guidelines developed in this work contribute both to the fundamental understanding of aluminium alloy behaviour under additive manufacturing and welding conditions. In addition, the results provide a practical foundation for future research and industrial implementation, supporting the broader adoption of additive manufacturing technologies for high-strength aluminium alloy structures.
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Gomes Nunes Silva, R. (2026). DED-Arc Manufacturing of High-Strength Aluminium 7075 Alloy and Weldability Assessment of Aluminium Alloy Parts Produced by Additive Manufacturing. https://hdl.handle.net/2078.5/274123