Fusion-based additive manufacturing (AM) techniques face some challenges for aluminium due to the necessity of material melting resulting in insufficient bonding. The present work provides a novel insight into the combination of fusion-based and solid-state AM approaches to successfully generate structures from different aluminium alloys. Specifically, the friction-based solid-state AM technique of friction surfacing (FS) is used to generate an interlayer structure on AA2050 substrate material. On top of this structure, additional AA5087 is deposited via Wire and Arc Additive Manufacturing (WAAM). For the FS interlayer structure, two different alloys, AA5083 and AA7050, are explored. Additionally, the effect of inter-layer rolling is investigated for the final WAAM structure. The built structures are investigated with special focus on the interfaces, i.e., FS deposit-to-substrate and WAAM deposit-to-FS deposit interfaces. In the cross sections, no defects could be detected at the FS deposit-to-substrate interfaces and the structures did not show visible cracks at the WAAM deposit-to-FS deposit interfaces. The investigation showed that the mechanical properties of the WAAM structure improve when inter-layer rolling is applied, leading to homogeneous mechanical properties across the interfaces. The study highlights that FS as friction-based solid-state AM process is capable to build interlayer structures for material combinations, which cannot be achieved directly via a fusion-based process. The approach of combining different AM techniques can be advantageous not only to achieve a dissimilar material combinations but also to build hybrid structures with locally optimized properties.

The Innovative Aluminium filler Wires for Aircraft Structures (IAWAS) project aimed to demonstrate the potential of Wire Arc Additive Manufacture (WAAM) for the production of aluminium lithium components. Preliminary testing demonstrated the possibility of depositing an 2395 aluminium lithium filler wire using a plasma arc heat source and a local shielding device. The deposit had a low porosity level but also low ductility caused by long, vertical, segregated grain boundaries. Both chemical composition and deposition conditions are known to impact the deposit microstructure. In-situ alloying, an efficient technique to develop new material, was implemented using plasma arc as a heat source on aluminium lithium alloys. The results aligned with the literature review on the impact of copper on crack sensitivity and led to the design of a new alloy. Unfortunately, the composition selected yielded challenges during the drawing process, and the filler material quality was poor, leading to a low WAAM deposit quality. Machine hammer peening was implemented on the AA2395 alloy, resulting in a drastic increase in ductility and yield strength of 480 MPa after solution treatment and ageing. This alloy was used to manufacture an aluminium lithium demonstrator to showcase the potential of WAAM to produce real-life components.

Additive manufacturing (AM) of Al-Mg-Sc alloys has received considerable interest from the aerospace industry owing to their high specific strength and suitability for AM processes. This study has investigated the fatigue crack growth behavior in an Al-Mg-0.3Sc alloy made by wire and arc additive manufacturing. Tests were conducted with two different crack orientations at cyclic load ratios of 0.1 and 0.5. At the lower load ratio, the horizontal crack showed a faster growth rate owing to the smaller grains and coarser second-phase particles that the crack tip had encountered when it propagated along the material build direction. The anisotropy in crack growth rate was mainly caused by the grain size effect. When the applied stress intensity factor range exceeded the value of 10 MPa m(1/2), an isotropic crack growth rate between the two crack orientations was measured. This is due to the microstructural influence being overcome by the governing parameter of fracture mechanics. At the higher load ratio of 0.5, crack growth rate is isotropic, and the threshold stress intensity factor range was much lower than that tested under load ratio 0.1. Finally, the modified Hartman-Schijve equation has been successfully employed to represent the crack growth rates in all three regions.

Aluminium copper magnesium alloys are widely used in the aerospace sector. Wire-based Directed Energy Deposition could replace conventional manufacturing routes to build large and semi-complex components for this industry if high mechanical performance can be achieved in the deposit. The scope of this study was to assess the effect of inter-pass rolling on a 2024 aluminium alloy wire-based DED built structure and to investigate the impact of cold work during the deposition process on the microstructure and mechanical performances. The 2024 aluminium alloy was deposited using two variants of gas metal arc process, and the effects of the deposition process, cold work and heat treatment were studied using macro and microstructural observations, hardness measurement and tensile tests. The material response to inter-pass rolling and the formation of rolling defects was found to depend on the deposition process variant and bead geometry. While a significant strengthening of the deposit was observed with one process, only a drastic reduction of defects was observed with the second. It was also found that the application of cold work and heat treatment led to lowering of anisotropy and higher ductility when compared with heat-treated deposit without any inter-pass rolling.

Wire + Arc Additive Manufacture is an Additive Manufacturing process that requires a substrate to initiate the deposition process. In order to reduce material waste, build and lead time, and improve process efficiency, it is desirable to include this substrate in the final part design. This approach is a valid option only if the interface between the substrate and the deposited metal properties conform to the design specifications. The effect of substrate type on the interface microstructure in an aluminium part was investigated. Microstructure and micro-hardness measurements show the effect of substrate alloy and temper on the interface between the substrate and deposited material. Microcracks in the as-deposited condition were only found in one substrate. The deposited material hardness is always lower than the substrate hardness. However, this difference can be minimised by heat treatment and even eliminated when the substrate and wire are made of the same alloy.

Aluminium zinc alloys are widely used in the aerospace industry due to their high strength. However, only a few studies have been reported on the additive manufacture of aluminium zinc alloys. This rarity is due to the difficulties occurring during the fusion processing of these alloys and to the lack of available raw material. This paper presents an alternative process used for the deposition of aluminium zinc alloys. In this study, a Wire Laser Arc Additive Manufacture (WLAAM) system was used. This consisted of a gas metal arc power source, used to generate the melt pool, and a laser beam applied to control the melt pool size. By using this approach, it was possible to produce an elongated melt pool and feed zinc into it with a cold wire without compromising the process stability. A welding camera along with a system measuring the arc voltage and current was used to monitor the process. Different process parameters and configurations were investigated along with their effect on process stability and deposited material microstructure. A very high zinc concentration was achieved in the deposited material without macro-segregation.

High deposition rate Wire and Arc Additive Manufacture (WAAM) can provide benefits to the aerospace industry, including a reduction in lead time, reduced material waste and, through higher solidification rates, refinement of the as-built microstructure relative to a cast material. However, candidate 2xxx series high strength alloys for this process normally require a solution treatment, which is problematic for large near-net-shape components, and age hardening to achieve maximum mechanical properties. With each layer being subject to multiple thermal cycles, exploiting the thermal conditions in the WAAM process to avoid post-build solution treatment is therefore of interest. A solutionisation model has been developed for the WAAM process, based on diffusion controlled dissolution using DICTRA, which was validated through thermal simulations combined with 2D and 3D image analysis. The model has subsequently been used to simulate the solutionisation behavior during a typical WAAM thermal cycle and to explore what could theoretically be achieved by, for example, refining the starting microstructure.

The aluminium alloy wire 2319 is commonly used for Wire + Arc Additive Manufacturing (WAAM). It is oversaturated with copper, like other alloys of the precipitation hardening 2### series, which are used for structural applications in aviation. Residual stress and distortion are one of the biggest challanges in metal additive manufacturing, however this topic is not widely investigated for aluminium alloys. Neutron diffraction measurements showed that the as-built component can contain constant tensile residual stresses along the height of the wall, which can reach the materials' yield strength. These stresses cause bending distortion after unclamping the part from the build platform. Two different rolling techniques were used to control residual stress and distortion. Vertical rolling was applied inter-pass on top of the wall to deform each layer after its deposition. This technique virtually elimiated the distortion, but produced a characteristic residual stress profile. Side rolling instead was applied on the side surface of the wall, after it has been completed. This technique was even more effective and even inverted the distortion. An interesting observation from the neutron diffraction measurements of the stress-free reference was the significantly larger FCC aluminium unit cell dimension in the inter-pass rolled walls as compared to the as-build condition. This is a result of less copper in solid solution with aluminium, indicating greater precipitation and thus, potentially contibuting to improve the strenght of the material.