With the advent of disruptive additive manufacturing (AM), there is an increasing interest and demand of high mechanical property aluminium parts built directly by these technologies. This has led to the need for continuous improvement of AM technologies and processes to obtain the best properties in aluminium samples and develop new alloys. This study has demonstrated that porosity can be reduced below 0.035% in area in Al-Mg samples manufactured by CMT-based WAAM with commercial filler metal wires by selecting the correct shielding gas, gas flow rate, and deposition strategy (hatching or circling). Three phase Ar+O₂+N₂O mixtures (Stargold^®) are favourable when the hatching deposition strategy is applied leading to wall thickness around 6 mm. The application of circling strategy (torch movement with overlapped circles along the welding direction) enables the even build-up of layers with slightly thicker thickness (8 mm). In this case, Ar shielding gas can effectively reduce porosity if proper flow is provided through the torch. Reduced gas flows (lower than 30 Lmin) enhance porosity, especially in long tracks (longer than 90 mm) due to local heat accumulation. Surprisingly, rather high porosity levels (up to 2.86 area %) obtained in the worst conditions, had a reduced impact on the static tensile test mechanical properties, and yield stress over 110 MPa, tensile strength over 270 MPa, and elongation larger than 27% were achieved either for Ar circling, Ar hatching, or Stargold^® hatching building conditions. In all cases anisotropy was lower than 11%, and this was reduced to 9% for the most appropriate shielding conditions. Current results show that due to the selected layer height and deposition parameters there was a complete re-melting of the previous layer and a thermal treatment on the prior bottom layer that refined the grain size removing the original dendritic and elongated structure. Under these conditions, the minimum reported anisotropy levels can be achieved.

Cold metal transfer (CMT)-based wire and arc additive manufacturing (WAAM) of Ti-6Al-4V alloy has been investigated to manufacture walls with two different building strategies. This study focuses on the influence of the application of thermal treatments on the resulting microstructure and mechanical properties. Deep microstructural analysis revealed different grades of growth of lamellae α phase after several thermal treatments at different temperatures, which lead to different tensile mechanical properties and better strength and ductility balance compared to the as-built condition. Results are compared with equivalent forged and casting standards and the state of the art for WAAM of Ti-6Al-4V alloy. At temperatures of 920 °C, anisotropy was maintained and elongation increased by 70% while yield strength and UTS was slightly decreased by 8%.

In this paper the effect of tool geometry and welding parameters on friction stir welded lap joints with AA2099-T83 and AA2060-T8E30 aluminium alloys has been investigated through the study of the material flow and weld formation along with the reaction forces during friction stir welding (FSW) for various sets of welding parameters and two FSW tools with different geometrical features. The results showed that welding parameters and tool probe geometry strongly affect the characteristics of the typical defect features (hook and cold lap defects) of the friction stir welded lap joints. From the relationship established between the welding parameters, tool probe geometry and the hook and cold lap defect formation, some guidelines are concluded with the objective of guaranteeing appropriate FSW lap joint properties.

The CMT-Twin-based wire and arc additive manufacturing (WAAM) process for 5356 aluminium alloy has been investigated focusing on the optimisation of welding parameters to maximise the deposition rate while avoiding segregation-related problems during solidification. For that, different conditions have been studied regarding interpass dwell time and the use of forced cooling. The larger heat input produced by the double-wire CMT-Twin process, compared to the single-wire CMT, creates vast segregations for less intensive cooling conditions and short dwell times that can induce cracks and reduce ductility. Thermography has been applied to set a maximum local temperature between consecutive layers avoiding those segregations and pores, and to optimise the total manufacturing time by varying the interpass dwell time along the height of the wall. Only a constant interpass long dwell time of 240 s and the new optimised strategy were effective in avoiding merged segregations, reducing the latest total manufacturing time by 36%. Obtained tensile properties are comparable to other works using WAAM for this alloy, showing lower properties in the vertical orientation. The use of CMT-Twin-based welding technology together with variable interpass dwell time controlled by thermography is an interesting alternative to build up parts with wall thicknesses around of 10 mm in a reduced time.

Reduced hot cracking susceptibility is essential to ensure the flawless manufacturing of nickel superalloys typically employed in welded aircraft engine structures. The hot cracking of precipitation strengthened alloy 718 mainly depends on chemical composition and microstructure resulting from the thermal story. Alloy 718 is usually welded in a solution annealed state. However, even with this thermal treatment, cracks can be induced during standard industrial manufacturing conditions, leading to costly and time-consuming reworking. In this work, the cracking susceptibility of wrought and investment casting alloy 718 is studied by the Varestraint test. The test is performed while applying different welding conditions, i.e., continuous tungsten inert gas (TIG), low frequency pulsed TIG, continuous laser beam welding (LBW) and pulsed LBW. Welding parameters are selected for each welding technology in order to meet the welding quality criteria requested for targeted aeronautical applications, that is, full penetration, minimum cross-sectional welding width and reduced overhang and underfill. Results show that the hot cracking susceptibility of LBW samples determined by the Varestraint test is enhanced due to extended center line hot cracking, resulting in a fish-bone like cracking pattern. On the contrary, the minor effect of material source (wrought or casting), grain size and pulsation is observed. In fact, casting samples with a 30 times coarser grain size have shown better performance than wrought material.