[en] One of the current challenges in the aeronautic sector is the reduction of fuel consumption aiming at energy efficiency, reduction of emissions as well as reductions in operational costs of the aircraft. In order to face this challenge, increasingly lighter structures are required for more efficient and environmental-friendly airframe systems. Therefore, research and development in new materials and manufacturing processes leading to innovative lightweight and cost-effective structures is of great interest for the aeronautic industry. The development of welded integral reinforced panels offers new opportunities for lightweight and cost-effective structure manufacturing. However, these applications present important challenges that must be overcome for a successful implementation due to the highly complex and multi-disciplinary approach required for the design, manufacturing, maintenance and disposal of such structures. From the manufacturing process point of view, Friction Stir Welding (FSW) is an innovative joining technology with potential to substitute the traditionally used riveting for aircraft structure manufacturing. From the material point of view, the development of Third-Generation aluminium-lithium alloys have created opportunities for the introduction of low density and high-performance aluminium alloys. The successful implementation of both innovations, i.e., FSW technology and Third-Generation aluminium-lithium alloys opens new perspectives for the development of advanced aircraft structures. However, it is necessary to develop appropriate FSW process conditions in order to maximize the quality of the joints and structures that comply with the stringent requirements of the aeronautic sector. This thesis is mainly focused on the FSW process development for its implementation in the integral reinforced panel manufacturing characterised by stringer-skin type joints, using Third-Generation aluminium-lithium alloys. Although several alloys of this type have been investigated, the work is mainly focused on the AA2060-T8E30 and AA2099-T83 alloys. Critical factors for FSW process development such as tool designs, welding parameters and effects introduced by innovative corrosion protection techniques (Cr-free surface treatments, sealants) are investigated. The impact of all these factors in the quality of FSW joints is investigated by metallographic examination and mechanical tests including optical and electron microscopy, static pull-out, static tensile and fatigue tests. As a result of the work, optimized FSW process conditions are defined including a new FSW tool design capable to produce high-quality FSW joints for overlap joint configurations. The thesis has been developed in the framework of the project ecoTECH, which is a core-partner project of the Clean Sky 2 initiative for research and development of new technologies for future aircraft. An excellent collaborative work has been carried out among project partners and the development of innovative fuselage panel demonstrators is in progress at the time when this thesis is being deposited. The conclusions obtained in the thesis are being applied to the FSW manufacturing of the fuselage demonstrators with the aim of increasing the TRL level of this type of advanced structures. This could permit to introduce FSW as an enabling technology for the advanced manufacturing of aircraft structures showing benefits such as weight savings, reduction of energy consumption, reduction in the manufacturing time and costs, as well as advances towards a more automatic and digital manufacturing. In order to present the work in the clearest way possible, the thesis mentions 11 articles presented in a chronological way that represent the work performed in the FSW technology development for different types of aluminium alloys and overlap joint configurations. The contributions of each article are explained in each corresponding chapter. Nevertheless, the core articles that led to the completion of this thesis are articles 9, 10 and 11. These are the relevant articles that comply with the academic requirements and must be considered as a compendium of publications in substitution of the traditional PhD dissertation.

[eu] Sektore aeronautikoaren erronka nagusienetako bat erregaien kontsumoa murriztea da, efizientzia energetikoa, emisioen murrizketa edota hegazkinen operazioetako kostuen murrizketa bilatze aldera. Erronka honi aurre egiteko, eranginkorragoak eta ingurumenarekiko errespetagarriak diren sistema aeronautikoentzat gero eta estruktura arinagoak beharrezkoak dira. Beraz, arinak eta ekonomikoki eranginkorrak diren estrukturen garapenerako material eta fabrikazio prozesu berrien ikerketa eta garapenerako aktibitateak interes handikoak dira industria aeronautikoan. Soldatutako panel integral errefortzatuen garapenak aukera berriak eskeintzen ditu estruktura arin eta ekonomikoki eranginkorren fabrikazioan. Hala ere, aplikazio hauek erronka garrantzitsuak aurkezten dituzte, konplexutasun eta disziplina anitzeko hurreratzea eskatzen baitute beraien diseinua, fabrikazioa, mantenketa eta erretiratze prozesuak kontutan izanda. Fabrikazio prozesuen ikuspuntutik, marruskadura-astintze soldadura edo "Friction Stir Welding" (FSW) estruktura aeronautikoen fabrikazioa betidanik erabili izan den errematxeen teknologia ordezkatzeko potentziala duen lotura teknologia berritzaile bat da. Materialeen ikuspuntutik, hirugarren belaunaldiko aluminio-litiozko aleazioen garapenak dentsitate baxuko eta erresistentzia handiko aluminiozko aleazioen erabilerarako aukera berriak zabaldu ditu. Bi berrikuntza hauen inplementazio arrakastatsuak ate berriak irekitzen ditu aeronautikarako estruktura aurreratuen fabrikazioan. Hala ere, sektore aeronautikoko eskaera zorrotzak beteko dituzten kalitate handiko soldadurak gauzatzeko ezinbestekoak diren FSW soldadura baldintzak garatzea beharrezkoa da. Tesi hau hirugarren belaunaldiko aluminio-litiozko aleazioak erabiliz, langa-azal moduko FSW soldadurez osaturiko panel errefortzatu integralen fabrikaziorako beharrezkoa den FSW soldadura prozesuaren garapenean murgiltzen da. Gisa honetako hainbat aleazio aztertu diren arren, egindako lanak bereziki AA2060-T8E30 eta AA2099-T83 aleazioetan du ardatza. FSW soldadura prozesuaren garapenerako kritikoak diren faktoreak ikertu dira, nola hala, erreminten diseinua, soldadura parametroak eta korrosioaren aurkako babesa eskeintzen dute teknika berritzaileen efektuak (Cr-rik gabeko gainazalen tratamentuak, zigitzaileak). Faktore hauek FSW bidez eginiko soldaduren kalitatean duten eragina azterketa metalografiko eta entseiu mekanikoen bidez ikertu da, mikroskopia optiko eta elektronikoa, deserrotze eta trakzio entseiu estatikoak eta neke entseiuak barne. Eginiko lanaren emaitza bezala, FSW soldadura prozesuaren baldintza optimizatuak definitu dira, gainjarritako loturetan kalitate handiko FSW soldadurak egiteko aukera ematen duen erreminta diseinu berri bat barne. Tesia ecoTECH proiektuaren barnean garatu da, etorkizuneko hegazkinen teknologia berrien ikerketa eta garapenerako "Clean Sky 2" inziatibaren barneko ezinbesteko bazkideen proiektu mota izanik. Proiektuko bazkideen artean oso elkarlan aberasgarria egin da eta fuselaia panel berritzaileen estruktura erakusleen fabrikazioa martxan da tesi hau aurkeztu den unean. Tesian lortutako ondorioak fabrikazio honetan aplikatzen ari dira garatutako FSW teknologia aplikatuz, non estruktura berritzaile hauen heldutasun teknologikoa igotzea den helburu. Helburu hau gauzatzeak, FSW soldadura teknologia estruktura aeronautikoen fabrikazio aurreraturako teknologia giltzarri bezala kokatzea ekarriko luke. Honen onurak pisu murrizketa, energía kontsumoaren murrizketa, fabrikazio kostu zein denboren murrizketa eta fabrikazio automatikoago eta digitalago baterako aurrerapenak izango lirateke. Egindako lana ahalik eta modu argienean aurkezteko asmoz, tesian 11 artikulu aipatzen dira kronologikoki aurkeztuta, zeintzuk FSW soldadura teknologiarekin gainjarritako loturetan eta aluminiozko aleazioekin egindako garapen lan guztiaren erakusle diren. Dena dela, tesiaren garapena bideratu duten ezinbesteko artikuluak 9, 10 eta 11 artikuluak dira. Hauek dira baldintza akademikoak betetzen dituzten artikuluak eta publikazioen konpendiorako kontutan izan beharrekoak, tesi tradizionalen memoria ordezkatuz.