[en] The restrictions on CO2 emissions into the atmosphere promoted by the European Union have obliged manufacturers to reduce the weight of their vehicles and, in turn, their individual components. This has led to a transition of materials, from cast iron to aluminium alloys, thanks to their lower density. However, aluminium alloys present inferior mechanical properties, and difficulties, therefore, in terms of complying with the requirements required of the parts, especially in those areas subjected to greater stresses. Hence, the present thesis is centred on the improvement of behaviour in service of components manufactured in low-pressure die-casting and subjected to strict loads, as could be the case with wheel rings and knuckle arms. Firstly, aluminium alloy alternatives to A356 (Al-Si-Mg), the most used currently, have been developed with the objective of increasing its mechanical properties. To this end, two routes were chosen: adding Cu to the A356 composition resulting in Al-Si-Cu-Mg alloys, in which it is necessary to combine high strength and elongation with good resistance to corrosion; and adapting 7xxx wrought alloys compositions series to be used in foundry processes. In both cases, the study was focused on the design of the composition and the optimum heat treatment to be applied. As a result, two alloys were obtained, one from each family which, once heat treated, reach up to 357 MPa of yield strength, 398 MPa of UTS and 11.1% of elongation, representing an improvement of 90, 53 y 120% respectively in the tensile properties of the A356 alloy. Additionally, due to their position in the vehicle, these components are subjected to high stresses over time, which can cause fatigue failure. The fatigue behaviour of a part depends on different factors, such as surface quality, stress concentrators, residual stresses... Furthermore, in casting components, defects introduced during this process are determining. Among these, porosity is the one that has a greater impact. The specific models developed thus far do not consider sufficiently the influence of this factor on fatigue life, with the result that they may provide errors in the estimation. As an alternative, in the present thesis, a new prediction model for fatigue life estimation in casting aluminium alloys is presented. It considers the effect of porosity in both initiation and propagation stages, giving predictions with logarithmic errors no greater than 2%.

[eu] Azken urteetan Europar Batasunak CO2 isurketekiko ezartzen joan den muga gero eta errestriktiboek ibilgailuen pisua murriztera bultzatu dute, eta ondorioz, iblgailuak osatzen dituzten konponenteen pisua. Hori dela eta, konponente estrukturaletan erabilitako materialeen eraldaketa bat suposatu du galdaratutako burnizko konponentetatik aluminiozkoetara, azken honek duen dentsitate baxua medio. Ala ere, alumino aleazioek propietate mekaniko mugatuagoek dituzte eta, ondorioz, aluminozko konponenteek zailtasunak izan ditzakete konponente estrukturalei eskatzen zaien karga eta bizitza betekizunei aurre egiteko. Muga honi aurre egite aldera, tesi honek presio baxuko aluminio galdaraketa bidez garatutako konponenteen zerbitzu portaera hobetzeko ekarpenak egitea du helburu. Lehenik eta behin, gaur egun gehien erabilia den A356 (Al-Si-Mg) aluminio aleazioaren alternatiba diren bi aleazio berri garatu dira. Hortarako bi garapen bide nagusi landu dira: A356 aleazioei Cu gehitzea (Al-Si-Cu-Mg) beste elementu aleanteak doituz erresitentzia, elongazio eta korrosiorako portaera orekatzeko, eta forjako 7xxx (Al-Zn-Mg) familiaren egokitzapena galdaratua izan ahal izateko. Bi garapenetan, aleazioaren diseinuaz gain aplikatutako tratamendu termikoaren optimizazioa landu da. Garapenaren fruitu, 357 MPa-aerteko muga elastikoa, 398 MPa-arte erresistentzia máximo eta %11,1-eko elongazioak lortu dira, non %90, %53 eta %120eko hobekuntza suposatzen duen ezaugarri bakoitzean erreferentziazko A356 aleazioarekiko galdarekta prozesu bera erabiliaz. Bestalde, konponent estrukutralek karga ziklikoak jasan behar izaten dituzte beraien erabileran zear, eta ondorioz neke arazoak izan ditzakete. Konponente batek nekera duen konportamendua faktore askok mugatu dezakete: gainazal kalitateak, tetsio konzentradoreak, ondar tentsioak,… are gehiago, galdaraketa bidezko konponenteetan, fabrikazio prozesuan sortutako defektuek berebiziko pisua dute. Defeketu ezberdinen artean porositatea da garrantzia gehien dueña. Aldiz, gaur egunerarte garatutako neke modeloek ez dute behar bezela kontutan hartzen parámetro honek konponentearen bizitzan duen eragina, eta ondorioz bizitza estimazioetan errore handiak egiten dira. Hori dela eta, tesi hontan galdaraketako aluminio aleazioentzako bizitza estimatzeko modelo espezifikoa garatu da porositateak pitzaduren sorrera eta garapenean duen eragina kontutan harturik. Aztertutako kasuetan modeloak %2 azpiko errore logaritmikoak erakutsi ditu.