[en] This thesis analyses the solidification, the microstructure and the mechanical properties of several magnesium alloys. The objective is to establish correlations between them in order to predict the local mechanical properties of magnesium cast components. On one hand, the solidification times have been related to the grain sizes and on the other, the grain sizes to the tensile yield strength, as for example, using the Hall-Petch equation. These relationships are integrated into numerical models for the prediction of the local mechanical properties in castings. Moreover, the effect of the alloying elements in the mechanical properties and in the generation of the texture in HPDC magnesium alloys after uniaxial deformation has been analysed. This work is aimed at the aeronautic sector, specifically to substitute aluminium alloys in applications for the interior of commercial aircrafts. Four casting technologies and four alloys have been selected. The casting technologies are sand, investment, gravity die and high-pressure die-casting. Two of the selected alloys are commercial, the AZ91 and AM50 alloys. The commercial alloys are reference alloys for two new alloys. Three alloys, including the two commercial alloys, are based in the Mg-Al system. The fourth alloy is a higher strength magnesium alloy based in the Mg-Zn-Zr-Nd-Gd-Y system and designated as MRI207S. This investigation is divided into three sections. The first task is the production of magnesium castings and the acquisition of cooling curves. A variety of alloys have been cast obtaining several microstructures and consequently, different mechanical properties. The second section relates to the microstructural characterisation in as-cast and heat treated conditions. The applied heat treatment is the solution heat treatment and artificial aging (T6). In this section the precipitates of each alloy are identified, as well as the grain sizes in different areas and the fracture mechanisms. Precipitates increasing the strength are present in the new alloys. Moreover, texture generation in uniaxial deformation is analysed in order to investigate the effect of the alloying elements on the deformation mechanisms. The basal plane (0001) is oriented parallel to the loading direction. The obtained intensity is smaller than that obtained in wrought alloys. It has been concluded that the alloying elements have not affected the generation of the texture. The third section involves the mechanical characterisation. Tensile tests have been carried out in order to obtain the ultimate tensile strength, the tensile yield strength and the elongation of the material. The properties of the MRI207S alloy are close to the ones of the A357 aluminium alloy. Vickers microhardness tests have also been performed to see the influence of the kind of precipitates in mechanical properties. The morphology of the precipitates in the AZ91E alloy varies in the same zone, and, therefore, varying the local mechanical properties. Correlating the results obtained in these three sections, relationships between solidification time, grain size and tensile yield strength have been established for the new MRI207S gravity-cast alloy (cast by sand, investment and gravity die-casting).

[eu] Hemen aurkezten den tesi honek hainbat aleazioren solidotzea, mikroegitura eta ezaugarri mekanikoak aztertzen ditu. Helburua euren arteko erlazioak ezarri eta galdatutako piezen ezaugarri mekanikoak igartzea da. Batetik solidotze denborak ale tamainarekin erlazionatu dira, eta bestetik ale tamainak trakzioko elastikotasun mugarekin, Hall-Petch ekuazioaren bidez adibidez. Lorturiko ekuazioak zenbakizko modeloetan sar daitezke galdaketako piezen lekuko ezaugarri mekaniko iragartzeko. Aleazio elementuek ezaugarri mekanikoetan duten eragina ere aztertu da. Bestalde, injekziozko magnesio aleazioen testura sorkuntza deformazio uniaxialean ere aztertu da. Lan hau sektore aeronautikoan kokatzen da, hegazkin komertzialen barne aplikazioetan aluminio aleazioak ordezteko asmoarekin. Lau galdaketa teknologia eta lau aleazio aukeratu dira. Lau teknologiak hondarrezko moldekatzea, argizari galduzkoa, maskorrezkoa eta injekzioa dira. Aukeraturiko aleazioen artean, bi komertzialak dira, AZ91 eta AM50 hain zuzen ere. Aleazio komertzialak erreferentzia moduan erabili dira beste bi aleazio berrirentzat. Hiru aleazio, tartean bi komertzialak, Mg-Al aleazio sisteman oinarriturik daude. Laugarren aleazioa erresistentzia handiagoko magnesio aleazio bat da, Mg-Zn-Zr-Nd-Gd-Y sisteman oinarritua eta MRI207S deiturikoa. Hiru etapa nagusi bereizi dira. Lehenengoa magnesio piezen galdaketa eta hozketa kurben neurketan oinarriturik dago. Etapa honetan hainbat aleazio galdatu dira mikroegitura desberdinak eta ondorioz, ezaugarri mekaniko desberdinak lortzearren. Bigarren etapa karakterizazio mikroegituralaz arduratzen da. Aleazio bakoitzean agerturiko prezipitatuak, ale tamainak eremu desberdinetan eta haustura mekanismoak aztertu dira. Aleazio berrietan, materialaren erresistentzia hobetzen duten prezipitatuak aurkitu dira. Bestalde, testuraren garapena aztertu da deformazio uniaxialean. Helburua aleazio elementuek deformazio mekanismoetan duten eragina aztertzea izan da. (0001) planoa karga norabideari paralelo orientatzen da eta lorturiko intentsitatea forja aleazioetan emandakoa baino txikiagoa da. Aleazio elementuek testura sorreran eraginik izan ez dutela ere erakutsi da. Hirugarren fasea karakterizazio mekanikoari buruzkoa da. Trakzio saiakuntzak egin dira aleazio desberdinen haustura erresistentzia, elastikotasun muga eta luzapena ezagutzeko asmoz. MRI207S aleazioak A357 aluminio aleazioaren pareko ezaugarri mekanikoak ditu. Honenbestez, aluminio aleazioak ordezkatzeko posibilitate handiak ditu aleazio honek. Mikrogogortasun neurketak ere egin dira AZ91 aleazioan prezipitatu motek ezaugarri mekanikoetan duen eragina jakiteko asmoz. Prezipitatuen morfologia aldakorra da eremu jakin batean, eta ondorioz, lekuko ezaugarri mekanikoak ez dira konstanteak. Hiru etapa hauetan lorturiko emaitzak batuz, solidotze denboraren, ale tamainaren eta elastikotasun mugaren arteko erlazioak garatu dira MRI207 aleazio berriarentzat hondarrezko moldekatzeaz, argizari galdukoaz edo maskorrezkoaz galdatzen den kasuetarako.