Influence of Si and Ge Microalloying Additions and Plastic Deformation on Precipitation Processes in Al-Cu Based Alloys

The combined effect of micro-alloying with Si and Ge and/or plastic deformationprior to ageing at 160˚C on age hardening has been studied in an Al-2 at%Cu alloy. The results obtained indicate that the hardness response is faster and the peak hardness is higher when plastic deformation and micro-alloying are applied together than performing each procedure individually. Different amounts of deformation, ranging from 0% to 30% have been utilized. An optimum deformation degree for the hardening response has been established around 8%for the Al-Cu-Si-Ge alloy. Characterization by transmission electron microscopy(TEM) shows that the peak hardness is due to a complex microstructurethat contained θ ′′ disc shaped precipitates, rod-shaped Si-Ge precipitatesand θ ′ plates that were heterogeneously nucleated on the Si-Ge particles.Pre-deformation has been found to stimulate the growth of the θ ′ platesdue to enhanced diffusion along dislocation cores. Increasing deformationreduces the influence of the Si-Ge precipitates on heterogeneous nucleation, leading to reduced peak hardness and faster over-ageing.Fil: Castro Riglos, Maria Victoria. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comision Nacional de Energía Atómica. Gerencia de Área Investigaciones y Aplicaciones no Nucleares. Gerencia de Física (Centro Atómico Bariloche). División Física de Metales; ArgentinaFil: Tolley, Alfredo Juan. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comision Nacional de Energía Atómica. Gerencia de Área Investigaciones y Aplicaciones no Nucleares. Gerencia de Física (Centro Atómico Bariloche). División Física de Metales; Argentin

Significant hardness enhancement in an Al–Cu–Mg alloy with high Cu:Mg ratio by microalloying with Si and Ge

The evolution of hardness in an Al-Cu-Mg based alloy with high Cu:Mg ratio (= 2, at. %) microalloyed with Si and Ge was studied during artificial ageing treatment performed at 190 °C. The results were compared to those obtained in a similar alloy with no Mg content. The hardness evolution in the Mg containing alloy was similar to that of the Mg free alloy, but shifted by about 50 Hv to higher values for all ageing times. The peak hardness occurred after 3 h ageing in both alloys, with a value slightly above 200 Hv in the Mg containing alloy. The microstructure of the peak aged and the overaged condition were characterized by means of transmission electron microscopy (TEM). For the Mg-containing alloy the microstructure of the peak aged condition consisted of plate-shaped precipitates, with a very similar structure to that of the θ′ phase and a high density of small needle-shaped precipitates lying along the Al directions. In the peak aged and overaged conditions the needle-shaped precipitates were found to belong to the Q′ phase (Al4Cu2Mg8Si7) or its precursor phases, previously observed in the Al–Mg–Si system with minor Cu additions.Fil: Castro Riglos, Maria Victoria. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Morello, Nicolas. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Tolley, Alfredo Juan. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentin

Improved kinetic behaviour of Mg(NH2)2-2LiH doped with nanostructured K-modified-LixTiyOz for hydrogen storage

The system Mg(NH2)2 + 2LiH is considered as an interesting solid-state hydrogen storage material owing to its low thermodynamic stability of ca. 40 kJ/mol H2 and high gravimetric hydrogen capacity of 5.6 wt.%. However, high kinetic barriers lead to slow absorption/desorption rates even at relatively high temperatures (>180 °C). In this work, we investigate the effects of the addition of K-modified LixTiyOz on the absorption/desorption behaviour of the Mg(NH2)2 + 2LiH system. In comparison with the pristine Mg(NH2)2 + 2LiH, the system containing a tiny amount of nanostructured K-modified LixTiyOz shows enhanced absorption/desorption behaviour. The doped material presents a sensibly reduced (∼30 °C) desorption onset temperature, notably shorter hydrogen absorption/desorption times and reversible hydrogen capacity of about 3 wt.% H2 upon cycling. Studies on the absorption/desorption processes and micro/nanostructural characterizations of the Mg(NH2)2 + 2LiH + K-modified LixTiyOz system hint to the fact that the presence of in situ formed nanostructure K2TiO3 is the main responsible for the observed improved kinetic behaviour.Fil: Gizer, Gökhan. Max-planck Strasse. Helmholtz-Zentrum Geesthacht GmbH. Institute of Materials Research; AlemaniaFil: Puszkiel, Julián Atilio. Max-planck Strasse. Helmholtz-Zentrum Geesthacht GmbH. Institute of Materials Research; Alemania. Comisión Nacional de Energía Atómica. Centro Atómico Ezeiza; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Castro Riglos, Maria Victoria. Max-planck Strasse. Helmholtz-Zentrum Geesthacht GmbH. Institute of Materials Research; Alemania. Comisión Nacional de Energía Atómica. Centro Atómico Ezeiza; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Pistidda, Claudio. Max-planck Strasse. Helmholtz-Zentrum Geesthacht GmbH. Institute of Materials Research; AlemaniaFil: Ramallo Lopez, Jose Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Mizrahi, Martin Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina. Max-planck Strasse. Helmholtz-Zentrum Geesthacht GmbH. Institute of Materials Research; AlemaniaFil: Santoru, Antonio. Max-planck Strasse. Helmholtz-Zentrum Geesthacht GmbH. Institute of Materials Research; AlemaniaFil: Gemming, Thomas. IFW Dresden; AlemaniaFil: Tseng, Jo Chi. German Electron Synchrotron; AlemaniaFil: Klassen, Thomas. Max-planck Strasse. Helmholtz-Zentrum Geesthacht GmbH. Institute of Materials Research; AlemaniaFil: Dornheim, Martin. Max-planck Strasse. Helmholtz-Zentrum Geesthacht GmbH. Institute of Materials Research; Alemani

Design of a Nanometric AlTi Additive for MgB2-Based Reactive Hydride Composites with Superior Kinetic Properties

Solid-state hydride compounds are a promising option for efficient and safe hydrogen-storage systems. Lithium reactive hydride composite system 2LiBH4 + MgH2/2LiH + MgB2 (Li-RHC) has been widely investigated owing to its high theoretical hydrogen-storage capacity and low calculated reaction enthalpy (11.5 wt % H2 and 45.9 kJ/mol H2). In this paper, a thorough investigation into the effect of the formation of nano-TiAl alloys on the hydrogen-storage properties of Li-RHC is presented. The additive 3TiCl3·AlCl3 is used as the nanoparticle precursor. For the investigated temperatures and hydrogen pressures, the addition of ∼5 wt % 3TiCl3·AlCl3 leads to hydrogenation/dehydrogenation times of only 30 min and a reversible hydrogen-storage capacity of 9.5 wt %. The material containing 3TiCl3·AlCl3 possesses superior hydrogen-storage properties in terms of rates and a stable hydrogen capacity during several hydrogenation/dehydrogenation cycles. These enhancements are attributed to an in situ nanostructure and a hexagonal AlTi3 phase observed by high-resolution transmission electron microscopy. This phase acts in a 2-fold manner, first promoting the nucleation of MgB2 upon dehydrogenation and second suppressing the formation of Li2B12H12 upon hydrogenation/dehydrogenation cycling.Fil: Le, Thi-Thu. Helmholtz Zentrum Geesthacht; AlemaniaFil: Pistidda, Claudio. Helmholtz Zentrum Geesthacht; AlemaniaFil: Puszkiel, Julián Atilio. Helmholtz Zentrum Geesthacht; Alemania. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Castro Riglos, Maria Victoria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Helmholtz Zentrum Geesthacht; Alemania. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Karimi, Fahim. Helmholtz Zentrum Geesthacht; AlemaniaFil: Skibsted, Jørgen. University Aarhus; DinamarcaFil: Gharibdoust, Seyedhosein Payandeh. University Aarhus; DinamarcaFil: Richter, Bo. University Aarhus; DinamarcaFil: Emmler, Thomas. Helmholtz Zentrum Geesthacht; AlemaniaFil: Milanese, Chiara. Università di Pavia; ItaliaFil: Santoru, Antonio. Helmholtz Zentrum Geesthacht; AlemaniaFil: Hoell, Armin. Helmholtz Zentrum Berlin für Materialien und Energie; AlemaniaFil: Krumrey, Michael. Physikalisch Technische Bundesanstalt; AlemaniaFil: Gericke, Eike. Universität zu Berlin; AlemaniaFil: Akiba, Etsuo. Kyushu University; JapónFil: Jensen, Torben R.. University Aarhus; DinamarcaFil: Klassen, Thomas. Helmholtz Zentrum Geesthacht; Alemania. Helmut Schmidt University; AlemaniaFil: Dornheim, Martin. Helmholtz Zentrum Geesthacht; Alemani

New Insight on the Hydrogen Absorption Evolution of the Mg-Fe-H System under Equilibrium Conditions

Mg2FeH6 is regarded as potential hydrogen and thermochemical storage mediumdue to its high volumetric hydrogen (150 kg/m3) and energy (0.49 kWh/L) densities. In this work, the mechanism of formation of Mg2FeH6 under equilibrium conditions is thoroughly investigated applying volumetric measurements, X-ray diffraction (XRD), X-ray absorption near edge structure (XANES), and the combination of scanning transmission electron microscopy (STEM) with energy-dispersive X-ray spectroscopy (EDS) and high-resolution transmission electron microscopy (HR-TEM). Starting from a 2Mg:Fe stoichiometric powder ratio, thorough characterizations of samples taken at different states upon hydrogenation under equilibrium conditions confirm that the formation mechanism of Mg2FeH6 occurs from elemental Mg and Fe by columnar nucleation of the complex hydride at boundaries of the Fe seeds. The formation of MgH2 is enhanced by the presence of Fe. However, MgH2 does not take part as intermediate for the formation of Mg2FeH6 and acts as solid-solid diffusion barrier which hinders the complete formation of Mg2FeH6. This work provides novel insight about the formation mechanism of Mg2FeH6.Fil: Puszkiel, Julián Atilio. Helmholtz–Zentrum Geesthacht; Alemania. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Castro Riglos, Maria Victoria. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Ramallo Lopez, Jose Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Mizrahi, Martin Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Gemming, Thomas. IFW Dresden; AlemaniaFil: Pistidda, Claudio. Helmholtz–Zentrum Geesthacht; AlemaniaFil: Arneodo Larochette, Pierre Paul. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Bellosta von Colbe, José. Helmholtz–Zentrum Geesthacht; AlemaniaFil: Klassen, Thomas. Helmut Schmidt University; Alemania. Helmholtz–Zentrum Geesthacht; AlemaniaFil: Dornheim, Martin. Helmholtz–Zentrum Geesthacht; AlemaniaFil: Gennari, Fabiana Cristina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Study and characterization of the effect of titanium-based compounds on the hydride system Li-B-Mg-H with high hydrogen storage capacity

La falta de un medio para el almacenamiento de hidrógeno de modo seguro y eficiente es uno de los principales inconvenientes para el empleo del hidrógeno como nuevo vector de energía. El almacenamiento de hidrógeno en estado sólido mediante la formación de compuestos hidruros presenta la ventaja de alcanzaraltas capacidades de almacenamiento a temperaturas y presiones moderadas.En el presente trabajo se investiga el efecto de aditivos en base titanio (TiB2, LixTiO2) sobre el comportamiento cinético del sistema hidruro reactivo 2LiBH4+MgH2. Los resultados obtenidos muestran que la presencia de partículas nanométricas de fases titanato (LixTiO2) mejoran notablemente la primeradeshidrogenación no isotérmica del 2LiBH4+MgH2, reduciendo el tiempo de liberación completa de hidrógeno desde 35 h. hasta 2 h. A su vez, la adición de LixTiO2 mejora las cinéticas de hidrogenación/deshidrogenación isotérmicas. Mediante el empleo de técnicas avanzadas como la microscopía electrónica de transmisión y la espectroscopía Raman, entre otras, se evidenció que adición de LixTiO2 al sistema hidruro 2LiBH4+MgH2 permite la absorción/desorción de hidrógeno través de un mecanismo novedoso y reversible.One of the main constraints for the implementation of hydrogen as energy carrier is the lack of an efficient and safe hydrogen storage system. Hydrogen storage in solid state through hydride compounds formation is a potential alternative to address this problem. In this work, it is studied the effect of different titanium based compounds (TiB2, LixTiO2) on the kinetic behavior of 2LiBH4+MgH2 reactive hydride composite. It is found that nanometric particles of titanates (LixTiO2) noticeably improve the first non-isothermal dehydrogenation behavior of the 2LiBH4+MgH2, reducing the complete H2 release time from 35 h to 2 h. Moreover, the LixTiO2 addition improves the isothermal hydrogenation/dehydrogenation kinetic behavior. The information gained by advanced techniques such as transmission electron microscopy and Raman spectroscopy, among others, help us to elucidate that the addition of LixTiO2 to 2LiBH4+MgH2 allows the hydrogen uptake/release via a novel and reversible mechanism.Fil: Martinelli, Hernan. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; ArgentinaFil: Castro Riglos, Maria Victoria. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Puszkiel, Julián Atilio. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Solute clustering behavior between 293K and 373K in a 6082 Aluminum alloy

We present a systematic study of the effect of pre-ageing between 293 K and 373 K in a 6082 Aluminum alloy using mainly differential scanning calorimetry in combination with Vickers hardness and transmission electron microscopy. The pre-ageing effects are characterized through the modifications of the β″ precipitation DSC signal. Pre-ageing at 293 K leads to a progressive increase of the peak temperature, until it reaches a plateau at long aging times (≥250min), while pre-ageing at 373 K leads to a continuous decrease of the peak temperature. The results indicate the formation of two different types of clusters, named 1 and 2, below and above a pre-ageing transition temperature, determined to be around 343 K. After pre-ageing below 343 K, the dissolution of clusters 1 superimposed with the β″ precipitation occurs, and the enthalpy change remains almost independent of pre-ageing time. Instead, pre-ageing above 343 K leads to the formation of type 2 clusters that transform on heating into β″ phase precipitates, with a decreasing enthalpy change as pre-ageing time increases. This result indicates that clusters 2 evolve during pre-ageing, reaching a structure/composition with formation enthalpy similar to that of β″ phase. Vickers hardness reveals the different evolution of both types of clusters with aging time. Transmission electron microscopy observations on samples subsequently aged at 453 K, show that type 2 clusters favour the nucleation of β″ precipitates, while type 1 clusters hamper such nucleation process.Fil: Noseda Grau, Victoria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil; Argentina. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Instituto de Física de Materiales; ArgentinaFil: Cuniberti, Adela Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil; Argentina. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Instituto de Física de Materiales; ArgentinaFil: Tolley, Alfredo Juan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Castro Riglos, Maria Victoria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Stipcich, Marcelo Fernando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil; Argentina. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Instituto de Física de Materiales; Argentin

Ultrafine-grained Al composites reinforced with in-situ Al3Ti filaments

Ultrafine-grained (UFG) Al matrix composites reinforced with 15 and 30vol% in-situ Al3Ti filaments were fabricated by extrusion of Al-Ti powder mixtures followed by solid-state reactive diffusion. Fine Al powder particles (1.3μm) heavily deformed the coarser Ti particles (24.5μm) into filaments during extrusion. Upon a subsequent operation of hot isostatic pressing (HIP), the micrometric Al3Ti filaments elongated along the extrusion direction and formed in situ in the UFG Al matrix. Fabricated composites are free of pores and voids with perfect bonding created at the Al-Al3Ti interfaces. In parallel, a small portion (2.4vol%) of nanoscale γ-Al2O3 particles, which originate from native amorphous films on fine Al powders, formed in situ and were homogenously dispersed in the Al matrix. The microstructures of as-extruded and after HIP composites were analyzed by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive spectrometry (EDS) and electron back-scattered diffraction (EBSD). Owing to the presence of nanometric γ-Al2O3 particles with Al high angle grain boundaries (HAGBs), the UFG Al matrix remained stable even after HIP at 600°C for 9h. The mechanical properties and creep performance of composites at testing temperatures of up to 600°C were systematically studied. The Al-Al3Ti composites exhibited a combination of increased strength and Young's modulus in addition to excellent creep performance and structural stability, which indicates that the studied composites are potential structural materials capable of service at elevated temperatures.Fil: Krizik, Peter. Slovak Academy of Sciences; EslovaquiaFil: Balog, Martin. Slovak Academy of Sciences; EslovaquiaFil: Nosko, Martin. Slovak Academy of Sciences; EslovaquiaFil: Castro Riglos, Maria Victoria. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Dvorak, Jiri. Institute of Physics of Materials; República ChecaFil: Bajana, Oto. Slovak Academy of Sciences; Eslovaqui

Forged HITEMAL: Al-based MMCs strengthened with nanometric thick Al2O3 skeleton

Bulk Al-Al2O3 metal matrix composites (MMCs) named HITEMAL (high temperature aluminum) were fabricated in situ by forging compaction of five different types of gas-atomized commercial purity Al powders with a mean particle size in the range of 1-9μm. As-forged HITEMAL consisted of (sub)micrometric Al grains (matrix) decorated with nanometric thick amorphous Al2O3 (a-Al2O3) skeleton. Low-angle grain boundaries (LAGBs) free of Al2O3 were located in the Al grain interior. The Al grain size and the portion of LAGBs increased with the increase in the relative powder surface area. As-forged HITEMAL shows excellent thermal stability up to 400°C for 24h. Annealing at temperatures ≥450°C led to crystallization and morphological transformation from a-Al2O3 skeleton to nanometric γ-Al2O3 particles. Owing to the pinning effect of Al2O3 phase, no Al grain growth took place during annealing up to 500°C. HITEMAL showed attractive mechanical properties especially when tested at 300°C (yield strength up to 220MPa, Young's modulus up to 58GPa). Despite the presence of a nearly continuous a-Al2O3 skeleton along adjacent Al grains, forged HITEMAL materials had reasonable room temperature elongation of 7-26%. HITEMAL's elongation decreased as the Al grain size decreased and with increased testing temperature. The loss in elongation (uniform and total) was attributed to the inhomogeneous flow, which occurred due to high densities of high angle grain boundaries (dislocation sinks) and small content of LAGBs. The strength of HITEMAL stemmed from grain boundary mediated strengthening mechanisms. The results showed a positive deviation from the Hall-Petch plot, which is typical behavior of ultrafine-grained metals. Transformation of a-Al2O3 skeleton to γ-Al2O3 particles led to deterioration of the HITEMAL strength and Young's modulus.Fil: Balog, Martin. Slovak Academy of Sciences. Institute of Botany; EslovaquiaFil: Krizik, Peter. Slovak Academy of Sciences. Institute of Botany; EslovaquiaFil: Nosko, Martin. Slovak Academy of Sciences. Institute of Botany; EslovaquiaFil: Hajovska, Zuzana. Slovak Academy of Sciences. Institute of Botany; EslovaquiaFil: Castro Riglos, Maria Victoria. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche); Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Rajner, Walter. No especifíca;Fil: Liu, De Shin. No especifíca;Fil: Simancik, Frantisek. Slovak Academy of Sciences. Institute of Botany; Eslovaqui

On the thermal stability of ultrafine-grained Al stabilized by in-situ amorphous Al2O3 network

Bulk Al materials with average grain sizes of 0.47 and 2.4μm, were fabricated by quasi-isostatic forging consolidation of two types of Al powders with average particle sizes of 1.3 and 8.9μm, respectively. By utilizing the native amorphous Al2O3 (am-Al2O3) film on the Al powders surfaces, a continuous, ~7nm thick, am-Al2O3 network was formed in situ in the Al specimens. Systematic investigation of the changes to the am-Al2O3 network embedded in the Al matrix upon heating and annealing up to 600°C was performed by transmission electron microscopy (TEM). At the same time, the stability of the Al grain structure was studied by transmission Kikuchi diffraction (TKD), electron back-scatter diffraction (EBSD), and TEM. The am-Al2O3 network remained stable after annealing at 400°C for 24h. In-situ TEM studies revealed that at temperatures ≥450°C, phase transformation of the am-Al2O3 network to crystalline γ-Al2O3 particles occurred. After annealing at 600°C for 24h the transformation was completed, whereby only nanometric γ-Al2O3 particles with an average size of 28nm resided on the high angle grain boundaries of Al. Due to the pinning effect of γ-Al2O3, the Al grain and subgrain structures remained unchanged during annealing up to 600°C for 24h. The effect of the am-Al2O3→γ-Al2O3 transformation on the mechanical properties of ultrafine- and fine-grained Al is discussed from the standpoint of the underlying mechanisms.Fil: Balog, Martin. Slovak Academy of Sciences; Eslovaquia. University of California at Davis; Estados UnidosFil: Hu, Tao. University of California at Davis; Estados UnidosFil: Krizik, Peter. Slovak Academy of Sciences; EslovaquiaFil: Castro Riglos, Maria Victoria. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Saller, Brandon D.. University of California at Davis; Estados UnidosFil: Yang, Hanry. University of California at Davis; Estados UnidosFil: Schoenung, Julie M.. University of California at Davis; Estados UnidosFil: Lavernia, Enrique J.. University of California at Davis; Estados Unido