Abstract: Crack turning or delamination behavior of AA 2050-T87 and AA 7050-T7451 ESE(T)
and hourglass coupons under cyclic fatigue conditions is presented. Fatigue crack growth rate
curves, fracture surface examinations, and the preferred manner of crack growth for each alloy are
discussed in an effort to better understand fatigue crack growth behavior of aluminum-lithium
alloys in structural components under service conditions.
Abstract: Discs of Al85Ce8Ni5Co2 amorphous alloy were severely deformed by high pressure
torsion. Severe plastic deformation exceeding equivalent strain of 8.2 induces the formation of
nanocrystalline fcc-Al in a more stable residual amorphous matrix. Calorimetric and X-ray
diffraction measurements revealed that the deformed outer part of the disc crystallizes into a
mixture of equilibrium phases during the first thermal event. However, in the amorphous ribbon the
same crystalline mixture develops only after the second stage.
Abstract: Aluminum foam is a class of porous materials; in which closed pores are produced by a
gas generation in liquid (or semi-liquid) aluminum. Aluminum foams are, generally, fabricated by
heating a foamable precursor (a powder compact consisting of aluminum and TiH2 powders).
Decomposition of TiH2, which is followed by a hydrogen gas release, produces bubbles in molten
aluminum. In this research, aluminum foam was fabricated with the help of a chemical
exothermic reaction. Titanium and boron carbide (B4C) powders were blended in the Al-TiH2
precursor as reactive powder elements. When one end of the precursor was heated, a strong
exothermic reaction between titanium and B4C took place (3Ti + B4C 2TiB2 +TiC + 761KJ), and
the neighboring part of the precursor was heated by the heat of reaction. Hence, once the reaction
happens at the end of the precursor, it propagates spontaneously throughout the precursor. The
blowing process takes place at the same time as the reaction because aluminum melts and TiH2
decomposes by the heat of reaction. The advantage of this process is that the energy to make
aluminum foam is not necessarily supplied form the external source, but generated form inside of
the precursor. Therefore the blowing process is self sustainable (Self-Blowing Process). In this
work, the effect of processing parameters on the Self-Blowing Process was observed. The
processing parameters we focused on were blending ratio of the starting powders (aluminum, TiH2,
titanium, B4C) and heating methods.
Abstract: To obtain further progress and a more detailed understanding of the mechanisms
involved in recrystallisation, new and more accurate techniques such as in-situ observations are
necessary. This innovative method has been used to monitor the recrystallisation process in a
FEGSEM equipped with hot stage. Observations are done in backscatter mode with particular
attention to orientation contrast. EBSD maps of the observed areas can be acquired before and after
recrystallisation. Details of the movement of the interfaces between the recrystallised region and the
parent structure are recorded and analysed.
The results show that the grain boundaries observed do not move smoothly but with a jerky motion.
The recrystallising front sweeps through small areas, corresponding to single sub-grains or small
groups of them, very rapidly and then stops at other sub-grain boundaries for varying time before
progressing to the following area.
Abstract: This paper presents two studies illustrating the possibilities of Small-Angle X-ray
Scattering for characterising quantitatively the state of precipitation in aluminium alloys. In the first
example, maps are presented, of precipitate size and volume fraction in the cross-section of friction
stir welds of AA7449 alloy. It is shown that the influence of welding speed on the distribution of
mechanical properties can be understood using this microstructural data. In the second example, the
precipitation kinetics in an Al-Zr-Sc alloy is evaluated by in-situ small angle X-ray scattering.
Evidence is given for the heterogeneous chemical structure of the Al3(Zr,Sc) precipitates, consisting
of a Zr-rich shell surrounding a Sc-rich core. It is shown that this particular distribution results in a
very good resistance to coarsening of the precipitate microstructure.
Abstract: Nuclear magnetic resonance (NMR) is shown to be a sensitive metallurgical
characterization technique for metastable phase development during early stage aging of the high
purity experimental alloy Al(1.05Cu 1.7Mg) (at.%). It is shown, using 63Cu NMR and positron
annihilation lifetime spectroscopy (PALS), how room temperature structural evolution proceeds in
Al(1.05Cu 1.7Mg) prepared in the form of supersaturated solid solution. The combination of NMR
and PALS allows identification of solute aggregate chemistry and defect kinetics during natural
aging. Guinier-Preston-Bagaryatsky (GPB) zone formation is detected by NMR within 0.5 h of
quench, and the percentage of Cu atoms in GPB zones increases to ~80% within 50 h at room
temperature, with the residual 20% of Cu atoms remaining in solid solution. The formation of GPB
zones corresponds with the Vickers hardness, in fact the hardness is shown to directly depend on the
amount of total Cu partitioned to GPB zones. The vacancy kinetics, as measured by PALS, show an
exponential decay in time following the quench with the majority of decay complete within 50 h
supporting the notion that early stage hardening by GPB zone formation is controlled by defect
concentration and availability.
Abstract: An X-ray microtomography combined with hard X-ray imaging microscopy, that
potentially has a spatial resolution of the order of 10 to 100 nm, has been applied to the
three-dimensional observation of internal microstructural features in overaged Al-Ag alloys. A
Fresnel zone plate is used as an objective with a magnification of 49.3 times. Imaging of resolution
test patterns has indicated spatial resolutions of around 180 and 200 nm in the vertical and horizontal
directions, respectively. This paper reports the first impression of the microstructural imaging by
means of such a high-resolution imaging microtomography. Precipitate microstructures are readily
observed and quantified in terms of volume fraction and orientation. Conventional microtomography
with a simple projection geometry is also applied for comparison purpose at the highest resolution
level currently available at a third generation synchrotron facility. It would appear that the present
technique provides a unique potential to observe the 3-D geometry and spatial distribution of
nanoscopic features inside samples that are several orders of magnitude thicker than thin-foil
specimens for TEM observation.
Abstract: This paper generally presents different techniques available to image the microstructure of
materials in three dimensions (3D) at different scales. It then focuses on the use of the more
versatile of these techniques for aluminum alloys : X-ray tomography. The paper describes the
recent improvements (spatial and the temporal resolution, grain imaging). Electron tomography is
also presented as a promising technique to improve the spatial resolution.
Abstract: Ultrasonic velocity and attenuation measurements are powerful tools to infer much
information about the microstructure and properties of aluminum and its alloys. Laser-ultrasonics is
a technology that enables doing these measurements remotely, in-situ or inline and in a fraction of a
second. Therefore, it is possible to characterize the thermomechanical processing of aluminum
alloys with unprecedented time resolution. This paper reviews the physical principles that allow
relating velocity and attenuation measurements to various materials properties and microstructural
features such as elastic moduli, crystallographic distribution orientation (texture), residual stresses,
recrystallization and dislocations. In-situ (in laboratory furnaces) and in-line measurement examples
from the Industrial Materials Institute research group are reviewed and presented.