Abstract: By 3 dimensional X-ray diffraction (3DXRD) using high energy X-rays from
synchrotron sources it is possible to study in-situ the nucleation and growth during recrystallization.
In this paper it is described and discussed how 3DXRD can supplement EBSP measurements of
nucleation and growth. Three types of studies are considered: i) orientation relationships between
nuclei and parent deformed matrix, ii) recrystallization kinetics of individual bulk grains and iii)
filming of growing grains in deformed single crystals.
Abstract: This study presents in situ observations of recrystallization texture formation in
Al-3mass%Mg using SEM concurrent with electron back scattering pattern (EBSP) with hot stage. In
the present discussion, the emphasis is on the characteristics of the preferred growth or the shrinkage
of Cube and other oriented grains. The in-situ observations of recrystallization demonstrate clearly
that the nucleation, growth and shrinkage of recrystallized grains occur simultaneously in each
orientation in each region. The overall development of recrystallization texture depends on the
balance of nucleation/growth and shrinkage/disappearance of each orientation during
recrystallization. The preferential growth is determined by the grain boundary mobility between
recrystallized grains or the clusters composed of several similar oriented grains, i.e. Cube clusters or S
clusters, and neighboring deformed matrix, and the competitive growth with the surrounding grains.
On the other hand, the isolated oriented grain and the strain-stored grains tend to shrink and disappear
during recrystallization and grain growth.
Abstract: For 2195-T8 plate, design properties are based on the mechanical properties at the
near surface location, corresponding to the load carrying thin membrane location in machined
integrally stiffened structure. Mechanical properties at the near surface location are lower than
those at the t/4 and t/2 locations. This work examined the effect of alternate temper and hot
rolling practices on near surface strength levels. Results showed that alternate hot rolling
practice were very effective in raising near surface strengths and improving property uniformity,
and were well correlated with crystallographic texture measurements.
Abstract: The softening behaviour during annealing was investigated in cold and hot rolled
AA3103 alloys after different heat treatments. It was found that the evolution of boundary spacing
determined using gallium enhanced microscopy gives a very good representation of the softening
behaviour. The results show that cold rolled Al-Mn alloys soften by continuous growth of the
subgrain structure, “continuous recrystallisation”, provided the pre-treatment of the ingots has been
made to avoid too high a density of dispersoids and the cold rolling reduction has been very large.
The very high strain creates a microstructure with a large fraction of high angle boundaries that are
mostly parallel to the sheet surface. A recently developed subgrain growth model which takes the
effect of solute drag into account, gives a good description of the softening kinetics. The solute drag
is controlled by bulk diffusion of Mn. The simultaneous precipitation of Mn from the solid solution
takes place by grain boundary diffusion of the Mn atoms mainly to pre-existing particles. The solute
concentration decreases as the inverse of the boundary spacing, which is due to the grain growth
mainly in the thickness (normal) direction.
Abstract: This paper described new characterization methods and data to quantify the influence of
solute atoms on grain boundary and sub-grain boundary mobilities in Al-Mn alloys with a view to
their integration into recovery and recrystallization modelling.
Detailed SEM measurements of grain boundary mobilities during recrystallization have been made
by in-situ annealing experiments on cold deformed Al – 0.1 and 0.3wt.% Mn binary alloys. Stored
energies are estimated from the sub-grain sizes and misorientations and the boundary velocities
directly measured in the temperature range 200-450°C. It is shown that in many cases good
agreement with the Cahn, Lücke, Stüwe model for solute drag is obtained, e.g. the activation
energies are intermediate between those of boundary and volume solute diffusion. Some particular
cases of rapid growth occur in Al-0.1%Mn indicating boundary breakaway from solute clouds.
A complementary study of sub-grain boundary mobilities has started on the same alloys; in this
case the average mobilities are estimated from FEG-SEM growth data for the average sub-grain
size for temperatures in the range 150-300°C. The results are compared with some previous data on
Al-Si and show similar rates.
Abstract: A simple model for recovery of a subgrain structure is used to distinguish and explain the
respective influence of the deformed microstructure characteristics, annealing temperature and
concurrent precipitation kinetics on the nucleation kinetics of recrystallisation. Simulation results
demonstrate how the balance between recovery and precipitation kinetics controls nucleation.
Abstract: The starting material, the deformed state, as well as the recrystallised microstructure and
texture have been analysed as a function of Zener-Hollomon parameter and strain for two
differently heat-treated AlMgSi alloys, deformed in torsion. An interesting and somewhat
surprising observation is that the grain size was always higher in the material heat treated to form
large Mg2Si particles. Moreover, no indications of PSN effects were observed in any of the
materials, even at the highest Zener-Hollomon parameters. This observation was quite unexpected
as the highest Zener-Hollomon parameters were well above the typical critical level for which
significant PSN effects have been observed in similar alloys. The results have been carefully
analysed and possible explanations are discussed.
Abstract: Severe plastic straining is an established method for producing submicron grain (SMG)
structures in alloys. However, the development of such a fine grained structure in single-phase alloys
is usually futile if they are to be exposed or processed at elevated temperatures. This is a direct
consequence of the natural tendency for rapid and substantial grain coarsening which completely
removes the benefits obtained by grain refinement. This problem may be avoided by the introduction
of nanosized, highly stable particles in the metal matrix. In this work, a SMG structure was generated
in an Al-0.3 wt.% Sc alloy by Equal Channel Angular Pressing (ECAP). The alloy was prepared
initially to produce a fine grained microstructure exhibiting a large fraction of high angle grain
boundaries and a dispersion of nanosized Al3Sc particles. The evolution of microstructure during
annealing at temperatures up to 550 °C was examined in detail and grain size distributions generated
from the data. It was shown that grain coarsening is rapid at temperatures above 450 °C and the
initial log-normal grain size distribution exhibiting low variance and skewness was altered
considerably. The statistical information generated from the grain size distributions confirms that
discontinuous grain coarsening occurs in this alloy only at temperatures greater than 500 °C.
Abstract: The Mesoalite alloy is formed using rapidly solidified powder metallurgy (RS-P/M) by
hot extruding the RS powder produced by the atomization method. Meso20 is a Mesoalite alloy with
a chemical composition of Al-9.5Zn3Mg-1.5Cu-4Mn-0.04Ag (mass%). Meso20 contains fine grains
and precipitated intermetallic Mn compounds, and has a tensile strength of 910 MPa. During hot
extrusion, dynamic recrystallization occurs and the fine grains develop.
During heat treatment of Meso20, rod-like and granular Mn intermetallic compounds precipitate.
The rod-like compounds are about 1 Ìm in length and the granular compounds are about 1 Ìm in
diameter. X-ray diffraction measurement, transmission electron microscopy and energy dispersive
X-ray (TEM/EDX) analysis and Rietveld analysis revealed the chemical composition of the granular
and rod-like Mn intermetallic precipitates to be 86.5Al-10.9Mn-0.4Cu-0.9Zn-1.3Mg and 80.5Al -
10.3Mn-4.2Cu-2.5Zn-2.5Mg (mass%), respectively. The granular and rod-like compounds were
identified as the Al6Mn and Q phases, respectively, with both belonging to the space group Cmcm.
The lattice constants of Al6Mn were a=0.754 nm, b=0.648 nm c=0.855 nm and those of the Q phase
were a=0.765 nm b=2.34 nm c=1.25 nm.
Meso10, with a chemical composition of Al-9.5Zn-3Mg-1.5Cu-0.04Ag (mass%), contains no Mn
and does not have fine grains, but rather coarse fibrous grains elongated along the extrusion direction.
Thus the Mn intermetallic precipitates in Meso20 clearly affect the formation of fine grains.
Microstructure development was studied during hot extrusion by observation using high resolution
Electron Back Scattering Pattern method. Fine grains were found to develop in areas, which were
relatively abundant in granular Mn intermetallic precipitates.
Abstract: This work describes the microstructure and properties of a range of Al-(4-6)Mg-
(1.2-1.6)Li-(0.3-0.4)Zr-(0-0.2)Sc alloys produced at Oxford University by spraycasting. Follow-
ing hot isostatic pressing of the as-spraycast billets to close any porosity and to precipitate a
¯ne, coherent dispersoid population, forging to a true strain of 1 at 250 and 400±C led to a
substantial re¯nement of the microstructure with grain sizes in the range 0.8 to 5¹m. A large
intra-granular orientation gradient with distance measured using EBSD showed that at 250±C,
partial dynamic recrystallisation by progressive lattice rotation led to a `necklace' structure of
very ¯ne grains surrounding larger deformed grains. At 400±C, dynamic recrystallisation oc-
curred by nucleation of new grains at prior grain boundaries and triple points. The strength
of as-forged alloys was 200-350MPa and the high ductilities of up to 30% rendered the alloys
amenable to post-forging cold work. A proof strength of 460MPa with 9.5% elongation was
achieved in a non-heat-treatable spraycast Al-6Mg-1.3Li-0.4Zr alloy, matching the best prop-
erties of similar mechanically alloyed AA5091, and exceeding the properties of AA7010-T74.
The as-forged alloys showed excellent thermal stability up to » 0.9Tm, with no abnormal grain
growth and grain size stagnation due to Zener pinning. Finally, strain rate sensitivity testing
revealed the potential for superplasticity at 400 and 500±C and strain rates of 0.001-0.05s¡1.