Materials Science Forum
Vols. 532-533
Vols. 532-533
Materials Science Forum
Vols. 530-531
Vols. 530-531
Materials Science Forum
Vols. 527-529
Vols. 527-529
Materials Science Forum
Vol. 526
Vol. 526
Materials Science Forum
Vols. 524-525
Vols. 524-525
Materials Science Forum
Vols. 522-523
Vols. 522-523
Materials Science Forum
Vols. 519-521
Vols. 519-521
Materials Science Forum
Vol. 518
Vol. 518
Materials Science Forum
Vol. 517
Vol. 517
Materials Science Forum
Vols. 514-516
Vols. 514-516
Materials Science Forum
Vol. 513
Vol. 513
Materials Science Forum
Vol. 512
Vol. 512
Materials Science Forum
Vols. 510-511
Vols. 510-511
Materials Science Forum Vols. 519-521
Paper Title Page
Abstract: The effect of welding, heat-affected zone (HAZ) simulation, and specimen orientation on
the microstructure and fatigue properties of 2195 Al-Li alloy was studied. HAZ simulation and
GTA welding with a 4043 filler alloy resulted in a significant change in the microstructure. In the
HAZ the primary strengthening phase, T1 (Al2CuLi), in the base alloy in T8 temper was replaced by
TB (Al7Cu4Li) phase and voids/microcracks, and the fusion zone (FZ) consisted of T (AlLiSi) phase
particles in the matrix, which consisted mainly of the filler alloy. The yield strength and fatigue
threshold of the 2195-T8 alloy were observed to be dependent upon the specimen orientation. The
HAZ simulation and welding led to a reduction in the tensile properties and fatigue strength. While
the post-weld heat treatment resulted in the re-precipitation of T1 phase in the HAZ, but no increase
in the fatigue strength was observed due to the presence of microcracks. Fatigue crack initiation
was observed to occur at the surface in the base alloy in T8 temper, and at the internal defects after
HAZ simulation and welding. Fatigue crack propagation exhibited characteristic striations in the
T8 alloy, and brittle cleavage-like feature after HAZ simulation and welding.
147
Abstract: Al-0.1Mg with a 3μm grain size was deformed in channel die plane strain compression
at temperatures up to 200oC. It was found that the reduction in grain thickness was significantly less
than that predicted from geometric considerations, and at larger strains, a minimum high angle grain
spacing, which was equal to the crystallite size was achieved. The velocity of the high angle
boundaries during this process is very many orders of magnitude larger than that predicted for
curvature driven grain growth, and some possible explanations for this are discussed.
153
Abstract: The development of grain structures after asymmetric rolling (ASR) and annealing was
investigated in Al-Mg alloys AA5754, AA5182 and AA5083. It has been demonstrated that a fine
grain structure could be produced through continuous recrystallization, but it is strongly affected by
the presence of large second phase particles. In AA5754 the volume fraction of large particles is
relatively low and continuous recrystallization is able to occur throughout the sheet thickness,
resulting in a fine grain structure of 2μm mean grain size. In AA5182 the fraction of large particles
increases to a level that the continuous recrystallization occurs only in the sheet surface, whereas
the sheet centre undergoes discontinuous recrystallization. The discontinuous recrystallization due
to particle stimulated nucleation (PSN) is dominant in AA5083 so that no continuous
recrystallization has been observed. The fully recrystallized grain structure is slightly finer in the
ASR processed AA5083 than the conventionally rolled one.
161
Abstract: The role of Cu in precipitation behavior of 6000 series aluminum alloys has been investigated by
isothermal calorimetry and transmission electron microscopy. The newly developed analytical
techniques have been used to evaluate the precipitation kinetics in alloys with or without an initial
pre-aging history. It has been found that Cu addition results in increasing the rate of precipitation
when artificial aging is applied immediately after solutionizing and quenching. However, Cu has no
significant effect on the kinetics of precipitation in alloys with the pre-aging history, while it
produces finer microstructures in the pre-aged and then artificially aged alloys. These observations
have been explained by the effect of Cu on increasing the rate of precipitate nucleation in 6000
series alloys. It has also been suggested that the effect of Cu on nucleation arises from the role of
Cu on the cluster formation during and/or immediately after quenching.
169
Abstract: AA6111 sheet alloy has been used in automotive panel applications in North America
and Europe for several years. This alloy exhibits an excellent combination of strength,
formability, ageing response and surface appearance following forming and painting operations.
Such a combination of properties is obtained by carefully tailoring the processing route to obtain
the desired microstructure of the alloy. In recent years, the ability to predict the phase stability in
different alloys has improved significantly, and it is now relatively easy to predict the particles
that could form in complex multi component alloys during different processing steps. The
accuracy of the predictions is dependent on whether or not the free energy expressions used in the
calculations are correct. In this study, the AA6111 alloy was subjected to various annealing
treatments that are reflective of different phase fields computed by the Thermo-Calc software.
The particles were extracted using the phenol extraction technique and were identified using
energy dispersive analysis. The interrelation of the particle analyses with the computed phase
stability in AA6111 is presented.
177
Abstract: This paper addresses the effect of microstructure on the formability of aluminium alloys
of interest for automotive sheet applications. The bulk of this work has been on the alloy AA5754 –
both conventional DC cast alloys and continuous cast alloys made by twin belt casting. It is known
that alloys such as these contain Fe as a tramp impurity which results in Fe-based intermetallic
particles distributed through microstructure as isolated particles and in stringers aligned along the
rolling direction. It is thought that these particles are the cause, both of the reduced ductility that is
observed as the Fe level rises, and the relatively poor formability of strip cast alloys, as compared
with those made by DC cast. Conventional wisdom suggests that the reduction of ductility is due to
the effect of particles as nucleating sites for damage. However, most studies show that these
materials are resistant to damage until just before fracture. We now believe that effect is actually
related to the development of shear bands in these materials. We present experimental data which
supports this conclusion. We then show how the FE models we have developed demonstrate the
role of shear instability on fracture and the role played by hard particles. We show how a unit cell
approach can be used to incorporate the effect of particle density and morphology on shear
localization in a way that includes statistical variability due to microstructural heterogeneity. This
leads to a set of constitutive equations in which the parameters are distributed from one region to
another. These are then fed into a macroscopic FE model at the level of the specimen or the
component in order to determine the effect of microstructural variability on shear instability and
ductility.
183
Abstract: Regardless of whether it is cast microstructure, the grain structure that is the product of
thermomechanical processing or the nanoscale dispersions of strengthening second-phase particles,
it is inescapable that the structural scale that controls mechanical properties in Al alloys is
determined primarily by processes of nucleation during either solidification, recrystallisation or
solid-state phase transformation. In those advanced alloys with bulk amorphous or nanocrystalline
structure, production of an amorphous precursor is reliant on initial suppression of the nucleation of
crystallisation, and subsequent controlled nucleation of dispersed nanocrystals within amorphous
matrix. The processes of nucleation that control structural scale in modern Al alloys are briefly
reviewed, with a focus on potential for further structural refinement and advances in properties.
191
Abstract: This is an initial report of a multi-technique study on the effect of Mg alloying on solute-vacancy
interactions during the early stages of ageing of dilute 2xxx Al-Cu-Mg alloys so as to better
understand the early rapid hardening (RH) that occurs in certain compositions of these alloys and
the more general phenomena of secondary hardening (SH) at ambient temperatures. Therefore, RH
at 150 °C and SH at room temperature from the as-quenched condition and after 60 sec ageing at
150 °C were studied in Al-1.1Cu and Al-1.1Cu-0.5Mg (at. %) variously by positron annihilation
lifetime spectroscopy (PALS), coincidence Doppler broadening (CDB) spectroscopy and atom
probe tomography (APT) and monitored by Vickers hardness measurements. The present results
indicate that Cu-Cu, Mg-Mg and Cu-Mg clusters are formed in the ternary alloy already in the asquenched
state and that they persist during ageing at 150 °C. The fraction of the solutes Cu and Mg
that were associated with vacancies after ageing was increased 10-fold and double, respectively and
the strength of the Cu clustering is enhanced greatly after 60 sec at 150 °C.
197
Abstract: The trace addition of Sn (0.01 at.%) to an Al-1.7Cu (at.%) alloy has been investigated
using atom probe tomography (APT), transmission electron microscopy (TEM) and high resolution
transmission electron microscope (HRTEM). We have studied samples in the as-quenched (AQ)
condition and following ageing at both 160 and 200 °C for very short ageing times so as to better
understand the early stages of the decomposition processes. Our data reveal independent Cu-Cu and
Sn-Sn clusters in the AQ condition, though we did not observe Cu-Sn clustering. We observed for
the first time that some of these initial Cu-clusters develop into GP zones during subsequent ageing
at temperatures as high as 200 °C. The Sn atom clustering results in precipitation of independent -
Sn particles after aging for 30 sec. The GP zones consequently undergo reversion and this liberates
Cu atoms which seem to participate in a cluster-assisted heterogeneous nucleation of the phase at
the interface of the -Sn. For ageing at 200 °C, this process is complete within 180 sec.
203