Early precipitation during cooling of an Al-Zn-Mg-Cu alloy revealed by in situ small angle X-ray scattering

Jean-Marie Drezet, Patrick Schloth, Helena Van Swygenhoven
American Institute of Physics, 2014
Article

Early subnanometre cluster formation during quenching of a high-strength AA7449 aluminium alloy was investigated using in situ small angle X-ray scattering. Fast quench cooling was obtained by using a laser-based heating system. The size and number density of homogeneous nucleated clusters were found to be strongly dependent on the cooling rate, while the volume fraction of cluster formation is independent of the cooling rate. Heterogeneous larger precipitation starts at higher temperatures in volume fractions that depend on the cooling rate. (C) 2014 AIP Publishing LLC.

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Jean-Marie Drezet, Patrick Schloth, Helena Van Swygenhoven
American Institute of Physics, 2014
Article

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https://infoscience.epfl.ch/record/203231?ln=fr

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Early cluster formation during rapid cooling of an Al-Cu-Mg alloy: In situ small-angle X-ray scattering

Jean-Marie Drezet, Patrick Schloth, Helena Van Swygenhoven

The formation of Cu-Mg clusters in an Al-Cu-Mg aluminum alloy is observed by small-angle X-ray scattering during cooling. Cooling rates are choosen to mimic the different conditions obtained at the surface and in the center of large forgings. Clusters of 0.45 nm start to form at 250 degrees C. Their volume fraction depends strongly on the cooling rate and the amount of excess vacancies. The difference in cluster kinetics explains the difference in rapid hardening across large forgings. (C) 2015 Acts Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Elsevier2015

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INTERNAL STRESS GENERATION DURING QUENCHING OF THICK HEAT TREATABLE ALUMINIUM ALLOYS

Nicolas Paul Henry Chobaut, Jean-Marie Drezet, Patrick Schloth, Helena Van Swygenhoven

In the current trend toward thicker aluminium plates, a major concern is the stress build-up during quenching which causes distortions during machining. Indeed, cooling rates are not high enough, especially at the core of such thick plates, to prevent any precipitation and quench induced precipitates lower the hardening potential. Multi-scale modelling is required when predicting macro-scale stresses after quenching for thick heat treatable aluminium components. The reason is the instantaneous strong coupling between phase precipitation at the nano-scale and material hardening due to precipitation or softening owing to solute depletion at the microscale. For thick parts, quenching intensities decrease when going from the skin to the core of the component, thus introducing a gradient of nanostructure and consequently a gradient of mechanical properties. In addition, large thermally induced deformations lead to high macroscale residual stresses although part of them is relaxed by plastic deformation. These stresses have been measured in water quenched thick plates of 7040 and 7449 aluminium alloys using neutron diffraction and layer removal techniques and the results when compared with a thermomechanical finite element model of quenching highlight the influence of precipitation

TMS2013

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In Situ Synchrotron X-Ray Diffraction and Small Angle X-Ray Scattering Studies on Rapidly Heated and Cooled Ti-Al and Al-Cu-Mg Alloys Using Laser-Based Heating

Christian Leinenbach, Patrick Schloth, Steven Van Petegem, Helena Van Swygenhoven

Beam-based additive manufacturing (AM) typically involves high cooling rates in a range of 10(3)-10(4) K/s. Therefore, new techniques are required to understand the non-equilibrium evolution of materials at appropriate time scales. Most technical alloys have not been optimized for such rapid solidification, and microstructural, phase, and elemental solubility behavior can be very different. In this work, the combination of complementary in situ synchrotron micro-x-ray diffraction (microXRD) and small angle x-ray scattering (SAXS) studies with laser-based heating and rapid cooling is presented as an approach to study alloy behavior under processing conditions similar to AM techniques. In rapidly solidified Ti-48Al, the full solidification and phase transformation sequences are observed using microXRD with high temporal resolution. The high cooling rates are achieved by fast heat extraction. Further, the temperature- and cooling rate-dependent precipitation of sub-nanometer clusters in an Al-Cu-Mg alloy can be studied by SAXS. The sensitivity of SAXS on the length scales of the newly formed phases allows their size and fraction to be determined. These techniques are unique tools to help provide a deeper understanding of underlying alloy behavior and its influence on resulting microstructures and properties after AM. Their availability to materials scientists is crucial for both in-depth investigations of novel alloys and also future production of high-quality parts using AM.

Springer2016

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