Laser-based metal additive manufacturing (AM) is an innovative process that permits the fabrication of near net-shaped metallic components with complex geometries.   The AM technique Laser Powder Bed Fusion (LPBF) is used for the fabrication of near-net-designed metallic components with complex geometry and higher material efficiency, typically replacing multiple conventional components with savings in material, tooling and assembly costs. However, there are still several scientific issues that need to be overcome. Investigations on all relevant length scales for AM are required which means on the scale from several cm down to the submicron range.
Aluminum alloys processed by LPBF have the potential to be used for a wide range of applications across aerospace, defense, transportation and industrial sectors. However, conventional Aluminum alloys adopted for LPBF show several drawbacks such as complicated post-processing and also unavoidable defects during AM or great variations in surface roughness that reduce the performance. Moreover, these alloys can contain volatile elements such as Mg or Zn that affect the outcome of the LPBF process. These issues can be overcome by developing new Al alloys specifically tailored for the LPBF process. Constellium developed a new structural AL-Fe-Zr alloy, Aheadd® CP1, that covers a temperature range beyond current aluminum alloys. The alloy does not contain any critical elements and is designed to exploit LPBF’s rapid solidification nature, resulting in stable microstructures with attractive excellent performances.
The microstructure evolution of this new alloy was investigated during intrinsic thermal treatments as a function of time using synchrotron-based characterization techniques. In-situ synchrotron nano-tomography (s-XCT) during thermal treatment at 400°C was conducted at the beamline ID16B of the ESRF in Grenobel, France. Tomographic scans were acquired in high quality and resolution at RT after different steps of thermal treatment by holotomography. During the holding time of thermal treatment, cycles of multiresolution single distance scans were obtained every 10min to monitor the evolution of intermetallics. Using voxel sizes of (40 nm)³, (100 nm)³ and (342 nm)³ allowed to obtain information about geometry and topology of the entire sample as well as the imaging of larger features like porosity. Higher resolutions allowed to reveal small Fe-rich intermetallics and to monitor their evolution during thermal treatments. Image segmentation of the acquired in situ datasets was supported by a deep learning approach using convolutional neural networks.
Complementary to tomography investigations, in situ high energy synchrotron X-ray diffraction (HXRD) was carried out at the P07-HEMS beamline of PETRA III/Deutsches Elektronen-Synchrotron (DESY) using a modified dilatometer Bähr 805 A/D with an inductive furnace for subsequent heat treatments.
First results reveal a morphological evolution of Fe-rich intermetallics during the heat treatment at 400 °C that grow decorating the Al-grain boundaries. The evolution of shape, size, distribution of these phases will be studied in relation to the processing and heat treatment conditions.